Electrode for the Electrochemical Generation of Hydrogen

Abstract

The present invention relates to electrodes, and in particular to electrodes suitable for use as cathodes for the generation of hydrogen in industrial electrolysis processes, equipped with a catalytic coating comprising an outer layer containing ruthenium and selenium, and to methods for making the same.

Description

Technical Field

[0001] The present invention relates to an electrode, in particular an electrode suitable for use as a cathode for the generation of hydrogen in industrial electrolysis processes, and a method for its preparation.

Background Art

[0002] In electrolysis process industries such as the electrolysis of alkaline brine for the simultaneous production of chlorine and alkali, and the process of water electrolysis for the production of hydrogen and oxygen, competitiveness is related to several factors, and the main factor is the reduction of energy consumption directly related to the current voltage of the whole process.

[0003] The above reduction of current voltage can be achieved by using an anode and a cathode having a catalyst coating designed to promote the necessary electrochemical process, as in the case of the generation of hydrogen, chlorine or oxygen.

[0004] For example, in the membrane process of electrolysis of alkaline brine, the overall voltage depends on factors related to the resistance drop and mass transport, the resistance of the ion exchange membrane and electrolyte, and the overvoltage of the anode and cathode, respectively related to the reactions of chlorine and hydrogen gas generation.

[0005] Although obtained using electrodes of chemically resistant materials, the cathode overvoltage lacking good catalytic activity, as in the case of carbon, has long been considered acceptable.

[0006] However, in certain cases, today's market demand is increasingly focused on obtaining high-concentration caustic products, which makes the use of carbon steel cathodes unrealistic due to obvious corrosion problems, and further attention has been paid to the research of catalyst coatings that can further reduce the overvoltage of the hydrogen generation reaction from the perspective of reducing energy consumption and the resulting costs.

[0007] Therefore, the use of activated electrodes with catalyst coatings that can reduce the cathodic overvoltage of hydrogen has become widespread. In the case of catalyst coatings based on ruthenium or platinum oxide, good results have been obtained, for example, by using metal substrates such as nickel, copper, or steel itself.

[0008] The use of activated electrodes with similar catalyst coatings has led to energy savings such as being able to compensate for the costs arising from the use of catalysts based on precious metals.

[0009] A further fundamental factor that affects the economic convenience of using electrodes activated with catalyst coatings based on precious metals relates to the operating life of the electrodes at high current densities.

[0010] However, most catalyst coatings based on precious metals tend to suffer severe damage as a result of current reversals that can occur in industrial plants when inefficient. As a result, switching to anodic current, which is accompanied by an increase in the value of the electrode potential, can cause uncontrolled dissolution of platinum or ruthenium oxide.

[0011] A partial solution to this problem has been obtained by adding elements of the rare earth group to the formulation of the catalyst coating. Cathodes with these coatings have proven to be sufficiently resistant under the normal operating conditions of the plant.

[0012] A further improvement in resistance to current reversal has been obtained by applying a catalyst coating consisting of a separate phase containing platinum, rhodium, and / or palladium to the metal substrate. However, this type of coating requires large amounts of platinum and rhodium in the catalyst phase, determining a rather high manufacturing cost.

[0013] Therefore, there is a need for a new cathode composition for industrial electrolysis processes, particularly for electrolysis processes involving cathodic hydrogen evolution, which is characterized by improved catalytic activity at high current densities, with a total cost equal to or lower than that of prior art formulations with respect to raw materials, and with a duration and resistance to accidental current reversals above normal operating conditions.

[0014] U.S. Patent No. 4,300,992 describes an electrode for hydrogen gas generation in an electrolysis process, comprising a metal substrate with a catalytic coating including an inner layer containing ruthenium and an outer layer of selenium. U.S. Patent No. 4,975,161 describes an electrode for hydrogen gas generation having a single catalytic coating containing ruthenium and selenium. U.S. Patent Application Publication No. 2014 / 008215 describes an electrode for hydrogen gas generation comprising a metal substrate with a catalytic coating made from a platinum layer followed by a layer containing ruthenium and praseodymium. U.S. Patent No. 3,990,957 describes an electrode for hydrogen gas generation comprising a metal substrate with a catalytic coating containing ruthenium and strontium.

