Electrode for electrolytic evolution of hydrogen

Abstract

The invention concerns an electrode for gas evolution in electrochemical processes and a method for its preparation, the electrode comprising a metal substrate provided with a single catalytic coating layer, wherein said catalytic coating layer consists essentially of a rare earth metal selected from praseodymium, cerium and lanthanum and noble metals selected from platinum and palladium, wherein the rare earth metal and the noble metals are present in a form of metals or oxides thereof, wherein said rare earth metal is present in an amount comprised between 20 and 80 wt.% of the total amount of metals in said catalytic coating layer, wherein said noble metals are present in an amount comprised between 20 and 80 wt.% of the total amount of metals in said catalytic coating layer, wherein said platinum is present in an amount comprised between 10 and 70 wt.% of the total amount of metals in said catalytic coating layer, wherein said palladium is present in an amount comprised between 10 and 70 wt.% of the total amount of metals in said catalytic coating, and wherein the catalytic coating layer has a total noble metal load comprised between 1 and 6 g / m2.

Description

[0001] INDUSTRIE DE NORA S.p.A.

[0002] 1

[0003] ELECTRODE FOR ELECTROLYTIC EVOLUTION OF HYDROGEN

[0004] SCOPE OF THE INVENTION

[0005] The invention concerns an electrode, preferably configured to be used as a cathode in the development of hydrogen in industrial electrolytic processes, and a method for its preparation.

[0006] BACKGROUND OF THE INVENTION

[0007] The invention concerns the preparation of a catalytic coating for electrodes used in electrolytic processes preferably for the production of hydrogen, applied on a metal substrate.

[0008] The use of hydrogen for energy production has experienced a considerable expansion in recent years, making the storage of this substance fundamental. In an increasingly widespread vision of an economy based on hydrogen as an energy carrier, the combination of water electrolysis with renewable energy is essential for sustainable hydrogen production, with a consequent reduction in carbon dioxide emissions.

[0009] Renewable energy sources, such as solar and wind ones, present programmability difficulties; in fact, it is difficult to foresee the delivery of energy over a defined period of time, and rarely does this delivery coincide with consumption demands. Therefore, it is necessary for these renewable energies to be integrated with a storage system for their effective use.

[0010] In sites where wind and solar energy is produced, excess electricity, not fed directly into the power grid, can be used to electrolyse water, producing hydrogen that can be stocked and stored for later use.

[0011] In the water electrolysis process, electric current is applied to split water into its components. The process consists of two semi-reactions: the oxygen evolution

[0012] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0013] 2 reaction, which takes place at the anode, and the hydrogen evolution reaction, which takes place at the cathode. The main challenge in implementing these semireactions is to overcome their slow kinetics. The kinetic complexities of these reactions require a surplus of cell voltage over their thermodynamic potential in order to achieve high process efficiency.

[0014] In many electrolysis processes, the cost for producing the desired product is significantly influenced by the cost of the materials used in the catalytic coatings applied on substrates serving as electrodes and their catalytic activity for the target reaction. In water electrolysis, noble metals such as rhodium, platinum and ruthenium have a low overpotential and excellent catalytic activity for the hydrogen evolution reaction. However, their scarcity and associated high costs limit their practical application on a large scale for the economical production of high purity hydrogen. Therefore, it is of fundamental importance to explore alternatives that use small amounts of noble metals and are characterized by lower costs.

[0015] In addition, due to the fluctuating and intermittent nature of renewable energies, water electrolysers must be adapted to a dynamic operation. In fact, numerous system start-up and shutdown cycles are possible, and power cutoff is often necessary due to technical problems. These factors cause polarity reversals that are harmful to the electrodes, negatively affecting their durability and accelerating their degradation.

[0016] Generally, these current reversals are avoided by using external polarization systems. However, in order to contain and reduce the costs of the entire process, the trend is to completely eliminate the use of such devices, with a consequent negative effect on the life of the electrodes.

[0017] Among the various water electrolysis processes, the electrolysis of alkaline solutions is one of the best known methods for the production of hydrogen. This method offers

[0018] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0019] 3 advantages in terms of flexibility, availability and high purity of the hydrogen produced. However, for widespread adoption, the production of hydrogen by electrolysis of alkaline solutions requires improvements in energy efficiency, safety, durability, reliability and, above all, a reduction in installation and operating costs.

