Electrodes for gas generation in electrolytic processes

Abstract

The present invention relates to an electrode suitable for gas generation, particularly one comprising a metal substrate and a catalyst coating. Such an electrode can be used as an anode for oxygen generation in electrolytic processes, such as in the alkaline electrolysis of water.

Description

[Technical Field]

[0001] The present invention relates to an electrode, more particularly to an electrode comprising a metal substrate and a catalyst coating, suitable for use in gas generation. This electrode can be used, for example, as an anode for oxygen generation in electrolytic processes such as alkaline water electrolysis. [Background technology]

[0002] The field of the present invention relates to the preparation of catalytic coatings for electrodes used in alkaline water electrolysis for hydrogen production, wherein such coatings are applied to a metal substrate.

[0003] In recent decades, global carbon dioxide emissions have reached increasingly high levels, resulting in adverse effects. Conscious resource use and attention to their environmental impact are the foundation for an effective and efficient energy transition.

[0004] In this context, hydrogen plays a crucial role and is a prime example of a cutting-edge solution that can significantly contribute to the energy transition, as it has the potential to decarbonize parts of the industrial sector, particularly so-called energy-intensive sectors such as refineries and the steel industry. Ultimately, hydrogen can make a significant contribution to sustainable mobility.

[0005] Hydrogen is the most abundant element in nature, found in its free gaseous state, and while not a direct source of energy, it can be considered an energy carrier, that is, a means of storing energy that can be supplied later. Indeed, hydrogen can be stored and used in various sectors such as transportation, or to produce heat for industrial use, until its introduction into gas transport and distribution networks.

[0006] Today, hydrogen is already produced and used, but it is mainly produced by processes that generate significant amounts of carbon dioxide emissions, such as methane reforming or coal gasification.

[0007] Only hydrogen produced in a sustainable manner, where carbon dioxide emissions into the atmosphere are avoided during the manufacturing process, is known as green or renewable hydrogen. It is obtained by the electrolysis of an aqueous solution in an electrochemical cell powered by electricity generated from renewable sources such as photovoltaic, hydroelectric, geothermal, or wind power.

[0008] There are several types of aqueous solution electrolysis processes that can be used to produce hydrogen, including alkaline electrolysis, proton exchange membrane electrolysis, and electrolysis using solid oxide electrolytic cells. Proton exchange membrane electrolysis and alkaline electrolysis are more commonly used, with the latter being more highly developed and seemingly better suited for large-scale implementations.

[0009] In the electrolysis of an aqueous solution, a power source is connected to two electrodes, which are placed in the solution, and the electrolysis process involves the splitting of water molecules into hydrogen and oxygen. This consists of two half-reactions: an oxygen evolution reaction occurring at the anode and a hydrogen evolution reaction occurring at the cathode. The hydrogen evolution reaction is a reduction reaction in which electrons from the cathode are transferred to a hydrogen cation to form hydrogen gas, while the oxygen evolution reaction is an oxidation reaction in which electrons go to the anode to produce oxygen.

[0010] The main challenge in realizing these two half-reactions is overcoming their slow reaction kinetics. In practice, the kinetic complexity exhibited by these two half-reactions necessitates an excess cell voltage exceeding their thermodynamic potential to obtain a highly efficient process.

[0011] Furthermore, recent advances in aqueous solution electrolysis have led to processes being carried out at high current densities. In addition, renewable energy sources are often used to provide the power to perform aqueous solution electrolysis. The use of high current densities, combined with the intermittency of renewable energy, can cause rapid electrode degradation. Therefore, there is a need for more durable electrodes that can maintain good performance even under high current density conditions with numerous power interruptions. In particular, anodes with low oxygen overpotential that are less susceptible to degradation caused by high current densities and shutdowns are required.

[0012] In most electrolytic processes, the cost of producing the desired product is largely determined by the cost of the materials used in the catalytic coating applied to the substrate acting as the electrode, and by their catalytic activity for the desired reaction. In aqueous electrolysis, precious metals such as iridium, rhodium, and ruthenium offer low overpotential and excellent catalytic activity for oxygen evolution reactions; however, their scarcity, combined with the resulting high cost, limits their large-scale application for the economical production of high-purity hydrogen and oxygen. Therefore, it is important to investigate alternative catalytic coatings that reduce the amount of precious metals and have lower costs.