[0015] The present invention aims to solve the above problems and relates to a cathode characterized by a low hydrogen overvoltage and excellent resistance to current reversals when electrolysis is interrupted. The present invention also relates to a method for manufacturing the same and an electrolysis apparatus containing the same.

Summary of the Invention

[0016] In the industry of electrolysis processes, a major driving factor for competitiveness is sought in the reduction of voltage. Cathode coatings are an important element for achieving such a voltage reduction, but all changes that bring about an improvement in voltage often result in a weaker coating against current reversals that can occur accidentally in the event of malfunction of an industrial plant.

[0017] The electrodes equipped with the catalyst coating described in the present invention solve the aforementioned problems by providing an improved cell voltage with respect to the state of the art and maintaining optimal robustness with respect to resistance to reversal.

[0018] Under a first aspect, the present invention relates to an electrode for gas generation in an electrochemical process comprising a metal substrate provided with a catalyst coating, said catalyst coating comprising an inner layer containing at least one element selected from the group of noble metals in the form of a metal or their oxides, and optionally one or more elements selected from the group of rare earths and / or elements selected from the group of alkaline earth metals in the form of a metal or their oxides, and an outer layer containing 80 to 99.5% by weight of ruthenium and 0.5 to 20% by weight of selenium with respect to the element of said metal in the form of a metal or their oxides.

[0019] The use of selenium makes it possible to significantly reduce the hydrogen cathode overvoltage and reach in a short time a stable cell voltage value comparable to that obtained by the use of a catalyst composition containing a much larger amount of noble metals. The use of ruthenium in the outer layer improves the resistance of the coating to current reversal.

[0020] Compositions such as those described in the present invention further make it possible to obtain an excellent robustness of the cathode coating with respect to shutdown events, equal to the best obtained with a large amount of ruthenium stabilized due to the presence of rare earths in the catalyst coating.

[0021] According to the present invention, the metal substrate can be any metal suitable for use as an electrode support for an electrochemical process. In particular, it is used in chlor-alkali electrolysis and water electrolysis processes as a metal substrate for the cathode. In this case, the most commonly used metal substrates can be selected from nickel, nickel alloys, copper and steel.

[0022] According to one embodiment of the electrode according to the present invention, said at least one element selected from the group of noble metals of said inner layer is platinum and / or ruthenium.

[0023] According to one embodiment of the electrode according to the present invention, the inner layer of the catalyst coating contains ruthenium in an amount of 60 to 100% by weight and a metal selected from the group of rare earths in an amount of 0 to 40% by weight.

[0024] The presence of one or more elements belonging to the group of rare earths has the purpose of stabilizing the noble metal matrix and making it more resistant to current reversals that can occur in the electrolyzer during uncontrolled shutdown events.

[0025] According to one embodiment of the electrode according to the present invention, the outer layer of the catalyst coating contains ruthenium in an amount of 90 to 99.5% by weight and selenium in an amount of 0.5 to 10% by weight based on the metal.

[0026] The inventors have surprisingly observed that adding selenium, even in small amounts, to a catalyst coating mainly containing ruthenium results in unexpectedly improved performance with respect to the catalytic activity of the hydrogen generation reaction.

[0027] In a further embodiment, the outer layer of the catalyst coating has a composition containing ruthenium in an amount of 95 to 99.5% by weight and selenium in an amount of 0.5 to 5% by weight based on the above metal.

[0028] In yet another embodiment, the outer layer of the catalyst coating has a composition containing ruthenium in an amount of 90 to 99% by weight and selenium in an amount of 1 to 10% by weight based on the above metal.