[0020] As for the efficiency of the process, low energy consumption, which translates into a reduction in cell voltage, is fundamental to maintain competitiveness in the market. The reduction of such cell voltage can largely be achieved by using anodes and cathodes with catalytic coatings that facilitate the required electrochemical processes. Such catalytic coatings play a crucial role in improving the efficiency of the water electrolysis process for hydrogen production, as they divert the pathway of the hydrogen and oxygen evolution reactions towards a lower activation energy. In particular, the cathode coating is a key element to achieve this voltage reduction. Over the years, the use of activated electrodes with a catalytic coating capable of reducing the cathode overvoltage of hydrogen has increased. Good results were obtained using metal substrates such as nickel, copper and steel, provided with catalytic coatings based on rhodium, platinum and ruthenium oxides.

[0021] Most catalytic coatings based on noble metals tend to suffer serious damage as a result of current reversals, which can occur, among other things, in the event of malfunctions on the industrial plants. The passage of anodic current, with consequent raising of the electrode potential to high values, can cause the uncontrolled dissolution of noble metals, such as ruthenium.

[0022] A partial solution to these problems was obtained by adding rare earth group elements to the catalytic coating formulation. The cathodes with these coatings are sufficiently resistant under normal operating conditions of the plant, although they do not have an optimal durability.

[0023] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0024] 4

[0025] A further improvement of the resistance to current reversals was obtained by applying to the metal substrate a catalytic coating consisting of distinct phases, comprising platinum, rhodium and / or palladium. However, this type of coating requires high amounts of platinum and rhodium in the catalytic phase, resulting in a rather high production cost.

[0026] Furthermore, for plants operating at low current densities (e.g. operating at 4kA / m2), the cost of the cathode is a crucial factor for process economics. At these current densities, the efficiency and durability of the cathode take on an even greater importance, directly affecting the operating costs and economic sustainability of the plant. The use of an optimal amount of noble metal in the catalytic coating of the cathode not only improves the electrochemical performance, but also contributes to the sustainability of the process. A moderate use of noble metal allows for excellent results without excessive waste of expensive or rare materials, making the process more environmentally and economically sustainable.

[0027] A further factor that negatively affects the performance of the electrodes and consequently reduces the efficiency of the process is the presence of iron in solution, which can occur, especially in older plants where iron components are widespread. This can have negative effects on the performance of the electrodes such as the formation of deposits that can clog the active surfaces and reduce the efficiency of the process. In addition, iron can catalyse unwanted reactions that increase energy consumption and reduce component life.

[0028] The need therefore arises for a new catalytic coating composition for industrial electrolytic processes, in particular for processes with hydrogen cathode evolution, characterized by:

[0029] • Excellent catalytic activity.

[0030] • Significantly reduced overall cost in terms of raw materials.

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[0032] 5

[0033] • Durability and resistance superior to accidental current reversals compared to the usual operating conditions, even in the presence of pollutants such as iron.

[0034] Recent developments in the field of cathodes for hydrogen evolution, such as those disclosed in US 2024 / 360572, rely on a multilayer catalytic coating architecture. According to this prior art, the electrode comprises a first protective layer in direct contact with the metal substrate, said layer consisting essentially of platinum, and a second catalytic layer disposed thereon and comprising platinum, palladium and a rare earth metal. While the presence of the protective layer improves tolerance to current inversions, the application of two chemically different coating solutions requires additional processing steps and increases manufacturing complexity and costs. Furthermore, it would be desirable to lower noble-metal loadings even further. The present invention aims to solve the problems described above and concerns a cathode characterized by a low hydrogen overvoltage and a good resistance to repeated current reversals, even in the absence of external polarization systems, when the electrolysis is interrupted, combined with a low cost. The invention further concerns a method for producing the same and an electrolyser containing the same. SUMMARY OF THE INVENTION

[0035] The object of the present invention is an electrode provided with a catalytic coating that effectively solves the problems listed above, providing excellent cell voltage and long-lasting robustness even in the presence of pollutants. This catalytic coating is made by using an optimized amount of noble metal, lower than the state of the art, crucial to maintain the optimal performance of the electrolyser.

