Cathode electrode for water electrolysis

Abstract

A cathode electrode for water electrolysis is provided that does not use any platinum (Pt) at all and achieves catalytic activity equivalent to or even greater than that of Pt. [Solution] The cathode electrode used in hydrogen production by water electrolysis is made of a sintered alloy in which nickel (Ni) and chromium (Cr) are used as binder phases between tungsten carbide (WC) particles. The sintered alloy that makes up the cathode electrode contains 5-25 wt% Ni and 0.5-3.0 wt% Cr. By using this sintered alloy as the cathode electrode for water electrolysis, the hydrogen overvoltage (ηH(V)) during hydrogen generation is reduced, achieving highly efficient and stable hydrogen generation.

Description

[Technical Field]

[0001] The present invention relates to a cathode electrode for water electrolysis. [Background technology]

[0002] The use of hydrogen energy has been attracting attention as a way to curb carbon dioxide emissions, which cause environmental destruction such as global warming, and to realize a decarbonized society. One method of producing hydrogen is water electrolysis, which uses abundant water resources.

[0003] Platinum (Pt) is used for the cathode electrode in hydrogen production devices and methods that employ water electrolysis. This is because Pt's hydrogen overvoltage (ηH(V)) is significantly lower than that of other metals. In particular, Pt activates oxygen and hydrogen, so it is used as an oxidation catalyst, hydrogenation catalyst, or dehydrogenation catalyst. Demand for Pt is particularly increasing as a catalyst to promote reactions at the electrodes in fuel cells, which are expected to become more common in various fields in the future as we move toward a decarbonized and hydrogen-based society. Pt is not only a rare and expensive resource, but its price is expected to continue to rise in the future.

[0004] Therefore, in the field of hydrogen production by water electrolysis, technologies to reduce the amount of Pt used and materials to replace Pt have been proposed.

[0005] Patent Document 1 proposes a catalyst for the cathode electrode in which a platinum skin layer is provided on the surface of alloy fine particles made of an alloy of Pt and a transition metal. This catalyst is said to have higher mass activity than commercially available Pt catalysts, and therefore can reduce the amount of Pt used.

[0006] Furthermore, Patent Document 2 proposes a catalyst for use in producing hydrogen by water electrolysis that contains 10 or more metal elements and is made nanoporous, thereby reducing the proportion of precious metal elements such as Pt. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-141792 [Patent Document 2] Japanese Patent Publication No. 2023-028320 Summary of the Invention [Problem to be solved by the invention]

[0008] The cathode electrodes and cathode electrode catalysts used in hydrogen production by water electrolysis that have been proposed to date all aim to reduce the proportion of Pt used, but they are not constructed without using Pt.

[0009] The technical object of the present invention is to provide a cathode electrode for water electrolysis that achieves catalytic activity equivalent to or even greater than that of Pt without using any Pt.

[0010] The present inventors have conducted extensive research into materials that can be used for cathode electrodes used in hydrogen production by water electrolysis, and have noticed that the electron configuration of tungsten carbide (WC) is similar to that of Pt. They have also noticed that by selecting a metal that constitutes the bonding phase that bonds WC fine particles together, it is possible to achieve a catalytic function for hydrogen production that is equivalent to, or even better than, Pt, and have completed the present invention. [Means for solving the problem]

[0011] The present invention was completed as a result of extensive research aimed at solving the above-mentioned technical problems, and relates to a cathode electrode used in hydrogen production by water electrolysis, which is made of a sintered alloy in which tungsten carbide (WC) particles are sintered with nickel (Ni) and chromium (Cr) as a binder phase. The binder phase is a Ni-Cr alloy in which Cr is dissolved in Ni.

[0012] The sintered alloy constituting the cathode preferably contains 5 to 25% by weight of Ni and 0.5 to 3.0% by weight of Cr, and the remainder of the sintered alloy may contain unavoidable impurities in addition to WC.