[0029] Selenium constitutes an active component that plays a role in improving the overvoltage of the hydrogen generation reaction and enables a clear improvement in catalytic activity even when present in low concentrations.

[0030] Furthermore, the presence of selenium in a matrix mainly composed of ruthenium, in combination with the presence of a metal selected from the group of rare earths, has the advantage of extending the operating life of the electrode and enables a reduction in the consumption of the catalyst coating, expressed as a percentage of the amount of noble metal consumed.

[0031] According to a further embodiment, the present invention relates to an electrode in which the inner layer contains one or more elements selected from the group of rare earths, and the metal selected from the group of rare earths is praseodymium, cerium and / or lanthanum.

[0032] Experiments conducted by the present inventors have shown that praseodymium provides better results than other elements belonging to the group of rare earths, but the present invention can also be successfully implemented using cerium and / or lanthanum.

[0033] In one embodiment, the inner layer of the catalyst coating has a weight composition containing 60 to 90% ruthenium and 10 to 40% praseodymium based on the above metal, and the outer layer has a weight composition containing 80 to 99.5% ruthenium and 0.5 to 20% selenium based on the above metal.

[0034] The present inventors have found that the indicated weight composition can impart high catalytic activity in combination with excellent resistance to current reversal.

[0035] In a further embodiment, the inner layer of the catalyst coating contains ruthenium and at least one other element selected from the group of alkaline earth metals, particularly selected from strontium, calcium and barium. Experiments conducted by the present inventors have shown that this type of formulation provides further improvement in hydrogen overvoltage and also enables the achievement of steady-state cell performance in an improved time compared to what is generally observed with other formulations.

[0036] In one embodiment, the inner layer of the catalyst coating has a composition containing 90 to 99% by weight of ruthenium and a metal selected from the group of alkaline earth metals in an amount of 1 to 10% by weight based on the metal, and the outer layer has a composition containing 80 to 99.5% by weight of ruthenium and 0.5 to 20% by weight of selenium based on the metal.

[0037] In one embodiment, the catalyst coating further comprises an additional layer in direct contact with a metallic substrate comprising platinum and / or palladium in the form of a metal or their oxides. This can lead to a further improvement in the resistance of the electrode to current reversal and, surprisingly, is the same as or even better than that characterizing electrodes activated with only large amounts of platinum.

[0038] It should be understood that the elements present in the catalyst coating can be in the form of a metal or an oxide.

[0039] In a further embodiment, the catalyst coating has a ruthenium specific loading of 4 - 15 g / m 2 The inventors have found that for the catalyst coatings shown, a reduction in ruthenium loading is sufficient to confer good resistance to current reversal in combination with excellent catalytic activity not seen in the prior art for ruthenium-based catalyst coatings.

[0040] In a further embodiment of the electrode according to the invention, the preferred metallic substrate is nickel or a nickel alloy.

[0041] In a further aspect, the invention relates to a method for preparing an electrode for the generation of a gaseous product in an electrolysis cell, for example for hydrogen generation in an alkaline brine electrolysis or water electrolysis cell, the following steps, a) applying a solution containing a precursor of the components of the inner layer to the metallic substrate; b) optionally drying at 30 - 100 °C for 5 - 60 minutes; c) decomposing the solution containing the precursor of the components of the inner layer by heat treatment at 400 - 600 °C; d) optionally repeating steps a - c one or more times until the desired loading is reached; e) applying a solution containing a precursor of the components of the outer layer; f) optionally drying at 30 - 100 °C for 5 - 60 minutes; g) a step of decomposing the solution containing the precursor of the components of the outer layer by heat treatment at 400 to 600 °C; h) a step of optionally repeating steps e to g one or more times until a desired loading amount is reached; It includes.

[0042] In one embodiment, the solution containing the precursor of the components of the inner layer contains a precursor of an element selected from the group consisting of ruthenium and rare earths, and the solution containing the precursor of the components of the outer layer contains a precursor of ruthenium and selenium.

