Operation method of oxygen reduction type salt electrolysis

Abstract

To produce an effect of extending life of salt electrolysis process by operating in a specific gas diffusion electrode potential.SOLUTION: An electrolysis method of an alkali metal chloride solution includes: supplying an oxygen containing gas to a cathode chamber; and performing an electrolysis while reducing oxygen on a gas diffusion electrode with a platinum catalyst. In the electrolysis method of the alkali metal chloride solution, the cathode potential separated from the electric resistance is between 0.20 V vs. RHE and 0.75 V vs. RHE.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an operating method for oxygen-reducing brine electrolysis. [Background technology]

[0002] In the salt electrolysis industry, the mainstream method is the ion exchange membrane method, which uses a chlorine generating electrode as the anode and a hydrogen generating electrode as the cathode, with a fluorine-based cation exchange membrane separating the anode and cathode.

[0003] On the other hand, by replacing the cathode with an oxygen reduction electrode, it is possible to reduce the theoretical electrolysis voltage by more than 1 V compared to ion exchange membrane method salt electrolysis, and this is attracting attention as a means of energy conservation toward promoting carbon neutrality.

[0004] However, with actual oxygen reduction electrodes, the voltage reduction effect is limited to about 0.7 V due to the high overpotential of the oxygen reduction reaction. Combined with the problem of not producing hydrogen that can be reused as an energy source as a by-product, this has prevented large-scale practical use.

[0005] As oxygen reduction electrodes for sodium chloride electrolysis that reduce overpotential, those using platinum or silver as catalysts have been widely studied.

[0006] For example, there are oxygen gas diffusion electrodes for sodium chloride electrolysis in which electrolysis voltage is reduced using a silver catalyst and a silver-platinum catalyst (Patent Document 1), and gas diffusion electrodes using silver and platinum catalysts (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5178959 [Non-patent literature]

[0008] [Non-Patent Document 1] Electrochemica Acta, 2000, vol.45, Issues 25, P.4251-4256 Summary of the Invention [Problem to be solved by the invention]

[0009] In Patent Document 1, the operating current (4.0 to 8.0 kA / m) of sodium chloride electrolysis is increased by using a silver catalyst. 2 When applied to the conventional electrolysis process, high overvoltages occurred, preventing energy conservation in the salt electrolysis process.

[0010] According to Non-Patent Document 1, a catalyst using platinum can reduce overvoltage more than a silver catalyst and contribute to energy saving in the salt electrolysis process. However, when a platinum catalyst is used as a cathode, platinum is dissolved into the electrolyte, and the amount of platinum available as a catalyst decreases, making it difficult to operate stably for a long period of time.

[0011] An object of the present invention is to provide an operating method for oxygen reduction type sodium chloride electrolysis that reduces the elution of platinum observed in conventional sodium chloride electrolysis methods using a platinum catalyst and is effective in saving energy and extending the life of the sodium chloride electrolysis process. [Means for solving the problem]

[0012] In this disclosure, it has been found that the potential of the cathode (hereinafter also referred to as the "gas diffusion electrode") affects the dissolution of platinum in sodium chloride electrolysis using a platinum catalyst, and an investigation has been carried out focusing on the potential of the gas diffusion electrode. As a result, it has been found that the dissolution of platinum before and after sodium chloride electrolysis can be reduced by controlling the potential of the gas diffusion electrode within a desired range.

[0013] That is, the present invention is as described in the claims, and the gist of the present invention is as follows. [1] A method for electrolyzing an aqueous alkali metal chloride solution by supplying an oxygen-containing gas to a cathode chamber and reducing oxygen with a gas diffusion electrode equipped with a platinum catalyst, in which the potential of the gas diffusion electrode separated by electrical resistance is 0.20 V vs. RHE or more and 0.75 V vs. RHE or less. [2] The current density during the electrolysis is 2 kA / m 2 More than 10kA / m 2 The method for electrolyzing an aqueous alkali metal chloride solution according to the above [1], [3] The method for electrolyzing an aqueous alkali metal chloride solution according to [1] or [2] above, wherein the oxygen concentration in the oxygen-containing gas is 8 vol % or more and 40 vol % or less. [4] The method for electrolyzing an alkali metal chloride aqueous solution according to any one of [1] to [3], wherein the gas diffusion electrode comprises, on one side of a conductive substrate, a gas diffusion layer containing hydrophobic carbon powder and a fluororesin, and a reaction layer containing carbon powder, a platinum catalyst, and a fluororesin. [5] The method for electrolyzing an aqueous alkali metal chloride solution according to [4] above, wherein the weight of platinum is 21 wt % or more when the total weight of the carbon powder and platinum contained in the reaction layer is 100 wt %. [6] The method for electrolyzing an aqueous alkali metal chloride solution according to any one of [1] to [5], wherein the platinum catalyst has a platinum crystallite size of 2 nm or more and 20 nm or less. [7] The platinum loading of the platinum catalyst is 0.1 mg / cm per geometric area of ​​the gas diffusion electrode. 2 More than 10mg / cm 2 The method for electrolyzing an aqueous alkali metal chloride solution according to any one of the items [1] to [6] below. [8] A method for producing chlorine gas and an alkali metal hydroxide, which uses the method for electrolyzing an aqueous alkali metal chloride solution according to any one of [1] to [7] above. Effect of the Invention

