An acidic electrolytic water oxygen evolution electrocatalyst, a preparation method and application thereof

Abstract

The application discloses an acidic electrolytic water oxygen evolution electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of hydrogen production materials by electrolytic water. The three-dimensional TiO2 nanowire array can provide a high specific surface area and a directional electron transmission channel, RuO2 is anchored by Ru-O-Ti bonding, and the stability of the catalyst is remarkably improved. Ru-O-Ti local coordination environment between RuO2 and TiO2 can optimize the d-band center of Ru sites, changes the adsorption behavior of oxygen-containing intermediates and the reaction step energy barrier. The RuO2-TiO2 NW / TF catalyst reaches 10 mA cm ‑2 The overpotential under a current density of 10 mA cm-2 is only 175 mV, and the attenuation rate after 1000 h of stability is 23.5 mu V h ‑1 .

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen production materials by electrolysis of water, and particularly relates to an acidic water electrolysis oxygen evolution electrocatalyst and a preparation method and application thereof. BACKGROUND

[0002] In the hydrogen production technology by electrolysis of water, the hydrogen production by proton exchange membrane electrolysis of water has the advantages of fast start-stop speed and high current density, and is considered as the most promising hydrogen production technology. Developing a high-efficiency and stable acidic oxygen evolution reaction (OER) catalyst is one of the key challenges for realizing large-scale application of the hydrogen production technology by proton exchange membrane electrolysis of water. Iridium oxide (IrO2) is still the only practical acidic OER electrocatalyst that can continuously work in the hydrogen production by proton exchange membrane electrolysis of water. However, iridium is very expensive (>$180 / g) and its reserves in the earth's crust are scarce (earth's crust abundance is 0.001 ppm), which greatly hinders the large-scale application of the hydrogen production technology by proton exchange membrane electrolysis of water. Ruthenium oxide (RuO2) is considered as the most potential acidic OER catalyst due to its excellent intrinsic activity, but it is prone to dissolution of Ru species and oxidation of lattice oxygen under strong acidic and high potential conditions, resulting in irreversible loss of active sites and structural collapse.

[0003] Patent CN118326436A provides a preparation method of a ruthenium-loaded catalyst, comprising the following steps: first providing hollow titanium-based nanotubes; uniformly mixing the hollow titanium-based nanotubes, a weak reducing agent and water to obtain a precursor I solution; dispersing a ruthenium salt in water to obtain a ruthenium salt solution; mixing and stirring the ruthenium salt solution and the precursor I solution to obtain a precursor II solution; performing hydrothermal treatment on the precursor II solution, then performing solid-liquid separation, washing and drying to obtain a precursor solid; and performing annealing treatment on the precursor solid to obtain the ruthenium-loaded catalyst. The prior art adopts a traditional hydrothermal loading-calcination process, which is prone to cause agglomeration of the powder material, thereby affecting the dispersibility and interface bonding strength of the active component.

[0004] Therefore, there is an urgent need in the art to provide a new catalyst to overcome the limitations of Ru and improve the stability while maintaining high catalytic activity. SUMMARY

[0005] In view of the above problems, and in order to improve the activity and stability of the catalyst, the application provides an acidic water electrolysis oxygen evolution electrocatalyst and a preparation method and application thereof.

[0006] A preparation method of an acidic water electrolysis oxygen evolution electrocatalyst, comprising the following steps: growing TiO2 nanowire arrays on a titanium-based carrier in situ by a sol-gel method and a hydrothermal method, then dropping and coating a ruthenium source solution onto the surface of the TiO2 nanowire arrays, and performing two-step annealing treatment to obtain the acidic water electrolysis oxygen evolution electrocatalyst.

[0007] Further, the preparation method of the acidic electrolytic water oxygen evolution electrocatalyst specifically comprises the following steps: adding a triblock copolymer, water, acetic acid, hydrochloric acid and tetrabutyl titanate into tetrahydrofuran, and heating for the first time to volatilize the solvent to obtain a TiO2 gel solution; dropping the gel solution onto a pretreated titanium-based carrier, and heating for the second time, cooling, washing and drying to obtain a TiO2 nanowire array; dropping a ruthenium source solution onto the surface of the TiO2 nanowire array, and drying and then performing two-step annealing treatment to obtain the acidic electrolytic water oxygen evolution electrocatalyst.