[0013] Furthermore, due to the fluid and intermittent behavior of renewable energy sources, numerous system start-up and stop-down cycles can occur, meaning that electrolytic cells for the electrolysis of aqueous solutions must be adapted to dynamic operation. All of this can cause polarity reversal, which is detrimental to the electrodes, potentially adversely affecting their lifespan and accelerating their degradation.

[0014] Generally, these current reversals can be avoided by using an external polarization system, but with a view to overall process containment and cost reduction, there is a tendency to completely eliminate the use of polarization devices, which would consequently negatively impact electrode lifespan.

[0015] International Patent Application Publication No. 2016 / 066544A1 describes an electrode suitable for use in an electrochlorination cell, in particular an anode for the production of active chlorine by electrolysis of seawater. The electrode comprises a titanium substrate and a first inner catalytic coating applied to the substrate, which contains a mixture of oxides of tantalum, ruthenium, and iridium, and an additional outer catalytic coating containing a mixture of oxides of titanium, ruthenium, and at least one element selected from nickel, iron, and cobalt.

[0016] International Patent Application Publication No. 00 / 06800A1 describes an anode for an electrolytic extraction cell having an oxygen barrier layer comprising at least one oxide selected from chromium oxide, niobium oxide, and nickel oxide; an intermediate protective layer comprising copper, or at least one of copper, nickel, and cobalt, and / or their oxides; and in one embodiment, a coating made of an electrochemically active layer made of iron together with at least one metal selected from nickel, copper, cobalt, aluminum, and zinc.

[0017] International Patent Application Publication No. 01 / 28714A1 describes a cathode for chlor-alkali electrolysis comprising a conductive metal substrate and a first layer comprising a matrix and catalyst powder dispersed therein. The matrix comprises a platinum group metal oxide, or a mixture of a platinum group metal oxide and a valve metal oxide. The catalyst powder comprises support metal particles made of nickel, cobalt, iron, steel, stainless steel, or copper, coated with an electrocatalytic metal coating made of ruthenium, iridium, osmium, platinum, palladium, rhodium, or rhenium.

[0018] Among the various water electrolysis processes, the electrolysis of alkaline solutions is one of the best-known methods for hydrogen production, and indeed, it has advantages in terms of the suppleness, availability, and high purity of the hydrogen produced. However, in order to achieve widespread use, hydrogen production by the electrolysis of alkaline solutions requires energy improvements in terms of efficiency, safety, durability, reliability, and above all, reduction of equipment and operating costs.

[0019] From a process efficiency standpoint, low energy consumption, or in other words, reduced cell voltage, is essential for market competitiveness.

[0020] The aforementioned reduction in cell voltage can be largely achieved by using anodes and cathodes with catalytic coatings designed to facilitate the required electrochemical processes. These catalytic coatings play a crucial role in improving the efficiency of water electrolysis processes for hydrogen production, as they redirect the hydrogen and oxygen evolution reaction pathways to lower activation energies.

[0021] In particular, the coating of the anode is a crucial factor in achieving such voltage reduction.

[0022] Nickel-based substrates, materials stable in highly alkaline aqueous solutions, are typically used for anodes in aqueous solutions. However, electrodes made solely of nickel exhibit high potential, leading to problems with poor efficiency.

[0023] In the prior art, preferred anodes for the electrolysis of alkaline aqueous solutions include bare nickel electrodes, Raney nickel electrodes, and electrodes having a catalyst coating based on iridium oxide.

[0024] The bare nickel electrode is in the form of a mesh (expanded, stretched, perforated, etc.) and consists only of a nickel substrate. It can generally be manufactured at low cost and easily, but has a high overvoltage with respect to the oxygen reaction, resulting in a slow reaction kinetics. Electrodes with iridium-based catalyst coatings are produced by pyrolysis. However, iridium is one of the currently scarcest precious metals and as a result is expensive, and it is difficult to obtain it in the large quantities required for industrial-scale manufacturing processes. A further fundamental factor affecting the economic expediency of using electrodes activated with precious metal-based catalyst coatings relates to the operating life of the electrodes at high current densities.

