Membrane-free alkaline water electrolysis method and membrane-free alkaline water electrolysis device

Abstract

To transform anodic reaction from oxygen evolution reaction to iodate ion formation reaction in a method for manufacturing hydrogen by electrolyzing alkali water, and to highly efficiently implement an alkaline water electrolysis method with low power consumption.SOLUTION: There are provided a membrane-free alkaline water electrolysis method which electrolyzes an alkali metal hydroxide aqueous solution which contains iodide ions and whose concentration is higher than or equal to 1 mol / L, generates a hydrogen gas in a cathode, and generates iodate ions in an anode, and a membrane-free alkaline water electrolysis device.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a diaphragm-free alkaline water electrolysis method and a diaphragm-free alkaline water electrolysis apparatus. [Background technology]

[0002] Hydrogen is a clean energy source that can help achieve carbon neutrality because it does not produce carbon dioxide when burned. For example, hydrogen can be used as fuel for automobiles and aircraft, and as a power generation fuel for fuel cells, and is therefore attracting attention from various quarters. Traditionally, hydrogen has been produced industrially, for example, by reforming fossil fuels using catalysts, separating and refining by-product gases from steelworks and chemical plants, extracting hydrogen from biogas generated from biomass, and electrolyzing water.

[0003] Hydrogen production methods using fossil fuels are undesirable from the perspective of carbon neutrality, since they produce not only hydrogen but also carbon dioxide. In addition, methods for separating and refining by-product gases from steelworks and chemical plants lack stability in terms of hydrogen production, since the amount of hydrogen produced depends on the amount of the main product. Methods for producing hydrogen from biogas have problems such as high transportation costs, since the supply areas are limited. For this reason, there is a demand for the establishment of technology to produce hydrogen cheaply and stably by electrolyzing water (alkaline water).

[0004] For example, Patent Document 1 describes an electrochemical system and method for producing hydrogen. Patent Document 1 proposes a hydrogen production device and method using an electrochemical cell in which an anolyte is made of an oxidation substrate that has a higher standard oxidation potential than water (i.e., is easily oxidized). Patent Document 2 discloses a diaphragm-less electrolysis device that electrolyzes seawater or salt water, and discloses a structure that realizes an electrolyte flow pattern that is less likely to cause scale deposition on the electrode plates.

[0005] In a method of electrolyzing water (alkaline water) to produce hydrogen, the reactions at each electrode are as follows: Anode: 2OH - →1 / 2O2+H2O+2e - Cathode: 2H2O+2e - →2OH - +H2 The hydrogen produced at the cathode is recovered and used for various purposes, but the oxygen produced as a by-product at the anode is mainly released into the atmosphere and has little industrial value.

[0006] For this reason, a method has been proposed in which sodium hypochlorite is produced instead of oxygen by electrolysis of water, and the sodium hypochlorite is used as a disinfectant. For example, Patent Document 3 discloses a method of producing a sodium hypochlorite solution by electrolyzing salt water in a membraneless electrolytic cell. Patent Document 4 discloses a method of electrolytically producing chlorate, which discloses a method of producing hexavalent chromium ions by the reaction of hypochlorite ions with trivalent chromium ions, and using the produced hexavalent chromium ions for electrolysis. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2012 / 097167 [Patent Document 2] Japanese Patent Application Publication No. 59-24193 [Patent Document 3] Japanese Patent Application Publication No. 57-1593 [Patent Document 4] Japanese Patent Application Publication No. 1-22356 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, if the anode reaction can be converted from an oxygen generating reaction to another by-product, the by-product can be effectively utilized in the hydrogen production method. For example, if a by-product other than sodium hypochlorite can be generated and effectively utilized, it will contribute to the spread and improvement of hydrogen production. In addition, in order to realize the implementation of a hydrogen society, in addition to simplifying and miniaturizing the alkaline water electrolysis device, it is also necessary to increase the efficiency and reduce the power consumption of alkaline water electrolysis.

[0009] In order to solve these problems of the conventional technology, the present inventors have carried out studies aimed at converting the anode reaction from an oxygen evolution reaction to an iodate ion production reaction in a method for producing hydrogen by electrolyzing alkaline water, thereby enabling alkaline water electrolysis to be carried out with high efficiency and low power consumption. [Means for solving the problem]

[0010] Examples of specific embodiments of the present invention are given below.

[0011] [1] A membrane-free alkaline water electrolysis method in which an aqueous alkali metal hydroxide solution containing iodide ions and with a concentration of 1 mol / L or more is electrolyzed to produce hydrogen gas at the cathode and iodate ions at the anode. [2] The method for membrane-free alkaline water electrolysis according to [1], wherein the aqueous alkali metal hydroxide solution further contains a cathode surface modifier. [3] The method for membrane-free alkaline water electrolysis according to [2], wherein the cathode surface modifier contains at least one selected from the group consisting of hexavalent chromium ions, pentavalent vanadium ions, hexavalent molybdenum ions, pentavalent niobium ions, and tetravalent titanium ions. [4] The method for membrane-free alkaline water electrolysis according to [2] or [3], wherein the cathode surface modifier contains hexavalent chromium ions. [5] The method for membrane-free alkaline water electrolysis according to any of [2] to [4], wherein the content of the cathode surface modifier is 0.05 mol / L or less. [6] The method for membrane-free alkaline water electrolysis according to [1], wherein the surface of the cathode contains a component derived from the cathode surface modifier. [7] The method for membrane-free alkaline water electrolysis according to [1] or [6], wherein a hydroxide or oxide containing at least one selected from the group consisting of chromium, vanadium, molybdenum, niobium, and titanium is present on a surface of the cathode. [8] The method for membrane-free alkaline water electrolysis according to any one of [1], [6] and [7], wherein a chromium-containing hydroxide or oxide is present on a surface of the cathode. [9] The method for membrane-free alkaline water electrolysis according to any of [1] to [8], wherein electrolysis is carried out at 30 to 250°C.

