Stability enhancement of electrode for seawater electrolysis

Abstract

Methods for stabilizing metal electrodes in saltwater electrolysis include pretreating the saltwater to obtain pretreated saltwater. The pretreated saltwater is mixed with a metal hydroxide to create a basic saltwater solution. The basic saltwater solution has about a 3 molar (M) or greater concentration of metal hydroxide. The basic saltwater solution is electrolysed in an electrolyzer system comprising an anode and a cathode, the anode comprising NiFe layered double hydroxide (LDH) and the cathode comprising NiFe; and producing hydrogen gas by the cathode.

Description

UH-2024-0057 (083203-000006)STABILITY ENHANCEMENT OF ELECTRODE FOR SEAWATER ELECTROLYSIS FIELD

[0001] The present disclosure relates to methods for stabilizing the electrodes of electrolyzer systems during saltwater electrolysis.BACKGROUND

[0002] Electrolysis of water to generate hydrogen fuel is an attractive renewable energy storage technology. However, grid-scale freshwater electrolysis would put a heavy strain on vital water resources. To obtain the renewable energy source available from water and not elevate the water scarcity issue, researchers have begun to study saltwater electrolysis. Due to its elevated concentrations of chlorine and chloride ions, saltwater quickly corrodes the electrodes of the electrolysis system. Such corrosion does not occur when using fresh water. To combat this issue, efforts have been directed towards the development of electrocatalysts and electrodes that can sustain seawater splitting without chloride corrosion.

[0003] Although there has been some progress in electrode development, the electrodes developed to date still suffer from chloride corrosion. The presence of chloride ions (CD) in seawater introduces chloride evolution reactions (C1ER) as a competitive reaction to oxygen evolution reactions (OER), resulting in severe corrosion to the metal electrodes and polar plates. Some approaches have utilized an anti-corrosion layer to protect the electrodes being used. The stability of anti-corrosion layers under saturated Cl" environments remains unknown and the development of highly stable electrodes under such conditions remains a serious challenge.SUMMARY

[0004] Embodiments of this disclosure include methods for stabilizing metal electrodes in saltwater electrolysis. Methods for stabilizing metal electrodes in saltwater electrolysis include pretreating the saltwater to obtain pretreated saltwater. The pretreated saltwater is mixed with a metal hydroxide to create a basic saltwater solution. The basic saltwater solution has about a 3 molar (M) or greater concentration of metal hydroxide. The basic saltwater solution is electrolysed in an electrolyzer system comprising an anode and a cathode; and producing hydrogen gas by the cathode.

[0005] These and other features and attributes of the disclosed methods of stabilizing an electrolyzer system of the present disclosure and their advantageous applications and / or uses will be apparent from the detailed description which follows.UH-2024-0057 (083203-000006)BRIEF DESCRIPTION OF THE DRAWINGS

[0006] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings. The following figures are included to illustrate certain aspects of the disclosure and should not be viewed as exclusive configurations. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0007] FIG. 1 A is an image of a nickel iron layered double hydroxide / nickel foam (NiFe LDH / NF) electrode upon initial submersion into 1 molar (M) potassium hydroxide (KOH) and 0.5 M sodium chloride (NaCl) solution.

[0008] FIG. IB is an image of a NiFe LDH / NF electrode after 30 minutes of electrolysis of 1 M KOH and 0.5 M NaCl solution.

[0009] FIG. 2 A is an image of a NiFe LDH / NF electrode upon initial submersion into 1 M KOH and 3 M NaCl solution.

[0010] FIG. 2B is an image of a NiFe LDH / NF electrode after 30 minutes of electrolysis in 1 M KOH and 3 M NaCl solution.

[0011] FIG. 3A is an image of a NiFe LDH / NF electrode upon initial submersion into 2 M KOH and 3 M NaCl solution.

[0012] FIG. 3B is an image of a NiFe LDH / NF electrode after 30 minutes of electrolysis in a 2 M KOH and 3 M NaCl solution.

[0013] FIG. 4 A is an image of a NiFe LDH / NF electrode upon initial submersion into 2 M KOH and saturated solution of NaCl.

[0014] FIG. 4B is an image of a NiFe LDH / NF electrode after 30 minutes of electrolysis in a 2 M KOH and saturated solution of NaCl.

