Cathode electrode for water electrolysis

Abstract

This invention provides a cathode electrode for water electrolysis that achieves catalytic performance equivalent to, or even exceeding, that of platinum (Pt), without using any platinum (Pt). [Solution] In a cathode electrode used for hydrogen production by water electrolysis, the spaces between tungsten carbide (WC) nanoparticles are composed of a sintered alloy with nickel (Ni) and chromium (Cr) as binder phases. The sintered alloy constituting the cathode electrode contains 5-25% by weight of Ni and 0.5-3.0% by weight of Cr. By using this sintered alloy as the cathode electrode for water electrolysis, the hydrogen overpotential (ηH(V)) during hydrogen production is reduced, enabling highly efficient and stable hydrogen production.

Description

Technical Field

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

Background Art

[0002] Conventionally, in order to suppress the emission of carbon dioxide, which causes environmental destruction such as global warming, and to realize a decarbonized society, the use of hydrogen energy has been attracting attention. As a method for producing hydrogen, there is a water electrolysis method that utilizes abundant water resources.

[0003] In an apparatus for producing hydrogen by the water electrolysis method or a hydrogen production method, platinum (Pt) is used for the cathode electrode. This is because the hydrogen overvoltage (ηH(V)) of Pt is sufficiently small compared to other metals. In particular, since Pt activates oxygen and hydrogen, it is used as an oxidation catalyst, a hydrogenation catalyst, or a dehydrogenation catalyst. In particular, for the realization of a decarbonized society and a hydrogen society, the demand for Pt as a catalyst for promoting reactions in electrodes in fuel cells, which is expected to increase in various fields in the future, will increase. Pt is a rare resource, not only expensive, but its price is expected to rise further in the future.

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

[0005] In Patent Document 1, as a catalyst constituting a cathode electrode, a platinum skin layer is provided on the surface of alloy fine particles composed of an alloy of Pt and a transition metal. This catalyst is said to be able to increase the mass activity compared to a commercially available Pt catalyst, and thus reduce the amount of Pt used.

[0006] Further, in Patent Document 2, as a catalyst used for hydrogen production by water electrolysis, a catalyst containing 10 or more metal elements and having a nanoporous structure, thereby reducing the proportion of noble metal elements such as Pt, has been proposed.

Prior Art Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-141792 [Patent Document 2] Japanese Patent Publication No. 2023-028320 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Conventional cathode electrodes and catalysts used in hydrogen production by water electrolysis have all aimed to reduce the proportion of Pt used, but they are not constructed without using Pt at all.

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

[0010] The inventors diligently researched materials that could be used in cathode electrodes for hydrogen production by water electrolysis. Focusing on the fact that the electron configuration of tungsten carbide (WC) is similar to that of Pt, they realized that by selecting a metal that constitutes the bonding phase that binds the fine particles of WC together, it is possible to achieve a catalytic function for hydrogen production equivalent to, or even better than, that of Pt. Based on this, they completed the present invention. [Means for solving the problem]

[0011] This invention was completed as a result of diligent research to solve the above-mentioned technical problems, and is a cathode electrode used in hydrogen production by water electrolysis, in which the spaces between tungsten carbide (WC) fine particles are composed of a sintered alloy in which nickel (Ni) and chromium (Cr) are used as binder phases. The binder phase is a Ni-Cr alloy in which Cr is solid-dissolved in Ni.

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

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

[0014] The cathode electrode for water electrolysis is constructed from sintered metal, in which WC fine particles are bonded together with Ni and Cr as the bonding phase. This reduces the hydrogen overpotential (ηH(V)) during hydrogen generation, enabling highly efficient and stable hydrogen production.

[0015] Furthermore, since the cathode electrode for water electrolysis does not use precious metal elements such as Pt, it can be supplied inexpensively and reliably. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram showing a cathode polarization curve measurement device. [Figure 2] This characteristic diagram shows 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 constituting the present invention as cathode electrodes. [Figure 3] This is a characteristic diagram showing the amount of hydrogen produced when hydrogen is generated using a hydrogen generation device that uses Pt, Ni, and the sintered alloy constituting the present invention as cathode electrodes. [Modes for carrying out the invention]

[0017] The following describes embodiments of the cathode electrode according to the present invention. This embodiment relates to a cathode electrode used in a water electrolysis method for producing hydrogen using water resources.

