Transition metal-coated nickel electrode for alkaline water electrolysis

Abstract

This invention relates to a method for manufacturing an anode for alkaline water electrolysis, the method comprising 100 A / m 2 With 2500 A / m 2 At current densities between [specific values], a coating comprising cobalt and optionally lanthanides is cathodically deposited on the surface of a nickel-containing substrate in the presence of an aqueous electrolyte having a pH between 1 and 6.5 as measured at 25°C and comprising a cobalt-containing hydrated salt and optionally a lanthanide-containing hydrated salt. The invention further relates to an anode comprising a nickel-containing substrate and a coating comprising cobalt and optionally lanthanides, wherein the bulk phase of the coating comprises metallic cobalt.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an anode for alkaline water electrolysis. The invention further relates to an anode for alkaline water electrolysis, such as an anode manufactured by the method of this invention. Background Technology

[0002] Green hydrogen is a form of hydrogen produced through a process that uses renewable energy sources, such as wind, solar, or hydropower, to generate the electricity needed for water electrolysis. Unlike traditional hydrogen production methods that rely on fossil fuels, green hydrogen is considered environmentally friendly because it largely avoids carbon emissions during its production process.

[0003] The production of green hydrogen involves the use of electrolyzers, which are devices that promote the electrolysis of water (H2O) into hydrogen (H2) and oxygen (O2). There are two main types of electrolyzers used in green hydrogen production: proton exchange membrane (PEM) electrolyzers and alkaline electrolyzers.

[0004] A PEM electrolyzer comprises a solid polymer electrolyte membrane sandwiched between the anode and cathode. When an electric current is applied across the electrolyzer, water molecules split at the anode into hydrogen ions (protons), electrons, and oxygen. The proton-selective membrane allows only protons to pass through, thus preventing hydrogen and oxygen from mixing. The protons move through the membrane to the cathode, where they combine with electrons from an external circuit to form hydrogen gas.

[0005] Alkaline electrolyzers use an alkaline electrolyte solution as the medium through which water electrolysis occurs. The alkaline electrolyte solution is typically potassium hydroxide (KOH) and is commonly referred to as an "alkaline solution." Similar to PEM electrolyzers, when an electric current is applied, water is separated into hydrogen and oxygen at the cathode and anode, respectively. The alkaline electrolyte allows hydroxide ions (OH-) to be produced. - The oxygen ions are transported from the cathode to the anode. At the anode, hydroxide ions are oxidized according to the following oxygen evolution reaction (OER): 4OH- - → O2 + 2H2O + 4e - This process produces oxygen and electrons. These electrons then travel through an external circuit to the cathode. At the cathode, water molecules are reduced according to the hydrogen evolution reaction (HER): 2H₂O + 2e⁻ - → H2 + 2OH - This process produces hydrogen gas. The overall water electrolysis reaction in an alkaline medium is: 2H₂O → 2H₂ + O₂.

[0006] Alkaline water electrolysis is one of the most promising technologies for producing green hydrogen from surplus renewable energy sources. However, to make green hydrogen more cost-competitive (i.e., cost-effective), improved anode materials with lower oxygen evolution reaction (OER) overpotentials are needed. Overpotential is the additional energy required, relative to the theoretical energy, to initiate and sustain the OER reaction.

[0007] Existing anodes include nickel alloys (particularly nickel 201 alloy) and nickel-plated steel substrates because nickel is relatively abundant on Earth, relatively inexpensive, and has a long service life. However, these anodes have relatively high overpotentials for oxygen evolution, especially at higher current densities (j > 5000 A / m). 2 Furthermore, at relatively high current densities, nickel often temporarily loses its activity (increasing its overpotential) due to the growth of a thick oxide layer that hinders efficient charge transport across the interface.

[0008] Several solutions are being developed to overcome the limitations of bulk nickel anodes and nickel-coated steel substrate anodes.

[0009] WO 2022 / 025208 describes an alkaline water electrolysis anode that exhibits stable electrolysis performance and catalytic activity, and has a long service life. The alkaline water electrolysis anode comprises a conductive surface and a catalyst layer disposed on the surface of a conductive substrate, the conductive surface comprising nickel or a nickel-based alloy. The catalyst layer contains a lithium complex oxide with a rock-salt-type structure, wherein the lithium complex oxide contains lithium, nickel, iron, and aluminum in a Li / Ni / Fe / Al / O atomic ratio of (0.4 to 1.1) / (0.4 to 0.8) / (0.05 to 0.2) / (0.05 to 0.2) / 2.0.

[0010] However, the presence of iron (Fe) and aluminum (Al) in the catalyst layer of the aforementioned alkaline water electrolysis anode has known drawbacks, namely that both tend to undergo oxidation and / or chemical dissolution under oxygen evolution conditions, which can impair the stability and activity of the catalyst layer and may also impair anode activity, especially for extended electrolysis duration.

[0011] Amorphous film of cerium-doped cobalt oxide as a highly efficient electrocatalyst for oxygen evolution reaction (OER), Shichen Xu, Cuncai Lv et al., J. Mater. Cjem. A [Materials Chemistry Journal A], 2019, DOI 10.1039 / C9TA00061E, discloses an amorphous film of cerium-doped cobalt oxide as an electrocatalyst for OER. The presence of cerium causes the cobalt oxide to become amorphous. This film exhibits an increased electrochemical surface area (ECSA; relative to cobalt oxide) and a decreased apparent activation energy of OER. The current density is 20 mA / cm² at an overpotential of 261 mV. -2 And at an overpotential of 302 mV, it is 100 mA·cm⁻¹. -2 It can maintain 60 mA.cm -2 The membrane maintained a stable and high current density for 40 hours. It was prepared by electrostatic spray deposition of a precursor solution containing 0.5 mmol Co(NO3)2·6H2O and 0.05 mmol Ce(NO3)2 in 80 mL of 1,2-propanediol and 20 mL of ethanol onto carbon fiber paper heated to 200°C at a flow rate of 2 mL / h under 12 kV DC. Due to rapid solvent evaporation, the membrane exhibited pores (50 nm in diameter) and cracks.

[0012] Amorphous cobalt-cerium binary metal oxides as high-performance electrocatalysts for oxygen evolution reaction, Lili Pan, Qingqing Wang et al., Journal of Catalysis 384 (2020) 14-21, discloses the high performance of Co0.9Ce0.1Ox on a fluorine-doped tin oxide-coated glass substrate at 10 mA cm⁻¹ in 1 M KOH. -2 It has an overpotential of 320 mV. It has been reported that if the cerium content is below 60%, due to surface area, Co... 3+The synergistic effect of cerium content and Me-OH bond strength enhances the OER activity of cobalt oxide. Co-Ce binary metal oxide films were deposited on a substrate by spin-coating a precursor solution containing 15% w / w 2-ethylhexanoic acid Co(II) and 2-ethylhexanoic acid Ce(III) in hexane at different molar ratios at 3000 rpm for 1 minute. Following spin-coating, the film was subjected to UV irradiation (wavelengths 185 nm and 254 nm) for 12 h to decompose the organic ligands, thereby converting the metal precursors into catalytically active oxides. The film was then calcined at 100°C for one hour before use.

[0013] The drawback of the aforementioned method is that it first forms a film on a substrate (carbon fiber paper, glass) that is not part of the anode, which requires an additional step of assembling the anode. Using the film together with the carbon fiber substrate for the anode has the following disadvantages: carbon fiber has low thermodynamic stability and will oxidize into CO2, which will in turn damage and corrode the anode substrate during alkaline water electrolysis.