[10] A method for recovering valuable metals, comprising oxidative leaching of valuable metals using the iodate ion-containing solution obtained by the method for alkaline water electrolysis without a diaphragm according to any one of [1] to [9].

[11] A non-diaphragm-type alkaline water electrolysis apparatus having an electrolytic cell equipped with a cathode and an anode, A non-diaphragm alkaline water electrolysis device that electrolyzes an aqueous solution of alkali metal hydroxide containing iodide ions and having a concentration of 1 mol / L or more, producing hydrogen gas at the cathode and iodate ions at the anode.

[12] The diaphragm-free alkaline water electrolysis apparatus according to

[11] , wherein the aqueous alkali metal hydroxide solution further contains a cathode surface modifier.

[13] The diaphragm-free alkaline water electrolysis device according to

[12] , wherein the cathode surface modifier contains at least one selected from the group consisting of a hexavalent chromium ion, a pentavalent vanadium ion, a hexavalent molybdenum ion, a pentavalent niobium ion, and a tetravalent titanium ion.

[14] The non-diaphragm alkaline water electrolysis apparatus according to

[12] or

[13] , wherein the cathode surface modifier contains a hexavalent chromium ion.

[15] The non-diaphragm alkaline water electrolysis device according to any one of

[12] to

[14] , wherein the content of the cathode surface modifier is 0.05 mol / L or less.

[16] The diaphragm-free alkaline water electrolysis apparatus according to

[11] , wherein a surface of the cathode contains a component derived from the cathode surface modifier.

[17] The non-diaphragm alkaline water electrolysis device according to

[11] or

[16] , wherein a hydroxide or oxide containing at least one selected from the group consisting of chromium, vanadium, molybdenum, niobium, and titanium is present on a surface of the cathode.

[18] The non-diaphragm alkaline water electrolysis apparatus according to any one of

[11] ,

[16] and

[17] , wherein a chromium-containing hydroxide or oxide is present on a surface of the cathode.

[19] The non-diaphragm alkaline water electrolysis apparatus according to any one of

[11] to

[18] , wherein the electrolysis is carried out at 30 to 250°C.

[20] The non-diaphragm alkaline water electrolysis apparatus according to any one of

[11] to

[19] , wherein the anode contains a carbon-based material.

[21] The diaphragm-free alkaline water electrolysis device according to any of

[11] to

[20] , wherein the electrolytic cell has a plurality of electrolytic cell units each including a cathode and an anode, and each of the electrolytic cell units is connected to a hydrogen gas recovery mechanism.

[22] The diaphragm-free alkaline water electrolysis apparatus according to any one of

[11] to

[21] , which has a mechanism for recovering the iodate ion-containing solution. Effect of the Invention

[0012] According to the present invention, in a method for producing hydrogen by electrolyzing alkaline water, the anode reaction is converted from an oxygen generating reaction to an iodate ion generating reaction, and the alkaline water electrolysis method can be performed with high efficiency and low power consumption. According to the present invention, in addition to hydrogen gas, iodate ions generated as a by-product can be effectively utilized. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a diaphragm-free alkaline water electrolysis device in Example 1. [Diagram 2] The graph shows the results of measuring the anodic polarization curve when the working electrode (anode) was made of graphite or nickel. [Diagram 3] This shows the results of measuring a cathodic polarization curve when the working electrode (cathode) was nickel. [Figure 4]The figures show the results of a model evaluation of the power consumption when potassium iodide is not added to the electrolyte and when potassium iodide is added to the electrolyte. [Diagram 5] FIG. 1 is a schematic diagram illustrating the configuration of a diaphragm-free alkaline water electrolysis device in Example 2. [Figure 6] This shows the results of measuring a cathodic polarization curve when the working electrode (cathode) was nickel. [Figure 7] FIG. 1 is a schematic diagram illustrating the configuration of a diaphragm-free alkaline water electrolysis device in Example 3. [Figure 8] This shows the results of measuring a cathodic polarization curve when the working electrode (cathode) was nickel. [Figure 9] FIG. 1 is a schematic diagram illustrating a configuration of an alkaline water electrolysis apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below. The following description may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "~" means a range including the numerical values ​​before and after "~" as the lower and upper limits.

