Electrocatalyst coated electrode for water electrolysis

Abstract

A method comprises at least partially submerging a conductive substrate in an alkaline solution comprising anions of one or more first metal elements, and applying a specified potential to the conductive substrate that is at least partially submerged in the alkaline solution to electrochemically deposit a coating compound comprising one or more of the first metal elements onto one or more surfaces of the conductive substrate.

Description

ELECTROCATALYST COATED ELECTRODE FOR WATER ELECTROLYSISCROSS-REFERENCE TO RELATED AFFLICTIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 63 / 579,664, filed on August 30, 2023, entitled “ELECTROCATALYST COATED ELECTRODE FOR WATER ELECTROLYSIS AND METHOD OF PRODUCING SAME,” the disclosure of which is incorporated herein by reference in its entirety.BACKGROUND

[0002] The production of hydrogen can play an important role because hydrogen gas is required for many chemical processes. As of 2022, roughly 75 million tons of hydrogen is produced annually worldwide for various uses, such as oil refining, in the production of ammonia (through the Haber process), in the production of methanol (though reduction of carbon monoxide), or as a fuel in transportation.

[0003] Historically, a large majority of hydrogen (~95%) has been produced from fossil fuels (e.g., by steam reforming of natural gas, partial oxidation of methane, or coal gasification). Other methods of hydrogen production include biomass gasification, low- or no-C02 emission methane pyrolysis, and electrolysis of water. Electrolysis uses electricity to split water molecules into hydrogen gas and oxygen gas. To date, electrolysis systems and methods have been generally more expensive than fossil-fuel based production methods. However, the fossil-fuel based methods can be more environmentally damaging, generally resulting in increased CO2 emissions. Therefore, there is a need for cost-competitive and environmentally friendly methods of hydrogen gas producing electrolysis systems and methods.SUMMARY

[0004] The present disclosure describes a catalyst coated electrode for use in an electrochemical device, such as a water electrolyzer for the production of hydrogen gas (H2). In an example, the catalyst comprises a metal (e.g., solid metal form of a metallic element) or a metal compound (such as a metal oxide, metal hydroxide, or metal oxyhydroxide) that has been electrochemically deposited onto the electrode from an alkaline solution that include ions of the metal of the catalyst coating.

[0005] The present disclosure also describes a method of producing a catalyst coated electrode, which includes electrolytically depositing anions of a first metal element from an alkaline solution that includes the first metal anions onto a conductive substrate (such as an electrode). The electrode onto which the metal anions are being electrolytically deposited is either the anode or the cathode in an electrolytic cell, e.g., for the production of hydrogen gas (H2) via electrolysis of water. The bias applied to the electrode in order to drive the electrolytic deposition is the bias that activates the watersplitting electrolysis reaction or reactions, e.g., for oxygen evolution if the electrode is the anode of the electrolytic cell or for hydrogen evolution if the electrode is the cathode of the electrolytic cell. In an example, the electrolytic deposition of the metal anions onto the conductive substrate of the electrode can be performed in situ during operation of the electrolytic cell, e.g., by including the metal ions in the electrolyte solution, so that the electrolytic deposition is a method of electrode maintenance to redeposit a catalyst material onto the electrode without having to take the electrolytic cell offline to do so.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0007] FIG. 1 is a schematic diagram of an example electrolyzer cell for the electrolysis of water to produce hydrogen gas.

[0008] FIG. 2 is a plan view of a woven mesh electrode with a catalyst coating to provide a catalyst coated electrode.

[0009] FIG. 3 is a cross-sectional view of the catalyst coated electrode of FIG. 2 taken along line 3 — 3.

[0010] FIG. 4 is a Pourbaix diagram of cobalt showing the phase of cobalt at various pHs and applied potentials.

[0011] FIG. 5 is a close-up cross sectional view of a surface of an example conductive substrate of an electrode with a porous catalyst coating formed by some methods of the present disclosure.

[0012] FIG. 6 is a flow diagram of an example method of preparing a catalyst coated conductive substrate by electrochemical deposition of a catalyst composition onto the conductive substrate.

[0013] FIG. 7 is a flow diagram of an example method of in situ electrochemical deposition of an electrocatalyst composition onto an electrode of an electrolyzer cell that is concurrent or substantially concurrent with electrolysis within the electrolyzer cell.

[0014] FIG. 8 is a flow diagram of another example method of in situ electrochemical deposition of electrocatalyst compositions onto both electrodes of an electrolyzer cell that is concurrent or substantially concurrent with electrolysis within the electrolyzer cell.

[0015] FIGS. 9A and 9B are micrographs of a nickel mesh electrode before and after coating with a cobalt-based catalyst composition by the electrochemical deposition method of the EXAMPLE.

[0016] FIG. 10 is an X-ray fluorescence spectra graph for the nickel mesh electrode of FIGS. 9A and 9B before and after coating with the cobalt-based catalyst composition.DETAILED DESCRIPTION

[0017] The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in enough detail to enable those skilled in the art to practice the invention. The example embodiments may be combined, other embodiments may be utilized, or structural, and logical changes may be made without departing from the scope of the present invention. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

[0018] References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0019] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a recited range of values of “about 0.1 to about 5” should be interpreted to include not only the explicitly recited values of about 0.1 and about 5, but also all individual concentrations within the indicated range of values (e.g., 1 , 1.23, 2, 2.85, 3, 3.529, and 4, to name just a few) as well as sub-ranges that fall within the recited range (e.g., about 0.1 to about 0.5, about 1.21 to about 2.36, about 3.3 to about 4.9, or about 1 .2 to about 4.7, to name just a few). The statement “about X to Y” has the same meaning as “about X to about Y,”” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

[0020] In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. Unless indicated otherwise, the statement “at least one of’ when referring to a listed group is used to mean one or anycombination of two or more of the members of the group. For example, the statement “at least one of A, B, and C” can have the same meaning as “A; B; C; A and B; A and C; B and C; or A, B, and C,” or the statement “at least one of D, E, F, and G” can have the same meaning as “D; E; F; G; D and E; D and F; D and G; E and F; E and G: F and G; D, E, and F; D, E, and G; D, F, and G; E, F, and G; or D, E, F, and G.” A comma can be used as a delimiter or digit group separator to the left or right of a decimal mark; for example, “0.000,1 ”” is equivalent to “0.0001.”

[0021] In the methods described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified steps can be carried out concurrently unless explicit language recites that they be carried out separately. For example, a recited act of doing X and a recited act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the process. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E (including with one or more steps being performed concurrent with step A or Step E), and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps can also be repeated.

[0022] Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0023] The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, within 1 %, within 0.5%, within 0.1 %,, within 0.05%, within 0.01 %, within 0.005%, or within 0.001 % of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0024] The term “substantially” as used herein refers to a majority of, or mostly, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%.

[0025] In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as thoughindividually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

[0026] Hydrogen gas (H2) can be formed electrochemically by a water-splitting reaction where water is split into oxygen gas (O2) and H2 gas at an anode and a cathode of an electrochemical cell, respectively. Examples of such electrochemical processes include, without limitation, proton electrolyte membrane (PEM) electrolysis and alkaline water electrolysis (AWE). In such electrochemical reactions, the operating energy necessary to drive the water-splitting electrolysis reaction is high due to additional energy costs as a result of various energy inefficiencies. For example, to reduce unwanted migration of ionic species between the electrodes, the cathode and the anode may be separated by a separator, such as a membrane, which can reduce migration of the ionic species. Although the separator can improve the overall efficiency of the cell, it can come at a cost of additional resistive losses in the cell, which in turn increases the operating voltage. Other inefficiencies in water electrolysis can include solution resistance losses, electric conduction inefficiencies, and / or electrode over- potentials, among others.

[0027] FIG. 1 is a schematic diagram of a generic water electrolyzer cell 100 that converts water (H2O) into hydrogen gas (H2) and oxygen gas (O2) with electrical power. In an example, the electrolyzer cell 100 comprises a housing, e.g., an overall chassis structure that defines and at least partially encloses an interior of the cell 100. The housing can divide the cell 100 into two half cells: a first half cell 111 and a second half cell 121 . In an example, the first and second half cells 111 , 121 are separated by a separator 131 , such as a membrane 131. In an example, the separator 131 comprises a porous membrane (e.g., a microporous membrane or a nanoporous membrane), an ionexchange membrane, or an ion solvating membrane. In examples wherein the separator 131 comprises an ion-exchange membrane, the membrane can be of different types, such as an anion exchange membrane (AEM), a cation exchange membrane (CEM), a proton exchange membrane (PEM), or a bipolar ion exchange membrane (BEM).