[0025] Most precious metal-based catalyst coatings tend to suffer severe damage resulting from current reversals that can occur in the event of a malfunction in an industrial plant, and as a result the flow of cathode current, which is accompanied by an increase in the value of the electrode potential to a high value, may cause uncontrolled dissolution of the electrode. A partial solution to this problem has been obtained by the preparation of multilayer catalyst coatings comprising an intermediate layer applied directly to the Ni substrate and at least one active layer containing iridium. These compositions have proven to be sufficiently resistant under the normal operating conditions of the system. However, their durability is not optimal.

[0026] All this makes it clear that there is a need for a new anode coating composition for industrial electrolysis processes, characterized by a lower overall cost from the raw material point of view, excellent catalytic activity at high current densities, and very high durability and resistance to accidental current reversals under normal operating conditions, especially for electrolysis processes involving oxygen evolution at the anode.

[0027] The present invention aims to solve the above problems and is characterized by a low oxygen overvoltage and excellent resistance to repeated current reversals in the absence of an external partial electrode system when electrolysis is interrupted, combined with low cost, and relates to an anode. The present invention also relates to a method for manufacturing the same and an electrolytic cell containing the same.

Summary of the Invention

[0028] In the electrolysis process industry, the main driving force for competitiveness is sought in the reduction of the electrical voltage. The anode coating is a crucial element in achieving this reduction. However, all modifications that improve the electrical voltage frequently result in coatings that are much weaker against current reversals that may occur accidentally in the case of malfunctions in industrial plants.

[0029] An object of the present invention is to solve the above problems by providing an anode coating that gives high robustness to the electrode from the viewpoint of resistance to current reversals while maintaining a good cell voltage. <M

[0030] The present invention provides an electrode suitable for use as an anode for the generation of oxygen, including an electrode and particularly a metal substrate having a catalyst coating, wherein the catalyst coating includes at least an outer layer containing nickel and at least one element selected from iridium, iron, and calcium, and at least one inner layer disposed between the metal substrate and the outer layer.

[0031] One of the problems observed with respect to the electrode is the structural instability of the catalyst coating during the current reversal phase when an electrode suitable for use as an anode is subjected to a cathodic current. Constant and repeated current reversals cause progressive peeling of the catalyst coating, and the cell voltage gradually decays.

[0032] The inventors observed that the presence of an outer layer makes it possible to solve the aforementioned problem by protecting the underlying inner layer, and that its mechanical stability is improved under unfavorable operating conditions.

[0033] The outer layer has a thickness between 0.05 and 0.8 microns.

[0034] According to the present invention, the metal substrate can be any metal suitable for use as an electrode substrate for electrochemical processes, particularly as a metal substrate for an anode used in the electrolysis process of aqueous solutions. In this case, the most commonly used metal substrates can be selected from nickel, nickel alloys, iron, and iron alloys. The metal substrate is preferably a flat substrate, i.e., an overall flat component having two dimensions significantly larger than a third dimension. Preferably, the metal substrate is a mesh.

[0035] In a first embodiment, the present invention relates to an electrode for gas generation in an electrochemical process, comprising a metal substrate coated with a catalyst, wherein the catalyst coating comprises at least one outer layer containing nickel and iron, and at least one inner layer disposed between the metal substrate and the outer layer.

[0036] The presence of an outer layer containing nickel and iron has the advantage of significantly improving the electrode's tolerance to current reversal, surprisingly bringing the tolerance very close to that of electrodes activated with large amounts of precious metals.

[0037] To their surprise, the inventors observed that the outer layer containing nickel and iron provided mechanical protection to the matrix of the underlying catalyst layer and also compressed morphological defects in the inner layer.

[0038] The aforementioned morphological defects mainly stem from both the method of processing the substrate to which the catalyst coating is applied, and the method of applying the catalyst coating to the substrate itself.

[0039] In a preferred embodiment of the electrode according to the present invention, the outer layer contains iridium.

[0040] Accordingly, in a second embodiment, the present invention relates to an electrode for gas generation in an electrochemical process, comprising a metal substrate coated with a catalyst, wherein the catalyst coating comprises at least one outer layer containing nickel and iridium, and at least one inner layer disposed between the metal substrate and the outer layer.

[0041] The inventors observed that the presence of an outer layer containing nickel and iridium has the advantage of reducing the amount of noble metal in the underlying inner layer without sacrificing catalytic activity for the oxygen evolution reaction.