[0013] The sintered alloy constituting the cathode electrode is characterized in that the WC has an average particle size of 1.0 to 10 μm. [Effects of the Invention]

[0014] The cathode electrode for water electrolysis is made by sintering WC particles with Ni and Cr as the binder phase. sintered alloy This configuration reduces the hydrogen overvoltage (ηH(V)) during hydrogen generation, achieving highly efficient and stable hydrogen generation.

[0015] Furthermore, since the cathode electrode for water electrolysis does not use a precious metal element such as Pt, a stable supply can be realized at low cost. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram showing a cathode polarization curve measuring device. [Figure 2] This is a characteristic diagram showing the cathode polarization curves measured in a 0.1 mol L-1 potassium hydroxide (KOH) aqueous solution at 298 K (25 ° C.) using Pt, Ni, and the sintered alloy of the present invention as cathode electrodes. [Figure 3] FIG. 2 is a characteristic diagram showing the amount of hydrogen generated when hydrogen is generated by a hydrogen generator using Pt, Ni, and the sintered alloy of the present invention as cathode electrodes. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the cathode electrode according to the present invention will be described. The present embodiment relates to a cathode electrode used in a water electrolysis method for producing hydrogen using a water resource.

[0018] The water electrolysis method for producing hydrogen by water electrolysis utilizes the phenomenon that a cathode electrode and an anode electrode are immersed in an aqueous solution containing an electrolyte, and when a current is applied between the cathode electrode and the anode electrode, water or hydrogen ions are reduced on the cathode electrode to generate hydrogen gas.

[0019] The cathode electrode according to this embodiment is made of a sintered alloy in which WC particles are sintered and bonded using Ni and Cr as a binder phase. In the sintered alloy according to this embodiment, the binder phase is a Ni-Cr alloy in which Cr is dissolved in Ni. This sintered alloy is produced from a starting raw material powder that is a mixture of WC powder with an average particle size of 1.0 to 10 μm, Ni powder with a particle size of 1.0 to 2.0 μm, and Cr3C2 powder with a particle size of 1.2 to 1.6 μm.

[0020] The starting powder is then mixed with an oil such as paraffin wax to form a powder material for molding. The powder material for molding is then compressed into a desired shape to form a green compact. This green compact is then degreased by heating to approximately 250-500°C in a furnace with a hydrogen atmosphere. The degreased green compact is then placed in a vacuum or reducing gas atmosphere, and then heated from room temperature to 800-1200°C in a furnace where it is held for 100-130 minutes to be pre-sintered. Argon gas is then introduced into the furnace containing the green compact to create an argon pressurized atmosphere of 0.85-0.95 MPa. The furnace is then heated to 1300-1400°C and held for 80-100 minutes, and the green compact is then subjected to HIP treatment at 55-65 MPa in a 1300-1400°C atmosphere to form a dense sintered alloy. During the sintering process of this raw material powder to produce a sintered alloy, the carbon component is released from the Cr3C2 starting material, and the chromium component dissolves in the nickel to form a Ni-Cr alloy, which forms the binder phase that bonds the WC particles together.

[0021] The cathode electrode manufactured in this embodiment is sintered alloyThe binder phase contains 5 to 25% by weight of Ni, 0.5 to 3.0% by weight of Cr, and the balance is WC. Sintering In alloys, Sintering May contain unavoidable impurities inherent in alloys.

[0022] The sintered alloy produced here is sintered to a predetermined size, and then cut and molded into the shape and size to be used as the cathode electrode of the water splitting device.

[0023] The sintered alloy used in this embodiment may be manufactured by forming a green compact produced in the manufacturing process into a shape and size to be used as the cathode electrode, and then sintering this.

[0024] In the water electrolysis method using the cathode electrode according to this embodiment, a neutral to alkaline electrolyte aqueous solution is used as the aqueous solution. In particular, in this embodiment, an alkaline aqueous solution using KOH as the electrolyte was used. This aqueous solution was degassed by bubbling nitrogen gas through it for about 30 minutes to remove the influence of dissolved oxygen.