[0028] In examples where the separator 131 is a cation exchange membrane, the cation exchange membrane can be a conventional membrane such as those available from, for example, Asahi Kasei Corp, of Tokyo, Japan, or from Membrane International Inc. of Glen Rock, NJ, USA, or from The Chemours Company of Wilmington, DE, USA. Examples of cation exchange membranes include, but are not limited to, the membrane sold under the N2030WX trade name by The Chemours Company and the membrane sold under the F8020 / F8080 or F6801 trade names by the Asahi Kasei Corp. Examples of materials that can be used to form a cationic exchange membrane include, but are not limited to, a perfluorinated polymer containing anionicgroups, for example sulphonic and / or carboxylic groups. It may be appreciated, however, that in some examples, depending on the need to restrict or allow migration of a specific cation or an anion species between the electrolytes, a cation exchange membrane that is more restrictive and thus allows migration of one species of cations while restricting the migration of another species of cations may be used. Similarly, in some embodiments, depending on the need to restrict or allow migration of a specific anion species between the electrolytes, an anion exchange membrane that is more restrictive and thus allows migration of one species of anions while restricting the migration of another species of anions may be used. Such restrictive cation exchange membranes and anion exchange membranes are commercially available and can be selected by one ordinarily skilled in the art.

[0029] In some examples, the separator 131 can be selected so that it can function in an acidic and / or an alkaline electrolytic solution, as appropriate. Other properties for the separator 131 that may be desirable include, but are not limited to, high ion selectivity, low ionic resistance, high burst strength, and high stability in electrolytic solution in a temperature range of room temperature to 150 °C or higher.

[0030] In an example, the separator 131 is stable in a temperature range of from about 0 °C to about 150 °C, for example from about 0 °C to about 100 °C, such as from about 0 °C to about 90 °C, for example from about 0 °C to about 80 °C, such as from about 0 °C to about 70 °C, for example from about 0 °C to about 60 °C, such as from about 0 °C, to about 50 °C, for example from about 0 °C to about 40 °C, or such as from about 0 °C to about 30 °C.

[0031] It may be useful to use an ion-specific ion exchange membrane that allows migration of one type of ion (e.g., cation for a CEM and anion for an AEM) but not another, or migration of one type of ion and not another, to achieve a desired product or products in the electrolyte solution.

[0032] In an example, the first half cell 111 comprises a first electrode 112, which can be placed proximate to the separator 131 , and the second half cell 121 comprises a second electrode 122, which can be placed proximate to the separator 131 , for example on an opposite side of the separator 131 from the first electrode 112. In an example, the first electrode 112 is the anode for the electrolyzer cell 100 and the second electrode 122 is the cathode for the electrolyzer cell 100, such that for the remainder of the present disclosure the first half cell 111 may also be referred to as the anode half cell 111 , the first electrode 112 may also be referred to as the anode 112, the second half cell 121 may also be referred to as the cathode half cell 121 , and the second electrode 122 may also be referred to as the cathode 122. In an example, each electrode 112, 122 can comprise a high surface area metal, such as a fine metal mesh. In an example, each electrode 112, 122 comprises a nickel mesh.

[0033] The electrodes 112, 122 are the locations of the cell 100 where the electron transfer reactions occur — e.g., oxidation of OH- at the anode 112 to produce O2 gas or reduction of H2O at the cathode 122 to produce H2 gas. Each of the electrodes 112, 122 can be coated with one or more electrocatalysts to speed the reaction toward the hydrogen gas (H2 gas) and / or the oxygen gas (O2 gas). In a typical example, one of both of the electrodes 112, 122 comprises a conductive substrate, such as a nickel substrate body, with an electrocatalyst coated onto one or more surfaces of the conductor substrate (described in more detail below). In most cases, the electrocatalyst lowers the activation energy for the electrochemical reaction so that the reaction can proceed without the electrocatalyst being consumed by the reaction. By lowering the activation energy, an electrocatalyst is able to facilitate specific reactions at the electrode so that the electrochemical device has a reduced energy demand. Examples of electrocatalyst materials include, but are not limited to, metals, metal alloys, metalmetalloid alloys, metal oxides, metal phosphides, and metal sulfides. Further details of some specific examples of electrocatalyst materials that can be applied to one or both electrodes 112, 122 are described in more detail below.

[0034] The ohmic resistance of the separator 131 can affect the voltage drop across the anode 112 and the cathode 122. For example, as the ohmic resistance of the separator 131 increases, the voltage across the anode 112 and the cathode 122 may increase, and vice versa. In an example, the separator 131 has a relatively low ohmic resistance and a relatively high ionic mobility. In an example, the separator 131 has a relatively high hydration characteristics that increase with temperature, and thus decreases the ohmic resistance. By selecting a separator 131 with lower ohmic resistance known in the art, the voltage drop across the anode 112 and the cathode 122 at a specified temperature can be lowered.

[0035] In an example, the anode 112 is electrically connected to an external positive conductor 116 (also referred to as “the anode conductor 116”) and the cathode 122 is electrically connected to an external negative conductor 126 (also referred to as “the cathode conductor 126”). In an example, when the separator 131 is wet and is in electrolytic contact with the electrodes 112 and 122, and an appropriate voltage is applied across the conductors 116 and 126, O2 gas is liberated at the anode 112 and H2 gas is liberated at the cathode 122. In certain configurations, an electrolyte, e.g., one comprising of a solution of potassium hydroxide (KOH) in water, is fed into the half cells 111 , 121 . For example, a first electrolyte can be fed into the anode half cell 111 through a first electrolyte inlet 114, such that the first electrolyte may also be referred to as “the anode electrolyte” or “the anolyte.” A second electrolyte can be fed into the cathode half cell 121 through a second electrolyte inlet 124, such that the second electrolyte may also be referred to as “the cathode electrolyte” or “the catholyte.” In some examples, the first and second electrolytes can be similar or even identical, e.g., both can bepotassium hydroxide having similar or the same pH. In other examples, the first electrolyte can be different from the second electrolyte, such as by being solutions of different compounds (such as one being potassium hydroxide (KOH) and the other being sodium hydroxide (NaOH), and / or by having different pHs (e.g., with the pH of the cathode electrolyte being lower (less alkaline or more acidic) than the pH of the anode electrolyte), and / or by having different additional compounds included in the first electrolyte solution versus that which is in the second electrolyte solution (e.g., with the first electrolyte comprising anions of one or more first metals in addition to KOH and the second electrolyte comprising only KOH and / or comprising anions of one or more second metals that are different than the one or more first metals and / or that have different concentrations of one or more of the metal anions compared to the concentration in the first electrolyte).

[0036] In an example, the flow of the electrolyte through the anode half cell 111 picks up produced O2 gas as bubbles 113 and exits the anode half cell 111 through a first outlet 115. Similarly, the flow of the electrolyte through the cathode half-cell 121 can pick up produced H2 gas as bubbles 123 and can exit the cathode half cell 121 through a second outlet 125. The gases can be separated from the electrolyte downstream of the electrolyzer cell 100 with one or more appropriate separators. In an example, the produced H2 gas is dried and harvested into high pressure canisters or fed into further process elements. The O2 gas can be allowed to simply vent into the atmosphere or can be stored for other uses. In an example, the electrolyte is recycled back into the half cells 111 , 121 as needed.

[0037] In an example, a typical voltage across the electrolyzer cell 100 (e.g., the voltage difference between the anode conductor 116 and the cathode conductor 126) is from about 1 .5 volts (V) to about 3.0 V. In an example, an operating current density for the electrolyzer cell 100 is from about 0.1 A / cm2to about 3 A / cm2. Each cell 100 has a size that is sufficiently large to produce a sizeable amount of H2 gas when operating at these current densities. In an example, an active area of each cell 100 (e.g., a width multiplied by a height for a rectangular cell) is from about 0.25 square meters (m2) to about 15 m2, such as from about 1 m2to about 5 m2, for example from about 2 m2to about 4 m2, such as from about 2.25 m2to about 3 m2, such as from about 2.5 m2to about 2.9 m2. In an example, the total volume of each cell (e.g., a width multiplied by a height multiplied by a depth) is from about 0.1 cubic meter (m3) to about 2 m3, such as from about 0.15 m3to about 1.5 m3, for example from about 0.2 m3to about 1 m3, such as from about 0.25 m3to about 0.5 m3, for example from about 0.275 m3to about 0.3 m3. In an example, the total volume of the entire electrolyzer system (e.g., the combined volume of all the cells in all the stacks in the plant) is from about 1 m3to about 25,000 m3, such as from about 5 m3to about 2,500 m3, for example fromabout 10 m3to about 100 m3, such as from about 25 m3to about 75 m3, for example from about 30 m3to about 50 m3.

[0038] In an example, one or both of the electrodes 112, 122 comprise a fine mesh structure, such as a fine woven mesh. Fine mesh, such as woven mesh, have been found to make an excellent electrode for electrolyzer cells because it provides a high relative surface area, a relatively large open area for electrolyte and gas flow to and from the electrode, and are readily available in sizes that are large enough for a large commercial electrolyzer cell, e.g., with an active area of at least 1 m2, such as from about 1 m2to about 4 m2.

