Method for operating electrolysis apparatus

Abstract

To provide a method for operating an electrolysis apparatus that can suppress deposition of metal on a cathode and dissolve and remove metal deposited on the cathode without shutdown.SOLUTION: A method for operating an electrolysis apparatus comprises an anode chamber 5a having an anode 2a and a cathode chamber 5c having a cathode 2c that are partitioned from each other by a diaphragm 4, wherein the anode chamber 5a and the cathode chamber 5c are filled with an electrolytic solution, and by controlling a potential Ec of the cathode 2c in a potential region more negative than a reversible hydrogen electrode (RHE), deposition of a substance that increases the potential Ec of the cathode 2c in a negative direction on the cathode 2c is suppressed and the substance that increases the potential Ec of the cathode 2c in the negative direction is removed from the cathode 2c.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for operating an electrolysis device. [Background technology]

[0002] In recent years, renewable energy technologies such as wind power generation and solar power generation have been attracting attention in order to solve problems such as global warming caused by greenhouse gases such as carbon dioxide and dwindling fossil fuel reserves.

[0003] Renewable energy output is highly variable because it depends on weather conditions. As a result, it is not always possible to transport the electricity generated by renewable energy to the general power grid, raising concerns about the potential for imbalances in power supply and demand and the instability of the power grid.

[0004] Therefore, research is being conducted into converting electricity generated from renewable energy into a form that can be stored and transported, and using this electricity.Specifically, research is being conducted into generating storable and transportable hydrogen through the electrolysis of water using electricity generated from renewable energy, and using this hydrogen as an energy source or raw material.

[0005] Hydrogen is widely used industrially in oil refining, chemical synthesis, metal refining, etc., and in recent years, the possibility of its use has expanded in hydrogen stations for fuel cell vehicles (FCVs), smart communities, hydrogen power plants, etc. For this reason, expectations are particularly high for the development of technology to obtain hydrogen from renewable energy sources.

[0006] Known methods for electrolyzing water include solid polymer water electrolysis, high-temperature steam electrolysis, and alkaline water electrolysis. However, alkaline water electrolysis is considered to be one of the most promising methods because it has been industrialized for several decades, can be carried out on a large scale, and is less expensive than other water electrolysis devices (see, for example, Patent Document 1 listed below). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2020 / 105369 Summary of the Invention [Problem to be solved by the invention]

[0008] However, because water electrolysis devices continuously replenish water consumed by electrolysis, even trace amounts of metals such as iron (Fe) in the make-up water can accumulate in the electrolytic cell of the electrolysis device, raising concerns that metal poisoning could cause an increase in cathode overvoltage. There is also concern that a sudden increase in metal ion concentration in the electrolysis device system due to piping work or other factors could also cause an increase in cathode overvoltage due to metal poisoning.

[0009] In response to this, the inventors have confirmed through three-electrode tests and current tests using a small electrolytic cell that when an electrolysis cell of an electrolysis device is energized with an electrolyte containing metal ions such as iron ions, metal deposits on the cathode surface and the cathode overvoltage increases due to the metal deposition. In particular, under current density conditions for highly efficient hydrogen generation, the cathode potential during energization is at the reduction potential of metal ions such as iron ions, causing metal to deposit on the cathode and increasing the cathode overvoltage. In response to this, shutting down the electrolytic cell of the electrolysis device to stop energization causes the cathode potential to pass through the dissolution potential of metals such as iron, thereby removing the metal deposited on the cathode surface. However, in this case, damage to the cathode due to the shutdown is unavoidable.

[0010] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional art and to provide a method for operating an electrolysis apparatus that can suppress metal deposition on the cathode and dissolve and remove the metal deposited on the cathode without shutting down the electrolysis apparatus. [Means for solving the problem]

[0011] As a result of extensive research into solving the above problems, the inventors discovered that by operating the reactor while controlling the cathode potential to a hydrogen generation potential and a dissolution potential of the deposited metal, it is possible to suppress metal deposition on the cathode and dissolve and remove the metal deposited on the cathode without shutting down the reactor, and thus completed the present invention. That is, the gist of the method for operating an electrolysis apparatus according to the present invention, which solves the above problems, is as follows.

[0012] [1] A method for operating an electrolysis device comprising an anode chamber having an anode and a cathode chamber having a cathode, the anode chamber and the cathode chamber being separated from each other by a diaphragm, comprising the steps of: the anode chamber and the cathode chamber are filled with an electrolyte; A method for operating an electrolysis device, characterized in that the potential Ec of the cathode is controlled in a potential region more negative than that of a reversible hydrogen electrode (RHE), thereby suppressing adhesion of substances that increase the potential Ec of the cathode in a negative direction to the cathode and removing substances that increase the potential Ec of the cathode in a negative direction from the cathode. The method for operating the electrolytic apparatus of the present invention described in the above [1] can suppress metal deposition on the cathode without shutting down the apparatus, and can also dissolve and remove the metal deposited on the cathode.

