Aqueous solution electrolysis method

Abstract

Provided is an aqueous solution electrolysis method whereby it becomes possible to reduce the amount of air bubbles covering an electrode and generate a gas of hydrogen, oxygen or the like with excellent energy efficiency. The method is an electrolysis method for electrolyzing an aqueous-solution-based electrolysis solution to generate at least one component selected from hydrogen, oxygen and chlorine, in which the electrolysis solution contains a water-soluble alcohol. The electrolysis solution contains about 0.1 to 10% by volume of a water-soluble alcohol including a tertiary alcohol such as 2-methylpropan-2-ol and 2-methylbutan-2-ol, an aqueous alkaline solution containing about 1 to 10 mol / L of an alkaline component may be water-electrolyzed, and the electrolysis solution is electrolyzed, for example, using an electrolysis cell equipped with an anode chamber and a cathode chamber.

Description

[Technical Field]

[0001] This invention relates to an energy-efficient method for electrolyzing aqueous solutions. [Background technology]

[0002] Hydrogen is suitable for storage and transportation, and as a secondary energy source with a low environmental impact, attracting attention to hydrogen energy systems that use hydrogen as an energy carrier. Currently, hydrogen is mainly produced by steam reforming of fossil fuels. However, from the perspective of global warming and the depletion of fossil fuels, hydrogen production by water electrolysis using renewable energy sources such as solar and wind power is important. Water electrolysis is low-cost and suitable for large-scale production, making it a promising technology for hydrogen production. When using a water electrolysis cell as a means of hydrogen generation, it is essential to lower the cell voltage in order to maintain high energy conversion efficiency.

[0003] Practical water electrolysis can be broadly divided into two types. One is alkaline water electrolysis, which uses a high-concentration alkaline aqueous solution as the electrolyte. The other is solid polymer water electrolysis, which uses a solid polymer membrane (SPE) as the electrolyte. The latter uses protons as ion carriers and can operate at low voltage even at high current densities, offering superior performance. However, when producing hydrogen on a large scale using water electrolysis, the former type of water electrolysis, which uses electrodes made of inexpensive materials such as iron-based metals, is more suitable than the latter type of water electrolysis, which uses electrodes made of large amounts of expensive precious metals. Recently, excellent anion exchange membranes have been developed, and research is underway to overcome these challenges. Another type of aqueous solution electrolysis that generates gas is sodium chloride electrolysis. In electrolysis systems that generate chlorine and hydrogen gas, promoting gas release remains an important technical challenge for improving energy efficiency.

[0004] Non-patent document 1 divides the terminal voltage "CV" in an aqueous solution electrolytic cell into its constituent elements and expresses it using the following formula (1). CV = V0 + η anode +η cathode+iR ···(1) V0: Theoretical decomposed voltage η anode Anode overvoltage η cathode Cathode overvoltage iR: Voltage loss due to resistance within the electrode, solution, and diaphragm.

[0005] The gas generated in the gas evolution reaction accumulates on the electrode surface as bubbles, reducing the reaction area of ​​the electrode, therefore η anode and η cathode This is a factor that increases the current resistance (iR). In addition, bubbles accumulate in the electrolyte near the electrodes and on the surface of the diaphragm, causing the current distribution in the electrolyte and within the diaphragm to become non-uniform, which also contributes to an increase in iR. Therefore, in order to reduce the terminal voltage (CV), it is necessary to quickly remove the bubbles generated by electrolysis from the surface of the electrodes.

[0006] Non-conductive bubbles increase the voltage through resistance, thereby increasing the overvoltage at the electrodes. Therefore, to lower the cell voltage, structures and means are needed to quickly remove the generated bubbles from the surface of the electrodes and diaphragm. Numerous techniques for improving the structure of electrodes and diaphragms, such as providing openings in the electrode substrate to quickly remove generated bubbles, have been reported in the field of salt electrolysis (Non-Patent Literature 2).

[0007] In alkaline water electrolysis, a highly conductive alkaline aqueous solution is used as the electrolyte, and the system operates at high temperatures where conductivity increases. Furthermore, because high-concentration alkaline aqueous solutions become more corrosive as the temperature rises, the upper limit of the operating temperature is restricted to 60-90°C. However, even when using such alkaline aqueous solutions as the electrolyte, oxygen and hydrogen bubbles tend to accumulate on the electrode surfaces, hindering smooth electrolysis. On the other hand, the fluidity of the electrolyte caused by bubbles also improves the agitation and circulation of the electrolyte. Therefore, in industrial-scale cells, cell structures that maximize the natural circulation generated by the difference in bubble density are commonly used.