[0015] (Alkaline water electrolysis method) The present embodiment relates to a diaphragm-free alkaline water electrolysis method in which an aqueous alkali metal hydroxide solution containing iodide ions and having a concentration of 1 mol / L or more is electrolyzed to generate hydrogen gas at the cathode and iodate ions at the anode. In this embodiment, iodate ions are generated at the anode in a hydrogen production method by alkaline water electrolysis. In this alkaline water electrolysis method, the electrode potential of the anode becomes more base (voltage drop can be reduced), so the electrical energy used for alkaline water electrolysis can be reduced (power saving in alkaline water electrolysis).

[0016] In this embodiment, since the alkali metal hydroxide solution contains iodide ions, hydrogen gas (H2) is generated at the cathode and iodate ions (IO3 - Hydrogen gas (H2) produced at the cathode is separated and collected through a gas-liquid separation mechanism. Meanwhile, iodate ions (IO3 - ) is present in the electrolyte. In this embodiment, iodate ions are generated at the anode instead of oxygen gas. In this case, a part of the oxygen gas generation reaction may be replaced by the iodate ion generation reaction, or the entire oxygen gas generation reaction may be replaced by the iodate ion generation reaction. When a part of the oxygen gas generation reaction is replaced by the iodate ion generation reaction, both oxygen and iodate ions may be generated at the anode.

[0017] During or after the electrolysis of alkaline water, iodate ions (IO3 - The electrolyte in which iodate ions are dissolved is recovered as a solution containing iodate ions, and can be used to separate and recover valuable metals. For example, valuable metals can be oxidized and leached from electronic waste (E-waste), and recovered from the solution by electrolytic deposition or neutralization. Examples of valuable metals include tin (Sn), zinc (Zn), lead (Pb), molybdenum (Mo), tungsten (W), and antimony (Sb). In this way, the solution containing iodate ions can be used to recover valuable metals in urban mine recycling, for example, as described below, and by-products obtained in the hydrogen production method can also be effectively utilized.

[0018] The by-product iodate ion (IO3 - ) can also be used as a food additive, in chemical synthesis, and in medicines. - ) can also be used as an oxidizing agent.

[0019] The alkaline water electrolysis method of the present embodiment is a diaphragm-less alkaline water electrolysis method. Here, the diaphragm-less alkaline water electrolysis method refers to an alkaline water electrolysis method using an electrolysis device that does not have a diaphragm (an ion-permeable membrane that prevents mixing of oxygen gas generated at the anode and hydrogen gas generated at the cathode) separating the catholyte chamber from the anolyte chamber. Performing alkaline water electrolysis in a diaphragm-less manner enables simplification and miniaturization of the alkaline water electrolysis device.

[0020] In the alkaline water electrolysis method of the present embodiment, an aqueous alkali metal hydroxide solution is used as the electrolyte. Examples of the aqueous alkali metal hydroxide solution include an aqueous potassium hydroxide (KOH) solution, an aqueous sodium hydroxide (NaOH) solution, and an aqueous lithium hydroxide (LiOH) solution. Among these, the aqueous alkali metal hydroxide solution is preferably an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution, and more preferably an aqueous potassium hydroxide solution.

[0021] The concentration of the alkali metal hydroxide in the aqueous alkali metal hydroxide solution is 1 mol / L or more, and more preferably 2 mol / L or more. The upper limit of the concentration of the alkali metal hydroxide in the aqueous alkali metal hydroxide solution is not particularly limited, but is preferably 10 mol / L or less, and more preferably 8 mol / L or less, for example. By setting the concentration of the alkali metal hydroxide in the aqueous alkali metal hydroxide solution within the above range, the ionic conductivity of the electrolyte can be increased, and as a result, power saving effects can be easily obtained.

[0022] The content of iodide ions contained in the aqueous alkali metal hydroxide solution is preferably 0.01 mol / L or more, more preferably 0.1 mol / L or more, and even more preferably 0.5 mol / L or more. The content of iodide ions contained in the aqueous alkali metal hydroxide solution is preferably 5 mol / L or less. The content of iodide ions contained in the aqueous alkali metal hydroxide solution can be controlled to the above range by dissolving, for example, a predetermined amount of potassium iodide (KI) or sodium iodide (NaI) in the aqueous alkali metal hydroxide solution.

[0023] By adding iodide ions to the alkali metal hydroxide solution, the anode reaction is changed from the oxygen evolution reaction to iodate ions (IO3 - The reactions at each electrode in the diaphragm-free alkaline water electrolysis method of the present embodiment are as follows: Anode: 1 / 3I - +2OH - →1 / 3IO3 - +H2O+2e - Cathode: 2H2O+2e - →2OH - +H2 And the overall reaction is as follows: 1 / 3I - +2H2O→H2+1 / 3IO3 -

[0024] In this embodiment, the anode reaction converts the oxygen generation reaction into iodate ions (IO - ) evolution reaction. In addition, the standard electrode potential when the anode reaction is the oxygen evolution reaction is 0.40 V (25 °C), while the anode reaction is the iodate ion (IO3 - ) The standard electrode potential in the case of the evolution reaction is 0.26 V (25°C), and the theoretical decomposition voltage of the electrolyte decreases by 0.14 V due to the conversion of the anodic reaction.

