Patent Description:
Hydrogen is emerging as an important part of the clean energy paradigm. It can be used as a high efficiency, low polluting fuel, as well as an energy carrier for moving, storing and delivering energy from renewable energy sources. Moreover, hydrogen can be produced from water, which is an abundant and relatively inexpensive feedstock.

A number of different processes can be used for producing hydrogen from water. These processes include water electrolysis, photo-electrolysis, photo-biological production and high temperature decomposition. Of these processes, water electrolysis is the most practical way to produce hydrogen using renewable energy sources, such as power from wind turbines and/or photovoltaic solar panels.

There are several types of water electrolysis processes that are used for hydrogen generation, namely alkaline electrolysis, proton exchange membrane (PEM) electrolysis, and solid oxide electrolytic cell (SOEC) electrolysis. Alkaline electrolysis and PEM electrolysis are more commonly utilized, with alkaline electrolysis being the most advanced and most suitable for large-scale implementation.

In water electrolysis, a DC electrical power source is connected to two electrodes, which are placed in water. Theoretically, a potential difference between the electrodes of <NUM> volts will split water into hydrogen and oxygen. Hydrogen is produced at the cathode, while oxygen is produced at the anode. More specifically, there is a hydrogen evolution reaction ("HER") at the cathode and an oxygen evolution reaction ("OER") at the anode. The HER is a reduction reaction in which electrons (e-) from the cathode are given to hydrogen cations to form hydrogen gas, while the OER is an oxidation reaction in which electrons are given to the anode and oxygen is generated.

While <NUM> volts will theoretically split water, a higher voltage is required in practice. The amount that exceeds <NUM> volts is called overpotential or overvoltage and represents lost energy or inefficiency. In the water electrolysis process, the largest overvoltage is the reaction overvoltage for the oxidation of water to oxygen at the anode. As such, significant effort has been exerted to reduce the overvoltage at the anode.

In alkaline electrolysis, the water contains an alkaline electrolyte, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH), and the electrodes are separated by a diaphragm. In PEM electrolysis, the water is deionized, and the electrodes are separated by a solid polymer electrolyte that permits protons from the anode to pass to the cathode, while insulating the electrodes electrically.

Recent advancements in water electrolysis have resulted in the process being operated at a higher current density. In addition, renewable energy sources are often used to provide electrical power for performing water electrolysis. The use of higher current densities, coupled with the intermittent nature of renewable energy, puts enhanced stress on the electrodes, causing conventional electrodes to deteriorate more rapidly. As such there is a need for more robust electrodes that provide good performance, while being less susceptible to degradation under conditions of high current density and intermittent power, i.e. numerous power shutdowns. In particular, there is a need for an anode with reduced oxygen overvoltage that is not susceptible to degradation due to high current density and shutdowns.

<CIT> describes an oxidized nickel foam electrode having a coating layer comprising crystalline nanoparticles which include nickel, nickel oxide and ion oxide. <CIT> describes an alkaline water electrolysis anode comprising a conductive substrate having an intermediate layer made of nickel oxide and a catalyst layer. <CIT> describes an anode for alkaline water electrolysis having a nickel substrate and a lithium-containing nickel oxide catalytic layer formed on the substrate. <CIT> describes an anode for electrochemical reactions which includes a nickel substrate and a nickel oxide layer on the conductive substrate and an oxidation catalyst layer disposed on the oxide layer.

In accordance with the present disclosure, an electrode is provided for use in an alkaline electrolysis process. The electrode includes a metal substrate and a catalytic layer disposed on the metal substrate. The catalytic layer includes nickel and nickel oxide and has a porosity less than about <NUM><NUM>/g measured by BET. An active composition is disposed both on and within the catalytic layer. The active composition includes one or more metal compounds selected from the group consisting of a cobalt compound, an iridium compound, a rhodium compound, an iron compound, a platinum compound, a lithium compound and a manganese compound.

Also provided in accordance with the present disclosure is an alkaline water electrolysis unit that includes the electrode, which functions as an anode. The unit also includes a cathode and an electrolyte solution that is substantially free of chlorine.

A method of forming an electrode is also disclosed herein. In accordance with the method, a metal substrate is provided and a catalytic layer is formed on the metal substrate. The catalytic layer includes nickel and nickel oxide formed by thermal spraying, cold spraying or other surface finishing process such as laser cladding and electroplating, and has a porosity less than about <NUM><NUM>/g (BET). An active composition is applied to the catalytic layer and is thermally decomposed. The active composition includes one or more metal compounds selected from the group consisting of a cobalt compound, an iridium compound, a rhodium compound, an iron compound, a platinum compound, a lithium compound and a manganese compound.

The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:.