[0013] [2] The method for operating an electrolytic device according to [1], wherein the electrolytic solution contains metal ions that are reduced by energizing the electrolytic device and deposited on the cathode surface. According to the method for operating an electrolysis apparatus described in [2] above, it is possible to recover from the overvoltage that has increased due to metal deposition in the electrolytic solution.

[0014] [3] The method for operating an electrolysis apparatus according to [2], wherein the metal ions are iron ions. According to the method for operating the electrolysis apparatus described in [3] above, it is possible to suppress the adhesion and deposition of iron, a common metal ion that significantly increases cathode overvoltage, on the cathode, and also to remove the iron that has adhered and deposited on the cathode from the cathode, thereby preventing and recovering from an increase in cathode overvoltage due to iron deposition.

[0015] [4] The method for operating an electrolysis apparatus according to any one of [1] to [3], wherein the potential Ec of the cathode alternately satisfies the ranges of [potential 1] and [potential 2] shown in the following formula: The values ​​of [potential 1] and [potential 2] are the potential [V] relative to RHE vs RHE. [Potential 1] Ec <Ed [Potential 2] Ed≦Ec<0[V] Ed:-9.9×10 -5 ×(pH-log 10 [M])×T+0.61 [V] pH: pH of the electrolyte [M]: Metal ion concentration in the electrolyte [mol / L] T: Absolute temperature of the electrolyte [K] According to the method for operating the electrolysis device described above in [4], high hydrogen generation efficiency (Nm 3 / h) and hydrogen production at high electrolysis efficiency due to the maintenance of low cathode overvoltage by operation at [potential 2].

[0016] [5] The method for operating an electrolysis apparatus according to any one of [1] to [3], wherein the potential Ec of the cathode alternately satisfies [Potential 1'] and [Potential 2'] shown in the following formula: The values ​​of [Potential 1'] and [Potential 2'] are the potential [V] relative to RHE vs RHE. [Potential 1'] Ec<-0.082[V] [Potential 2'] -0.082[V]≦Ec<0[V] According to the method for operating the electrolysis device described above in [5], high hydrogen generation efficiency (Nm 3 / h) and hydrogen production at high electrolysis efficiency due to the maintenance of low cathode overvoltage by operation at [potential 2'].

[0017] [6] The method for operating an electrolytic device according to [4] or [5], wherein the electrolytic solution contains 0.20 mg / L or more of iron ions. According to the method for operating an electrolysis apparatus described in the above [6], the recovery range of the cathode overvoltage due to operation at the [potential 2] or [potential 2'] is increased.

[0018] [7] The method for operating the electrolytic apparatus according to [4] or [6], wherein the potential Ec of the cathode is maintained at the [potential 2] for one hour or more. According to the method for operating an electrolysis apparatus described in the above [7], the recovery range of the cathode overvoltage due to operation at the [potential 2] is increased.

[0019] [8] The method for operating an electrolysis device according to any one of [4] to [7], wherein the pH of the electrolytic solution is 14 or higher. According to the method for operating an electrolysis apparatus described in the above [8], the recovery range of the cathode overvoltage due to operation at the [potential 2] or [potential 2'] is increased.

[0020] [9] The method for operating an electrolysis apparatus according to any one of [4] to [8], wherein the temperature of the electrolytic solution is 70°C or higher. According to the method for operating the electrolysis device described in [9] above, the hydrogen generation efficiency (Nm 3 / h) is improved, and the recovery range of the cathode overvoltage by operation at the [potential 2] or [potential 2'] is increased.

[0021]

[10] The method for operating an electrolytic apparatus according to any one of [4] to [9], wherein the electrolytic apparatus comprises a system for removing metal ions from the electrolytic solution. According to the method for operating the electrolysis apparatus described in

[10] above, the time for which the electrolysis apparatus is held at [potential 2] or [potential 2'] is shortened, and high hydrogen generation efficiency (Nm 3 / h) can be realized.

[0022]

[11] The method for operating an electrolytic device according to any one of [4] to

[10] , wherein a reference electrode is used to measure the potential Ec of the cathode, and the value of the potential Ec of the cathode is controlled. According to the method for operating an electrolysis apparatus described in

[11] above, it becomes easy to accurately control the cathode potential Ec, and it becomes easy to avoid an unintended rise in the cathode potential Ec.

[0023]

[12] The method for operating an electrolysis device according to any one of [4] to

[11] , wherein a current value is used as an input value, and the potential Ec of the cathode is controlled by changing the current value. According to the method for operating the electrolysis apparatus described in

[12] above, it becomes easy to accurately control the cathode potential Ec, and it becomes easy to avoid an unintended rise in the cathode potential Ec.

