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13.5: The Structure and Properties of Water

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With 70% of our earth being ocean water and 65% of our bodies being water, it is hard to not be aware of how important it is in our lives. There are 3 different forms of water, or H 2 O: solid (ice), liquid (water), and gas (steam). Because water seems so ubiquitous, many people are unaware of the unusual and unique properties of water, including:

Boiling Point and Freezing Point

Surface tension, heat of vaporization, and vapor pressure.

• Viscosity and Cohesion
• Solid State
• Liquid State

If you look at the periodic table and locate tellurium (atomic number: 52), you find that the boiling points of hydrides decrease as molecule size decreases. So the hydride for tellurium: H 2 Te (hydrogen telluride) has a boiling point of -4°C . Moving up, the next hydride would be H 2 Se (hydrogen selenide) with a boiling point of -42°C . One more up and you find that H 2 S (hydrogen sulfide) has a boiling point at -62°C . The next hydride would be H 2 O (WATER!) . And we all know that the boiling point of water is 100°C . So despite its small molecular weight, water has an incredibly big boiling point. This is because water requires more energy to break its hydrogen bonds before it can then begin to boil. The same concept is applied to freezing point as well, as seen in the table below. The boiling and freezing points of water enable the molecules to be very slow to boil or freeze, this is important to the ecosystems living in water. If water was very easy to freeze or boil, drastic changes in the environment and so in oceans or lakes would cause all the organisms living in water to die. This is also why sweat is able to cool our bodies.

Besides mercury, water has the highest surface tension for all liquids. Water's high surface tension is due to the hydrogen bonding in water molecules. Water also has an exceptionally high heat of vaporization . Vaporization occurs when a liquid changes to a gas, which makes it an endothermic reaction. Water's heat of vaporization is 41 kJ/mol. Vapor pressure is inversely related to intermolecular forces, so those with stronger intermolecular forces have a lower vapor pressure. Water has very strong intermolecular forces, hence the low vapor pressure, but it's even lower compared to larger molecules with low vapor pressures.

• Viscosity is the property of fluid having high resistance to flow. We normally think of liquids like honey or motor oil being viscous, but when compared to other substances with like structures, water is viscous. Liquids with stronger intermolecular interactions are usually more viscous than liquids with weak intermolecular interactions.
• Cohesion is intermolecular forces between like molecules; this is why water molecules are able to hold themselves together in a drop. Water molecules are very cohesive because of the molecule's polarity. This is why you can fill a glass of water just barely above the rim without it spilling.

Solid State (Ice)

All substances, including water, become less dense when they are heated and more dense when they are cooled. So if water is cooled, it becomes more dense and forms ice. Water is one of the few substances whose solid state can float on its liquid state! Why? Water continues to become more dense until it reaches 4°C. After it reaches 4°C, it becomes LESS dense. When freezing, molecules within water begin to move around more slowly, making it easier for them to form hydrogen bonds and eventually arrange themselves into an open crystalline, hexagonal structure. Because of this open structure as the water molecules are being held further apart, the volume of water increases about 9%. So molecules are more tightly packed in water's liquid state than its solid state. This is why a can of soda can explode in the freezer.

Liquid State (Liquid Water)

It is very rare to find a compound that lacks carbon to be a liquid at standard temperatures and pressures. So it is unusual for water to be a liquid at room temperature! Water is liquid at room temperature so it's able to move around quicker than it is as solid, enabling the molecules to form fewer hydrogen bonds resulting in the molecules being packed more closely together. Each water molecule links to four others creating a tetrahedral arrangement, however they are able to move freely and slide past each other, while ice forms a solid, larger hexagonal structure.

Gas State (Steam)

As water boils, its hydrogen bonds are broken. Steam particles move very far apart and fast, so barely any hydrogen bonds have the time to form. So, less and less hydrogen bonds are present as the particles reach the critical point above steam. The lack of hydrogen bonds explains why steam causes much worse burns that water. Steam contains all the energy used to break the hydrogen bonds in water, so when steam hits your face you first absorb the energy the steam has taken up from breaking the hydrogen bonds it its liquid state. Then, in an exothermic reaction, steam is converted into liquid water and heat is released. This heat adds to the heat of boiling water as the steam condenses on your skin.

Water as the "Universal Solvent"

Because of water's polarity, it is able to dissolve or dissociate many particles. Oxygen has a slightly negative charge, while the two hydrogens have a slightly positive charge. The slightly negative particles of a compound will be attracted to water's hydrogen atoms, while the slightly positive particles will be attracted to water's oxygen molecule; this causes the compound to dissociate. Besides the explanations above, we can look to some attributes of a water molecule to provide some more reasons of water's uniqueness:

• Forgetting fluorine, oxygen is the most electronegative non-noble gas element, so while forming a bond, the electrons are pulled towards the oxygen atom rather than the hydrogen. This creates 2 polar bonds, which make the water molecule more polar than the bonds in the other hydrides in the group.
• A 104.5° bond angle creates a very strong dipole.
• Water has hydrogen bonding which probably is a vital aspect in waters strong intermolecular interaction

Why is this important for the real world?

The properties of water make it suitable for organisms to survive in during differing weather conditions. Ice freezes as it expands, which explains why ice is able to float on liquid water. During the winter when lakes begin to freeze, the surface of the water freezes and then moves down toward deeper water; this explains why people can ice skate on or fall through a frozen lake. If ice was not able to float, the lake would freeze from the bottom up killing all ecosystems living in the lake. However ice floats, so the fish are able to survive under the surface of the ice during the winter. The surface of ice above a lake also shields lakes from the cold temperature outside and insulates the water beneath it, allowing the lake under the frozen ice to stay liquid and maintain a temperature adequate for the ecosystems living in the lake to survive.

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Contributors and Attributions

• Corinne Yee (UCD), Desiree Rozzi (UCD)

The Interaction of Electromagnetic Waves with Water

• First Online: 21 April 2021

Cite this chapter

• Vasily Artemov 5  

Part of the book series: Springer Series in Chemical Physics ((CHEMICAL,volume 124))

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Water is the most important substance in our everyday life, and has been studied as no other medium. While it has a relatively simple atomic composition, water nevertheless presents an astonishing variety of manifestations of its interaction with electromagnetic waves of the different wavelengths from radio frequencies to X-rays, representing its uniqueness compared to other dielectrics. In this chapter, the response of water to external electromagnetic radiation is considered in an extended frequency range from 0 to 10 \(^{15}\) Hz. The independent view on the separate parts of the spectrum, such as the dielectric constant, DC conductivity, radio wave, microwave, terahertz, and IR absorption, is provided along with a comprehensive view on the entire spectrum as a whole by means of sum rules, Kramers–Kronig analysis and the isotope effect. A curious reader will find a complete description of water’s electrodynamic parameters, as well as specific questions regarding the dynamic structure of water.

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Note that in classical electrodynamics it is customary to divide currents into the conduction and displacement components, writing the dielectric function as follows:

where \(\sigma _{dc}\) is the direct current conductivity and F ( \(\omega \) ) is a frequency-dependent dielectric function. However, () is incorrect and contains a wrong physical meaning. Since both the conduction current and the displacement currents are indistinguishable for the infinite sample and obviously have the same nature, hereinafter, by \(\sigma \) = \(\epsilon \) " \(\epsilon _0\omega \) , where \(\epsilon _0\) being the vacuum permittivity, we mean the frequency-dependent dynamic conductivity, which includes both DC and AC conductivity parts, and assume that formula ( 2.5 ) is a definition of the electrical conductivity function, which is valid at any frequency (including \(\omega =0\) ).

Note that the sample is not a material, because it always has finite size and boundaries, which can affect the dielectric measurement at low frequencies (see [ 2 ]). Thus, one should be careful with the transfer of the sample parameters to the material properties, and use the corresponding equivalent schemes.

The loss tangent is defined as the ratio (or angle in a complex plane) of the lossy reaction to the electric field E in the curl equation to the lossless reaction: tg \(\delta \) = \(\epsilon ''\) / \(\epsilon '\) .

Equation ( 2.22 ) has an important consequence. It connects the dielectric relaxation band with the static dielectric constant, which means that they both have the same microscopic nature discussed in Sect.  4.5 .

In a linear response, a weak perturbation generates a small out-of-equilibrium response that is proportional to this perturbation. The response is expected to be proportional to this perturbation, where the response coefficient is independent of the strength of the external electric field [ 15 ].

The difference between experimental viscosity and that calculated by Stokes–Einstein formula is observed for all polar liquids and, depending on the conditions, ranges from ten to several thousand times.

1 D (Debye) = 3.33 \(\cdot \) 10 \(^{-30}\) C \(\cdot \) m.

The same is true for alcohols (see, for instance, [ 21 ]).

This is despite the fact that the relaxation time changes by seven orders of magnitude (see Chap.  4 for details).

The absorption of the electromagnetic waves by water vapor is used in IR astronomy and radio astronomy in the IR, and microwave or millimeter wave bands. For earth-based astrophysical observations, atmospheric water vapor creates distortions. The South Pole Telescope was constructed because there is very little water vapor in the atmosphere above the poles, caused by the low temperatures.

https://hitran.org/ .

The maximum of the IR absorption of water and ice is only an order of magnitude lower than that for the ionic crystal of NaCl, but three orders of magnitude lower than the absorption of covalently bounded crystalline silicon.

LO–TO splitting manifests itself in a frequency difference between the longitudinal optical (LO) and transverse optical (TO) phonon modes.

For ice, the \(\nu _s\) mode splits and has a structure of at minimum two components, which is presumably caused by the longitudinal- and transverse-phonon modes splitting.

Note that the acoustic waves involve the motions of entire H \(_2\) O molecule and describe the irregular molecular arrangement, whereas the X-ray RDF analysis (see Sect.  1.2.3 ) gives diffusion-averaged O–O distances. That is why an additional small maximum of the radial distribution function near 3.5 Å can be caused by the molecules in the state of diffusion between two quasi-equilibrium positions.

Note that the Debye model of relaxation is based on the diffusion limit, where extremely complex dipolar relaxations at long timescales can be treated statistically, neglecting the moment of inertia of the dipoles and intermolecular interactions. However, for highly anisotropic and strongly dipolar molecules such as water, their effects should be rigorously taken into account at such short time frames as an equilibrium statistical description is inapplicable [ 102 ].

They also found that the product \(\tau _{D1}\cdot D\) , where D is the self-diffusion coefficient of water, is nearly independent of both light and heavy water

The spectral transparency window allows animals to see under and through the water, and makes water transparent for light of optical frequencies. If our eyes were sensitive to IR frequencies instead of optical, water would be completely opaque. Obviously, evolution chooses the optical region for vision due to the special electrodynamic properties of water.

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Artemov, V. (2021). The Interaction of Electromagnetic Waves with Water. In: The Electrodynamics of Water and Ice. Springer Series in Chemical Physics, vol 124. Springer, Cham. https://doi.org/10.1007/978-3-030-72424-5_2

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Article Contents

Introduction, structuring water alters the physico-chemical properties of the water, effects of sw on animal growth and development, sheep and goats, effects of drinking sw on milk yield and composition, effects of drinking sw on blood hematology and biochemistry, effects of sw on reproduction, effects of drinking sw on blood antioxidant/immune status, effects of drinking sw on serum lipid profile, glycemic responses and type 2 diabetes, other biological effects of drinking sw, perspectives, conclusions, acknowledgment, conflict of interest statement, literature cited.

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Structured water: effects on animals

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Michael I Lindinger, Structured water: effects on animals, Journal of Animal Science , Volume 99, Issue 5, May 2021, skab063, https://doi.org/10.1093/jas/skab063

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This review focuses on the effects of structured water (SW) on animals when it is consumed on a daily basis. SW is liquid water that is given altered H-bonding structure by treatment with various forms of energy including magnetic fields and light. While most of the research has been conducted on ‘magnetized’ water, which has structure of short duration, recent research has examined effects of a SW with stability of at least 3.5 mo. A variety of laboratory and farm animals have been studied over the past 20 yr. Consistent (3 or more studies) responses among animals consuming SW for 1 mo or more include increased rate of growth, reduced markers of oxidative stress, improved glycemic and insulinemic responses in diabetics, improved blood lipid profile, improved semen and spermatozoa quality, and increased tissue conductivity as measured using bioelectrical impedance analysis. While it is known that fluids in and around cells and molecules are structured, it remains unknown if this endogenous water structuring is influenced by drinking SWs. The mechanisms by which SW affects biological systems are unknown and require investigation. Effects of SW, when taken up by biological systems, are likely associated with altered water structuring around biological surfaces, such as proteins and membranes.

Only in the past 2 decades has it been consistently shown that structured water (SW), when used as a nutrient source for animals, results in many positive responses including increased growth and productivity in agricultural settings ( Ebrahim and Azab, 2017 ). Water is an essential nutrient and also the most abundant molecule in biological systems; when water is not in adequate supply or of adequate quality organisms do not thrive and may die. While the importance of water in biology may be taken for granted ( Warner, 1970 ), it is universally recognized that water is needed for hydration and for optimizing health and performance ( Bondy and Campbell, 2018 ). The importance of water in general, and SW in particular, remains underestimated and underappreciated in biology—the science of life. It is important that biologists are well trained in the fundamental principles underlying the physics and chemistry of water, whether it is in a beaker or in living systems. SW is very complex and poorly understood and, accordingly, the topic of SW and its effects on biological systems has been largely ignored.

In order to begin the story of SW 2 unrelated discoveries need to be mentioned. The first is that water treated with electromagnetic radiation gains structure ( Del Giudice et al., 1988 ); see Pang 2014 for extensive review. The second is that the consumption of “magnetized” water was shown to have positive effects on animals, including those in agricultural production systems ( Patterson and Chestnutt, 1994 ; Ebrahim and Azab, 2017 ). A theme of the SW research in agricultural settings continues to be improvement of water quality ( Goldsworthy et al., 1999 ) while simultaneously improving animal wellness and productivity ( Ebrahim and Azab 2017 ; Gilani et al. 2017 ).

Let is consider what is meant by “water gains structure”. As depicted in Figure 1 , SW may be defined as liquid water that has gained structure compared with unstructured liquid water (often referred to as bulk water). Structure refers to increases in the numbers of aggregated hydrogen and oxygen atoms that form clusters comprising 2 to hundreds of water molecules ( Del Giudice et al., 1988 ; Chaplin, 2000 ; Pang, 2014 ; Chibowski and Szcześ, 2018 ), as exemplified in Figure 2 . The clusters are capable of getting very large and may have 3-dimensional shapes that are spherical ( Pang 2014 ), helical ( Lo et al., 2012 ; Ho, 2014 ; Elia et al., 2017 ), and planar ( Hwang et al., 2018 ; Elton et al., 2020 ) as shown in Figure 3 . It is important to point out that the structures are unlike those found in ice, which has a very structured, hexameric configuration ( Figure 4 ). The mechanisms by which water becomes structured remain poorly understood ( Chaplin, 2000 ; Pang, 2014 ; Ball, 2017 ; Chibowski and Szcześ, 2018 ; Elton et al., 2020 ). Yet, the present review reports that water structured in different ways are capable of having many and profound effects on the biological systems that come into direct contact with these waters.

A glass of water comprises billions of H 2 O molecules (top) that are capable of accepting/releasing protons (H + ) up to 1 million times/s ( Edsall and Wyman, 1958 ; Harned and Owen, 1958 ). However, protons tend to not exist on their own in aqueous solutions and readily bind to H 2 O to form H 3 O + (hydronium). In theory, 2 H 2 O molecules can form 1 hydronium and 1 hydroxyl.