It should be noted that in the detailed descriptions that follow, identical components have the same reference numerals, regardless of whether they are shown in different embodiments of the present disclosure. It should also be noted that for purposes of clarity and conciseness, the drawings may not necessarily be to scale and certain features of the disclosure may be shown in somewhat schematic form.

The present disclosure is directed to an electrode <NUM> constructed for use in an electrolysis process. The electrode <NUM> is especially suited for use in an alkaline electrolysis process and, more particularly, as an anode in such a process. A unit <NUM> that may be used for performing alkaline water electrolysis is shown in <FIG>. The unit <NUM> may include the electrode <NUM>, functioning as an anode, and a cathode <NUM>. The electrode (anode) <NUM> and the cathode <NUM> are separated by a diaphragm <NUM> and are disposed in a vessel <NUM> containing an electrolyte solution. The electrolyte solution used in the electrolysis process preferably does not include chlorine or other halides. The electrolyte solution may comprise water and potassium hydroxide (KOH) or water and sodium hydroxide (NaOH). The diaphragm <NUM> is composed of a microporous material with an average pore size of less than <NUM>, which allows ions to move between the electrode (anode) <NUM> and the cathode <NUM>, but is impermeable to gas, thereby preventing the intermixing of generated hydrogen and oxygen gases. The diaphragm <NUM> may be composed of a porous polymer, such as polytetrafluoroethylene (PTFE), or a composite material comprising zirconium dioxide (ZrO<NUM>) and polysulfone, which at the time of writing is commercially sold under the trademark Zirfon®.

The reactions that occur at the electrode (anode) <NUM> and the cathode <NUM> are as follows:.

The cathode <NUM> is composed of conductive metal, which may be nickel, low carbon steel, or stainless steel. The cathode <NUM> may have a structure as described below for the electrode <NUM> and may be coated with nickel or a nickel-iron alloy.

Referring now to <FIG>, the electrode <NUM> includes a substrate <NUM> upon which a catalytic layer <NUM> is disposed. The catalytic layer <NUM> has pores formed therein, but is only moderately porous. An active composition <NUM> is disposed in and/or on the catalytic layer <NUM>. The active composition <NUM> may form a layer and/or its constituent components may be interspersed into the pores of the catalytic layer <NUM>. In some embodiments, the active composition <NUM> does not form a layer and its constituent parts are distributed throughout the porosity of the catalytic layer <NUM>. In other embodiments, the active composition <NUM> forms a layer on the catalytic layer <NUM> and its constituent parts are also distributed throughout the porosity of the catalytic layer <NUM>. The catalytic layer <NUM> may be disposed over all of the outer surfaces of the substrate <NUM> and, similarly, the active composition <NUM> may be disposed in and/or on all of the catalytic layer <NUM>. In <FIG>, the electrode <NUM> is shown as having a rectangular configuration, with opposing major surfaces being covered with the catalytic layer <NUM> and the active composition <NUM>. While not shown, end surfaces of the electrode <NUM> may also be covered with the catalytic layer <NUM> and the active composition <NUM>. The catalytic layer <NUM> and the active composition <NUM> are applied to the substrate <NUM> so as to be substantially uniform in thickness and composition over the exterior of the substrate <NUM>. Preferably, deiviations in thickness are mostly within a +/- <NUM> range.

Structurally, the substrate <NUM> may be punched plate, woven wire, wire mesh, metal sponge, expanded metal, perforated or unperforated metal sheet, flat or corrugated lattice work, spaced apart rods or strips, or other structural forms. The wire mesh has been found to work particularly well in the execution of the invention. The thickness of the substrate <NUM> is preferably from about <NUM> to about <NUM> and more preferably from about <NUM> to about <NUM>. Preferably, the substrate <NUM> has openings to reduce current density. The substrate <NUM> is composed of a conductive metal, such as iron, iron alloy, nickel, nickel alloy or stainless steel. Iron alloys that may be used include iron-nickel alloys, iron-chromium alloys and iron-nickel-chromium alloys. Nickel alloys that may be used include nickel-copper alloys and nickel chromium alloys. Preferably, the substrate <NUM> is comprised of nickel, a nickel alloy or an iron alloy. A nickel plain weave wire mesh has been found especially suitable for use as the substrate <NUM>.

The catalytic layer <NUM> is formed from a metal using a suitable thermal spraying process, such as flame spraying, wire-arc spraying, plasma spraying, high velocity oxyfuel (HVOF) spraying, high velocity air-fuel (HVAF) spraying, detonation gun and combustion wire spraying. Wire-arc spraying and plasma spraying have been observed to work particularly well in the execution of the invention. The catalytic layer <NUM> may alternatively be formed from a metal using cold spraying or another type of surface finishing process, such as laser cladding and electroplating.