[0043] In a further embodiment, the solution containing the precursor of the components of the inner layer contains a precursor of ruthenium and praseodymium, and the solution containing the precursor of the components of the outer layer contains a precursor of ruthenium and selenium.

[0044] In one embodiment, the solution containing the precursor of the components of the inner layer contains a precursor of an element selected from the group consisting of ruthenium and alkaline earth metals, and the solution containing the precursor of the components of the outer layer contains a precursor of ruthenium and selenium.

[0045] According to one embodiment of the above method, the method includes, before step (a), a step of applying by directly contacting a metal substrate with a solution containing platinum, an optional drying step at 30 to 100 °C for a time consisting of 5 to 60 minutes, and a step of decomposing the solution containing platinum by heat treatment at 400 to 600 °C.

[0046] In a further aspect, the present invention relates to a cell for the electrolysis of an alkaline chloride solution comprising an anode compartment and a cathode compartment separated by an ion exchange membrane or diaphragm, wherein the cathode compartment is equipped with one of the above forms of electrodes used as a cathode for hydrogen generation.

[0047] Under a further aspect, the present invention relates to an electrolysis device for the production of chlorine and alkali starting from alkaline brine, comprising a modular arrangement of electrolysis cells having an anode and a cathode compartment separated by an ion exchange membrane or diaphragm, the cathode compartment comprising an electrode of one of the above-mentioned forms used as cathode.

[0048] Under a further aspect, the present invention relates to an electrolysis device for the production of hydrogen by electrolysis of water, comprising an anode compartment and a cathode compartment separated by a diaphragm, the cathode compartment being equipped with an electrode of one of the above-mentioned configurations.

[0049] The following examples are included to demonstrate certain embodiments of the invention, the utility of which has been extensively tested within the range of values ​​claimed. It will remain apparent to those skilled in the art that the compositions and techniques described in the following examples represent compositions and techniques that the inventors have found to work well in the practice of the invention, but those skilled in the art will also understand in light of this specification that various modifications can be made to the various embodiments described that will still produce the same or similar results without departing from the scope of the invention. EXAMPLES

[0050] Example 1 100mmx100mmx0.89mm 2 was subjected to the process of sandblasting with corundum, pickling in HCl and stress relief by heat treatment according to procedures known in the art.

[0051] A solution containing ruthenium and strontium precursors was prepared having a composition expressed as weight percent equal to 95% Ru and 5% Sr.

[0052] A second solution was prepared containing ruthenium and selenium precursors having a composition expressed as weight percent equal to 92% Ru and 8% Se.

[0053] The first solution was applied to the nickel mesh by brushing in 6 coats.

[0054] After each coating, it was dried at 40 - 60 °C for about 10 minutes and then heat - treated at 500 °C for 10 minutes. The mesh was air - cooled each time before applying the next coat.

[0055] 8 g / m 2 The procedure was repeated until the total Ru loading of 8 g / m was reached.

[0056] Subsequently, the second solution was applied by brushing in 6 coats. After each coating, it was dried at 40 - 60 °C for about 10 minutes and then heat - treated at 500 °C for 10 minutes. The mesh was air - cooled each time before applying the next coat.

[0057] 15 g / m 2 The procedure was repeated until the total Ru loading of 15 g / m was reached.

[0058] The resulting electrode was designated as sample E1.

[0059] Example 2 A nickel mesh having dimensions of 100 mm x 100 mm x 0.89 mm² was subjected to a process of sandblasting with corundum, pickling in HCl, and stress removal by heat treatment according to procedures known in the art.

[0060] A solution containing precursors of ruthenium and praseodymium having a composition expressed as equal weight percentages of 83% Ru and 17% Pr was prepared.

[0061] A second solution containing precursors of ruthenium and selenium having a composition expressed as equal weight percentages of 95% Ru and 5% Se was prepared.

[0062] The first solution was applied to the nickel mesh by brushing in 5 coats.