[0015] FIG. 5 is a graph of current density as a function of potential.

[0016] FIG. 6 is a graph of the potential of NiFe LDH anode as a function of time.

[0017] FIG. 7 is a graph of production of hydrogen gas (H2) or oxygen gas (O2) in mL as a function of time in IM K0H / 3M NaCl at 500 milliamps per centimeter squared (mA / cm2).

[0018] FIG. 8 is a bar graph of saturated concentration of NaCl at different KOH electrolyte concentrations.

[0019] FIG. 9 is a graph of the collapsing currents density of NiFe LDF / NF in several solutions having varying concentrations of KOH and NaCl.UH-2024-0057 (083203-000006)

[0020] FIG. 10A is a graph of stability of Ni-SSM(— ) || NiFe LDF / NF(+) (nickel stainless steel mesh || nickel iron layer double hydroxide / nickel foam) in 4 M KOH / saturated NaCl.

[0021] FIG. 10B is a graph of potential as a function of time for NiFe LDH / NF in 6 M KOH and pretreated seawater.DETAILED DESCRIPTION

[0022] The present disclosure relates to methods for stabilizing the electrodes of electrolyzer systems during saltwater electrolysis.

[0023] Through electrolysis, water can be used as a renewable source to generate energy via hydrogen gas and oxygen gas production. However, fresh water is not an infinite source, so studies are directed towards saltwater as an alternative. Problems arise with the use of saltwater, however, as it corrodes the electrodes due to an abundance of Cl’ ions. Attempts have been made to protect electrodes by forming a coating thereon. Although coatings may delay the onset of corrosion, they do not prevent the corrosion. Therefore, alternative methods need to be developed to continue to use saltwater as a source to generate energy.

[0024] The present disclosure shows how corrosion resulting from chloride-hydroxide formation reactions during saltwater electrolysis may be mitigated. More specifically, by adding metal hydroxide, the corrosive effects of saltwater may be mitigated.

[0025] Embodiments of this disclosure include methods for stabilizing metal electrodes in saltwater electrolysis. The term “saltwater” means water with an amount of chloride ions. The amount may range from 1 part per million (ppm) to a saturation point, which when the chloride ions are coupled with sodium is about 4.2 mole per liter (mol / L or molar). Saltwater may optionally include magnesium, sodium, calcium, alkaline and alkali earth cations. Natural sources of saltwater include seawater and brine, for example.

[0026] Methods for stabilizing metal electrodes in saltwater electrolysis include pretreatment of the saltwater to remove metals such as calcium (Ca), magnesium (Mg), aluminum (Al), manganese (Mn), zinc (Zn), arsenic (As), copper (Cu), lead (Pb), cadmium (Cd), nickel (Ni), and iron (Fe), etc. The pretreatment of the saltwater does not include the removal of sodium ions. The pretreated saltwater is then mixed with a metal hydroxide to create a basic saltwater solution. The basic saltwater solution has about a 3 molar (M) or greater concentration of metal hydroxide. The basic saltwater solution is electrolysed in an electrolyzer system comprising an anode and a cathode, the anode comprising NiFe layered double hydroxide (LDH) and the cathode comprising NiFe; and producing hydrogen gas by the cathode. The NiFe LDH may facilitate oxygen production via an oxygen evolution reaction (OER)UH-2024-0057 (083203-000006) at the anode, and the NiFe may facilitate hydrogen production via a hydrogen evolution reaction (HER) at the cathode.

[0027] Electrolyzer systems use electricity to split water into hydrogen and oxygen gas. In various embodiments, the electrolyzer systems in the methods of this disclosure may be an alkaline water electrolyzer, an anion exchange membrane (AEM) electrolyzer. Other types of electrolyzer systems may also be suitable.

[0028] The term “water electrolysis” means splitting water using electricity. The net chemical reaction of water electrolysis is H2O — ► H2 + 'Z>02, and the electrical power provided to the electrolyzer makes this reaction happen.