[0025] The cathode electrode according to this embodiment is placed in an electrolytic cell filled with an aqueous electrolyte solution. An anode electrode is placed opposite the cathode electrode in the electrolytic cell. In this embodiment, the anode electrode is formed from a carbon rod.

[0026] As described above, when a DC power supply is applied between the cathode electrode and the anode electrode placed in an electrolytic cell filled with an aqueous electrolyte solution, a hydrogen generation reaction in an alkaline aqueous solution occurs on the cathode electrode side, as shown in the following formula (1), and hydrogen (H2) is generated.

[0027] 2H2O+2e - → H2+2OH - ···(1)

[0028] On the anode electrode side, an oxygen generating reaction occurs in the alkaline aqueous solution, as shown in formula (2) below, and oxygen (O2) is generated.

[0029] 4OH - → 2H2O+O2+4e - ···(2)

[0030] When water electrolysis was performed using a sintered alloy according to this embodiment, in which Ni and Cr were sintered as binder phases between WC particles, as a cathode electrode, the hydrogen overvoltage (ηH(V)) value was small and approximated the value when Pt was used as the cathode electrode. This is believed to be due to the synergistic effect of WC, which has an electronic structure similar to that of Pt, and Ni and Cr, in the sintered alloy constituting the cathode electrode of this embodiment. The cathode electrode using the sintered alloy according to this embodiment can be used in place of Pt as a cathode electrode for water electrolysis.

[0031] Here, hydrogen overvoltage (ηH(V)) is the voltage that is generated by hydrogen ions (H + ) discharges on the surface of the cathode electrode, generating a cathode (reduction) current, and then to the potential at which atomic hydrogen (H) and then hydrogen gas (H2) begin to emerge. [Example]

[0032] In the examples shown below, several sintered alloys with different Ni and Cr content ratios were produced in sintered alloys obtained by sintering WC fine particles with Ni and Cr as binder phases, and the ease of hydrogen generation when these sintered alloys were used as cathode electrodes in water electrolysis was confirmed by measuring the cathode polarization curves.

[0033] The cathodic polarization curve was measured using a polarization curve measuring device configured as shown in FIG.

[0034] As shown in Fig. 1, this polarization curve measuring device includes a constant temperature water bath 1. The constant temperature water bath 1 is filled with constant temperature water 2 controlled to a constant temperature. Inside the constant temperature water bath 1, an electrolyte bath 3 is installed, which is immersed in the constant temperature water 2 and controlled to a constant temperature. The electrolyte bath 3 is filled with an electrolyte 4.

[0035] A working electrode 5 constituting a cathode electrode and a counter electrode 6 constituting an anode electrode are disposed in the electrolyte tank 3, and a reference electrode 7 is disposed between the working electrode 5 and the counter electrode 6. The working electrode 5, counter electrode 6, and reference electrode 7 are connected to a potentiostat 8. The potentiostat 8 used was HSV-110V (product name) manufactured by Hokuto Denko Corporation.

[0036] When measuring the cathodic polarization curve of the cathode electrode according to this example using the polarization curve measuring device shown in FIG. 1, the electrolyte 4 was 0.1 mol L with a pH of 13. -1 An aqueous solution of potassium hydroxide (KOH) was used. 150 mL of this electrolyte 4 was measured and poured into the electrolyte tank 3. A 200 mL glass beaker was used as the electrolyte tank 3. The electrolyte tank 3 was placed inside the electrolyte tank 3, immersed in constant temperature water 2 maintained at a temperature of 293 K (25°C), so that the electrolyte 4 poured into the electrolytic tank 3 was maintained at the temperature of the constant temperature water 2.

[0037] The working electrode 5 was formed from the sintered alloy that constitutes the cathode electrode according to this example. This working electrode 5 was formed to a width of 8.8 mm, a length of 25.8 mm, and a thickness of 0.8 mm. The working electrode 5 was supported so that the depth of the immersed portion in the electrolyte 4 was 10 mm.