[0008] Through the development of electrolytic cell components and various piping materials that can withstand high temperatures and high concentrations of alkaline aqueous solutions, as well as the development of low-resistance diaphragms and electrodes with increased surface area and highly active catalysts, the electrolytic cell voltage has been increased to a current density of 0.6 A / cm². 2 The voltage has been reduced to below 1.8V. However, current density tends to increase in order to improve productivity. There are concerns that the shielding effect of bubbles will increase, leading to a decrease in energy conversion efficiency.

[0009] Electrode catalysts, one of the cell components, have been studied for some time. Platinum group metals, platinum group metal oxides, valve metal oxides, iron group oxides, and lanthanide group metal oxides have been proposed as anode catalysts for oxygen generation used in alkaline water electrolysis. Other known materials include nickel-based alloys such as Ni-Co and Ni-Fe; nickel and nickel oxides with enlarged surface area; spinel-based Co3O4 and NiCo2O4; perovskite-based conductive oxides such as LaCoO3 and LaNiO3; and oxides composed of lanthanide group metals and noble metals (Non-Patent Literature 3).

[0010] Porous nickel with a large surface area and Ni-Mo-based materials are known as cathode catalysts for hydrogen generation. Other examples include Raney nickel-based materials such as Ni-Al, Ni-Zn, and Ni-Co-Zn, sulfide-based materials such as Ni-S, and hydrogen storage alloy-based materials such as Ti2Ni. Other catalysts include metals such as platinum, palladium, ruthenium, and iridium, and their oxides (Non-Patent Literature 3). For both the anode and cathode, catalysts with low overpotential, strong short-circuit stability, and high poisoning resistance are preferred.

[0011] In recent years, a self-healing technology has been proposed in which catalyst precursor nanosheets are added to an electrolyte and a catalyst is formed on-site on the electrode by electrolysis (Patent Document 1). Particles with a negatively charged surface adhere to the anode, and particles with a positively charged surface adhere to the cathode. The nanoparticles disappear from the aqueous solution by electrodeposition.

[0012] Regarding the bubble distribution, which is one of the factors contributing to increased cell voltage, technical studies are progressing due to the growing interest in fine bubble technology, which has recently attracted attention. For example, it has been reported that the bubble size can increase to 20 μm by increasing the current density and alkali concentration (Non-Patent Document 4). However, no specific studies on reducing the bubble effect have been reported. In addition, bubble removal in alkaline water electrolysis using pressure swing has been reported (Non-Patent Document 5). Furthermore, it has been disclosed that the amount of dissolved hydrogen increases by setting the catalyst distribution on the electrode surface to 30-60% and the particle size and surface roughness to 0.05-0.5 μm (Patent Document 2). However, the effect on bubble behavior and cell voltage remains unclear.

[0013] Furthermore, an electrolysis cell has been proposed that uses electrodes with a surface textured to have fine irregularities to promote the release of bubbles generated on the electrode surface (Patent Document 3). In addition, it has been proposed to improve the stability of the dissolved hydrogen molecule concentration by supplying an aqueous solution containing a dissolved hydrogen molecule stabilizer consisting of sugars or polyphenols (Patent Document 4). A method for generating oxygen nanobubble water by reducing the size of bubbles has also been disclosed (Patent Document 5). Patent Document 5 proposes forming microbubbles by applying shock waves associated with a 200-300V underwater discharge to bubbles with a diameter of 10-50 μm in an aqueous solution, without using surfactants or organic substances. It is known that the zeta potential of microbubbles in an aqueous solution changes when alcohol such as ethanol is added (Non-Patent Document 6).

[0014] In recent years, technologies for producing high-pressure gases of 10 atmospheres or higher using alkaline water electrolysis have been investigated. During high-pressure operation, it is necessary to use high-pressure resistant materials to prevent electrolyte leakage and ensure safety. Furthermore, higher pressure offers the advantage of reducing the gas bubble rate. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] International Publication No. 2020-184607 [Patent Document 2 Japanese Unexamined Patent Application Publication No. 2016-121382 [Patent Document 3 Japanese Unexamined Patent Application Publication No. 2017-31508 [Patent Document 4 Japanese Unexamined Patent Application Publication No. 2017-60941 [Patent Document 5 Japanese Patent No. 4080440 [Non-Patent Document

[0016] [Non-Patent Document 1 Handbook of Electrochemistry, 6th Edition, 433 (2009) [Non-Patent Document 2 Soda Handbook, 5th Edition, 61 (2009) [Non-Patent Document 3 Hydrogen Energy System, vol. 36, No. 1, 11 (2011) [Non-Patent Document 4 N. Nagai, Hydrogen Energy System, 30, 66 (2005) [Non-Patent Document 5 M. Bakker, et al., Electrochimica Acta, vol. 3, 19, 148 (2019) [Non-Patent Document 6 M. Takahashi, J. Physical Chemistry B, 109, 21858 (2005) [Summary of the Invention [Problems to be Solved by the Invention

[0017] As described above, various techniques related to bubble control have been disclosed. However, no essential technique for chemically removing generated bubbles and improving the energy conversion efficiency of aqueous solution electrolysis has been found so far.