[0024]

[13] A method for operating the electrolysis apparatus according to any one of [4] to

[12] , which is used for alkaline water electrolysis. The method for operating an electrolysis apparatus described in

[13] above can be carried out on a large scale. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide a method for operating an electrolysis apparatus that is capable of suppressing metal deposition on the cathode and dissolving and removing the metal deposited on the cathode without shutting down the electrolysis apparatus. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram of an example of an electrolysis device that can be used in the method for operating an electrolysis device of the present embodiment. [Figure 2] FIG. 1 is a side view of an example of an electrolytic cell of an electrolytic apparatus that can be used in the method for operating an electrolytic apparatus of this embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the part enclosed by the dashed square frame in the electrolytic cell shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] The method of operating the electrolysis apparatus of the present invention will be described in detail below by way of example based on an embodiment thereof.

[0028] <Electrolyzer> The method for operating an electrolysis apparatus of this embodiment is a method for operating an electrolysis apparatus comprising an anode chamber having an anode and a cathode chamber having a cathode, which are separated from each other by a diaphragm. The electrolysis apparatus is not particularly limited as long as it comprises an anode chamber having an anode and a cathode chamber having a cathode, which are separated from each other by a diaphragm. An electrolysis apparatus that can be used in the method for operating an electrolysis apparatus of this embodiment will be described in detail below with reference to the drawings.

[0029] FIG. 1 shows a schematic diagram of an example of an electrolysis device that can be used in the method for operating the electrolysis device of this embodiment, FIG. 2 shows a side view of an example of an electrolytic cell of the electrolysis device that can be used in the method for operating the electrolysis device of this embodiment, and FIG. 3 shows a cross-sectional view of the part of the electrolytic cell enclosed by a dashed square frame in FIG. 2.

[0030] The electrolysis device 70 shown in FIG. 1 comprises an electrolytic cell 50, a liquid feed pump 71 for circulating the electrolytic solution, and a gas-liquid separation tank 72 for separating the electrolytic solution from hydrogen and / or oxygen.

[0031] (electrolytic cell) The electrolytic cell of the electrolytic device used in the method for operating the electrolytic device of this embodiment is not particularly limited and may be either a monopolar or bipolar type. However, from an industrial perspective, a bipolar electrolytic cell is preferred, as in the electrolytic cell 50 shown in FIG. 2 . The bipolar system is one method of connecting a large number of cells to a power source, and as in the electrolytic cell 50 shown in FIG. 2 , multiple bipolar elements 60, each with an anode 2a on one side and a cathode 2c on the other, are arranged in the same direction and connected in series, with only both ends connected to the power source. A bipolar electrolytic cell can reduce the current of the power source, allowing for the production of large quantities of compounds, specified substances, etc., through electrolysis in a short period of time. For power supply equipment with the same output, a constant current, high voltage system is cheaper and more compact, so from an industrial perspective, a bipolar system is preferable to a monopolar system.

[0032] In the electrolytic cell (bipolar electrolytic cell) 50 shown in FIG. 2, a plurality of bipolar elements 60 each including an anode 2a, a cathode 2c, a partition wall 1 separating the anode 2a and the cathode 2c, and an outer frame 3 that frames the partition wall 1 are stacked with a diaphragm 4 sandwiched between them.

[0033] The electrolytic cell (bipolar electrolytic cell) 50 shown in FIG. 2 is constructed by stacking the required number of bipolar elements 60. In the example shown in FIG. 2, the electrolytic cell (bipolar electrolytic cell) 50 includes a fast head 51g, an insulating plate 51i, and an anode terminal element 51a arranged in this order from one end. Furthermore, the anode side gasket portion 7, a diaphragm 4, a cathode side gasket portion 7, and a bipolar element 60 are arranged in this order. The bipolar element 60 is arranged so that the cathode 2c faces the anode terminal element 51a. The anode side gasket portion 7 through the bipolar element 60 are arranged repeatedly the number of times required for the designed production volume. After arranging the anode side gasket portion 7 through the bipolar element 60 repeatedly the required number of times, the anode side gasket portion 7, the diaphragm 4, and the cathode side gasket portion 7 are again arranged in this order. Finally, the cathode terminal element 51c, the insulating plate 51i, and the loose head 51g are arranged in this order. The electrolytic cell (bipolar electrolytic cell) 50 is integrated by clamping the entire cell together using a clamping mechanism such as a tie rod system 51r (see FIG. 2) or a hydraulic cylinder system. The arrangement of the electrolytic cell (bipolar electrolytic cell) 50 can be selected arbitrarily, either from the anode 2a side or the cathode 2c side, and is not limited to the above-mentioned order.

[0034] 2, a bipolar element 60 is disposed between an anode terminal element 51a and a cathode terminal element 51c. Diaphragms 4 are disposed between the anode terminal element 51a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51c.

[0035] In the electrolytic cell 50 shown in FIG. 2, an electrode chamber 5 through which the electrolyte passes is defined by the partition wall 1, outer frame 3 and diaphragm 4, as shown in FIG.

[0036] In this embodiment, the portion between the partition walls 1 between two adjacent bipolar elements 60 in the electrolytic cell (bipolar electrolytic cell) 50 and the portion between the partition walls 1 between adjacent bipolar elements 60 and a terminal element are particularly referred to as the electrolytic cell 65. The electrolytic cell 65 includes the partition wall 1, anode chamber 5a, anode 2a, and diaphragm 4 of one element, and the cathode 2c, cathode chamber 5c, and diaphragm 1 of the other element. In other words, the electrolytic cell 50 of the electrolytic device 70 used in this embodiment includes an anode chamber 5a having an anode 2a and a cathode chamber 5c having a cathode 2c, which are separated from each other by the diaphragm 4.

