Electrode for the Electrochemical Generation of Hydrogen

Abstract

The present invention relates to an electrode comprising a catalytic coating containing ruthenium and at least one other element selected from the group of alkaline earth metals, suitable for use in industrial electrochemical processes for hydrogen generation, and to a method for producing the electrode, the catalytic coating comprising 93-99 wt-% ruthenium and 1-7 wt-% alkaline earth metal, based on total metals.

Description

Technical Field

[0001] The present invention relates to an electrode suitable for use in an industrial electrochemical process for hydrogen generation, and a method for manufacturing the same.

Background Art

[0002] The present invention relates to an electrode suitable for use in an electrolysis process, particularly a cathode suitable for hydrogen generation in an industrial electrolysis process. The electrolysis of alkaline brine for the simultaneous production of chlorine and alkali, as well as the electrolysis process of water, are the most typical examples of industrial electrolysis applications involving the generation of hydrogen at the cathode, but the electrode is not limited to specific uses.

[0003] In the industry of electrolysis processes such as those described above, competitiveness is related to several factors, the main of which is the reduction of energy consumption, which is directly related to the voltage of the global process.

[0004] In the membrane process of alkaline brine electrolysis, for example, the global voltage is determined by the resistance drop and factors related to mass transport, the resistance of the ion exchange membrane and electrolyte, and the overvoltage of the chlorine and hydrogen gas generation reactions.

[0005] In industrial practice, these overvoltages are minimized and controlled by the use of a suitable catalyst applied on the electrode where the electrochemical reaction occurs. For this purpose, for example, it is possible to use a cathode made of a metal substrate such as nickel, nickel alloy, copper, or steel, provided with a catalyst coating based on ruthenium dioxide.

[0006] This type of cathode is generally characterized by excellent cathode overvoltage. However, they have a limited lifespan, probably due to poor adhesion of the coating to the substrate. Furthermore, these types of coatings leave completely unresolved the problem of resistance to current reversal that occurs in industrial electrolyzers during downtime. By adding elements from the group of rare earths such as praseodymium, cerium, or lanthanum to the formulation of the catalyst layer, the adhesion of the catalyst coating on the substrate can be partially improved. It has been found that cathodes with these coatings are sufficiently durable under normal operating conditions. Moreover, by sandwiching a platinum-based layer between the metal substrate and the catalyst coating, it is possible to increase the strength of these electrodes.

[0007] By applying a catalyst coating to a metal substrate consisting of two distinct phases, a first phase based on platinum and rhodium and a second phase containing palladium with a protective function, a further improvement in resistance to current reversal can be obtained. However, this type of formulation requires a high addition of platinum and rhodium in the catalyst phase, which determines a rather high manufacturing cost.

[0008] US3,990,957A describes a gas-generating cathode for electrolyzing an aqueous alkali metal chloride electrolyte. The cathode includes a catalyst layer of a perovskite-forming platinum group metal and an alkaline earth metal oxy compound on a conductive substrate. Typical oxy compounds include calcium ruthenate or strontium ruthenate.

[0009] WO2019 / 175280A1 describes an electrode for an electrochlorination process, comprising an active layer with a doped Ru-Ti catalyst composition.

[0010] US4,300,992A describes an active cathode for use in aqueous electrolysis, comprising a metal substrate and a metal oxide layer formed on the surface of the substrate, which consists of an oxide of ruthenium and an oxide of, for example, calcium, magnesium, strontium, barium, or zinc, and an oxide of chromium, molybdenum, tungsten, selenium or tellurium.

[0011] GB1260645A describes a conductive anode having a coating comprising a conductive oxy compound containing a platinum metal and an alkaline earth metal or a rare earth metal.

SUMMARY OF THE INVENTION

[0012] The present invention aims to solve the above problems and relates to a cathode characterized by a low hydrogen overvoltage and good resistance to current reversal when electrolysis is interrupted. The present invention also relates to a method for manufacturing the cathode and an electrolysis device containing the cathode.

[0013] Various aspects of the present invention are set forth in the appended claims.

[0014] In a first aspect, the present invention relates to an electrode comprising a conductive substrate provided with at least one catalyst coating containing ruthenium and at least one other element selected from the group of alkaline earth metals.

[0015] The inventors have surprisingly found that adding an element belonging to the group of alkaline earth metals to a catalyst coating mainly containing ruthenium makes it possible to obtain unexpectedly improved performance with respect to the catalytic activity of the hydrogen generation reaction.