[0029] Oxygen evolution reactions (OER) need four electrons to produce one molecule of O2, consume multiple hydroxide (OH ) anions, and form multiple adsorbed intermediates on the surface of the catalyst. These multiple steps of reaction create a high energy barrier, and thus, a high overpotential, which usually causes OER to be slow or require a great amount of energy. The overpotential of OER may be reduced with an efficient catalyst that increases the reaction rate. Specifically, the catalyst may refer to the chemical composition of at least an active surface of the cathode or the anode. Hydrogen evolution reaction (HER) kinetics in alkaline solutions are usually slower than in acidic solutions, because of additional water dissociation and the formation of hydrogen intermediate (H*) that are not present in acidic conditions.

[0030] In Equations 1- 7, the superscript indicates where the species absorbed to the surface of the catalyst.* + OH *OH + e (1)OH + OH — > *0 + e + H2O (2)*O+ OH — > *OOH + e (3)*OOH + OH * + e + H2O + O2(4)

[0031] In the cathode, the reaction starts with water adsorption and dissociation in Volmer step (Equation 5) and either hydrogen desorption in the Tafel step (Equation 6) or Heyrovsky step (Equation 7).2* + 2H2O + 2e 2*H + 2OH (5)2*H H2(6)H2O + *H+ 2e ^ * + H2+ OH (7)

[0032] In order for Equations 1 - 7 to produce H2 gas and O2 gas, a cathode and an anode are immersed in an ionic solution. A current flows from a cathode to an anode in the outer circuit.UH-2024-0057 (083203-000006)Electrons will flow in the opposite direction from the anode to the cathode. Oxidation reaction occurs on the anode and reduction reactions occur on the cathode.

[0033] The electrolyzer system in the method of this disclosure includes an anode and cathode.

[0034] The cathode may include nickel, titanium, carbon, and combinations thereof. In some embodiments, the cathode may be nickel with a stainless steel mesh (Ni-SSM) support. The carbon material may be graphite, modified graphite, or carbon nanotubes. The cathode may include a catalyst layer and optionally a substrate support. The substrate support may conduct electricity, support the catalyst mechanically, and remove gaseous products. The catalyst layer can be deposited on the membrane or the substrate support to form catalyst-coated substrate or catalyst-coated membrane.

[0035] The catalyst layer, comprising the first catalyst or the second catalyst, is typically made by mixing catalyst powder and ionomer to produce an ink or slurry that is applied by spraying or painting. Other methods include electrodeposition, magnetron sputtering, chemical electroless plating, and screen printing onto the substrate. In some embodiments, the second catalyst, which is on the cathode, may include NiMoN, Ni doped Fe20.3, and Pt / C.

[0036] The anode may include nickel foam, nickel-iron foam, copper foam, titanium foam. The catalyst may include nickel -iron layered double hydroxide (NiFe LDH), NiMoN, Fe and Mo codoped NiO, NiFeOOHIn some embodiments, the anode may include a substrate.

[0037] In some embodiments, the substrate support may include nickel foam, nickel-iron foam, copper foam, or titanium foam. Nickel, nickel-iron, or copper is typically used as a substrate for AEM. In various embodiments, the substrate support may be titanium. Titanium is generally used in PEM. However, while both nickel, nickel-iron, copper, and titanium may be included in either AEM or PEM, they are not mutually exclusive. Carbon materials are usually not suitable for the anode because of their degradation by OH' ions

[0038] In some embodiments, the cathode can be coated or uncoated. Additionally, the anode may be coated or uncoated with NiFe layer double hydroxide (LDH), NiFeOOH, Fe and Mo codoped NiO, or Ni doped Fe2Ch. Coatings are used to accelerate the OER kinetics and protect the electrodes. Generally, uncoated electrodes would rapidly degrade when electrolyzing saltwater, while the corrosion of the coated electrodes is delayed. In contrast, the coating is not necessary with the methods of this disclosure, although electrode coatings may be used in some embodiments. Since there is not as much wear (degradation) on the electrode, the electrode can be uncoated

[0039] As previously stated, the methods of the present disclosure include pretreating the saltwater and mixing the pretreated saltwater with metal hydroxide to create a basic saltwater solution. In oneUH-2024-0057 (083203-000006) or more embodiments, the metal hydroxide comprises one Group T metal or more than one Group I metal. The Group I metal may be lithium, sodium, potassium, rubidium, cesium, or any combination thereof. In some embodiments, the Group I metal is potassium.