[0037] To increase the rigidity of the anode and cathode and achieve a structure that minimizes deformation even when the two electrodes are pressed together, the electrodes may be provided with ribs 6 (rectifying plates) as shown in Fig. 3. For the same reason, a current collector 2r may be attached to the tip of the rib 6 (rectifying plate), a conductive elastic body 2e may be attached to the top surface of the current collector 2r, i.e., the side opposite the partition wall 1, and an electrode 2 may be further laminated on the top surface of the current collector 2r, i.e., the part adjacent to the conductive elastic body 2e that faces the diaphragm 4, to form at least a three-layer structure.

[0038] The electrolytic cell (bipolar electrolytic cell) 50 preferably has 29 to 500 bipolar elements 60, more preferably has 50 to 500 bipolar elements 60, further preferably has 70 to 300 bipolar elements 60, and particularly preferably has 100 to 200 bipolar elements 60.

[0039] The electrolytic cell (bipolar electrolytic cell) 50 preferably has 30 or more electrolytic cells 65 , more preferably has 100 or more electrolytic cells 65 , and even more preferably has 150 to 200 electrolytic cells 65 .

[0040] -Bulkhead- The shape of the partition wall 1 is not particularly limited and may be a plate shape having a predetermined thickness. As a material for the partition wall 1, a conductive material is preferable from the viewpoint of realizing a uniform supply of power, and nickel, a nickel alloy, mild steel, or a nickel alloy plated with nickel is preferable from the viewpoint of alkali resistance and heat resistance.

[0041] -electrode- The electrolysis voltage for water electrolysis can be divided into the theoretically required voltage for water electrolysis, the overvoltage for the anodic reaction (oxygen generation), the overvoltage for the cathodic reaction (hydrogen generation), and the voltage due to the distance between the electrodes 2, the anode 2a and the cathode 2c. Here, overvoltage refers to the voltage that must be applied in excess of the theoretical decomposition potential when a certain current is passed, and its value depends on the current value. When the same current is passed, power consumption can be reduced by using an electrode 2 with a low overvoltage. Requirements for the electrode 2 to achieve a low overvoltage include high conductivity, high oxygen generation capacity (or hydrogen generation capacity), and high wettability of the electrode 2 surface with the electrolyte.

[0042] As the electrode 2 for water electrolysis, in addition to having a low overvoltage, the electrode 2 is unlikely to suffer from corrosion of the substrate and catalytic layer of the electrode 2, detachment of the catalytic layer, dissolution in the electrolyte, or adhesion of inclusions to the diaphragm 4, even when an unstable current such as that from renewable energy is used.

[0043] The electrode 2 is preferably a porous body in order to increase the surface area available for electrolysis and to efficiently remove gas generated by electrolysis from the surface of the electrode 2. Examples of porous bodies include plain woven mesh, punched metal, expanded metal, and metal foam.

[0044] The electrode 2 may be the substrate itself, or may have a highly reactive catalyst layer on the surface of the substrate, but is preferably one having a highly reactive catalyst layer on the surface of the substrate.

[0045] The material of the substrate is not particularly limited, but mild steel, stainless steel, nickel, and nickel-based alloys are preferred in terms of resistance to the usage environment.

[0046] The catalytic layer of the anode 2a preferably has high oxygen generating capacity, and nickel, cobalt, iron, platinum group elements, or the like can be used. To achieve the desired activity and durability, the catalytic layer can be formed as a single metal, a compound such as an oxide, a composite oxide or alloy made of multiple metal elements, or a mixture thereof. An organic substance such as a polymer may be included to improve durability and adhesion to the substrate.

[0047] The catalytic layer of the cathode 2c preferably has high hydrogen generation capacity, and nickel, cobalt, iron, platinum group elements, or the like can be used. To achieve the desired activity and durability, the catalytic layer can be formed as a single metal, a compound such as an oxide, a composite oxide or alloy made of multiple metal elements, or a mixture thereof. An organic substance such as a polymer material may be included to improve durability and adhesion to the substrate.

[0048] Examples of methods for forming a catalyst layer on a substrate include plating, thermal spraying such as plasma spraying, thermal decomposition in which a precursor layer solution is applied to a substrate and then heated, a method in which a catalyst substance is mixed with a binder component and fixed to the substrate, and vacuum film formation such as sputtering.

[0049] -Outer frame- The shape of the outer frame 3 is not particularly limited as long as it can frame the partition wall 1, and may be a shape that has an inner surface along a direction perpendicular to the plane of the partition wall 1, extending along the outer periphery of the partition wall 1. The shape of the outer frame 3 is not particularly limited and may be determined appropriately in accordance with the shape of the partition wall 1 in a plan view.