[0025] In the first embodiment of the present invention, the aqueous alkali metal hydroxide solution preferably further contains a cathode surface modifier. Here, since the alkaline water electrolysis method of the present embodiment is a diaphragm-free alkaline water electrolysis method, iodate ions (IO3 - When iodate ions (IO3) are reduced at the cathode, the efficiency of hydrogen production and the efficiency of iodate ions production decrease. Therefore, in the first embodiment, a cathode surface modifier is added to the aqueous alkali metal hydroxide solution. In this specification, the cathode surface modifier refers to a surface modifier that modifies the iodate ions (IO3) generated at the anode. - It is an agent that modifies the cathode surface to suppress the reduction of iodate ions (IO3) at the cathode. By adding a cathode surface modifier to an aqueous solution of an alkali metal hydroxide, for example, a film (a film that prevents the reduction of iodate ions) can be applied to the cathode surface. This film modifies the cathode surface and prevents the reduction of iodate ions (IO3) at the start of electrolysis. - ) can be suppressed from being reduced. In addition, by including a cathode surface modifier in the aqueous alkali metal hydroxide solution, the hydrogen generation reaction can be preferentially promoted at the cathode even during alkaline water electrolysis over a long period of time.

[0026] In this embodiment, the cathode surface modifier is iodate ion (IO - The cathode surface modifier is not particularly limited as long as it is an agent capable of modifying the surface of the cathode so as to suppress the reduction reaction of ), but it is preferable that the cathode surface modifier contains at least one selected from the group consisting of hexavalent chromium ions, pentavalent vanadium ions, hexavalent molybdenum ions, pentavalent niobium ions, and tetravalent titanium ions. Among these, it is particularly preferable that the cathode surface modifier contains hexavalent chromium ions.

[0027] Examples of the cathode surface modifier added to the aqueous alkali metal hydroxide solution include potassium chromate (K2Cr2O7), sodium chromate (Na2Cr2O7), potassium vanadate (KVO3), and ammonium vanadate (NH4VO3).

[0028] The content of the cathode surface modifier in the aqueous alkali metal hydroxide solution is preferably 0.0001 mol / L or more, more preferably 0.0005 mol / L or more, and even more preferably 0.001 mol / L or more. The content of the cathode surface modifier is preferably 0.1 mol / L or less, and more preferably 0.05 mol / L or less. By setting the content of the cathode surface modifier within the above range, it is possible to prevent the generation of iodate ions (IO3 - ) can be effectively inhibited from being reduced.

[0029] In the second embodiment of the present invention, the surface of the negative electrode (cathode) preferably has a component derived from the cathode surface modifier. For example, the component derived from the cathode surface modifier may be attached to at least a portion of the surface of the negative electrode (cathode), or may cover the surface of the negative electrode (cathode). When the component derived from the cathode surface modifier covers the surface of the negative electrode (cathode), the negative electrode (cathode) may have a thin film (coating) containing the component derived from the cathode surface modifier.

[0030] Here, the component derived from the cathode surface modifier is preferably a hydroxide or oxide containing at least one selected from the group consisting of chromium, vanadium, molybdenum, niobium, and titanium, and more preferably a hydroxide or oxide containing at least one selected from the group consisting of trivalent chromium, trivalent vanadium, tetravalent molybdenum, tetravalent niobium, and trivalent titanium. In particular, the surface of the cathode is preferably coated with a thin film of a hydroxide containing chromium or a hydroxide containing vanadium, and more preferably coated with a thin film of a hydroxide containing trivalent chromium or a hydroxide containing trivalent vanadium.

[0031] When the surface of the negative electrode (cathode) has a component derived from the cathode surface modifier, it is preferable to perform a pre-modification treatment on the negative electrode (cathode) before the alkaline water electrolysis treatment. The pre-modification treatment is a treatment for precipitating the component derived from the cathode surface modifier on the surface of the negative electrode (cathode). As the pre-modification treatment, for example, electrolysis is performed in an electrolyte solution containing the cathode surface modifier, so that the component derived from the cathode surface modifier can be precipitated on the surface of the negative electrode (cathode). The pre-modification treatment can also be performed by dry plating such as sputtering.

[0032] The electrolysis temperature in the diaphragm-free alkaline water electrolysis method of the present embodiment is preferably 25° C. or more, more preferably 30° C. or more, even more preferably 35° C. or more, and particularly preferably 40° C. or more. The electrolysis temperature is preferably 250° C. or less, more preferably 200° C. or less. The electrolysis temperature refers to the temperature of the aqueous alkali metal hydroxide solution serving as the electrolytic solution.

[0033] In the diaphragm-free alkaline water electrolysis apparatus of the present embodiment, stirring may be performed during electrolysis. Stirring conditions may include, for example, a stirrer at 100 to 1000 rpm, but the electrolytic solution may also be flow-stirred by liquid circulation.

[0034] (Alkaline water electrolysis equipment) The present embodiment relates to a diaphragm-free alkaline water electrolysis apparatus having an electrolytic cell equipped with a cathode and an anode, which electrolyzes an aqueous alkali metal hydroxide solution containing iodide ions and having a concentration of 1 mol / L or more to generate hydrogen gas at the cathode and iodate ions at the anode. In the present embodiment, iodate ions are generated at the anode of the alkaline water electrolysis apparatus. In such an alkaline water electrolysis method, the resistance of the anode reaction, the diaphragm resistance, and the electrolyte resistance (the absence of a diaphragm allows the gap between the electrodes to be narrowed) can be reduced, thereby reducing the electrical energy used for alkaline water electrolysis.