[0016] It should be understood that the elements present in the catalyst coating may be in metallic form or in oxide form.

[0017] The above catalyst coating contains 93 to 99 weight percent (i.e., 93 to 99 wt-%) of ruthenium based on the total amount of metal, and 1 to 7 weight percent (i.e., 1 to 7 wt-%) of a metal selected from the group of alkaline earth metals. This enables further improvement of the hydrogen overvoltage.

[0018] The inventors have also found that such a catalyst coating enables the cell performance to reach a steady state in a much shorter time than is generally seen with other formulations of the prior art.

[0019] While not wishing to limit the present invention to any particular theory, this may be due to the fact that a suitable percentage of alkaline earth metals in the catalyst coating combines with the transition metal oxide to form a special structure that modifies the stoichiometry of the resulting oxide and makes the oxide more active.

[0020] According to a further embodiment, the present invention relates to an electrode in which the alkaline earth metal is selected between strontium, calcium, and barium.

[0021] The inventors have noticed that this type of formulation provides better resistance to current reversal compared to prior art formulations based only on ruthenium dioxide on the one hand, and is comparable to formulations containing noble metals such as ruthenium and rare earths but with a substantially reduced specific addition amount of noble metals on the other hand. In fact, a surprising reduction in the consumption rate of the electrode, expressed as a percentage of the amount of noble metal consumed, is observed, which indicates excellent resistance to current reversal. The inventors have found that alkaline earth metals such as strontium, calcium, and barium seem to stabilize the noble metal.

[0022] In a further embodiment, the catalyst coating is from 5 g / m 2 to 15 g / m 2It has a relative addition amount of ruthenium with respect to [the other component]. The inventors have found that, in the case of the catalyst coating shown, the reduced ruthenium addition amount is sufficient or more than sufficient to provide good resistance to current reversal, combined with excellent catalytic activity not seen in the prior art of ruthenium-based catalyst coatings.

[0023] In a further embodiment of the electrode according to the invention, the preferred conductive substrate is nickel.

[0024] In a further aspect, the present invention is a method for preparing an electrode for the generation of a gas product in an electrolytic cell, for example for hydrogen generation in an electrolytic cell of alkaline brine or for the electrolysis of water, the method comprising the following steps: Process (a) . Applying a solution containing a precursor of ruthenium and a precursor of said metal selected from the group of alkaline earth metals to a conductive substrate and , a solution containing 93 to 99 wt% of ruthenium and 1 to 7 wt% of a metal selected from the group of alkaline earth metals, based on the total amount of metals, the solution The step of applying to a conductive substrate ; Process (b) . Subsequent steps of drying at 30 - 80 °C and pyrolysis at 450 - 600 °C and; Process (c) . 5 g / m 2 and 15 g / m 2 in between of ruthenium addition amount until a catalyst coating having [the specified amount] is obtained Process (a) and Process (b) to Repeat Process and including. The precursor solution contains ruthenium and alkaline earth metals at a concentration that enables the above electrode coating to be obtained. including.

[0025] According to an embodiment of the above method, the method includes an initial treatment step before step (a), and the initial treatment step includes heat treatment of the conductive substrate at a temperature of 450 ° C or higher for a time of 15 minutes or longer.

[0026] In a further aspect, the present invention relates to a cell for the electrolysis of an alkali chloride solution, comprising an anode compartment and a cathode compartment separated by an ion exchange membrane or a partition wall, wherein the cathode compartment is used as a cathode for hydrogen generation. The cell is provided with an electrode as described in one of the above forms.

[0027] In a further aspect, the present invention relates to an electrolysis apparatus for producing chlorine and alkali from an alkaline brine, comprising a module arrangement of an electrolytic cell having an anode compartment and a cathode compartment separated by an ion exchange membrane or a partition wall, wherein the cathode compartment is a cathode. The electrolysis apparatus includes an electrode in one of the above forms used as such.

[0028] In a further aspect, the present invention relates to an electrolysis apparatus for producing hydrogen by electrolysis of water, comprising an anode compartment and a cathode compartment separated by a partition wall, wherein the cathode compartment is provided with an electrode in one of the above forms. The electrolysis apparatus.

Embodiments for Carrying Out the Invention

[0029] The following examples are incorporated to demonstrate specific embodiments of the present invention, and their feasibility has been widely verified in the field of useful articles whose feasibility is claimed. It will still be apparent to those skilled in the art that the compositions and techniques described in the following examples correspond to the compositions and techniques in which the inventors have found good functions in the practice of the present invention. However, those skilled in the art will also understand that various changes can be made to the various embodiments described without departing from the scope of the present invention while still achieving the same or similar results.