[0014] When an anode containing a membrane is used for alkaline water electrolysis, membrane cracks and pores can lead to instability, thus limiting the anode's lifespan.

[0015] The disadvantage of using UV irradiation to obtain catalytically active coatings is that it is not suitable for porous layers and substrates because the irradiation is a directional technique and therefore cannot easily reach the interior of the bulk phase of the porous material, resulting in incomplete conversion and low catalytic activity.

[0016] Therefore, there is a need for improved anodes for alkaline water electrolysis, namely so-called oxygen-evolving anodes, which exhibit high activity (low overpotential) as well as high stability and durability (typically expressed by the change in current density over time), and thus a long operating life. Furthermore, there is a need for methods for manufacturing such anodes that are relatively uncomplicated and simultaneously produce high-quality anodes exhibiting high activity, high stability, and high durability. Summary of the Invention

[0017] The present invention aims to overcome one or more of the above-mentioned disadvantages. One object is to provide an anode for alkaline water electrolysis (i.e., an oxygen-evolving anode) that has similar or higher activity compared to prior art nickel-based anodes, particularly bulk nickel 201 alloy anodes. Another object is to provide such anodes that also exhibit better stability and durability compared to prior art oxygen-evolving anodes, i.e., stable performance over a longer period of time (i.e., improved operating life), especially in high current density applications.

[0018] Another objective is to provide a method for producing anodes for alkaline water electrolysis that have similar or higher activity and better stability and durability compared to existing oxygen-evolving anodes, i.e., stable performance over a longer period of time (i.e., improved operating life), particularly in high current density applications.

[0019] The terms “oxygen-evolving anode”, “anode for alkaline water electrolysis” and “anode” are used interchangeably in this disclosure.

[0020] The term "oxygen evolution reaction," abbreviated as "OER," refers to the reaction that occurs at the anode in alkaline water electrolysis and electrolytic cells, and is the following chemical reaction: 4OH⁻ - → O2 + 2H2O + 4e - .

[0021] The term "hydrogen evolution reaction," abbreviated as "HER," refers to the reaction that occurs at the cathode in alkaline water electrolysis and an electrolytic cell, and is the following chemical reaction: 2H₂O + 2e⁻ - → H2 + 2OH - .

[0022] The terms “alkaline environment” and “alkaline solution” are used for environments and solutions with a pH above 7, respectively, wherein the pH of the environment (e.g., the solution) is measured at 25°C by means known in the art (e.g., a standard glass electrode pH meter).

[0023] The terms “acidic environment” and “acidic solution” are used in this disclosure for an environment and a solution with a pH below 7, respectively, wherein the pH of the environment (e.g., the solution) is measured at 25°C by means known in the art (e.g., a standard glass electrode pH meter).

[0024] The pH value of the solution is measured by means known in the art, particularly by a standard glass electrode pH meter, and at temperatures typically used in the art. In this invention, the pH value is measured (reported, determined) at 25°C. According to a first aspect of this disclosure, a method for manufacturing an anode for alkaline water hydrolysis is provided as set forth in the appended claims.

[0025] The anode manufactured by the method of the first aspect comprises a nickel-containing substrate and a coating containing cobalt and optional lanthanide elements.

[0026] The term "lanthanides" is used in this disclosure for chemical elements with atomic numbers 57 to 71 in the periodic table, i.e., chemical elements from lanthanum (La) to lutetium (Lu). Preferred examples of lanthanides include, but are not limited to, cerium (Ce), praseodymium (Pr) and holmium (Ho).

[0027] The method involves cathodic electrodeposition of a coating comprising or substantially comprising cobalt and optional lanthanide elements on a surface of a substrate containing nickel or substantially thereof.

[0028] The substrate contains nickel or is substantially composed of it. In other words, the substrate can be a substantially pure nickel substrate, or it can contain other elements besides nickel, i.e., it can be a nickel alloy. A particularly preferred nickel-containing substrate used in the method of the present invention is a nickel-carbon alloy, such as nickel-201 alloy.

[0029] In this disclosure, cathodic electrodeposition refers to a method in which a current is applied through an electrolyte containing dissolved ions of the material to be deposited, depositing the material (as a coating) onto the surface of a conductive substrate (here, a nickel-containing substrate), which acts as the cathode in an electrochemical cell during cathodic electrodeposition. During this method, positively charged ions migrate toward the cathode (i.e., the substrate) under the influence of an electric field and are reduced at the cathode surface, thereby forming the coating.

[0030] Cathodic electrodeposition of the coating on the surface of a nickel-containing substrate occurs in the presence of an aqueous electrolyte.

[0031] The aqueous electrolyte has a pH between 1 and 6.5, preferably between 2 and 5, wherein the pH is measured at room temperature by means known in the art, such as a standard glass electrode pH meter.

[0032] Aqueous electrolytes contain cobalt-containing hydrated salts. Advantageously, the cobalt-containing hydrated salts are CoCl2·6H2O, CoSO4·7H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, or Co(SO3NH2)2·6H2O. It should be understood that aqueous electrolytes may contain two or more cobalt-containing hydrated salts.

[0033] Advantageously, the aqueous electrolyte comprises a cobalt-containing hydrated salt at a concentration between 20 g / L and 250 g / L, preferably between 25 g / L and 200 g / L, more preferably between 50 g / L and 150 g / L (e.g., between 75 g / L and 125 g / L or between 90 g / L and 100 g / L), wherein the weight of the cobalt-containing hydrated salt includes hydrated water.

[0034] When the coating contains lanthanides, the lanthanides are advantageously Ce, Pr, or Ho, with Ce being preferred.

[0035] When the coating contains lanthanides, the aqueous electrolyte further contains a lanthanide-containing hydrated salt. Advantageously, the lanthanide-containing hydrated salt is a chloride salt, nitrate salt, sulfate salt, or acetate salt, preferably a chloride salt. Advantageously, the lanthanide-containing hydrated salt is CeCl3·7H2O, PrCl3·7H2O, or HoCl3·6H2O.

[0036] Advantageously, the aqueous electrolyte comprises a lanthanide-containing hydrated salt at a concentration between 1 g / L and 20 g / L, preferably between 2 g / L and 15 g / L, more preferably between 5 g / L and 10 g / L (e.g., between 7 g / L and 9 g / L), wherein the weight of the lanthanide-containing hydrated salt includes hydrated water.

[0037] Aqueous electrolytes further advantageously contain acids and / or their corresponding salts. It should be understood that aqueous electrolytes may contain two or more acids and / or their corresponding salts.

[0038] The acid and / or the corresponding salt are advantageously added at a concentration that gives the aqueous electrolyte a pH between 1 and 6.5, preferably between 2 and 5, as measured at 25°C. It should be understood that the concentration of the acid and / or the amount (by weight) of the corresponding acid depends on the intended pH of the aqueous electrolyte and on the acidity (strength) of the acid and / or the corresponding salt. Strong acids, i.e., those having a pKa value equal to or less than 1, preferably equal to or less than 0, as measured in water at 25°C, will typically require lower concentrations than weak acids (i.e., those having a pKa value greater than 1, as measured in water at 25°C).

[0039] Advantageously, when the aqueous electrolyte contains an acid, the acid is boric acid (H3BO3) or citric acid (C6H8O7). Advantageously, when the aqueous electrolyte contains the corresponding salt of the acid, the salt is a borate or citrate.