[0018] This invention has been made in view of the problems of the prior art, and its objective is to provide an aqueous solution electrolysis method that can reduce the amount of bubble coating on the electrodes and generate gases such as hydrogen and oxygen with excellent energy efficiency. [Means for solving the problem]

[0019] In other words, the present invention provides the following method for electrolysis of an aqueous solution. [1] An aqueous solution electrolysis method comprising electrolyzing an aqueous electrolyte to generate at least one of hydrogen, oxygen, and chlorine, wherein the electrolyte contains a water-soluble alcohol. [2] The aqueous solution electrolysis method according to [1], wherein the alcohol is a tertiary alcohol. [3] The aqueous solution electrolysis method according to [2], wherein the tertiary alcohol is at least one of 2-methylpropan-2-ol and 2-methylbutan-2-ol. [4] The aqueous solution electrolysis method according to any one of [1] to [3], wherein the electrolyte is an alkaline aqueous solution containing an alkaline component, and the concentration of the alkaline component in the alkaline aqueous solution is 1 to 10 mol / L. [5] The aqueous solution electrolysis method according to any one of [1] to [4], wherein the concentration of the alcohol in the electrolyte is such that the surface tension of the electrolyte is 90% or less of the surface tension of a control electrolyte that does not contain the alcohol. [6] The aqueous solution electrolysis method according to any one of [1] to [4], wherein the concentration of the alcohol in the electrolyte is 0.1 to 10 by volume. [7] An aqueous solution electrolysis method according to any one of [1] to [6] above, using an electrolytic cell having an anode chamber and a cathode chamber, and supplying a common electrolyte to the anode chamber and the cathode chamber, respectively for electrolysis. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an aqueous solution electrolysis method that can reduce the amount of air bubbles covering the electrodes and generate gases such as hydrogen and oxygen with excellent energy efficiency.

[0021] The aqueous solution electrolysis method of the present invention allows for the electrolysis of aqueous solutions at a lower voltage compared to conventional electrolysis methods. Furthermore, since it is possible to increase the applied current while reducing the voltage, productivity can be increased. Moreover, even if the harsh electrolysis conditions of the conventional method, such as electrolyte concentration and temperature, are relaxed, aqueous solution electrolysis can be performed with the same or better efficiency. In addition, since electrode potential fluctuations are suppressed, it is expected that deterioration and peeling of materials such as electrode catalysts and membranes will be suppressed. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram showing an example of an electrolysis apparatus for implementing the aqueous solution electrolysis method of the present invention. [Figure 2] This graph shows the current-potential characteristics of the nickel anode when an electrolyte solution containing 2-methylpropan-2-ol is subjected to water electrolysis. [Figure 3] This graph shows the nickel anode current-potential characteristics when electrolytes containing 2-methylpropan-2-ol and 2-methylbutan-2-ol, respectively, are electrolyzed with water. [Figure 4] This graph shows the current-potential characteristics of the nickel anode when an electrolyte solution containing ethanol is subjected to water electrolysis. [Figure 5] This graph shows the change in cell voltage when electrolyzing an electrolyte solution to which 2-methylpropan-2-ol has been added using water. [Figure 6] This graph shows the change in oxygen evolution potential during long-term operation. [Figure 7] This graph shows the change in interfacial tension with respect to the concentrations of 2-methylpropan-2-ol, 2-methylbutan-2-ol, and ethanol. [Figure 8A] This is a microscopic image showing the microstructure of bubbles generated during the electrolysis of an alkaline aqueous solution. [Figure 8B] This is a micrograph showing the microstructure of bubbles generated when an alkaline aqueous solution containing 2-methylpropan-2-ol is electrolyzed. [Figure 8C] This is a micrograph showing the microstructure of bubbles generated when an alkaline aqueous solution containing 2-methylbutan-2-ol is electrolyzed. [Figure 9] This graph shows the change in interfacial tension with respect to the concentrations of 2-methylpropan-2-ol, 2-methylbutan-2-ol, and pinacol. [Modes for carrying out the invention]

[0023] The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below. The aqueous solution electrolysis method of the present invention is an aqueous solution electrolysis method that generates at least one of hydrogen, oxygen, and chlorine by electrolyzing an aqueous solution, wherein the electrolyte contains a water-soluble alcohol. That is, the aqueous solution electrolysis method of the present invention is a method of electrolyzing an aqueous solution to which a water-soluble alcohol has been added. By electrolyzing an electrolyte to which a water-soluble alcohol has been added, the adhesion of bubbles to the electrode surface can be suppressed, the coalescence of bubbles near the electrode can be suppressed, and the amount of bubble coverage on the electrode can be reduced. As a result, gases such as hydrogen, oxygen, and chlorine can be generated with excellent energy efficiency.