[0038] The counter electrode 6 was made of a carbon rod. The carbon rod constituting the counter electrode 6 had a diameter of 6 mm and a length of 200 mm. This carbon rod was supported so that the depth of the immersed portion in the electrolyte 4 was 30 mm. An Ag / AgCl (saturated KCl) electrode was used as the reference electrode 7. The reference electrode 7, the sintered alloy plate constituting the working electrode 5, and the carbon rod constituting the counter electrode 6 were supported so that the distance between the electrodes was 20 mm.

[0039] Here, in order to measure the cathodic polarization curve, the natural immersion potential of the working electrode 5 made of sintered alloy is measured, and the potential is increased by 0.01 Vs from the vicinity of the natural immersion potential. -1 The cathode current generated by sweeping the electrode in the less noble direction at a speed of 0 V was measured. The potential was measured relative to the Ag / AgCl constituting the reference electrode 7 and converted to a reversible hydrogen electrode (RHE) standard, where the potential at which hydrogen is generated on Pt in the electrolyte 4 made of the aforementioned KOH aqueous solution with a pH of 13 was set to 0 V. The measured cathode current was converted to a current density by dividing it by the area of ​​the portion of the working electrode 5 immersed in the electrolyte made of the aqueous solution.

[0040] Next, several embodiments of the present invention will be described.

[0041] Example 1 Example 1 is a cathode electrode made of a sintered alloy in which Ni and Cr are sintered between WC particles as a binder phase. The sintered alloy constituting this cathode electrode contains 5 wt % Ni and 0.58 wt % Cr, with the remainder being WC and unavoidable impurities.

[0042] The sintered alloy constituting this cathode electrode was manufactured using a sintered alloy raw material powder made by mixing WC powder with an average particle size of 1.5 μm, 5 wt. % Ni powder with an average particle size of 1.1 μm, and 0.665 wt. % Cr3C2 powder with an average particle size of 1.4 μm. The WC powder, Ni powder, and Cr3C2 powder used here are all commercially available products.

[0043] The cemented carbide raw material powder, which is a mixture of WC powder, Ni powder, and Cr3C2 powder, is placed in a stainless steel pot along with an ethanol solvent and cemented carbide balls, and mixed and ground in the pot for 30 hours. The cemented carbide powder material mixed and ground in the pot is removed from the pot and dried. Paraffin wax is added to this ground and dried cemented carbide raw material powder. The cemented carbide raw material powder with the paraffin wax added is compressed into a specified size to form a green compact.

[0044] The compact formed by compression molding the sintered alloy raw material powder is heated to approximately 350°C in a furnace in a hydrogen atmosphere and debound. The debound compact is then pre-sintered by evacuating the furnace and heating it from room temperature to 900°C and holding it there for 120 minutes. Argon gas is then introduced into the furnace containing the pre-sintered compact to create an argon pressurized atmosphere of 0.9 MPa. The furnace is then heated to 1390°C and held there for 90 minutes for sintering. The compact is then subjected to HIP treatment at 1370°C under a 60 MPa atmosphere, resulting in a dense sintered alloy. The sintered alloy produced here contains 5% by weight of Ni and 0.58% by weight of Cr.

[0045] The sintered alloy thus produced is cooled and then machined to the cathode electrode having the aforementioned size by cutting or the like. Alternatively, a green compact may be formed in advance to form the cathode electrode having the aforementioned size.

[0046] The sintered alloy thus prepared was placed as the working electrode 5 of the polarization curve measuring device, which was a cathode electrode, and the natural immersion potential of the working electrode 5 was measured. The potential was then increased by 0.01 Vs from the vicinity of the natural immersion potential. -1 The cathode current generated by sweeping the electrode in the less noble direction at a speed of 0.001 m / s was measured, and a cathode polarization curve was obtained. The potential was measured relative to the Ag / AgCl constituting the reference electrode 7 and converted to a reversible hydrogen electrode (RHE) potential, where the potential at which hydrogen evolves on Pt in the electrolyte 4 of pH 13 was set to 0 V. The measured cathode current was converted to a current density by dividing it by the area of ​​the portion of the working electrode 5 immersed in the electrolyte consisting of an aqueous KOH solution. The results are shown in the cathode polarization curve in FIG. 2. From these measurement results, the hydrogen overvoltage ηH (V) of Example 1 was 0.129 V.