Examples of how individual H 2 O may combine into linear or nonlinear clusters. Water molecules are connected by hydrogen bonds as depicted by black dashes. Adapted from Pang (2014) .

Networked hydrogen bonding (black dashes) of water molecules into an hexameric-shaped water cluster. Adapted from Pang (2014) .

Ordered, hexameric structure of ice.

Most of what we know about SW comes from research where water has been structured using energy from magnetic fields ( Pang and Deng, 2008 ; Pang et al., 2012 ; Pang, 2014 ; Chibowski and Szcześ, 2018 ). It is these types of “magnetized” waters that have been studied for their effects on plants and animals, and particularly with an agricultural focus ( Ebrahim and Azab, 2017 ). While some of the published literature in this area is scientifically weak, the consistency among the publications permits one to draw conclusions and formulate designs for future research. The main purpose of this review is to summarize what is currently known about the effects of SW on animals. In so doing, an aim is to highlight the types of research that need to be undertaken in order to understand how biological effects occur.

Chibowski and Szcześ (2018) concluded from their detailed review of the literature on magnetized water that the results of experiments performed over the past 20 yr do not provide a consistent mechanism that accounts for effects of magnet treatments on altering the physico-chemical properties of water, including water clustering and water-ion interactions. This was echoed in a recent review by Elton et al. (2020) on planar forms of structured, mostly interfacial, water. Chibowski and Szcześ (2018) stated that research conducted in the past decade strongly implicates changes in the structure of water via hydrogen bonding in intraclusters and between interclusters. According to one theory, upon exposure to a magnetic field clusters can be transformed in size, such that water intercluster bonds are weakened while intraclusters bonds are strengthened, with a slight increase in the amount of the bonding ( Chang and Weng, 2006 ).

That the structuring of water has been altered is known from scans made by measuring the absorption of different visible and ultraviolet light wavelengths by water, changes in the absorption of the infrared spectrum, changes in the absorption of Raman spectra as well as other approaches ( Pang and Deng, 2008 , , 2009 ; Slavchev et al., 2015 ; Tsenkova et al., 2018 ). The increase in structuring, as evidenced from the increase in infrared absorption, is proportional to both the magnetic field intensity and the duration of treatment ( Figure 5 ). Upon removal of the magnetic field, the effects are short-lasting and, in all of the experiments of Pang and Deng (2008) represented by Figure 5 , infrared absorbance had returned to baseline by 60 min after removal of the water from the magnetic field.

Representation of the effects of treating water with different magnetic field intensities for different durations. G, Gauss; 1 T, 10,000 G. Adapted from Pang and Deng (2008) .

Prior to the work of Pang and colleagues, it was known that magnetically treating water altered the physical properties of the water and that the altered physical properties were due to “changed dimensions of water clusters” ( Baranov et al., 1995 ; Ibrahim, 2006 ). Table 1 highlights some of the changes in physical properties that can occur when treating water with magnetic fields. Several researchers have reported increases in conductivity and pH while there are decreases in density and surface tension. In addition to these, there are reports of increased dielectric constant ( Ibrahim, 2006 ; Pang and Deng, 2008 ), an increase in vaporization enthalpy ( Toledo et al., 2008 ).

Some of the physical properties of untreated and magnetically treated tap water 1

1 Values are mean ± SEM.

*Significantly different from untreated tap water. Data from Al-Hilali (2018) .

While it is important to understand the changes in physical properties that occur with pure water, from an applications point of view it is also important to understand what occurs when tap water or ground (well) water is used. Tap water, ground water, lake water, and reservoir water are universally used in plant and animal agricultural. These types of water vary with respect to mineral and organic material contents and exposure to effects (light, heat, and mechanical disturbances). Each of these influences appears to affect the magnitude, type of structuring, and stability of structuring that may occur ( Chibowski and Szcześ, 2018 ). Presently, in the peer-reviewed scientific literature, there is evidence for 2 main types of SW based on stability. Water that is intentionally structured by treating with magnets, either statically or with flow-through systems, is stable for relatively short periods of time, typically hours and not more than 3 d. The degree of structuring is proportional to the intensity and duration of the imposed energy, whether it be magnetic or light and the decay of structuring is approximately exponential in time course ( Pang, et al., 2012 ; Chibowski and Szcześ 2018 ). The second type of SW has long-term stability (months).

Nearly 20 yr ago, a SW with months-long stability was developed by treating purified water with ~0.1% by weight of selected minerals that include potassium and silica, magnetic energy and light energy ( Lorenzen, 1988 , , 2000 ). This water has been tested in biological systems, including humans ( Ling et al., 2004 ; Wang et al., 2004 ; Chen et al., 2005 ). More recently, this water was used in a clinical field trial of Thoroughbred race horses in training ( Lindinger and Northrop, 2020 ). This highly stable SW has been analyzed using the aquaphotomics approach developed by Dr. Roumiana Tsenkova at Kobe University in Japan ( Slavchev et al., 2015 ; Tsenkova et al., 2018 ; Kraats et al., 2019 ). When analyzed up to 3.5 mo after date of manufacture, this SW was found to retain significant structuring, even after boiling in a microwave for 5 min. Infrared spectroscopy and aquaphotomics analysis determined structures in this liquid SW to include protonated water clusters, hydrated water, and water dimers ( Lindinger and Northrop, 2020 ). This SW is available commercially as Defiance Fuel (Defiance Brands Inc., Nashville, TN).

As detailed in the following paragraphs, there are more than 2 dozen studies that have reported beneficial effects of drinking or using SW on animals, including 2 studies that examined effects on oral health in children. The other species include horses, cattle, fish, sheep, goats, mice, rats, rabbits, Japanese quail, ducks, and chickens. A few studies have reported adverse effects (see below), and these appear to occur with waters that have been treated for a prolonged duration with magnets or with too great a magnetic field. A few studies have examined the effects of duration of “magnetization” or of magnetic field strength on biological effects and is evident from these that there is a “dose–response” effect. Relatively, few studies have reported key indicators of water structuring such as electrical conductivity, pH, infrared spectrum, UV–vis spectrum, and surface tension—this is a limitation of most studies to date.

Patterson and Chestnutt (1994) cited 3 animal research reports in which SW was used—these studies are no longer readily available and commentary is taken from Patterson and Chestnutt as well as others ( El-Hanoun et al., 2013 ; Balieiro Neto et al., 2017 ). Increased growth has been claimed in calves and sheep, with a reduction in fat in carcasses ( Lin and Yotvat, 1988 ). A 75-d study using Jersey cows drinking water treated with a static 324,000 G magnetic field reported a significant increase in subcutaneous fat thickness as measured using ultrasound ( Balieiro Neto et al., 2013 ).

The first reasonably well-designed experimental research study investigating effects of SW on animals appears to be that of Patterson and Chestnutt (1994) . The authors magnetized local tap water or ground water which was “hard,” i.e., 236 and 332 mg/L total solids (in Hillsborough, Northern Ireland, UK) and provided the control water or SW to groups of lambs ( n = 10/group) 1 wk after weaning. The intensity of, and duration of exposure to, the magnetic field was not provided. The effects of water treatment on water physical or chemical properties was not determined. Lambs continued with the treatment until they reached a live weight of 54 kg (~40 to 80 d after weaning). The data indicate that the study was underpowered: there were tendencies ( P > 0.05 and < 0.10) for water intake to be lower with SW and for an increased feed conversion ratio. There were no effects on growth performance or carcass composition. The authors concluded that the more intense the water treatment, the greater the tendency for adverse effects on lamb performance. In contrast, Shamsaldain and Al Rawee (2012) reported significantly increased weight of lambs and ewes when ewes consumed magnetized water (1,000 G) compared with control, but this study also did not report water properties.

Yacout et al. (2015) studied goat bucks and lactating does that consumed magnetized waters (1,200 and 3,600 G) for 60 d. Consuming the 3,600 G water, compared with control and 1,200 G water, resulted in significantly increased dry matter intake (DMI)—with water consumption matched to DMI and increased digestibility with both magnetic waters compared with control. This was associated with increased rumen microbial population, reduced ruminal ammonia production, with markedly increased volatile fatty acid concentrations and decreased methane production.

Adult mice were given tap water treated with 1,000 G or 2,000 G magnets or consumed normal tap water (controls; Alhammer et al., 2013 ). The magnetic treatment reduced the water density (~10%), increased total dissolved solids at 2,000 G and was without effect on electrical conductivity, dissolved oxygen, pH, and salinity. The duration of the experiment was not provided but appears to have been 4 wk. There was no effect of drinking 1,000 G water on body weight, while body weights were significantly lower (~13%) for mice drinking the 2,000 G water. There was no effect on feed consumption, although water consumption was increased by 40% to 50% in both groups drinking SW. The results of this study suggest a possible dose–response effect.

In the study by Lee and Kang (2013) , SW by passing it through a magnetic field of 9,000 to 13,000 G and the water was consumed within 1 d. The authors studied a group of control rats and a group of rats with streptozotocin-induced type 2 diabetes, with the diabetic rats further split into 2 groups, 1 consuming control water and the other SW over a period of 8 wk. There was no control group of rats that consumed SW. The diabetic rats showed a >60% reduction in weight gain compared with control rats despite a 15% increase in daily food intake and 2.5-fold greater daily water intake compared with controls. Diabetic rats drinking SW gained ~30% less weight than diabetic rats drinking control water, and daily food intake between the 2 diabetic groups was similar. These results imply that consuming SW may result in an increased metabolic rate and energy expenditure. The results of this study also demonstrated a negative effect when using water treated with the relatively high magnetic field when consumed over an 8-wk period.

Balieiro Neto et al. (2014 , , 2017 ) conditioned the drinking water of rats by using a magnetic monopole field of 32,000 G and studied a variety of parameters at 15, 30, and 45 d. Compared to control water, the magnetically treated water had an increased pH and reduced turbidity—other physical parameters were not assessed. Over the 45 d, the authors reported a significant 25% reduction in daily weight gain which was associated with increased mass-specific dietary nitrogen retention. There were no effects on DMI, water intake, urine output, fecal nitrogen, and urine nitrogen. This study, similar to that of ( Lee and Kang, 2013 ), also suggested that 32,000 G field strength was excessive.

El-Hanoun et al. (2013) provided tap water and well water either untreated or treated with a 4,000 G magnetic field to rabbit does ( n = 10 per group; aged 6 to 7 mo) for 28 wk, with 12 wk prior to mating and 12 wk postgestation (time of weaning). Magnetic treatment of both tap and well water resulted in increased pH, salinity, electrical conductivity, reduced organic matter, and reduced hardness of well water. There were no effects on dissolved oxygen and individual ion concentrations (Na + , K + , Ca 2+ , Mg 2+ , Cl − , CO 3 2− , and HCO 3 − ). The growth performance of litters was followed from 6 to 12 wk postparturition and prior to weaning ( n = 143 to 266 per group). Does drinking SW, compared to tap water or well water controls, for 12 wk had significant 2-fold greater weight gains at mating and at 7 d after mating, accompanied by increased daily feed intake. Litter size and litter weight at birth and at 28 d were significantly increased for does that consumed SW. The body weight gain of offspring of does drinking SW from tap water, from 6 to 12 wk postparturition, was 9.5% greater than that offspring of does drinking control tap water, and this was 3-fold greater in magnitude than the gains seen with offspring of does drinking SW from well water. Increased weight gain was accompanied by significant decreases in feed intake, feed conversion ratio (g feed/g weight gain) and mortality. This study demonstrated that water treated with a magnetic field of 4,000 G was beneficial, and no adverse effects were reported.

Attia et al. (2015) provided tap water and well water treated at a magnetic field strength of 4,000 G and provided as drinking water to 7.5-mo-old-rabbit bucks ( n = 10 per group, 4 groups) for 28 wk. The magnetic treatment increased pH, conductivity, salinity, dissolved oxygen of both tap, and well water and reduced the hardness of well water. Compared to control tap or control well water, both SWs resulted in significantly increased body weight gain (23% for tap water; 84% for well water) which was associated with increased daily feed intake. The larger relative effect for the well water was because untreated well water had negative effects on growth (weight gain) that were substantially mitigated when magnetically treated water was used. Thus, magnetic treatment of the well water completely reversed the negative effects of the hard well water on growth and performance.

Rabbit does aged 7 to 8 mo were given normal tap water or magnetized tap water treated with 1,200 G or 3,600 G for 30 d ( Ragab and Mahmoud, 2015 ). Magnetically treating the water increased pH, increased electrical conductivity, salinity, oxygen content and reduced surface tension, evaporating temperature, and chloride concentration with no effect on viscosity or bacterial count. After 30 d of drinking SW, the does were then inseminated by a rabbit buck, and live body weight (LBW) was measured at mating and kidding. Water magnetized using the 1,200 G magnet resulted in the highest LBW at mating and kidding. Does drinking the 3,600 G water had an intermediate LBW to that of control and 1,200 G water. Litter weight gain was also significantly higher (by ~10%) with both magnetized waters. At weaning, the weight of the 1,200 G kids was significantly greater at 2,807 ± 104 g compared with 2,434 g (controls) and 2,635 g (3,600 G water). It was concluded that drinking water magnetized with 1,200 G magnets conferred a number of important growth benefits without adverse effects, and that the results with 1,200 G water were significantly better than those obtained using 3,600 G water.

The first study using an SW for the drinking water supply in poultry was performed using growing chickens ( Al-Mufarrej et al., 2005 ). Tap water was passed through a magnetic funnel (7 circular magnets of 450 to 500 G each) at low speed and collected in graduated cylinders, with fresh SW provided at 12-hr intervals. There was no effect of SW on growth, water consumption, feed intake, and feed conversion ratio during the 32 d after hatching. There was also no significant effect on carcass composition at 32 d, nor on antibody response to sheep red blood cells. The authors concluded that drinking the SW had no influence on measured parameters. It appears that the degree of water structuring was too low to produce any effects.

Alhassani and Amin (2012) provided chickens with water treated by a 500-G magnetic device, with tap water (control) flowing past the magnet at 3 different speeds: slow (10 L/15 min), medium, and fast (10 L/5 min). Effects of water treatment on physicochemical properties was not reported. Birds were studied from hatching till 42 d, with weekly measures. There was a weak dose–response effect between duration of magnetic water treatment and gain in LBW, with no statistical difference in body weight, weekly weight gain, and feed conversion ratio between the 4 groups. Because the tendency for a dose–response effect was present, this raises the possibility that the intensity/duration of magnetic treatment of the water was not adequate to elicit the types of biological responses reported in most studies.

El-Katcha et al. (2017) studied the effects of drinking magnetized (details not provided except that exposure to magnets occurred every 6 hr) water on the growth of Pekin ducklings from age 1 d posthatching to 12 wk. The characteristics of the water were not reported. There was no effect of the water treatment on body weight gain, nor on any measured parameter (hematology, serum biochemistry, liver function, renal function, serum lipids, immune parameters, and tissue weights) compared with nontreated water. Histological examination of the duodenal, jejunal ileum epithelium showed an increase in intestinal villi length, width, and surface area with SW compared with controls. The authors postulated that these effects of magnetically treated water would be associated with increased nutrient absorption. The paucity of effects in this very detailed study suggests that the intensity of water treatment was inadequate compared to that performed by most other studies.