[0024] The reason why electrolysis of an electrolyte solution containing water-soluble alcohols can reduce the amount of bubbles covering the electrodes is not entirely clear, but it is thought that a change in interfacial tension (surface tension) is one of the contributing factors. Figure 7 is a graph showing the change in interfacial tension with respect to the concentrations of 2-methylpropan-2-ol, 2-methylbutan-2-ol, and ethanol. Two types of aqueous solutions were used: a 2M (2 mol / L) KOH aqueous solution and a 4M (4 mol / L) KOH aqueous solution. As shown in Figure 7, it can be seen that the interfacial tension of the aqueous solution decreases with increasing concentrations of the water-soluble alcohols 2-methylpropan-2-ol, 2-methylbutan-2-ol, and ethanol, meaning that the physical properties of the solution change significantly.

[0025] Figure 9 is a graph showing the change in interfacial tension with respect to the concentration of 2-methylpropan-2-ol, 2-methylbutan-2-ol, and pinacol. For 2-methylpropan-2-ol, a 7M (7mol / L) KOH aqueous solution was used. For 2-methylbutan-2-ol, a 4M (4mol / L) KOH aqueous solution was used. For pinacol, a 4M (4mol / L) KOH aqueous solution was used. As shown in Figure 9, it can be seen that dissolving pinacol, a tertiary alcohol, reduces the interfacial tension of the alkaline aqueous solution, similar to the cases when 2-methylpropan-2-ol and 2-methylbutan-2-ol are dissolved.

[0026] By adding a water-soluble alcohol to the electrolyte, it can be confirmed by microscopic high-speed video recording that the bubbles generated by electrolysis on the electrode surface remain small and detach into the electrolyte. Figure 8A is a micrograph showing the microstructure of bubbles generated when an alkaline aqueous solution is electrolyzed. Figure 8B is a micrograph showing the microstructure of bubbles generated when an alkaline aqueous solution with 2-methylpropan-2-ol added is electrolyzed, and Figure 8C is a micrograph showing the microstructure of bubbles generated when an alkaline aqueous solution with 2-methylbutan-2-ol added is electrolyzed. As shown in Figures 8A to 8C, it can be seen that adding a water-soluble alcohol to the electrolyte reduces the diameter of the bubbles generated by electrolysis.

[0027] Furthermore, changes in zeta potential are also considered to be one of the factors that reduce the amount of bubble coating on the electrode. Non-patent document 6 shows the changes in zeta potential with respect to ethanol concentration and the changes in zeta potential with respect to 1-propanol concentration. It can be seen that the zeta (ζ) potential decreases as the alcohol concentration increases, and the amount of charge on the bubbles decreases. When the zeta potential is negative on the surface of fine oxygen bubbles, an attractive force acts on the oxygen bubbles toward the positively charged anode. It is thought that the presence of water-soluble alcohol mitigates the negative charge on the oxygen bubbles, thereby reducing the attractive force toward the positively charged anode.

[0028] (Water-soluble alcohol) As a water-soluble alcohol, it is preferable to use one that can dissolve in water at a sufficient concentration, and also one that is stable in aqueous solution electrolysis. Furthermore, it is preferable to use an alcohol with a relatively high boiling point, as this makes it easier to use under high-temperature conditions. Specific examples of water-soluble alcohols include ethanol, 1-propanol, 2-propanol, butanol, 2-methylpropan-2-ol, 2-methylbutan-2-ol, 2-methylpentan-2-ol, 2-methylhexane-2-ol, 2-methylheptan-2-ol, 3-methylpentan-3-ol, 3-methyloctan-3-ol, and 2,3-dimethyl-2,3-butanediol (pinacol).

[0029] To stably maintain the release effect of oxygen bubbles generated during the oxygen evolution reaction, it is preferable to use an alcohol with a structure that is resistant to oxidative decomposition. Among these, tertiary alcohols are preferred, and alcohols that do not contain structures such as carbon-carbon double bonds or benzene rings are preferred. Specific examples of such alcohols include 2-methylpropan-2-ol, 2-methylbutan-2-ol, 2-methylpentan-2-ol, 2-methylhexane-2-ol, 2-methylheptan-2-ol, 3-methylpentan-3-ol, 3-methyloctane-3-ol, and 2,3-dimethyl-2,3-butanediol (pinacol). Among these, 2-methylpropan-2-ol is preferred because it has a compact structure in which the -OH group is surrounded by methyl groups, making it resistant to decomposition, and it also has extremely high solubility in water and a high boiling point (82.3°C).