[0008] The preparation method of the pretreated titanium-based carrier is as follows: etching a cut titanium-based carrier with an acid (for example, etching at 80℃ for 20-60min), and then ultrasonic cleaning with deionized water and drying; the acid used in the acid etching includes at least one of oxalic acid, hydrochloric acid, sulfuric acid and hydrofluoric acid; the titanium-based carrier is selected from a titanium felt, a titanium mesh, a titanium fiber felt or a titanium foam.

[0009] Further, the temperature of the first heating is 40℃; and the temperature of the second heating is 150℃, and the time is 12-48h.

[0010] Further, the use amount ratio of the triblock copolymer, water, acetic acid, hydrochloric acid, tetrabutyl titanate and tetrahydrofuran is 0.8g:0.1mL:1.43mL:1.26mL:1.7mL:15mL.

[0011] Further, the specific operation of dropping the ruthenium source solution onto the surface of the TiO2 nanowire array is as follows: sequentially dropping the ruthenium source solution onto the TiO2 nanowire array surfaces of the two sides of the titanium-based carrier.

[0012] Further, the mass concentration of the ruthenium source solution is 10-30mg / mL.

[0013] Further, the ruthenium source solution is selected from an aqueous solution of ruthenium trichloride, ruthenium trichloride hydrate or ruthenium nitrate.

[0014] Further, the triblock copolymer is selected from F127 (PEO 106 PPO 70 PEO 106 , Mw=12600g / mol).

[0015] Further, the two-step annealing treatment is first annealing treatment in an inert gas atmosphere, and then annealing treatment in air.

[0016] Further, the annealing treatment in the inert gas atmosphere is: heating at a temperature increasing rate of 5 DEG C / min in the inert gas atmosphere, and keeping at 300-500 DEG C for 2-4 h; and the annealing treatment in the air is: heating at a temperature increasing rate of 5 DEG C / min in the air, and keeping at 250-450 DEG C for 1-2 h.

[0017] An acidic electrolytic water oxygen evolution electrocatalyst prepared by the preparation method.

[0018] By constructing a strong interaction between the catalyst and the carrier, the electronic structure of RuO2 can be effectively regulated, the excessive oxidation of the active metal can be inhibited, and the interface charge transmission can be enhanced. The present application proposes that loading RuO2 nanoparticles on a TiO2 nanowire array carrier exhibits unique advantages: the three-dimensional TiO2 nanowire array provides a high specific surface area and a directional electron transmission channel, forms a Ru-O-Ti bonding effect with RuO2, and significantly improves the stability of the catalyst; meanwhile, the Ru-O-Ti local coordination environment at the interface between TiO2 and RuO2 can optimize the d-band center of the Ru site, change the adsorption behavior of the oxygen-containing intermediate, and the reaction step energy barrier.

[0019] An application of the above-mentioned acidic electrolytic water oxygen evolution electrocatalyst in electrolytic water hydrogen production.

[0020] Compared with the prior art, the present application has the following advantages and technical effects:

[0021] The present application takes titanium felt as a substrate, grows TiO2 nanowire arrays on the titanium felt in situ through a sol-gel method and a hydrothermal method, then, drops and coats RuCl3 as a ruthenium source on the surface of the TiO2 nanowire array, and then, performs two-step annealing treatment to prepare an acidic electrolytic water oxygen evolution electrocatalyst of the RuO2-loaded TiO2 nanowire array, which can be used as a self-supporting electrode for an acidic oxygen evolution reaction. In the present application, the one-dimensional TiO2 nanowire array can provide a high specific surface area and a directional electron transmission channel, anchor RuO2 through a Ru-O-Ti bonding effect, and significantly improve the stability of the catalyst. The Ru-O-Ti local coordination environment between RuO2 and TiO2 can optimize the d-band center of the Ru site, change the adsorption behavior of the oxygen-containing intermediate, and the reaction step energy barrier. The RuO2-TiO2NW / TF catalyst reaches a current density of 10 mA cm-2 in a 0.5M H2SO4 solution, and the overpotential is only 175 mV, and the attenuation rate after 1000 h of stability is 23.5 mu V h -2 . -1 . BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0023] Figure 1 Scanning electron microscope (SEM) image of RuO2-TiO2 NW / TF catalyst;