The metal from which the catalytic layer <NUM> is formed may be nickel or a nickel alloy and/or nickel oxide (NiO). However, nickel is preferred. In this regard, it has been found that using a nickel-aluminum alloy that is de-alloyed after deposition with a caustic solution produces a porous nickel layer that tends to be too brittle and deteriorates too quickly. Preferably, nickel is deposited on the substrate <NUM> using nickel powder in an atmospheric plasma spraying (APS) process, a cold gas spraying process or a wire-arc spraying process. More preferably, nickel is deposited on the substrate <NUM> using nickel powder in an APS process. The nickel powder that is used to form the catalytic layer <NUM> has a mean particle size of from about <NUM> to about <NUM>, more preferably from about <NUM> to about <NUM>.

Before the metal (e.g., nickel) powder is sprayed onto the substrate <NUM>, the substrate <NUM> is treated to remove contaminants and condition its surface for receipt of the metal powder. The treatment may include removing oil and grease through a degreasing process using a solvent. A grit blasting process is preferably performed on the substrate <NUM> after any degreasing process has been performed. In the grit blasting process, abrasive media, such as chilled iron or aluminum oxide, is pressurized with compressed air and directed against the surfaces of the substrate <NUM>. The grit blasting further removes any contaminants and roughens the surfaces to form pits and crevices that promote mechanical bonding of the metal powder that is sprayed on the surfaces. Debris from the grit blasting may be removed by vacuum cleaning, brushing and/or air blowing.

An APS process may be performed with a plasma torch in which a strong electric arc is generated between a positively charged pole (anode) and a negatively charged pole (cathode). The arc ionizes flowing process gas (such as a mixture of argon, hydrogen, nitrogen and helium) into a plasma state to form a plasma jet, which may have a temperature in range of from about <NUM>,<NUM> to about <NUM>,<NUM>. Typically, the anode is circular and helps form a nozzle through which the plasma jet is ejected. The anode may be composed of copper, while the cathode may be composed of thoriated tungsten. Metal (e.g. nickel) powder is fluidized in a carrier gas (which may include hydrogen) and fed into the plasma jet, melting the powder particles and propelling them at high speeds (such as between <NUM> to <NUM>/s) onto the substrate <NUM>. During their travel to the substrate <NUM>, some of the molten metal particles are oxidized to form oxides, such as nickel oxide (NiO). As such, when the catalytic layer <NUM> is formed using APS, the catalytic layer <NUM> includes both nickel and nickel oxide.

The molten metal particles sprayed from the plasma torch impact the substrate <NUM>, where they flatten into "splats", which shrink and solidify to form stacked lamellae with micro-features, such as pores. As the splats shrink and solidify, they mechanically bond to the substrate <NUM> through mechanical hooking. As such, the adhesion of the sprayed metal particles is primarily due to mechanical bonding.

In a cold spraying process, metal (e.g. nickel) powder is fluidized in a highpressure stream of carrier gas, which is preheated to a temperature of up to <NUM>,<NUM> and may be comprised of nitrogen, helium or air. The stream of carrier gas and metal particles is passed through a converging-diverging DeLaval nozzle, where the stream is cooled and accelerated to a supersonic velocity of over <NUM>,<NUM>/s. The supersonic stream of metal particles and carrier gas is directed onto the substrate <NUM>, where the metal particles undergo plastic deformation upon impact. The accelerated metal particles impact the substrate <NUM> with enough kinetic energy to induce mechanical and/or metallurgical bonding between the metal particles and the substrate <NUM>. Unlike in a thermal spraying process, such as APS, the metal particles are not melted during the cold spraying process.

In some embodiments, after the catalytic layer <NUM> has been formed, such as by APS or cold spraying, the substrate <NUM> coated with the catalytic layer <NUM> is heated in an oven at a temperature of from about <NUM> to about <NUM> for a period of from about <NUM> to about <NUM> minutes. In some embodiments, the substrate <NUM> coated with the catalytic layer <NUM> may be heated in an atmosphere comprising hydrogen.

The catalytic layer <NUM> is formed so as to have a thickness on one side of the substrate <NUM> of between about <NUM> to about <NUM>. Surprisingly, it has been found that with a thickness of <NUM> or less on each side of the substrate <NUM>, the electrode <NUM> exhibits surprisingly good properties, in that it may reduce the reversal currents generated during shutdowns. As such, the catalytic layer <NUM> may have a thickness of <NUM> or less and more specifically in a range of from about <NUM> to about <NUM>, even more specifically in a range of from about <NUM> to about <NUM>.

As set forth above, the catalytic layer <NUM> is only moderately porous. Porosity may be measured by different methods, such as the well-known Brunauer-Emmett-Teller (BET) method or mercury (Hg) porosimetry. The BET method determines the overall specific external and internal surface area of a porous solid (per unit mass) from a measurement of the physical adsorption of gas molecules (e.g. nitrogen) by the porous solid. The determined BET surface area in m<NUM>/g provides a measure of porosity. Using the BET method, the catalytic layer <NUM> has a porosity of less than <NUM><NUM>/g.