Hassan et al. (2018) had growing chickens (hens) drink tap water treated with 2,000, 3,000, and 4,000 G or control water for 21 wk. Body weight gain of hens was ~25% greater when drinking the 2,000 and 3,000 G waters compared with control and 4,000 G waters. This was associated with an increased daily feed intake only with 3,000 G water, and feed conversion ratio (g feed/g egg) and daily water intake were significantly reduced with all SWs.

The poultry studies indicate that waters treated with magnetic field strengths of less than 1,000 G do not result in any differences in measured parameters related to growth and performance. The study by Hassan et al. (2018) indicates that water treated with a 4,000 G magnetic field strength resulted in effects that were less than optimal compared with waters treated with 2,000 and 3,000 G.

In one of the first reported studies on animals, Zhang and Wu (1987) demonstrated that fish living in magnetized water had a reduction in renal calcium crystal and in tissue calcium content. No additional details are readily available.

The 28-d milk yield of rabbit does drinking SW was increased by 300 to 500 g, compared with yields of 3,808 to 4,200 g in tap and well water control groups, respectively ( El-Hanoun et al., 2013 ). The milk from does drinking SW had significantly greater fat, lactose, and total energy, with no effect on milk protein and total solids, compared to milk from does drinking control waters.

Balieiro Neto et al. (2014) studied the effects of drinking a magnetized water (static magnetic field of 32,300 G applied to water troughs) on cows for a period of 75 d. There were significant increases in milk protein, urea, and casein, with no effect on daily milk yield, milk fat, and milk lactose.

Milk yield and milk composition of lactating goats has been reported in 3 studies ( Sargolzehi et al., 2009 ; Ragab and Mahmoud, 2015 ; Yacout et al., 2015 ). All studies used tap water as a control, as well as waters conditioned using 1,200 and 3,600 G magnets using a flow-through system. Animals consumed the water for 60 d. The water used by Sargolzehi et al. (2009) was “low quality” and very hard (2,168 ppm CaCO 3 ) with concentrations of SO 4 2− , Na + , and Cl − that greatly exceeded the recommended upper level for livestock ( Ayers and Westcot, 1985 ). The study was also greatly underpowered as there were only 4 animals per treatment. The authors reported no effect of consuming magnetized, low-quality water on milk composition and serum biochemistry. No adverse effects were reported. Yacout et al. (2015) also studied daily milk yield of lactating goats consuming control or 1,200 or 3,600 G waters ( n = 3 to 5 per group). Animals consuming 3,600 G water had greater milk yield than both other groups. Milk from does drinking SW also has high total solids, solids not fat, fat, protein, and lactose than those drinking control water. Shamsaldain and Al Rawee (2012) studied 3 groups of sheep that received control water or water magnetized at 500 and 1,000 G ( n = 8 per group). The authors reported increased milk production, total solids, fat, and protein from sheep consuming 1,000 G water compared with control. In the study by Ragab and Mahmoud (2015) , daily milk yield was also highest (10% to 40% higher than controls), with significantly greater fat, protein, lactose, and total solids when consuming the 1,200 G water; values with 3,600 G water were intermediate.

The results of these milk studies indicate consistent improvements in milk production and quality when animals drink SW treated with magnets at field strengths between 1,000 and 3,000 G, with field strength greater than 3,000 G showing less than optimal outcomes, although still better than outcomes on control waters.

The 75-d study using cows ( Balieiro Neto et al., 2013 , , 2014 ) also reported on arterial and venous blood acid–base and ion status when drinking water treated with a 32,400 G magnetic field in a water trough. While all parameters remained within normal reference ranges, there were statistically significant decreases in base excess, bicarbonate concentration, osmolality, and PCO 2 . There were significant increases in arterial pH, venous oxygen saturation, and blood urea, and no effects on serum glucose and ion concentrations.

The study performed using goats by Yacout et al. (2015) reported a positive dose–response effect of consuming 0, 1,200, or 3,600 G magnetized water on the concentrations of erythrocytes, hemoglobin, and white blood cells. Similar dose–response increases were reported for serum glucose, total protein, albumin, and globulin, while cholesterol was reduced. A study on goats ( n = 4 per group), also receiving “low-quality” hard water treated at 0, 1,200, and 3,600 G ( Sargolzehi et al., 2009 ) reported no effects on serum biochemistry. Similar effects were reported when sheep consumed water treated with 1,000 G magnet ( Shamsaldain and Al Rawee, 2012 ) and plasma protein concentration was also significantly increased when rabbits consumed magnetically treated water for 30 or 60 d ( Khudiar and Ali, 2012 ).

Lindinger and Northrop (2020) also reported an absence of effect on all full-panel indices of hematology serum biochemistry when Thoroughbred racehorses drank 10 L per day of a stable SW product for 4 wk.

The study by El-Hanoun et al. (2013) on rabbit does reported significantly lower serum concentrations of liver enzymes (aspartate aminotransferase, AST; alanine transaminase, ALT) and significantly greater serum concentrations of ovarian hormones (estrogen and progesterone). In contrast, mice given 1,000 and 2,000 G water to drink reported no effect on blood concentrations of the liver enzymes AST and alkaline phosphatase (ALP; Alhammer et al., 2013 ). In the study by Ragab and Mahmoud (2015) rabbit does were given normal tap water or magnetized tap water treated with 1,200 or 3,600 G for a total of 60 d, before and during gestation and during lactation. There were minor differences in serum biochemistry between waters, with all parameters within normal reference ranges, and no adverse effects. The study by Attia et al. (2015) reported significantly increased serum albumin without change in globulin or albumin:globulin ratio, a reduction in ALT, and significant decreases in serum urea and urea:creatine ratio indicative of improve renal function. There were no effects on RBC count, WBC count nor on white cell differentials. Mahmoud et al. (2019) using rabbit bucks consuming SW for 90 d, reported increases in RBC count, hematocrit and hemoglobin without effect on WBC count and platelet count.

A study on Japanese quail used tap water treated with 500 or 1,000 G magnets, which the birds drank for 60 d ( Al-Hilali, 2018 ). Magnetic treatment of water resulted in significantly increased electrical conductivity and pH, with significant reductions in density, dissolved oxygen, surface tension, and Cl − concentration. At 60 d, there were significant increases in RBC count, hematocrit, and hemoglobin concentration with both SWs. With 1,000 G, but not 500 G, SW, there were significant increases in WBC count, ALP, and serum total protein.

In chicken hens consuming control 2,000, 3,000, or 4,000 G treated waters for 21 wk, the authors reported increased RBC count and hemoglobin without change in hematocrit, increased serum pH, glucose, globulin, phosphorous and triiodothyronine concentrations and a reduced albumin:globulin ratio, with 2,000 and 3,000 G waters. There were no effects on total protein, albumin, calcium, and calcium:phosphorous ratio.

Forty female mice drank a pure SW (exposed to 4,000 G field at 37.5 °C for 4 hr), compared with a control group ( n = 40) that drank normal tap water ( Hafizi et al., 2014 ). Two weeks after starting to drink the water, mice were stimulated to ovulate and 48 hr later bred to males. After a further 54 hr, pregnant mice were killed and the reproductive system examined. The mean ± SD number of corpus lutea in SW mice was significantly greater (9 ± 4) than in the control group (5 ± 2), with a ~10% increase in height of fallopian tube epithelial cells and a ~5% increase ( P = 0.052) in height of uterine epithelial cells. The authors postulated that drinking SW had positive effects on cell growth, mediated by unknown mechanisms. The increased number of corpus lutea, and increased reproductive tract epithelial cell height, may translate to improved implantation and litter size.

In the study by Ragab and Mahmoud (2015) , rabbit does aged 7 to 8 mo were given normal tap water or magnetized tap water treated with 1,200 or 3,600 G for 30 d. After 30 d of drinking SW does were then inseminated by a rabbit buck. Water magnetized using the 1,200 G magnet resulted in the highest first conception rate (50% compared with 40% control and 30% with 3,600 G magnetization). There was no effect on gestation duration. The litter size per doe averaged ~10% higher for does receiving 1,200 G water and mortality rate was similarly reduced by ~10%. Litter weight gain was also significantly higher (by ~10%) with both magnetized waters.

Effects of drinking SW on reproductive indices in rabbit bucks show consistent beneficial effects on semen and sperm quality. Mahmoud et al. (2019) reported increased libido, improved semen volume and quality, increased spermatozoa count and motility, and reduced numbers of abnormal and dead spermatozoa when drinking 2,000 G SW for 4 wk. El-ratel and Fouda (2017) reported improved semen quality and sperm output when consuming SW (3,600 G) for 90 d. Both these studies confirmed previously reported effects ( Attia et al., 2015 ), and these authors additionally reported significantly increased testosterone concentration.

In the study on chicken hens ( Hassan et al., 2018 ), the authors reported a tendency ( P < 0.1) toward increased egg production and, importantly there were significant increases in egg weight and egg mass/hen day −1 with all 3 SWs (2,000, 3,000, and 4,000 G). The eggs from hens consuming 2,000 and 3,000 G SW were characterized by significantly increased albumin and yolk weights compared with controls and 4,000 G water, and shell thickness was increased with all 3 SWs.

Adult male rabbits ( n = 10 per group) were provided with magnetically treated tap water (resulted in elevated pH and oxygen content, with reduced surface tension and chloride) or control water for 60 d ( Khudiar and Ali, 2012 ). Drinking the magnetically treated water resulted in a significant ~40% increase in serum glutathione concentration by 30 d. The study on rabbit does by El-Hanoun et al. (2013) reported significant increases in serum total antioxidant capacity with reduced TBARS in both groups drinking SW compared with the control tap and well water groups. El-Ratel and Fouda (2017) a decrease in blood markers of oxidant stress (malonyl dialdehyde, TBARS, and lysozyme content) while total antioxidant capacity and antibody titer were increased when rabbit bucks consumed SW for 90 d.

Rats with induced type 2 diabetes consumed magnetized water for 4 wk and, compared with controls had decreased activities of glutathione and superoxide dismutase 2 that the authors associated with a reduced level of oxidative stress ( Saleh et al., 2019 ). In the earlier study using rats with induced diabetes ( Lee and Kang, 2013 ) found no effect of drinking SW on erythrocyte activities of catalase, glutathione peroxidase, and superoxide dismutase. In the mouse study of Alhammer et al. (2013) , a significant increase in adenosine deaminase when drinking 1,000 G water, but not with 2,000 G water, was attributed as an immune system response.

Japanese quail drinking SW for 60 d had significantly increased serum glutathione concentrations, with the increase positively correlated with intensity of water treatment (500 G and 1,000 G magnets; Al-Hilali, 2018 ). In rabbit bucks ( Attia et al., 2015 ), 28 wk of drinking magnetized tap water or magnetized well water significantly increased the serum concentrations of glutathione, glutathione peroxidase, glutathione S -transferase, IgA, and antibody titer. These were associated with significantly reduced concentrations of the lipid peroxidation marker malonyl dialdehyde and TBARS, with no effect on IgG, IgM, lysozyme concentrations, superoxide dismutase activity, and total antioxidant capacity.

In the study of male rabbits by Khudiar and Ali (2012) , the authors reported that drinking magnetically treated water resulted in significant reductions in serum triacylglycerol and very low density lipoproteins (VLDL) concentrations, and significantly increase high-density lipoproteins (HDL), at 60 d, compared with controls. A 28-wk study on 7.5-mo-old rabbit bucks reported a significant (~20%) increase in serum total lipid concentration with no effect on total cholesterol concentration ( Attia et al., 2015 ). In rats with induced type 2 diabetes, drinking SW prevented a 50% increase in plasma triglycerides (TGs) compared with diabetic rats drinking control water, with no effect on total cholesterol, HDL, and low-density lipoproteins (LDL; Lee and Kang, 2013 ). In the study on in Japanese quail ( Al-Hilali, 2018 ), both SWs had similar effects on lowering by ~20% total serum cholesterol and TG concentrations and increasing HDL. The magnitude of decrease in LDL and VLDL was positively correlated with the intensity of magnetic treatment of the water (550 G and 1,000 G). These are considered to be positive, beneficial effects on serum lipid profile.

Adult mice were given tap water treated with 1,000 G or 2,000 G magnets or consumed normal tap water (controls; Alhammer et al., 2013 ). The magnetic treatment reduced the water density (~10%), increased total dissolved solids at 2,000 G, and was without effect on conductivity, dissolved oxygen, pH, and salinity. Mice that consumed 1,000 G or 2,000 G water (duration not stated) had a ~30% and ~40% decrease, respectively, in blood glucose with no effect on AST or ALP activities. Japanese quail that drank 500 G and 1,000 G SW for 60 d also showed significant large (12% to 15%) decreases in serum glucose with the magnitude of decrease positively correlated with intensity of water treatment (500 and 1,000 G magnets; Al-Hilali, 2018 ).

Rats with induced type 2 diabetes consumed water treated by passing through a magnetic field of 9,000 to 13,000 G for 4 weeks. Compared to diabetic rats drinking control water, diabetic rats drinking the SW showed decreased blood glucose and glycated hemoglobin concentrations, with reductions in blood and liver DNA damage, but there was no difference in the results of the intra-peritoneal glucose tolerance test or plasma insulin ( Lee and Kang, 2013 ). In another study of induced type 2 diabetes in rats, water was passed through a 600 G magnet, and the water consumed for 4 wk; the authors reported increased pancreatic β-cell mass and insulin expression ( Saleh et al., 2019 ).

In an abstract and study report, the results of a clinical study performed using diabetic patients are presented ( Wang et al., 2004 ). In this multicenter, clinical trial subjects with type II diabetes ( n = 164) were provided 250 mL of SW (control group received distilled water; n = 162) twice daily for 4 wk; this represents about 20% of daily water intake. In subjects with blood glucose lower than 8 mmol/L, there were no changes in cellular hydration, and no adverse effects. In subjects with blood glucose >8 mmol/L, there were significant increases in cellular hydration and health as determined using bioelectrical impedance analysis. It was concluded that SW has beneficial effects on cell health and metabolism in subjects with moderate-to-severe type 2 diabetes.

The consumption of magnetized water by children infected with the parasitic condition ascariasis resulted in resolution of the condition in “most cases” with “no side effects” ( Wu 1989 ). Further details on both these studies are not readily available.

Adult rats ( n = 5 per group) were given drinking water from the tap (controls) or magnetized water at intensities of 250, 750, 1,000, 1,500 G every day for 30 d, after which the heart, lung, and spleen were examined ( Al-Saffar et al., 2013 ). There were no gross or histological effects reported for heart. Histological examination of lung tissues showed lymphoid hyperplasia when rats consumed the 750 and 1,000 G waters. Examination of spleen also showed hyperplasia of the white pulp with 250 G water, and lymphoid hyperplasia with 750 and 1,000 G waters, with lesions progressing to areas of necrosis with 1,500 G water.

In the study by Lee and Kang (2013) using diabetic rats, the authors also tested the lymphocyte and hepatocyte populations for evidence of DNA damage using comet assays. DNA damage was significantly greater in diabetic rats consuming control water or SW compared with control rats drinking control water. However, in diabetic rats consuming SW, there was a significant ~70% reduction in DNA damage compared with diabetic rats drinking control water. Al-Hilali (2018) used the mitotic index of bone marrow cells (a measure of the rate of cell division) to assess “genetic” damage after quail drank SW for 60 d. The magnitude of increase in mitotic index was positively correlated with the intensity (500 and 1,000 G) of the tap water (probability of DNA damage: control 0.055, 500 G water 0.063, and 1,000 G water 0.085) all of which are well below the probability (0.20) that begins to be associated with genetic damage ( Pedersen et al., 2016 ). Thus, the increase in mitotic index indicates only small increases in mitotic cells division; one could even consider this to be a beneficial effect.