[0040] In some embodiments, the basic saltwater solution has a 3 M (molar) or greater concentration of metal hydroxide. In some embodiments, the basic saltwater solution has a 4 M or greater concentration of metal hydroxide, or 5 M or greater, or 6 M or greater. The molar concentration of the metal hydroxide in the basic saltwater solution may be from 3 M to 10 M, 3 M to 9 M, 3 M to 8 M, 3 M to 7 M, 3 M to 6 M, 4 M to 10 M, 4 M to 9 M, 4 M to 8 M, 4 M to 7 M, 4 M to 6 M, 5 M to 10 M, 5 M to 9 M, 5 M to 8 M, 5 M to 7 M, 5 M to 6 M. In some embodiments, the metal hydroxide has a molar concentration of greater than 5 M or approximately 6 M.

[0041] When utilizing the methods of this disclosure, the anode of the electrolyzer system is stable as measured by a collapsing current density of greater than or equal to 0.5 A cm'2for 0 to 200 hours. Without intent to be bound by theory, it is believed that higher OH' concentration suppresses the oxidation of Cl , resulting in the stability of the anode.

[0042] Methods of pretreating the salt water may include passing the saltwater through a filtration system or precipitating the metals out of the water by adding a counter anion that forms an insoluble complex and filtering the precipitant. Additional methods include introducing a source of solublizing anions to the saltwater. The solubilizing anions may include oxalate ions (C2O42), phosphate ions (PO4 ) or a combination thereof. The solubilizing anions may be introduced to the saltwater in amounts sufficient to reduce the metal ion content of the low grade water to some user and / or process desired level. In one or more aspects of the present disclosure, the metal ion content of the saltwater is reduced to a level that provides for at least one of the features of DI water (except for sodium ions).

[0043] Particularly, the amount of C2O 12and PO 13introduced to the saltwater may be sufficient to form insoluble salts of the metal ions present in the saltwater. For example, the introduction of C2O42and PO43to the saltwater may result in the formation of insoluble salts such as CaC2C>4, MgC2O4, A12(C2O4)3, Ca3(PO4)2, Mg3(PO4)2, and AIPO4, which may be removed via gravity precipitation, centrifugation, simple filtration, or decanting

[0044] Additional information may be found in PCT International Application No PCT / US2024 / 016384.Additional Embodiments

[0045] Embodiments disclosed herein include:UH-2024-0057 (083203-000006)

[0046] A. Methods for stabilizing metal electrodes in saltwater electrolysis, the method comprising: pretreating saltwater to obtain pretreated saltwater; mixing the pretreated saltwater with a metal hydroxide to create a basic saltwater solution, wherein the basic saltwater solution has about a 3 molar (M) or greater concentration of metal hydroxide; electrolyzing the basic saltwater solution in an electrolyzer system comprising an anode and a cathode; and producing hydrogen gas at the anode and the cathode producing the oxygen gas.

[0047] Embodiment A may have one or more of the following elements in any combination:

[0048] Element 1, wherein pretreating the saltwater comprises removing impurities.

[0049] Element 2, wherein the impurities comprise calcium ions, magnesium ions, strontium, barium, and insoluble material.

[0050] Element 3, wherein the metal hydroxide comprises at least one Group I metal.

[0051] Element 4, wherein the at least one Group I metal comprises potassium.

[0052] Element 5, wherein the cathode is coated.

[0053] Element 6, wherein the cathode is uncoated.

[0054] Element 7, wherein the basic saltwater solution has about a 4 M or greater concentration of metal hydroxide.

[0055] Element 8, wherein the basic saltwater solution has about a 5 M or greater concentration of metal hydroxide.

[0056] Element 9, wherein the basic saltwater solution has about a 6 M or greater concentration of metal hydroxide.

[0057] Element 10, wherein the basic saltwater solution has a molar concentration of metal hydroxide of about 3 M to about 10 M.

[0058] Element 11, wherein the anode comprises nickel foam, nickel iron foam, copper foam, or titanium foam.

[0059] Element 12 further comprises a catalyst deposited on the anode.