[0024] Figure 2 Scanning electron microscope (SEM) image of RuO2 / TF catalyst;

[0025] Figure 3 Scanning electron microscope (SEM) image of c-RuO2-TiO2 NW / TF catalyst;

[0026] Figure 4 Transmission electron microscope (TEM) image of RuO2-TiO2 NW / TF catalyst;

[0027] Figure 5 Linear sweep voltammetry curves of RuO2-TiO2 NW / TF catalysts with different drop-casted amounts of RuCl3 in Example 1 for oxygen evolution performance test;

[0028] Figure 6 Linear sweep voltammetry curves of RuO2-TiO2 NW / TF catalyst (40 μL each, a total of 80 μL), RuO2 / TF catalyst and c-RuO2-TiO2 NW / TF catalyst for oxygen evolution performance test;

[0029] Figure 7 Stability test results of RuO2-TiO2 NW / TF catalyst (40 μL each, a total of 80 μL), RuO2 / TF catalyst and c-RuO2-TiO2 NW / TF catalyst at 10 mA cm-2current density. -2 Stability test results of RuO2-TiO2 NW / TF catalyst (40 μL each, a total of 80 μL), RuO2 / TF catalyst and c-RuO2-TiO2 NW / TF catalyst at 10 mA cm-2current density. DETAILED DESCRIPTION

[0030] The various exemplary embodiments of the present application will now be described in detail, which should not be considered as limiting the present application, but should be understood as a more detailed description of certain aspects, features and embodiments of the present application.

[0031] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where a range of values is provided, it is understood that each intervening value, to the upper and lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges can independently be included or excluded in the range, and are also encompassed by the application, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

[0032] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in detail the methods and / or materials useful in connection to the documents. In the event of conflict between the content of the specification and that of any document incorporated herein by reference, the content of the specification controls.

[0033] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0034] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to mean including, but not limited to.

[0035] Room temperature of the present application refers to 25±2℃.

[0036] The triblock copolymer in the embodiments of the present application adopts polyethylene glycol-polypropylene glycol-polyethylene glycol block copolymer (PEG-PPO-PEG).

[0037] Example 1 Preparation method of an acidic electrolytic water oxygen evolution electrocatalyst

[0038] S1. After cutting the titanium felt (TF) into a size of 1*1 cm, it was placed in an oxalic acid solution (10 wt.%) and heated at 80℃ for 20 min, then ultrasonic treatment was performed for 10 min with deionized water, and then washed with deionized water until the solution color was colorless, and placed in a 60℃ oven for drying, to obtain a pretreated TF, ready for use;

[0039] S2. 1.6 g of F127 (PEO 106 PPO 70 PEO 106 , Mw = 12600 g / mol), 0.2 mL of H2O,

[0040] 2.86 mL of acetic acid and 2.52 mL of concentrated hydrochloric acid (36 wt.%) were dissolved in 30 mL of tetrahydrofuran, then 3.4 mL of tetrabutyl titanate was added dropwise to form a clear solution, and then the solvent was evaporated in an oven at 40°C for 8 h to obtain a TiO2 gel solution (the gel solution had a certain flowability and was a semi-transparent white gel), then the S1 pretreated TF was immersed in the TiO2 gel solution, placed in a polytetrafluoroethylene lined reaction kettle, heated at 150°C for 24 h, after cooling to room temperature, washed with deionized water for 10 s under ultrasonic three times, and then dried in an oven at 40°C to prepare a TiO2 nanowire array, denoted as TiO2 NW / TF. x NW / TF;