When rats drank SW for up to 45 d, there was an increase in bone mineral content, bone mineral density and increased breaking resistance by 45 d ( Balieiro Neto et al., 2017 ).

The study performed on Thoroughbred racehorses in active training showed that compared with control water, horses drinking 10 L per day of SW for 4 wk showed an increase in whole body and extracellular hydration ( Lindinger and Northrop, 2020 ). The horses also had improved upper airway health (less mucous, swelling, and indications of inflammation) when examined endoscopically after workout gallops, and an increased heart rate variability when resting quietly in their stalls. The increase in resting heart rate variability is indicative of a more restful autonomic state.

In an abstract, Chen et al. (2005) provided by gavage 0.5 mL of 0, 33.3% or 100% of a stabilized SW product to mice ( n = 14 treatment and 14 controls) for 30 d. Mice normally drink 4 to 6 mL/d, and a 25-g mouse has a maximum stomach volume of 0.5 mL. Before provided SW, and after 30 d, the mice performed a swim endurance test. Compared to baseline and a control group that did not receive SW, mice that were given SW increased swim duration from 16 ± 8 to 24 ± 10 min (33.3% SW; P <0.05) and to 38 ± 30 min (100% SW). The authors correlated increased swim time with increased pre-exercise liver glycogen stores g/100 g; control: 41 ± 12 vs. 33.3 % SW: 65 ± 20 ( P < 0.002 compared with control) and 100% SW: 67±16 ( P < 0.0002 compared with control) in a separate group of mice treated the same way except for no exercise. It was concluded that providing 3% to 10% of the daily water intake in the form of SW was able to increase liver glycogen content and increase swim duration.

While not a drinking study, Gupta and Bhat (2011) examined the effects of water magnetized for 24 or 72 hr on the ability to inhibit oral Streptococcus mutans . The details of the water treatment are not provided, other than 72 but not 24 hr of treatment results in increased pH and a 55% reduction in electrical conductivity. Children were provided with 10 mL of the SWs or 10 mL of a 0.2% chlorhexidine solution and instructed to rinse the mouth for 1 or 3 min. The authors reported significant reductions in S. mutans with 1 min (72 hr treated water) and 3 min (24 hr treated water) of rinsing with SW, and that results obtained with 1 min of rinsing with 72 hr-treated water were similar to those obtained with chlorhexidine. Goyal et al. (2017) also magnetized pure, still water for 72 hr. When children used 10 mL of this water as a mouth rinse, twice daily for 2 wk, there was a significant reduction in S. mutans count in samples of dental plaque and saliva. Therefore, water structured in this way appears to exhibit anti-microbial effects.

Research conducted during the past 2 decades provide scientific evidence that the consumption of SW, compared with unstructured liquid water, confers a wide range of benefits to all of the animals studied to date so long as intensity and duration of water treatment are not excessive. The few studies that examined “dose–response” effects consistently showed that water exposed to magnetic fields of between 1,000 and 4,000 G for brief periods, i.e., flow-through systems, provided a number of physiological benefits compared with control waters. Some studies, however, indicate that field strengths of 3,000 G and higher may generate undesirable effects. There is evidence of increased growth, egg mass, milk yield, carcass mass, improved reproductive indices, improved blood lipid and glycemic profiles and improved blood/systemic antioxidant and inflammation profiles. It is both interesting and disappointing that none of these studies have examined putative mechanisms for these effects, so we are left with descriptive studies. These descriptive studies, however, can be used to guide innovative and well-designed research to examine effects of SW on biological systems. Based on these descriptive studies, the applications are broad and include all aspects of agriculture, as well as plant and animal health. The potential for applications in animal and human medicine was also exemplified in studies that focused on diabetes, and other animal studies indicated improvements in blood lipid profile. Based on what is known about how water is organized around cells, it is likely that perfusing the cells with an SW product will change cellular functions, protein functions, and molecular interactions in numerous and various ways. Future studies need to be aimed at elucidating main effects using cellular and organ physiology techniques.

Magnetic field strengths used to treat water vary from 500 to 32,400 G, with duration of treatment ranging from seconds (magnetic flow-through systems using several high field strength magnets) to 72 hr using small volumes with static, low field strength magnets. Inadequate water treatment results in no or minimal biological effect, whereas excessive treatment may be associated with adverse effects (see below). Based on the results of the studies presented below, a magnetic field strength of 1,000 to 3,000 G is required to generate water capable of exerting beneficial effects, while waters treated with field strengths greater than 5,000 G may result in detrimental effects. Future studies need to provide detailed methodology and some key physico-chemical properties that are changed by the structuring process, and the duration of structural stability. Future research needs to determine the water treatment conditions that optimize for specific biological outcomes and the researchers must measure and report several key indicators that demonstrate water structuring. The latter, in particularly, would be most helpful in performing comparison between studies. The animal research conducted to date consistently demonstrated beneficial effects of SW consumption. Additional research is needed to demonstrate how these effects occur, and if these types of SWs are safe to consume and use over the long term.

Abbreviations

alkaline phosphatase

alanine aminotransferase

aspartate aminotransferase

dry matter intake

high-density lipoproteins

immunoglobulin A

immunoglobulin G

immunoglobulin M

low-density lipoproteins

red blood cells

structured water

thiobarbituric acid substances

triglyceride

ultraviolet–visible

very low density lipoproteins

while blood cells

The research for this review was conducted as part of a larger paid research contract to The Nutraceutical Alliance Inc. by Defiance Brands, Inc., Nashville, TN, USA.

The authors declare no real or perceived conflicts of interest.

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Zhang , Y. S. , and H. W. Wu . 1987 . Effect of magnetic water on urinary calculi—an experimental and clinical study . Z. Urol. Nephrol . 80 : 517 – 523 .

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 1.

• Hydrogen bonding in water
• Hydrogen bonds in water
• Capillary action and why we see a meniscus
• Surface tension
• Cohesion and adhesion of water
• Water as a solvent
• Specific heat, heat of vaporization, and density of water
• Importance of water for life

Lesson summary: Water and life

• Structure of water and hydrogen bonding

Unique properties of water

• Water is polar. Water molecules are polar, with partial positive charges on the hydrogens, a partial negative charge on the oxygen, and a bent overall structure. This is because oxygen is more electronegative , meaning that it is better than hydrogen at attracting electrons.
• Water is an excellent solvent. Water has the unique ability to dissolve many polar and ionic substances. This is important to all living things because, as water travels through the water cycle, it takes many valuable nutrients along with it!
• Water has high heat capacity. It takes a lot of energy to raise the temperature of a certain amount of water by a degree, so water helps with regulating temperature in the environment. For example, this property allows the temperature of water in a pond to stay relatively constant from day to night, regardless of the changing atmospheric temperature.
• Water has high heat of vaporization. Humans (and other animals that sweat) use water’s high heat of vaporization to cool off. Water is converted from its liquid form to steam when the heat of vaporization is reached. Since sweat is made mostly of water, the evaporating water absorbs excess body heat, which is released into the atmosphere. This is known as evaporative cooling .
• Water has cohesive and adhesive properties. Water molecules have strong cohesive forces due to their ability to form hydrogen bonds with one another. Cohesive forces are responsible for surface tension , the tendency of a liquid’s surface to resist rupture when placed under tension or stress. Water also has adhesive properties that allow it to stick to substances other than itself. These cohesive and adhesive properties are essential for fluid transport in many forms of life. For example, they allow nutrients to be transported to the top of a tree against the force of gravity.
• Water is less dense as a solid than as a liquid. As water freezes, the molecules form a crystalline structure that spaces the molecules further apart than in liquid water. This means that ice is less dense than liquid water, which is why it floats. This property is important, as it keeps ponds, lakes, and oceans from freezing solid and allows life to continue to thrive under the icy surface.

Common mistakes and misconceptions

• Water dissolves everything because it is the “universal solvent." Water has the ability to dissolve many substances but the term “universal solvent" is misleading. Water is able to dissolve other polar molecules and ions, such as sugars and salts. However, nonpolar molecules like oils lack partial positive or partial negative charges, so they are not attracted to water molecules. This is why nonpolar substances like oil remain separate when added to water.

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New study offers a cleaner path for controlling water, transforming greenhouse gases

by Paul Dailing, University of Chicago

Scientists looking to convert carbon dioxide into clean fuels and useful chemicals often make hydrogen gas and carbonates as unwanted byproducts. A new paper from the UChicago Pritzker School of Molecular Engineering has found a cleaner path.

Carbon dioxide is the greenhouse gas, singlehandedly responsible for 78% of the change in energy balance in Earth's atmosphere between 1990 and 2022.

A byproduct of burning fossil fuels , carbon dioxide enters the atmosphere from car exhaust and coal-fired power plants. Even some renewable energy resources produce a small amount of carbon dioxide, although at a tiny fraction of the amount coal and natural gas create.

At its core, this molecule is just an arrangement of one carbon and two oxygen atoms that can be reorganized through a process called electrochemical carbon dioxide reduction (CO 2 R) into clean fuels and useful chemicals. But the process is often done at a loss, with competing processes pulling the atoms in unwanted directions that create unwanted byproducts.

In a paper published today in Nature Catalysis , researchers from the UChicago Pritzker School of Molecular Engineering's Amanchukwu Lab outlined a way to manipulate water molecules to make CO 2 R more efficient, with the ultimate goal of creating a clean energy loop.

Through their new method, the team was able to perform CO 2 R with nearly 100% efficiency under mildly acidic conditions, using either gold or zinc as catalysts.

"Imagine we can have green electricity from solar and wind, and then use this electricity to convert any carbon dioxide back into fuels," said PME Ph.D. candidate Reggie Gomes, first author of the new paper.

Competing with HER

Electrochemically disassembling a molecule is like the break shot in a game of pool. The previous arrangement disappears and the balls scatter across the table, coming to rest in new combinations—not always the ones the player intended.

Similarly, researchers performing CO 2 R use electricity and water to break up and rearrange the harmful greenhouse gas . This sends atoms of carbon and oxygen from the carbon dioxide caroming across the table with hydrogen atoms from the water.

If it works as intended, the atoms form other, more desirable molecules that can be used as fuels or chemicals.

But as the atoms scatter, stable pairings of two hydrogen atoms often form, a process called the hydrogen evolution reaction (HER). This makes CO 2 R less efficient, as energy and atoms that become hydrogen gas can't be part of the molecules the scientists were trying to create.

Even in small quantities of water, CO 2 R is always competing with HER.

The Amanchukwu Lab—which is most notable for its battery research —applied insights from aqueous batteries to the problem, hypothesizing that controlling the water with organic solvents could provide a solution.

All that glitters

Both CO 2 R and HER rely on water as a proton donor. Using organic solvents and acid additives, the team was able to tune the water behavior, finding the sweet spot where it donated the right amount of protons to create the intended molecules, not the hydrogen gas and other unwanted materials like carbonates.

"In general chemistry we learn that carbon dioxide reacts with hydroxide to form carbonate. That's undesired because it depletes the molecule we want to valorize," said Neubauer Family Assistant Professor of Molecular Engineering Chibueze Amanchukwu.

Many of the most-effective ways to perform CO 2 R rely on precious metals .

"Platinum, silver, gold—for research purposes, they're great catalysts," Gomes said. "They're very stable materials. But when you're thinking about industrial applications, they become cost-prohibitive."

By engineering the electrolyte, the new method can get similar results using cheaper, more abundant materials.

"Right now, the best way to do this electrochemically at room temperature is to use precious metals. Gold and silver can suppress the hydrogen evolution reaction a little bit," Amanchukwu said. "Because of our discovery, we can now use an earth-abundant metal, zinc, because we now have a separate way to control water."

Journal information: Nature Catalysis

Provided by University of Chicago

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• v.8(4); Oct-Dec 2018

Daily ingestion of alkaline electrolyzed water containing hydrogen influences human health, including gastrointestinal symptoms

Yoshinori tanaka.

1 Appliances Company, Panasonic Corporation, Shiga, Japan

Yasuhiro Saihara

Kyoko izumotani.

2 Osaka Municipal Health Promotion Center, Osaka, Japan

Hajime Nakamura

3 Osaka City University, Graduate School of Medicine, Osaka, Japan

Author contributions

In Japan, alkaline electrolyzed water (AEW) apparatus have been approved as a medical device. And for the patients with gastrointestinal symptoms, drinking AEW has been found to be effective in relieving gastrointestinal symptoms. But some users of AEW apparatus do not have abdominal indefinite complaint. Little attention has been given to the benefit for the users which have no abdominal indefinite complaint. The object of this study is to evaluate the effect on health, including gastrointestinal symptoms, when a person without abdominal indefinite complaint, etc ., drinks AEW on a daily basis. A double-blind, randomized controlled trial has been designed. Four-week period of everyday water drinking, PW drinking group: drink purified tap water as a placebo, AEW drinking group: drink alkaline electrolyzed water which made by electrolysis of purified tap water. Before the experiment and after the 4-week period of water drinking, Blood tests, physical fitness evaluations, and questionnaire evaluations is conducted. In this study, we did not specifically select patients with gastrointestinal symptoms. Sufficiently clear effect could not be confirmed. But the stools were more normal, and, as shown in the previous report, that drinking AEW is considered to contribute to intestinal normalization. In addition, when drinking AEW, a high proportion of the respondents said that they felt they were able to sleep soundly, and the proportion of subjects who answered that they felt good when awakening increased. The effect of reducing oxidative stress, thus allowing for improved sleep, was exhibited by drinking AEW containing hydrogen, which is considered to be an antioxidant substance. This research were approved by the Ethics Committee of the Osaka City University Graduate School of Medicine (No. 837) and were registered in the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN ID: UMIN000031800) on March 22, 2018.

I NTRODUCTION

In Japan, water which is obtained on the cathode side by the electrolysis of tap water is called alkaline electrolyzed water (AEW) or reduced hydrogen water. 1 Improvement of gastrointestinal symptoms by ingesting AEW has been confirmed by Japanese researchers. For example, Naito et al. 2 reported the inhibitory effect of AEW ingestion on gastric mucosal disorder caused by aspirin, and Hayakawa et al. 3 reported the inhibitory effect of AEW ingestion on abnormal intestinal fermentation. Tashiro et al. 4 examined the effect of ingesting AEW or purified tap water (PW; as a placebo) at a rate of at 500 mL per day for 4 weeks in patients who had abdominal pain such as heartburn, stomach discomfort, abdominal bloating, diarrhea, constipation, etc ., and reported that the results of the AEW group were superior to those of the placebo group. 5 , 6 From these results, apparatus that produce AEW have been approved as medical devices by the Japanese Ministry of Health, Labour and Welfare. AEW is thought to be effective for functional gastrointestinal disorders. 5

Since AEW is produced by electrolyzing water, hydroxide ions, which are alkaline in nature, are generated. Hydrogen molecules are also generated on the electrode surface and dissolved in water. Therefore, AEW is alkaline water containing hydrogen. 1 In conventional efficacy studies, evaluations with respect to ingesting AEW have typically been conducted focusing on the alkalinity of the water. 2 , 3 , 4 , 5 In recent years, however, the assumed effectiveness of the antioxidant effect of dissolved hydrogen on various diseases has been reported. 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 Nevertheless, some users of AEW apparatus do not have any definite abdominal symptoms. In many cases, they are drinking AEW on a daily basis to improve their health, and many users also feel health benefits such as improvement in exercise capacity 12 . These may be thought to be due to the action of dissolved hydrogen. There have been no researched studies of these in detail. The object of this study is to evaluate the effect of daily ingestion of AEW on health, including gastrointestinal symptoms, in subjects without any definite abdominal symptoms.