[0047] Here, the potential (E RHE ) was converted based on the potential of the reversible hydrogen electrode (RHE) and calculated based on the following formula (3).

[0048] ERHE =E SSCE +0.05914·ph+E ○ SSCE ···(3)

[0049] In equation (3), E SSCE is the potential of the reference electrode 7, and E ○ SSCE is the standard potential of the reference electrode 7. Here, pH is 13, and E ○ SSCE is set to 0.199. The cathodic polarization curve for Example 1 is shown in FIG. 2 a, and the hydrogen overvoltage ηH (V) was found to be 0.129V.

[0050] Here, the linearly changing range is approximated by a straight line, and the -2 was extrapolated up to

[0051] The hydrogen production rate (R HER The water splitting measurement can be carried out using a known water splitting apparatus.

[0052] The water splitting apparatus used in Example 1 includes an electrolyte tank into which an aqueous solution to be split is introduced. A cathode electrode and an anode electrode are installed in the electrolyte tank. A 0.1 mol dm -3 An aqueous solution of potassium hydroxide (KOH) was used. This aqueous solution had a pH of 13. The cathode electrode was made of the sintered alloy according to Example 1. The anode electrode was made of a carbon rod.

[0053] A constant voltage of 6.0 V was applied between the anode and cathode electrodes to perform water electrolysis. This water electrolysis was carried out for 30 minutes, and the volume of hydrogen generated was measured every 5 minutes. This measurement was carried out 10 times, and the average value is shown in Figure 3 (a).

[0054] In addition, the amount of hydrogen produced can be calculated by the unit area of ​​the cathode electrode (m 2 ) hydrogen production rate (RHER ) was calculated. HER ) was calculated from the hydrogen production rate (R HER ) was calculated.

[0055] The hydrogen evolution rate (R HER ) is 3.3 × 10 -3 ±3.7×10 -3 (mol m -2 min -1 ) was.

[0056] Example 2 In Example 2, a cathode electrode was formed from a sintered alloy in which Ni and Cr were used as a binder phase between WC particles, as in Example 1. The sintered alloy constituting this cathode electrode contained 15% by weight of Ni and 1.7% by weight of Cr, with the remainder of this sintered alloy also containing WC and inevitable impurities.

[0057] The sintered alloy constituting this cathode electrode was manufactured using raw material powders that were a mixture of WC powder with an average particle size of 1.5 μm, 15 wt. % Ni powder with an average particle size of 1.1 μm, and 1.995 wt. % Cr3C2 powder with an average particle size of 1.4 μm. The WC powder, Ni powder, and Cr3C2 powder used here were all commercially available.

[0058] The sintered alloy of Example 2 was manufactured through the same manufacturing process as Example 1, but in Example 2, the sintering after pre-sintering was carried out by heating the material to 1390°C in a pressurized argon atmosphere of 0.9 MPa in a furnace and holding the temperature for 90 minutes, followed by the HIP treatment similar to that of Example 1. The sintered alloy of Example 2 obtained by sintering the raw material powders mixed in the above-mentioned compounding ratio was manufactured to contain 15 wt% Ni and 1.7 wt% Cr.

[0059] The sintered alloy produced here is cooled and then machined into a cathode electrode of the aforementioned size by cutting or the like, as in Example 1. Alternatively, a green compact is preformed to form a cathode electrode of the aforementioned size.

[0060] The sintered alloy thus prepared was placed as the cathode working electrode 5 of the polarization curve measuring device in the same manner as in Example 1, and the natural immersion potential of the working electrode 5 was measured. The potential was then increased by 0.01 Vs from the vicinity of the natural immersion potential. -1 The cathode current generated by sweeping the electrode in the less noble direction at a speed of 0.168 V was measured, and a cathode polarization curve was obtained. The results are shown in Figure 2(b). From these results, the hydrogen overvoltage ηH (V) was determined to be 0.168 V.