[0035] In this embodiment, the cathode and the anode are connected to a power source. The power source may be a renewable energy source such as wind power or solar power. By using renewable energy as the electric energy used in alkaline water electrolysis in this manner, hydrogen gas, which is a clean energy source, can be produced without generating carbon dioxide.

[0036] The alkaline water electrolysis apparatus of this embodiment is a diaphragm-less alkaline water electrolysis apparatus. The diaphragm-less alkaline water electrolysis apparatus does not have a diaphragm (an ion-permeable membrane that prevents mixing of oxygen gas generated at the anode and hydrogen gas generated at the cathode) separating the catholyte chamber and the anolyte chamber. By performing alkaline water electrolysis in a diaphragm-less manner, it is possible to simplify and reduce the size of the alkaline water electrolysis apparatus. Furthermore, the compact size of the alkaline water electrolysis apparatus can reduce the energy used to heat the electrolyte, and it may be possible to heat the electrolyte using only Joule heat from solution resistance.

[0037] The alkaline water electrolysis apparatus of this embodiment uses an aqueous alkali metal hydroxide solution as the electrolytic solution. The alkali metal hydroxide contained in the aqueous alkali metal hydroxide solution is the same as the alkali metal hydroxide exemplified in the alkaline water electrolysis method described above. The concentration of the alkali metal hydroxide in the aqueous alkali metal hydroxide solution is the same as the concentration in the alkaline water electrolysis method described above.

[0038] The aqueous alkali metal hydroxide solution used as the electrolyte in the alkaline water electrolysis apparatus of the present embodiment contains iodide ions. The content of iodide ions in the aqueous alkali metal hydroxide solution is the same as that in the alkaline water electrolysis method described above.

[0039] In the first embodiment of the present invention, the aqueous alkali metal hydroxide solution used as the electrolyte in the alkaline water electrolysis apparatus preferably further contains a cathode surface modifier. Here, since the alkaline water electrolysis apparatus of the present embodiment is a non-diaphragm type alkaline water electrolysis apparatus, iodate ions (IO3 -When iodate ions (IO3) are reduced at the cathode, the efficiency of hydrogen production and the efficiency of iodate ions production decrease. Therefore, in the first embodiment, a cathode surface modifier is added to the aqueous alkali metal hydroxide solution. By including the cathode surface modifier in the aqueous alkali metal hydroxide solution, the cathode surface is modified and the iodate ions (IO3 - ) can be suppressed from being reduced. Furthermore, when the aqueous alkali metal hydroxide solution contains a cathode surface modifier, the hydrogen generation reaction can proceed preferentially at the cathode even during long-term alkaline water electrolysis. The type and content of the cathode surface modifier are the same as those of the cathode surface modifier in the alkaline water electrolysis method described above.

[0040] In the second embodiment of the present invention, the surface of the cathode preferably contains a component derived from the cathode surface modifier. For example, the component derived from the cathode surface modifier may be attached to at least a part of the surface of the cathode, or may cover the surface of the cathode. When the component derived from the cathode surface modifier covers the surface of the cathode, the cathode may have a thin film (coating) containing the component derived from the cathode surface modifier. Examples of the component derived from the cathode surface modifier include those listed in the alkaline water electrolysis method described above.

[0041] When the surface of the cathode contains a component derived from the cathode surface modifier, the cathode is preferably subjected to a pre-modification treatment prior to alkaline water electrolysis. The pre-modification treatment method is the same as that described in the alkaline water electrolysis method.

[0042] In this embodiment, by making iodide ions present in the alkali metal hydroxide aqueous solution, the anode reaction is changed from an oxygen generation reaction to an iodate ion (IO -) generation reaction. In this case, a part of the oxygen generation reaction may be replaced by the iodate ion generation reaction, or the entire oxygen generation reaction may be replaced by the iodate ion generation reaction. There is no particular limitation on the material constituting the anode of the alkaline water electrolysis apparatus as long as it is a material that can carry out the following reaction. Anode: 1 / 3I - +2OH - →1 / 3IO3 - +H2O+2e - Examples of the material constituting the anode include carbon-based materials, nickel, and nickel-based alloys. Among them, it is preferable that the material constituting the anode is a carbon-based material. Examples of the carbon-based material include graphite, plastic formed carbon, glassy carbon, and carbon coating materials, and it is particularly preferable to use graphite. By using a carbon-based material as the material constituting the anode, it is possible to reduce the amount of iodate ions (IO3 - ) The overvoltage of the generated reaction can be reduced, and power saving can be achieved more effectively.

[0043] The material constituting the cathode of the alkaline water electrolysis apparatus of the present embodiment is not particularly limited as long as it is a material that can carry out the following reaction. Cathode: 2H2O+2e - →2OH - +H2 Examples of materials constituting the negative electrode (cathode) include nickel, nickel-based alloys, iron, iron-based alloys, etc. Among these, the material constituting the negative electrode (cathode) is preferably nickel or a nickel-based alloy.