[0039] FIGS. 2 and 3 show a non-limiting example of a woven mesh electrode 150 that can be used as either the anode 112 or the cathode 122 of the example electrolyzer cell 100 of FIG. 1. In an example, the woven mesh electrode 150 comprises a network of sets of crossing wires 152, 154, which can be perpendicular or angled relative to one another, that alternative cross and bend over one another. For example, any particular wire 152 can alternate between passing under a cross wire 154 and then over the next adjacent cross wire 154. In an example, the mesh electrode 150 comprises a woven wire mesh electrode formed from wires 152, 154 having a wire diameter of about 0.18 mm diameter with openings in the mesh of about 0.44 mm and with an open area of from about 50% to about 60%, such as from about 50% to about 55%.

[0040] The example woven mesh electrode 150 shown in FIG. 2 is a plain / double weave comprising warp wires 152 and shute wires 154, e.g., with each warp wire 152 passing alternatively over and under the shute wires 154 at right angles so that rectangular or substantially rectangular openings are formed in the mesh electrode 150. Those having skill in the art will appreciate that the catalyst coating described herein can be applied to other types of meshes, including, but not limited to: a twill square weave, a twill Dutch weave, a plain Dutch weave, and a reverse plain Dutch weave. In other examples, an electrode that is coated with the catalyst material of the present disclosure can be a type of electrode other than a mesh electrode, such as a flat plate electrode or some other configuration of electrode.Catalyst Coating

[0041] One or both of the electrodes 112, 122 of the electrochemical cell 100 of FIG. 1 can be at least partially coated with one or more catalyst compositions via the methods described below. For example, the woven mesh electrode 150 of FIGS. 2 and 3 includes a catalyst coating 156. As shown in FIG. 3, in an example, the catalyst coating 156 comprises a layer of one or more electrocatalyst materials that have been coated or plated onto the conductive substrate of the mesh electrode 150, i.e., onto the conductive material of the wires 152, 154.

[0042] Many methods have been used to apply catalyst materials onto electrodes used for electrochemical reactions, such as the electrodes 112, 122 of the electrolyzer cell 100 in FIG. 1 or the mesh electrode 150 of FIGS. 2 and 3. These methods have included spray coating (such as airbrush coating, electrostatic coating, and thermal spray coating), slurry coating (such as dip coating, painting, doctor blade coating, slot die coating, comma bar coating, or tensioned web coating), thermal coating methods (such as hydro / solvothermal coating or thermal decomposition), vapor deposition methods (such as chemical vapor deposition or physical vapor deposition), and electrochemical methods (such as electrochemical deposition, which is also known as electrolytic deposition, electrodeposition or electroplating, underpotential or overpotential deposition, or electrophoretic coating).

[0043] As described in more detail below, the electrocatalyst material of the conductive coating 156 is deposited onto the conductive substrate of the electrode 150 (i.e., onto the wires 152, 154) by electrodeposition. A typical electrodeposition process includes placing a conductive substrate to be coated into a bath of a salt solution of the metal that will form the catalyst coating 156 (also referred to herein as the “electroplating bath”). For example, if the catalyst coating 156 is to comprise a cobalt- containing electrocatalyst material, then the salt solution that forms the electroplating bath can comprise a cobalt salt, such as cobalt (II) chloride (C0CI2). The conductive substrate to be coated acts as one of the electrodes of an electrolytic cell, with the electroplating bath solution acting as the electrolyte. When an electric current is applied to the conductive substrate, ions of the metal salt in the electroplating bath react to form a solid compound of the metal on the surface of the conductive substrate, e.g., metal cations are reduced to form the solid metal compound or metal ions are oxidized to form the solid metal compound.

[0044] Electrodeposition can be particularly useful for coating electrodes with one or more catalytic materials because it allows for a wide range of electrocatalyst chemistries by varying the composition of the electroplating bath solution. Electrodeposition can also produce a robust catalyst coating onto a wide range of physical structures and geometries.

[0045] Electrodeposition has been shown to be useful for formation of coatings that include nickel, cobalt, and their alloys, which have been explored as cost-effective alternatives to commonly used platinum group metal catalyst materials such as platinum-based, ruthenium-based, and iridium-based catalysts. Electrodeposition does present some limitations, however. First, electrodeposition has typically been performed in an acidic plating bath so that the metal cations are reduced onto a cathode when an electrical bias is applied. Thus, acidic-based electrodeposition generally has been limited to applying catalyst materials onto the cathode of electrolyzer cells, not onto the anode.

[0046] In addition, additives such as buffers (e.g., boric acid) and mediators (e.g., saccharin) are commonly added to the solution to improve electrodeposition efficiency. These additive increase the complexity of the bath. In addition, the acidic environment and additives often require the electrode to be removed from the plating bath and rinsed before being installed in the electrolyzer cell, especially if the electrode is intended to support anodic reactions and / or is to be used in an alkaline environment. Furthermore, when the electrode becomes less active over time (e.g., because the catalyst coating loses activity or because the coating is abraded or otherwise damaged), the electrolyzer cell must be taken offline and the electrode must be removed for recoating or exchanged with a replacement electrode, which reduces the overall operational efficiency of the electrolyzer cell.

[0047] The methods of the present disclosure and the resulting catalyst coating 156 formed therefrom provide solutions to the limitations. First, the methods of the present disclosure comprise electrochemically depositing a catalyst material from an alkaline solution, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), by oxidizing anions of one or more first metals to form solid one or more catalytic compounds comprising the one or more first metals. The one or more first metals can comprise any metal element that forms an anion in an alkaline solution without the presence of an electrical bias (e.g., when the applied voltage is 0 V) and that is electrodeposited as a solid when at least a specified potential is applied to a conductive substrate that is at least partially submerged in the alkaline solution comprising the first metal anions.

[0048] FIG. 4 is a Pourbaix diagram of cobalt to illustrate an example of the concept of the one or more first metals being any metal that forms a metal ion in the alkaline electroplating solution without the presence of an applied bias (i.e., at 0 V) and that is electrochemically deposited as a solid when a specified potential is applied. As can be seen in FIG. 4, at 0 V and a pH of at least about 10.5, cobalt exists as a stable ion, e.g., CoOH2‘ (in region 172 of the Pourbaix diagram of FIG. 4). When a sufficient positive bias is applied, the cobalt transforms into a solid state (for example as CoO in region 174, as C03O4 in region 176, or as CoO(OH) in region 178 of the Pourbaix diagram of FIG. 4). In an example, when a sufficient negative bias is applied, then the cobalt can transform into solid cobalt metal (e.g., in region 180 of the Pourbaix diagram of FIG. 4). The cobalt remains in a solid form above the oxygen stability line 182and below the hydrogen stability line 184. Those having skill in the art will appreciate that different but similar Pourbaix diagrams may exist for other potential first metals, and the Pourbaix diagram for cobalt shown in FIG. 4 is merely one example and is not meant to limit the present disclosure or invention in any way.

[0049] Examples of first metals that can be used in the electrochemical deposition method of the present disclosure include, but are not limited to: nickel (Ni), cobalt (Co), copper (Cu), and silver (Ag).

[0050] Electrochemical deposition of the one or more metal anions from an alkaline solution allows the methods of the present disclosure to be used to form a catalyst coating onto the anode or the cathode of the electrolyzer cell, not just onto the cathode. In addition, the inventors have found that the electrochemical deposition from the alkaline solution can be achieved without requiring a buffer compound or a mediator compound.

[0051] In some examples, if the current density being applied to the conductive substrate for the electrochemical deposition is sufficiently high, e.g., greater than or equal to about 1 A / cm2, than the applied voltage can also generate bubbles (for example, the high electroplating voltage may also drive an oxygen evolution reaction to form O2 gas bubbles 113 from an anode and / or a hydrogen evolution reaction to form H2 gas bubbles 123 from a cathode). The formation of bubbles at a high enough gas generation rate can result in the catalytic material that is plated onto the conductive substrate having a highly porous, foam-like structure, which can increase the overall active surface area of the catalytic material and provide pathways for evolved H2 or O2 gas to pass through and escape the catalytic material during electrolysis more easily. FIG. 5 shows a close-up cross-sectional view of an example coated article 160 that has been coated under just such bubble-generating conditions. The example coated article 160 includes a conductive substrate 162 onto which has been coated a catalyst coating 166. The example electrode 160 of FIG. 5 could be, for example, the electrode 150 of FIGS. 2 and 3 or could be either electrode 112, 122 in the electrolyzer cell 100 of FIG. 1.