[0061] The hydrogen production rate (R HER The water splitting measurement was carried out using the same well-known water splitting apparatus as that used in the measurement in Example 1.

[0062] The water splitting apparatus used in Example 2 also includes an electrolyte tank into which an aqueous solution to be split is introduced. A cathode electrode and an anode electrode are installed in this electrolyte tank. A 0.1 mol dm -3 An aqueous solution of potassium hydroxide (KOH) was used. The cathode electrode was made of the sintered alloy according to Example 2. The anode electrode was made of a carbon rod.

[0063] A constant voltage of 6.0 V was applied between the anode and cathode electrodes to perform water electrolysis. This water electrolysis was carried out for 30 minutes, and the volume of hydrogen generated was measured every 5 minutes. This measurement was carried out 10 times, and the average value is shown in Figure 3(b).

[0064] In addition, the amount of hydrogen produced can be calculated by the unit area of ​​the cathode electrode (m 2 ) hydrogen production rate (R HER ) was calculated. HER) was calculated from the hydrogen production rate (R HER ) was calculated.

[0065] The hydrogen evolution rate (R HER ) is 2.3 × 10 -3 ±1.5×10 -3 (mol m -2 min -1 ) was.

[0066] Example 3 Example 3 is a cathode electrode made of a sintered alloy in which Ni and Cr are sintered as a binder phase between WC particles, as in Examples 1 and 2. The sintered alloy constituting this cathode electrode contains 25 wt % Ni and 2.9 wt % Cr, with the remainder of this sintered alloy also containing WC and inevitable impurities.

[0067] The sintered alloy constituting this cathode electrode was manufactured using a sintered alloy raw material powder that was a mixture of WC powder with an average particle size of 1.5 μm, 25 wt% Ni powder with an average particle size of 1.1 μm, and 3.325 wt% Cr3C2 powder with an average particle size of 1.4 μm. The WC powder, Ni powder, and Cr3C2 powder used here were all commercially available.

[0068] The sintered alloy of Example 3 was also manufactured through the same manufacturing process as Examples 1 and 2, but in Example 3, the degreased green compact was pre-sintered by heating the furnace in a vacuum atmosphere from room temperature to 600°C and holding it for 120 minutes. Then, after pre-sintering, the furnace was sintered in a pressurized argon atmosphere of 0.9 MPa, heating the furnace to 1350°C and holding it for 90 minutes, followed by the same HIP treatment as in Examples 1 and 2. The sintered alloy of Example 3 obtained by sintering the raw material powders mixed in the above-mentioned composition ratio was produced to contain 25 wt% Ni and 2.9 wt% Cr.

[0069] The sintered alloy produced here is cooled and then machined into a cathode electrode of the aforementioned size by cutting or the like, as in Examples 1 and 2. Alternatively, a green compact is preformed to form a cathode electrode of the aforementioned size.

[0070] The sintered alloy thus prepared was placed as the working electrode 5 of the polarization curve measuring device as the cathode electrode in the same manner as in Examples 1 and 2. The natural immersion potential of the working electrode 5 was measured, and the potential was increased by 0.01 Vs from the vicinity of the natural immersion potential. -1 The cathode current generated by sweeping the electrode in the less noble direction at a speed of 0.154 V was measured, and a cathode polarization curve was obtained. The results are shown in Figure 2c. From these measurement results, the hydrogen overvoltage ηH (V) was determined to be 0.154 V.

[0071] The hydrogen production rate (R HER The water splitting measurement was carried out using the same well-known water splitting apparatus as used in the measurements in Examples 1 and 2.

[0072] The water splitting apparatus used in Example 3 also includes an electrolyte tank into which an aqueous solution to be split is introduced. A cathode electrode and an anode electrode are installed in this electrolyte tank. A 0.1 mol dm -3 An aqueous solution of potassium hydroxide (KOH) was used. The cathode electrode was made of the sintered alloy according to Example 2. The anode electrode was made of a carbon rod.