Examples

[0030] Example 1 A nickel mesh with dimensions of 100 mm × 100 mm × 0.89 mm was subjected to a sandblasting process with corundum, etching in HCl, and stress relaxation by heat treatment according to procedures known in the art.

[0031] A 100 ml solution containing ruthenium and strontium precursors with a composition expressed as a weight percentage corresponding to 95% Ru and 5% Sr based on the total amount of metal was prepared.

[0032] The solution was then applied to the nickel mesh in 6 layers by brushing.

[0033] After each coating, drying was carried out at 40 - 60 °C for about 10 minutes, followed by heat treatment at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next layer.

[0034] 8 g / m 2 This procedure was repeated until the total addition amount of Ru corresponding to 8 g / m was reached.

[0035] The electrode thus obtained was identified as sample E1.

[0036] Example 2 A nickel mesh with dimensions of 100 mm × 100 mm × 0.89 mm was subjected to a sandblasting process with corundum, etching in HCl, and stress relaxation by heat treatment according to procedures known in the art.

[0037] A 100 ml solution containing ruthenium and strontium precursors with a composition expressed as a weight percentage corresponding to 97% Ru and 3% Sr based on the total amount of metal was prepared.

[0038] The solution was then applied to the nickel mesh in 6 layers by brushing.

[0039] After each coating, drying was performed at 40 to 60 °C for about 10 minutes, followed by heat treatment at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next layer.

[0040] 11 g / m 2 This procedure was repeated until the total addition amount of Ru corresponding to

[0041] The electrode thus obtained was identified as sample E2.

[0042] Example 3 A nickel mesh with dimensions of 100 mm × 100 mm × 0.89 mm was subjected to a sandblasting process with corundum, etching in HCl, and stress relaxation by heat treatment according to procedures known in the art.

[0043] A 100 ml solution containing ruthenium and strontium precursors with a composition expressed as a weight percentage corresponding to 96% Ru and 4% Sr based on the total amount of metal was prepared.

[0044] The solution was then applied to the nickel mesh in 6 layers by brushing.

[0045] After each coating, drying was performed at 40 to 60 °C for about 10 minutes, followed by heat treatment at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next layer.

[0046] 7 g / m 2 This procedure was repeated until the total addition amount of Ru corresponding to

[0047] The electrode thus obtained was identified as sample E3.

[0048] Comparative Example 1 A nickel mesh with dimensions of 100 mm × 100 mm × 0.89 mm was subjected to a sandblasting process with corundum, etching in HCl, and stress relaxation by heat treatment according to procedures known in the art.

[0049] A 100 ml solution containing ruthenium and praseodymium precursors with a composition expressed as a weight percentage corresponding to 83% Ru and 17% Pr based on the total amount of metal was prepared.

[0050] The solution was then applied to a nickel mesh in 8 layers by brushing.

[0051] After each coating, drying was carried out at 40 - 60 °C for about 10 minutes, followed by heat treatment at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next layer.

[0052] 11 g / m 2 This procedure was repeated until the total addition amount of Ru corresponding to was reached.

[0053] The electrode thus obtained was identified as sample CE1.

[0054] Counterexample 2 A nickel mesh with dimensions of 100 mm × 100 mm × 0.89 mm was subjected to a sandblasting process with corundum, etching in HCl, and stress relaxation by heat treatment according to procedures known in the art.

[0055] A 100 ml solution containing ruthenium and praseodymium precursors with a composition expressed as a weight percentage corresponding to 83% Ru and 17% Pr based on the total amount of metal was prepared.

[0056] The solution was then applied to the nickel mesh in 10 layers by brushing.

[0057] After each coating, drying was carried out at 40 - 60 °C for about 10 minutes, followed by heat treatment at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next layer.

[0058] 11.5 g / m 2 This procedure was repeated until the total addition amount of Ru corresponding to was reached.

[0059] The electrode thus obtained was identified as sample CE2.

[0060] Counterexample 3 A nickel mesh with dimensions of 100 mm × 100 mm × 0.89 mm was subjected to a sandblasting process with corundum, etching in HCl, and stress relaxation by heat treatment according to procedures known in the art.

[0061] A 100 ml solution containing a ruthenium precursor was prepared.