Porosity can be correlated with electrochemical properties. As is known, the double layer capacitance of an electrode is directly related to the total surface area of the electrode. With respect to the BET, the measurement of the double layer capacitance allows to more specifically gauge the "active porosity" of the electrode, i.e. the surface area that is actually accessible to the electrolyte for the electrochemical reaction. Therefore, in alternative or in addition to the the determined BET surface area in m<NUM>/g, the porosity of catalytic layer <NUM> may be characterized in terms of its double layer capacitance, before or after being coated with the active composition <NUM>, normalisied by the loading of the catalytic layer <NUM>. The loading of the catalytic layer <NUM> is measured as the amount of metal (in grams) per cm<NUM>. The normalised double layer capacitance of the catalytic layer <NUM> is between from about <NUM> to about <NUM> mF/g, and preferably between from about <NUM> to about <NUM> mF/g. The double layer capacitance before normalization is measured in mF/cm<NUM> according to the procedure set forth below. Typical loading of the catalytic layer <NUM> is <NUM> and <NUM>/m<NUM>, more preferably between <NUM> and <NUM>/m<NUM>. Lower loadings of the catalytic layer <NUM> are more cost efficient as they obviously require less material in the catalytic layer but also less of the the usually costly active composition <NUM>, which otherwise may get excessively diluted. In some applications, for example, without limitation, applications involving leaching of the active composition <NUM>, typical loadings may be higher, between <NUM>-<NUM>/m<NUM> referred to the metal.

The double layer capacitance of catalytic layers <NUM> having different compositions was studied in relevant conditions, i.e. KOH <NUM>% and T = <NUM>, using test electrodes <NUM>. Each test electrode <NUM> included a substrate <NUM> of nickel expanded mesh. In a first test electrode 11a, the substrate <NUM> was plasma coated with nickel; in a second test electrode 11b, the substrate <NUM> was plasma sprayed with a nickel-aluminum alloy; in a third test electrode 11c, the substrate <NUM> was wire-arc sprayed using two nickel wires; in a fourth test electrode 11d, the substrate was wire-arc sprayed with two wires, each composed of a nickel-aluminum alloy. The test electrodes <NUM> were initially conditioned by performing <NUM> minutes polarization at <NUM> kA/m<NUM>. Successively, voltammetric scans were performed in the potential region from <NUM> V to <NUM> V vs Hg/HgO at different scan rates (it is understood that, in general, the skilled person will select appropriate potential regions compatible with the active composition <NUM>, in order to avoid interference due to possible faradic processes). The electrochemical double layer capacitance was estimated using the standard equation dE/dt = Cdl · dQ/dt. The test electrodes <NUM> showed a specific capacitance (normalized by the catalytic layer <NUM> load) in a range of from about <NUM> to about <NUM> mF/g, as shown in <FIG>, which plots the average capacitance versus electrode type (11a-11d). Notably, the test electrodes 11a, 11c, 11d were desirably in a range of from about <NUM> to about <NUM> mF/g. The electrodes 11b and 11d containing Al were preventively leached in a KOH (<NUM>%) solution at <NUM> for <NUM> hours.

The test electrodes <NUM> were characterized by the amount of charge they could release when subjected to a reverse current in relevant conditions, i.e. KOH <NUM>% and T = <NUM>. The test electrodes <NUM> were each initially conditioned by performing <NUM> hours of anodic polarization at <NUM> kA/m<NUM>. Successively, a chronopotentiometric step was performed, by applying a cathodic current of <NUM> A/m<NUM> until the electrode potential was recorded as -<NUM>. 8V vs SHE (standard hydrogen electrode). The total amount of charge released from the test electrode <NUM> was then calculated by integrating the current over time. The test electrodes <NUM> were able to release a controlled charge (normalized by the coating load) in a range of from about <NUM>,<NUM> to about <NUM>,<NUM> mC/g, as shown in <FIG>, which plots the normalized average charge versus electrode type (11a-11d). Notably, the test electrodes 11a, 11c and 11d were desirably in a range of from about <NUM>,<NUM> to about <NUM>,<NUM> mC/g.

In certain embodiments, more than <NUM> percent by weight of nickel in the catalytic layer is in its metal form while up to <NUM> percent by weight of nickel is in its oxide form, predomently NiO, i.e. in the latter case, the weight percentage refers to NiO. Preferably, the metallic nickel content in the catalytic layer is in the range from <NUM> to <NUM> wt%, preferably in the range from <NUM> to <NUM> wt. The nickel oxide content in the catalytic layer can be in a range from at least <NUM> wt% to <NUM> wt% and is preferably in the range from <NUM> to <NUM> wt%.