[0044] The alkaline water electrolysis apparatus of this embodiment preferably includes a heating mechanism and a stirring mechanism. The electrolysis temperature in the alkaline water electrolysis apparatus is preferably 25°C or higher, more preferably 30°C or higher, further preferably 35°C or higher, and particularly preferably 40°C or higher. The electrolysis temperature is preferably 250°C or lower, more preferably 200°C or lower. The electrolysis temperature refers to the temperature of the aqueous alkali metal hydroxide solution serving as the electrolytic solution. The non-diaphragm-type alkaline water electrolysis apparatus of this embodiment preferably includes a heating mechanism capable of heating the aqueous alkali metal hydroxide solution to the above temperature.

[0045] The alkaline water electrolysis apparatus of this embodiment may be an apparatus having at least one cathode and one anode and at least one electrolytic cell, but the electrolytic cell may have a plurality of electrolytic cell units (unit cells) each including a cathode and an anode. Each electrolytic cell unit is a membrane-less electrolytic cell unit, but each electrolytic cell unit may be separated by a bipolar electrode ( FIG. 9 ).

[0046] In the case of a bipolar electrolytic cell, the upper limit of the number of units is not particularly limited and can be appropriately adjusted depending on the production scale of hydrogen and iodate ions. Since the alkaline water electrolysis device of the present embodiment does not use a diaphragm, it is possible to shorten the inter-electrode distance and increase the cell integration, thereby improving the efficiency of hydrogen production.

[0047] The alkaline water electrolysis device of this embodiment is also a hydrogen production device and has a hydrogen gas recovery mechanism. In the hydrogen gas recovery mechanism, gas-liquid separation is performed, and the hydrogen gas generated at the cathode is recovered and sent to a storage container. Meanwhile, the liquid after hydrogen separation is recycled and reused as an electrolyte.

[0048] The alkaline water electrolysis apparatus of this embodiment may have a mechanism for recovering the iodate ion-containing solution. For example, the alkaline water electrolysis apparatus of this embodiment may have a mechanism for monitoring the content of iodate ions in the electrolytic solution, and may recover a part or all of the iodate ion-containing solution when the content of iodate ions in the electrolytic solution reaches a predetermined amount or more. In this case, fresh electrolytic solution (aqueous alkali metal hydroxide solution containing iodide ions) may be supplied at the same time as recovering a part of the iodate ion-containing solution, and alkaline water electrolysis may be performed continuously.

[0049] (Method of recovering valuable metals) This embodiment relates to a valuable metal recovery method including oxidative leaching of valuable metals from various raw materials including waste using an iodate ion-containing solution obtained by the above-mentioned diaphragm-free alkaline water electrolysis method. For example, electronic waste (E-waste) is immersed in the iodate ion-containing solution, and the valuable metals are oxidatively leached, and the valuable metals can be recovered from the liquid by electrodeposition or neutralization. In this specification, recovery of valuable metals from electronic waste (E-waste) is also referred to as urban mine recycling. In this way, in this embodiment, in addition to producing hydrogen gas, the iodate ion-containing solution generated as a by-product can be effectively used for urban mine recycling.

[0050] Examples of valuable metals include tin (Sn), zinc (Zn), lead (Pb), molybdenum (Mo), tungsten (W), and antimony (Sb). Among them, the valuable metal is preferably tin. That is, the present embodiment preferably relates to a method for recovering tin, including oxidative leaching of tin using an iodate ion-containing solution obtained by the above-mentioned diaphragm-free alkaline water electrolysis method. Tin is an essential metal for the electrical and electronics industry, and the need for securing its resources is expected to increase in the future. For this reason, there is great significance in developing a recycling method that can efficiently and directly separate and recover tin contained in solder or plating.

[0051] For example, when tin is oxidatively leached, the leaching reaction is as follows: Sn+2 / 3IO3 - +2OH - → SnO3 2- +2 / 3I - +H2O The generated SnO3 2- In the above leaching reaction, iodide ions (I - Since iodide ions are contained in the electrolyte of the alkaline water electrolysis method of the present embodiment, the iodide ions produced in the leaching reaction can be recovered and reused in alkaline water electrolysis. EXAMPLES

[0052] The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0053] (Example 1) An aqueous solution of NaOH (Kanto Chemical Co., Ltd.; 48 w / w%) and deionized water were mixed to prepare an aqueous solution with a NaOH concentration of 1 mol / L. Next, potassium iodide (Kanto Chemical Co., Ltd.; special grade) was added to obtain an aqueous solution with a concentration of 0 mol / L or 1 mol / L to obtain the electrolyte of Example 1. The pH of the solution predicted from the concentration of NaOH was about 14.

[0054] The above electrolyte was placed in a membrane-less electrolytic cell equipped with a cathode and an anode as shown in Figure 1, and the solution was heated to 70°C while stirring at 600 rpm using a stirrer. Anode polarization measurements were performed by sweeping the potential in the noble direction at 10 mV / s from the natural immersion potential. The working electrode (anode) was a graphite electrode or a nickel electrode (both manufactured by EC Frontier Co., Ltd., electrode size Φ3 mm, surface buffed and polished), and the counter electrode (cathode) was a platinum electrode (manufactured by EC Frontier Co., Ltd., 2.5 cm 2 ) and the reference electrode was a silver-silver chloride electrode.