[0050] The material of the outer frame 3 is preferably a conductive material, and from the viewpoint of alkali resistance and heat resistance, nickel, nickel alloy, mild steel, or nickel alloy plated with nickel is preferred.

[0051] -diaphragm- An ion-permeable diaphragm is used as the diaphragm 4 to separate the generated hydrogen gas and oxygen gas while conducting ions. This ion-permeable diaphragm can be an ion exchange membrane with ion exchange capacity or a porous membrane that can be permeated by the electrolyte. This ion-permeable diaphragm preferably has low gas permeability, high ionic conductivity, low electronic conductivity, and high strength.

[0052] The porous membrane has a structure with multiple fine through-holes that allows the electrolyte to pass through the diaphragm 4. Ion conduction occurs when the electrolyte permeates the porous membrane, so control of the porous structure, such as pore size, porosity, and hydrophilicity, is extremely important. On the other hand, it is required that not only the electrolyte but also the generated gas does not pass through, i.e., the membrane must have gas barrier properties.

[0053] The porous membrane has a plurality of fine through-holes, and examples thereof include polymer porous membranes, inorganic porous membranes, woven fabrics, nonwoven fabrics, etc. These can be produced by known techniques. Ion exchange membranes include cation exchange membranes that selectively allow cations to pass through and anion exchange membranes that selectively allow anions to pass through, and either type of exchange membrane can be used. The material of the ion exchange membrane is not particularly limited, and known materials can be used. For example, fluorine-containing resins and modified resins of polystyrene-divinylbenzene copolymers are preferably used. Fluorine-containing ion exchange membranes are particularly preferred because of their excellent heat resistance and chemical resistance.

[0054] Furthermore, as a means for reducing the interelectrode distance, it is preferable to adopt a configuration in which a spring, which is a conductive elastic body 2e, is disposed between the electrode 2 and the partition wall 1 and this spring supports the electrode. For example, a spring made of a conductive material may be attached to the partition wall 1, and the electrode 2 may be attached to this spring, or a spring may be attached to a rib 6 attached to the partition wall 1, and the electrode 2 may be attached to this spring. Note that when adopting such a configuration using an elastic body, the strength, number, shape, etc. of the spring must be appropriately adjusted as necessary to prevent uneven contact pressure between the electrode 2 and the diaphragm 4.

[0055] Furthermore, by increasing the rigidity of the other electrode 2 that is paired with the electrode 2 supported via an elastic body (for example, by making the rigidity of the anode 2a stronger than that of the cathode 2c), a structure can be achieved that is less likely to deform when pressed. On the other hand, by making the electrode 2 supported via an elastic body have a flexible structure that deforms when the diaphragm 4 is pressed against it, it is possible to absorb unevenness due to manufacturing tolerances of the electrolytic cell 50 and deformation of the electrode 2, thereby maintaining the zero gap structure Z.

[0056] Examples of the zero gap structure Z include a zero gap structure formed between an anode terminal element 51a and an element, between elements, or between an element and a cathode terminal element 51c. For example, as shown in Fig. 3, a conductive elastic body 2e and a current collector 2r are preferably provided between a cathode 2c and a partition wall 1 so that the conductive elastic body 2e is sandwiched between the cathode 2c and the current collector 2r. In addition, the current collector 2r is preferably in contact with a rib 6 of the cathode.

[0057] As shown in FIG. 3 , the zero gap structure Z preferably has a structure in which a rib 6 and an anode 2a are stacked in this order on the anode 2a side of the partition wall 1, and a bipolar element 60 is stacked in this order on the cathode 2c side of the partition wall 1, with a diaphragm 4 sandwiched between them, and the diaphragm 4 is in contact with the anode 2a and the cathode 2c.

[0058] -Electrode chamber- 3, in an electrolytic cell (bipolar electrolytic cell) 50, an electrode chamber 5 through which an electrolytic solution passes is defined by a partition wall 1, an outer frame 3, and a diaphragm 4. Here, the electrode chamber 5 on the anode side across the partition wall 1 is an anode chamber 5a, and the electrode chamber 5 on the cathode side is a cathode chamber 5c. In other words, the electrolytic cell 50 comprises an anode chamber 5a having an anode 2a and a cathode chamber 5c having a cathode 2c, which are mutually separated by the diaphragm 4.

[0059] -Rib (rectifier plate)- The ribs 6 are generally made of a conductive metal. For example, nickel-plated mild steel, stainless steel, nickel, etc. are usable. The ribs are preferably made of the same material as the partition walls, and nickel is most preferred.

[0060] The ribs 6 are preferably physically connected to the electrodes 2. According to this configuration, the ribs 6 serve as supports for the electrodes 2. In addition, the ribs 6 are preferably electrically connected to the partition walls 1. In FIG. 3, a structure is adopted in the cathode chamber 5c, in which the cathode rib 6, the cathode current collector 2r, the conductive elastic body 2e, and the cathode 2c are stacked in this order, and a structure is adopted in the anode chamber 5a, in which the anode rib 6 and the anode 2a are stacked in this order.