It is believed that the optimal performances of the electrode configuration is due to the controlled charge release from the porous nickel layer. Also, a certain amount of porosity of the nickel/nickel oxide layer is desired in order to enhance the number of accessible catalytic sites. It can be expected that the relation between porosity and charge release will vary depending on nature of the layer. The control of the porosity/capacitance is used to control electrode robustness (charge). As shown in <FIG>, which plots average capacitance (y-axis) versus average charge (x-axis) for electrodes 11a-11d, a linear relationship exists between capacitance and released charge for the electrodes <NUM> having a catalytic layer <NUM>. It was thus demonstrated that the examined electrode configurations are characterized by the same, appropriate relationship between porosity/capacitance and charge release.

The active composition <NUM> includes one or more metals selected from the group consisting of iridium (Ir), cobalt (Co), rhodium (Rh), Iron (Fe), Platinum (Pt), Lithium (Li), manganese (Mn). The iridium in the active composition <NUM> may be an iridium compound, such as iridium oxide (IrO<NUM>). The cobalt in the active composition <NUM> may be a cobalt compound, such as a cobalt oxide, namely cobalt (II) oxide (CoO) or cobalt (II, III) oxide (Co<NUM>O<NUM>), or nickel cobaltite (NiCo<NUM>O<NUM>). Preferably, cobalt that is in the active composition <NUM> is nickel cobaltite. Even more preferably, nickel cobaltite that is in the active composition <NUM> is in the form of spinels. The rhodium in the active composition <NUM> may be a rhodium compound, such as rhodium (III) oxide (Rh<NUM>O<NUM>); the manganese in the active composition <NUM> may be a manganese compound, such as manganese oxide (MnO<NUM>); the iron in the active composition <NUM> may be an iron compound, such as iron oxide (Fe<NUM>O<NUM>) or Fe<NUM>O<NUM>; the platinum in the active composition <NUM> may be a platinum compound, such as platinum oxide (PtO<NUM>); the lithium in the active composition <NUM> may be a mixed compound, such as lithium nickel oxide (LiNiO<NUM>).

In some embodiments, the active composition <NUM> may consist essentially of a cobalt compound, a nickel compound, an iridium compound, a lithium compound (e.g. lithium nickel oxide), or an iron compound (e.g. iron oxide). Alternately, the active composition <NUM> may consist essentially of a cobalt compound and an iridium compound, or the active composition <NUM> may comprise a cobalt compound or an iridium compound or both a cobalt compound and an iridium compound. Preferably, the active composition <NUM> comprises a cobalt compound or an iridium compound, more preferably both a cobalt compound and an iridium compound, still more preferably the active composition <NUM> comprises nickel cobaltite and iridium oxide. Thus, the active composition <NUM> may comprise: <NUM>-<NUM> mole percent of an iridium compound, <NUM>-<NUM> mole percent of a cobalt compound and <NUM>-<NUM> mole percent of one or more transition metal compounds selected from the group consisting of a rhodium compound, a manganese compound, an iron compound, a platinum compound, a lithium compound. More preferably, the active composition <NUM> may comprise: about <NUM>-<NUM> mole percent of an iridium compound, about <NUM>-<NUM> mole percent of a cobalt compound and <NUM>-<NUM> mole percent of one or more transition metal compounds selected from the group consisting of a rhodium compound, a manganese compound, an iron compound, a platinum compound, a lithium compound. More preferably, the active composition <NUM> may comprise: about <NUM>-<NUM> mole percent of an iridium compound, more than <NUM> mole percent of a cobalt compound and <NUM>-<NUM> mole percent of one or more transition metal compounds selected from the group consisting of a rhodium compound, a manganese compound, an iron compound, a platinum compound, a lithium compound. Still more preferably, the active composition <NUM> may comprise: <NUM>-<NUM> mole percent of an iridium compound, <NUM>-<NUM> mole percent of a cobalt compound and <NUM>-<NUM> mole percent of one or more transition metal compounds selected from the group consisting of a rhodium compound, a manganese compound, an iron compound, a platinum compound, a lithium compound.

The catalytic layer <NUM> and the active layer <NUM>, taken together as a combination, comprise from about <NUM> mole percent to about <NUM> mole percent nickel, from <NUM> to about <NUM> mole percent nickel oxide, from about <NUM> mole percent to about <NUM> mole percent of an iridium compound, from about <NUM> mole percent to about <NUM> mole percent of a cobalt compound, and from about <NUM> to about <NUM> mole percent of one or more transition metal compounds selected from the group consisting of a rhodium compound, a manganese compound, an iron compound, a platinum compound, a lithium compound.