[0063] After each coating, it was dried at 40 - 60 °C for about 10 minutes and then heat - treated at 500 °C for 10 minutes. The mesh was air - cooled each time before applying the next coat.

[0064] 5 g / m 2 The procedure was repeated until the total Ru loading of 5 g / m was reached.

[0065] Subsequently, the second solution was applied by brushing in 6 coats. After each coating, it was dried at 40 - 60 °C for about 10 minutes and then heat - treated at 500 °C for 10 minutes. The mesh was air - cooled each time before applying the next coat.

[0066] 11 g / m 2 The procedure was repeated until the total Ru loading of 11 g / m was reached.

[0067] The resulting electrode was designated as sample E2.

[0068] Example 3 A nickel mesh with dimensions of 100 mm x 100 mm x 0.89 mm² was subjected to a process of sandblasting with corundum, pickling in HCl, and stress relief by heat treatment according to procedures known in the art.

[0069] A solution containing a precursor of ruthenium and praseodymium with a composition expressed as equal weight percentages of 84% Ru and 16% Pr was prepared.

[0070] A second solution containing a precursor of ruthenium and selenium with a composition expressed as equal weight percentages of 98.5% Ru and 1.5% Se was prepared.

[0071] The first solution was applied to the nickel mesh by brushing in 5 coats.

[0072] After each coating, it was dried at 40 - 60 °C for about 10 minutes and then heat - treated at 500 °C for 10 minutes. The mesh was air - cooled each time before applying the next coat.

[0073] 5 g / m 2 The procedure was repeated until the Ru loading reached

[0074] Subsequently, the second solution was applied by brushing in 5 coats. After drying at 40 - 60 °C for about 10 minutes after each coating, heat treatment was performed at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next coat.

[0075] 10.5 g / m 2 The procedure was repeated until the total Ru loading reached

[0076] The resulting electrode was designated as sample E3.

[0077] Counterexample 1 Nickel mesh with dimensions of 100 mm x 100 mm x 0.89 mm was subjected to a process of sandblasting with corundum, pickling in HCl, and stress removal by heat treatment according to procedures known in the art. 2

[0078] A 100 ml solution containing a precursor of ruthenium and praseodymium with a composition expressed as equal weight percentages of 83% Ru and 17% Pr was prepared.

[0079] Subsequently, the solution was applied to the nickel mesh by brushing in 8 coats.

[0080] After drying at 40 - 60 °C for about 10 minutes after each coating, heat treatment was performed at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next coat.

[0081] 11 g / m 2 The procedure was repeated until the total Ru loading reached

[0082] The resulting electrode was designated as sample CE1.

[0083] Counterexample 2 ​100mm x 100mm x 0.89mm 2 A nickel mesh with the dimensions of 2 was subjected to a process of sandblasting using corundum, pickling in HCl, and stress relief by heat treatment according to procedures known in the art.

[0084] A 100 ml solution containing precursors of ruthenium and strontium with a composition represented by a weight percentage equal to 97% Ru and 3% Sr was prepared.

[0085] The solution was then applied to the nickel mesh by brushing in 6 coats.

[0086] After each coating, it was dried at 40 - 60 °C for about 10 minutes and then heat - treated at 500 °C for 10 minutes. The mesh was air - cooled each time before applying the next coat.

[0087] 11 g / m 2 The procedure was repeated until the total Ru loading of 11 g / m 2 was reached.

[0088] The resulting electrode was designated as the CE2 sample.

[0089] The samples of the above - mentioned examples were subjected to a performance test under hydrogen evolution in an experimental cell supplied with 32% NaOH at a temperature of 90 °C, and several samples were subsequently subjected to a cyclic voltammetry test at a scan rate of 10 mV / s in the potential range of - 1 to +0.5 V / NHE.