[0061] -gasket- In the electrolytic cell (bipolar electrolytic cell), it is preferable that a gasket 7 having a diaphragm 4 is sandwiched between the outer frames 3 that frame the partition walls 1. The gasket 7 is used to seal the spaces between the bipolar element 60 and the diaphragm 4 and between the bipolar elements 60 against the electrolyte and the generated gas, and can prevent leakage of the electrolyte or the generated gas to the outside of the electrolytic cell and mixing of gases between the two electrode chambers.

[0062] The gasket 7 generally has a rectangular or annular structure with the electrode surface hollowed out to match the surface that contacts the element frame. The diaphragm 4 can be stacked between elements by sandwiching it between two such gaskets. Furthermore, the gasket 7 preferably has a slit that can accommodate the diaphragm 4 so that it can hold the diaphragm 4, and also has openings that allow the accommodated diaphragm 4 to be exposed on both surfaces of the gasket 7. This allows the gasket 7 to accommodate the edge of the diaphragm 4 within the slit, thereby covering the end faces of the edge of the diaphragm 4. This more reliably prevents electrolyte and gas from leaking from the end faces of the diaphragm 4.

[0063] The material of the gasket 7 is not particularly limited, and may be any known insulating rubber material, resin material, etc. Specific examples of the rubber material or resin material include natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated polyethylene rubber (CSM); fluororesin materials such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE); and resin materials such as polyphenylene sulfide (PPS), polyethylene, polyimide, and polyacetal. Among these, ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) are particularly suitable from the viewpoint of elastic modulus and alkali resistance.

[0064] (liquid transfer pump) The liquid feed pump 71 is not particularly limited and may be determined as appropriate. The liquid feed pump 71 of the electrolysis device 70 that can be used in this embodiment may include a cathode-side liquid feed pump for feeding liquid to the cathode chamber 5c and an anode-side liquid feed pump for feeding liquid to the anode chamber 5a, and these pumps can be operated separately.

[0065] (Gas-liquid separation tank) The gas-liquid separation tank 72 preferably includes a hydrogen separation tank that separates the electrolytic solution from hydrogen gas, and an oxygen separation tank that separates the electrolytic solution from oxygen gas. Here, the hydrogen separation tank is connected to the cathode chamber 5c, and the oxygen separation tank is connected to the anode chamber 5a. The gas-liquid separation tank 72 is made of an alkali-resistant metal such as nickel. On the other hand, when a general-purpose metal such as iron is used as the tank housing material, the electrolyte-contacting surface inside the tank may be coated with a fluorine-based resin or the like, but this is not a limitation on the material of the gas-liquid separation tank 72 in this embodiment.

[0066] (others) The electrolysis apparatus 70 shown in FIG. 1 includes a rectifier 74, an oxygen concentration meter 75, a hydrogen concentration meter 76, a flow meter 77, a pressure meter 78, a heat exchanger 79, and a pressure control valve 80, in addition to the electrolytic cell 50, the liquid feed pump 71, and the gas-liquid separation tank 72 described above. In addition to the components shown in FIG. 1, the electrolysis apparatus used in the method for operating the electrolysis apparatus of this embodiment preferably includes a system for removing metal ions from the electrolytic solution.

[0067] <Operation method of electrolysis device> As described above, the method for operating an electrolysis apparatus of this embodiment is a method for operating an electrolysis apparatus comprising an anode chamber having an anode and a cathode chamber having a cathode, which are separated from each other by a diaphragm. The method for operating an electrolysis apparatus of this embodiment is characterized in that the anode chamber and the cathode chamber are filled with an electrolyte, and the potential Ec of the cathode is controlled in a potential region more negative than a reversible hydrogen electrode (RHE), thereby suppressing adhesion of substances that increase the potential Ec of the cathode in the negative direction to the cathode and removing substances that increase the potential Ec of the cathode in the negative direction from the cathode.

[0068] In the method for operating the electrolysis apparatus of this embodiment, the cathode potential Ec is controlled in a potential region that is more negative than the reversible hydrogen electrode (RHE), thereby preventing damage to the cathode due to shutdown and suppressing deposition and adhesion of substances that increase the cathode potential Ec in the negative direction on the cathode, and also removing from the cathode substances that have deposited and adhered to the cathode and increase the cathode potential Ec in the negative direction. Furthermore, in the method for operating the electrolysis apparatus of the present embodiment, by not performing a shutdown (stopping the flow of current), it is possible to prevent and recover from an increase in the overvoltage of the cathode without causing wear and tear or detachment of the cathode (particularly the catalyst layer) due to a reverse current. When the system is shut down (power supply is stopped), the cathode potential shifts to the oxidizing side due to the reverse current, resulting in oxidation of not only the substances (deposits) that adhere to the cathode but also the cathode itself. In contrast, in the method for operating the electrolysis system of this embodiment, the cathode potential Ec is controlled in a potential region that is more negative than the reversible hydrogen electrode (RHE), and such control of the cathode potential Ec keeps the cathode from being oxidized while maintaining a potential at which the substances (deposits) that adhere to the cathode are oxidized. This makes it possible to suppress metal deposition on the cathode and dissolve and remove metal deposited on the cathode while suppressing damage to the cathode.