[0042] According to an alternative embodiment of the electrode according to the present invention, the outer layer contains calcium.

[0043] The outer layer, comprising nickel and at least one element selected from iridium, iron, and calcium, appears to act as a charge absorber during current reversal, and indeed, thanks to this function, the impact of charges on the catalyst layer is substantially reduced in terms of potential and therefore without sacrifice in energy consumption, making it possible to observe a significant reduction in the consumption of the components of the inner layer.

[0044] According to a further embodiment of the electrode, the coating includes a further outer layer containing nickel, iron, and calcium, which is applied on the outer layer containing nickel, iron, and / or calcium.

[0045] The inventors observed how the combination of the outer layer and the further outer layer is particularly efficient in protecting a metal substrate and an inner layer directly applied to the metal substrate, and how it is possible to obtain surprisingly improved performance in terms of resistance to inversion.

[0046] In a further embodiment, the inner layer comprises one or more metallic elements selected from the group consisting of cobalt, iridium, rhodium, nickel, platinum, lithium, strontium, calcium, and manganese.

[0047] In some embodiments, the coating includes an additional inner layer containing nickel deposited in direct contact with the substrate.

[0048] According to one embodiment of the electrode according to the present invention, the outer layer contains 40-60% nickel and 40-60% iron by elemental weight.

[0049] Preferably, the total amount of nickel and iron is at least 90% by weight on an elemental basis, more preferably at least 95% by weight of the outer layer, i.e., other elements are present in amounts of 10% by weight or less or 5% by weight or less. In one embodiment, the outer layer is essentially made of nickel and iron, i.e., the total amount of nickel and iron is essentially 100% by weight, and other elements are present in trace amounts of less than 1% by weight.

[0050] According to one embodiment of the electrode according to the present invention, the outer layer contains 50-95% nickel and 5-50% iridium by elemental weight.

[0051] Preferably, the total amount of nickel and iridium is at least 90% by weight on an elemental basis, more preferably at least 95% by weight in the outer layer, i.e., other elements are present in amounts of 10% by weight or less or 5% by weight or less. In one embodiment, the outer layer is essentially made of nickel and iridium, i.e., the total amount of nickel and iridium is essentially 100% by weight, and other elements are present in trace amounts of less than 1% by weight.

[0052] The inventors demonstrated that the presence of the outer layer makes it possible to obtain excellent catalytic activity for the oxygen evolution reaction even with a reduced amount of noble metal filling, thanks to the affinity of the elements present in the outer layer for the oxygen evolution reaction.

[0053] Experiments conducted by the inventors have shown that such a formulation, including the presence of at least one outer layer as described in the present invention, provides an improvement in oxygen overpotential and enables the realization of steady-state cell performance over a longer time compared to that generally observed with respect to other formulations. Furthermore, this type of formulation has been shown to confer several times greater resistance to current reversal than prior art formulations, and the specific filler amount of noble metals is substantially reduced.

[0054] According to one embodiment of the electrode according to the present invention, the further outer layer disposed on the outer layer contains, by elemental weight, 20-50% nickel, 20-50% iron, and 20-50% calcium.

[0055] It should be understood that elements present in the catalyst coating may be in metallic or oxide form. In the case of metal oxides, the concentration range given above refers to the metal.

[0056] In one embodiment, the outer layer is 1-15 g / m² 2 It has a total metal filling amount between [values]. The inventors found that the composition of the indicated weights can impart high catalytic activity combined with excellent resistance to current reversal.

[0057] In a further embodiment, the further outer layer is 3-20 g / m² 2 It has a total metal filling amount between the two.

[0058] In a further embodiment of the electrode according to the present invention, the metal substrate comprises one or more metals selected from the group consisting of nickel, nickel alloys, iron, and iron alloys. Preferred metal substrates are nickel, nickel alloys, or iron alloys.

[0059] The electrodes of the present invention can be used in several electrochemical applications. Due to their low oxygen overpotential, the electrodes of the present invention are preferably used as anodes for oxygen generation, and in particular as anodes in electrolytic cells for the electrolysis of aqueous solutions and alkaline water.