The active composition <NUM> may be formed from one single precursor composition that is applied to the catalytic layer <NUM> in one or more application processes, or the active composition <NUM> may be formed from a plurality of different precursor compositions that are applied to the catalytic layer <NUM> in a plurality of application processes. As set forth above, the active composition <NUM> may form a layer on top of the catalytic layer <NUM> as schematically depicted in <FIG> and/or the active composition <NUM> may be absorbed into the catalytic layer <NUM> and become distributed throughout the porosity of the catalytic layer <NUM>. In this manner, the layer of the active composition <NUM> may have a thickness from about <NUM> to about <NUM>, more preferably from about <NUM> to about <NUM>.

Generally, the precursor composition(s) include precursor compounds (such as organic or inorganic metal salts) that are thermally decomposable to form the metal compounds in the active composition <NUM>. The metal salts may be chlorides and may be dissolved in solvents, including acids (such as hydrochloric acid and nitric acid) and alcohols, such as isopropyl alcohol, n-propyl alcohol, n-butyl alcohol and ethyl alcohol. Some examples of the precursor compound(s) are given below.

For iridium oxide, the precursor compound(s) may include the chloride, sulfate or nitrate salt of iridium dissolved in a solvent, such as an acid or an alcohol. More specifically, the precursor compound(s) may include a solution of iridium (III) chloride (IrCl<NUM>) in its trihydrate form (IrCl<NUM>(H<NUM>O)<NUM>), together with hydrochloric acid and isopropyl alcohol and/or ethyl alcohol.

For cobalt (II) oxide, the precursor compound(s) may include cobalt chloride (CoCl<NUM>) and water. For cobalt (II, III) oxide, the precursor compound(s) may include cobalt (II) acetate tetrahydrate (C<NUM>H<NUM>CoO<NUM>_4H<NUM>O), ethyl alcohol and oxalic acid (C<NUM>H<NUM>O<NUM>).

For nickel cobaltite, the precursor compound(s) may include nickel (II) acetate tetrahydrate (C<NUM>H<NUM>NiO<NUM> _4H<NUM>O) and cobalt (II) acetate tetrahydrate (C<NUM>H<NUM>CoO4_<NUM><NUM>O) mixed with urea (CO(NH<NUM>)<NUM>, deionized water, ethyl alcohol, glycerol and tetraethylene glycol (TEG), wherein the nickel (II) acetate and the cobalt (II) acetate are co-precipitated. Alternately, the precursor compound(s) may include nickel (II) nitrate hexahydrate (Ni(NO<NUM>)<NUM>·<NUM><NUM>O) and cobalt(II) nitrate hexahydrate (Co(NO<NUM>)<NUM>·<NUM><NUM>O), which may be dissolved in NH<NUM>OH.

The precursor composition(s) may be applied to the catalytic layer <NUM> using a brush, or by electrospraying, roller coating or dip coating.

After the precursor composition(s) have been applied to the catalytic layer <NUM>, the substrate <NUM> coated with the catalytic layer <NUM> and the precursor composition(s) is heated to thermally decompose the precursor compound(s) to form the active composition <NUM>. The heating may take place in an oven at a temperature of from about <NUM> to about <NUM> for a period of from about <NUM> to about <NUM> minutes.

A 100X100 mm piece of nickel wire woven mesh, with a <NUM> diameter wire, was plasma sprayed with <NUM>% purity nickel powder with a particle size of -<NUM> / +<NUM> (Fe <<NUM>, O<<NUM>, C<<NUM>, S<<NUM> in ambient air on both sides in an amount of <NUM> ± <NUM>/dm<NUM> and with a target thickness of <NUM> (on each side). Afterwards, the sprayed wire mesh was heated in an oven at <NUM> for <NUM> minutes in air. The plasma-sprayed woven mesh was allowed to cool and then was coated with a precursor composition, by means of a brush, in a series of coating, heating and cooling steps. The precursor composition comprised <NUM> of nickel(II) nitrate hexahydrate and <NUM> of cobalt(II)/nitrate hexahydrate, brought to a volume of <NUM> with DI water. Initially, the plasma-sprayed wire mesh was coated with the precursor composition and then heated in air in an oven at <NUM> for <NUM> minutes. After cooling, the wire mesh was again coated with the precursor composition and again heated in the oven at <NUM> for <NUM> minutes. This process of coating, heating and cooling was repeated to achieve a load of <NUM>METAL/m<NUM>.

The foregoing process produced an electrode E1 having, on each side, a catalytic layer and an active composition. The catalytic layer was mostly nickel with a small amount of NiO. The active composition comprised <NUM> mol/ m<NUM> of nickel cobaltite. When viewed with a scanning electron microscope (SEM), the catalytic layer was a nickel matrix formed by nickel particles and a thin crust of NiO, with the nickel cobaltite being distributed into the porosity of the catalytic layer.