[0018] The water electrolysis method, which produces hydrogen by water electrolysis, utilizes the fact that when a cathode electrode and an anode electrode are immersed in an aqueous solution containing an electrolyte and an electric current is passed between the cathode electrode and the anode electrode, water or hydrogen ions are reduced on the cathode electrode, generating hydrogen gas.

[0019] The cathode electrode according to this embodiment is made of a sintered alloy in which fine particles of WC are bonded together using Ni and Cr as binder phases. In the sintered alloy that constitutes this embodiment, the binder phase is a Ni-Cr alloy in which Cr is solid-dissolved in Ni. This sintered alloy is made from a 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 raw material powder used as the starting material is treated with an oil such as paraffin wax to form a molding raw material powder. The molding raw material powder is compressed into a predetermined shape to form a compact. This compact is degreased by heating it to approximately 250-500°C in a furnace under a hydrogen atmosphere. The degreased compact is then subjected to a vacuum or reducing gas atmosphere and pre-sintered by being held for 100-130 minutes in a furnace heated from room temperature to 800-1200°C. Subsequently, argon gas is introduced into the furnace containing the compact to create an argon pressurized atmosphere of 0.85-0.95 MPa, and the furnace is heated to 1300-1400°C and held for 80-100 minutes. Finally, a HIP treatment at 55-65 MPa in a 1300-1400°C atmosphere is performed, resulting in the compact being transformed into a dense sintered alloy. In the process of sintering this raw material powder to create a sintered alloy, the carbon component is separated from the Cr3C2 used as the starting material, and the chromium component dissolves in the nickel to form a Ni-Cr alloy. This Ni-Cr alloy constitutes the bonding phase that binds the WC fine particles together.

[0021] Furthermore, the sintered metal constituting the cathode electrode manufactured in this embodiment contains 5 to 25% by weight of Ni and 0.5 to 3.0% by weight of Cr, with the remainder being WC. Note that this sintered metal may contain unavoidable impurities characteristic of sintered metals.

[0022] The sintered alloy produced here is sintered to a predetermined size, and then cut and shaped to the form and size required for use as a cathode electrode in a water splitting apparatus.

[0023] Furthermore, the sintered alloy used in this embodiment may be manufactured by shaping a compacted powder produced during the manufacturing process into a shape and size suitable for use as a cathode electrode, and then sintering it.

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

[0025] In this embodiment, the cathode electrode is placed in an electrolytic cell filled with an electrolyte solution. An anode electrode is placed in the electrolytic cell opposite the cathode electrode. 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 electrolyte solution, the cathode electrode side exhibits the hydrogen evolution reaction in an alkaline aqueous solution shown in equation (1) below, and hydrogen (H2) is generated.

[0027] 2H2O + 2e - → H2 + 2OH - ...(1)

[0028] Furthermore, on the anode electrode side, the oxygen evolution reaction in an alkaline aqueous solution, as shown in equation (2) below, occurs, and oxygen (O2) is generated.

[0029] 4OH - → 2H2O + O2 + 4e - ...(2)

[0030] Incidentally, when water electrolysis was performed using a sintered alloy, in which Ni and Cr were used as the bonding phases between the fine particles of WC according to this embodiment, as the cathode electrode, the hydrogen overpotential (ηH(V)) was small and showed a value close to that when Pt was used as the cathode electrode. This is considered to be due to the synergistic effect of WC, which has an electronic structure similar to 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 as a cathode electrode for water electrolysis in place of Pt.

[0031] Note that, here, the hydrogen overpotential (ηH(V)) is the hydrogen ion (H) when water electrolysis is performed. + This is the potential difference from the potential at which a cathode (reduction) current is generated when a discharge occurs on the surface of the cathode electrode, to the potential at which hydrogen (H) in its atomic state and then hydrogen gas (H2) begins to be emitted. [Examples]

[0032] In the following examples, several sintered alloys were prepared by sintering WC fine particles with Ni and Cr as the binder phases, and the ease of hydrogen generation when these sintered alloys were used as cathode electrodes in a water electrolysis method was confirmed by measuring the cathode polarization curve.