[0060] In a further embodiment, the present invention relates to a method for preparing electrodes for generating gaseous products in an electrolytic cell, for example, for generating oxygen in a cell for the electrolysis of an aqueous solution, the following: a) A step of applying a solution containing the precursor of the inner layer to a metal substrate, followed by drying at 50-100°C and thermal decomposition at 450-600°C for a period of 5-30 minutes, b) A process of repeating step a) until the desired filling amount is obtained, c) Applying a solution containing the precursor of the outer layer, followed by drying at 50-100°C and thermal decomposition at 450-600°C for 5-30 minutes, d) A process of repeating step c) until the desired filling amount is obtained. Regarding methods including

[0061] A further embodiment comprising a further step, which precedes step a), in which a solution containing the precursor of the further inner layer in direct contact with the substrate is applied, followed by drying at 50-100°C and thermal decomposition at 450-600°C for a period of 5-30 minutes until the desired filling amount is obtained.

[0062] A further embodiment comprising a further step following step d), which involves applying a solution containing the precursor of the further outer layer, followed by drying at 50-100°C and thermal decomposition at 450-600°C for a period of 5-30 minutes until the desired filling amount is obtained.

[0063] In one particular embodiment, the drying process is carried out at a temperature of 50-60°C. In other embodiments, the drying process is carried out at a temperature of 70-90°C, preferably around 80°C.

[0064] The application of the above precursor solution is carried out by brush application, spraying, immersion, or other known techniques.

[0065] The precursor of the solution containing the precursors of the outer layer and the further outer layer can be selected from the group consisting of metal nitrates, nitrosyl nitrates, and mixtures thereof.

[0066] The inventors observed that the use of the specified precursor under the described preparation conditions is favorable for the formation of a tight outer layer that can protect the underlying inner layer.

[0067] The precursor of the solution containing the precursors of the inner layer and the further inner layer is a compound selected from the group consisting of metal chlorides, nitrates, nitrosyl nitrates, and mixtures thereof.

[0068] In a further aspect, the present invention relates to a cell for electrolysis of an aqueous solution, comprising an anode compartment and a cathode compartment separated by an ion exchange membrane or a diaphragm, wherein the anode compartment is equipped with an electrode according to any one of the above-described forms used as an anode for oxygen generation.

[0069] In a further embodiment, the present invention relates to an electrolytic cell for the production of hydrogen by electrolysis of an aqueous solution, comprising a modular arrangement of electrolytic cells having anode and cathode compartments separated by an ion exchange membrane or a diaphragm, wherein the anode compartment is equipped with an electrode according to any one of the embodiments described above.

[0070] In a further aspect, the present invention relates to a cell for electrolysis of an alkaline solution, comprising an anode compartment and a cathode compartment separated by an ion exchange membrane or diaphragm, wherein the anode compartment is equipped with an electrode according to any one of the above-described forms used as an anode for oxygen generation.

[0071] In a further aspect, the present invention relates to an electrolytic cell for the production of hydrogen and oxygen starting from an alkaline solution, comprising a modular arrangement of an electrolytic cell having anode and cathode compartments separated by an ion exchange membrane or a diaphragm, wherein the anode compartment includes an electrode according to any one of the above-described forms used as an anode.

[0072] The following examples are included to demonstrate specific embodiments of the present invention, and their feasibility has been broadly verified within the scope of the claimed values. It will be apparent to those skilled in the art that the compositions and techniques described in the following examples correspond to compositions and techniques that the inventors have found to be effective in the practice of the present invention; however, those skilled in the art will also recognize that various modifications to the various embodiments described can be made in light of this disclosure, still yielding the same or similar results without departing from the scope of the present invention. [Examples]

[0073] Example 1 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0074] A second solution containing an iridium precursor, a nickel precursor, and a cobalt precursor was prepared.

[0075] A third solution containing nickel precursors and iron precursors was prepared.

[0076] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for approximately 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating. The inner layer in direct contact with the substrate was thus obtained.

[0077] Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The inner layer was thus obtained.

[0078] Next, the third solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The outer layer was thus obtained.

[0079] 10g / m 2 Repeat the procedure until the entire amount of metal filling in the outer layer is reached.

[0080] The electrode obtained in this manner was identified as sample E1.

[0081] Example 2 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0082] A second solution containing an iridium precursor, a nickel precursor, and a cobalt precursor was prepared.

[0083] A third solution containing nickel precursors and iridium precursors was prepared.

[0084] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for approximately 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating. The inner layer in direct contact with the substrate was thus obtained.