[0040] Advantageously, when the aqueous electrolyte contains an acid, it contains an acid in the range of 0.01 M to 1 M, preferably between 0.05 M and 0.8 M, more preferably between 0.075 M and 0.75 M, and most preferably between 0.1 M and 0.5 M.

[0041] Cathodic electrodeposition of coating on nickel-containing substrate surface at 100 A / m 2 With 2500 A / m 2 Between, preferably at 250 A / m 2 With 2000 A / m 2 Between, more preferably at 500 A / m 2 With 1000 A / m 2 It occurs at the first current density between.

[0042] The coating deposited on the substrate has a bulk phase and an exposed surface, which is opposite to the surface of the coating that contacts (i.e. adheres to) the substrate.

[0043] The bulk phase of the coating deposited by cathodic electrodeposition as described above comprises metallic cobalt and optional lanthanide elements, or is substantially composed of them. In other words, the cobalt contained in the bulk phase of the coating is at least partially, and preferably substantially entirely, in the form of metallic cobalt. This differs from prior art coating deposition methods such as thermal decomposition and / or anodic electrodeposition, in which cobalt exists in the bulk phase as cobalt oxide.

[0044] Although cobalt oxides are known to have limited (electro)chemical stability in the alkaline environment of alkaline water electrolysis (they are (electro)chemically sensitive), leading to the loss of cobalt in both the exposed surface and the bulk phase during the oxygen evolution reaction at the anode, it was unexpectedly found that the loss of cobalt was significantly reduced when a coating containing metallic cobalt in the bulk phase was used. Additionally, the anode activity was also higher (lower overpotential).

[0045] Without being bound by any theory, the inventors attribute this improvement in anode performance to the (e)chemical stability of metallic cobalt compared to cobalt oxide. It is known that during the oxygen evolution reaction, an oxide layer (in this case, cobalt oxide) forms on the exposed surface of the anode coating. As explained above, this oxide layer is not electrochemically stable and is subject to degradation. In contrast to prior art coatings, where the bulk phase contains (e)chemically stable metallic cobalt, the degradation of the coating of the present invention (the anode of the present invention) is limited to the exposed surface. After the cobalt oxide at the exposed surface is degraded, the metallic cobalt in the bulk phase is gradually exposed, converted to cobalt oxide (i.e., activated), and degraded in a controlled manner. Therefore, the advantage of the method and anode of the present invention is that, compared to prior art cobalt oxide coatings, cobalt degradation is significantly reduced and slowed down, resulting in controlled degradation and extended service life.

[0046] Optionally, and advantageously, the method further includes heating a nickel-containing substrate comprising a coating containing cobalt and optionally lanthanides.

[0047] Advantageously, the optional heating step includes heating to a temperature between 100°C and 750°C, preferably between 200°C and 500°C, for a duration between 10 minutes and 180 minutes, preferably between 20 minutes and 60 minutes.

[0048] In this disclosure, the heating duration refers to the duration during which the nickel-containing substrate, including the coating, is at a predetermined heating temperature. In other words, the heating duration does not include the time during which the coated substrate is heated or cooled.

[0049] The advantages of heat treatment include improved adhesion of the coating to the substrate surface and a reduced coating loss rate (expressed as the amount of coating lost per oxygen molecule (or mole) generated) compared to anodizing with the same substrate and coating but without heat treatment.

[0050] Whether heat treatment is necessary (and whether this results in an improvement in anodic performance) depends on the composition of the coating. When the coating is substantially composed of cobalt, the method of the present invention advantageously includes heat treatment. When the coating contains cobalt and lanthanides, heat treatment is advantageously optional.

[0051] Optionally, and advantageously, the method further includes electrochemically etching the substrate prior to electrodepositing the coating cathode onto the surface of the nickel-containing substrate.

[0052] Advantageously, optional electrochemical etching of nickel-containing substrates at 250 A / m 2 With 5000 A / m 2 Between, preferably at 500A / m 2 With 3000 A / m 2 Between, more preferably at 1000 A / m 2 With 2000 A / m 2 Between (e.g., at 750 A / m) 2 With 2500 A / m 2 Between or at 1000 A / m 2 With 2000 A / m 2 It occurs at the second current density (between).

[0053] Advantageously, the optional electrochemical etching of the nickel-containing substrate is carried out (occurs) in the presence of a solution containing a first acid having a pKa equal to or less than 1, preferably equal to or less than 0 (so-called a strong acid), as measured in water at 25°C. Advantageously, the solution is an aqueous solution containing the first acid.

[0054] Advantageously, the concentration of the first acid in the solution (advantageously an aqueous solution) is between 0.05 M and 10 M, preferably between 0.075 M and 7.5 M, and more preferably between 0.1 M and 6 M.

[0055] Advantageously, strong acids are HCl or H₂SO₄. It should be understood that aqueous solutions can contain two or more (different) acids.

[0056] Alternatively or additionally, and advantageously, the solution contains a nickel-containing hydrated salt and a second acid having a pKa greater than 1, preferably equal to or greater than 2, as measured in water at 25°C.

[0057] Advantageously, the nickel-containing hydrated salt is a chloride salt, nitrate salt, sulfate salt, aminosulfonate salt, or acetate salt, preferably NiCl2·6H2O or Ni(NH2SO3)2·6H2O.

[0058] Advantageously, when the aqueous solution contains a nickel-containing hydrated salt and a second acid, the aqueous solution contains a nickel-containing hydrated salt at a concentration between 25 g / L and 500 g / L, preferably between 50 g / L and 400 g / L, wherein the weight of the nickel-containing hydrated salt includes hydrated water.

[0059] Advantageously, the second acid is boric acid or citric acid.

[0060] Advantageously, when the aqueous solution contains a nickel-containing hydrated salt and a second acid, the concentration of the second acid is between 0.01 M and 1.5 M, preferably between 0.05 M and 1 M, more preferably between 0.1 M and 0.8 M, and most preferably between 0.3 M and 0.75 M.

[0061] The inventors have discovered that electrochemical etching of a substrate, particularly at least the surface on which a coating is to be applied, can positively improve the adhesion between the coating and the substrate surface. Better adhesion reduces the risk of coating delamination during anodic use, thereby contributing to improved mechanical stability and operational life.

[0062] Whether to electrochemically etch the substrate before depositing the coated cathode onto its surface depends in particular on the substrate’s composition and structure (e.g., surface roughness) and the composition of the coating.

[0063] According to a second aspect of this disclosure, an anode for alkaline water hydrolysis as set forth in the appended claims is provided.

[0064] The anode of the second aspect comprises a nickel-containing substrate and a coating on the surface of the substrate containing cobalt and optionally lanthanide elements. The anode of the second aspect can be manufactured (produced) by the method of the first aspect.

[0065] Advantageously, the nickel-containing substrate is as described above. Advantageously, the optional lanthanide elements are as described above.

[0066] The inventors have discovered that the presence of lanthanides (especially Ce, Pr, or Ho) in cobalt-containing coatings contributes to higher anode activity (lower overpotential) compared to coatings that are essentially composed of cobalt.

[0067] The coating has a bulk phase and an exposed surface, the latter being opposite to the surface of the coating that contacts the nickel-containing substrate. The bulk phase of the coating contains metallic cobalt and optional lanthanide elements, or is essentially composed of them.

[0068] In other words, the cobalt contained in the bulk phase of the coating is at least partially, and preferably substantially entirely, in the form of metallic cobalt.

[0069] Advantageously, the exposed surface of the coating contains cobalt oxide. In other words, the cobalt contained in the exposed surface of the coating is at least partially present in the form of cobalt oxide.