[0041] S3. 5 mg of RuCl3 was dissolved in 200 μL of ethanol-water (v / v, 1 / 1) solution, and the obtained solution was drop-coated on the TiO2 NW / TF with a size of 1*1 cm (10 / 15 / 20 / 25 / 30 / 35 / 40 / 45 / 50 μL was drop-coated before and after), and dried under an infrared lamp to obtain a sample, which was first placed in a tube furnace, heated at a rate of 5°C / min under an argon atmosphere, and kept at 350°C for 2 h, and then placed in a muffle furnace, heated at a rate of 5°C / min, and kept at 250°C for 1 h to prepare an acidic electrolytic water oxygen evolution electrocatalyst, denoted as RuO2-TiO2 NW / TF catalyst. x -1 -1

[0042] The scanning electron microscope (SEM) image of the RuO2-TiO2 NW / TF catalyst prepared in Example 1 is shown in FIG. 1, and the morphology of the RuO2-TiO2 NW / TF catalyst prepared in the present example can be seen from the TiO2 nanowire array structure, and no obvious RuO2 particle aggregation is observed. Figure 1

[0043] The transmission electron microscope (TEM) image of the RuO2-TiO2 NW / TF catalyst prepared in Example 1 is shown in FIG. 2, and it can be seen from the RuO2 particles that are uniformly loaded on the TiO2 nanowire array. Figure 4 Figure 4

[0044] The acidic oxygen evolution reaction catalytic performance of the RuO2-TiO2 NW / TF catalyst was tested by linear voltammetry in a three-electrode system, and the specific test method was as follows: the RuO2-TiO2 NW / TF catalyst was used as a self-supporting electrode and as a working electrode, reversible hydrogen was used as a reference electrode, and a carbon rod was used as a counter electrode, and the electrocatalytic oxygen evolution performance was studied in 0.5 M H2SO4 solution.

[0045] ​​​​​​The oxygen evolution performance test linear cyclic voltammetry curves of RuO2-TiO2 NW / TF catalysts with different RuCl3 drop coating amounts prepared in Example 1 are shown below. Figure 5 As shown, the performance is optimal when the RuCl3 drop volume is 80 μL.

[0046] The linear cyclic voltammetric curve for oxygen evolution performance testing of the RuO2-TiO2 NW / TF catalyst (RuCl3 drop coating amount of 80 μL) prepared in Example 1 is shown below. Figure 6 As shown, RuO2-TiO2 NW / TF at 10 mA cm -2 The overpotential at the current density is 175mV.

[0047] The calculation method for overpotential (η) is shown in equation (1):

[0048] η=E-1.23V (1)

[0049] Where E is 10 mA cm -2 Voltage corresponding to current density.

[0050] The RuO2-TiO2 NW / TF catalyst prepared in Example 1 (RuCl3 drop coating amount of 80 μL) was subjected to 10 mA cm⁻¹ -2 Stability test under current density, such as Figure 7 As shown, the decay rate of RuO2-TiO2 NW / TF after 1000 hours of stable operation is only 23.5 μV / h. -1 .

[0051] Comparative Example 1

[0052] S1. Cut titanium felt (TF) into 1*1cm size and put it into oxalic acid solution (10wt.%). Heat it at 80℃ for 20min, then sonicate it with deionized water for 10min, then rinse it with deionized water until the solution is colorless. Dry it in an oven at 60℃ to obtain pretreated TF for later use.

[0053] S2. Dissolve 5 mg RuCl3 in 200 μL of ethanol-water (v / v, 1 / 1) solution. Drop the resulting solution onto a 1*1 cm pretreatment TF plate (40 μL before and after, totaling 80 μL). Dry under an infrared lamp. The resulting sample is first placed in a tube furnace under an argon atmosphere at 5 °C for 1 minute. -1 Heating was carried out at a rising rate and held at 350°C for 2 hours. After cooling to room temperature, the mixture was placed in a muffle furnace and heated at 5°C / min. -1 The RuO2 / TF catalyst was prepared by heating at a rising rate and holding at 250℃ for 1 hour.