[0033] The cathode polarization curve was measured using a polarization curve measuring device configured as shown in Figure 1.

[0034] As shown in Figure 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, there is an electrolyte tank 3 that is immersed in the constant temperature water 2 and controlled to a constant temperature. The electrolyte tank 3 is filled with electrolyte 4.

[0035] The electrolyte cell 3 contains a working electrode 5 which constitutes the cathode electrode and a counter electrode 6 which constitutes the anode electrode, and a reference electrode 7 is positioned between the working electrode 5 and the counter electrode 6. These working electrode 5, counter electrode 6, and reference electrode 7 are connected to a potentiostat 8. The potentiostat 8 used is the HSV-110V (product name) manufactured by Hokuto Denko Co., Ltd.

[0036] When measuring the cathode polarization curve of the cathode electrode according to this embodiment using the polarization curve measuring device shown in Figure 1, 0.1 molL of electrolyte 4 with a pH of 13 is used. -1 An aqueous solution of potassium hydroxide (KOH) was used. 150 mL of this electrolyte 4 was measured and added to the electrolyte cell 3. A 200 mL glass beaker was used for the electrolyte cell 3. The electrolyte cell 3 was placed inside the electrolyte cell 3 by being immersed in constant temperature water 2 maintained at a temperature of 293 K (25 °C), so that the electrolyte 4 added to the electrolyte cell 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 embodiment. The working electrode 5 used was molded to have a width of 8.8 mm, a length of 25.8 mm, and a thickness of 0.8 mm. At this time, the working electrode 5 was supported such that the depth of the portion immersed in the electrolyte 4 was 10 mm.

[0038] Furthermore, the counter electrode 6 was formed from 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 immersion depth in the electrolyte 4 was 30 mm. For the reference electrode 7, an Ag / AgCl (saturated KCl) electrode was used. The sintered alloy plate constituting the reference electrode 7 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 cathode polarization curve, the spontaneous immersion potential of the working electrode 5, which is made of sintered alloy, is measured, and the potential is measured from around that spontaneous immersion potential to 0.01 Vs. -1 The cathode current generated by running the electrode in the negative direction at a certain speed was measured. The potential was measured relative to the Ag / AgCl component of the reference electrode 7 and converted to a reversible hydrogen electrode (RHE) relative to the potential at which hydrogen is generated on Pt in the electrolyte 4 consisting of a KOH aqueous solution with a pH of 13, as described above, where 0V was used. The measured cathode current was also converted to current density by dividing it by the area of ​​the portion of the working electrode 5 immersed in the aforementioned aqueous electrolyte.

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

[0041] (Example 1) Example 1 is a cathode electrode in which WC fine particles are sintered with Ni and Cr as the bonding phase, and the sintered alloy constituting this cathode electrode contains 5% by weight of Ni and 0.58% by weight of 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 prepared by mixing WC powder with an average particle size of 1.5 μm, 5% by weight of Ni powder with an average particle size of 1.1 μm, and 0.665% by weight of 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.

[0043] The cemented carbide raw material powder, a mixture of WC powder, Ni powder, and Cr3C2 powder, is placed in a stainless steel pot along with 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 and dried. Paraffin wax is added to this ground and dried cemented carbide raw material powder. The cemented carbide raw material powder with added paraffin wax is compressed and molded to a predetermined size to form a compact.

[0044] The green compact formed by compression molding of the sintered metal raw material powder is heated to about 350 °C in a furnace in a hydrogen atmosphere for degreasing. After the degreased green compact makes the furnace atmosphere a vacuum atmosphere, it is pre-sintered by raising the temperature from room temperature to 900 °C and holding for 120 minutes. Then, argon gas is introduced into the furnace in which the pre-sintered green compact is charged to form an argon pressurized atmosphere of 0.9 MPa, and the temperature of this furnace is raised to 1390 °C and held for 90 minutes for sintering treatment. Further, by performing HIP (Hot Isostatic Pressing) treatment under an atmosphere of 60 MPa at 1370 °C, the green compact charged into the furnace becomes a dense sintered alloy. The sintered alloy produced here contains 5 wt% of Ni and 0.58 wt% of Cr.