[0070] It was found that the presence of cobalt in the form of cobalt oxides on exposed surfaces can stabilize the surfaces to resist the electrochemical dissolution of cobalt, especially metallic cobalt.

[0071] Advantageously, when the coating contains cobalt and lanthanides, the loading ratio of cobalt to lanthanides (g Co / m) is measured, as by X-ray fluorescence spectroscopy (XRF). 2 Compared to g lanthanides / m 2 The ratio is between 1:1 and 20:1, preferably between 2:1 and 15:1, more preferably between 5:1 and 10:1, and most preferably between 6:1 and 9:1. Attached Figure Description

[0072] Aspects of the invention will now be described in more detail with reference to the accompanying drawings, in which the same reference numerals illustrate the same features, and in the drawings:

[0073] Figure 1 The activity of five anodes of the present invention when heated at different temperatures is shown, which is represented as overpotential.

[0074] Figure 2 It shows Figure 1 The mechanical stability of the five anodes of the present invention varies with the duration of heat treatment, which is expressed as the steady-state loss rate of the coating.

[0075] Figure 3 It shows Figure 1 and Figure 2 The activity of one anode of the present invention and three other anodes of the present invention when heated at different temperatures is expressed as overpotential.

[0076] Figure 4 The mechanical stability of eight additional anodes of the present invention as a function of heat treatment duration is shown, expressed as the steady-state loss rate of the coating.

[0077] Figure 5 The activity of a reference anode and four additional anodes of the present invention is shown, which is represented as overpotential.

[0078] Figure 6 It shows Figure 1 and Figure 2 The invention provides an anode of the present invention and six other anodes of the present invention with overpotentials varying with electrochemical test current densities, the six other anodes of the present invention being prepared with / without heat treatment using different cathode electrodeposition current densities. Detailed Implementation

[0079] This invention relates to a method for manufacturing (producing, preparing) an anode for alkaline water electrolysis, and an anode for alkaline water electrolysis.

[0080] The anode comprises a nickel-containing substrate and a coating on the surface of the substrate, wherein the coating contains cobalt and optional lanthanide elements.

[0081] The substrate contains nickel or is substantially composed of it. In other words, the substrate can be a substantially pure nickel substrate, but it can also contain other elements besides nickel, i.e., it can be a nickel alloy. Non-limiting examples of other elements include carbon (C), iron (Fe), cobalt (Co), copper (Cu), chromium (Cr), molybdenum (Mo), and aluminum (Al).

[0082] Non-limiting examples of nickel alloys suitable for use or as a base material in this disclosure include nickel 201 alloy (an alloy containing equal to or less than 0.02% carbon and equal to or greater than 99.5% nickel by weight, and optionally small amounts of Fe, Mn, Si, Cu and / or S as impurities), nickel 200 alloy (same as nickel 201 alloy but with a slightly higher carbon content), NiFe alloys, NiCo alloys, NiCu alloys (e.g., Monel®), and NiCr alloys (e.g., Inconel®).

[0083] The coating contains cobalt and optional lanthanide elements, or is substantially composed of them. The term "lanthanide elements" is used in this disclosure for chemical elements with atomic numbers 57 to 71 in the periodic table, i.e., chemical elements from lanthanum (La) to lutetium (Lu). Preferred examples of lanthanide elements include, but are not limited to, cerium (Ce), praseodymium (Pr), and holmium (Ho).

[0084] The coating has a bulk phase and an exposed surface, the latter being the opposite of the coating being attached to (i.e. in contact with) the surface of the nickel-containing substrate.

[0085] According to a first embodiment of the invention, the coating is substantially composed of cobalt, and the methods are configured to manufacture an anode comprising a coating substantially composed of cobalt.

[0086] Advantageously, the bulk phase of the coating comprises or is substantially composed of metallic cobalt. Advantageously, at least 10 at.%, preferably at least 50 at.%, more preferably at least 75 at.%, and most preferably at least 80 at.% (e.g., at least 90 at.%, at least 95 at.%, or at least 99 at.%) of the cobalt in the bulk phase of the coating are in the form of metallic cobalt.

[0087] Advantageously, and optionally, the exposed surface of the coating comprises cobalt oxide. In other words, the cobalt contained in the exposed surface of the coating is at least partially present in the form of cobalt oxide. Advantageously, at least 10 at.%, preferably at least 25 at.%, more preferably at least 30 at.%, and most preferably at least 40 at.% (e.g., at least 50 at.%) of the cobalt in the exposed surface of the coating is present in the form of cobalt oxide.

[0088] The presence of cobalt oxides at the exposed surface advantageously reduces the risk of electrochemical dissolution of cobalt metal from the bulk phase, thereby improving the mechanical stability of the anode.

[0089] According to a second embodiment of the invention, the coating comprises or is substantially composed of cobalt and lanthanides, and the methods are configured to manufacture an anode comprising a coating comprising or substantially composed of cobalt and lanthanides.

[0090] Advantageously, the bulk phase of the coating contains or is substantially composed of metallic cobalt and lanthanide elements.

[0091] Advantageously, at least 10 at.%, preferably at least 50 at.%, more preferably at least 75 at.%, and most preferably at least 80 at.% (e.g., at least 90 at.%, at least 95 at.%, or at least 99 at.%) of the cobalt in the bulk phase of the coating are in the form of metallic cobalt.

[0092] The exposed surface of the anolyte coating of the second embodiment of the invention is advantageously as described above with respect to the exposed surface of the anolyte coating of the first embodiment.

[0093] "On a surface" means that the coating can be present on one or both surfaces of the substrate. Therefore, the methods for producing an anode explained below for an anode with a coating on one surface can also be used to produce an anode with coatings on both surfaces. When the anode includes coatings on both surfaces, the coatings can be identical, i.e., they can have the same composition, or they can be different. Different coatings can be obtained by changing the process steps and parameters during the deposition of the first and second coatings. These methods also allow coatings to be applied to both surfaces of the substrate simultaneously.

[0094] The method according to the invention includes optional pretreatment of the substrate, a coating deposition step, and optional post-treatment.

[0095] Prior to coating deposition, optional pretreatment of the substrate advantageously includes electrochemical etching of a nickel-containing substrate or a substrate thereof. Advantageously, a thin outer layer of the substrate is removed during electrochemical etching, resulting in a substantially contamination-free surface.

[0096] Optional pretreatment of the substrate, particularly electrochemical etching, has the technical effect of improving the adhesion between the coating and the substrate surface. Better adhesion reduces the risk of coating delamination during anodic use, thereby contributing to improved mechanical stability and operational life.

[0097] The coating deposition step includes cathodic electrodeposition of a coating comprising or consisting of cobalt and, optionally, lanthanides on the surface of a (optionally pretreated) substrate.

[0098] The inventors have unexpectedly discovered that, unlike existing methods where cobalt exists in the bulk phase as cobalt oxide, the bulk phase of a coating deposited by cathodic electrodeposition contains cobalt that is at least partially and substantially entirely in the form of metallic cobalt.

[0099] Optional post-processing includes or consists of heat treatment, wherein the substrate including the coating is heated to a predetermined temperature for a predetermined heating duration.

[0100] One advantage of heat treatment is that it improves the adhesion of the coating to the substrate surface compared to the same anode produced without heat treatment. This results in a lower risk of coating delamination during the anode's service life, which helps improve mechanical stability and thus operational stability, and ultimately, service life.