[0073] A constant voltage of 6.0 V was applied between the anode and cathode electrodes to perform water electrolysis. This water electrolysis was carried out for 30 minutes, and the volume of hydrogen generated was measured every 5 minutes. This measurement was carried out 10 times, and the average value is shown in Figure 3c.

[0074] In addition, the amount of hydrogen produced can be calculated by the unit area of ​​the cathode electrode (m 2 ) hydrogen production rate (R HER ) was calculated. HER) was calculated from the hydrogen production rate (R HER The hydrogen evolution rate (R HER ) is 2.7 × 10 -3 ±2.3×10 -3 (mol m -2 min -1 ) was.

[0075] (Comparative Example 1) The present invention sintered alloy In order to evaluate the hydrogen overvoltage when Pt was used as the cathode electrode, the cathode polarization curve was measured when Pt was used as the cathode electrode. At this time, Pt was formed into a plate shape of approximately the same size as the cathode electrodes shown in Examples 1 to 3.

[0076] The Pt prepared here was set as a working electrode, which is a cathode electrode, in the polarization curve measuring device described above, as in Examples 1 to 3. The natural immersion potential of this working electrode 5 was measured, and the potential was increased by 0.01 Vs from the vicinity of the natural immersion potential. -1 The cathode current generated by sweeping the electrode in the less noble direction at a speed of 1000 kJ / cm was measured, and a cathode polarization curve was obtained. The results are shown in Figure 2(d). In this measurement, the hydrogen overvoltage ηH (V) was set to 0.0 V.

[0077] The hydrogen production rate (R HER The water splitting measurement was carried out using the same well-known water splitting apparatus as that used in the measurements in Examples 1 to 3.

[0078] The water splitting device of Comparative Example 1 using Pt as the cathode electrode also includes an electrolyte tank into which an aqueous solution to be split is introduced. The electrolyte tank contains a cathode electrode and an anode electrode. A 0.1 mol dm -3 An aqueous solution of potassium hydroxide (KOH) was used. As in Examples 1 to 3, the anode electrode was made of a carbon rod.

[0079] A constant voltage of 6.0 V was applied between the anode and cathode electrodes to perform water electrolysis. This water electrolysis was carried out for 30 minutes, and the volume of hydrogen generated was measured every 5 minutes. This measurement was carried out 10 times, and the average value is shown in Figure 3(d).

[0080] In addition, the amount of hydrogen produced can be calculated by the unit area of ​​the cathode electrode (m 2 ) hydrogen production rate (R HER ) was calculated. HER ) was calculated from the hydrogen production rate (R HER ) was calculated.

[0081] The hydrogen evolution rate (R HER ) is 2.6 × 10 -3 ±1.5×10 -3 (mol m -2 min -1 ) was.

[0082] (Comparative Example 2) The present invention sintered alloy In order to evaluate the hydrogen overvoltage when used as a cathode electrode, the cathode polarization curve was measured when Ni was used as the cathode electrode. At this time, the Ni was formed into a plate shape of approximately the same size as the cathode electrodes shown in Examples 1 to 3.

[0083] The Ni prepared here was set as a working electrode, which is a cathode electrode, in the polarization curve measuring device described above, as in Examples 1 to 3. The natural immersion potential of this working electrode 5 was measured, and the potential was increased by 0.01 Vs from around the natural immersion potential. -1 The cathode current generated by sweeping the electrode in the less noble direction at a speed of 0.01 V was measured, and a cathode polarization curve was obtained. The results are shown in Figure 2(e). From these results, the hydrogen overvoltage ηH (V) was determined to be 0.201 V.

[0084] The hydrogen production rate (R HERThe water splitting measurement was carried out using the same well-known water splitting apparatus as that used in the measurements in Examples 1 to 3.

[0085] The water splitting apparatus of Comparative Example 2 using Ni as the cathode electrode also includes an electrolyte tank into which an aqueous solution to be split is introduced. The electrolyte tank contains a cathode electrode and an anode electrode. A 0.1 mol dm -3 An aqueous solution of potassium hydroxide (KOH) was used. As in Examples 1 to 3, the anode electrode was made of a carbon rod.