[0069] In the method for operating the electrolysis device of this embodiment, the anode chamber and the cathode chamber of the electrolysis device are filled with an electrolytic solution. The electrolytic solution may be one generally used in water electrolysis, such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution. The electrolyte concentration in the electrolytic solution is not particularly limited, but is preferably 1N or more and 12N or less, and more preferably 4N or more and 10N or less.

[0070] In the method for operating the electrolysis device of this embodiment, water electrolysis is performed by applying a current to an electrolysis device (particularly an electrolytic cell of the electrolysis device) comprising an anode chamber and a cathode chamber filled with an electrolytic solution, thereby producing hydrogen at the cathode. In this case, for example, a variable power supply can be used as the power source. A variable power supply is a power source derived from a renewable energy power plant whose output fluctuates every few seconds to every few minutes, as opposed to a power source that provides a stable output, such as grid power. The method for generating renewable energy is not particularly limited, but examples include solar power generation and wind power generation. For example, in the case of electrolysis using an alkaline water electrolysis cell, cationic electrolytes in the electrolytic solution migrate from the anode chamber of one element through the diaphragm to the cathode chamber of an adjacent element, and anionic electrolytes migrate from the cathode chamber of one element through the diaphragm to the anode chamber of the adjacent element. Thus, current during electrolysis flows in the direction in which the elements are connected in series. In other words, current flows from the anode chamber of one element to the cathode chamber of the adjacent element through the diaphragm. Then, as electrolysis proceeds, oxygen gas is produced in the anode chamber and hydrogen gas is produced in the cathode chamber.

[0071] In the method for operating the electrolytic device of this embodiment, the electrolytic solution preferably contains metal ions that are reduced by energizing the electrolytic device and precipitate on the cathode surface. According to the method for operating the electrolytic device of this embodiment, by controlling the cathode potential Ec in a potential region more negative than that of a reversible hydrogen electrode (RHE), deposition and deposition of substances that increase the cathode potential Ec in the negative direction on the cathode is suppressed, and substances that have deposited and deposited on the cathode and increase the cathode potential Ec in the negative direction are removed from the cathode. Therefore, even if the electrolytic solution contains metal ions that are reduced by energizing the electrolytic device and precipitate on the cathode surface, the overvoltage that increased due to metal deposition in the electrolytic solution can be restored. Furthermore, the cathode is not oxidized, but is maintained at a potential at which substances (deposits) that adhere to the cathode are oxidized. Therefore, metal deposition on the cathode can be suppressed and metal deposited on the cathode can be dissolved and removed while suppressing damage to the cathode.

[0072] The metal ion is not particularly limited, but examples thereof include iron (Fe) ions and nickel (Ni) ions, among which iron ions are preferred. Iron ions are commonly used metal ions and also cause a significant increase in cathode overvoltage. However, according to the method for operating the electrolysis apparatus of this embodiment, by controlling the cathode potential Ec in a potential region more negative than that of a reversible hydrogen electrode (RHE), the metal used at the cathode is not oxidized, while iron attached to the cathode is maintained at a potential at which it is oxidized. This suppresses the attachment of iron to the cathode, and also removes iron attached and deposited on the cathode from the cathode, thereby preventing and recovering from an increase in cathode overvoltage due to iron deposition. The concentration of metal ions in the electrolyte is not particularly limited, but is preferably 0.10 mg / L or more, more preferably 0.20 mg / L or more, and is preferably 3.0 mg / L or less, more preferably 2.0 mg / L or less.

[0073] In the method for operating the electrolysis apparatus of this embodiment, it is preferable that the potential Ec of the cathode alternately satisfies the ranges of [potential 1] and [potential 2] shown in the following formula. The values ​​of [potential 1] and [potential 2] are the potential [V] relative to RHE vs. RHE. That is, they are the potential relative to RHE when RHE is set to 0 [V]. For example, when the potential Ec of the cathode is −1.0 [V], this means that the potential of the cathode is 1.0 [V] higher in the negative direction than RHE. [Potential 1] Ec <Ed [Potential 2] Ed≦Ec<0[V] Ed:-9.9×10 -5 ×(pH-log 10 [M])×T+0.61 [V] pH: pH of the electrolyte [M]: Metal ion concentration in the electrolyte [mol / L] T: Absolute temperature of the electrolyte [K] That is, the method of operating an electrolysis apparatus according to a preferred embodiment of the present invention comprises the steps of: A method for operating an electrolysis apparatus comprising an anode chamber having an anode and a cathode chamber having a cathode, the anode chamber and the cathode chamber being separated from each other by a diaphragm, the method comprising the steps of: the anode chamber and the cathode chamber are filled with an electrolyte; The potential Ec of the cathode alternately falls within the range of [potential 1] and the range of [potential 2].