[0101] Another advantage of heat treatment is that the coating loss rate (expressed as the amount of coating lost per oxygen molecule (or mole) generated) can be significantly lower compared to an anode with the same substrate and coating but without heat treatment. Without being bound by any theory, the inventors attribute this reduction in loss to the fact that during heat treatment, the exposed surface of the coating is stabilized to resist the electrochemical dissolution of cobalt metal during the use of the anode in alkaline water electrolysis by forming (so-called "thermal") oxides of cobalt at the exposed surface. These oxides are instantaneously transformed into so-called "electrochemical" oxides during anodic use due to the nature of the oxygen evolution reaction.

[0102] The method of the first embodiment, namely the method for producing an anode comprising a nickel-containing substrate and a coating substantially composed of cobalt, advantageously includes electrochemical etching of the substrate, cathodic electrodeposition of the coating on the etched substrate, and heating of the coated substrate.

[0103] Electrochemical etching at 250 A / m 2 With 2500 A / m 2 Between, preferably at 500 A / m 2 With 2000 A / m 2 Between, more preferably at 750 A / m 2 With 1500 A / m 2 Between (e.g., at 850 A / m)2 With 1150 A / m 2 Between, for example, 1000 A / m 2 It occurs at the etching current density of ).

[0104] Electrochemical etching involves contacting a substrate with an aqueous solution containing a nickel-hydrated salt and a weak acid, i.e., an acid having a pKa greater than 1, preferably equal to or greater than 2, as measured in water at 25°C.

[0105] Non-limiting examples of nickel-containing hydrated salts include NiCl2.6H2O, Ni(NO3)2.6H2O, NiSO4.7H2O, Ni(CH3COO)2.4H2O, and Ni(NH2SO3)2.6H2O, with NiCl2.6H2O and Ni(NH2SO3)2.6H2O being preferred.

[0106] Non-limiting examples of suitable weak acids include H3BO3 and citric acid, with H3BO3 being preferred.

[0107] Advantageously, the aqueous solution contains a nickel-containing hydrated salt at a concentration between 25 g / L and 500 g / L, preferably between 50 g / L and 400 g / L, and more preferably between 75 g / L and 350 g / L (e.g., between 300 g / L and 350 g / L, such as 330 g / L), wherein the weight of the nickel-containing hydrated salt includes the hydrated water.

[0108] Advantageously, the concentration of the weak acid in the aqueous solution is between 0.01 M and 1.5 M, preferably between 0.02 M and 1.25 M, more preferably between 0.1 M and 0.8 M, for example between 0.3 M and 0.75 M.

[0109] The electrochemical etching is carried out for a duration between 3 and 30 minutes, preferably between 4 and 20 minutes, and more preferably between 5 and 15 minutes (e.g., between 6 and 12 minutes).

[0110] Electrochemical etching is performed at a temperature between 10°C and 50°C, preferably between 20°C and 40°C, and more preferably at room temperature.

[0111] Advantageously, the electrochemically etched substrate has a relatively smooth surface, i.e., a surface with a Ra value of 1.5 µm or less, preferably 1 µm or less, and more preferably between 0.5 µm and 1 µm, as measured by a standard roughness meter.

[0112] Cathodic electrodeposition occurs in the presence of an aqueous electrolyte having a pH between 1 and 6.5, preferably between 2 and 5, wherein the pH is measured at room temperature by means known in the art, such as a standard glass electrode pH meter.

[0113] Cathode electrodeposition at 100 A / m 2 With 2500 A / m 2 Between, preferably at 200 A / m 2 With 2000 A / m 2 Between, more preferably at 250 A / m 2 With 1500 A / m 2 Between (e.g., at 500 A / m) 2 With 1000 A / m 2 Between, for example, 500 A / m 2 It occurs at a current density of ).

[0114] Advantageously, the aqueous electrolyte contains an acid and / or its corresponding salt. It should be understood that the aqueous electrolyte may contain two or more acids and / or their corresponding salts. Advantageously, the composition and concentration of the acid are selected according to the desired pH of the aqueous electrolyte.

[0115] Advantageously, when the aqueous electrolyte contains an acid, the acid is boric acid (H3BO3) or citric acid (C6H8O7). Advantageously, when the aqueous electrolyte contains the corresponding salt of the acid, the salt is a borate or citrate.

[0116] Advantageously, when the aqueous electrolyte contains an acid, it contains an acid in the range of 0.01 M to 1 M, preferably between 0.05 M and 0.8 M, more preferably between 0.075 M and 0.75 M, and most preferably between 0.1 M and 0.5 M.

[0117] Advantageously, when the acid is boric acid, the aqueous solution contains boric acid in amounts between 0.1 M and 0.6 M, preferably between 0.3 M and 0.5 M. Advantageously, when the acid is citric acid, the aqueous solution contains citric acid in amounts between 0.1 M and 0.4 M, preferably between 0.25 M and 0.35 M (e.g., 0.3 M).

[0118] The aqueous electrolyte contains a cobalt-containing hydrated salt. Advantageously, the cobalt-containing hydrated salt is a chloride salt, nitrate salt, sulfate salt, aminosulfonate salt, or acetate salt. Non-limiting examples include CoCl2·6H2O, CoSO4·7H2O, Co(NO3)2·6H2O, or Co(CH3COO)2·4H2O, preferably CoCl2·6H2O. It should be understood that the aqueous electrolyte may contain two or more cobalt-containing hydrated salts.

[0119] Advantageously, the aqueous electrolyte comprises a cobalt-containing hydrated salt at a concentration between 20 g / L and 250 g / L, preferably between 25 g / L and 200 g / L, more preferably between 50 g / L and 150 g / L (e.g., between 75 g / L and 125 g / L or between 90 g / L and 100 g / L), wherein the weight of the cobalt-containing hydrated salt includes hydrated water.

[0120] Advantageously, the cathode electrodeposition is carried out at a temperature between 10°C and 50°C, preferably between 20°C and 40°C, and more preferably at room temperature.

[0121] Advantageously, the cathode electrodeposition is carried out for a duration between 1 minute and 10 minutes, preferably between 2 minutes and 5 minutes (e.g., 3 minutes).

[0122] The heating step includes heating the nickel-containing substrate, including the coating, to a temperature between 100°C and 750°C, preferably between 200°C and 500°C, and more preferably between 250°C and 400°C.

[0123] The heating step has a heating duration between 1 minute and 240 minutes, preferably between 10 minutes and 180 minutes, more preferably between 15 minutes and 120 minutes, and most preferably between 20 minutes and 60 minutes (e.g., between 30 minutes and 45 minutes).

[0124] Advantageously, the nickel-containing substrate, including the coating, is heated to a temperature between 100°C and 750°C, preferably between 200°C and 500°C, more preferably between 350°C and 450°C (e.g., 400°C), for a duration between 10 minutes and 180 minutes, preferably between 20 minutes and 60 minutes, more preferably between 20 minutes and 40 minutes (e.g., 30 minutes).

[0125] The inventors have discovered that the heating intensity (expressed by heating temperature and heating duration) of the selected heating step affects both the mechanical strength (stability, robustness) and the activity (overpotential) of the anode. Lower intensity (i.e., lower heating temperature and / or shorter heating duration) results in higher activity (lower overpotential) but lower mechanical stability, while higher heating intensity (i.e., higher heating temperature and / or longer heating duration) results in lower activity (higher overpotential) but higher mechanical stability. Therefore, it should be understood that if heat treatment is performed, the optimal heating temperature is closely related to the heating duration and will depend on the anode's performance requirements.