P ARTICIPANTS AND M ETHODS

Participants.

Healthy men and women (20–60 years) who use the Osaka City Citizen Health Development Consultation Center were selected as test subjects to determine the health effect of daily AEW ingestion. It was aimed to clarify whether general subjects without gastrointestinal symptoms have another good effect besides gastrointestinal symptoms by drinking AEW which is good for gastrointestinal symptoms. We explained this purpose to the subjects and asked for research participation. Written informed consent was obtained from all subjects. All procedures used in this research were approved by the Ethics Committee of the Osaka City University Graduate School of Medicine (No. 837) and were registered in the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN ID: UMIN000031800) on March 22, 2018. This study follows the Consolidated Standards of Reporting Trials (CONSORT) guidelines. A double-blind, randomized controlled trial has been designed, and the research design is shown in Figure 1 .

Research design.

Note: PW: Purified tap water; AEW: alkaline electrolyzed water.

Subjects were randomly divided into two groups, with an AEW group ( n = 30) and a PW group ( n = 30). Blood tests, physical fitness evaluations, and questionnaire evaluations were conducted before the experiment was initiated. Subjects were provided with AEW apparatus 1 that had been modified to produce only AEW or PW. They ingested 500 mL or more of freshly produced AEW or PW per day (they were required to ingest 200 mL immediately after awakening, and 300 mL or more during the rest of the day). After the end of the four-week period, blood tests, physical fitness evaluations, and questionnaire evaluations were conducted again to check whether the ingestion of AEW for four weeks had beneficial effects on the health of the subjects.

Blood sample/urinalysis

General blood test: Red blood cell count, white blood cell count, hemoglobin, hematocrit, and platelet count.

Blood biochemical examination: Total protein, albumin, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), γ-GTP, total cholesterol, high-density lipoprotein (HDL), cholesterol, low-density lipoprotein (LDL) cholesterol, neutral fat, uric acid, creatinine, and blood sugar.

Urinalysis: Urine sugar, urine protein, urine occult blood, and urine pH.

Physical measurements

Right/left grip strength, right/left leg muscle strength, vertical jump, whole body reaction time, standing time on one leg with eyes closed, sit-up, seated forward bend, and resting blood pressure.

Questionnaire variables

Gastrointestinal symptoms (stomachache, heartburn, heavy stomach, lower abdominal pain, bloated stomach), urinary frequency, condition of the stools (fecal properties and bowel movement), and physical condition (sleep quality and upon awakening).

Statistical analysis

In the blood data, the urinalysis and physical measurement values, the statistical significance of the average difference (before and after AEW, PW drinking) was analysed using a paired t -test (Statcel 4 Software [OMS Publishing, Saitama, Japan). The questionnaire data (before and after AEW, PW drinking) was analysed by the Wilcoxon signed-rank test using the same Statcel 4 software. Differences for which P values of < 0.05 and < 0.01 were inferred as significant.

Conditions of subjects and water quality

Subjects with abdominal symptoms such as heartburn, stomach discomfort, abdominal bloating, diarrhea, and constipation were used in the study previously performed. 4 , 5 For the current study, subjects aged 20 to 69 years were randomly selected among medical checkup examinees who visited the Osaka City Citizen Health Development Consultation Center, and then divided into two groups. One group ingested PW while the other ingested AEW. Neither the subjects nor the experimenters knew which group the subjects belonged to. Figure 2 shows that no significant differences were found in dispersion of mean values and distribution values.

Age distribution of subjects.

Each subject was provided with an AEW apparatus that had been modified to either produce or not produce AEW, and asked to install it at their home. In order to verify the quality of the drinking water, the water produced by the apparatus was taken into aluminum containers and collected when the subjects came in for measurement. Figure 3 shows the water quality distribution of each drinking water.

Water quality distribution of two types of drinking water.

Because we selected subjects who live in or around Osaka City, the tap water from either the same or a nearby water source was used for the evaluation. For this reason, the tests have been conducted using water of equivalent quality and which shows little bias in the distribution of ions.

Regarding the water before and after the electrolysis, the pH was 7.6 ± 0.2 for the PW group, and 9.2 ± 0.2 for the AEW group. Dissolved hydrogen concentration was not measurable at the subjects’ houses because hydrogen easily escapes water. However, for non-electrolyzed and electrolyzed tap water from the same water source and using the same water apparatus, the hydrogen concentration was confirmed as 0 mg/L in the PW group and 0.2 mg/L for the AEW group for the characteristics of the device.

Comparison of hematological values

The hematological data of subjects in the PW group and the AEW group were compared before and after the four-week period, but no significant differences were observed in both groups. This is consistent with the contents of the previous report. 5 However, the HDL cholesterol level, a newly measured value this time, of the AEW group showed a tendency to increase with P = 0.097, as shown in Figure 4 .

Change in HDL cholesterol before and after drinking.

Note: (A) alkaline electrolyzed water (AEW) drinking group, (B) purified tap water (PW) drinking group. HDL: High-density lipoprotein.

Comparison of data related to physical abilities

For the seated forward bend, vertical jump, right/left grip strength, and sit-up, there was no significant difference before and after the 4-week period for both the PW group and the AEW group.

Regarding the whole body reaction time, no significant differences were observed before and after the 4-week period in the case of the PW group, as seen in Figure 5B . However, a significant difference (decrease) ( P < 0.05) was observed in the AEW group, as seen in Figure 5A . As for standing time on one leg with eyes closed, longer times were observed in the AEW group ( P = 0.09), as seen in Figure 6A .

Change in whole body reaction time before and after drinking.

Note: (A) Alkaline electrolyzed water (AEW) drinking group; (B) purified tap water (PW) drinking group.

Changes in the standing time on one leg with eyes closed before and after drinking.

Note: (A) alkaline electrolyzed water (AEW) drinking group, (B) purified tap water (PW) drinking group.

Questionnaire to subjects

As for the questionnaire items, we asked the subjects to provide answers in 3 to 5 points about gastrointestinal symptoms ( Table 1 ), defecation and urination ( Table 2 ), and physical condition ( Table 3 ).

Gastrointestinal symptoms

Note: Scoring 1 to 4, where: Not at all = 1, and Very much = 4.

Defecation and urination

Physical conditionn

Note: Scoring 1 to 3, where: Good = 1, and Bad = 3.

First, as seen in Figures ​ 7 7 to ​ to 11 , 11 , as for gastrointestinal symptoms, sufficiently clear effect could not be confirmed in this study. Next, as seen in Figure 12 , the urinary frequency significantly increased in both groups, likely due to an increase in urine volume resulting from water ingestion. Regarding bowel movement, the stools slightly changed from slightly soft to normal or slightly hard, or from soft to normal ( P < 0.05) in the AEW group, as can be seen in Figure 13A . There was no difference between subjects of the two groups who had answered that they were in “good” or “bad” physical condition.

Change in stomach ache before and after drinking.

Note: Left side: alkaline electrolyzed water (AEW), and right side: purified tap water (PW).

Change in bloated stomach before and after drinking.

Change in urinary frequency before and after drinking.

Note: (A) Alkaline electrolyzed water (AEW) drinking group, and (B) purified tap water (PW) drinking group.

Changes in the condition of stools before and after drinking.

Change in heartburn before and after drinking.

Change in heavy stomach before and after drinking.

Change in lower abdominal pain before and after drinking.

Regarding sleep quality, there was a significant increase ( P < 0.01) in the number of AEW group subjects who responded that they were able to sleep well, as shown in Figure 14A , and there was a significant increase ( P < 0.05) in the number of subjects from the same group who said that they felt good upon awakening, as seen in Figure 15A .

Change in sleep quality before and after drinking.

Changes in the state of getting up before and after drinking.

D ISCUSSION

In Japan, AEW apparatus have been approved as medical devices, and ingesting AEW has been found to be effective in relieving gastrointestinal symptoms. A clinical evaluation of this effect was conducted with patients with gastrointestinal symptoms (heartburn, stomach discomfort, and abdominal symptoms such as abdominal bloating, diarrhea, and constipation). 5

Antioxidant action by hydrogen and gastric acid neutralization by alkaline pH have been considered. 6 In addition, recent studies have shown that the intestinal bacterial flora distribution changes. It seems that these are involved in the normalization of the gastrointestinal activity. 11 However, for this study, patients with gastrointestinal symptoms were not specifically selected. As for these as well as the previous results, in general, there was no difference in the hematological values between the PW group and the AEW group. 5 However, the newly measured HDL cholesterol value showed a tendency to increase with P = 0.097. The increase in HDL cholesterol by ingesting water containing hydrogen is reported by Gadek and colleagues. 16 The effect of hydrogen can be considered to have had an effect in the AEW group this time as well.

As for gastrointestinal symptoms—which showed a significant difference during the previous study (significant improvement of abdominal symptoms and improvement of abnormal bowel movement) 4 , 5 —sufficiently clear effect could not be confirmed by this study because the subjects did not show gastrointestinal symptoms, and very few of them responded that they had abnormal abdominal symptoms and bowel movement before participating in this study. Therefore, we believe this is the reason the answers of the subjects were the same before and after their participation in the study.

However, with respect to bowel movement, the stools slightly changed from soft to normal or slightly hard, or from loose to normal in the AEW group. This reflects that the stools are more normal, and, as shown in the previous report, that ingesting AEW is considered to contribute to intestinal normalization. 4 , 5 , 6 Regarding items other than the gastrointestinal tract, a high proportion of the respondents said that they felt they were able to sleep well, and the proportion of subjects who answered that they felt good when awakening increased. Various studies on the relationship between the ingestion of antioxidant substances and the condition of sleep have been undertaken, 17 and the effect of reducing oxidative stress, thus allowing for improved sleep quality, is exhibited by ingesting AEW containing hydrogen, which is considered an antioxidant substance.

Regarding sports performance, various reports on the effects of sleep on sports performance have concluded that willingly sleeping longer can lead to faster running, shortened reaction time, and improved motivation during practice and games. 18 Improved sleep quality by ingesting AEW is, therefore, believed to help reduce fatigue, ensure appropriate endurance recovery, and improve overall sports performance.

The findings of this study indicate that ingesting AEW on a daily basis improves health and exercise capacity, even in healthy people who do not have gastrointestinal symptoms.

Funding: The study was supported by a grant from Matsushita Electric Works Co., Ltd. Home Appliances R&D Center (to HN).

Conflicts of interest

The corresponding author (YT) is a salaried employee of the Panasonic Corporation. One of the authors (SY) was a salaried employee of the Panasonic Corporation. This study does not alter our adherence to Medical Gas Research policies on sharing data and materials. Another authors (KI and HN) report no conflict of interest related to this manuscript.

Financial support

The study was supported by a grant from Matsushita Electric Works Co., Ltd. Home Appliances R&D Center (to HW).

Institutional review board statement

All procedures used in this research were approved by the Ethics Committee of the Osaka City University Graduate School of Medicine (No. 837) and were registered in the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN ID: UMIN000031800) on March 22, 2018.

Declaration of participant consent

The authors certify that they have obtained participant consent forms. In the form, participant have given their consent for their images andother clinical information to be reported in the journal. The patients understand that their names and initials not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Reporting statement

This study follows the Consolidated Standards of Reporting Trials (CONSORT) guidelines.

Biostatistics statement

The statistical methods of this study were reviewed by the biostatistician of the Osaka City University, Osaka, Japan.

Copyright license agreement

The Copyright License Agreement has been signed by all authors before publication.

Data sharing statement

Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures, and appendices). Study protocol and informed consent form will be available immediately following publication, without end date. Results will be disseminated through presentations at scientific meetings and/or by publication in a peer-reviewed journal. Anonymized trial data will be available indefinitely at www.figshare.com .

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• Published: 06 December 2019

Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide

• Bryan H. R. Suryanto   ORCID: orcid.org/0000-0001-9759-6362 1   na1 ,
• Yun Wang   ORCID: orcid.org/0000-0001-8619-0455 2   na1 ,
• Rosalie K. Hocking   ORCID: orcid.org/0000-0002-2213-8786 3 ,
• William Adamson 1 &
• Chuan Zhao 1  

Nature Communications volume  10 , Article number:  5599 ( 2019 ) Cite this article

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• Electrocatalysis
• Nanoparticles

Efficient generation of hydrogen from water-splitting is an underpinning chemistry to realize the hydrogen economy. Low cost, transition metals such as nickel and iron-based oxides/hydroxides have been regarded as promising catalysts for the oxygen evolution reaction in alkaline media with overpotentials as low as ~200 mV to achieve 10 mA cm −2 , however, they are generally unsuitable for the hydrogen evolution reaction. Herein, we show a Janus nanoparticle catalyst with a nickel–iron oxide interface and multi-site functionality for a highly efficient hydrogen evolution reaction with a comparable performance to the benchmark platinum on carbon catalyst. Density functional theory calculations reveal that the hydrogen evolution reaction catalytic activity of the nanoparticle is induced by the strong electronic coupling effect between the iron oxide and the nickel at the interface. Remarkably, the catalyst also exhibits extraordinary oxygen evolution reaction activity, enabling an active and stable bi-functional catalyst for whole cell water-splitting with, to the best of our knowledge, the highest energy efficiency (83.7%) reported to date.

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Introduction.

Electrochemical water-splitting has been considered as one of the most promising approaches to store renewable electricity in the form of hydrogen fuel 1 . Hydrogen can be generated in a water electrolyzer consisting of a hydrogen evolution reaction (HER) cathode and an oxygen evolution reaction (OER) anode 2 , 3 . However, due to the distinctly different catalytic mechanisms, active HER catalysts are often found to be poor OER catalysts, and vice versa 4 , 5 . The current benchmark electrolyzer utilizes Pt-based cathode and RuO 2 /IrO 2 anodes to expedite HER and OER, respectively 6 , 7 . From a commercialization point-of-view, it is not only the significant cost of noble metal elements that creates economic pressure but also the additional cost generated due to the complications of producing different cathode–anode materials and possible cross-contaminations 8 . Hence the development of a universally active water-splitting catalyst based on Earth-abundant materials is of key interest and a significant innovation 9 .

Recent progress in the development of Earth-abundant-based electrode materials for OER has revealed that Ni and Fe mixed oxides/hydroxides system is inherently active in alkaline media, comparable to that of RuO 2 /IrO 2 -based electrocatalysts 10 , 11 , 12 . To this end, several strategies such as nanosizing, heteroatoms-doping, surface engineering, vacancy engineering, and carbon nanomaterials coupling have been demonstrated to improve the OER catalytic performance 11 , 13 , 14 , 15 , 16 . However, Ni–Fe-based alloys and oxide/hydroxide are not good cathode catalysts for HER, exhibiting sluggish kinetics at the oxides surface 17 , 18 . It is known that most of the Earth-abundant transition metals (M=Ni, Co, Fe, Mo, etc.) bind to H + either too strongly or too weakly which results in poor HER activities 19 . As a result, Pt-based catalysts (e.g. Pt/C) remain the primary cathode material option to achieve extremely low overpotentials and large current densities 20 .