[0052] As can be seen in FIG. 5, the catalyst coating 166 includes pores 166 into or through the catalytic material of the coating 166. The pores 168 are formed because of the presence of bubbles evolving from an outer surface 170 of the conductive substrate 162 at the same time that the electrochemical deposition of the catalytic material from the electroplating bath solution onto the conductive substrate 162 occurs to form the catalyst coating 166. The bubbles evolving from the outer surface 170 displace the catalytic material as it is solidifying from the electrodeposition process so that the at some locations along the surface 170, the pores 168 are formed. As can be seen in FIG. 5, some of the pores 168 extend entirely through the catalyst coating 166 and expose a portion of the outer surface 170 of the conductive substrate 162, and some of the pores 168 are only formed partially into the catalyst coating 168. In either case, the formation of the pores 168 during the electrochemical deposition causes the catalyst coating 166 to have a higher active surface area than it would have without the presence of the evolving gas bubbles and the pores 168, which can lead to improvedcatalytic activity of the catalyst coating 166. The pores 168 can also provide pathways for evolving gas to escape the catalyst coating 166 during the water-splitting electrolysis reaction (i.e., the pores 168 can provide pathways for the O2 gas bubbles 113 or the H2 gas bubbles 123 to escape the catalyst coating 166) and free up surface area on the catalyst coating 166 to catalyze the water splitting, which can further improve catalytic activity.

[0053] In addition, because the methods of the present disclosure include electrodeposition from an alkaline solution, the electroplating bath solution can be formed as part of the electrolyte solution that is fed to the electrolyzer cell 100 so that separate electroplating bath and electrolyte solutions are not required. Using a common solution for both the electrolyte and the electroplating bath removes the need for rinsing before using the catalyst coated electrode in the electrolyzer cell 100. The common solution for both the electroplating bath and the electrolyte also allows the electrochemical deposition of the present disclosure to be carried out in situ with normal operation of the electrolyzer cell 100. As used herein, the term “in situ," in relation to electrochemical deposition of a catalytic material onto an electrode substrate to form a catalyst coating, refers to performing the electrodeposition at the same time as, i.e., concurrent or substantially concurrent with, the electrolysis operation of an electrolyzer cell and while the electrode substrate is installed within the electrolyzer cell as one of the cell’s electrodes. In situ electrodeposition allows the methods of the present disclosure to provide for on-demand application of catalytic material to one or both of the electrodes 112, 122 of the electrolyzer cell 100. For example, the electrochemical deposition can be performed during or just before startup of the electrolyzer cell 100 to initially form the catalyst coating 156, but can also be performed at a later time for maintenance of the electrode 150, such as when it is determined that the activity of the catalyst coating 156 has gone down and it is believed it is because the original catalyst coating 156 has been damaged or worn away from the conductive substrate of the electrode 150 (e.g., from the wires 152, 154).

[0054] Although much of the present disclosure describes in situ electrodeposition of the catalytic material, including advantages that in situ electrodeposition provides, the present disclosure is not limited to in situ electrodeposition. Rather, the methods of the present disclosure can also be used for ex situ electrodeposition of a catalyst coating onto a conductive substrate, such as the catalyst coating 156 plated onto the wires 152, 154 of the electrode 150 in FIGS. 2 and 3. As used herein, the term “ex situ," in relation to electrodeposition of catalytic material onto an electrode substrate, refers to performing the electrochemical deposition of the catalyst coating separate from the primary electrolysis for which the electrode is to be used. In other words, “ex situ" electrodeposition refers to the electrode being coated either outside of the electrolyzer cell and using a separate electroplating bath, or wherethe electrochemical deposition takes place at a different time from the primary electrolysis (e.g., during a maintenance shutdown).

[0055] The specific metal compound or compounds that is or are dissolved in the electrolyte solution to form the electroplating bath solution can be selected depending on various factors, including which electrode is being coated. For example, the anode-side electrolyte solution that is to be fed to the anode half cell 11 1 of the electrolyzer cell 100 can comprise anions of one or more first metals while the cathodeside electrolyte solution is to be fed to the cathode half cell 121 can comprise anions of one or more second metals. The one or more first metals can be selected specifically for the oxygen evolution reaction that is to take place at the anode 1 12 of the electrolyzer cell 100. Similarly, the one or more second metals can be selected specifically for the hydrogen evolution reaction that is to take place at the cathode 122 of the electrolyzer cell 100. This selection can include selecting the concentration of each of the metal anions in the electrolyte solution, as well as the specific compounds of each of the one or more metals that are added to the electrolyte to form the one or more metal anions that will provide for a desired final composition for the resulting electroplating catalyst coating 156. The selection can also include setting a pH for the electroplating bath solution. For example, a higher pH for the bath can allow for a larger concentration of the metal anions to be stable in the electroplating bath solution before applying the potential to electrochemically deposit the catalyst compound. In some examples, more than one metal anion (i.e., metal anions of more than one metal element) can be included in the electroplating bath solution, which can allow for the formation of a metal alloy coating material (e.g., if the metal anions include Ni anions and cobalt anions, than the resulting catalyst coating material can be a NiCo alloy).Methods of Electrodeposition of Catalyst Coating

[0056] FIG. 6 is a flow diagram of an example general method 200 for preparing a catalyst coated conductive substrate in accordance with the present disclosure, such as the example mesh electrode 150 with the catalyst coating 156 shown in FIGS. 2 and 3 or the example article 160 with the catalyst coating 166 shown in FIG. 5. The method 200 of FIG. 6 could comprise ex situ electrochemical deposition of the catalyst coating or in situ electrochemical deposition of the catalyst coating. FIGS. 7 and 8 are flow diagrams of addition example methods 210 and 220 wherein formation of a catalyst coating on at least one of the electrodes is via in situ electrochemical deposition wherein an electrolyte solution for the primary electrolysis also acts as the electroplating solution for the in situ electrochemical deposition.

[0057] In an example, the method 200 includes, at step 202, forming an alkaline solution comprising anions of one or more first metal elements (also referred to hereinafter as “first metal anions”). In an example, forming the alkaline solutioncomprising dissolving one or more precursor metal compounds each comprising one or more of the first metal elements in an alkaline solvent, e.g., such that the first metal anions become dissociated anions of the one or more first metal elements in the alkaline solvent. As described in more detail, the dissociated first metal anions will be electrochemically deposited out of the alkaline solution (which may also be referred to hereinafter as “the alkaline electroplating solution” or simply as “the electroplating solution”) onto a conductive substrate as a solid catalytic material that comprises the one or more first metal elements when a specified potential is applied to the conductive substrate. In an example, the alkaline solution has a pH of at least about 8, for example at least about 9, at least about 10, at least about 11 , or at least about 12. In an example, the alkaline solvent comprises a dissociated compound that provides for the specified pH, such as a hydroxide, for example sodium hydroxide (NaOH) or potassium hydroxide (KOH) at a specified concentration. Examples of other alkaline solvents that can be used include, but are not limited to, a carbonate (e.g., potassium carbonate (K2CO3)), or ammonia (NH3).

[0058] The one or more first metal elements that are dissociated in the alkaline solution as the one or more first metal anions (which are then electrodeposited onto a conductive substrate to form a coating, such as a catalyst coating) can be any metal element that will dissociate as a metal anion in an alkaline solution when a bias is not being applied (e.g., when the applied voltage is 0 V) and that can be electroplated onto the material of the conductive substrate when a specified potential is applied. In particular, at least one of the one or more first metal elements dissociated in the alkaline solution is useful as an electrocatalyst for a desired electrochemical reaction in its electroplated solid form. In an example, the one or more first metal elements that form the as one or more first metal anions in the alkaline electroplating solution include, but are not limited to, one or more of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Ph). Examples of the precursor metal compounds that can be dissolved in the alkaline solution to form the one or more first metal anions include, but are not limited to, a chloride of a first metal element having the general formula MCIa, wherein M is the first metal element, and a is an integer from 1 to 6, inclusive (such as cobalt (II) chloride (C0CI2) or nickel (II) chloride (NiCh)), a hydroxide of the first metal element (such as cobalt (II) hydroxide (Co(OH)2) or nickel (II) hydroxide (Ni(OH)2)), an oxide of the firm metal element (such as cobalt (II) oxide (CoO) or nickel (II) oxide (NiO)), a nitrate of the first metal element (such as cobalt (II) nitrate (Co(NC>3)2) or nickel (II) nitrate (Ni(NOs)2)), another halide of the first metal element (such as a bromide, iodide, or fluoride), a sulfate of the first metal element (such as cobalt (II) sulfate (C0SO4) or nickel (II) sulfate (NiSC )), and a selenide of the first metal element (such as cobalt (II) selenide (CoSe) or nickel (II) selenide (NiSe)).

[0059] In an example, the specific first metal element or elements that are included as part of the alkaline solution are selected depending on the intended use for the conductive substrate that is to be coated by the method 200. In an example wherein the conductive substrate that is to be coated is the anode 112 of the electrolyzer cell 100, then one or more specific metal elements may be chosen to form the metal anions in the electroplating solution, while in another example wherein the conductive substrate to be coated is the cathode 122, then one or more different specific metal elements can be chosen to form the metal anions.