[0126] Advantageously, the heat treatment is carried out in air.

[0127] The method of the second embodiment, namely the method for producing an anode comprising a nickel-containing substrate and a coating comprising or substantially composed of cobalt and lanthanide elements, advantageously includes electrochemical etching of the substrate and cathodic electrodeposition of the coating on the etched substrate. These methods may further optionally include heating the coated substrate.

[0128] Electrochemical etching at 500 A / m 2 With 5000 A / m 2 Between, preferably at 750 A / m 2 With 4000 A / m 2 Between, more preferably at 1000 A / m 2 With 3000 A / m 2 Between (e.g., at 1500 A / m) 2 With 2500 A / m 2 Between, for example, 2000 A / m 2 It occurs at the etching current density of ).

[0129] Electrochemical etching involves contacting a substrate with an aqueous solution containing a strong acid (i.e., an acid having a pKa equal to or less than 1, preferably equal to or less than 0, as measured in water at 25°C).

[0130] Advantageously, the concentration of the strong acid in the aqueous solution is between 0.05 M and 10 M, preferably between 0.075 M and 7.5 M, and more preferably between 0.1 M and 6 M (e.g. between 0.5 M and 2.5 M or between 1 M and 2 M).

[0131] Advantageously, strong acids are HCl or H2SO4.

[0132] The electrochemical etching is carried out for a duration between 1 minute and 30 minutes, preferably between 2 minutes and 20 minutes, and more preferably between 3 minutes and 15 minutes (e.g., between 3 minutes and 6 minutes).

[0133] Electrochemical etching is performed at the temperature described above for the first embodiment.

[0134] Advantageously, the electrochemically etched substrate has a rough surface, i.e., a surface with a Ra value of more than 1.5 µm, preferably equal to or greater than 2 µm, and more preferably between 2 µm and 3 µm, as measured by a standard roughness meter.

[0135] Cathodic electrodeposition occurs in the presence of an aqueous electrolyte having a pH between 1 and 6.5, preferably between 2 and 5, wherein the pH is measured at room temperature by means known in the art, such as a standard glass electrode pH meter.

[0136] Cathode electrodeposition at 100 A / m 2 With 2500 A / m 2 Between, preferably at 250 A / m 2 With 2000 A / m 2 Between, more preferably at 500 A / m 2 With 1500 A / m 2 Between (e.g., at 750 A / m) 2 With 1250 A / m 2 Between, for example, 1000 A / m 2 It occurs at a current density of ).

[0137] Advantageously, the aqueous electrolyte contains an acid and / or its corresponding salt. It should be understood that the aqueous electrolyte may contain two or more acids and / or their corresponding salts. Advantageously, the composition and concentration of the acid are selected based on the desired pH of the aqueous electrolyte. Advantageously, the acid and / or its corresponding salt (including chemical composition and concentration (amount)) are as described above with respect to the first embodiment.

[0138] The aqueous electrolyte contains a cobalt-containing hydrated salt, as described above. Advantageously, the amount (g / L) of the cobalt-containing hydrated salt in the aqueous electrolyte is as described above with respect to the first embodiment.

[0139] The aqueous electrolyte further comprises a lanthanide-containing hydrated salt. Advantageously, the lanthanide-containing hydrated salt is a chloride salt, nitrate salt, sulfate salt, or acetate salt, preferably a chloride salt.

[0140] Advantageously, when the hydrated salt containing lanthanides is a chloride salt, it is based on the formula LnCl x .yH2O, wherein Ln is a lanthanide element, preferably Ce, Pr, or Ho. Advantageously, the hydrated chloride salt containing a lanthanide element is CeCl3·7H2O, PrCl3·7H2O, or HoCl3·6H2O.

[0141] Advantageously, when the lanthanide-containing hydrated salt is a nitrate, it is based on the formula Ln(NO3). x .yH2O, wherein Ln is a lanthanide element, preferably Ce, Pr or Ho. Advantageously, the hydrated nitrate containing a lanthanide element is Ce(NO3)3.6H2O, Pr(NO3)3.6H2O or Ho(NO3)5.5H2O.

[0142] Advantageously, when the lanthanide-containing hydrated salt is a sulfate, it is based on the formula Ln(SO4). x .yH2O, wherein Ln is a lanthanide element, preferably Ce, Pr or Ho. Advantageously, the hydrated sulfate containing a lanthanide element is Ce(SO4)3.8H2O, Pr(SO4)3.8H2O or Ho(SO4)3.8H2O.

[0143] Advantageously, when the hydrated salt containing lanthanides is an acetate, it is based on the formula Ln(CH3COO). x .yH2O, wherein Ln is a lanthanide element, preferably Ce, Pr or Ho. Advantageously, the hydrated acetate containing a lanthanide element is Ce(CH3COO)3.4H2O, Ce(CH3COO)3.6H2O, Pr(CH3COO)3.4H2O or Ho(CH3COO)3.4H2O.

[0144] Advantageously, the aqueous electrolyte comprises a lanthanide-containing hydrated salt at a concentration between 1 g / L and 20 g / L, preferably between 2 g / L and 15 g / L, more preferably between 5 g / L and 10 g / L (e.g., between 7 g / L and 9 g / L), wherein the weight of the lanthanide-containing hydrated salt includes hydrated water.

[0145] Advantageously, the cathode electrodeposition is performed at the temperature described above for the first embodiment.

[0146] Advantageously, the cathode electrodeposition continues for the duration described above for the first embodiment.

[0147] The inventors have unexpectedly discovered that, unlike existing methods for producing (mixed) cobalt-lanthanide oxides, cathodic electrodeposition using an aqueous electrolyte containing cobalt-containing hydrated salts and lanthanide-containing hydrated salts produces a coating in which the bulk phase comprises metallic cobalt and one or more lanthanide hydroxides.

[0148] Without being bound by any theory, the co-electrodeposition of cobalt and lanthanides into metallic cobalt and lanthanide hydroxides is due to the mild pH change at the substrate surface during cathodic electrodeposition and the interaction between cobalt and lanthanides, which causes the lanthanides to precipitate and be incorporated into the coating during deposition.

[0149] When the method according to the second embodiment includes heat treatment, the heat treatment is advantageously as described above with respect to the first embodiment.

[0150] Example

[0151] Example 1

[0152] Nickel-201 alloy sheet was used as the nickel-containing substrate. An aqueous solution of 330 g NiCl2·6H2O and 45 g H3BO3 per liter of water was used at room temperature and 1000 A / m. 2Electrochemical etching was performed on multiple nickel-201 alloy substrates at a current density for durations between 6 and 12 minutes. The electrochemically etched substrates had surface Ra values ​​between 0.5 µm and 1 µm, as measured by a standard roughness meter.

[0153] Next, cathodic electrodeposition was performed on the etched substrates by placing them in a rectangular polycarbonate electroplating bath with the same internal length / width dimensions as the substrate. Electrodeposition was controlled using a Voltcraft PPS-11810, PPS-11815, or LSP-1403 power supply. The aqueous electrolyte used contained 100 g / L CoCl2·6H2O as a Co-containing hydrated salt and 23 g / L H3BO3 (0.372 M), where the weight of the hydrated salt includes the weight of the hydrated water, and the weight of H3BO3 is the dry weight, expressed per liter of water. Cathodic electrodeposition was performed at room temperature at 500 A / m 2 The current density was maintained for three minutes.

[0154] The Co-coated Ni substrate was then heat-treated in air. The heating duration (expressed as the dwell time at the heating temperature) and the heating temperature varied according to the combinations presented in Table 1.