[0045] After the sintered alloy produced here is subjected to cooling treatment, it is machined by cutting or the like to be processed into the cathode electrode having the size described above. Alternatively, the green compact may be pre-molded so as to be the cathode electrode having the size described above.

[0046] The sintered alloy produced here is installed as the working electrode 5 of the polarization curve measuring device described above as the working electrode that is the cathode electrode, the natural immersion potential of this working electrode 5 is measured, and the potential is 0.01 Vs from near the natural immersion potential -1 The cathode current generated by drawing in the base metal direction at a speed of is measured to obtain a cathode polarization curve. Here, the potential was measured based on the Ag / AgCl standard constituting the reference electrode 7 and converted to the reversible hydrogen electrode standard (RHE) with the potential at which hydrogen is generated on Pt in the electrolyte 4 of pH 13 set as 0 V. Further, the measured cathode current was converted to current density by dividing by the area of the immersed portion in the electrolyte composed of an aqueous KOH solution of the working electrode 5. The results are shown in the cathode polarization curve of FIG. 2. From this measurement result, the hydrogen overvoltage ηH (V) of Example 1 was 0.129 V.

[0047] Here, the potential (E RHE ) of the working electrode 5 used as the cathode electrode was converted based on the potential of the reversible hydrogen electrode (RHE) and determined based on the following formula (3).

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

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

[0050] Here, we approximate the range of linear change with a straight line, and obtain 0 A·m -2 I extrapolated to this point.

[0051] Furthermore, the hydrogen production rate (R) when water electrolysis is performed using the sintered alloy shown in Example 1 as the cathode electrode is... HER The following measurements were taken: This water splitting measurement can be performed using a well-known water splitting apparatus.

[0052] The water splitting apparatus used in this embodiment 1 includes an electrolyte tank into which the aqueous solution to be split is introduced. A cathode electrode and an anode electrode are installed in this electrolyte tank. The water electrolysis medium is 0.1 mol·dm³ -3 An aqueous solution of potassium hydroxide (KOH) was used. This 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] Then, a constant voltage of 6.0V was applied between the anode and cathode electrodes to perform water electrolysis. This water splitting was carried out for 30 minutes, and the volume of hydrogen produced was measured every 5 minutes. This measurement was performed 10 times, and the average value is shown in Figure 3a.

[0054] Furthermore, from the amount of hydrogen generated, the unit area (m²) of the cathode electrode can be calculated. 2 Hydrogen production rate per unit (RHER The hydrogen production rate (R) was calculated. HER The calculation of the hydrogen production rate (R) every 5 minutes during the 30-minute water splitting is performed. HER ) was calculated.

[0055] The hydrogen generation rate (R) when the sintered alloy of Example 1 is used as the cathode electrode. HER ) is 3.3 × 10 -3 ±3.7 × 10 -3 (mol·m -2 ·min -1 ) was.

[0056] (Example 2) Example 2 is a cathode electrode in which the spaces between WC fine particles are formed by sintering a sintered alloy with Ni and Cr as the binder phase, similar to Example 1. This sintered alloy constituting the cathode electrode contains Ni in an amount of 15% by weight and Cr in an amount of 1.7% by weight. The remainder of this sintered alloy also contains WC and unavoidable impurities.

[0057] The sintered alloy constituting this cathode electrode was manufactured using a raw material powder prepared by mixing WC powder with an average particle size of 1.5 μm with 15% by weight of Ni powder with an average particle size of 1.1 μm and 1.995% by weight of 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.