[0036] This result is achieved by using an electrode comprising a substrate and a catalytic coating layer comprising a rare earth metal, platinum and palladium at specific percentages.

[0037] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0038] 6

[0039] The optimization of the ratio between the rare earth metal, platinum and palladium allows a reduction of the noble metal load without penalty on efficiency and durability compared to coating with higher percentages of noble metal.

[0040] These and other objects and advantages of the invention will become apparent from the following detailed description.

[0041] DETAILED DESCRIPTION OF THE INVENTION

[0042] A first object of the invention therefore concerns an electrode for the development of gases in electrochemical processes comprising a metal substrate provided with a single catalytic coating layer, wherein said catalytic coating layer consists essentially of a rare earth metal selected from praseodymium, cerium and lanthanum and noble metals selected from platinum and palladium in the form of metals or oxides thereof, wherein said rare earth metal is present in an amount comprised between 20 and 80 wt.% (percent by weight) of the total amount of metals in said catalytic coating layer, wherein said noble metals are present in an amount comprised between 20 and 80 wt.% of the total amount of metals in said catalytic coating layer, wherein said platinum is present in an amount comprised between 10 and 70 wt.% of the total amount of metals in said catalytic coating layer, wherein said palladium is present in an amount comprised between 10 and 70 wt.% of the total amount of metals in said catalytic coating layer, characterized in that the catalytic coating layer has a total noble metal load comprised between 1 and 6 g / m2In the context of the present invention, the expression “consisting essentially of” is intended to mean that the catalytic coating layer contains the recited metals as its essential constituents, while permitting the presence of other components only in amounts that do not materially affect the catalytic activity, overvoltage performance,

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[0044] 7 or resistance to current inversion of the electrode. Such additional components, if present, are limited to unavoidable impurities or trace amounts of other metals or oxides arising from precursor salts or processing conditions, typically in a total amount of not more than 5 wt.%, preferably not more than 1 wt.% referred to the total metal content of the coating layer.

[0045] For the purposes of this discussion, the term “comprise” or “include” also includes the term “consist of” or “consist essentially of”.

[0046] For the purposes of the present invention the definitions of the ranges always comprise the extreme values unless otherwise specified. Specifically, as used herein, the term “comprised between” denotes a closed interval and therefore includes the lower and upper boundary values unless expressly stated otherwise.

[0047] As used herein, the expression “single coating layer” denotes a catalytic coating that is structurally continuous and compositionally homogeneous across its thickness, and that is formed directly on the metal substrate without any intermediate protective, adhesion-promoting or catalytic sub-layers. A single coating layer may be produced by depositing one or more successive coats of the same coating solution, each coat being subjected to drying and thermal treatment, provided that the resulting coating forms a single continuous layer rather than distinct layers of different composition. Multiple coats therefore contribute jointly to one and the same catalytic layer and do not constitute separate coating layers.

[0048] Therefore, in one embodiment of the invention, the single catalytic coating layer is formed directly on the metal substrate, without any intermediate protective or adhesion-promoting layer.

[0049] Preferably, the entire catalytic coating layer is obtained by the deposition and thermal treatment of a single coating solution. The same solution is applied for each

[0050] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0051] 8 coat, and the sequence of deposition, optional drying and thermal treatment may be repeated as required to obtain the desired total noble-metal loading. Using a single coating solution ensures that the catalytic coating layer is compositionally homogeneous throughout its thickness, in contrast to multilayer systems derived from different coating compositions. This homogeneous structure improves coating integrity, reduces the likelihood of interfacial degradation under demanding electrochemical conditions, and simplifies the overall manufacturing process by avoiding the need for distinct protective and catalytic layers.

[0052] In a particularly preferred embodiment, the single catalytic coating layer has a total noble-metal load between 1 and 4 g / m2, more preferably between 1 and less than 2.5 g / m2. The inventors have found that the indicated weight compositions are able to impart a good catalytic activity combined with a good resistance to the current reversals. The ability to achieve high performance at such reduced noble-metal loadings provides a substantial economic advantage and is believed to result from the homogeneous distribution of platinum, palladium and the rare earth metal within the single coating layer. This uniform structure avoids the inefficiencies inherent in multilayer coatings and allows more effective utilisation of the noble metals present. Preferably, said rare earth metal is present in an amount comprised between 30 and 70 wt.% of total metals and said noble metal is present in an amount comprised between 30 and 70 wt.% of total metals.