[0155] Table 1: Heating duration and heating temperature of Co-coated Ni substrate

[0156]

[0157] Electrochemical tests were performed on eight anodes using a standard three-electrode cell in a borosilicate glass beaker. The working electrodes (anodes) were encapsulated in a PVDF housing with O-rings to precisely define a depth of approximately 1 cm. 2 The surface area of ​​the electrode was [not specified]. The reference electrode was a Hydroflex® reversible hydrogen electrode purchased from Gaskatel. The counter electrode was a bulk Ni 201 plate with a surface area approximately 10 times that of the working electrode. The electrolyte used for testing was KOH 30%m (reagent-grade purity, at 50°C). Electrochemical tests were controlled using an OctoStat 5000 multichannel potentiostat manufactured by Ivium.

[0158] Figure 1 The activity (overpotential) of anodes 1-5 after heating at 400°C for different durations is shown. Figure 2 The mechanical stability of the same anodes 1-5 is shown, expressed as steady-state loss rate (g Co / MAh operating time, or amount of coating lost per unit of oxygen generated). From these... Figure 1 and Figure 2As can be seen, a longer heating duration at 400°C has a positive effect on mechanical stability (lower loss rate), but a slight negative effect on activity (overpotential).

[0159] Figure 3 The activity (overpotential) of anodes 4, 6, 7, and 8 after heating at different temperatures for 60 minutes is shown. Higher temperatures result in lower activity.

[0160] from Figures 1-3 It can be concluded that for Co coatings, higher heat treatment intensity (higher temperature and / or longer duration) results in lower activity (overpotential) but higher stability, while lower heat treatment intensity (lower temperature and / or shorter duration) results in higher overpotential but lower stability. The inventors have found that for anodes 1-9, the optimal heat treatment parameters (resulting in the best balance between overpotential and mechanical stability) are at 400°C for 30 minutes.

[0161] Example 2

[0162] The same nickel 201 alloy sheet as in Example 1 was used as the nickel-containing substrate. Multiple nickel 201 alloy substrates were electrochemically etched in the same manner as in Example 1. The electrochemically etched substrates had surfaces with Ra values ​​between 0.5 µm and 1 µm, as measured by a standard roughness meter.

[0163] Next, cathodic electrodeposition was performed on the etched substrate in a rectangular glass electroplating bath to deposit a coating substantially composed of cobalt. Electrodeposition was controlled using a Voltcraft PPS-11810, PPS-11815, or LSP-1403 power supply. The aqueous electrolyte used contained 100 g / L CoCl2·6H2O as a Co-containing hydrated salt and 0.3 M citric acid, where the weight of the hydrated salt includes the weight of the hydrated water, and the weight of the citric acid is dry weight, expressed per liter of water. Cathodic electrodeposition was performed at room temperature at 425 A / m 2 The test was conducted for three minutes at a current density of 850 A / m at room temperature. 2 It was performed for three minutes at a current density.

[0164] The Co-coated Ni substrate was then heat-treated in air. The heating duration was 30 minutes, and the heating temperature varied as follows: 350°C, 400°C, 450°C, and 500°C.

[0165] As explained in Example 1, electrochemical tests were performed on eight anodes (two cathode electrodeposition current densities and four heat treatment heating temperatures).

[0166] Figure 4 The mechanical stability of eight anodes is shown, expressed as steady-state loss rate (g Co / MAh operating duration, or amount of coating lost per unit of oxygen generated). It is evident that, for a constant heating duration, the loss rate varies with heating temperature, with the worst results (highest loss rate) obtained at 450°C. It is also evident that when citric acid is used as the acid, with 425 A / m... 2 Compared to the current density of 850 A / m 2 The higher current density results in better coating quality (lower loss rate).

[0167] Example 3

[0168] The same nickel-201 alloy sheet as in Example 1 was used as the nickel-containing substrate. A 1 M HCl aqueous solution was used at room temperature and 2000 A / m. 2 Electrochemical etching was performed on multiple nickel-201 alloy substrates at a current density for durations between 3 and 6 minutes. The electrochemically etched substrates had surface Ra values ​​between 2 µm and 3 µm, as measured by a standard roughness meter.

[0169] Next, the etched substrate was subjected to cathodic electrodeposition at room temperature in a rectangular polycarbonate electroplating bath having the same internal length / width dimensions as the substrate to deposit a coating containing cobalt and cerium (Ce), praseodymium (Pr), and holmium (Ho) (respectively). Electrodeposition was controlled using a Voltcraft PPS-11810, PPS-11815, or LSP-1403 power supply. The aqueous electrolyte used contained 90 g / L CoCl2·6H2O as a Co-containing hydrated salt, 9 g / L CeCl3·7H2O, PrCl3·7H2O, or HoCl3·6H2O (respectively) as lanthanide-containing hydrated salts, and 23 g / L H3BO3, wherein the weight of the hydrated salts includes the weight of the hydrated water, and the weight of H3BO3 is dry weight, expressed per liter of water. The cathodic electrodeposition current density was 500 A / m. 2 The process was repeated for three minutes. Then, the Co-lanthanide-coated Ni substrate was heat-treated in air at 400°C for 30 minutes. Table 2 summarizes the cathode electrodeposition parameters and heat treatment parameters for the different anodes prepared.

[0170] Table 2: Cathode electrodeposition parameters and heat treatment parameters for anodes containing Co-lanthanides

[0171]

[0172] As explained in Example 1, but at 60°C instead of 50°C, electrochemical tests were performed on the three anodes to measure overpotential (activity). Anode 2 of Example 1 and the original nickel 201 alloy substrate were also tested under the same conditions (60°C).

[0173] Figure 5 The overpotentials (activities) of anodes 2, 9, 10, and 11, as well as a bare nickel 201 alloy substrate (as a reference anode, "reference"), are shown. It is clear that the activity of all the anodes of this invention is significantly higher than that of the reference anode (significantly lower overpotentials). Furthermore, the anodes with a Co-lanthanide coating (anodes 9-11) outperform the Co-coated anode (anode 2), with the Co-Ce coating exhibiting the best performance, demonstrating the beneficial effects of the presence of lanthanides in the coating.

[0174] Example 4

[0175] The same nickel 201 alloy sheet as in Example 1 was used as the nickel-containing substrate. Multiple nickel 201 alloy substrates were electrochemically etched in the same manner as in Example 3. The electrochemically etched substrates had a surface with a Ra value between 2 µm and 3 µm, as measured by a standard roughness meter.

[0176] Next, a coating containing cobalt and cerium (Ce) was deposited on the etched substrate by cathodic electrodeposition at room temperature in a rectangular polycarbonate electroplating bath having the same internal length / width dimensions as the substrate. Electrodeposition was controlled using a Voltcraft PPS-11810, PPS-11815, or LSP-1403 power supply. The aqueous electrolyte used contained 90 g / L CoCl2·6H2O as a Co-containing hydrated salt, 9 g / L CeCl3·7H2O, and 23 g / L H3BO3, where the weight of the hydrated salt includes the weight of the hydrated water, and the weight of H3BO3 is the dry weight, expressed per liter of water. The cathodic electrodeposition current density varied as follows: 125 A / m 2 250 A / m 2 and 500 A / m 2 The durations were twelve minutes, six minutes, and three minutes, respectively. The coated substrates were then heat-treated in air at 400°C for 30 minutes. Replicas of each coated substrate were also prepared without heat treatment. Table 3 summarizes the cathodic electrodeposition and heat treatment parameters for the different anodes prepared.