[0055] Figure 2 shows the measurement results of the anodic polarization curve when the temperature of the electrolyte is 70°C and the working electrode (anode) is made of graphite or nickel. As shown in Figure 2, by adding potassium iodide to the electrolyte, the anodic reaction changes from oxygen generation to iodate ions (IO3 - ) generation, and the rise potential of the oxidation current shifted to a less noble value. In addition, when the working electrode (anode) was a graphite electrode, iodate ions (IO3 - ) The overpotential of the formation was particularly small.

[0056] Next, a new electrolyte solution with the same composition was prepared and placed in a membrane-less electrolytic cell. It was heated to 70°C while being stirred at 600 rpm with a stirrer, and a cathodic polarization measurement was performed in which the potential was swept in the less noble direction at 10 mV / s from the natural immersion potential. Figure 3 shows the cathodic polarization curve when the working electrode (cathode) was nickel. It was found that the addition of potassium iodide had no significant effect on the hydrogen evolution reaction on the nickel cathode.

[0057] Figure 4 shows the results of a model evaluation of the power consumption when potassium iodide is not added to the electrolyte and when potassium iodide is added to the electrolyte. From the polarization curves in Figures 2 and 3, it can be seen that the current density is 100 mA / cm 2 The electrode potential was read and compared. By adding potassium iodide to the electrolyte and using graphite as the anode, the anode reaction was changed from oxygen generation to iodate ion (IO3 - ) generation and reduce power consumption by about 0.5 V (Figure 4, arrow).

[0058] (Example 2) Aqueous KOH solution (Kanto Chemical Co., Ltd.; 48 w / w%) and deionized water were mixed to prepare an aqueous solution with KOH at 5 mol / L. Next, potassium iodide (Kanto Chemical Co., Ltd.; special grade) was added to 1 mol / L, potassium iodate (FUJIFILM Wako Pure Chemical Co., Ltd.; special grade) was added to 0 mol / L or 0.02 mol / L, and potassium dichromate (K2Cr2O7; Kanto Chemical Co., Ltd.; special grade) was added as a cathode surface modifier to 0 mol / L or 0.0068 mol / L to prepare the electrolyte of Example 2. The pH of the solution predicted from the concentration of KOH was about 14.

[0059] The above electrolyte was placed in a membrane-less electrolytic cell equipped with a cathode and an anode as shown in Figure 5, and the electrolyte was stirred at 600 rpm while being heated to 70°C, and a cathode polarization measurement was performed in which the potential was swept in the less noble direction at 10 mV / s from the natural immersion potential. The working electrode (cathode) was a nickel electrode (a plate material with a purity of 99+% purchased from Nilaco Corporation, electrode size Φ8 mm), the counter electrode (anode) was a graphite electrode (a plate material made of high-density CIP molding, electrode size Φ8 mm), and the reference electrode was a silver-silver chloride electrode.

[0060] Figure 6 shows the results of measuring the cathodic polarization curve when the temperature of the electrolyte was set to 70°C. As shown in Figure 6, the addition of potassium dichromate (K2Cr2O7) increased the amount of iodate ions (IO3 - ) reduction was suppressed, whereas no significant effect was observed on the hydrogen evolution at the cathode.

[0061] (Example 3) The surface of the nickel electrode was modified by the following procedure. A nickel electrode (a plate material of 99+% purity purchased from Nilaco, electrode size 3.7 x 3.7 cm) was immersed in an electrolyte at approximately 25°C, the composition of which was 0.0068 mol / L K2Cr2O7, 0.02 mol / L KIO3, 0.08 mol / L KI, and 0.88 mol / L NaOH, and electrolysis was performed for 600 s at 300 mA using this as the cathode. Graphite (a plate material of a high-density CIP molded product, electrode size 3.7 x 3.7 cm) was used as the anode. This treatment is intended to modify the surface of the nickel electrode and to form a hydroxide-based or oxide-based film containing trivalent chromium on the surface of the nickel electrode.

[0062] An aqueous solution of NaOH (Kanto Chemical Co., Ltd.; 48 w / w%) and deionized water were mixed to prepare an aqueous solution with a NaOH concentration of 0.88 mol / L. Next, potassium iodide (Kanto Chemical Co., Ltd.; special grade) was added to the aqueous solution with a concentration of 0.08 mol / L, and potassium iodate (FUJIFILM Wako Pure Chemical Co., Ltd.; special grade) was added to the aqueous solution with a concentration of 0 mol / L or 0.02 mol / L to prepare the electrolyte solution of Example 3. The pH of the solution predicted from the concentration of NaOH was about 14.