[0060] Element 13, wherein the cathode comprises nickel, titanium, carbon, and combinations thereof.

[0061] Element 14 further comprises a second catalyst deposited on the cathode.

[0062] Element 15, wherein the second catalyst comprising NiMoN, Ni doped Fe2O3 or platinum on carbon (Pt / C).

[0063] Element 16, wherein the cathode comprises nickel and a stainless steel mesh substrate and the second catalyst comprises nickel doped iron (III) oxide (Fe2O3).UH-2024-0057 (083203-000006)

[0064] Element 17, wherein the anode of the electrolyzer system is stable as measured by a collapsing current density of greater than or equal to 0.5 A cm'2for 0 to 200 hours.

[0065] Element 18, wherein the electrolyzer system comprises an Anion Exchange Membrane (AEM) water electrolyzer or alkaline water electrolyzer (AWE).

[0066] Element 19, wherein the electrolyzer system further comprises a substrate.

[0067] Element 20, wherein the substrate comprises nickel foam, nickel-iron foam, copper foam, and titanium foam.

[0068] Other embodiments disclosed herein include the following:

[0069] Embodiment 1. A method for stabilizing metal electrodes in saltwater electrolysis, the method comprising: pretreating saltwater to obtain pretreated saltwater; mixing the pretreated saltwater with a metal hydroxide to create a basic saltwater solution, wherein the basic saltwater solution has about a 3 molar (M) or greater concentration of metal hydroxide; electrolyzing the basic saltwater solution in an electrolyzer system comprising an anode and a cathode; and producing hydrogen gas at the anode and oxygen gas at the cathode.

[0070] Embodiment 2. The method of embodiment 1, wherein pretreating the saltwater comprises removing impurities.

[0071] Embodiment 3. The method of embodiment 1, wherein the impurities comprise calcium ions, magnesium ions, strontium, barium, and insoluble material.

[0072] Embodiment 4. The method of embodiment 1, wherein the metal hydroxide comprises at least one Group I metal.

[0073] Embodiment 5. The method of embodiment 4, wherein the at least one Group I metal comprises potassium.

[0074] Embodiment 6. The method of embodiment 1, wherein the cathode is coated.

[0075] Embodiment 7. The method of embodiment 1, wherein the cathode is uncoated.

[0076] Embodiment 8. The method of embodiment 1, wherein the basic saltwater solution has about a 4 M or greater concentration of metal hydroxide.

[0077] Embodiment 9. The method of embodiment 1, wherein the basic saltwater solution has about a 5 M or greater concentration of metal hydroxide or the basic saltwater solution has about a 6 M or greater concentration of metal hydroxide.

[0078] Embodiment 10. The method of embodiment 1, wherein the basic saltwater solution has a molar concentration of metal hydroxide of about 3 M to about 10 M.UH-2024-0057 (083203-000006)

[0079] Embodiment 1 1. The method of embodiment 1, wherein the anode comprises nickel foam, nickel iron foam, copper foam, or titanium foam.

[0080] Embodiment 12. The method of embodiment 1 further comprises a catalyst deposited on the anode.

[0081] Embodiment 13. The method of embodiment 1, wherein the cathode comprises nickel, titanium, carbon, and combinations thereof.

[0082] Embodiment 14. The method of embodiment 1 further comprises a second catalyst deposited on the cathode.

[0083] Embodiment 15. The method of embodiment 14, wherein the second catalyst comprising NiMoN, Ni doped Fe2O3 or platinum on carbon (Pt / C).

[0084] Embodiment 16. The method of embodiment 13, wherein the cathode comprises nickel and a stainless steel mesh substrate and the second catalyst comprises nickel doped iron (III) oxide (Fe2O3).

[0085] Embodiment 17. The method of embodiment 1, wherein the anode of the electrolyzer system is stable as measured by a collapsing current density of greater than or equal to 0.5 A cm'2for 0 to 200 hours.

[0086] Embodiment 18. The method of embodiment 1, wherein the electrolyzer system comprises an Anion Exchange Membrane (AEM) water electrolyzer or alkaline water electrolyzer (AWE).

[0087] Embodiment 19. The method of embodiment 1, wherein the electrolyzer system further comprises a substrate.