[0054] The scanning electron microscope (SEM) image of the RuO2 / TF catalyst prepared in Comparative Example 1 is shown below. Figure 2 As shown, RuO2 particles are observed to aggregate on the surface of the titanium felt from the morphology of the RuO2 / TF catalyst.

[0055] The catalytic performance of RuO2 / TF catalyst in acidic oxygen evolution reaction was tested using linear voltammetry in a three-electrode system. Specifically, the RuO2 / TF catalyst was used as a self-supporting electrode and as the working electrode, reversible hydrogen was used as the reference electrode, and a carbon rod was used as the counter electrode. The electrocatalytic oxygen evolution performance was studied in 0.5M H2SO4 solution.

[0056] The oxygen evolution performance test linear cyclic voltammetry curve of the RuO2 / TF catalyst prepared in Comparative Example 1 is shown below. Figure 6 As shown, RuO2 / TF at 10 mA cm -2 The overpotential at the current density is 197mV.

[0057] The RuO2 / TF catalyst prepared in Comparative Example 1 was tested at 10 mA cm⁻¹. -2 Stability test under current density, such as Figure 7 As shown, RuO2 / TF decays to 1.8V in 400 hours, with a decay rate of 923 μVh. -1 .

[0058] Comparative Example 2

[0059] S1. Cut titanium felt (TF) into 1*1cm size and put it into oxalic acid solution (10wt.%). Heat it at 80℃ for 20min, then sonicate it with deionized water for 10min, then rinse it with deionized water until the solution is colorless. Dry it in an oven at 60℃ to obtain pretreated TF for later use.

[0060] S2. Add 1.6g of F127 (PEO) 106 PPO 70 PEO 106 , Mw=12600g / mol), 0.2mLH2O,

[0061] 2.86 mL of acetic acid and 2.52 mL of concentrated hydrochloric acid (36 wt.%) were dissolved in 30 mL of tetrahydrofuran, and then 3.4 mL of tetrabutyl titanate was added dropwise to form a clear solution. The solvent was then evaporated in an oven at 40 °C for 8 h to obtain a TiO2 gel solution. This TiO2 gel solution was then drop-coated onto S1-pretreated TF substrate and placed in a PTFE-lined reactor. The reactor was heated at 150 °C for 24 h, cooled to room temperature, and then washed three times with deionized water under ultrasonication for 10 s each time. Finally, it was dried in an oven at 40 °C to prepare TiO2. x NW / TF;

[0062] S3. First, the TiO2 NW / TF prepared in S2 was placed in a tube furnace and heated at a rate of 5℃ min x under an argon atmosphere, and then heated at a rate of 5℃ min -1 under an argon atmosphere, and then heated at a rate of 5℃ min -1 under an argon atmosphere, and then heated at a rate of 5℃ min

[0063] S4. 5mg RuO2 was dissolved in a mixed solution of 495μL deionized water, 495μL isopropanol and 10μL Nafion solution, and the mixed solution was drop-coated on the TiO2 NW / TF with a size of 1*1cm, and then dried under an infrared lamp to prepare the c-RuO2-TiO2 NW / TF catalyst.

[0064] The scanning electron microscope (SEM) image of the c-RuO2-TiO2 NW / TF catalyst prepared in Comparative Example 2 is shown in Figure 3 From the morphology of the c-RuO2-TiO2 NW / TF catalyst, the TiO2 nanowire array structure can be seen, and the RuO2 particles loaded on the surface of the TiO2 nanowire array can be observed.

[0065] The acid oxygen evolution reaction catalytic performance of the c-RuO2-TiO2 NW / TF catalyst was tested by linear voltammetry in a three-electrode system. The specific test method was as follows: the c-RuO2-TiO2 NW / TF catalyst was used as a self-supporting electrode and as a working electrode, reversible hydrogen was used as a reference electrode, and a carbon rod was used as a counter electrode, and the electrocatalytic oxygen evolution performance was studied in 0.5M H2SO4 solution.