Significant recent effort has been made in the development of Earth-abundant transition metal chalcogenides and pnictogenides that exhibit bi-functional activity towards both HER and OER 21 , 22 , 23 , 24 , 25 , 26 . It is established that the modification of transition metal with electronegative chalcogens/pnictogens (X=N, P, S, and Se) can generate localized negative charges within the M–X surface structures which favors the initial adsorption of H + (acidic) or H 2 O (alkaline), and near-surface electronic structure modulation, resulting in weakened M–H bond and lowered HER energy barriers 27 , 28 , 29 , 30 . However, OER at these materials normally occurs at the high valence metal active sites formed in operando during anodic polarization 31 , 32 . This anodic process inevitably leads to oxidative corrosion and restructuring of the M–X materials 32 , 33 , 34 . Concomitantly, the HER catalytic activity of the M–X materials degrades eventually due to the corrosion-induced compositional and structural changes. This issue is exacerbated if the electrolyzer is powered by intermittent renewable energy such as solar or wind, where electrode degradation is accelerated as a result of depolarization and reversed current induced by frequent power interruptions and shut-downs 35 .

Hence, the development of low cost and robust catalysts with intrinsic active sites that are capable of catalyzing distinctly different HER and OER processes is highly challenging but imperative to realize efficient and sustained intermittent water-splitting. A common method of achieving bi-functional catalyst is through the design of catalysts that exhibit multiple active sites or multi-site functionalities. One approach is the adoption of Janus particle design, a term coined Casagrande et al. in ref. 36 , to describe an asymmetric particle which surface exhibit distinct composition/physical properties and therefore exhibits a distinct interface. Furthermore, it is also widely accepted that the creation of strongly coupled interface could benefits electrocatalysis due to the modulated electronic structure of the material 37 .

Herein, we show a Janus Ni–Fe nanoparticle (denoted Ni–Fe NP) exhibiting a Ni metal domain interconnected to a γ-Fe 2 O 3 , creating a heterojunction/interface (Fig.  1 ). Density functional theory (DFT) calculations indicate that the Ni–O–Fe bridge at Ni-γ-Fe 2 O 3 interface modifies the Gibbs free energy of the adsorption of the intermediate H atoms (Δ G H * ), thereby further promoting the performance of HER catalysis. As a result, the Ni–Fe NPs exhibit extraordinary HER catalytic activity, comparable to that of the benchmark Pt/C catalyst. Intriguingly, the overpotential for OER is also lowered due to the multi-site functionalities created at the interface as previously proposed by Nørskov and co-workers 38 . Through the combination of physical and electrochemical characterization methods, we have demonstrated that the Ni–Fe NPs exhibit extraordinary physical and electrochemical stability for both HER and OER processes.

Nanoparticle design and electron microscopies. a Schematic representation of the Ni and Fe nanoparticles and the Ni-Fe Janus nanoparticles synthesis through the oleate-assisted micelle formation and the illustration on the HER across the Ni-γ-Fe 2 O 3 interface in alkaline medium. b STEM-HAADF image of a single Ni–Fe NP nanoparticle and its corresponding EDS line-scan spectrum (scale bar: 1 nm). c High-resolution EDS mapping on STEM-HAADF images of the nanoparticles for Ni and Fe, selected area electron diffraction inset (image scale bars: 20 nm; SAED scale bar: 2 nm −1 ).

Physical characterizations

Important to this catalyst design is the synthesis of monodispersed Ni–Fe nanoparticles with controlled composition and very small size so that iron oxides (γ-Fe 2 O 3 ) are formed adjacent to metallic Ni, and abundant and stable interfaces are available for catalyzing water-splitting processes. In this study, Ni–Fe NPs were prepared by initially synthesizing Ni, Fe ion-oleate metal-surfactant complexes. Subsequently, micelle formation by the complexes was induced by the use of non-polar solvent ( n -hexane), serving as templates for nanoparticle formation during the thermal reduction process as illustrated in Supplementary Fig.  1 . This approach is scalable and enables precise control over the composition and size of the nanoparticles (details in Methods) 39 .

The transmission electron microscopy (TEM) images (Supplementary Fig.  5 ) display the structure and size distribution of the as-synthesized Ni–Fe NPs, which exhibit a Gaussian profile with the majority of particles having diameters of 5–8 nm. Supplementary Figure  5a also reveals that the ion-oleate surfactants are carbonized to form conductive carbon network that may facilitate facile electron transfer between the nanoparticle and the support 8 . Utilizing a high angle annular dark-field (HAADF) STEM technique, Fig.  1b reveals the presence of interfaces which divide the Ni–Fe NP into two phases with distinctly different crystal structures and electron densities. The phase with higher electron density appears brighter in Fig.  1b , which reveals a closely packed Ni crystal structure. The darker phase exhibits a more sparsely packed, less-dense crystal structure filled with smaller oxygen atoms consistent with the γ-Fe 2 O 3 structure, which was verified with the EDS line-scan elemental profiling shown in Fig.  1b . The EDS line scan indicates a distinct cross-over between the Ni and Fe elemental counts, confirming the presence of the Ni-γ-Fe 2 O 3 heterojunction. The slightly increased Ni counts within the Fe-rich phase could be ascribed to the presence of another Ni-rich phase or overlapping nanoparticle. Lower-magnification EDS elemental mapping shows that the asymmetric distribution of Ni and Fe are also commonly observed in other particles. Importantly, the HR-STEM imaging reveals the formation of Ni–O–Fe bridge at the interface as highlighted in Supplementary Fig.  6 . The selected area electron diffraction (SAED) of Ni–Fe NPs in Fig.  1c displays two clear diffraction rings with radius of 2.51 and 2.10 Å, indexed for (311) and (111) in γ-Fe 2 O 3 and Ni crystal lattices, respectively. To understand the Ni–Fe NP formation mechanism, Ni- and Fe-based nanoparticles (denoted as Ni NPs and Fe NPs) were also synthesized via the identical method. The micrograph in Supplementary Fig.  7 shows that the Fe NPs are evenly distributed, exhibiting average particle diameters of 6–7 nm, similar to Ni–Fe NPs. On the other hand, the Ni NPs display an uneven distribution of large nanoparticles (~50 nm diameter, Supplementary Fig.  8 ). The nanoparticle size difference suggests that the thermal nucleation of Fe NPs occurs at lower temperatures (~70 °C) and is instantaneous, while the Ni NPs nucleate at higher temperature following a progressive mechanism 40 , 41 . These results suggest that the Ni–Fe NPs are formed by growth of Ni on the pre-formed Fe NP, rather than simultaneous nucleation.

X-ray diffraction (XRD) analysis shown in Fig.  2a also reveals the unique features of Ni–Fe NPs. XRD pattern of Ni NP indicates the formation of core-shell structure of Ni/NiO as identified by the presence of peaks correspond to both Ni and NiO (ICDD: 04-001-3331; 04-011-9039), as a result of instantaneous formation of passivating NiO outer shell 42 . The XRD of Fe NP indicates that γ-Fe 2 O 3 (ICDD: 01-078-6916) was formed. In contrast, the nickel oxide diffraction peak was not observed in all the Ni–Fe NP samples and the strong peak at 44.5° corresponds to the (111) facet of metallic Ni, consistent to the STEM characterizations. Furthermore, the presence of γ-Fe 2 O 3 in the Ni–Fe NP sample was confirmed by the identification of a set of diffraction peaks that match the Fe NP control material.

X-ray characterizations. a X-ray diffraction spectra showing the reference stick patterns of NiO (purple line, ICDD: 04-011-9039), Ni (green line, ICDD: 04-001-3331), and γ-Fe 2 O 3 (magenta line, ICDD:01-078-6916). The peaks marked with black dots correspond to CFP substrate; X-ray photoelectron spectroscopy (XPS) of Ni–Fe NP. b Ni 2 p , c Fe 2 p , d O 1 s .

The oxidation states of Ni and Fe in Ni–Fe NPs were further analyzed by X-ray photoelectron spectroscopy (XPS). Two main peaks related to Ni 2 p exist at ~855.2 eV (Ni 2 p 3/2 ) and 873.0 eV (Ni 2 p 1/2 ) in Ni–Fe NPs as shown in Fig.  2b are related to the unintended formation of large Ni/NiO NP (~50 nm in diameter) present in the Ni–Fe NP samples, as shown in Supplementary Fig.  10a . Further quantification based on area analysis of Supplementary Fig.  10b reveals that there are approximately 17% of NiO NP present in the Ni–Fe NP sample. The Ni 2 p 3/2 peak at 852.9 eV that corresponds to Ni 0 (ref. 43 ) is observed only for the Ni–Fe NPs but not for the Ni NPs (Supplementary Fig.  11 ), in which clear Ni 2 p 3/2 multiplet-splitting were observed at ~855.2 and 873.1 eV, indicating the presence of Ni oxides. The significantly larger proportion of Ni 2 p peaks for Ni 2+ compared to that for Ni 0 in the Ni–Fe NP sample can be attributed to the presence of the significantly larger NiO NP, which can be detected relatively easily by XPS compared to the smaller Ni–Fe NP (~5–8 nm) that are well embedded in the carbon fiber substrate. Additionally, the presence of Fe 2 O 3 in the Ni–Fe NP sample is validated by the deconvolution of the high-resolution Fe 2 p scan which reveals peaks for both Fe 3+ and Fe 2+ (Fig.  2c ), giving an Fe 3+/ Fe 2+ ratio of less than 2, corresponding to the high Fe oxidation state in maghemite (γ-Fe 2 O 3 ) 11 , 44 . It is worth noting that the binding energy of Fe 2 p 3/2 in the Ni–Fe NPs is higher than that in both Fe 2 O 3 and Fe NPs (Supplementary Fig.  12 ), despite sharing an identical crystal XRD pattern (Fig.  2a ), indicating modifications to its electronic structure. The presence of Fe 2 O 3 was also consistent to the observation of a metal bound O 1 s peak at 530.6 eV (Fig.  2d ). The asymmetric oxidation of the Fe-rich domain in the Janus Ni–Fe NP structure can be ascribed to the oxygen scavenging property and lower electronegativity of Fe (Pauling scale, Fe = 1.83, Ni = 1.91). Additionally, the presence of interface enables partial charge transfer from the Fe-rich domain to Ni-rich domain across the interface due to the electronegativity asymmetry. Hence due to the higher electronegativity of Ni, electron from Fe domain is partially transferred into the Ni-rich domain, protecting the Ni-rich domain from oxidation.

Further investigation of the Ni–Fe NP structure was carried out with X-ray absorption spectroscopy (XAS). Supplementary Figure  13 shows the Ni XANES data collected on the materials compared to key reference materials. The physical mixture of Ni NP and Fe NP (Ni/Fe NP) is a well fit by a combination of 80% metallic nickel and 20% NiO, consistent with previous characterizations (XRD and TEM), indicating the formation of core-shell Ni/NiO NP. On the other hand, the Ni XANES of Ni–Fe NP shift to lower energy consistent with the presence of interface between the γ-Fe 2 O 3 phase and metallic nickel. This change is not well described by the Ni reference materials (blue arrow) indicating that it has properties that are distinct from any of them. By correlation with the TEM (Fig.  1b ) the most plausible explanation is the formation of an interface between Ni and γ-Fe 2 O 3 . The EXAFS data at the Ni edge (Supplementary Fig.  14 ) are dominated by metallic nickel are substantially dampened probably due to structural disorder. The Fe XAS spectra of the same set of materials are presented in Supplementary Fig.  15 . The XANES taken at the Fe edge show a shift to lower energy from the nanoparticle with interface (Ni–Fe NP). This is consistent with the contribution of a reduced Fe phase at the interface between Fe and Ni and is consistent with the XPS. This would be consistent with what was expected from the formation of an interface between metallic nickel and γ-Fe 2 O 3 interface as observed in the TEM. The EXAFS of these materials are dominated by that of γ-Fe 2 O 3 , which is expected as the majority of the Fe in the sample are in the form of γ-Fe 2 O 3.

Electrochemical performance

Figure  3a shows the HER activity of Ni–Fe NP supported on carbon fiber paper (CFP) obtained in 1.0 M KOH by using linear sweep voltammetry (LSV) at a scan rate ( v ) of 5 mV s −1 . CFP was chosen for HER activity evaluation due to its negligible HER activity. The catalyst mass loading and mole ratio of Ni to Fe were optimized based on the HER performance (Supplementary Figs.  16 and 17 ), and the best ratio of 5:1 was chosen for HER testing. Shown in Fig.  3a , the Ni–Fe NP exhibits an HER onset potential of −0.18 V vs. RHE (as determined by baseline extrapolation method (Supplementary Fig.  4 ), accompanied by visual detection of H 2 -gas bubbles formation on the electrode surface. Additionally, the Ni–Fe NPs exhibit a very low HER overpotential ( ɳ ) of 100 mV (without iR -corrections) to achieve a current density ( j ) of 10 mA cm −2 . Only 46 mV is required after the iR -correction (Supplementary Fig.  18 ). This HER performance is comparable to the benchmark Pt catalyst (20% Pt/C) supported on CFP at the same catalyst loading, and outperforms most, if not all, non-precious metal-oxides, -chalcogenides, -nitrides, and -phosphides-based HER catalysts in similar alkaline media (Supplementary Table  2 ). In contrast, significantly higher HER overpotentials are required for Ni NPs (260 mV) and Fe NPs (410 mV) to achieve 10 mA cm −2 , suggesting the distinct HER catalytic activity of the Ni–Fe NPs. Consistent trend in performance is also observed in Supplementary Fig.  22a where LSV curves are normalized against the electrochemical active surface area (ECSA) determined from double layer capacitance measurements (Supplementary Figs.  2 and 3 ). Ni–Fe NP exhibits the lowest ɳ of 200 mV for j ECSA  = −10 mA cm −2 . The stability of catalyst was also tested under a high current condition (Supplementary Fig.  19a ); the test was configured at j HER   =   − 100 mA cm −2 . Shown by the E–t trace (Supplementary Fig.  19b ), it is revealed that Ni–Fe NP remains stable at relatively low η of 180 mV for an extended period of 10 h at a constant current (−10 mA cm −2 ). Additionally, based on Supplementary Fig.  19d , assuming that all Ni and Fe in the Ni–Fe NP participate in HER catalysis, the turn over frequency (TOF) of Ni–Fe NP at ɳ  = 200 mV is 0.056 s −1 (Supplementary Information for details), an order of magnitude lower than that of Pt (0.9 s −1 ) but comparable to other state-of-the-art metal chalcogenide/phosphide and metal alloy, catalysts such as MoS 2 (0.02 s −1 ), Ni 5 P 4 (0.06 s −1 ), and Ni–Mo catalyst (0.05 s −1 ) 45 , 46 , 47 , 48 .

Electrochemistry. a HER-LSV curves for Ni–Fe NP, Ni/Fe NP, Ni NP, Ni–Fe alloy NP, Fe NP, and 20% Pt/C electrode (no iR -correction). b Tafel plots for all nanoparticles and benchmark catalysts. c The LSVs shows the presence of metal reduction peaks from Ni/Fe NP electrode. The peaks at 0 and −0.2 V is identical to Fe 3+/2+ and Fe 2+/1+ reduction peaks on the HER-LSV of Fe NP electrode shown in a and Supplementary Fig.  20 . d The OER LSV curves for Ni–Fe NP, Ni–Fe LDH, Ni–Fe alloy NP, Ni/Fe NP, 20% Ir/C, and NF electrode. e LSV comparing the water-splitting performance of Ni–Fe NP cell and Ir/C-Pt/C cell. f The stability test of Ni–Fe NP cell at current of 10 and 20 mA cm −2 (magenta trace), the blue trace represent the stability of Ir/C-Pt/C cell. All voltammetry was collected in 1 M KOH, with a scan rate of 5 mV s −1 .