[0014] The present disclosure makes it possible to provide an energy-saving and highly stable operating method for oxygen-reduction type sodium chloride electrolysis that uses a platinum catalyst and can suppress the elution of platinum. [Brief description of the drawings]

[0015] [Figure 1] An example of the structure of a two-chamber electrolytic cell [Diagram 2] An example of the structure of a three-chamber electrolytic cell DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the present disclosure will be described with reference to an example of an embodiment thereof.

[0017] The present embodiment relates to a method for electrolyzing an aqueous alkali metal chloride solution by supplying an oxygen-containing gas to a cathode chamber and reducing oxygen with a gas diffusion electrode equipped with a platinum catalyst, in which the potential of the gas diffusion electrode separated by electrical resistance is 0.20 V vs. RHE or more and 0.75 V vs. RHE or less.

[0018] In the present embodiment, the electrolysis of an aqueous alkali metal chloride solution is carried out by supplying an oxygen-containing gas to the cathode chamber and reducing oxygen with a gas diffusion electrode equipped with a platinum catalyst.

[0019] In this embodiment, the reaction formula of electrolysis of an aqueous alkali metal chloride solution while reducing oxygen is expressed by the following reaction formula. (Anode)2Cl - → Cl2+ 2e - Formula (1-1) (Cathode)O2+ 2H2O + 4e - → 4OH - Formula (1-2) (Total) O2+ 4Cl - + 2H2O → 2Cl2+4OH - Formula (1-3)

[0020] In a gas diffusion electrode, the reaction for reducing oxygen is represented by the cathodic reaction shown in formula (1-2).

[0021] In the present embodiment, the aqueous alkali metal chloride solution used is not particularly limited as long as it is an aqueous solution of an alkali metal chloride, and examples thereof include one or more selected from the group consisting of an aqueous lithium chloride solution, an aqueous sodium chloride solution, an aqueous potassium chloride solution, an aqueous rubidium chloride solution, and an aqueous cesium chloride solution, and an aqueous sodium chloride solution is preferred.

[0022] In this embodiment, the potential of the gas diffusion electrode with the electrical resistance separated is 0.20 V vs. RHE or more and 0.75 V vs. RHE or less (based on the reversible hydrogen electrode).

[0023] If the potential of the gas diffusion electrode with the electrical resistance is less than 0.20V vs. RHE, hydrogen gas will be generated from inside the gas diffusion electrode, and the stress generated may peel off the reaction layer. Similarly, if hydrogen gas is mixed with oxygen gas generated in the cathode chamber at a certain ratio, it may form a detonation gas and cause an explosion.

[0024] If the potential of the gas diffusion electrode separated from the electrical resistance is greater than 0.75 V vs. RHE, the platinum component of the platinum catalyst in the gas diffusion electrode will dissolve, shortening the life of the gas diffusion electrode.

[0025] The method for maintaining the potential of the gas diffusion electrode separated from the electrical resistance within the above range is not particularly limited, but it can be maintained, for example, by adjusting the current density during electrolysis or adjusting the oxygen concentration of the oxygen-containing gas.

[0026] The potential of the gas diffusion electrode with the electrical resistance separated is 0.20 V vs. RHE or more, or 0.35 V vs. RHE or more, and 0.75 V vs. RHE or less, preferably 0.20 V vs. RHE or more and 0.75 V vs. RHE or less, or 0.35 V vs. RHE or more and 0.75 V vs. RHE or less. By setting the potential in this range, it is possible to promote the re-precipitation of dissolved platinum and suppress the elution of platinum in the gas diffusion electrode.

[0027] The potential of the gas diffusion electrode with the electrical resistance separated can be determined as follows by a current interrupter method using a constant current pulse generator.