The combination of the catalytic layer and the active composition had a thickness (on one side) of <NUM> ± <NUM> and had a porosity of <NUM><NUM>/g (BET). The combination comprised <NUM> mole percent nickel, <NUM> mole percent nickel oxide and <NUM> mole percent nickel cobaltite.

A 100X100 mm piece of nickel expanded mesh was plasma sprayed with <NUM>% purity nickel powder with a particle size of -<NUM> / +<NUM> (Fe <<NUM>, O<<NUM>, C<<NUM>, S<<NUM> in ambient air on both sides in an amount of <NUM> ± <NUM>/dm<NUM> and with a target thickness of <NUM> (on each side). Afterwards, the sprayed wire mesh was heated in an oven at <NUM> for <NUM> minutes in air. The plasma-sprayed expanded mesh was allowed to cool and then was coated with first and second precursor compositions, as described below.

The first precursor compostion was the same as the precursor composition applied in Example <NUM>, i.e. the solution of nickel (II) nitrate hexahydrate and cobalt (II) nitrate hexahydrate. The first precursor composition was also applied to the mesh in the same manner as in Example <NUM> to achieve a load of <NUM>METAL/m<NUM>.

The second precursor composition comprised <NUM> of hexa-ammineiridium(III) hydroxide [Ir(NH<NUM>)<NUM>](OH)<NUM> brought to a volume of <NUM> with deionized water. After the application of the first precursor composition, the second precursor composition was applied by brush in a series of coating, heating and cooling steps. Initially, the plasma-sprayed and coated mesh was coated with the second precursor compositions and then heated in an oven at <NUM> for <NUM> minutes in air. After cooling, the mesh was again coated with the second precursor composition and again heated in the oven at <NUM> for <NUM> minutes. This process of coating, heating and cooling was repeated to achieve a load of <NUM>METAL/m<NUM>.

The foregoing process produced an electrode E2 having, on each side, a catalytic layer and an active composition. The catalytic layer was mostly nickel with a small amount of NiO. The active composition was <NUM> mmol/m<NUM> of iridium oxide and <NUM> mmol/m<NUM> of nickel cobaltite, which corresponds to <NUM> mole percent iridium oxide and <NUM> mole percent nickel cobaltite. When viewed with a scanning electron microscope (SEM), the catalytic layer was a nickel matrix formed by nickel particles and a thin crust of NiO, with the iridium oxide and the nickel cobaltite being distributed into the porosity of the catalytic layer. The combination of the catalytic layer and the active composition had a thickness (on one side) of just less than <NUM> and had a porosity of <NUM><NUM>/g (BET). The combination comprised comprised <NUM> mole percent nickel, <NUM> mole percent iridium oxide and <NUM> mole percent cobaltite.

A 100X100 mm piece of nickel expanded mesh was plasma sprayed with <NUM>% purity nickel powder with a particle size of -<NUM> / +<NUM> (Fe <<NUM>, O<<NUM>, C<<NUM>, S<<NUM> in ambient air on both sides in an amount of <NUM> ± <NUM>/dm<NUM> and with a target thickness of <NUM> (on each side). Afterwards, the sprayed expanded mesh was heated in an oven at <NUM> for <NUM> minutes in air. The plasma-sprayed expanded mesh was then allowed to cool and then was coated with a precursor composition, by means of a brush in a series of coating, heating and cooling steps. The precursor composition was the same as the second precursor composition of Example <NUM>, i.e., hexa-ammineiridium(III) hydroxide [Ir(NH<NUM>)<NUM>](OH)<NUM> brought to a volume of <NUM> with deionized water. Initially, the plasma-sprayed expanded mesh was coated with the precursor composition and then heated in an oven at <NUM> for <NUM> minutes in air. After cooling, the mesh was again coated with the precursor composition and again heated in the oven at <NUM> for <NUM> minutes. This process of coating, heating and cooling was repeated to achieve a load of <NUM>METAL/m<NUM>.

The foregoing process produced an electrode E3 having, on each side, a catalytic layer and an active composition. The catalytic layer was mostly nickel with a small amount of NiO. The active composition was <NUM> mmol/m<NUM> of iridium oxide. When viewed with a scanning electron microscope (SEM), the catalytic layer was a nickel matrix formed by nickel particles and a thin crust of NiO, with the iridium oxide being distributed into the porosity of the catalytic layer (see <FIG>). The combination of the catalytic layer and the active composition had a thickness (on each side) of just less than <NUM> and had a porosity of <NUM><NUM>/g (BET). The combination comprised comprised <NUM> mole percent nickel, <NUM> mole percent nickel oxide and <NUM> mole percent iridium oxide.