Furthermore, the physical stability of Ni–Fe NP was also verified with inductively coupled plasma-mass spectrometry (ICP-MS) measurement of Ni and Fe in the electrolyte (Supplementary Table  3 ) during a 10 h constant current electrolysis at −50 mA cm −2 . As shown in Supplementary Table  3 , no metal dissolution was observed in the first hour of electrolysis. After 10 h of electrolysis, trace amount of Fe (70 μg L −1 ) was detected in the electrolyte which corresponds to only 1.5 wt% of Fe in the fresh electrode. Additionally, Supplementary Fig.  19d shows the loss of HER activity is minimal, which is validated by the LSVs obtained before and after the stability testing. The stability is also confirmed by HAADF-STEM (Supplementary Fig.  19c ), showing insignificant changes in the physical features of Ni–Fe NP. The crystal structure of the Ni–Fe NPs is also preserved after the stability test, as confirmed by XRD (Supplementary Fig.  27a ).

To investigate the HER reaction kinetics, Tafel plots were derived from the LSVs and shown in Fig.  3b . The Ni–Fe NP exhibits a much smaller slope of 58 mV dec −1 than Ni NP (167 mV dec −1 ), Fe NP (186 mV dec −1 ), and Ni/Fe NP (212 mV dec −1 ), and an extremely large exchange current density of 1.58 × 10 −3 A cm −2 which even matches with Pt/C catalyst in acidic media 49 , 50 . This slope value is also distinctly different from the previously reported Ni–Fe-based catalysts, which typically exhibit Tafel slopes above 80 mV dec −1   51 , 52  and approaches 20% Pt/C-CFP (Tafel slope: 50 mV dec −1 ), suggesting the HER at the Ni–Fe NP follows a Volmer–Heyrovsky HER mechanism 50 .

To understand the role of the interface between Ni and γ-Fe 2 O 3 for HER , a physical mixture of Ni NPs and Fe NPs (denoted as Ni/Fe NPs) and an Ni–Fe alloy mixture (Supplementary Fig.  9 , denoted as Ni–Fe alloy NP) were prepared at a molar ratio of 5 to 1, and their HER activities were evaluated. The physically mixed Ni/Fe NP was produced by drop-casting Ni(oleate) 2 and Fe(oleate) 2 at different stages, instead of the standard pre-mixing procedure of Ni 2+ and Fe 2+ with the oleate anion prior to the micellization step (Supplementary Fig.  1 ). The Ni–Fe alloy NP were prepared by annealing the precursor of Ni–Fe NP in high temperature H 2 atmosphere to achieve better alloying. Shown in Fig.  3c , the Ni/Fe NP and Ni–Fe alloy NP require overpotentials of 112 and 307 mV, respectively, to achieve 10 mA cm −2 , which are significantly higher than that required for Ni–Fe NP. Importantly, it is noted that the Fe 3+ reduction peaks at 0 and −0.2 V observed in both Ni/Fe NPs (Fig. 3c ) and Fe NPs (Supplementary Fig. 20 ) are not present in the LSV of Ni–Fe NPs, suggesting the redox behavior of the interconnected γ-Fe 2 O 3 is altered as a result of the formation of Ni-γ-Fe 2 O 3 interface.

Intriguingly, the Ni–Fe NP also exhibits extraordinary activity towards OER. We further examined the OER performance of the Ni–Fe NPs supported on nickel foam substrate (NF, Fig.  3d ) and CFP (Supplementary Fig.  21 ). Nickel foam was used as substrate due to its excellent electrochemical properties, e.g. corrosion resistance against OER, electrical conductivity, 3-D porous structure, and robust mechanical strength 11 , 22 , 52 . The state-of-the-art NiFe layered double hydroxide (NiFe-LDH) electrocatalysts were also synthesized according to the established method to provide comparison 14 . Figure  3d shows that OER process catalyzed by Ni–Fe NP reaches a current density of 10 mA cm −2 at a low overpotential of 210 mV. Higher current densities of 20 mA and 100 mA cm −2 were achieved at η of 230 and 270 mV, respectively. These values outperform 20% Ir/C (Fig.  3d ) as well as most reported transition metal oxides, chalcogenides, phosphides, and nitrides electrocatalysts (Supplementary Table  4 ). The TOF at η of 350 mV, by assuming all Ni and Fe in Ni–Fe NP participate in catalysis, is calculated to be 0.052 s −1 (Supplementary Information for details), which is comparable to benchmark 20% Ir/C (0.027 s −1 ) and electrodeposited NiFe/NF (0.075 s −1 ) at η of 400 mV, respectively 11 . It is worth noting that due to the small proportion of Ni–Fe interfaces on the Ni–Fe NP surface, the amount of Ni–O–Fe active sites are far less than the loaded amount of Ni and Fe, and therefore the actual TOF should be higher than the calculated values. Additionally, the LSVs were also normalized against ECSA (Supplementary Fig.  22b ). Consistent with Fig.  3d , Supplementary Fig.  22b shows that Ni–Fe NP exhibits the highest OER performance with j ECSA  = 10 mA cm −2 achieved at η of 300 mV, which is also higher than electrodeposited NiFe/NF 11 . These comparisons indicate the crucial role of Ni-γ-Fe 2 O 3 interface present in the Ni–Fe NP for OER electrocatalysis.

Supplementary Figure  23 shows that the Tafel slope of Ni–Fe NP is lower than that of NiFe-LDH and the linearity of the plot is also maintained at high j , indicating fast electron transfer and mass transport properties of the catalyst 12 , 53 . Supplementary Figure  24 shows chronopotentiometric response of Ni–Fe NP for OER with j increasing gradually from 50 mA to 500 mA cm −2 in nine-equal current steps of 50 mA cm −2 . The potential response was observed to level off quickly on each stepping with high consistency, suggesting excellent mass transport properties as well as physical stability 11 . Excellent stability of the Ni–Fe NP for prolonged OER is illustrated in Supplementary Fig.  25a, b . Further, ICP-MS, HAADF-STEM, LSVs, and XRD analyses of Ni–Fe NP following OER stability tests also show negligible dissolution of the catalyst during OER (Supplementary Table  5 ), and no significant change to structure and OER activity (Supplementary Figs.  25c–d and 27b ), compared to fresh Ni–Fe NP electrode.

Importantly, Fig.  3d shows the Ni oxidation peak prior to the onset of OER is greatly suppressed in the Ni–Fe NP configuration (Supplementary Fig.  26 for greater magnification of the Ni peak). The oxidation peak corresponds to the oxidation of Ni from low valence states (Ni 0 , Ni 2+ ) to high valence states (Ni 3+ or Ni 4+ ), the latter are believed to be the active sites for OER 54 , 55 . The greatly reduced Ni oxidation peak, compared to that observed for Ni NP, Ni/Fe NP, and Ni–Fe alloy NPs (Fig.  3d ), suggests that OER active sites already exist in the Ni–Fe NP, rather in operando formed. Compared to the structures and electrochemical results obtained for Ni NP, Ni/Fe NP, and Ni–Fe alloy NPs, where no Ni/Fe 2 O 3 interface present, it is clear that the Ni-γ-Fe 2 O 3 interface play a major role as the OER active site. Similar behavior is observed for HER, where the Fe reduction peaks prior to the onset of HER currents are observed for Ni/Fe NP (Fig.  3c ) and Fe NP (Supplementary Fig.  20 ) but not for Ni–Fe NP, suggesting that the HER active sites in Ni–Fe NP are also present at the start of HER. Collectively, these results suggest that both OER and HER occur at the similar sites at the interface of Ni–Fe NP. It is also important to note that the presence of metallic Ni enables fast electron transport within the nanoparticle that is required for efficient electrocatalysis.

Further, Ni–Fe NP was used as both the anode and cathode in a whole cell water electrolyzer (details in Methods). The polarization curve of the Ni–Fe NP cell is recorded and compared to the cell constructed using benchmark noble metal catalysts, 20% Ir/C (OER) and 20% Pt/C (HER). Shown in Fig.  3e , the Ni–Fe NP cell exhibits superior performance to the Ir/C || Pt/C cell. The cell potential required for Ni–Fe NP cell to achieve 10 mA cm −2 is only 1.47 V (1.55 V without iR -correction; Supplementary Fig.  28 ), which is among the lowest bi-functional water-splitting catalysts reported recently (Supplementary Table  6 ). Based on the calculated HER and OER Faradaic efficiency of approximately ~100% at j  = 10 mA cm −2 (Supplementary Fig.  31 ), the energy efficiency of the Ni–Fe NP cell is calculated to be 83.7% with iR- correction (79.4% without iR- correction). The Ni–Fe NP cell also shows excellent stability during the 24 h bulk water electrolysis at j  = 10 and 20 mA cm −2 (Fig.  3f ). In comparison, the Ir/C || Pt/C cell requires a cell voltage of 1.62 V to achieve 10 mA cm −2 and the performance was observed to deteriorate after 2 h, which is consistent to previous report 4 . In addition, to further demonstrate the Ni–Fe NP electrochemical stability against power interruptions, an accelerated degradation test (ADT) was performed by alternating the polarity of the electrode repeatedly. In this experiment, the electrolysis current is switched between 100 mA cm −2 (OER) and −100 mA cm −2 (HER), and the Ni–Fe NP electrode is subjected to anodic oxidation for OER for 600 s before switching to HER, and vice versa. Supplementary Figure  29 displays the stable potential response throughout the 4200 s duration of the ADT, confirming the exceptional stability of Ni–Fe NP as a reversible, bi-functional catalyst for water electrolysis under intermittent conditions.

DFT simulation

To offer insights into the superior HER and OER performance of the Ni–Fe NP, the first-principles DFT calculations were conducted (more details in Supplementary Information). The interface model between the γ-Fe 2 O 3 (311) and Ni (111) surfaces (Fig.  4a ) was built based on the experimentally observed STEM-HAADF image of a single Ni–Fe NP (Fig.  1b ). The Fe and Ni atoms are coupled via the bridge O atoms at the interface as highlighted in Supplementary Fig.  6 . The strong interaction between Ni and O at the interface can be further confirmed by their overlapped O 2 p and Ni 3 d states around the Fermi energy level (Supplementary Fig.  31 ).

Theoretical understanding. a Optimized interface structure of the Ni–Fe heterojunction. b Standard free energy diagram of the HER process on the γ-Fe 2 O 3 (311) and Ni(111) surfaces and their interface in the Ni–Fe heterojunction. c Standard free energy diagram of the OER process on the γ-Fe 2 O 3 (311) and Ni(111) surfaces and their interface in the Ni–Fe heterojunction. The insets show the optimized structures and the catalytic sites for OERs. Key—brown: iron, red: oxygen, gray: nickel, and blue: catalytic site.

The Δ G H* is a key descriptor for evaluating the performance of HER electrocatalysts 56 . The DFT results reveal that the H atom can either adsorb on the top site of O atoms in γ-Fe 2 O 3 (311) or the fcc site of Ni(111) with the Δ G H* of −0.62 and −0.31 eV, respectively. It is worth noting that our Δ G H* value on the Ni(111) surface is almost identical to that calculated by Nørskov et al. 56 . The negative Δ G H* values suggest that the activity of both surfaces are too high for HER. At the interface of the Ni–Fe NP, however, both the interfacial O and Ni atoms have more optimal activity to the HER as demonstrated by corresponding Δ G H* of −0.27 and −0.14 eV, respectively (Fig.  4b ). It suggests that both the activities of the interfacial Ni and O atoms are reduced due to the formation of Ni–O bond and thereafter the charge transfer, which is beneficial to the HERs, as observed in experiments (Fig.  3a ).

To understand the OER activities, the change of the Gibbs free energies, Δ G n ( n  = 1, 4), for the four fundamental OER steps were calculated since the magnitude of ɳ has been demonstrated to be the difference of the practical potential (maximum Δ G n over the charge e ) and the standard Nernstian potential (1.23 V vs. SHE). Thus, the Δ G n values of intermediates need to reach the minimal difference between each other to reduce the ɳ . The calculated Δ G n on the γ-Fe 2 O 3 (311), Ni(111), and heterojunction are shown in Fig.  4b –d. The theoretical results indicate that the γ-Fe 2 O 3 itself is a good OER electrocatalysts with the theoretical ɳ of 0.55 eV. The rate-determination step is the formation of O * , in which the binding strength of Fe and O * is considerably weak. As a comparison, the Ni metal possess large ɳ of 2.05 V with the rate-determination step for the formation of OOH * intermediate. This is largely due to much stronger binding between the surface Ni atom and the O * intermediate (Supplementary Table  8 ). At the interface of Ni–Fe NPs, the binding energy of O * is optimized since it adsorbs at the bridge site between Fe and Ni. As such, the smallest theoretical ɳ of 0.28 V is attained among three systems, which greatly matches the experimental observation (Fig.  3d ). Our theoretical studies, therefore, demonstrate that only the interface of the Ni–Fe NPs has the superior OER performance (Supplementary Fig.  32 ).

Discussions

The unusually high electrocatalytic HER activity of the Ni–Fe NP can be ascribed to the electronic coupling effect arising from the interface due to the asymmetrical distribution of Ni and Fe 2 O 3 in the nanoparticle. Based on the Bader charge analysis result (Supplementary Table  7 ), Ni atoms at the interface are slightly oxidized due to the direct interaction with O anions (Fig.  4a ). The Δ G H* of −0.30 eV on the Ni(111) indicates that the surface Ni atoms bind H* too strongly. Consequently, relatively large overpotential is required for the formation and desorption of H 2 product. The slight oxidation of surface Ni atoms at the interface can reduce their activity, which can optimize the Δ G H* value to approach the optimal value of 0.0 eV. Moreover, the presence of metallic Ni provides metallic-type electron conduction which warrants facile electron transport towards the active HER sites at the interface as revealed by both experimental and computational results. Concomitantly, the HER onset of Ni–Fe NP is markedly lowered to RHE potential comparable to that of Pt/C due to the significantly lowered energy barrier for the initial Volmer step 57 that is determined by electron transfer kinetic (Eq.  1 ):

The following H 2 evolution was then promoted by the unique Ni–O–Fe configuration at the interface (Fig.  4a ). Experimentally, this is manifested in distinctly different Tafel slope in the order of 20% Pt/C ~Ni–Fe NP  ≪  Ni NP < Fe NP, suggesting a significantly altered secondary H 2 evolving step, in contrast to Ni NP and Fe NP.