[0028] A constant current pulse generator (device name: HC-2005, manufactured by Hokuto Denko) is used to separate the electrical resistance component and the overvoltage component using the current interrupter method. The current interruption time of the constant current pulse is set to 1 ms, and the potential of the gas diffusion electrode relative to the mercury oxide electrode is obtained by reading the potential of the gas diffusion electrode relative to the mercury oxide electrode immediately after the current is interrupted.

[0029] That is, the current interrupter method is a method in which a constant current pulse is applied and the electrical resistance component is separated by utilizing the polarization transient phenomenon.

[0030] Furthermore, the potential of the gas diffusion electrode relative to the mercury oxide electrode is taken as the potential of the gas diffusion electrode with electrical resistance separated, which is the potential relative to the reversible hydrogen electrode, according to the following formula (2). Potential of gas diffusion electrode with electrical resistance separated (reversible hydrogen standard: V vs. RHE) = potential of the gas diffusion electrode relative to the mercury oxide electrode (V vs. Hg / HgO) + Mercury oxide electrode potential based on reversible hydrogen electrode: 1.01 (V vs. RHE) Equation (2) The method for measuring the potential of the gas diffusion electrode from which the electrical resistance is separated is not particularly limited as long as it is a general measurement method. For example, the potential of the gas diffusion electrode from which the electrical resistance is separated is obtained at regular time intervals from the start of electrolysis, and the obtained potentials are averaged to obtain the potential of the gas diffusion electrode from which the electrical resistance is separated during electrolysis.

[0031] In this embodiment, the current density during electrolysis is set to, for example, 2 kA / m, so that the potential of the gas diffusion electrode separated by the electrical resistance can be reduced within a desired range. 2 or more than 4kA / m 2 and 10 kA / m 2 Less than or equal to 8kA / m 2 The maximum value is 2 kA / m 2 More than 10kA / m 2Less than 4kA / m is preferable. 2 More than 8kA / m 2 The following is more preferred:

[0032] The cathode chamber in this embodiment is a space that serves as a reaction field for a gas diffusion electrode in an ion exchange membrane electrolytic cell (hereinafter also referred to as an electrolytic cell) used for oxygen reduction-type salt electrolysis, and is, for example, a space that corresponds to (4) in FIG. 1 showing an example of a two-compartment electrolytic cell or (4) in FIG. 2 showing an example of a three-compartment electrolytic cell, which will be described later.

[0033] In the present embodiment, the electrolytic cell is preferably a two-compartment electrolytic cell or a three-compartment electrolytic cell. The use of a two-compartment electrolytic cell is more preferable because the electrolysis voltage is lower.

[0034] An example of a two-chamber electrolytic cell is shown in Figure 1. The gas diffusion electrode (5) is in close contact with the ion exchange membrane (3) by the elastic repulsive force of the elastic current collector (6). In some cases, a hydrophilic layer (not shown) such as carbon cloth may be placed between the ion exchange membrane (3) and the gas diffusion electrode (5).

[0035] Purified salt water is supplied to the anode chamber (1) through the anode chamber supply nozzle (7), and the produced chlorine gas and fresh salt water are discharged through the anode chamber discharge nozzle (8).

[0036] The alkali metal ions that have permeated the ion exchange membrane (3) react with water and with oxygen in the oxygen-containing gas supplied from the cathode chamber supply nozzle (9) at the gas diffusion electrode (5) to produce an aqueous alkali metal hydroxide solution, which is discharged together with the exhaust gas from the cathode chamber discharge nozzle (10).

[0037] The anode (2), ion exchange membrane (3) and the like used in the two-chamber electrolytic cell may be appropriately selected from known components.

[0038] An example of a three-compartment electrolytic cell is shown in Figure 2. The anode chamber (1) is the same as the two-compartment electrolytic cell described above. The cathode chamber (4) is divided into an intermediate chamber (11) and a gas chamber (14) by a gas diffusion electrode (5).

[0039] Water or a low-concentration aqueous alkali metal hydroxide solution is supplied to the intermediate chamber (11) through an intermediate chamber supply nozzle (12), and the aqueous alkali metal hydroxide solution produced is discharged through an intermediate chamber discharge nozzle (13).

[0040] An oxygen-containing gas is supplied to the gas chamber (14) through a gas chamber supply nozzle (15) and exhaust gas is discharged from a gas chamber exhaust nozzle (16).

[0041] In this embodiment, the oxygen concentration in the oxygen-containing gas supplied to the cathode chamber is, for example, 8% by volume or more or 10% by volume or more, or 40% by volume or less or 35% by volume or less, preferably 8% by volume or more and 40% by volume or less, and more preferably 10% by volume or more and 35% by volume or less. By setting the oxygen concentration in this range, the potential of the gas diffusion electrode with isolated electrical resistance can be lowered.