[0060] The concentration of the one or more first metal anions in the alkaline solution can be selected to achieve one or more desired properties for the coating material that is formed by the electrochemical deposition of the first metal anions. When the concentration of the one or more first metal anions is relatively lower, than the electrochemical deposition reaction will be slower, and thus the electrochemical deposition process overall will be less efficient. If the concentration of the one or more first metal anions is too high, than the metal anions may not be sufficiently stable in the solution and may precipitate out of solution. In addition, it has been found that the lower the concentration of the one or more metal anions in the solution, the lower the pH of the solution can be while still being able to electrochemically deposit the catalyst material satisfactorily. The concentration that is selected for the one or more first metal anions will depend on the metal element or elements being used and the pH that is chosen for the electroplating solution. In an example, a total concentration of the one or more first metal anions in the alkaline solution is up to about 100,000 molar (M), such as up to about 10,000 M, for example up to about 1 ,000 M, such as up to about 500 M, up to about 450 M, up to about 400 M, up to about 400 M, up to about 350 M, up to about 300 M, up to about 275 M, up to about 250 M, up to about 225 M, up to about 200 M, up to about 190 M, up to about 180 M, up to about 175 M, up to about 170 M, up to about 160 M, up to about 150 M, up to about 140 M, up to about 130 M, up to about 125 M, up to about 120 M, up to about 110 M, up to about 100 M, up to about 95 M, up to about 90 M, up to about 85 M, up to about 80 M, up to about 85 M, up to about 70 M, up to about 65 M, up to about 60 M, up to about 55 M, up to about 50 M, up to about 49 M, up to about 48 M, up to about 47 M, up to about 46 M, up to about 45 M, up to about 44 M, up to about 43 M, up to about 42 M, up to about 41 M, up to about 40 M, up to about 39 M, up to about 38 M, up to about 37 M, up to about 36 M, up to about 35 M, up to about 34 M, up to about 33 M, up to about 32 M, up to about 31 M, up to about 30 M, up to about 29 M, up to about 28 M, up to about 27 M, up to about 26 M, up to about 25 M, up to about 24 M, up to about 23 M, up to about 22 M, up to about 21 M, up to about 20 M, up to about 19 M, up to about 18 M, up to about 17 M, up to about 16 M, up to about 15 M, up to about 14 M, up to about 13 M, up to about 12 M, up to about 11 M, up to about 10 M, up to about 9.9 M, up to about 9.8 M, up to about 9.7 M, up to about 9.6 M, up toabout 9.5 M, up to about 9.4 M, up to about 9.3 M, up to about 9.2 M, up to about 9.1 M, up to about 9 M, up to about 8.9 M, up to about 8.8 M, up to about 8.7 M, up to about8.6 M, up to about 8.5 M, up to about 8.4 M, up to about 8.3 M, up to about 8.2 M, up to about 8.1 M, up to about 8 M, up to about 7.9 M, up to about 7.8 M, up to about 7.7 M, up to about 7.6 M, up to about 7.5 M, up to about 7.4 M, up to about 7.3 M, up to about 7.2 M, up to about 7.1 M, up to about 7 M, up to about 6.9 M, up to about 6.8 M, up to about 6.7 M, up to about 6.6 M, up to about 6.5 M, up to about 6.4 M, up to about 6.3 M, up to about 6.2 M, up to about 6.1 M, up to about 6 M, up to about 5.9 M, up to about 5.8 M, up to about 5.7 M, up to about 5.6 M, up to about 5.5 M, up to about 5.4 M, up to about 5.3 M, up to about 5.2 M, up to about 5.1 M, up to about 5 M, up to about 4.9 M, up to about 4.8 M, up to about 4.7 M, up to about 4.6 M, up to about 4.5 M, up to about 4.4 M, up to about 4.3 M, up to about 4.2 M, up to about 4.1 M, up to about 4 M, up to about 3.9 M, up to about 3.8 M, up to about 3.7 M, up to about 3.6 M, up to about 3.5 M, up to about 3.4 M, up to about 3.3 M, up to about 3.2 M, up to about 3.1 M, up to about 3 M, up to about 2.9 M, up to about 2.8 M, up to about 2.7 M, up to about 2.6 M, up to about 2.5 M, up to about 2.4 M, up to about 2.3 M, up to about 2.2 M, up to about 2.1 M, up to about 2 M, up to about 1 .9 M, up to about 1 .8 M, up to about 1 .7 M, up to about1 .6 M, up to about 1 .5 M, up to about 1 .4 M, up to about 1 .3 M, up to about 1 .2 M, up to about 1.1 M, up to about 1 M, up to about 950 millimolar (mM), up to about 900 mM, up to about 850 mM, up to about 800 mM, up to about 750 mM, up to about 700 mM, up to about 650 mM, up to about 600 mM, up to about 550 mM, up to about 500 mM, up to about 475 mM, up to about 450 mM, up to about 425 mM, up to about 400 mM, up to about 375 mM, up to about 350 mM, up to about 325 mM, up to about 300 mM, up to about 275 mM, up to about 250 mM, up to about 225 mM, up to about 200 mM, up to about 175 mM, up to about 150 mM, up to about 125 mM, or up to about 100 mM.

[0061] Other parameters than can be chosen for the electroplating solution includes a temperature of the solution or a voltage applied to the solution for the electroplating. In an example, the temperature of the electroplating solution is from about 5 °C to about 100 °C, such as from about 10 °C to about 60 °C. In an example, the voltage applied is from about + / - 0.1 V to about + / - 10 V.

[0062] In an example, the alkaline solution can be prepared with reduced usage of additives beyond the alkaline solvent (e.g., NaOH or KOH) and the one or more metal precursor compounds that form the one or more first metal anions (e.g., the first metal chloride). For example, the alkaline solution can be prepared without including a buffer (such as boric acid) and / or without including a mediator (such as saccharin) in the alkaline solution. In an example, the alkaline solution consists essentially of the one or more precursor metal compounds of the one or more first metal elements (e.g., the first metal chloride) at least partially dissolved into the alkaline solvent (e.g., NaOH or KOH). In an example, the alkaline solution consists of the one ormore precursor metal compounds of the one or more first metal elements at least partially dissolved into the alkaline solvent (e.g., NaOH or KOH).

[0063] In some examples, however, a buffer such as borate or N-cyclohexyl-2- aminoethanesulfonic acid (CHES) can be included in the solution. In other examples one or more mediators or other additives can be added to the solution, including, but not limited to: benzene sulfonate, benzoic acid sulfimide (saccharin), coumarin, dibenzene sulfonic acid, naphalene trisulfonic acid, phenol safanine, and tisulfonated naphtalene.

[0064] After the alkaline solution has been prepared (step 202), the method 200 can include, at step 204, at least partially submerging a conductive substrate in the prepared alkaline solution. For example, the conductive substrate 162 shown in FIG. 5 or the mesh electrode 150 shown in FIGS. 2 and 3 can be partially or totally submerged in the alkaline solution. In an example, the portions of the conductive substrate that are submerged in the alkaline solution are the portions that are desired to be coated via the electrochemical deposition step (step 206, described below). The conductive substrate that is at least partially submerged in the alkaline solution in step 202 can be the anode or the cathode of an electrolyzer cell, such as the anode 112 or the cathode 122 of the electrolyzer cell 100 of FIG. 1.

[0065] After at least partially submerging the conductive substrate in the alkaline solution (step 204), the method 200 can include, at step 206, applying a specified potential to the conductive substrate in order to electrochemically deposit a solid coating compound comprising the first metal element onto the conductive substrate. In an example, the solid coating compound that is formed by electrochemical deposition of step 206 can be a catalytic compound for an electrochemical reaction that is to occur at the conductive substrate, e.g., with the conductive substrate acting as one of the electrodes in an electrochemical cell. For example, if the conductive substrate is to be used as the anode 112 in the water electrolyzer cell 100 of FIG. 1 , the coating compound can be an electrocatalyst for the oxygen generation reaction that takes place at the anode 112. Similarly, if the conductive substrate is to be used as the cathode 122 in the water electrolyzer cell 100, the coating compound can be an electrocatalyst for the hydrogen generation reaction that takes place at the cathode 122. Examples of electrocatalyst compounds that might be formed by the electrochemical deposition of step 206 can include, but are not limited to, an oxide of the first metal element (e.g., having the general formula M&OC, wherein M is the first metal, b is an integer from 1 to 3, inclusive, and c is an integer from 1 to 6, inclusive, such as cobalt (II) oxide (CoO), cobalt (II, III) oxide (C03O4), copper (I) oxide (CU2O) or copper (III) oxide (CU2O3) (which may result in copper (II) oxide (CuO) when the conductive substrate is removed from the bath), iron (III) oxide (Fe2Os), iron (II, III) oxide (FesO4), manganese (III) oxide (Mn2O3), manganese (IV) oxide (MnO2), manganese (II, III) oxide (Mn3O4), rhodium (IV) oxide (RhO2), lead (IV) oxide (PbO2), or silver (II) oxide (AgO) (which may result in silver(I) oxide (Ag2O) when the conductive substrate is removed from the bath), a metal hydroxide oxide (e.g., having the general formula MO(OH), such as cobalt hydroxide oxide (CoO(OH)) or nickel hydroxide oxide (NiO(OH)) (which may result in nickel (II) oxide (NiO) when the conductive substrate is removed from the bath), and non-oxide metal compounds such as a metal boride (MB) or a metal phosphide (MP).