[0085] Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The inner layer was thus obtained.

[0086] Next, the third solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The outer layer was thus obtained.

[0087] 10g / m 2 Repeat the procedure until the entire amount of metal filling in the outer layer is reached.

[0088] The electrode obtained in this manner was identified as sample E2.

[0089] Example 3 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0090] A second solution containing an iridium precursor, a nickel precursor, and a lithium precursor was prepared.

[0091] A third solution containing nickel precursors and iron precursors was prepared.

[0092] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating. The inner layer in direct contact with the substrate was thus obtained. Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The inner layer was thus obtained.

[0093] Next, the third solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The outer layer was thus obtained.

[0094] 10g / m 2 Repeat the procedure until the entire amount of metal filling in the outer layer is reached.

[0095] The electrode obtained in this manner was identified as sample E3.

[0096] Example 4 A first solution containing an iridium precursor, a nickel precursor, and a lithium precursor was prepared.

[0097] A second solution containing nickel and iron precursors was prepared.

[0098] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating. The inner layer was thus obtained.

[0099] Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The outer layer was thus obtained.

[0100] 10g / m 2 Repeat the procedure until the entire amount of metal filling in the outer layer is reached.

[0101] The electrode obtained in this manner was identified as sample E4.

[0102] Example 5 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0103] A second solution containing an iridium precursor, a nickel precursor, and a lithium precursor was prepared.

[0104] A third solution containing nickel precursors and iron precursors was prepared.

[0105] A fourth solution containing a nickel precursor, an iron precursor, and a calcium precursor was prepared.

[0106] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating. The inner layer in direct contact with the substrate was thus obtained. Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The inner layer was thus obtained.

[0107] Next, the third solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. The outer layer was thus obtained.

[0108] Next, the fourth solution was applied by brush application. After each coating, drying was performed at 40-100°C for about 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled each time before applying the next coating. Further outer layers were obtained in this manner.

[0109] 15g / m 2 Repeat the procedure until the total amount of metal filling is reached in the further outer layers.

[0110] The electrode obtained in this manner was identified as sample E5.

[0111] Counterexample 1 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0112] A second solution containing an iridium precursor, a nickel precursor, and a lithium precursor was prepared.

[0113] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for approximately 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating.

[0114] Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for approximately 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating each time.

[0115] The electrodes obtained in this manner were identified as the CE1 sample.

[0116] Counterexample 2 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0117] A second solution containing an iridium precursor, a nickel precursor, and a cobalt precursor was prepared.

[0118] The first solution was applied to the nickel mesh by brush application. Drying was performed at 40-100°C for approximately 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating.

[0119] Next, the second solution was applied by brush application. After each coating, drying was performed at 40-100°C for approximately 10 minutes, followed by heat treatment at 400-500°C. The mesh was air-cooled before applying the next coating each time.

[0120] The electrode thus obtained was identified as the CE2 sample.

[0121] Counterexample 3 A first solution containing a nickel precursor and a lithium precursor was prepared.

[0122] A second solution containing a nickel precursor and a cobalt precursor was prepared.

[0123] The first solution was applied to the nickel mesh by brush coating. Drying was carried out at 40 - 100 °C for about 10 minutes, followed by heat treatment at 400 - 500 °C. The mesh was air-cooled before applying the next coating.

[0124] Next, the second solution was applied by brush coating. After each coating, drying was carried out at 40 - 100 °C for about 10 minutes, followed by heat treatment at 400 - 500 °C. The mesh was air-cooled each time before applying the next coating. The electrode thus obtained was identified as the CE3 sample.

[0125] In a laboratory cell into which 25% KOH was fed at a temperature of 80 °C, the samples of the above-mentioned examples and counterexamples were subjected to an operation test under oxygen generation.

[0126] Table 1 reports the initial anode potential (not corrected with respect to the resistance drop value) measured at a current density of 10 kA / m, and the reported values indicate that the electrodes having the catalyst coating according to the present invention exhibit an equivalent anode overvoltage even if they are not improved compared to the catalyst coatings known in the art. 2 The lifetime of the catalyst layer was estimated using an accelerated life test in which current reversals were repeated. Table 2 shows the behavior of the electrodes after repeated current reversals. TIFF2026516967000001.tif98170

[0127] The lifetime of the catalyst layer was estimated using an accelerated life test in which current reversals were repeated. Table 2 shows the behavior of the electrodes after repeated current reversals.