[0042] The oxygen-containing gas contains oxygen and components other than oxygen.

[0043] The components other than oxygen are not particularly limited as long as they are not involved in the electrolytic reaction of the aqueous alkali metal chloride solution, and examples thereof include one or more selected from the group consisting of nitrogen, helium, neon, argon, krypton, and xenon, and preferably one or more selected from the group consisting of nitrogen, helium, and argon.

[0044] The gas diffusion electrode in this embodiment includes, on one side of a conductive substrate, a gas diffusion layer containing hydrophobic carbon powder and a fluororesin, and a reaction layer containing carbon powder, a platinum catalyst, and a fluororesin.

[0045] The conductive substrate of the gas diffusion electrode in this embodiment is not particularly limited as long as it has the functions of increasing the strength of the gas diffusion electrode, improving current collection and electronic conductivity, and quickly supplying an oxygen-containing gas to a reaction layer described below. Examples of the conductive substrate include one or more selected from the group consisting of carbon fiber (e.g., at least one of carbon paper and carbon cloth), carbon black (e.g., at least one selected from the group consisting of acetylene black, furnace black, and Ketjen Black (registered trademark)), graphite, activated carbon, conductive carbon (e.g., at least one of carbon nanotubes and carbon nanofibers), and metal materials (e.g., at least one of expanded metal and mesh). Carbon fiber is preferred because of its excellent corrosion resistance and ease of processing.

[0046] The material of the metallic material is at least one selected from the group consisting of Ag, Cu, Fe, Ni, Ti and stainless alloy steel.

[0047] The conductive substrate in this embodiment may have a surface coated with a water repellent agent in order to ensure long-term gas permeability.

[0048] The water repellent agent may be one or more selected from the group consisting of fluororesin, silicon resin, silane coupling agent and wax, and is preferably a fluororesin whose structure and composition do not change easily even in a high-temperature and high-concentration aqueous alkaline solution.

[0049] The fluororesin may be one or more selected from the group consisting of polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) and tetrafluoroethylene-ethylene copolymer (ETFE).

[0050] The gas diffusion layer of the gas diffusion electrode in this embodiment contains hydrophobic carbon powder and a fluororesin.

[0051] The hydrophobic carbon powder contained in the gas diffusion layer is not particularly limited as long as it imparts electrical conductivity to the gas diffusion electrode, does not impair the oxygen-containing gas permeability of the gas diffusion electrode even during long-term electrolysis, is stable to such an extent that its structure and composition do not change even in a high-temperature and high-concentration alkaline aqueous solution, and is hydrophobic. For example, it may be one or more selected from the group consisting of acetylene black, furnace black, ketjen black, graphite, activated carbon, carbon nanotubes, and carbon nanofibers, and preferably one or more selected from the group consisting of acetylene black, ketjen black, furnace black, and graphite.

[0052] The fluororesin contained in the gas diffusion layer is not particularly limited as long as it increases the strength of the gas diffusion electrode, optimizes hydrophilicity and hydrophobicity, and is stable enough that its structure and composition do not change even in a high-temperature and high-concentration alkaline aqueous solution. Examples of the fluororesin include at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0053] The fluororesin contained in the gas diffusion layer may be a commercially available powder (for example, 6-J, manufactured by Mitsui-Chemours Fluoroproducts).

[0054] The fluororesin contained in the gas diffusion layer may be in the form of a suspension dispersed in an aqueous solution.

[0055] The reaction layer of the gas diffusion electrode in this embodiment contains carbon powder, a platinum catalyst, and a fluororesin.

[0056] The material of the carbon powder contained in the reaction layer is not particularly limited as long as it is stable enough that its structure and composition do not change even in a high-temperature and high-concentration alkaline aqueous solution. For example, one or more materials selected from the group consisting of acetylene black, furnace black, ketjen black, graphite, activated carbon, carbon nanotubes, and carbon nanofibers can be used.

[0057] The platinum catalyst contained in the reaction layer is not particularly limited as long as it is a catalyst that has activity in the oxygen reduction reaction, and examples thereof include one or more types selected from the group consisting of platinum alone and alloys of platinum and metals other than platinum (hereinafter also referred to as platinum alloys).

[0058] The metal other than platinum is not particularly limited as long as it does not inhibit the oxygen reduction reaction, and examples thereof include one or more selected from the group consisting of Ag, Au, Co, Cu, Fe, Ir, Mn, Ni, Pd, Ru, Ti, and Zr.

[0059] The platinum alloy may have a multi-layer structure (eg, a core-shell structure).

[0060] The platinum catalyst may be a commercially available product (for example, AY-1050, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.).