A 100X100 mm piece of nickel expanded mesh was plasma sprayed with <NUM>% purity nickel powder with a particle size of -<NUM> / +<NUM> (Fe <<NUM>, O<<NUM>, C<<NUM>, S<<NUM> in ambient air on both sides in an amount of <NUM> ± <NUM>/dm<NUM> and with a target thickness of <NUM> and <NUM> on the other side. Afterwards, the sprayed mesh was heated in an oven at <NUM> for <NUM> minutes. The sprayed expanded mesh was then allowed to cool, thereby forming an electrode CE1 with only a catalytic layer comprising nickel and nickel oxide. The catalytic layer had a thickness (on each side) of just less than <NUM> and had a porosity of <NUM><NUM>/g (BET).

A 100X100 mm piece of nickel expanded mesh was plasma sprayed with <NUM>% purity nickel powder with a particle size of -<NUM> / +<NUM> (Fe <<NUM>, O<<NUM>, C<<NUM>, S<<NUM> in ambient air on both sides in an amount of <NUM> ± <NUM>/dm<NUM> and with a target thickness of <NUM>. Afterwards, the sprayed expanded mesh was heated in an oven at <NUM> for <NUM> minutes. The sprayed wire mesh was then allowed to cool, thereby forming an electrode CE2 with only a catalytic layer comprising nickel and nickel oxide. The catalytic layer had a thickness (on one side) of just less than <NUM> and had a porosity of <NUM><NUM>/g (BET).

Except as noted below, Example <NUM> was re-performed on another 100X100 mm piece of nickel expanded mesh. The mesh was not plasma sprayed, or otherwise coated with a layer of nickel/nickel oxide or other metal. The active composition was formed directly on the expanded mesh. The same first and second precursor compositions were applied to the expanded mesh in the same manner as in Example <NUM>, except the there was no plasma sprayed layer.

The process produced an electrode CE3 having, on each side, an active composition. The active composition was <NUM> mmol/m<NUM> of iridium oxide and. <NUM> mmol/m<NUM> of nickel cobaltite, which corresponds to <NUM> mole percent iridium oxide and <NUM> mole percent nickel cobaltite.

The electrodes E1, E2, E3, , CE1, CE2 and CE3 were each used as anodes in electrolysis cells and the oxygen overvoltages at the anodes were measured in KOH <NUM>% at <NUM> with a three electrodes set-up, using a SCE reference electrode and a VMP3 Biologic potentiostat equipped with a 20A Booster. The iR drop was measured by means of Electrochemical Impedance Spectroscopy (EIS). The resulting electrode potential determined at <NUM> kA/m<NUM> was subtracted by the thermodynamic oxygen evolution potential at pH14. Results of these measurements are shown in Table <NUM> below. In addition, electrolysis cells with the E2, E3, CE1, CE2 and CE3 anodes, respectively, were connected to receive electric power having a current of <NUM> kA/m<NUM> and were then subjected to a series of <NUM> shutdowns of electric power, with on/off cycles of the duration of <NUM> hours. The voltages at <NUM> kA/m<NUM> of the cells were measured after each shutdown. The results of these measurements are also shown in Table <NUM> below.

The results of the tests show that while the catalytic layer of electrode CE2 is substantially thinner than the catalytic layer of electrode CE1 (≈<NUM> versus ≈<NUM>), the oxygen overvoltage of electrode CE2 was not that much greater than electrode CE1 (<NUM> mV versus <NUM> mV). The electrodes E1-E3 had substantially better oxygen overvoltages than both the electrodes CE1 and CE2. The electrode E2 had significantly better oxygen overvoltage than CE1 and CE2 and had better shutdown tolerance than the electrodes E3, and CE3. The electrode CE3 had good oxygen overvoltage, but not very good shutdown tolerance. The results show that an electrode with only the active composition <NUM>, without the catalytic layer <NUM>, has a good oxygen overvoltage, but poor shutdown tolerance. Conversely, electrodes with only catalytic layer <NUM>, without the active composition <NUM>, has good shutdown tolerance, but poor overvoltage. The synergic combination of catalytic layer <NUM> and active composition <NUM> yields an electrode with enhanced properties, i.e. both good shutdown tolerance and good overvoltage. , particularly an active layer comprising both a cobalt compound and an iridium compound. Such an electrode (e.g. electrode E2) also has an improved oxygen overvoltage.

Claim 1:
An electrode for use in an alkaline electrolysis process, the electrode comprising:
a metal substrate;
a catalytic layer disposed on the metal substrate, the catalytic layer comprising nickel and nickel oxide and having a porosity less than about <NUM><NUM>/g measured by BET; and
an active composition disposed both on and within the catalytic layer, the active composition comprising one or more metal compounds selected from the group consisting of a cobalt compound, an iridium compound, a rhodium compound, an iron compound, a platinum compound, a lithium compound and a manganese compound.