[0053] According to one embodiment of the electrode said platinum is present in an amount comprised between 15 and 55 wt.% of total metals and said palladium is present in an amount comprised between 15 and 55 wt.% of total metals.

[0054] It is to be understood that the elements present in the catalytic coating layer can be in the form of metal or in the form of oxides.

[0055] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0056] 9

[0057] The presence of a rare earth metal is aimed at stabilizing the noble metal matrix, making it more resistant to current reversals that can occur in electrolysers during uncontrolled stop events.

[0058] As mentioned, the optimization of the ratio between the rare earth metal, platinum and palladium allows a reduction of the noble metal load without penalty on efficiency and durability compared to coating with higher percentages of noble metal.

[0059] According to a further embodiment, the invention relates to an electrode wherein said rare earth metal is praseodymium, cerium or lanthanum.

[0060] The experimentation conducted by the inventors has pointed out that praseodymium provides better results than the other elements belonging to the rare earth group, but the invention is also successfully practicable with cerium and / or lanthanum.

[0061] Without wishing to limit the invention to a particular theory, the role of rare earths in general, and praseodymium in particular, appears to be to create a peculiar morphology that optimizes electrode performance. This morphology increases the active surface of the electrode, providing more active sites for the electrochemical reactions and improving energy efficiency. In addition, an even distribution of the electric current on the electrode surface improves the overall operational efficiency. The morphology is characterized by a highly porous and finely distributed microstructure, which significantly enlarges the active surface area and provides a greater density of electrochemically active sites. It further improves grain uniformity and prevents agglomeration.

[0062] The optimized morphology of the electrode of the present invention also reduces the overvoltage needed to initiate electrochemical reactions, further contributing to energy efficiency. Moreover, such well-designed morphology can mitigate the

[0063] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0064] 10 impact of pollutants, such as iron, that may be present in the electrolyte solutions, keeping the electrode performance stable over time.

[0065] This peculiar morphology not only reduces the impact of the operational stops, but also acts as an area promoter, improving the robustness and durability of the cathode. The combination of these factors makes the electrode more efficient, robust and sustainable, helping to reduce the operating costs and the environmental impact of the electrolysis process.

[0066] In a further embodiment the catalytic coating layer has a total platinum load comprised between 1 and 3.5 g / m2The inventors have found that, in the case of the indicated catalytic coating, reduced loads of platinum are more than sufficient to impart a good resistance to current reversals combined with an excellent catalytic activity not found in the known art of the catalytic coatings based on high amounts of noble metals.

[0067] In addition, platinum can tolerate the presence of pollutants such as iron; therefore, the catalytic composition of the present invention is particularly suitable even in the presence of iron in solution, which can occur, especially in older plants where iron components are widespread.

[0068] The presence of iron can affect electrode performance by deposition on the electrode itself. This deposition can reduce the active surface area of the electrode, leading to an increase in current density and an increased electrical consumption and a consequent reduction in process efficiency.

[0069] In addition, iron can catalyse unwanted reactions that increase energy consumption and reduce component life.

[0070] In a further embodiment of the electrode according to the invention, the preferred metal substrate is nickel or nickel alloy.

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[0072] 11

[0073] The electrode of the present invention may be employed in a variety of electrochemical applications. Due to its low hydrogen overvoltage value, the electrode of the present invention is preferably used as a cathode for hydrogen evolution, in particular as a cathode in an electrolysis cell for alkaline water electrolysis.

[0074] In a further aspect, the present invention relates to a method for the preparation of an electrode for evolution of gaseous products in electrolytic cells, for example for hydrogen evolution in alkaline brine electrolysis or water electrolysis cells, comprising the following steps:

[0075] (a) applying a catalytic coating solution comprising precursors of platinum, palladium and a rare earth metal selected from praseodymium, cerium and lanthanum to a substrate, thus obtaining a coated substrate;

[0076] (b) optionally drying said coated substrate at a temperature comprised between 30 and 100 °C for a time comprised between 2 and 60 minutes;

[0077] (c) baking said coated substrate at a temperature comprised between 400 and 600 °C;

[0078] (d) optionally repeating steps a), b) and c) until a catalytic coating layer having a total noble metal load comprised between 1 and 6 g / m2is formed.