[0066] As mentioned above, the electrochemical deposition methods of the present disclosure can include in situ electrochemical deposition of a coating material (which can include an electrocatalyst) onto one or both of the electrodes of an electrolyzer cell that is concurrent or substantially concurrent with electrolysis at the same electrode or electrodes of the electrolyzer cell, e.g., to produce hydrogen gas (H2) via water electrolysis. FIG. 7 is a flow diagram of an example method 210 of electrochemically depositing a coating material onto an electrode of an electrolyzer cell in situ during hydrogen electrolysis by the same electrolyzer cell.

[0067] The example method 210 includes, at step 212, providing or receiving an electrolyzer cell comprising a first half cell with a first electrode, a second half cell with a second electrode, and (optionally) a separator separating the first half cell from the second half cell. For example, step 212 can include providing or receiving the electrolyzer cell 100 shown in FIG. 1 , which includes the first half cell 111 with the first electrode 112, the second half cell 121 with the second electrode 122, and the separator 131 .

[0068] Next, the method 210 can include, at step 214, feeding a first alkaline electrolyte solution to the first half cell of the electrolyzer cell (e.g., feeding the anode electrolyte to the anode half cell 111), wherein the first alkaline electrolyte solution comprises anions of one or more first metal elements. The one or more first metal elements that form the anions in the first alkaline solution that is fed in step 214 can be similar or the same as the first metal elements and first metal anions described above with respect to step 202 of the method 200 of FIG. 6. For example, the one or more first metal elements can comprise any metal element that will dissociate as a metal anion in the first alkaline solution when a bias is not being applied (e.g., when the applied voltage is 0 V) and that can be electroplated onto the material of the first electrode in the first half cell when a specified potential is applied. Furthermore, as described above, the one or more metal elements can result in electroplating a coating material that is useful as an electrocatalyst for the electrochemical reaction that is to be performed in the first half cell in its electroplated solid form, such as an electrocatalyst that is useful for an oxygen evolution reaction if the first electrode is the anode (e.g., the anode 112 of the electrolyzer cell 100) or that is useful for a hydrogen evolution reaction if the first electrode is the cathode (e.g., the cathode 122 of the electrolyzer cell 100).

[0069] As described above with respect to the method 200 of FIG. 6, in an example the one or more first metal elements that are included as one or more metalanions in the first alkaline electrolyte solution of step 214 can include, but are not limited to, one or more of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Pb). The first alkaline electrolyte solution comprising one or more first metal anions can be formed by dissociating one or more first metal compounds in the first alkaline electrolyte solution, including, but not limited to, a chloride of the first metal element (such as cobalt (II) chloride (C0CI2) or nickel (II) chloride (NiCh)).

[0070] Other aspects of the first alkaline electrolyte solution can be similar or identical to those described above for the alkaline electrolyte solution of the method 200 of FIG. 6, such as the specific first metal anion or first metal anions, the concentration of the one or more first metal anions in the first alkaline electrolyte solution, or the presence (or absence) of additives in the first alkaline electrolyte solution.

[0071] The method 210 can also include, at step 216, feeding a second alkaline electrolyte solution to the second half cell of the electrolyzer cell (e.g., to the cathode half cell 121). In an example, the feeding of the second alkaline electrolyte solution to the second half cell (step 216) is performed concurrently or substantially concurrently with the feeding of the first alkaline electrolyte solution to the first half cell (step 214), for example as part of a water electrolysis process of splitting water into hydrogen gas (H2) within the cathode chamber of the cathode half cell and oxygen gas (O2) within the anode chamber of the anode half cell.

[0072] In an example, the second alkaline electrolyte solution is different from the first alkaline electrolyte solution. For example, the second alkaline electrolyte solution can comprise only the alkaline forming component, such as the hydroxide compound (e.g., NaOH or KOH), and need not include anions of a metal element as is the case with the first alkaline electrolyte solution. In other words, in an example, the method 200 only includes feeding an electrolyte solution comprising anions of one or more first metal elements to the first half cell and not into the second half cell. As described in more detail below, the purpose of including the one or more first metal anions only in the first alkaline electrolyte solution is so that a first metal compound will be electrochemically deposited onto a conductive substrate within the first half cell (e.g., the first electrode) and not onto a substrate within the second half cell. For example, if the first half cell comprises the anode half cell of the electrolyzer cell, then the first metal anions may be selected because the resulting electrodeposited first metal compound is a catalytic material for the oxygen evolution reaction that takes place at the anode. Conversely, if the first half cell comprises the cathode half cell of the electrolyzer cell, then the first metal anions may be selected because the resulting electrodeposited first metal compound is a catalytic material for the hydrogen evolution reaction that takes place at the cathode.

[0073] Next, the method 210 can include, at step 218, applying a specified potential between the first electrode and the second electrode. The specified potential is such that it is sufficient to electrolytically generate hydrogen gas (H2) at the cathode of the electrolyzer cell (which may be the first electrode in the first half cell or the second electrode in the second half cell) and to electrochemically deposit a coating compound comprising the first metal element. In some examples, the coating compound comprising the first metal element is an electrocatalyst for the electrochemical reaction that occurs at the first electrode (i.e., the oxygen generation reaction if the first electrode is the anode or the hydrogen generation reaction if the first electrode is the cathode), also referred to as a “first metal catalytic compound,” onto the first electrode (which may be the anode or the cathode). The electrolytic generation of the H2 gas at the cathode and the electrochemical deposition of the first metal catalytic compound can occur concurrently or substantially concurrently. In an example, the specified potential between the first electrode and the second electrode can also be sufficient to electrolytically generate oxygen gas (O2) at the anode (e.g., the other of the first electrode and the second electrode of the electrolyzer cell).

[0074] In an example, the step of applying the specified potential 218 can include applying a small positive bias to the anode before or at the same time as applying the overall specified potential between the anode and cathode, which improves electrostatic attraction of anions from the alkaline anolyte solution onto the anode surface without further dissociating the anions in the solution. When this occurs, then when the overall specified potential is applied, the electric force from the cathode is significantly weaker compared to that provided at the anode, which enhances the probability of the desired metal cations plate onto the anode instead of the cathode. For example, if it is desired to plate cobalt (Co) onto the anode, then a small positive bias applied to the anode can attract CoHC>2' anions onto the anode surface, and when the overall potential is applied for the purpose of electrochemically depositing Co, the Co is more likely to be attracted to the anode rather than the cathode. In an example, the small positive bias that is applied can be from about +1 mV to about +250 mV, such as up to about +225 mV, up to about +200 mV, up to about +175 mV, up to about +150 mV, up to about +125 mV, up to about +120 mV, up to about +115 mV, up to about +110 mV, up to about +105 mV, up to about +100 mV, up to about +95 mV, up to about +90 mV, up to about +85 mV, up to about +80 mV, up to about +75 mV, up to about +70 mV, up to about +65 mV, up to about +60 mV, up to about +55 mV, up to about +50 mV, up to about +45 mV, up to about +40 mV, up to about +35 mV, up to about +30 mV, up to about +25 mV, up to about +20 mV, up to about +15 mV, up to about+10 mV.

[0075] The method 210 is not limited to in situ electrochemical deposition during water-splitting electrolysis to form H2 gas, as shown in the example method 210of FIG. 7. In some examples (not shown in FIG. 7), step 218 of the method 210 can include activating an electrochemical reaction other than one or more water electrolysis reactions (e.g., a hydrogen evolution reaction and / or an oxygen evolution reaction) in situ with the electrochemical deposition of the catalytic compound comprising the one or more first metal elements onto the first electrode. In other words, rather than a hydrogen evolution reaction at the cathode and / or an oxygen evolution reaction at the anode, step 218 can comprise activating a different electrochemical reaction at the first electrode . For example, it may be possible to design the method to allow for in situ deposition of the catalytic compounds onto the first electrode of an electrolyzer configured for chloralkali electrolysis or another type of electrochemical reaction. In other examples, the coating compound comprising the first metal element that is electrodeposited onto the first electrode in step 218 can comprise a non-catalytic compound in addition to or in place of the electrocatalyst compounds described above.