[0058] The sintered alloy of Example 2 was manufactured through the same manufacturing process as in Example 1. However, in Example 2, after pre-sintering, the sintering was carried out by creating a 0.9 MPa argon pressurized atmosphere in the furnace, raising the temperature to 1390°C and holding it for 90 minutes, after which the same HIP (Heat Injection Precipitation) treatment as in Example 1 was performed. The sintered alloy of Example 2, obtained by sintering the raw material powders mixed in the above proportions, was prepared containing 15% by weight of Ni and 1.7% by weight of Cr.

[0059] The sintered alloy produced here is cooled and then machined to form a cathode electrode of the aforementioned size, similar to the process described in Example 1. Alternatively, the compacted powder can be pre-formed into a cathode electrode of the aforementioned size.

[0060] The sintered alloy produced here was set up as the working electrode 5 of the polarization curve measuring device described above, as the cathode electrode, similar to Example 1. The natural immersion potential of this working electrode 5 was measured, and the potential was set to 0.01 Vs from around that natural immersion potential. -1 The cathode current generated by running the material in the negative direction at a certain speed was measured, and a cathode polarization curve was obtained. The result is shown in Figure 2b. From this measurement result, the hydrogen overpotential ηH(V) was determined to be 0.168V.

[0061] Furthermore, the hydrogen production rate (R) when water electrolysis is performed using the sintered alloy shown in Example 2 as the cathode electrode is... HER The following measurements were taken: This water splitting measurement was performed using a well-known water splitting apparatus similar to the one used in the measurement in Example 1.

[0062] The water splitting apparatus used in this second embodiment also includes an electrolyte tank into which the aqueous solution to be split is introduced. A cathode electrode and an anode electrode are installed in this electrolyte tank. The water electrolysis medium is 0.1 mol·dm³. -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] Then, a constant voltage of 6.0V was applied between the anode and cathode electrodes to perform water electrolysis. This water splitting was carried out for 30 minutes, and the volume of hydrogen produced was measured every 5 minutes. This measurement was performed 10 times, and the average value is shown in Figure 3b.

[0064] Furthermore, from the amount of hydrogen generated, the unit area (m²) of the cathode electrode can be calculated. 2 Hydrogen production rate per unit (R HER The hydrogen production rate (R) was calculated. HERThe calculation of the hydrogen production rate (R) every 5 minutes during the 30-minute water splitting is performed. HER ) was calculated.

[0065] The hydrogen generation rate (R) when the sintered alloy of Example 2 is used as the cathode electrode. 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 in which the spaces between WC fine particles are composed of a sintered alloy in which Ni and Cr are used as the bonding phase, similar to Examples 1 and 2. This sintered alloy constituting the cathode electrode contains Ni in an amount of 25% by weight and Cr in an amount of 2.9% by weight. The remainder of this sintered alloy is composed of WC and unavoidable impurities.

[0067] The sintered alloy constituting this cathode electrode was manufactured using a sintered alloy raw material powder prepared by mixing WC powder with an average particle size of 1.5 μm, 25% by weight of Ni powder with an average particle size of 1.1 μm, and 3.325% by weight of 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.

[0068] The sintered alloy of Example 3 was also manufactured through the same manufacturing process as Examples 1 and 2. However, in Example 3, the pre-sintering of the degreased compacted powder was performed by raising the temperature of the furnace from room temperature to 600°C in a vacuum atmosphere and holding it for 120 minutes. After pre-sintering, the sintering was performed by raising the temperature to 1350°C in an argon pressurized atmosphere of 0.9 MPa and holding it for 90 minutes, after which the same HIP treatment as in Examples 1 and 2 was performed. The sintered alloy of Example 3, obtained by sintering the raw material powders mixed in the above proportions, was prepared containing 25% by weight of Ni and 2.9% by weight of Cr.

[0069] The sintered alloy produced here is cooled and then machined to form a cathode electrode of the aforementioned size, similar to Examples 1 and 2. Alternatively, the compacted powder is pre-formed to form a cathode electrode of the aforementioned size.