[0079] According to an embodiment of the above method, said method comprises an initial treatment step prior to step (a) comprising a heat treatment of said metal substrate for a time of not less than 15 minutes and at a temperature of not less than 400 °C. The aforesaid application of said precursor solution may be performed by brushing, spraying, dipping or other known technique.

[0080] The precursors of said solution may be selected from the group consisting of chlorides, nitrates and nitrosyl nitrates of metals and mixtures or organoacetic

[0081] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0082] 12 complexes thereof, preferably selected from a group consisting of hydroxyacetate acetate, chloroacetate and nitric acetate complex.

[0083] The inventors have observed that the use of the specified precursors, under the adopted preparation conditions, favours the formation of catalysts with a particularly ordered crystalline lattice, with a positive impact in terms of activity, durability and resistance to the current reversals.

[0084] In a further aspect, the invention relates to a cell for the electrolysis of water comprising an anode compartment and a cathode compartment, separated by an ion exchange membrane or a diaphragm where the cathode compartment is equipped with an electrode in one of the forms as described above used as a cathode for hydrogen evolution.

[0085] In a further aspect, the invention relates to an electrolyser for the production of hydrogen by electrolysis of water comprising an anode compartment and a cathode compartment separated by an ion exchange membrane or a diaphragm wherein the cathode compartment is equipped with an electrode in one of the forms as described above.

[0086] In a further aspect, the invention relates to a cell for the electrolysis of alkaline solutions comprising an anode compartment and a cathode compartment, separated by a diaphragm wherein the cathode compartment is equipped with an electrode in one of the forms as described above used as a cathode for hydrogen evolution.

[0087] In a further aspect, the invention relates to an electrolyser for the production of hydrogen and oxygen from alkaline solutions comprising a modular arrangement of electrolytic cells with the anode and cathode compartments separated by ion exchange membranes or diaphragms, wherein the cathode compartment comprises an electrode in one of the forms as described above used as a cathode.

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[0089] 13

[0090] In a further aspect, the invention relates to a cell for the electrolysis of alkali chloride solutions comprising an anode compartment and a cathode compartment, separated by an ion exchange membrane or a diaphragm where the cathode compartment is equipped with an electrode in one of the forms as described above used as a cathode for hydrogen evolution.

[0091] In a further aspect, the invention relates to an electrolyser for the production of chlorine and alkalis from alkaline brine comprising a modular arrangement of electrolytic cells with the anode and cathode compartments separated by ion exchange membranes or diaphragms, wherein the cathode compartment comprises an electrode in one of the forms as described above used as a cathode.

[0092] The following examples are included to demonstrate particular embodiments of the invention, the practicability of which has been extensively verified in the claimed range of values. It will be apparent to the person skilled in the art that the compositions and techniques described in the examples which follow represent compositions and techniques of which the inventors have found good performance in the practice of the invention; however, the person skilled in the art will also appreciate that in light of the present disclosure, various changes may be made to the various embodiments described still resulting in identical or similar results without departing from the scope of the invention.

[0093] EXAMPLE 1

[0094] A nickel mesh measuring 100 mm x 100 mm x 0.89 mm was subjected to a sandblasting process with corundum, pickling in HCI according to a procedure known in the art.

[0095] A solution containing platinum, palladium and praseodymium precursors was prepared having a composition expressed as a percentage by weight equal to 39 wt.% Pt, 25 wt.% Pd and 36 wt.% Pr of total metals.

[0096] M / 66036-PCT (415PCT) INDUSTRIE DE NORA S.p.A.

[0097] 14

[0098] The solution was applied to the nickel mesh by brushing in 4 coats. After each coat, drying at 40-80 °C for about 10 minutes, then a heat treatment at 500 °C were carried out. The mesh was air-cooled each time before the next coat was applied.

[0099] The procedure was repeated until a total noble metal load equal to 2.7 g / m2was reached.

[0100] The electrode thus obtained was identified as sample E1 .