[0061] The platinum catalyst may be a synthesized one.

[0062] The method for synthesizing the platinum catalyst is not particularly limited, but examples thereof include a wet method in which a reducing agent such as an alcohol is added to a platinum compound solution such as a dinitrodiammineplatinum nitrate solution to precipitate platinum particles, and a dry method such as vapor deposition or sputtering.

[0063] The reaction layer can be formed by mixing a platinum catalyst with carbon powder when preparing the gas diffusion electrode described below, or by using carbon powder on which platinum has been previously supported (hereinafter, also referred to as platinum-supported carbon powder) when preparing the gas diffusion electrode.

[0064] The platinum-supported carbon powder may be a commercially available product (e.g., TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.). The platinum-supported carbon powder may be a synthesized powder.

[0065] The method for synthesizing the platinum-supported carbon powder is not particularly limited, but an example of such a method is to add a platinum compound solution such as dinitrodiammineplatinum nitrate solution and carbon powder as a carrier to the platinum solution, mix them, and then add a reducing agent such as an alcohol to precipitate platinum particles directly on the carbon powder.

[0066] The fluororesin contained in the reaction layer is not particularly limited as long as it increases the strength of the gas diffusion electrode, optimizes hydrophilicity and hydrophobicity, and is stable enough that its structure and composition do not change even in a high-temperature and high-concentration alkaline aqueous solution. Examples of the fluororesin include at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0067] The fluororesin contained in the reaction layer may be a commercially available powder (for example, 6-J, manufactured by Mitsui-Chemours Fluoroproducts).

[0068] The fluororesin contained in the reaction layer may be in the form of a suspension dispersed in an aqueous solution.

[0069] When the total weight of the carbon powder and platinum contained in the reaction layer in this embodiment is taken as 100 wt%, the weight of the platinum can be, for example, 21 wt% or more or 25 wt% or more, and can be 85 wt% or less or 80 wt% or less, with 21 wt% or more and 85 wt% or less being preferred, and 25 wt% or more and 80 wt% or less being more preferred.

[0070] The weight of platinum can be calculated by the following formula (3). Weight of platinum (wt%) = (mass of platinum catalyst (g) / (mass of platinum catalyst (g) + mass of carbon powder (g))) × 100 Formula (3) The platinum crystallite size of the platinum catalyst is, for example, 2 nm or more, and 20 nm or less or 15 nm or less, preferably 2 nm or more and 20 nm or less, and more preferably 2 nm or more and 15 nm or less, which allows a high catalyst specific surface area to be obtained.

[0071] The platinum crystallite size of the platinum catalyst is measured using an X-ray diffractometer (for example, Ultima4, manufactured by Rigaku Corporation) under the following conditions to obtain a powder X-ray diffraction pattern (XRD pattern). Target (light source): CuKα(λ=1.5418Å) Output: 1.6kW (40mA-40kV) Filter: Kβ filter Divergence slit: 1° Divergence vertical limit slit: 10mm Scattering slit: open Receiving slit: Open Scanning Mode: Continuous Scan speed: 4.000° / min Sampling width: 0.04°(2θ / θ) Number of times: 1 Measurement range: 10~80°(2θ / θ) The obtained XRD pattern (XRD data) is analyzed using analysis software (e.g., PDXL2, manufactured by Rigaku), and the XRD peak having a peak top at 2θ=39.5±1.0° is regarded as the peak corresponding to the (111) plane of the platinum catalyst, and its half-width is calculated. Using the obtained half-width, the platinum crystallite diameter corresponding to the (111) plane of the platinum catalyst can be determined as the platinum crystallite diameter of the platinum catalyst according to the Scherrer formula shown in the following formula (4). Platinum crystallite size of platinum catalyst (nm) = (K: Scherrer constant (=0.94)) × (λ: wavelength of X-ray light source used (nm)) / ((B: half-width of peak corresponding to (111) plane of platinum catalyst (°)) × cosθ (θ: angle of incidence (°))) Equation (4) The amount of platinum supported in the platinum catalyst is, for example, 0.1 mg / cm per geometric area of ​​the gas diffusion electrode. 2 or more than 0.2 mg / cm 2 and 10 mg / cm or more. 2 The following are listed as being below: 0.1 mg / cm 2 More than 10mg / cm 2 Less than 0.2 mg / cm is preferred. 2 More than 10mg / cm 2The following is more preferable. This makes it possible to reduce overvoltage even under high current density conditions.