[0070] The sintered alloy produced here was installed as the working electrode (cathode electrode) of the polarization curve measuring device described above, as in Examples 1 and 2, and the natural immersion potential of this working electrode 5 was measured. The potential was then measured from around the natural immersion potential to 0.01 Vs. -1 The cathode current generated by running the atom in the negative direction at a certain speed was measured, and a cathode polarization curve was obtained. The result is shown in c in Figure 2. From this measurement result, the hydrogen overpotential ηH(V) was determined to be 0.154V.

[0071] Furthermore, the hydrogen production rate (R) when water electrolysis is performed using the sintered alloy shown in this Example 3 as the cathode electrode is... HER The following measurements were taken: This water splitting measurement was performed using a well-known water splitting apparatus similar to the one used in the measurements in Examples 1 and 2.

[0072] The water splitting apparatus used in this Example 3 also includes an electrolyte tank into which the aqueous solution to be split is introduced. A cathode electrode and an anode electrode are installed in this electrolyte tank. The water electrolysis medium is 0.1 mol·dm³ -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] Then, a constant voltage of 6.0V was applied between the anode and cathode electrodes to perform water electrolysis. This water splitting was carried out for 30 minutes, and the volume of hydrogen produced was measured every 5 minutes. This measurement was performed 10 times, and the average value is shown in c in Figure 3.

[0074] Furthermore, from the amount of hydrogen generated, the unit area (m²) of the cathode electrode can be calculated. 2 Hydrogen production rate per unit (R HER The hydrogen production rate (R) was calculated. HERThe calculation of the hydrogen production rate (R) every 5 minutes during the 30-minute water splitting is performed. HER The hydrogen generation rate (R) when the sintered alloy of Example 3 was used as the cathode electrode was calculated. HER ) is 2.7 × 10 -3 ±2.3 × 10 -3 (mol·m -2 ·min -1 ) was.

[0075] (Comparative Example 1) To evaluate the hydrogen overpotential when the sintered metal according to the present invention is used as the cathode electrode, the cathode polarization curve was measured when Pt was used as the cathode electrode. In this case, the 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 fabricated here was installed as the working electrode (cathode electrode) of the polarization curve measuring device described above, as in Examples 1-3, and the natural immersion potential of this working electrode 5 was measured. The potential was then measured from around the natural immersion potential to 0.01 Vs. -1 The cathode current generated by running the atom in the negative direction at a certain speed was measured, and a cathode polarization curve was obtained. The result is shown in Figure 2, d. In this measurement, the hydrogen overpotential ηH(V) was set to 0.0V.

[0077] And the hydrogen production rate (R) when water electrolysis is performed using Pt as the cathode electrode. HER The following measurements were taken: This water splitting measurement was performed using a well-known water splitting apparatus similar to the one used in the measurements in Examples 1 to 3.

[0078] The water splitting apparatus in Comparative Example 1, which uses Pt as the cathode electrode, also includes an electrolyte tank into which the aqueous solution to be split is introduced. The cathode electrode and the anode electrode are installed in this electrolyte tank. The aqueous electrolysis medium is 0.1 mol·dm³ -3 A potassium hydroxide (KOH) aqueous solution was used. As in Examples 1-3, the anode electrode was constructed from a carbon rod.

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

[0080] Furthermore, from the amount of hydrogen generated, the unit area (m²) of the cathode electrode can be calculated. 2 Hydrogen production rate per unit (R HER The hydrogen production rate (R) was calculated. HER The calculation of the hydrogen production rate (R) every 5 minutes during the 30-minute water splitting is performed. HER ) was calculated.

[0081] Hydrogen production rate (R) when Pt of Comparative Example 1 is used as the cathode electrode HER ) is 2.6 × 10 -3 ±1.5 × 10 -3 (mol·m -2 ·min -1 ) was.

[0082] (Comparative Example 2) To evaluate the hydrogen overpotential when the sintered metal according to the present invention is used as the cathode electrode, the cathode polarization curve was measured when Ni was used as the cathode electrode. In this case, 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 installed as the working electrode (cathode electrode) of the polarization curve measuring device described above, as in Examples 1-3, and the natural immersion potential of this working electrode 5 was measured. The potential was then measured from around the natural immersion potential to 0.01 Vs. -1 The cathode current generated by running the material in the negative direction at a certain speed was measured, and a cathode polarization curve was obtained. The result is shown in Figure 2e. From this measurement, the hydrogen overpotential ηH(V) was determined to be 0.201V.