[0101] EXAMPLE 2

[0102] A nickel mesh measuring 100 mm x 100 mm x 0.89 mm was subjected to a sandblasting process with corundum, pickling in HCI according to a procedure known in the art.

[0103] A solution containing platinum, palladium and praseodymium precursors was prepared having a composition expressed as a percentage by weight equal to 46 wt.% Pt, 29 wt.% Pd and 25 wt.% Pr of total metals.

[0104] The solution was applied to the nickel mesh by brushing in 3 coats. After each coat, drying at 40-80 °C for about 10 minutes, then a heat treatment at 500 °C were carried out. The mesh was air-cooled each time before the next coat was applied.

[0105] The procedure was repeated until a total noble metal load equal to 2.2 g / m2was reached.

[0106] The electrode thus obtained was identified as sample E2.

[0107] EXAMPLE 3

[0108] A nickel mesh measuring 100 mm x 100 mm x 0.89 mm was subjected to a sandblasting process with corundum, pickling in HCI according to a procedure known in the art.

[0109] A solution containing platinum, palladium and praseodymium precursors was prepared having a composition expressed as a percentage by weight equal to 25 wt.% Pt, 17 wt.% Pd and 58 wt.% Pr of total metals.

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[0111] 15

[0112] The solution was applied to the nickel mesh by brushing in 4 coats. After each coat, drying at 40-80 °C for about 10 minutes, then a heat treatment at 500 °C were carried out. The mesh was air-cooled each time before the next coat was applied.

[0113] The procedure was repeated until a total noble metal load equal to 3 g / m2was reached.

[0114] The electrode thus obtained was identified as sample E3.

[0115] COUNTER-EXAMPLE 1

[0116] A nickel mesh measuring 100 mm x 100 mm x 0.89 mm was subjected to a sandblasting process with corundum, pickling in HCI according to a procedure known in the art.

[0117] A solution containing platinum precursor was prepared.

[0118] A second solution containing ruthenium and praseodymium precursors was also prepared having a composition expressed as a percentage by weight equal to 75 wt.% Ru and 25 wt. % Pr of total metals.

[0119] The first solution was applied to the nickel mesh by brushing in one coat. Drying at 40-80 °C for about 10 minutes, then a heat treatment at 500 °C were carried out. The mesh was air-cooled before the next coat was applied.

[0120] Subsequently, the second solution was applied by brushing in 7 coats. After each coat, drying at 40-80 °C for about 10 minutes, then a heat treatment at 500 °C were carried out. The mesh was air-cooled each time before the next coat was applied.

[0121] The procedure was repeated until a total noble metal load equal to 9 g / m2was reached.

[0122] The electrode thus obtained was identified as sample CE1 .

[0123] COUNTER-EXAMPLE 2

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[0125] 16

[0126] A nickel mesh measuring 100 mm x 100 mm x 0.89 mm was subjected to a sandblasting process with corundum, pickling in HCI according to a procedure known in the art.

[0127] No additional coating was added.

[0128] The electrode thus obtained was identified as sample CE2.

[0129] Characterisation studies

[0130] The following characterisation studies were conducted on the samples of the examples and of the comparative examples.

[0131] The samples of the examples described above were subjected to functional tests, under hydrogen evolution, in a laboratory cell fed with 32% NaOH at a temperature of 90 °C, in addition some samples were subsequently subjected to cyclic voltammetry tests in the potential range from -1 to +0.5 V / NHE.

[0132] Table 1 reports the initial cathode potential (corrected by the ohmic drop value) measured at a current density of 4 kA / m2; the reported values indicate that electrodes with a catalytic coating layer according to the present invention exhibit a comparable, if not improved, cathode overvoltage with respect to catalytic coatings known in the art.

[0133] TABLE 1 :

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[0135] 17

[0136] The tolerance of the electrodes to the presence of iron in solution was measured in a KOH solution containing 9 ppm of iron at a temperature above 80 °C.

[0137] Table 2 reports the cathode potential (corrected by the ohmic drop value) measured at a current density of 4 kA / m2; the values reported indicate that electrodes with a catalytic coating according to the present invention have an improved high tolerance to the presence of iron, with respect to that of the catalytic coatings known in the art. TABLE 2:

[0138] The above description is not intended to limit the invention, which can be used according to different embodiments without thereby departing from the purposes and whose scope is unequivocally defined by the appended claims.