[0072] From the weight of platinum calculated from formula (3), the amount of platinum supported in the platinum catalyst in the gas diffusion electrode can be calculated from the following formula (5). Platinum loading of platinum catalyst (mg / cm 2 ) = (mass of platinum catalyst (g) × 1000 / (geometric area of ​​gas diffusion electrode (cm 2 )) Equation (5) The above geometric area corresponds to the projected area of ​​the gas diffusion electrode, and does not take into consideration the thickness of the gas diffusion electrode.

[0073] Using this embodiment, chlorine gas and alkali metal hydroxides can be produced.

[0074] The alkali metal hydroxide produced is an alkali metal hydroxide corresponding to the alkali metal of the above-mentioned alkali metal chloride, and examples thereof include one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, an aqueous solution of rubidium hydroxide, and cesium hydroxide.

[0075] In the present embodiment, the reaction temperature is, for example, 82° C. or more or 86° C. or more, and 92° C. or less or 90° C. or less in order to suppress the two-electron oxygen reduction reaction and improve the efficiency of producing the alkali metal hydroxide. 82° C. or more and 92° C. or less are preferable, and 86° C. or more and 90° C. or less are more preferable.

[0076] As a method for evaluating the gas diffusion electrode according to this embodiment, a half cell that reproduces the reaction only in the cathode chamber of the electrolytic cell may be used. That is, a half cell is prepared in which the electrolyte has the same composition as the electrolyte in the cathode chamber, the intended anode is used as the counter electrode, and the gas diffusion electrode is used as the working electrode. The gas diffusion electrode according to this embodiment can be evaluated by evaluating the gas diffusion electrode after the electrolytic reaction of the electrolyte.

[0077] The anode used as the counter electrode of the half cell is not particularly limited as long as it does not inhibit the electrolytic reaction of the aqueous alkali metal chloride solution, and for example, a Ni coil can be used. The gas diffusion electrode described above is used as the working electrode of the half cell.

[0078] The concentration of the alkali metal chloride aqueous solution in the liquid composition in the cathode chamber may be, for example, 24 wt% or more or 28 wt% or less, and may be 48 wt% or less or 40 wt% or less, with 24 wt% or more and 48 wt% or less being preferred, and 28 wt% or more and 40 wt% or less being more preferred. EXAMPLES

[0079] The present invention will be described in more detail below by way of examples, but the present invention should not be construed as being limited to these examples in any way.

[0080] <Preparation of gas diffusion electrode> A suspension for a gas diffusion layer was prepared by mixing 50 mg of hydrophobic carbon black (trade name: Li-100, manufactured by Denka), 37 μL of a 60% PTFE suspension (trade name: 31-JR, manufactured by Mitsui-Chemours Fluoroproducts), 288 μL of a surfactant (trade name: Triton (registered trademark) X-100, manufactured by Union Carbide) and 1.44 mL of pure water in a planetary centrifugal mixer (trade name: AR-100, manufactured by Thinky).

[0081] The obtained suspension for gas diffusion layer was applied to a carbon cloth (manufactured by ElectroChem) that had been previously subjected to a water-repellent treatment, and dried for 20 minutes at 100° C. The obtained sheet was fired for 1 hour at 305° C. in a nitrogen atmosphere to obtain a gas diffusion electrode sheet.

[0082] A catalyst ink for the reaction layer was prepared by mixing 120 mg of carbon black carrying 45 wt% platinum (product name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), 48 μL of a 60% PTFE suspension, 100 μL of a surfactant, and 500 μL of pure water in a centrifugal mixer.

[0083] The obtained catalyst ink for the reaction layer was applied to the surface of the gas diffusion electrode sheet on which the suspension for the gas diffusion layer had been applied, and dried for 20 minutes at 100° C. The dried gas diffusion electrode sheet was baked for 15 minutes at 305° C. in a nitrogen atmosphere to obtain a gas diffusion electrode equipped with a gas diffusion layer and a reaction layer.

[0084] The resulting gas diffusion electrode had a platinum loading of 1.00 mg / cm 2 It was.

[0085] <Measurement of platinum crystallite size> The powder X-ray diffraction of the obtained gas diffusion electrode was measured using an X-ray diffraction apparatus (Ultima4, manufactured by Rigaku). The radiation source used was CuKα radiation (λ = 1.5405 Å), the measurement mode was step scan, the scanning conditions were sampling width 2θ = 0.04°, the measurement time was 4 seconds, and the measurement range was 2θ from 10° to 80°. The half-width (full width at half maximum: FWHM) of the diffraction line near 2θ = 39.5° ± 1.0° was obtained by peak fitting using the analysis software PDXL-2 attached to the X-ray diffraction apparatus. The platinum crystallite diameter of the platinum catalyst in the obtained gas diffusion electrode was 2.7 nm.