[0076] FIG. 8 is a flow diagram of another example method 220 of electrochemically depositing a first coating material onto the anode of an electrolyzer cell and electrochemically depositing a second coating material onto the cathode of the electrolyzer cell in situ during hydrogen electrolysis by the same electrolyzer cell. In a preferred example, one or both of the first and second coating materials that are electrochemically deposited onto the anode and cathode, respectively, comprise an electrocatalyst material for the electrochemical reaction that occurs at that electrode. For example, the first coating material can comprise an electrocatalyst for the oxygen evolution reaction that occurs at the anode (also referred to as the “first catalyst material”) and / or the second coating material can comprise an electrocatalyst for the hydrogen evolution reaction that occurs at the cathode (also referred to the “second catalyst material”). The example method 220 includes, at step 222, providing or receiving an electrolyzer cell comprising an anode half cell with an anode, a cathode half cell with a cathode, and (optionally) a separator separating the anode half cell from the cathode half cell. For example, step 222 can include providing or receiving the electrolyzer cell 100 shown in FIG. 1 , which includes the anode half cell 111 with the anode 112, the cathode half cell 121 with the cathode 122, and the separator 131.

[0077] Next, the method 220 can include, at step 224, feeding an alkaline anolyte solution to the anode half cell of the electrolyzer cell, wherein the alkaline anolyte solution comprises anions of one or more first metal elements. The method 220 can also include, at step 226, feeding an alkaline catholyte solution to the cathode half cell of the electrolyzer cell, wherein the alkaline catholyte solution comprises anions of one or more second metal elements. In an example, step 224 (feeding the alkaline anolyte solution to the anode half cell) and step 226 (feeding the alkaline catholyte solution to the cathode half cell) are performed concurrently or substantially concurrently.

[0078] In examples where both the first and second coating materials are electrocatalyst compounds, the one or more first metal elements that form the anions in the alkaline anolyte solution that is fed in step 224 and the one or more second metal elements that form the anions in the alkaline catholyte solution that is fed in step 226 can each be similar or the same as the first metal elements and first metal anions described above with respect to step 202 of the method 200 of FIG. 6. For example, the one or more first metal elements can comprise any metal element that will dissociate as a metal anion in the alkaline anolyte solution when a bias is not being applied between the anode and the cathode (e.g., when the applied voltage is 0 V) and that can be electroplated onto the material of the anode when a specified potential is applied and that is useful as an electrocatalyst for the electrochemical reaction that is to be performed at the anode (e.g., an oxygen evolution reaction) in its electroplated solid form. Similarly, the one or more second metal elements can comprise any metal element that will dissociate as a metal anion in the alkaline catholyte solution when a bias is not being applied between the anode and the cathode (e.g., when the applied voltage is 0 V) and that can be electroplated onto the material of the cathode when a specified potential is applied and that is useful as an electrocatalyst for the electrochemical reaction that is to be performed at the cathode (e.g., a hydrogen evolution reaction) in its electroplated solid form.

[0079] In some examples, the one or more first metal elements that form the anions in the alkaline anolyte solution are the same as the one or more second metal elements that form the anions in the alkaline catholyte solution. In other examples, the one or more first metal elements can be different from the one or more second metal elements, such as by including a different combination of metal element or elements to comprise the one or more first metal elements versus the combination of metal element or elements that comprise the one or more second metal elements. The specific first metal element or elements that are selected to form the anions of the one or more first metal elements in the alkaline anolyte solution can be selected to provide for a desired anode catalytic material or combination of catalytic materials suitable for the reaction or reactions desired to be carried out at the anode (e.g., an oxygen evolution reaction). Similarly, the specific second metal element or elements that are selected to form the anions of the one or more second metal elements in the alkaline catholyte solution can be selected to provide for a desired cathode catalytic material or combination of catalytic materials suitable for the reaction or reactions desired to be carried out at the cathode (e.g., a hydrogen evolution reaction).

[0080] As described above with respect to the method 200 of FIG. 6, in an example the one or more first metal elements and the one or more second metal elements that form the anions in the alkaline anolyte solution and the alkaline catholyte solution of steps 224 and 226, respectively, can include, but are not limited to, one ormore of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Pb). The alkaline anolyte solution comprising one or more first metal anions can be formed by dissociating one or more first metal precursor compounds into the alkaline anolyte solution, including, but not limited to, a chloride of the one or more first metal elements. Similarly, the alkaline catholyte solution comprising one or more second metal anions can be formed by dissociating one or more second metal compounds into the alkaline catholyte solution, including, but not limited to, a chloride of the one or more second metal elements. For example, if the first metal element for the alkaline anolyte solution is cobalt (Co) and the second metal element for the alkaline catholyte solution is nickel (Ni), then cobalt (II) chloride (C0CI2) can be dissolved into the alkaline anolyte solution to provide cobalt anions ([C0CI4]2) and nickel (II) chloride (NiCh) can be dissolved into the alkaline catholyte solution to provide nickel anions ([NiCk]2).

[0081] Other aspects of the alkaline anolyte solution and the alkaline catholyte solution can be similar or identical to those described above for the alkaline electrolyte solutions in the method 200 of FIG. 6 and the method 210 of FIG. 7, such as the specific metal anion or anions that will comprise the one or more first metal anions and the one or more second metal anions, the concentration of the one or more first metal anions in the alkaline anolyte solution, the concentration of the one or more second metal anions in the alkaline catholyte solution, the presence (or absence) of additives in the alkaline anolyte solution, or the presence (or absence) of additives in the alkaline catholyte solution.

[0082] Next, the method 220 can include, at step 228, applying a specified potential between the anode and the cathode. In an example, the specified potential is such that it is sufficient to electrolytically generate hydrogen gas (H2) at the cathode, to electrochemically deposit a first catalytic compound comprising the first metal element (also referred to as a “first metal catalytic compound”) onto the anode, and to electrochemically deposit a second catalytic compound comprising the second metal element (also referred to as a “second metal catalytic compound”) onto the cathode. In an example, the electrolytic generation of the H2 gas at the cathode and the electrochemical deposition of the first metal catalytic compound onto the anode and / or with the electrochemical deposition of the second metal catalytic compound onto the cathode can occur concurrently or substantially concurrently, i.e., so that the electrochemical deposition of one or both of the first metal catalytic compound and the second metal catalytic compound is in situ with the electrolytic formation of H2 gas within the electrochemical cell. In an example, the specified potential between the anode and the cathode can also be sufficient to electrolytically generate oxygen gas (O2) at the anode. In an example, the electrolytic generation of the O2 gas at the anode occurs concurrently or substantially concurrently with the electrolytic generation of theH2 gas at the cathode and / or with the electrochemical deposition of the first metal catalytic compound onto the anode and / or with the electrochemical deposition of the second metal catalytic compound onto the cathode.

[0083] In an example, the step of applying the specified potential 228 can include applying a small positive bias to the anode before or at the same time as applying the overall specified potential between the anode and cathode, which can be similar or identical to the optional application of a small bias described above for step 218 of the method 210 of FIG. 7.

[0084] The method 220 is not limited to in situ electrochemical deposition during water-splitting electrolysis to form H2 gas, as shown in the example method 220 of FIG. 8. In some examples (not shown in FIG. 8), step 228 of the method 220 can include activating an electrochemical reaction other than one or more water electrolysis reactions (e.g., a hydrogen evolution reaction and / or an oxygen evolution reaction) in situ with the electrochemical deposition of the first catalytic compound comprising the one or more first metal elements onto the anode and of the second catalytic compound comprising the one or more second metal elements onto the cathode. In other words, rather than a hydrogen evolution reaction at the cathode and / or an oxygen evolution reaction at the anode, step 228 can comprise activating a different electrochemical reaction at the cathode and / or at the anode. For example, it may be possible to design the method to allow for in situ deposition of the first and second catalytic compounds onto the anode and the cathode, respectively, of an electrolyzer configured for chloralkali electrolysis or another type of electrochemical reaction.EXAMPLE

[0085] Various embodiments of the present invention can be better understood by reference to the following Example which is offered by way of illustration. The present invention is not limited to the Example given herein.

[0086] An electroplating solution was formed by dissolving 40 milligrams (mg) of cobalt (II) chloride (C0CI2) powder in 35 milliliters (mL) of a 40 wt.% solution of sodium hydroxide (NaOH). A nickel mesh electrode was submerged in the electroplating solution and subjected to a bias of 3 V for 5 minutes so that a cobaltbased catalyst coating was electrochemically deposited onto the nickel mesh electrode (similar to the catalyst coating 156 described above with respect to FIGS. 2 and 3). After the electrochemical deposition, the coated nickel mesh electrode was removed from the electroplating solution and rinsed with deionized water.

[0087] FIG. 9A shows an optical micrograph image of the nickel mesh electrode taken before the cobalt-based catalyst coating was electrochemically deposited onto the nickel mesh electrode, and FIG. 9B shows an optical micrograph image of the same nickel mesh electrode after the electrochemical deposition of the cobalt-based catalyst coating and rinsing with the deionized water. As can be seen inFIG. 9B, a cobalt-based catalyst coating was produced that substantially covers the nickel substrate of the mesh electrode.

[0088] FIG. 10 is an X-ray fluorescence (XRF) spectra graph for the nickel mesh electrode before coating with the cobalt-based catalyst coating via electrochemical deposition, e.g., the bare nickel mesh electrode (line 230) and after the electrochemical deposition of the cobalt-based catalyst coating (line 232). As can be seen in FIG. 10, the presence of cobalt Ka peaks 234 and 236 for the XRF spectrum 232 for the coated electrode confirms the formation of a cobalt-based coating on the nickel mesh electrode.