[0030] Furthermore, 2-methylbutan-2-ol is also preferable because it has a compact structure in which the -OH group is surrounded by methyl groups, making it resistant to decomposition, and it also has extremely high solubility in water (approximately 120 g / L) and a high boiling point (approximately 102°C). In the case of alkaline water electrolysis, since the anode solution and cathode solution are common, it is required that not only the potential of the cathode where hydrogen is generated, but also the potential of the anode where oxygen is generated be stable. From these viewpoints, it is preferable to use 2-methylpropane-2-ol or 2-methylbutan-2-ol.

[0031] The concentration of water-soluble alcohol in the electrolyte is preferably such that the interfacial tension (surface tension) of the electrolyte is moderately reduced. Specifically, the concentration of water-soluble alcohol in the electrolyte is preferably such that the surface tension of the electrolyte is 90% or less of the surface tension of an electrolyte that does not contain water-soluble alcohol (control electrolyte), more preferably 80% or less, and particularly preferably 75% or less. Furthermore, considering the solubility in aqueous solution and the effect of reducing interfacial tension (surface tension), the concentration of water-soluble alcohol in the electrolyte is preferably 0.1 to 10 volume%, more preferably 0.1 to 8 volume%, and particularly preferably 0.1 to 6 volume%.

[0032] (Electrolysis apparatus and operating method (aqueous solution electrolysis method)) When operating a DC power supply using renewable energy as electricity, it is preferable to construct a control system in which frequent power outages do not directly affect the electrolytic cell. FIG. 1 is a schematic diagram showing an example of an electrolysis apparatus for implementing the water electrolysis method of the present invention. The electrolysis apparatus 1 shown in FIG. 1 includes an electrolytic cell 2. The electrolytic cell 2 includes an anode chamber 5 having an anode 4 and a cathode chamber 7 having a cathode 6. The anode 4 and the cathode 6 are arranged opposite each other via a diaphragm 8. In order to reduce the cell voltage, it is preferable to bring the electrodes (anode 4 and cathode 6) closer to each other. The electrolytic cell 2 is assembled using the anode 4, the cathode 6, the diaphragm 8, and a gasket having corrosion resistance. By driving the electrolyte supply pump 19, the electrolyte in the electrolyte tank 20 heated by the heater 23 can be supplied to the electrolytic cell 2. After filling the electrolytic cell 2 with the electrolyte, the DC power supply 3 is started, and the current is gradually increased to start electrolysis. Water-soluble alcohol may be added in advance to the electrolyte supplied to the anode chamber 5 and the cathode chamber 7, or may be added after the start of electrolysis. In addition, configuring the apparatus such that the common electrolyte in the electrolyte tank 20 is supplied to the anode chamber 5 and the cathode chamber 7 respectively for electrolysis simplifies the entire apparatus, and by simply adding water-soluble alcohol to the electrolyte in the electrolyte tank 20, it is possible to easily replenish the amount that has become insufficient due to volatilization or the like, which is preferable.

[0033] The lower the temperature, the lower the solution conductivity, and the higher the overvoltage of the electrode and the cell voltage. On the other hand, the higher the temperature, the higher the evaporation amount of the added alcohol. Therefore, the temperature during electrolysis is preferably 40 to 90°C. Also, the higher the pressure, the smaller the bubble volume, and a decrease in the cell voltage is expected. However, since a higher pressure requires an expensive material design with sufficient durability and safety to prevent leakage from the electrolytic cell, the pressure during electrolysis is preferably atmospheric pressure to 30 atmospheres. In the case of an aqueous solution electrolysis process that is in practical use, the current density is 0.5 to 2 A / cm 2 and is used. However, it also exhibits an effect even at a high current density (2 to 10 A / cm 2 ).

[0034] <000~0196>The electrolyte containing the generated fine oxygen bubbles reaches the oxygen gas separator 11 through the oxygen gas / anode liquid piping 9, where it is separated into gas (oxygen gas 13) and liquid. The separated liquid is recovered into the electrolyte tank 20 through the anode liquid return piping 17. Meanwhile, the electrolyte containing the generated fine hydrogen bubbles reaches the hydrogen gas separator 12 through the hydrogen gas / cathode liquid piping 10, where it is separated into gas (hydrogen gas 14) and liquid. The separated liquid is recovered into the electrolyte tank 20 through the cathode liquid return piping 18. The water consumed by electrolysis is replenished by supplying pure water from the raw material pure water tank 21 to the system. If the added water-soluble alcohol decreases due to water electrolysis, an additive tank 22 equipped with a pump may be provided to replenish the decreased amount as needed. The materials constituting the piping and tanks used are preferably resistant to high-temperature alkaline aqueous solutions, such as polytetrafluoroethylene (PTFE) or stainless steel.