[0084] And the hydrogen production rate (R) when water electrolysis is performed using Ni as the cathode electrode. HER The following measurements were taken: This water splitting measurement was performed using a well-known water splitting apparatus similar to the one used in the measurements in Examples 1 to 3.

[0085] The water splitting apparatus in Comparative Example 2, which uses Ni as the cathode electrode, also includes an electrolyte tank into which the aqueous solution to be split is introduced. The cathode electrode and the anode electrode are installed in this electrolyte tank. The aqueous electrolysis medium is 0.1 mol·dm³ -3 A potassium hydroxide (KOH) aqueous solution was used. As in Examples 1-3, the anode electrode was constructed from a carbon rod.

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

[0087] Furthermore, from the amount of hydrogen generated, the unit area (m²) of the cathode electrode can be calculated. 2 Hydrogen production rate per unit (R HER The hydrogen production rate (R) was calculated. HER The calculation of the hydrogen production rate (R) every 5 minutes during the 30-minute water splitting is performed. HER ) was calculated.

[0088] The hydrogen production rate (R) when Ni of Comparative Example 2 is used as the cathode electrode. HER ) is 1.2 × 10 -4 ±3.5 × 10 -4 (mol·m -2 ·min -1 ) was.

[0089] (evaluation) As shown in Comparative Example 1 above, when the hydrogen overpotential (ηH) when Pt is used as the cathode electrode for water splitting is set to 0.0V, the hydrogen overpotential (ηH(V)) when the sintered metals according to Examples 1 to 3 of the present invention are used as the cathode electrode for water splitting was 0.129 to 0.168V.

[0090] When water splitting was performed using Ni as the cathode electrode in Comparative Example 2, the hydrogen overpotential (ηH(V)) was 0.201V.

[0091] When a sintered alloy according to the present invention was used as a cathode electrode and water electrolysis was performed, 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 Figure 3. In particular, when the sintered metal of Example 1 was used as the cathode electrode, the amount of hydrogen generated was greater than that when Pt was used 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 overpotential (ηH(V)) was larger than that of the present invention, the hydrogen production rate was smaller than that of the present invention, and the amount of hydrogen produced was small, as shown in Figure 3, and a sufficient amount could not be obtained.

[0093] In contrast, when a sintered alloy, obtained by sintering WC fine particles with Ni and Cr as the bonding phase, was used as the cathode electrode, it was found that hydrogen was generated from a potential of -0.15V, regardless of the Ni-Cr composition ratio used in the bonding phase, as shown in Examples 1 to 3 above. From this hydrogen generation potential, it was confirmed that the hydrogen overpotential of the WC-Co sintered alloy constituting the cathode electrode according to the present invention is approximately 0.15V.

[0094] By using the sintered metal according to the present invention as the cathode electrode for water electrolysis, a small hydrogen overpotential (ηH(V)) that is not significantly different from that when Pt is used is achieved, enabling water-based hydrogen production by water electrolysis with a high-efficiency hydrogen generation rate. [Industrial applicability]

[0095] This invention makes it possible to supply a large quantity of cathode electrodes for a hydrogen production device that produces hydrogen, which is expected to be an energy source to replace fossil fuels, by water electrolysis, at a low cost and in a stable manner. [Explanation of Symbols]

[0096] 1. Constant temperature water bath 2 Constant temperature water 3 Electrolyte tank 4 Electrolyte 5 Working electrode 6 Opposite poles 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. The cathode electrode for water electrolysis according to claim 1, characterized in that the bonding phase has Cr solid-dissolved in Ni.

3. The cathode electrode for water electrolysis according to claim 1 or claim 2, characterized in that the sintered metal contains 5 to 25% by weight of Ni and 0.5 to 3.0% by weight of Cr.

4. The cathode electrode for water electrolysis according to any one of claims 1 to 3, characterized in that the sintered alloy has an average particle size of WC of 1.0 to 10 μm.

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