[0139] Discussion of documents, acts, materials, apparatuses, articles and the like is included in the text for the sole purpose of providing context to the present invention; it is not to be understood, however, that this subject matter or part thereof constituted general knowledge in the field relating to the invention prior to the priority date of each of the claims appended to the present application.

[0140] M / 66036-PCT (415PCT)

Claims

INDUSTRIE DE NORA S.p.A.18CLAIMS1 . Electrode for gas evolution in electrochemical processes comprising a metal substrate provided with a single catalytic coating layer, wherein said catalytic coating layer consists essentially of a rare earth metal selected from praseodymium, cerium and lanthanum and noble metals selected from platinum and palladium, wherein the rare earth metal and the noble metals are present in a form of metals or oxides thereof, wherein said rare earth metal is present in an amount comprised between 20 and 80 wt.% of the total amount of metals in said catalytic coating layer, wherein said noble metals are present in an amount comprised between 20 and 80 wt.% of the total amount of metals in said catalytic coating layer, wherein said platinum is present in an amount comprised between 10 and 70 wt.% of the total amount of metals in said catalytic coating layer, wherein said palladium is present in an amount comprised between 10 and 70 wt.% of the total amount of metals in said catalytic coating, and wherein the catalytic coating layer has a total noble metal load comprised between 1 and 6 g / m22. Electrode according to claim 1 , wherein said catalytic coating layer is formed directly on said metal substrate in one or more coats.

3. Electrode according to any one of claims 1 or 2, wherein said coating layer is obtained by, optionally repeated, deposition and thermal treatment of a single coating solution.

4. Electrode according to any one of claims 1 to 3, wherein said total noble metal load is comprised between 1 and 4 g / m2, preferably between 1 and 4 g / m2, and more preferably between 1 and less than 2.5 g / m2.M / 66036-PCT (415PCT)INDUSTRIE DE NORA S.p.A.

195. Electrode according to any one of claims 1 to 4 wherein said rare earth metal is present in an amount comprised between 30 and 70 wt.% of total metals and said noble metals are present in an amount comprised between 30 and 70% of total metals.

6. Electrode according to claim 5 wherein said platinum is present in an amount comprised between 15 and 55 wt.% of total metals and said palladium is present in an amount comprised between 15 and 55 wt.% of total metals.

7. Electrode according to any one of the preceding claims wherein said rare earth metal is praseodymium.

8. Method for the preparation of an electrode according to any one of the preceding claims, said method comprising the steps of: a) applying a catalytic coating solution comprising precursors of platinum, palladium and the rare earth metal selected from praseodymium, cerium and lanthanum to a metal substrate, thus obtaining a coated substrate; b) optionally drying said coated substrate at a temperature comprised between 30 and 100°C for a time comprised between 2 and 60 minutes; c) baking said coated substrate at a temperature comprised between 400 and 600°C, d) optionally repeating steps a), b) and c) until a catalytic coating layer having a total noble metal load comprised between 1 and 6 g / m2is formed.

9. Method according to claim 8, wherein said rare earth metal is praseodymium.

10. Method according to any one of claims 8 or 9, wherein said precursors of platinum, palladium and rare earth metal are organoacetic complexes, preferably selected from a group consisting of hydroxyacetate, acetate, chloro acetate and nitric acetate complex.11 . Cell for the electrolysis processes comprising an anodic compartment and a cathodic compartment separated by an ion exchange membrane or a diaphragmM / 66036-PCT (415PCT)INDUSTRIE DE NORA S.p.A.20 where the cathodic compartment is equipped with an electrode according to any one of claims 1 to 7.

12. Electrolyser comprising a modular arrangement of cells, wherein each cell of the cells is a cell according to claim 11 .

13. Use of the cell of claim 11 for the production of hydrogen by electrolysis of water or for the production of chlorine and alkali by electrolysis of alkaline brine.

14. Use of the electrolyser of claim 12 for the production of hydrogen by electrolysis of water or for the production of chlorine and alkali by electrolysis of alkaline brine.M / 66036-PCT (415PCT)

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