[0086] <Separation of electrical resistance> The separation of the electrical resistance at the potential of the gas diffusion electrode was carried out as follows.

[0087] A constant current pulse generator (device name: HC-2005, manufactured by Hokuto Denko) was used to separate the electrical resistance component by the current interrupter method. The current interruption time of the constant current pulse was set to 1 ms. The potential of the gas diffusion electrode with the electrical resistance separated was obtained by reading the potential immediately after the current was interrupted.

[0088] That is, the current interrupter method separates the electrical resistance component by applying a constant current pulse and measuring the polarization transient phenomenon.

[0089] Furthermore, the potential of the gas diffusion electrode with the electrical resistance separated was calculated by adding 1.01 V, which is the mercury oxide electrode potential relative to the reversible hydrogen electrode, to the potential of the gas diffusion electrode relative to the mercury oxide electrode, as shown in equation (2).

[0090] <Measurement of platinum elution amount> Using an ICP emission spectrometer (device name: Optima 5300DV, manufactured by PerkinElmer), the amount of platinum in the sodium hydroxide solution obtained after 3 hours of electrolysis was measured. The measurement wavelength was 265.945 nm. The platinum elution rate was calculated by dividing the obtained amount of platinum by the mass of the platinum catalyst in the reaction layer.

[0091] Example 1 In the following examples, the liquid composition in the cathode chamber when an aqueous solution of an alkali metal chloride was electrolyzed was reproduced in a simple manner. The resulting gas diffusion electrode was used as the working electrode, a Ni coil as the counter electrode, and a mercury oxide electrode as the reference electrode. The current density was 8 kA / m in a 32 wt% aqueous solution of sodium hydroxide at a liquid temperature of 88°C. 2 Electrolysis was carried out for 3 hours under the above conditions. During electrolysis, oxygen-containing gas with an oxygen concentration of 33.3% by volume, which was adjusted by mixing pure oxygen gas and pure nitrogen gas, was supplied to the back of the working electrode. According to <Separation of Electrical Resistance>, the potential of the working electrode with the electrical resistance separated was measured three times every hour from the start of electrolysis, and the potential of the working electrode during electrolysis was calculated by averaging the potentials at the three points obtained. In addition, the platinum dissolution rate was calculated according to <Measurement of Platinum Dissolution Amount>. The potential of the gas diffusion electrode with the electrical resistance separated at this time was 0.71 V vs. RHE, and the platinum dissolution rate was 21.3%.

[0092] Example 2 Electrolysis was carried out in the same manner as in Example 1, except that the oxygen concentration of the oxygen-containing gas, which was adjusted by mixing pure oxygen gas and pure nitrogen gas, was 32.2% by volume. The potential of the gas diffusion electrode with the electrical resistance separated at this time was 0.61 V vs. RHE, and the platinum dissolution rate was 14.4%.

[0093] Example 3 Electrolysis was carried out in the same manner as in Example 1, except that the oxygen concentration of the oxygen-containing gas, which was adjusted by mixing pure oxygen gas and pure nitrogen gas, was 31.0% by volume. The potential of the gas diffusion electrode with the electrical resistance separated at this time was 0.49 V vs. RHE, and the platinum dissolution rate was 7.2%.

[0094] Example 4 The oxygen concentration of the oxygen-containing gas prepared by mixing pure oxygen gas and pure nitrogen gas is 23.1% by volume, and the current density is 6 kA / m 2 Except for this, electrolysis was carried out in the same manner as in Example 1. The potential of the gas diffusion electrode with the electrical resistance separated was 0.59 V vs. RHE, and the platinum dissolution rate was 2.8%.

[0095] Example 5 The oxygen concentration of the oxygen-containing gas, which was prepared by mixing pure oxygen gas and pure nitrogen gas, was 20.0% by volume, and the current density was 4 kA / m 2 Except for this, electrolysis was carried out in the same manner as in Example 1. At this time, the potential of the gas diffusion electrode with the electrical resistance separated was 0.58 V vs. RHE, and the platinum dissolution rate was 8.2%.

[0096] Example 6 The oxygen concentration of the oxygen-containing gas, which was prepared by mixing pure oxygen gas and pure nitrogen gas, was 9.0% by volume, and the current density was 2 kA / m 2 Except for this, electrolysis was carried out in the same manner as in Example 1. At this time, the potential of the gas diffusion electrode with the electrical resistance separated was 0.63 V vs. RHE, and the platinum dissolution rate was 6.4%.