[0089] The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

[0090] In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls.

[0091] In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0092] Method examples described herein can be machine or computer- implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assemblylanguage code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code can be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer- readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[0093] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

CLAIMSWhat is claimed is:1 . A method of comprising: at least partially submerging a conductive substrate in an alkaline solution comprising anions of one or more first metal elements; and applying a specified potential to the conductive substrate that is at least partially submerged in the alkaline solution to electrochemically deposit a coating compound comprising one or more of the first metal elements onto one or more surfaces of the conductive substrate.

2. The method of claim 1 , wherein the alkaline solution has a pH of at least about 9.

3. The method of claim 1 or claim 2, wherein the one or more first metal elements comprise one or more of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Pb).

4. The method of any one of claims 1-3, further comprising preparing the alkaline solution by dissolving one or more precursor metal compounds each comprising one or more of the first metal elements into an alkaline solvent.

5. The method of claim 4, wherein each of the one or more precursor metal compounds comprises a chloride of one or more of the first metal elements.

6. The method of claim 4 or claim 5, wherein the alkaline solution consists essentially of the one or more precursor metal compounds dissolved in the alkaline solvent.

7. The method of any one of claims 4-6, wherein the alkaline solution consists of the one or more precursor metal compounds dissolved in the alkaline solvent.

8. The method of any one of claims 1-6, wherein the alkaline solution is free or substantially free of buffers and mediators.

9. The method of any one of claims 1-8, wherein the coating compound comprises an oxide of one or more of the first metal elements.

10. A method comprising:feeding a first alkaline electrolyte solution to a first half cell of an electrolyzer cell, wherein a first electrode is located in the first half cell, and wherein the first alkaline electrolyte solution comprises anions of one or more first metal elements; feeding a second alkaline electrolyte solution to a second half cell of the electrolyzer cell, wherein a second electrode is located in the second half cell; and applying a specified potential between the first electrode and the second electrode to activate an electrochemical reaction at the first electrode or at the second electrode and to electrochemically deposit a coating compound comprising one or more of the first metal elements onto one or more surfaces of the first electrode.11 . The method of claim 10, wherein feeding the first alkaline electrolyte solution to the first half cell of the electrolyzer cell and feeding the second alkaline electrolyte solution to the second half cell of the electrolyzer cell occur concurrently or substantially concurrently.

12. The method of claim 10 or claim 11 , wherein the electrochemical reaction occurs at the first electrode and the coating compound acts as a catalyst for the electrochemical reaction.

13. The method of any one of claims 10-12, wherein activating the electrochemical reaction at the first electrode or the second electrode and electrochemically depositing the coating compound onto the first electrode occur concurrently or substantially concurrently.

14. The method of any one of claims 10-13, wherein the electrochemical reaction comprises a hydrogen evolution reaction that electrolytically generates hydrogen gas at the first electrode or at the second electrode.

15. The method of any one of claims 10-14, wherein the electrochemical reaction comprises an oxygen evolution reaction that electrolytically generates oxygen gas at the first electrode or at the second electrode.

16. The method of any one of claims 10-15, wherein the first alkaline electrolyte solution comprises one or more precursor metal compounds dissolved in an alkaline solvent, wherein each of the one or more precursor metal compounds comprises one or more of the first metal elements.

17. The method of claim 16, wherein each of the one or more precursor metal compounds comprises a chloride of one or more of the first metal elements.

18. The method of claim 16 or claim 17, wherein the first alkaline electrolyte solution consists essentially of the one or more precursor metal compounds dissolved in the alkaline solvent.

19. The method of any one of claims 16-18, wherein the first alkaline electrolyte solution consists of the one or more precursor metal compounds dissolved in the alkaline solvent.

20. The method of any one of claims 10-18, wherein the first alkaline electrolyte solution is free or substantially free of buffers and mediators.21 . The method of any one of claims 10-20, wherein one or both of the first alkaline electrolyte solution and the second alkaline electrolyte solution has a pH of at least about 9.

22. The method of any one of claims 10-21 , wherein the one or more first metal elements comprise one or more of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Pb).

23. The method of any one of claims 10-22, wherein the coating compound comprises an oxide of one or more of the first metal elements.

24. The method of any one of claims 10-23, further comprising adding a positive bias of up to about 100 mV to the first electrode or to the second electrode before or while applying the specified potential between the first electrode and the second electrode.

25. A method comprising: feeding an alkaline anolyte solution to an anode half cell of an electrolyzer cell, wherein an anode is located in the first half cell, and wherein the alkaline anolyte solution comprises anions of one or more first metal elements; feeding an alkaline catholyte solution to a cathode half cell of the electrolyzer cell, wherein a cathode is located in the cathode half cell, and wherein the alkaline catholyte solution comprises anions of one or more second metal elements; and applying a specified potential between the anode and the cathode to activate a first electrochemical reaction at the anode, to activate a second electrochemical reaction at the cathode, to electrochemically deposit a first coating compound comprising one or more of the first metal elements onto one or more surfaces of the anode, and toelectrochemically deposit a second coating compound comprising one or more of the second metal elements onto one or more surfaces of the cathode.

26. The method of claim 25, wherein the first coating compound acts as a catalyst for the first electrochemical reaction.

27. The method of claim 25 or claim 26, wherein the second coating compound acts as a catalyst for the second electrochemical reaction.

28. The method of any one of claims 25-27, wherein feeding the alkaline anolyte solution to the anode half cell and feeding the alkaline catholyte solution to the cathode half cell occur concurrently or substantially concurrently.

29. The method of any one of claims 25-28, wherein activating the first electrochemical reaction at the anode and activating the second electrochemical reaction at the cathode occur concurrently or substantially concurrently.

30. The method of any one of claims 25-29, wherein activating the first electrochemical reaction at the anode and electrochemically depositing the first coating compound onto the anode occur concurrently or substantially concurrently.31 . The method of any one of claims 25-30, wherein activating the second electrochemical reaction at the cathode and electrochemically depositing the second coating compound onto the cathode occur concurrently or substantially concurrently.

32. The method of any one of claims 25-31 , wherein electrochemically depositing the first coating compound onto the anode and electrochemically depositing the second coating compound onto the cathode occur concurrently or substantially concurrently.

33. The method of any one of claims 25-32, wherein the first electrochemical reaction comprises an oxygen evolution reaction that electrolytically generates oxygen gas at the anode.

34. The method of any one of claims 25-33, wherein the second electrochemical reaction comprises a hydrogen evolution reaction that electrolytically generates hydrogen gas at the cathode.

35. The method of any one of claims 25-34, wherein the alkaline anolyte solution comprises one or more first precursor metal compounds dissolved in a first alkalinesolvent, wherein each of the one or more first precursor metal compounds comprises one or more of the first metal elements.

36. The method of claim 35, wherein each of the one or more first precursor metal compounds comprises a chloride of one or more of the first metal elements.

37. The method of claim 35 or claim 36, wherein the alkaline anolyte solution consists essentially of the one or more first precursor metal compounds dissolved in the first alkaline solvent.

38. The method of any one of claims 35-37, wherein the alkaline anolyte solution consists of the one or more first precursor metal compounds dissolved in the first alkaline solvent.

39. The method of any one of claims 35-37, wherein the alkaline anolyte solution is free or substantially free of buffers and mediators.

40. The method of any one of claims 25-39, wherein the alkaline catholyte solution comprises one or more second precursor metal compounds dissolved in a second alkaline solvent, wherein each of the one or more second precursor metal compounds comprises one or more of the second metal elements.41 . The method of claim 40, wherein each of the one or more second precursor metal compounds comprises a chloride of one or more of the second metal elements.

42. The method of claim 40 or claim 41 , wherein the alkaline catholyte solution consists essentially of the one or more second precursor metal compounds dissolved in the second alkaline solvent.

43. The method of any one of claims 40-42, wherein the alkaline catholyte solution consists of the one or more second precursor metal compounds dissolved in the second alkaline solvent.

44. The method of any one of claims 40-42, wherein the alkaline catholyte solution is free or substantially free of buffers and mediators.

45. The method of any one of claims 25-44, wherein one or both of the alkaline anolyte solution and the alkaline catholyte solution has a pH of at least about 9.

46. The method of any one of claims 25-45, wherein the one or more first metal elements comprise one or more of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Pb).

47. The method of any one of claims 25-46, wherein the one or more second metal elements comprise one or more of: nickel (Ni), cobalt (Co), copper (Cu), silver (Ag), manganese (Mn), iron (Fe), rhodium (Rh), and lead (Pb).

48. The method of any one of claims 25-47, wherein the first coating compound comprises an oxide of one or more of the first metal elements.

49. The method of any one of claims 25-48, wherein the second coating compound comprises an oxide of one or more of the second metal elements.

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