Intriguingly, the synergy between Ni and Fe 2 O 3 at the interface of their NPs can also benefit the OER process. Based on the analyses of Gibbs free energy diagrams, the Fe 3+ cation and Ni 0 atom possess too weak or too strong activities to the OER, respectively. The spontaneous interaction of the OER intermediates formed at the bridge site between Ni and Fe can greatly optimize their Gibbs free energies, improving the OER performance as evidenced by the theoretically optimized atomic structures shown in Fig.  4c . Moreover, the unique Ni–O–Fe configuration at the interface as indicated in Fig.  4a provides a great platform to achieve multi-site functionality for the electrocatalysts. The multi-site functionalization can offer several active sites to stabilize one adsorbed state or transition state without stabilizing others, which can, therefore, break the limit of energy scaling relations of OER to lower the overpotential 58 . Previous studies reveals that the Δ G 2  + Δ G 3 values are within 3.2 ± 0.2 eV range due to their scaling relation among reactive intermediates 38 . Our Δ G 2  + Δ G 3 values on the γ-Fe 2 O 3 (311) and Ni(111) surfaces are 3.32 and 3.25 eV, respectively, which are the examples of this scaling relations. At the interface of Ni–Fe NPs, the OOH* intermediate is stabilized through the formation of hydrogen bonding between its H atom and neighboring interfacial O atom (Supplementary Fig.  33 ). Consequently, the energy scaling relations are circumvented with a reduced Δ G 2  + Δ G 3 value of 2.79 eV and smallest theoretical ɳ of 0.28 V. This multi-site functionalization mechanism found in our system can also explain other Ni–Fe-based OER electrocatalysts with the overpotential lower than the theoretical limit (~0.3 V) due to the scaling relation, such as LDH, metal organic framework, or amorphous mixture 11 , 14 , 57 , 59 .

In summary, this work demonstrates that the introduction of asymmetry in an electrocatalyst structure could induce unprecedented synergistic effect for electrocatalysis. Through this approach, we have overcome the practical limitation of Ni–Fe mixed oxides for overall water electrolysis due to the poor HER activity. Additionally, having similar active sites for both OER and HER results in the preservation of catalyst structure and activity against electrode corrosion induced by power interruptions, which is ideal for a water electrolyzer powered by intermittent renewable energy sources. Beyond, it is also our hope that this multi-site functionality catalyst design can help to expedite the conception-to-commercialization process of other multi-metallic nanoparticle electrocatalysts with different compositions and structures that exhibit distinct interfaces for various electrolytic applications such as CO 2 reduction reactions and nitrogen reduction reactions.

Nanoparticles and electrodes preparation

To prepare Ni–Fe NP, initially 5 mmol of Ni(NO 3 ) 2 .6H 2 O (UNIVAR grade, Ajax Finechem, Australia) and 1 mmol Fe(Cl) 2 .4H 2 O (Sigma-Aldrich, USA) were dissolved into a mixture of 2 mL of de-ionized water and 1 mL of ethanol. Four grams of Na(oleate) (TCI, Japan) was dissolved into a separate mixture of 4 mL de-ionized water and 3 mL of ethanol. The two mixtures were then mixed in a round-bottomed flask to yield thick and waxy green-yellow substances, and into the mixture, 14 mL of hexane was added. Upon the addition of hexane, immediate transfer of the colored metallic elements into the hexane phase was observed (Supplementary Fig.  1 ); the mixture was then stirred at 400 r.p.m. for 60 min. Two well-separated layers of water (colorless/opaque) and colored hexane layer (dark-green) were obtained at the end of stirring. Other oleate complexes with different Ni and Fe ratios were made by the same method by adjusting the mole ratio between Ni and Fe salts precursors to yield metal-oleate complex solution with a concentration of 0.43 mmol (metal) mL −1 (6 mmol of metals in 14 mL of hexane).

Electrodes were prepared by employing substrate materials such as CFP (FuelCell Store, Spectracarb 2050A-1535, USA) and nickel foam (NF, thickness: 1.6 mm, bulk density: 0.45 g cm −3 , Goodfellow, UK). The substrates were modified with metal-oleate complexes dissolved hexane solution via the drop-casting method. For the preparation of Ni NP, Fe NP, and Ni–Fe NP on CFP, 180 μL of the corresponding metal/metals oleate complex in hexane was drop casted onto 3 cm 2 of CFP. In case of NF, 300 μL (7.5 mg of metal) were drop casted onto 0.22 g of NF (GSA = 3 cm 2 , Supplementary Information for conversion calculation). For the preparation of Ni/Fe NP onto CFP electrode, 150 μL of Ni(oleate) 2 was drop casted onto a 3 cm 2 CFP, followed by 30 μL of Fe(oleate) 2 . The substrate was then dried under bench-top condition until the remaining hexane was evaporated and a waxy film was formed at the electrode surface. The modified substrates were subsequently annealed in Ar-protected horizontal tube furnace at 350 °C for 2 h at a ramp rate of 10 °C min −1 with an Ar-flow rate of 5 mL min −1 . Upon completion, the annealing chamber was allowed to cool down naturally to room temperature. For the preparation of Ni–Fe alloy NP, following the micellization step (Supplementary Fig.  1 ), the Ni–Fe oleate complex were further incubated at 70 °C for 7 h to allow further equilibration of Ni 2+ and Fe 2+ distribution within the micellar metal complex 8 , then following immobilization step the modified substrates were annealed under in H 2 atmosphere at 700 °C for 2 h at a ramp rate of 10 °C min −1 with a gas flow rate of 5 mL min −1 . The annealed electrodes were washed ultrasonically with Milli-Q water to remove the loosely bound nanoparticles for 5 min. Catalyst mass loadings ( m l ) of CFP and NF modified with metal nanoparticles were 1.5 and 2.5 mg cm −2 , respectively, and these values were determined according to the calculations shown in the Supplementary Information, unless otherwise stated. To verify the mass loading nanoparticles on CFP, thermogravimetric (TGA) measurement was carried out on 0.5 cm × 0.5 cm of Ni–Fe NP/CFP and the result is shown in Supplementary Fig.  30 . TGA measurement was carried out with a temperature ramp rate of 10 °C min −1 with a measurement range of 100–1000 °C in air to remove all of the non-metal components of the electrode. It is shown that at the end of the measurement 0.41 mg of residual weight was observed, corresponding to m l of 1.64 mg cm −2 . The slight discrepancy can be attributed to the weight gains from the formation of metal oxides.

The noble metal modified electrodes were prepared through drop-casting method. An ink of 20% Pt/C was prepared by the addition 10 mg of 20% Pt/C or 20% Ir/C (Premetek, USA) into 1.96 mL of 50% ethanol solution containing 0.04 mL 5% Nafion binder solution (Sigma-Aldrich, USA). The ink was then loaded onto substrate and dried under vacuum at 40 °C, resulting in catalyst mass loading of 3.0 mg cm −2 .

Electrochemical characterization

All electrochemical measurements were carried out with a CHI 760 electrochemical workstation (CH Instruments, USA). Electrochemical measurements were performed with a standard three-electrode cell configuration composed of working electrode, graphite rod counter electrode, and standard calomel electrode (SCE) as the reference electrode, unless otherwise stated. The potential of the SCE reference electrodes were routinely calibrated before and after experiments against a SCE that is conserved in saturated KCl solution. For all electrochemical measurement, the recorded SCE potential was converted into RHE using the following formula, E RHE  =  E SCE  + 0.241 + 0.059 × pH. OER and HER polarization curves were recorded at the scan rate of 5 mV s −1 , in 1 M KOH at 25 °C with 95% iR- corrections using the automated iR -correction function of the potentiostat 60 . Two-electrode water electrolysis cell was constructed from two NF electrodes modified with Ni–Fe NP with mass loading of 2.5 mg cm −2 in 1 M KOH. Energy efficiency of the cell was calculated using the following equation:

where E f,o  = 1.23 V; V e,i is the input voltage required to drive the electrolysis at the current density of interest. The energy efficiency calculated in this study was obtained at j  = 10 mA cm −2 .

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on request.

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Acknowledgements

The authors thank UNSW Mark Wainwright Analytical Centre (MWAC) for the access to all characterization instruments and Dr. Bin Gong for his assistance in XPS characterization. The authors also thank University of Wollongong Electron Microscopy Centre (EMC) and Dr. Gilberto C. Garcia for the access to their STEM unit. The DFT calculations were undertaken on the supercomputers in National Computational Infrastructure (NCI) in Canberra, Australia, which is supported by the Australian Commonwealth Government, and Pawsey Supercomputing Centre in Perth with the funding from the Australian government and the Government of Western Australia. We acknowledge the Australian Synchrotron (part of ANSTO) for providing access to the XAS beamline (project ID M11320). Dr. P. Kappen and B. Johannesson for support during XAS experiments. This study was financed by Australian Research Council (ARC), Discovery Grants (DP160103107, DP 170104834, FT170100224).

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These authors contributed equally: Bryan H. R. Suryanto, Yun Wang.

Authors and Affiliations

School of Chemistry, The University of New South Wales, Kensington, NSW, 2052, Australia

Bryan H. R. Suryanto, William Adamson & Chuan Zhao

Centre for Clean Environment and Energy, School of Environment and Science, Griffith University, Gold Coast, QLD, 4222, Australia

Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn, Melbourne, VIC, 3122, Australia

Rosalie K. Hocking

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C.Z. directed the project. B.H.R.S. and C.Z. designed the experiments. B.H.R.S carried out all material synthesis, characterization, and electrochemical experiments. R.K.H. carried out XAS measurements and analysis. W.A. carried out ICP measurement and Y.W. carried out the DFT calculations. All authors contribute to the data analysis and manuscript writing.

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Correspondence to Chuan Zhao .

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C.Z. and B.H.R.S. filed an Australian provisional patent (No. 2018900539) based on this work. The other authors declare no competing interests.

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Suryanto, B.H.R., Wang, Y., Hocking, R.K. et al. Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide. Nat Commun 10 , 5599 (2019). https://doi.org/10.1038/s41467-019-13415-8

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Research study at Hollings points to new combination strategy for pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic cancer and is projected to become the second-leading cause of cancer-related death by 2030. Although progress has been made in improving outcomes, the five-year survival rate remains stubbornly low at just 13%.

Now, researchers at MUSC Hollings Cancer Center  have identified a promising therapeutic strategy. Published in Cell Death and Differentiation , the study describes a new role of HSP70, or heat shock protein 70, and suggests that simultaneously blocking HSP70 and a survival mechanism called autophagy may reduce the growth of pancreatic cancer. This is the inaugural publication for the Barnoud Lab, headed by Tim Barnoud, Ph.D ., who joined Hollings in late 2021. Co-first authors on the paper are Colleen Quaas, Ph.D., and Giulia Ferretti, Ph.D., who have both been awarded fellowships by Hollings. Ferretti is a current HCC Abney Fellow while Quaas has completed her T32 ITOS fellowship and is headed a few blocks north to a faculty position at The Citadel. Barnoud said he’s grateful for Hollings’ commitment to educating the next generation of scientists by funding these fellowships. Not only do they provide opportunities for young researchers, but by funding salary support, they enable his lab to direct more funds toward the research. Quaas pointed out that this investigation required a significant amount of research effort and collaboration from everyone in the lab as well as other labs at Hollings. “A lot of techniques were involved, and one of the benefits of the fellowship is that we were able to have the funds to use a lot of really cutting-edge techniques – such as live cell video-microscopy to study mitochondrial dynamics in real-time – and to perform all of the preclinical efficacy studies of our inhibitors in mouse models. And we’re fortunate that we have an environment at Hollings where we are all collaborative and work really well together,” she said.

Why is HSP70 important in cancer?

Cells utilize heat shock proteins (HSPs) especially when they are under stress. These HSPs act as “chaperones,” ensuring that other proteins are folded correctly in order to do their jobs when facing a stressful environment. Barnoud explained that cancer cells, because they grow and divide at abnormally fast rates, are in a constant state of stress, which includes instances where they have limited oxygen and nutrients necessary to grow. Because of this, they produce significantly more HSP70 than normal cells. Researchers’ attention was drawn to HSP70 as a therapeutic target, although there were still unknowns about everything it was doing in cancer cells. During his postdoctoral fellowship at The Wistar Institute in Philadelphia, Barnoud found that there was an especially large amount of HSP70 in the mitochondria of tumor cells, including pancreatic cancer cells. Mitochondria, the “powerhouse” of the cell, supplies the energy that cells need to live. However, HSP70 wasn’t showing up in the mitochondria of normal cells. “This was quite surprising. But these findings led us to ask a simple question: What is HSP70 doing in the mitochondria of cancer cells?” Barnoud said. At his lab at Hollings, Barnoud set out to find out. Mitochondrial dynamics, a process that regulates the size, shape and position of mitochondria within cells, has been implicated in pancreatic cancer progression and metastasis. The mechanisms that regulate mitochondrial dynamics still aren’t fully understood, however. Barnoud’s lab showed that inhibiting HSP70 with a small-molecule inhibitor impaired the function of a protein called DRP1, which is critical for mitochondrial health and integrity. The buildup of compromised mitochondria in turn can lead to the death of cancer cells. However, another consequence of HSP70 inhibition is the buildup of reactive oxygen species and oxidative stress in the mitochondria, which can activate a critical metabolic sensor in cells known as AMPK. In turn, AMPK activation triggers a survival mechanism known as autophagy, which cancer cells often use to combat a variety of stresses, including chemotherapy. “Autophagy is an interesting way for pancreatic cancer cells to survive, in that cells essentially undergo ‘self-eating’ to obtain critical nutrients needed for important biological processes,” Barnoud said. “What was fascinating is that blocking HSP70 made this self-eating process go into over-drive in order for the pancreatic cancer cells to survive the stress we were throwing at them,” Ferretti said. The team showed that blocking autophagy improved the efficacy of HSP70 inhibition and slowed the growth of pancreatic tumors in mice. As with other cancers, research is showing that a multi-faceted intervention is more effective. “The exciting part of our story is that there is an FDA-approved drug that can block autophagy. Now, more potent autophagy-specific inhibitors are currently in clinical trials for pancreatic cancer,” Barnoud said. “The long-term goal of the lab is to advance the first small molecule HSP70 inhibitor to the clinic, which we hope will be beneficial in the fight against pancreatic cancer but perhaps also for other cancers that are ‘addicted’ to HSP70.”

TB was supported by NIH NCI R00 CA241367. Portions of the study were also performed with support from the MUSC Digestive Disease Research Core Center (P30 DK123704) and the MUSC COBRE in Digestive and Liver Disease Animal Models Core and the Imaging Core. Additional funding was awarded in the form of a pilot project to TB from the MUSC COBRE in Digestive and Liver Disease (P20 GM130457). GDSF was supported by the MUSC Hollings Cancer Center (MUSC) Postdoctoral Fellowship Program and CEQ was supported by NIH NCI T32 CA193201. JR-B was supported by NIH NINDS K01 NS119351, a Rally Foundation Career Development Award (20CDN46), a V Foundation Scholar Award (V2022-008), and a Vince Lombardi Cancer Foundation Grant. AAD was supported by NIH K01 CA245231 and ACS PF-1818301-TBG. GAH was supported by a 2022 Pancreatic Cancer Action Network Career Development Award in memory of Skip Viragh (22-20-HOBB), a 2022 Concern Foundation Career Development Award, and by NIGMS P20 GM130457. JPO is supported in part by a Merit Review Award (1I01BX002095) from the United States Department of Veterans Affairs Biomedical Laboratory Research and Development Service and by NIH awards (R01 CA212608, P30 CA138313, and P20 GM130457). JMS was supported by NIH awards S10 OD030245 and P30 CA010815. DFK was supported by NIH 1U54 CA274499-01-9941. OS was supported, in part, by NIH R01 CA251374 and NIH R01 CA267101. Support for the MUSC Core Facilities used in this study was provided in part by the MUSC Hollings Cancer Center Support Grant P30 CA138313, including support by the Biorepository & Tissue Analysis Shared Resource and the Cell & Molecular Imaging Shared Resource. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health, the U.S. Department of Veterans Affairs, not the United States government. Open access funding provided by the Carolinas Consortium.

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