[0177] Table 3: Cathode electrodeposition parameters and heat treatment parameters for anodes containing Co-Ce

[0178]

[0179] As explained in Example 3, electrochemical tests were performed on six anodes and the four No. 2 anodes from Example 1 to measure overpotential (activity). During the tests, the applied current density was 500 A / m. 2 With 20000 A / m 2 The changes between them.

[0180] Figure 6 The overpotential (activity) of each anode as a function of current density during the test is shown. It is clear that for all anodes, the overpotential increases with increasing test current density, as expected. When comparing anodes 12-13, 14-15, and 16-17 separately to evaluate the effect of heat treatment, a limited effect is noted. When evaluating anodes 12, 14, and 16, and anodes 13, 15, and 17 to evaluate the effect of cathode electrodeposition current density, at higher current densities (500 A / m²), the effect is more pronounced. 2 In Example 4, better results were obtained with anodes 12 and 13. All anodes in Example 4 outperformed anode 2 (Co only), further confirming the positive effect of Ce in the coating.

[0181] For anodes 12 to 15, the loading of Co and Ce in the coating (g / m³) was measured by X-ray fluorescence spectroscopy. 2 Each anode was measured three times. The loading ratio of all four anodes (g Co / m³) was measured. 2 Compared to g Ce / m 2 The ratio is between 6:1 and 9:1.

Claims

1. A process for manufacturing an anode for alkaline water electrolysis, the anode comprising a nickel-containing substrate and a coating comprising cobalt and optionally a lanthanide series element, the process comprising cathodically electrodeposition of the coating comprising cobalt and optionally a lanthanide series element on the surface of the nickel-containing substrate in the presence of an aqueous electrolyte having a pH between 1 and 6.5 as measured at 25°C, the process being characterized in that the aqueous electrolyte comprises a cobalt-containing hydroxide salt and, when the coating comprises the lanthanide series element, a lanthanide series element-containing hydroxide salt, and the cathodic electrodeposition occurs at a first current density between 100 A / m 2 and 2500 A / m 2 .

2. The method according to claim 1, wherein, The cobalt-containing hydrated salt is CoCl2·6H2O, CoSO4·7H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O, or Co(SO3NH2)2·6H2O.

3. The method according to any one of the preceding claims, wherein, The aqueous electrolyte comprises a cobalt-containing hydrated salt at a concentration between 20 g / L and 250 g / L, preferably between 50 g / L and 150 g / L, wherein the weight of the cobalt-containing hydrated salt includes hydrated water.

4. The method according to any one of the preceding claims, wherein, The lanthanide element is Ce, Pr, or Ho.

5. The method according to any one of the preceding claims, wherein, The lanthanide-containing hydrated salt is a chloride salt, nitrate salt, sulfate salt, or acetate salt.

6. The method according to claim 5, wherein, The lanthanide-containing hydrated salt is CeCl3·7H2O, PrCl3·7H2O, or HoCl3·6H2O.

7. The method according to any one of the preceding claims, wherein, The coating contains the lanthanide element, wherein the aqueous electrolyte contains the lanthanide-containing hydrated salt between 1 g / L and 20 g / L, preferably between 5 g / L and 10 g / L, wherein the weight of the lanthanide-containing hydrated salt includes hydrated water.

8. The method according to any one of the preceding claims, wherein, The aqueous electrolyte further contains an acid and / or its corresponding salt.

9. The method according to claim 8, wherein, The aqueous electrolyte contains an acid, wherein the acid is H3BO3 or citric acid.

10. The method according to claim 8 or claim 9, wherein, The concentration of the acid in the aqueous electrolyte is between 0.01 M and 1 M, preferably between 0.1 M and 0.5 M.

11. The method according to any one of claims 8 to 10, wherein, The aqueous electrolyte contains the corresponding salt of the acid, wherein the corresponding salt is a borate or a citrate.

12. The method according to any one of the preceding claims, wherein, The first current density is 500 A / m 2 With 1000A / m 2 between.

13. The method according to any one of the preceding claims, further comprising heating the nickel-containing substrate comprising the coating containing cobalt and optionally lanthanides to a temperature between 100°C and 750°C for a duration between 1 minute and 240 minutes.

14. The method according to claim 13, wherein, The nickel-containing substrate, including the coating containing cobalt and optional lanthanides, is heated to a temperature between 200°C and 500°C for a duration between 20 minutes and 60 minutes.

15. The method according to any one of the preceding claims, further comprising, prior to the cathode electrodeposition, at 250 A / m 2 With 5000 A / m 2 Electrochemical etching of the nickel-containing substrate was performed at a second current density.

16. The method according to claim 15, wherein, The second current density is 1000 A / m 2 With 2000 A / m 2 between.

17. The method according to claim 15 or claim 16, wherein, The nickel-containing substrate is electrochemically etched in the presence of an aqueous solution containing a first acid having a pKa equal to or less than 1, preferably equal to or less than 0, as measured in water at 25°C, or containing a nickel-containing hydrated salt and a second acid having a pKa greater than 1, preferably equal to or greater than 2, as measured in water at 25°C.

18. The method according to claim 17, wherein, The aqueous solution contains the first acid, wherein the concentration of the first acid is between 0.05 M and 10 M, preferably between 0.1 M and 6 M.

19. The method according to claim 17 or claim 18, wherein, The first acid is HCl or H2SO4.

20. The method of claim 17, wherein, The aqueous solution contains the nickel-containing hydrated salt and the second acid, wherein the nickel-containing hydrated salt is a chloride salt, nitrate salt, sulfate salt, aminosulfonate salt or acetate salt, preferably NiCl2·6H2O or Ni(NH2SO3)2·6H2O.

21. The method according to claim 17 or claim 20, wherein, The aqueous solution contains the nickel-containing hydrated salt and the second acid, wherein the aqueous solution contains the nickel-containing hydrated salt at a concentration between 25 g / L and 500 g / L, preferably between 50 g / L and 400 g / L, wherein the weight of the nickel-containing hydrated salt includes hydrated water.

22. The method according to any one of claims 17, 20 or 21, wherein, The aqueous solution contains the nickel-containing hydrated salt and the second acid, wherein the second acid is boric acid or citric acid.

23. The method according to any one of claims 17, 20, 21 or 22, wherein, The aqueous solution contains the nickel-containing hydrated salt and the second acid, wherein the concentration of the second acid is between 0.01 M and 1.5 M, preferably between 0.1 M and 0.8 M.

24. An anode for alkaline water electrolysis, comprising a nickel-containing substrate and a coating comprising cobalt and optionally lanthanide elements on the surface of the substrate, wherein the coating has a bulk phase and an exposed surface, the anode being characterized in that the bulk phase comprises metallic cobalt.

25. The anode according to claim 24, wherein, The exposed surface contains cobalt oxide.

26. The anode according to claim 24 or claim 25, wherein, The optional lanthanide element is Ce, Pr, or Ho.

27. The anode according to any one of claims 24 to 26, wherein, The substrate comprises a nickel alloy, preferably a nickel 201 alloy.

28. The anode according to any one of claims 24 to 27, wherein, The coating contains cobalt and lanthanides, wherein the loading ratio of cobalt to lanthanides in the coating (g cobalt / m³) is as measured by X-ray fluorescence spectroscopy. 2 Compared to g lanthanides / m 2 The ratio is between 1:1 and 20:1, preferably between 2:1 and 15:1, and more preferably between 5:1 and 10:1.

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