[0062] The solution was then applied to the nickel mesh in 14 layers by brushing.

[0063] After each coating, drying was performed at 40 - 60 °C for about 10 minutes, followed by heat treatment at 500 °C for 10 minutes. The mesh was air-cooled each time before applying the next layer.

[0064] 14 g / m 2 This procedure was repeated until the total addition amount of Ru corresponding to 14 g / m was reached.

[0065] The electrode thus obtained was identified as sample CE3.

[0066] In a laboratory cell where 32% NaOH was supplied at a temperature of 90 °C, under hydrogen evolution, the samples of the above examples were subjected to a performance test, and some of the samples were further subjected to a cyclic voltammetry test at a scan rate of 10 mV / s at potentials in the range of -1 to +0.5 V / NHE.

[0067] Table 1 shows the initial cathode potential measured at a current density of 6 kA / m 2 and corrected for the resistance drop. TIFF0007702941000001.tif73170

[0068] Table 2 shows the [3 kA / m] 2Shows the initial cathode potential measured at the current density, and the cathode potential after 25 cycles (25CV) of cyclic voltammetry, which is an indicator of resistance to inversion. TIFF0007702941000002.tif45170

[0069] Table 3 shows the time to reach steady-state cell performance, and the consumption rate of the electrodes, expressed as the percentage of residual precious metal and presented as a further indicator of resistance to current inversion. Using a laboratory membrane cell with an active cathode area corresponding to 0.2 dm 2 Data were obtained after 4,000 hours of activity (HOL) at 8 kA / m 2 in an accelerated test. The tests were conducted at T = 89 °C with a 210 g / l NaCl anode solution and a 32 wt% NaOH cathode solution. TIFF0007702941000003.tif45170

[0070] The foregoing description is not intended to limit the invention, which can be used according to various embodiments without departing from the objectives of the invention, and the scope of the invention is uniquely defined by the appended claims.

[0071] In the specification and claims of this application, the terms "comprising" and "containing" and their variants such as "comprises" and "contains" are not intended to exclude the presence of other additional elements, components, or steps.

[0072] The discussion of documents, documents, materials, devices, articles, etc. are incorporated into the text for the sole purpose of providing the background of the invention. However, it should not be understood that this matter or a part thereof constituted common general knowledge in the field related to the invention prior to the priority date of each of the claims appended to this application.

Claims

1. A cathode for gas generation in an electrochemical process, comprising a conductive substrate and at least one catalyst coating containing at least one other metal selected from the group consisting of ruthenium and alkaline earth metals, wherein the catalyst coating contains 93 to 99 wt% ruthenium based on the total amount of metals and 1 to 7 wt% of a metal selected from the group consisting of alkaline earth metals.

2. The cathode according to claim 1, wherein the metal selected from the group consisting of alkaline earth metals is strontium, calcium, or barium.

3. The catalyst coating has a ruthenium addition amount between 5 g / m ２ and 15 g / m ２ The cathode according to claim 1 or 2.

4. The cathode according to claim 1 or 2, wherein the conductive substrate is nickel.

5. A method for preparing the cathode according to claim 1 or 2, comprising the following steps: Step (a). A step of applying a solution containing a precursor of ruthenium and a precursor of the metal selected from the group consisting of alkaline earth metals to the conductive substrate, wherein the solution contains 93 to 99 wt% ruthenium based on the total amount of metals and 1 to 7 wt% of the metal selected from the group consisting of alkaline earth metals, and applying the solution to the conductive substrate; Step (b). A subsequent step of drying at 30 to 80°C and pyrolyzing at 450 to 600°C. Step (c). 5 g / m ２ and 15 g / m ２ repeating steps (a) and (b) until a catalyst coating having a ruthenium addition amount between them is obtained A method comprising the above steps.

6. The method according to claim 5, further comprising an initial treatment step preceding step (a), wherein the initial treatment step comprises heat-treating the conductive substrate at a temperature of 450°C or higher for a time of 15 minutes or longer.

7. 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 a partition, wherein the cathode compartment is provided with the cathode according to claim 1 or 2.

8. An electrolyzer for producing chlorine and an alkali starting from an alkaline brine, comprising the arrangement of the cell, wherein the cell according to claim 7 is provided.

9. An electrolyzer for producing hydrogen by the electrolysis of water, comprising an anode compartment and a cathode compartment separated by a partition, wherein the cathode compartment is provided with the cathode according to claim 1 or 2.

Images