[0086] A constant voltage of 6.0 V was applied between the anode and cathode electrodes to perform water electrolysis. This water electrolysis was carried out for 30 minutes, and the volume of hydrogen generated was measured every 5 minutes. This measurement was carried out 10 times, and the average value is shown in Figure 3(e).

[0087] In addition, the amount of hydrogen produced can be calculated by the unit area of ​​the cathode electrode (m 2 ) hydrogen production rate (R HER ) was calculated. HER ) was calculated from the hydrogen production rate (R HER ) was calculated.

[0088] The hydrogen evolution rate (R HER ) is 1.2 × 10 -4 ±3.5×10 -4 (mol m -2 min -1 ) was.

[0089] (evaluation) As shown in the above-mentioned Comparative Example 1, when the hydrogen overvoltage (ηH) when water decomposition was performed using Pt as the cathode electrode was set to 0.0 V, the hydrogen overvoltage (ηH) of Examples 1 to 3 of the present invention was sintered alloy When water splitting was carried out using this as a cathode, the hydrogen overvoltage (ηH(V)) was 0.129 to 0.168V.

[0090] When water decomposition was carried out using Ni of Comparative Example 2 as a cathode electrode, the hydrogen overvoltage (ηH(V)) was 0.201V.

[0091] When water electrolysis was performed using a cathode made of the sintered alloy according to the present invention, the hydrogen generation rate was equivalent to that when Pt was used as the cathode electrode, and the amount of hydrogen generated was equivalent to that of Pt, as shown in FIG. sintered alloy The amount of hydrogen generated when using Pt as the cathode electrode was greater than that when using Pt as the cathode electrode.

[0092] On the other hand, when water electrolysis was performed using Ni as the cathode electrode as shown in Comparative Example 2, the hydrogen overvoltage (ηH (V)) was higher than that of the present invention, the hydrogen production rate was lower than that of the present invention, and the amount of hydrogen produced was small and insufficient, as shown in FIG. 3.

[0093] In contrast, when the sintered alloy according to the present invention, in which Ni and Cr are sintered as a binder phase between WC particles, is used as a cathode electrode, it was found that hydrogen is generated from a potential of −0.15 V, without being significantly dependent on the composition ratio of Ni—Cr used as the binder phase, as shown in Examples 1 to 3. From this hydrogen generation potential, it was confirmed that the hydrogen overvoltage of the WC—Co sintered alloy constituting the cathode electrode according to the present invention is approximately 0.15 V.

[0094] The present invention sintered alloy By using this as the cathode electrode for water electrolysis, a small hydrogen overvoltage (ηH(V)) that is not significantly different from that when Pt is used is realized, enabling aqueous production by water electrolysis with a highly efficient hydrogen production rate. [Industrial Applicability]

[0095] The present invention makes it possible to inexpensively and stably supply large quantities of cathode electrodes for hydrogen production devices that produce hydrogen by water electrolysis, which is expected to be an alternative energy source to fossil fuels. [Explanation of symbols]

[0096] 1 constant temperature water bath 2 Constant temperature water 3 Electrolyte tank 4 Electrolyte 5 Working electrode 6. Opposite 7 Reference pole 8. Potentiostat

Claims

1. A cathode electrode used in water electrolysis, A cathode electrode for water electrolysis made of a sintered alloy in which nickel (Ni) and chromium (Cr) are used as binder phases between fine particles of tungsten carbide (WC).

2. 2. The cathode electrode for water electrolysis according to claim 1, wherein the binder phase comprises the Ni and the Cr dissolved therein.

3. 3. The cathode electrode for water electrolysis according to claim 1, wherein the sintered alloy contains 5 to 25 wt % of Ni and 0.5 to 3.0 wt % of Cr.

4. 3. The cathode electrode for water electrolysis according to claim 1, wherein the sintered alloy has an average particle size of the WC of 1.0 to 10 μm.

5. A cathode electrode for water electrolysis according to claim 3, characterized in that the sintered alloy has an average particle size of the WC of 1.0 to 10 μm.

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