[0088] Embodiment 20. The method of embodiment 19, wherein the substrate comprises nickel foam, nickel-iron foam, copper foam, and titanium foam.

[0089] To facilitate a better understanding of the embodiments of the present disclosure, the following examples of preferred or representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.EXAMPLES

[0090] The NiFe LDH / NF electrode without a coating was studied to test the stability of a highly active electrode in different seawater electrolytes. Examples 1 to 4 detail various changes in corrosion behavior in the presence of varying concentrations of KOH and NaCl. Examples 6 and 7 detail the potential and longevity of the electrode over 1000 hours under 4 M KOH / saturated NaCl and 6 M KOH / pretreated seawater.UH-2024-0057 (083203-000006)

[0091] Example 1 - 1 M KOH / O.5 M NaCl

[0092] A solution containing 1 molar (M) KOH and 0.5 M NaCl was made, in which molar is moles per liter. The NiFe LDH / NF electrode was immersed in the solution and a photographic image was taken (FIG. 1 A). A second photographic image was taken after 30 minutes (FIG. IB). In FIGS. 1 A and IB, there was no obvious corrosion observed on the NiFe LDH / NF.

[0093] Example 2 - 1 M KOH / 3 M NaCl

[0094] A solution containing 1 M KOH and 3 M NaCl was made. The NiFe LDH / NF electrode was immersed in the solution and a photographic image was taken (FIG. 2A). A second photographic image was taken after 30 minutes (FIG. 2B).

[0095] In contrast to FIGS. 1A and IB (Example 1), severe corrosion was observed in FIGS. 2A and 2B. Some blue-green solids were generated in the solution of Example 2; the images are black and white, and the blue-green corrosion is circled for identification purposes. The blue-green solids can be attributed to Ni(0H)2 produced by the chloride-hydroxide formation reaction.

[0096] Example 3 - 2 M KOH / 3 M NaCl

[0097] A solution containing 2 M KOH and 3 M NaCl was made. The NiFe LDH / NF electrode was immersed in the solution and a photographic image was taken (FIG. 3 A). A second photographic image was taken after 30 minutes (FIG. 3B).

[0098] When the concentration of KOH was increased to 2 mole / L from 1 mole / L (Example 2), there was no corrosion or blue-green solid formation observed on the NiFe LDH / NF electrode. The absence of corrosion indicated that the increased OH concentration may have effectively suppressed the corrosion induced by Cl".

[0099] Example 4 - 2 M KOH / Saturated NaCl

[0100] A solution containing 2 M KOH and saturated NaCl (~4.2 M) was made. The NiFe LDH / NF electrode was immersed in the solution and a photographic image was taken (FIG. 4A). A second photographic image was taken after 30 minutes (FIG. 4B).

[0101] In comparison with Example 3, when the NaCl concentration was further increased to saturation (~4.2 M) in 2 M KOH electrolyte, a small portion of NiFe LDH / NF was corroded after 30 minutes of exposure, as shown by comparing FIGS. 4A and 4B. The corrosion, which was evident by the blue-green solids, is circled in FIG. 4B. Therefore, the above results demonstrate that a higher concentration of Cl" may accelerate the chloride-hydroxide formation, but a higher concentration of OH" can effectively suppress the corrosion of Cl".

[0102] Additional Studies of the solutions of Examples 1-4UH-2024-0057 (083203-000006)

[0103] In salt water electrolysis, the generation of CI2 or CIO may cause severe corrosion of metal electrodes and polar plates. Although previous reports have shown that alkaline seawater electrolyte can secure a near 100% Faradaic efficiency of oxygen evolution reaction (OER) with an NaCl concentration of approximately 0.5 mole / L, the OER selectivity under higher NaCl concentration remain unknown.