[0090] Table 1 reports the initial cathode potential corrected for the resistance drop measured at a current density of 9 kA / m 2 Table 1: Table 1: TIFF0007690499000001.tif36170

[0091] Table 2 reports the... at a current density of 6 kA / m 2Report the initial cathode potential measured at a current density of Table 2: TIFF0007690499000002.tif36170

[0092] Table 3 shows the time to reach steady-state cell performance and the specific consumption of the electrodes, and is presented as a further indicator of the proportion of residual noble metal and resistance to current reversal. After 8000 hours of activity (HOL) at 8 kA / m 2 in 0.2 dm 2 Data were obtained using an experimental membrane cell with an active cathode area equal to. Tests were conducted at T = 89 °C using a 210 g / l NaCl anolyte and a 32 wt% NaOH catholyte. Table 3: TIFF0007690499000003.tif41170

[0093] The foregoing description is not intended to limit the present invention, which can be used according to different embodiments without departing from this purpose, and its scope is uniquely defined by the appended claims.

[0094] In the description and claims of this application, the terms "comprises", "contains", and their variants as "comprising" and "containing" are not intended to exclude the presence of other additional elements, components, or process steps.

[0095] The discussion of documents, documents, materials, devices, articles, etc. are included in the text only for the purpose of providing context to the present invention, but it is not understood that this matter or a part thereof constitutes general knowledge in the field related to the present invention prior to the priority date of each claim appended to this application.

Claims

1. An electrode for gas generation in an electrolytic method, comprising a metal substrate with a catalyst coating, wherein the catalyst coating comprises at least one element selected from the group of noble metals in the form of a metal or their oxides, and optionally one or more elements selected from the group of rare earths and / or elements selected from the group of alkaline earth metals in the form of a metal or their oxides, and an inner layer containing: an outer layer containing 80 to 99.5% by weight of ruthenium and 0.5 to 20% by weight of selenium based on the element of the metal.

2. The electrode according to claim 1, wherein the at least one element selected from the group of noble metals in the inner layer is platinum and / or ruthenium.

3. The electrode according to claim 1 or 2, wherein the outer layer contains 90 to 99% by weight of ruthenium and 1 to 10% by weight of selenium based on the element of the metal.

4. The electrode according to any one of claims 1 to 3, wherein the inner layer contains one or more elements selected from the group of rare earths, and the one or more elements selected from the group of rare earths in the inner layer are praseodymium, cerium and / or lanthanum.

5. The electrode according to any one of claims 1 to 3, wherein the inner layer contains ruthenium and an element selected from the group of alkaline earth metals.

6. The electrode according to any one of claims 1 to 5, wherein the catalyst coating comprises a further layer in direct contact with a metal substrate containing platinum and / or palladium in the form of a metal or their oxides.

7. The following steps: a. Applying a solution containing a precursor of the components of the inner layer to the metal substrate; b. Optionally, drying at 30 to 100 °C for 5 to 60 minutes; c. Decomposing the solution by heat treatment at 400 to 600 °C; d. Optionally, repeating steps a to c one or more times until the desired loading is reached; e. Applying a solution containing a precursor of the components of the outer layer; f. Optionally, drying at 30 to 100 °C for 5 to 60 minutes; g. Decomposing the solution by heat treatment at 400 to 600 °C; h. Optionally, repeating steps e to g one or more times until the desired loading is reached; A method for preparing an electrode according to any one of claims 1 to 6, comprising the steps of:

8. A cell for the electrolysis of an alkaline chloride solution, comprising an anode compartment and a cathode compartment separated by an ion exchange membrane or diaphragm, the cathode compartment being equipped with the electrode according to any one of claims 1 to 6.

9. An electrolysis apparatus for producing chlorine and alkali from an alkaline brine, comprising a modular arrangement of cells, each cell being the cell according to claim 8.

10. An electrolysis apparatus for the production of hydrogen by electrolysis of water, comprising an anode compartment and a cathode compartment separated by a diaphragm, the cathode compartment being equipped with the electrode according to any one of claims 1 to 6.

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