[0097] Comparative Example 1 Except for using pure oxygen gas instead of the oxygen-containing gas prepared by mixing pure oxygen gas and pure nitrogen gas, electrolysis was carried out in the same manner as in Example 1. The potential of the gas diffusion electrode with isolated electrical resistance was 0.87 V vs. RHE, and the platinum dissolution rate was 32.0%.

[0098] Comparative Example 2 Electrolysis was carried out in the same manner as in Example 1, except that the oxygen concentration of the oxygen-containing gas, which was adjusted by mixing pure oxygen gas and pure nitrogen gas, was 66.0% by volume. The potential of the gas diffusion electrode with the electrical resistance separated at this time was 0.83 V vs. RHE, and the platinum dissolution rate was 32.7%.

[0099] Comparative Example 3 Electrolysis was carried out in the same manner as in Example 1, except that the oxygen concentration of the oxygen-containing gas, which was adjusted by mixing pure oxygen gas and pure nitrogen gas, was 50.0% by volume. The potential of the gas diffusion electrode with the electrical resistance separated at this time was 0.79 V vs. RHE, and the platinum dissolution rate was 39.9%.

[0100] Comparative Example 4 Electrolysis was carried out in the same manner as in Example 1, except that the oxygen concentration of the oxygen-containing gas, which was adjusted by mixing pure oxygen gas and pure nitrogen gas, was 45.6% by volume. The potential of the gas diffusion electrode with isolated electrical resistance at this time was 0.76 V vs. RHE, and the platinum dissolution rate was 38.2%.

[0101] The electrolysis conditions and platinum elution rates for Examples 1 to 6 and Comparative Examples 1 to 4 are shown in Table 1.

[0102] [Table 1]

[0103] From Examples 1 to 6 and Comparative Examples 1 to 4, it was confirmed that under electrolysis conditions in which the potential of the gas diffusion electrode with separated electrical resistance was 0.20 V vs. RHE or more and 0.75 V vs. RHE or less, a lower platinum dissolution rate was observed compared to electrolysis conditions that did not satisfy this condition. [Industrial Applicability]

[0104] The electrolysis method of the present invention can be used, for example, for sodium chloride electrolysis. By using the electrolysis method of the present invention, it is possible to provide an industrially excellent sodium chloride electrolysis process having a long life. [Explanation of symbols]

[0105] 1 Anode chamber 2 Anode 3. Ion exchange membrane 4. Cathode Chamber 5 Gas diffusion electrode 6 Elastic current collector 7 Anode chamber supply nozzle 8 Anode chamber discharge nozzle 9. Cathode chamber supply nozzle 10 Cathode chamber exhaust nozzle 11 Caustic chamber 12 Caustic chamber supply nozzle 13 Caustic chamber discharge nozzle 14 Gas Chambers 15 Gas chamber supply nozzle 16 Gas chamber exhaust nozzle

Claims

1. A method for electrolyzing an aqueous solution of an alkali metal chloride, in which an oxygen-containing gas is supplied to a cathode chamber and oxygen is reduced by a gas diffusion electrode equipped with a platinum catalyst, and the potential of the gas diffusion electrode separated by electrical resistance is 0.20 V vs. RHE or more and 0.75 V vs. RHE or less.

2. The current density during the electrolysis is 2 kA / m ２ 10kA / m or more ２ The method for electrolyzing an aqueous alkali metal chloride solution according to claim 1, wherein:

3. 3. The method for electrolyzing an aqueous alkali metal chloride solution according to claim 1, wherein the oxygen-containing gas has an oxygen concentration of 8% by volume or more and 40% by volume or less.

4. 3. The method for electrolyzing an alkali metal chloride aqueous solution according to claim 1, wherein the gas diffusion electrode comprises, on one side of a conductive substrate, a gas diffusion layer containing hydrophobic carbon powder and a fluororesin, and a reaction layer containing carbon powder, a platinum catalyst, and a fluororesin.

5. 5. The method for electrolyzing an aqueous alkali metal chloride solution according to claim 4, wherein the weight of platinum is 21 wt % or more when the total weight of the carbon powder and platinum contained in said reaction layer is taken as 100 wt %.

6. 3. The method for electrolyzing an aqueous alkali metal chloride solution according to claim 1 or 2, wherein the platinum catalyst has a platinum crystallite size of 2 nm or more and 20 nm or less.

7. The platinum loading of the platinum catalyst is 0.1 mg / cm per geometric area of ​​the gas diffusion electrode. ２ 10mg / cm or more ２ The method for electrolysis of an aqueous alkali metal chloride solution according to claim 1 or 2, wherein:

8. A method for producing chlorine gas and alkali metal hydroxides, which uses the method for electrolyzing an aqueous alkali metal chloride solution according to claim 1 or 2.

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