[0104] FIG. 5 is a graph of current density as a function of potential, where potential was measured as voltage verses reversable hydrogen electrode (V vs RHE). RHE has a potential of Engo / iig + 0.059V*pH in water. Knowing the materials of the other two electrodes, the potential of those electrodes could be measured against RHE. The curves of NiFe LDH / NF electrode in different electrolyte solutions, as shown in FIG. 5, indicated that the oxygen evolution reaction (OER) potentials within 1000 mA / cm2were far below 1.72 V vs. RHE, which suggests that the hypochlorite formation can be thermodynamically suppressed. The thermodynamic potential of C1 C10" is 1.72 V vs RHE. When the OER potential is below 1.72 V vs RHE, the Cl" cannot be oxidized to CIO since the potential is below its oxidation potential, and this is the so-called ‘thermodynamically suppression of CIO production’ . Thus, the production of CIO is not the main cause of the corrosion. The main cause of the corrosion is the chloride-hydroxide formation reaction, which can be suppressed by adding OH .

[0105] FIG. 6 is a graph of the potential as a function of time. In FIG. 6, the chrono-potentiometric (CP) measurements indicated that the NiFe LDH / NF suffered a severe corrosion in 1 M KOH and 3 M NaCl solution (Example 2) and remained stable in both 1 M KOH and 0.5 M NaCl (Example 1) and 2 M KOH and 3 M NaCl (Example 3) at 500 mA / cm2. The Faradaic efficiency results shown in FIG. 7, a graph of the volume of O2 or H2 produced as a function of time, revealed that the OER selectivity remained 100% during the corrosion process of NiFe LDH / NF. The graph of FIG. 6 and FIG. 7 indicates that the corrosion process was not related to the hypochlorite formation and was mainly caused by the chloride-hydroxide formation. The NiFe LDH / NF displayed stable performance in 1 M KOH and 0.5 M NaCl. However, the electrode was severely corroded in 1 M KOH and 3 M NaCl, indicating that the increase of NaCl concentration accelerated the corrosion. The NiFe LDH / NF electrode became stable again in 2 M KOH and 3 M NaCl electrolyte again, showing the increase of KOH concentration can delay the corrosion. The NiFe LDH / NF displayed stable performance in 1 M KOH and 0.5 M NaCl and experienced severe corrosion in 1 M KOH and 3 M NaCl, showing that the increase of NaCl concentration accelerate the corrosion. The NiFeUH-2024-0057 (083203-000006)LDH / NF electrode became stable again in 2 M KOH and 3 M NaCl electrolyte again, showing the increase of KOH concentration can delay the corrosion.

[0106] The results shown in FIGS. 6 and 7 suggest that the increase of OH concentration can effectively suppress the corrosion and the increase of CH concentration accelerated the corrosion. In the salt water electrolyte, an increased KOH concentration will decrease the saturation concentration of NaCl .

[0107] FIG. 8 is a bar graph showing the saturation concentration of NaCl in different concentrations of KOH. The rapid drop of saturation NaCl concentration and the effective suppression of corrosion with respect to the increased KOH concentration strongly suggest that increasing the KOH concentration can eventually achieve a high stability of NiFe LDH / NF under a saturated NaCl environment. To quickly obtain the stability of NiFe LDH / NF, the collapsing current densities in different electrolytes were systematically measured. The NiFe LDH / NF electrode was employed as anode for seawater oxidation tests. In a certain KOH + NaCl electrolyte, a 15 minutes’ chrono- potentiometric (CP) test was conducted at a specific current density. If no corrosion can be observed, the CP test will be repeated at higher current density. If obvious corrosion can be observed, the CP test will be repeated at lower current density. The lowest current density with obvious corrosion was then determined as the collapsing current density in that specific KOH + NaCl electrolyte.

[0108] FIG. 9 is a graph of collapsing current density as a function of NaCl concentrations for solutions having various KOH concentrations. The results in FIG. 9 demonstrate that the collapsing current density of NiFe LDH / NF increases with higher OH concentration and decreases with higher CL concentration. Furthermore, the collapsing current density was higher than 8 A / cm2in 4 M KOH + saturated NaCl (~2.0 mole / L), which suggests a stable saltwater electrolysis process can be achieved with NiFe LDH / NF electrode in alkaline seawater with a OH concentration higher than 4 mole / L.

[0109] Example 6 - 4 M KOH and Sat. NaCl

[0110] Stability of the salt water electrolysis was studied in 4 M KOH / saturated NaCl electrolyte at 65°C. As shown in FIG. 10A, a graph of voltage as a function of time, the Ni-SSM(-)||NiFe LDH / NF(+) (nickel stainless steel mesh||nickel iron layered double hydroxide / nickel foam) two- electrode electrolyzer exhibited an excellent stability at 1 A / cm2for 200 h under the above conditions. The result indicated that the electrolyzer can perform stably in saturated NaCl containing 4 M KOH.