[0035] (Conductive base material) The electrodes (anode and cathode) typically comprise a conductive substrate and a catalyst layer provided on the surface of the conductive substrate. The conductive substrate is a conductor for conducting electricity and also functions as a carrier for supporting the catalyst layer. At least the surface of the conductive substrate is formed of nickel or a nickel-based alloy. The conductive substrate may be entirely made of nickel or a nickel-based alloy, or only the surface may be made of nickel or a nickel-based alloy. The conductive substrate may also be a metal material such as iron, stainless steel, aluminum, and titanium, with a nickel or nickel-based alloy coating layer formed on its surface by plating or the like.

[0036] The thickness of the conductive substrate is preferably 0.05 to 5 mm. The shape of the conductive substrate is preferably such that it has openings to remove bubbles such as oxygen and hydrogen that are generated. For example, expanded mesh or porous expanded mesh can be used as the conductive substrate. If the conductive substrate has an opening, the opening ratio (area ratio) of the conductive substrate is preferably 10 to 95%. The anode and cathode may be formed from a conductive substrate having similar properties.

[0037] (Pretreatment of conductive substrates) It is preferable to pre-treat the conductive substrate with chemical etching to remove contaminating particles such as metals and organic matter adhering to the surface. Furthermore, it is preferable to pre-treat the surface of the conductive substrate with roughening to improve adhesion with the catalyst layer. Roughening treatments include blasting with powder, etching using a substrate-soluble acid, and plasma spraying. Generally, catalysts with a larger surface area and greater porosity can be expected to exhibit higher activity.

[0038] (Catalyst layer and intermediate layer) For alkaline water electrolysis, catalysts with low overpotential and low cost are preferred. However, when using renewable energy for water electrolysis, it is preferable to use a catalyst that is resistant to frequent power outages. Furthermore, to maintain the stability of the catalyst and conductive substrate, it is preferable to provide an intermediate layer between the catalyst layer and the conductive substrate.

[0039] To improve reverse electrolysis resistance, it has also been proposed to form a catalyst on an intermediate layer formed on a conductive substrate. An intermediate layer made of lithium-containing nickel oxide, provided at the anode, has been reported to have sufficient conductivity for water electrolysis and to exhibit excellent physical strength and chemical stability even after long-term use. In the case of electrodes positioned in contact with a diaphragm, the electrode surface is preferably smooth and hydrophilic so as not to damage the diaphragm.

[0040] (diaphragm) As the diaphragm, asbestos, nonwoven fabrics, ion exchange membranes, porous polymer membranes, and composite membranes of inorganic substances and organic polymers can be used. More specifically, an ion-permeable diaphragm can be used in which an organic fiber cloth is embedded in a mixture of hydrophilic inorganic materials such as calcium phosphate compounds and calcium fluoride and organic binders such as polysulfone, polypropylene, and polyvinylidene fluoride. Alternatively, an ion-permeable diaphragm can be used in which a stretched organic fiber cloth is embedded in a film-forming mixture of granular inorganic hydrophilic substances such as antimony and zirconium oxides and hydroxides and organic binders such as fluorocarbon polymers, polysulfone, polypropylene, polyvinyl chloride, and polyvinyl butyral. By using a thin diaphragm, voltage loss due to resistance can be reduced. However, using a thin diaphragm reduces the separation performance of oxygen gas and hydrogen gas. For this reason, it is preferable to use a hydrophilic diaphragm of appropriate thickness, specifically 0.05 to 1 mm.

[0041] (electrolyte) As the electrolyte in the aqueous solution system, an alkaline aqueous solution containing an alkaline component as an electrolyte, or a metal chloride aqueous solution containing metal chlorides such as sodium chloride (table salt) and potassium chloride can be used. It is preferable to use alkali metal hydroxides such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) as the alkaline component. The concentration of the alkaline component in the alkaline aqueous solution used as the electrolyte is preferably 1 to 10 mol / L, as this provides high conductivity and reduces power consumption. Furthermore, the concentration of the metal chloride in the metal chloride aqueous solution is preferably 1 to 5 mol / L. [Examples]

[0042] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0043] (Example 1) A nickel wire (0.2 mm in diameter) was used as the anode, and a 4 mol / L potassium hydroxide (KOH) aqueous solution with 2-methylpropan-2-ol (0.5-5 vol%) added was subjected to water electrolysis at a solution temperature of 30°C. Figure 2 shows the current-potential characteristics of the nickel anode (dashed line). The percentage of the surface tension of the potassium hydroxide (KOH) aqueous solution with 2-methylpropan-2-ol added, with the surface tension of the potassium hydroxide (KOH) aqueous solution without 2-methylpropan-2-ol being set as the standard (100%), is as follows. 2-Methylpropane-2-ol 0.5% by volume: 66% • 2-Methylpropane-2-ol 1 volume %: 56% • 2-Methylpropane-2-ol 2 vol%: 48% • 2-Methylpropane-2-ol 4% by volume: 37% • 2-Methylpropane-2-ol 5% by volume: 37%

[0044] (Comparative Example 1) Water electrolysis was carried out in the same manner as in Example 1 described above, except that a 4 mol / L potassium hydroxide (KOH) aqueous solution without 2-methylpropan-2-ol was used. Figure 2 shows a graph (solid line) illustrating the nickel anode current-potential characteristics. As shown in Figure 2, it can be seen that under higher current densities, there is a range in which the anode potential becomes negative (oxygen overpotential decreases) with the addition of 2-methylpropan-2-ol.