[0063] The above electrolyte was placed in an electrolytic cell of a membraneless alkaline water electrolysis device having an electrolytic cell equipped with a cathode and an anode as shown in Figure 7, and the solution was heated to 28°C while stirring at 600 rpm, and a cathode polarization measurement was performed by sweeping the potential in a less noble direction at 10 mV / s from the natural immersion potential. The working electrode (cathode) was a nickel electrode that had been surface-modified in advance (a plate material with a purity of 99+% purchased from Nilaco Corporation, electrode size 3.7 x 3.7 cm) or a nickel electrode that had not been modified in advance (a plate material with a purity of 99+% purchased from Nilaco Corporation, electrode size 3.7 x 3.7 cm), the working electrode (anode) was a graphite electrode (a plate material made of a high-density CIP molded product, electrode size 3.7 x 3.7 cm), and the reference electrode was a silver-silver chloride electrode.

[0064] As shown in the cathodic polarization curves in FIG. 8, when a nickel electrode with a surface modification treatment was used (Example), the amount of iodate ions (IO3 - ) reduction was suppressed. In addition, the surface modification treatment did not have a significant effect on the hydrogen evolution reaction, compared with the measurement of a nickel electrode that had not been subjected to surface modification treatment in advance, immersed in an electrolyte that did not contain KIO3.

Claims

1. A non-diaphragm alkaline water electrolysis method comprising electrolyzing an aqueous alkali metal hydroxide solution containing iodide ions and having a concentration of 1 mol / L or more to generate hydrogen gas at the cathode and iodate ions at the anode.

2. The method for membrane-free alkaline water electrolysis according to claim 1 , wherein the aqueous alkali metal hydroxide solution further contains a cathode surface modifier.

3. The diaphragm-free alkaline water electrolysis method according to claim 2, wherein the cathode surface modifier comprises at least one selected from the group consisting of hexavalent chromium ions, pentavalent vanadium ions, hexavalent molybdenum ions, pentavalent niobium ions, and tetravalent titanium ions.

4. The method for membrane-free alkaline water electrolysis according to claim 2, wherein the cathode surface modifier contains hexavalent chromium ions.

5. The method for membrane-free alkaline water electrolysis according to claim 2, wherein the content of the cathode surface modifier is 0.05 mol / L or less.

6. The method for membrane-free alkaline water electrolysis according to claim 1, wherein a surface of the cathode contains a component derived from a cathode surface modifier.

7. The method for membrane-free alkaline water electrolysis according to claim 1, wherein a hydroxide or oxide containing at least one selected from the group consisting of chromium, vanadium, molybdenum, niobium, and titanium is present on a surface of the cathode.

8. The method for alkaline water electrolysis without a diaphragm according to claim 1, wherein a hydroxide or oxide containing chromium is present on a surface of the cathode.

9. The method for membrane-free alkaline water electrolysis according to claim 1, wherein the electrolysis is performed at 30 to 250°C.

10. A method for recovering valuable metals, comprising oxidative leaching of valuable metals using the iodate ion-containing solution obtained by the method for membrane-free alkaline water electrolysis according to any one of claims 1 to 9.

11. A non-diaphragm-type alkaline water electrolysis apparatus having an electrolytic cell equipped with a cathode and an anode, A non-diaphragm-type alkaline water electrolysis device that electrolyzes an aqueous alkali metal hydroxide solution containing iodide ions and having a concentration of 1 mol / L or more, generates hydrogen gas at the cathode, and generates iodate ions at the anode.

12. The non-diaphragm alkaline water electrolysis apparatus according to claim 11, wherein the alkali metal hydroxide aqueous solution further contains a cathode surface modifier.

13. The diaphragm-free alkaline water electrolysis apparatus according to claim 12, wherein the cathode surface modifier comprises at least one selected from the group consisting of hexavalent chromium ions, pentavalent vanadium ions, hexavalent molybdenum ions, pentavalent niobium ions, and tetravalent titanium ions.

14. The non-diaphragm alkaline water electrolysis apparatus according to claim 12, wherein the cathode surface modifier contains hexavalent chromium ions.

15. The non-diaphragm alkaline water electrolysis apparatus according to claim 12, wherein the content of the cathode surface modifier is 0.05 mol / L or less.

16. The non-diaphragm-type alkaline water electrolysis apparatus according to claim 11, wherein a surface of the cathode has a component derived from a cathode surface modifier.

17. The non-diaphragm alkaline water electrolysis apparatus according to claim 11, wherein a hydroxide or oxide containing at least one selected from the group consisting of chromium, vanadium, molybdenum, niobium, and titanium is present on a surface of the cathode.

18. The non-diaphragm alkaline water electrolysis apparatus according to claim 11, wherein a hydroxide or oxide containing chromium is present on a surface of the cathode.

19. The non-diaphragm alkaline water electrolysis apparatus according to claim 11, wherein the electrolysis is performed at 30 to 250°C.

20. The non-diaphragm alkaline water electrolysis apparatus according to claim 11 , wherein the anode comprises a carbon-based material.

21. The non-diaphragm alkaline water electrolysis apparatus according to claim 11, wherein the electrolytic cell has a plurality of electrolytic cell units each including a cathode and an anode, and each of the electrolytic cell units is connected to a hydrogen gas recovery mechanism.

22. The diaphragm-free alkaline water electrolysis apparatus according to claim 11, further comprising a mechanism for recovering the iodate ion-containing solution.

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