[0111] Example 7 - 6 M KOH and Pretreated Seawater

[0112] 14 g of K3PO4 was added into 1 L natural seawater to remove the Mg2+and Ca2+ions as a pretreatment. The natural seawater with K3PO4 were first centrifuged then filtered to remove theUH-2024-0057 (083203-000006)Mg2(PC>4)3 and Ca2(PO4 .i and the pretreated seawater was prepared. A 6 M KOH and pretreated seawater electrolyte was prepared, and a 1000 h CP test was conducted to measure the OER stability of NiFe LDH / NF.

[0113] To simulate the working conditions of the method presented in this disclosure, pretreated seawater was added into 6 M KOH and pretreated seawater electrolyte to compensate for the consumed water during the stability test. As shown in FIG. 10B, a graph of potential as a function of time, the performance of NiFe LDH / NF decreased during the stability test due to the consistent increase of ions formed during electrolysis. However, there was no rapid corrosion on the NiFe LDH / NF during the 1000 h test. In contrast, there was evidence of corrosion in the graph of FIG. 6. Therefore, the 6 M KOH and pretreated seawater satisfies all the requirements and can be applied to the industrial application of direct seawater electrolysis.

[0114] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the incarnations of the present inventions. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0115] One or more illustrative incarnations incorporating one or more invention elements are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment incorporating one or more elements of the present invention, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill in the art and having benefit of this disclosure.

[0116] While compositions and methods are described herein in terms of “comprising” various components or steps, the compositions and methods can also “consist essentially of’ or “consist of’ the various components and steps.

Claims

UH-2024-0057 (083203-000006)CLAIMSThe invention claimed is:

1. A method for stabilizing metal electrodes in saltwater electrolysis, the method comprising: pretreating saltwater to obtain pretreated saltwater; mixing the pretreated saltwater with a metal hydroxide to create a basic saltwater solution, wherein the basic saltwater solution has about a 3 molar (M) or greater concentration of metal hydroxide; electrolyzing the basic saltwater solution in an electrolyzer system comprising an anode and a cathode; and producing hydrogen gas at the anode and oxygen gas at the cathode.

2. The method of claim 1, wherein pretreating the saltwater comprises removing impurities, such as calcium ions, magnesium ions, strontium, barium, and insoluble material.

3. The method of claim 1 or claim 2, wherein the metal hydroxide comprises at least one Group I metal.

4. The method of claim 3, wherein the Group I metal is potassium.

5. The method of any one of claims 1 to 4, wherein the anode comprises nickel foam, nickel iron foam, copper foam, or titanium foam.

6. The method of any one of claims 1 to 5, wherein the anode further comprises a catalyst deposited thereon.

7. The method of any one of claims 1 to 6, wherein the cathode is uncoated.

8. The method of any one of claims 1 to 7, wherein the cathode comprises nickel, titanium, carbon, and combinations thereof.

9. The method of any one of claims 1 to 8, wherein the cathode further comprises a second catalyst deposited thereon.UH-2024-0057 (083203-000006)10. The method of claim 9, wherein the second catalyst comprises NiMoN, Ni doped Fe2O3, or platinum on carbon (Pt / C).

11. The method of claim 9, wherein the cathode comprises nickel and a stainless steel mesh substrate and the second catalyst comprises nickel doped iron (III) oxide (Fe2O3).

12. The method of any one of claims 1 to 11, wherein the anode of the electrolyzer system is stable as measured by a collapsing current density of greater than or equal to 0.5 A cm-2 for 0 to 200 hours.

13. The method of any one of claims 1 to 12, wherein the electrolyzer system comprises an Anion Exchange Membrane (AEM) water electrolyzer or alkaline water electrolyzer (AWE).

14. The method of any one of claims 1 to 13, wherein the electrolyzer system further comprises a substrate.

15. The method of claim 14, wherein the substrate comprises nickel foam, nickel-iron foam, copper foam, and titanium foam.

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