[0045] (Example 2) A nickel wire (0.2 mm in diameter) was used as the anode, and 4 mol / L potassium hydroxide (KOH) aqueous solutions, each containing 2-methylpropan-2-ol (4 vol%) and 2-methylbutan-2-ol (0.5 vol%), were electrolyzed with water at a solution temperature of 30°C. Figure 3 shows the current-potential characteristics of the nickel anode (dotted and dashed lines). The surface tension of potassium hydroxide (KOH) aqueous solution with 2-methylpropan-2-ol and 2-methylbutan-2-ol added, respectively, is set as the baseline (100%), and the percentages of surface tension are as follows. • 2-Methylpropane-2-ol 4% by volume: 37% 2-Methylbutan-2-ol 0.5% by volume: 56%

[0046] (Comparative Example 2) Water electrolysis was carried out in the same manner as in Example 2 described above, except that a 4 mol / L potassium hydroxide (KOH) aqueous solution without 2-methylbutan-2-ol was used. Figure 3 shows a graph (solid line) illustrating the nickel anode current-potential characteristics. As shown in Figure 3, it can be seen that under higher current densities, there is a range in which the anode potential becomes negative (oxygen overpotential decreases) with the addition of 2-methylbutan-2-ol.

[0047] (Example 3) Water electrolysis was carried out in the same manner as in Example 1 described above, except that a 4 mol / L potassium hydroxide (KOH) aqueous solution with ethanol (4 vol%) added was used. Figure 4 shows a graph (solid line) illustrating the nickel anode current-potential characteristics. The percentage of the surface tension of the potassium hydroxide (KOH) aqueous solution with ethanol added, with the surface tension of the potassium hydroxide (KOH) aqueous solution without ethanol being set as the reference (100%), was 78%.

[0048] (Comparative Example 3) Water electrolysis was carried out in the same manner as in Example 3 described above, except that a 4 mol / L potassium hydroxide (KOH) aqueous solution without ethanol was used. Figure 4 shows a graph (dashed line) illustrating the nickel anode current-potential characteristics. As shown in Figure 4, it can be seen that under higher current densities, there is a range in which the anode potential becomes negative (oxygen overpotential decreases) due to the addition of ethanol.

[0049] (Example 4) NiCoO is applied to the surface of nickel expanded mesh (6.0mmLW×3.7mmSW×0.9mmST×0.8mmT) by thermal decomposition. x An anode with a catalyst formed on it was prepared. RuPrO was formed on a nickel plain weave mesh (No. 40) by pyrolysis. x A cathode with a catalyst formed on it was prepared. AGFA's product name "Zirfon Perl-UTP500A" was used as the diaphragm. An electrolytic cell was assembled using the prepared anode, cathode, and diaphragm. The effective projected area of ​​the electrode and diaphragm was 19 cm². 2 The following was done. A 4 mol / L potassium hydroxide (KOH) aqueous solution was prepared as the electrolyte. This electrolyte was supplied to the electrolytic cell at a rate of 30 mL / min, with a current density of 1 A / cm². 2 After operating for 48 hours at 40°C, the output was 1.2 A / cm². 2 The system was operated for 1,000 seconds. Next, 2-methylpropan-2-ol was added to the electrolyte in the anode chamber to a concentration of 4% by volume, and the system was operated for another 1,000 seconds. Subsequently, 2-methylpropan-2-ol was added to the electrolyte in the cathode chamber to a concentration of 4% by volume, and the system was operated. The surface tension of the electrolyte with 2-methylpropan-2-ol added (4% by volume) was 37%, compared to the surface tension of the electrolyte without 2-methylpropan-2-ol (100%) as the baseline.

[0050] Figure 5 shows a graph illustrating the change in cell voltage during aqueous electrolysis of an electrolyte solution to which 2-methylpropan-2-ol has been added. As shown in Figure 5, it can be seen that the cell voltage decreased with the addition of 2-methylpropan-2-ol. Furthermore, observation of the generated bubbles revealed that the bubble size rapidly decreased and the number of bubbles increased with the addition of 2-methylpropan-2-ol. Bubbles quickly detached from the electrodes, and the electrolyte solution, which was transparent when 2-methylpropan-2-ol was not added, became cloudy.