[0066] The linear cyclic voltammetry curve of the c-RuO2-TiO2 NW / TF catalyst prepared in Comparative Example 2 is shown in Figure 6 The overpotential of the c-RuO2-TiO2 NW / TF catalyst at a current density of 10mA cm -2 was 407mV.

[0067] The stability test of the c-RuO2-TiO2 NW / TF catalyst prepared in Comparative Example 2 at a current density of 10mA cm -2 is shown in Figure 7 From Figure 7 it can be seen that the c-RuO2-TiO2 NW / TF catalyst has only 20h of stability.

[0068] Through performance testing of the RuO2-TiO2NW / TF, RuO2 / TF and c-RuO2-TiO2NW / TF catalysts, it can be seen that: the local Ru-O-Ti structure is constructed by strong metal oxide carrier interaction between RuO2 and TiO2 nanowire array, so that the electrons are transferred from Ti to Ru sites through bridging oxygen, the peroxidation of Ru is inhibited, and the stability of the catalytic property is improved. At the same time, the d-band center of the Ru site is optimized, the adsorption behavior and reaction step energy barrier of the oxygen-containing intermediate are changed. The RuO2-TiO2NW / TF catalyst reaches 10mA cm -2 at a current density of 10mA cm-2in a 0.5M H2SO4 solution, and the overpotential is only 175mV, and the attenuation rate after 1000h of stabilization is 23.5μV h-1, which exhibits excellent activity and stability. -1

[0069] The above merely describes the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered within the protection scope of the present application.​

Claims

1. A method for preparing an acidic electrolytic water oxygen evolution electrocatalyst, characterized by, The method comprises the following steps: The TiO2 nanowire array is grown on the titanium-based carrier in-situ by a sol-gel method and a hydrothermal method, a ruthenium source solution is drop-coated on the surface of the TiO2 nanowire array, and the acidic electrolytic water oxygen evolution electrocatalyst is obtained through two-step annealing treatment; The step of growing the TiO2 nanowire array on the titanium-based carrier in-situ by the sol-gel method and the hydrothermal method comprises: adding a triblock copolymer, water, acetic acid, hydrochloric acid and tetrabutyl titanate into tetrahydrofuran, heating for the first time to volatilize the solvent to obtain a TiO2 gel solution; immersing a pretreated titanium-based carrier in the gel solution, heating for the second time, cooling, washing and drying to obtain the TiO2 nanowire array; the triblock copolymer is selected from F127; The specific step of drop-coating the ruthenium source solution on the surface of the TiO2 nanowire array is: sequentially drop-coating the ruthenium source solution on the surface of the TiO2 nanowire array on both sides of the titanium-based carrier; The temperature of the first heating is 40℃, and the temperature of the second heating is 150℃, and the time is 12-48h; The two-step annealing treatment is first annealing treatment in an inert gas atmosphere, and then annealing treatment in air; The annealing treatment in inert gas atmosphere is heating at a rate of 5℃ / min -1 in inert gas atmosphere, and holding at 300-500℃ for 2-4h; the annealing treatment in air is heating at a rate of 5℃ / min -1 in air, and holding at 250-450℃ for 1-2h.

2. The production method according to claim 1, characterized by, The amount ratio of the triblock copolymer, water, acetic acid, hydrochloric acid, tetrabutyl titanate and tetrahydrofuran is 0.8g:0.1mL:1.43mL:1.26mL:1.7mL:15mL.

3. The preparation method according to claim 1, characterized in that, The mass concentration of the ruthenium source solution is 10-30mg / mL.

4. The method of claim 1, wherein, The ruthenium source solution is selected from an aqueous solution of ruthenium trichloride, ruthenium trichloride hydrate or ruthenium nitrate. 5.An acidic electrolytic water oxygen evolution electrocatalyst prepared by the preparation method in any one of claims 1-4. 6.Use of the acidic electrolytic water oxygen evolution electrocatalyst in claim 5 in electrolytic water hydrogen production.

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