[0128] 10 kA / m 2The difference in anode potential recorded after a series of current reversals, compared to the initial anode potential, measured against a standard hydrogen electrode (NHE) at the specified current density, is reported in millivolts (mV) in column 2 of Table 2. Column 2 of Table 2 shows the potential difference in millivolts (mV) compared to the standard hydrogen electrode (NHE). Column 3 shows the percentage of Nobel metal residue after these current reversals, measured by X-ray fluorescence (XRF) analysis. Nobel metal content measured before and after the reversal test. The reported values ​​indicate that the electrode with the catalyst coating according to the present invention has excellent resistance to current reversal. TIFF2026516967000002.tif71170

[0129] The foregoing description is not intended to limit the present invention, and the present invention can be used in different embodiments without departing from its purpose, the scope of which is uniquely defined by the appended claims.

[0130] In the description and claims of this application, the terms “comprises” and “contains,” and their variants such as “comprising” and “containing,” are not intended to exclude the presence of other elements, components, or additional process steps.

[0131] References to literature, records, materials, equipment, and articles are included solely for the purpose of providing context to the present invention; however, it should not be understood that any or all of these matters constitute general knowledge in the art relating to the present invention prior to the priority date of each claim attached to this application.

Claims

1. An electrode for gas generation in an electrochemical process, comprising a metal substrate and a catalytic coating, wherein the catalytic coating comprises at least one outer layer containing nickel and at least one element selected from iridium, iron, and calcium, and at least one inner layer disposed between the metal substrate and the outer layer.

2. The electrode according to claim 1, wherein the outer layer contains iron.

3. The electrode according to claim 1 or 2, wherein the outer layer contains iridium.

4. The electrode according to any one of claims 1 to 3, wherein the inner layer disposed between the metallic substrate and the outer layer comprises one or more metallic elements selected from the group consisting of cobalt, iridium, rhodium, nickel, platinum, lithium, strontium, calcium, and manganese.

5. The electrode according to any one of claims 1 to 4, further comprising a further inner layer in direct contact with a nickel-containing substrate.

6. The electrode according to any one of claims 1 to 5, wherein the outer layer contains 40-60% nickel and 40-60% iron by elemental weight.

7. The electrode according to any one of claims 1 to 6, wherein the outer layer contains 50 to 95% nickel and 5 to 50% iridium by elemental weight.

8. The electrode according to any one of claims 1 to 7, wherein the metal substrate comprises one or more metals selected from the group consisting of nickel, nickel alloys, iron, and iron alloys.

9. A method for manufacturing an electrode as defined in any one of claims 1 to 8, the following: a) A step of applying a solution containing the precursor of the inner layer to a metal substrate, followed by drying at 50 to 100°C, and then thermally decomposing at 450 to 600°C for a period of 5 to 30 minutes, b) A process of repeating step a) until the desired filling amount is obtained, c) A step of applying a solution containing the precursor of the outer layer, followed by drying at 50 to 100°C, and then thermally decomposing at 450 to 600°C for a time between 5 and 30 minutes, d) A process of repeating step c) until the desired filling amount is obtained. A method that includes this.

10. The method according to claim 9, comprising a further step of applying a solution containing the precursor of the further inner layer in direct contact with the substrate, prior to step a), followed by drying at 50 to 100°C and thermal decomposition at 450 to 600°C for 5 to 30 minutes until a desired filling amount is obtained.

11. The method according to claim 9 or 10, comprising a further step of applying a solution containing the precursor of the further outer layer, which follows step d), followed by drying at 50 to 100°C, and then thermally decomposing at 450 to 600°C for 5 to 30 minutes until a desired filling amount is obtained.

12. A cell for electrolysis of an aqueous solution comprising an anode compartment and a cathode compartment, wherein the anode compartment is equipped with an electrode according to any one of claims 1 to 8.

13. The cell for electrolysis according to claim 12, wherein the anode compartment and the cathode compartment are separated by a diaphragm or an ion exchange membrane.

14. An electrolytic cell for the production of hydrogen and oxygen starting from an alkaline solution, comprising a modular arrangement of cells as described in claim 13.

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