[0051] The cell voltage is defined as follows: • V0: Cell voltage before adding 2-methylpropan-2-ol to the anode chamber • V1: Cell voltage when 2-methylpropan-2-ol is added to the anode chamber • V2: Cell voltage when 2-methylpropan-2-ol is added to the cathode chamber

[0052] From the results shown in Figure 5, the change in cell voltage was calculated as follows, and it was confirmed that the cell voltage decreased with the addition of 2-methylpropan-2-ol. V1-V0=18mV V2 - V0 = 23mV

[0053] (Example 5) A nickel wire (0.2 mm in diameter) was used as the anode, and a 4 mol / L potassium hydroxide (KOH) aqueous solution containing 2-methylpropan-2-ol (4 vol%) and 2-methylbutan-2-ol (0.5 vol%) was added to it, while the current density was 3 A / cm². 2Continuous electrolysis of water was performed. The surface tension of potassium hydroxide (KOH) aqueous solution with 2-methylpropan-2-ol and 2-methylbutan-2-ol added, respectively, is set as the baseline (100%), and the percentages of surface tension are as follows. Figure 6 shows a graph illustrating the change in oxygen evolution potential during long-term operation. As shown in Figure 6, the addition of 2-methylpropan-2-ol and 2-methylbutan-2-ol resulted in a stably low anode potential, demonstrating that the effect is maintained stably for a long period even under electrolysis. • 2-Methylpropane-2-ol 4% by volume: 37% 2-Methylbutan-2-ol 0.5% by volume: 56%

[0054] (Comparative Example 4) Except for not adding either 2-methylpropan-2-ol or 2-methylbutan-2-ol, and using a 4 mol / L potassium hydroxide (KOH) aqueous solution, water electrolysis was carried out continuously in the same manner as in Example 5 described above. As a result, as shown in Figure 6, the anode potential fluctuated significantly due to the influence of bubbles adhering to the electrode surface, and a nobler potential was observed compared to Example 5. This suggests that it also contributes to improved electrode durability. [Industrial applicability]

[0055] According to the aqueous solution electrolysis method of the present invention, electrolysis can be performed at a lower voltage compared to the cell voltage under conventional electrolysis conditions. When the power supply is fixed, the reduced voltage allows for an increase in the applied current, thereby improving productivity. Even if the harsh electrolysis conditions of the past, such as alkali concentration and temperature, are relaxed, operation with similar electrolysis efficiency is possible, improving the durability of cell materials such as electrodes and diaphragms, and also opening up possibilities for applications other than alkaline water electrolysis. [Explanation of Symbols]

[0056] 1: Electrolysis apparatus 2: Electrolytic cell 3:DC power supply 4: Anode 5: Anode Room 6: Cathode 7: Cathode Chamber 8: Diaphragm 9: Oxygen gas / anode liquid piping 10: Hydrogen gas / cathode liquid piping 11: Oxygen gas separator 12: Hydrogen gas separator 13: Oxygen gas 14: Hydrogen gas 15: Anode liquid supply piping 16: Cathode fluid supply piping 17: Anode liquid return piping 18: Cathode fluid return piping 19: Electrolyte supply pump 20: Electrolyte tank 21: Raw material pure water tank 22: Coating Tank 23: Heater

Claims

1. An aqueous solution electrolysis method for generating at least one of hydrogen and oxygen by electrolyzing an electrolyte solution, The electrolyte contains a water-soluble alcohol, The aforementioned alcohol is a tertiary alcohol, The electrolyte is an alkaline aqueous solution containing an alkaline component. Current density 2A / cm ２ The above describes an aqueous solution electrolysis method for electrolyzing the aforementioned electrolyte.

2. The aqueous solution electrolysis method according to claim 1, wherein the tertiary alcohol is at least one of 2-methylpropan-2-ol and 2-methylbutan-2-ol.

3. The aqueous solution electrolysis method according to claim 1 or 2, wherein the concentration of the alkaline component in the alkaline aqueous solution is 1 to 10 mol / L.

4. The concentration of the alcohol in the electrolyte is The aqueous solution electrolysis method according to claim 1 or 2, wherein the concentration of the electrolyte is such that the surface tension of the electrolyte is 90% or less of the surface tension of the control electrolyte that does not contain alcohol.

5. The aqueous solution electrolysis method according to claim 1 or 2, wherein the concentration of the alcohol in the electrolyte is 0.1 to 10% by volume.

6. Using an electrolytic cell having an anode chamber and a cathode chamber, The method for electrolyzing an aqueous solution according to claim 1 or 2, wherein the common electrolyte is supplied to the anode chamber and the cathode chamber, respectively, for electrolysis.

7. Current density 10A / cm ２ The method for electrolyzing an aqueous solution according to claim 1 or 2, wherein the electrolyte is electrolyzed as follows.

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