[0074] By operating the electrolysis device at the above [potential 1], high hydrogen generation efficiency (Nm 3 / h) can be realized. Furthermore, by operating the electrolysis device at the [potential 2], dissolution and removal of metal deposited on the cathode proceeds more rapidly, the cathode overvoltage is maintained low, and hydrogen can be produced with high electrolysis efficiency. Furthermore, by alternately satisfying the range of the [potential 1] and the [potential 2], high hydrogen generation efficiency (Nm 3 / h) and hydrogen production at high electrolysis efficiency due to the maintenance of low cathode overvoltage by operation at [potential 2]. The amount of hydrogen generated (Nm 3 To increase the electrolysis efficiency (kWh / Nm), a high current density is required, but the substances in the electrolyte are more likely to be reduced and to adhere to and deposit on the cathode. As a result, the cathode overvoltage increases, and the electrolysis efficiency (kWh / Nm 3 Therefore, by maintaining the cathode at potential 2, which is the potential at which the cathode deposits are oxidized, for a certain period of time during operation at a high current density, it is possible to prevent an increase in the cathode overvoltage while maintaining a high electrolysis efficiency (kWh / Nm 3 ) can also be maintained.

[0075] In the method for operating the electrolysis apparatus of this embodiment, it is also preferable that the potential Ec of the cathode alternately satisfies [Potential 1'] and [Potential 2'] shown in the following formula. The values ​​of [Potential 1'] and [Potential 2'] are the potential [V] relative to RHE vs. RHE. That is, they are the potential relative to RHE when RHE is set to 0 [V]. For example, when the potential Ec of the cathode is −1.0 [V], this means that the potential of the cathode is 1.0 [V] higher in the negative direction than RHE. [Potential 1'] Ec<-0.082[V] [Potential 2'] -0.082[V]≦Ec<0[V] That is, a method for operating an electrolysis apparatus according to another preferred embodiment of the present invention comprises the steps of: A method for operating an electrolysis apparatus comprising an anode chamber having an anode and a cathode chamber having a cathode, the anode chamber and the cathode chamber being separated from each other by a diaphragm, the method comprising the steps of: the anode chamber and the cathode chamber are filled with an electrolyte; The potential Ec of the cathode alternately fills the range of [Potential 1'] and [Potential 2'].

[0076] By operating the electrolysis device at the above [potential 1'], high hydrogen generation efficiency (Nm 3 / h) can be realized. In addition, by operating the electrolysis device at the [potential 2'], dissolution and removal of metal deposited on the cathode proceeds more rapidly, the cathode overvoltage is maintained low, and hydrogen can be produced with high electrolysis efficiency. Furthermore, by alternately satisfying the range of the [potential 1'] and the [potential 2'], high hydrogen generation efficiency (Nm 3 / h) and hydrogen production at high electrolysis efficiency due to the maintenance of low cathode overvoltage by operation at [potential 2'].

[0077] The electrolyte preferably contains iron ions at 0.10 mg / L or more, more preferably 0.20 mg / L or more. When the electrolyte contains iron ions at 0.20 mg / L or more, the recovery range of the cathodic overvoltage during operation at the [potential 2] or [potential 2'] increases. Here, the concentration of iron ions in the electrolyte is more preferably 0.30 mg / L or more, particularly preferably 0.50 mg / L or more, and is preferably 2.0 mg / L or less, more preferably 1.5 mg / L or less.

[0078] In the method for operating the electrolysis apparatus of this embodiment, the cathode potential Ec is preferably maintained at [potential 2] or [potential 2'] for 0.5 hours or more, and more preferably maintained for 1 hour or more. By maintaining the cathode potential Ec at [potential 2] or [potential 2'] for 1 hour or more, the recovery extent of the cathode overvoltage due to operation at [potential 2] or [potential 2'] is increased. Here, the maintenance time at [potential 2] or [potential 2'] is particularly preferably 1.5 hours or more, and is preferably 5 hours or less, and more preferably 3 hours or less.

[0079] The electrolytic solution is preferably alkaline. The pH of the electrolytic solution is preferably 12 or higher, more preferably 13 or higher, and particularly preferably 14 or higher. When the pH of the electrolytic solution is 14 or higher, the recovery range of the cathode overvoltage by operation at the [potential 2] or [potential 2'] increases. The pH of the electrolytic solution is preferably 16 or lower.

[0080] The temperature of the electrolytic solution is preferably 50°C or higher, more preferably 60°C or higher, particularly preferably 70°C or higher, and is preferably 100°C or lower. When the temperature of the electrolytic solution is 70°C or higher, the hydrogen generation efficiency (Nm 3 / h) is improved, and the recovery range of the cathode overvoltage by operation at the [potential 2] or [potential 2'] is increased.

[0081] The electrolysis device preferably includes a system for removing metal ions from the electrolytic solution. When the electrolysis device includes a system for removing metal ions from the electrolytic solution, the time for maintaining the electrolytic solution at [potential 2] or [potential 2'] is shortened, and high hydrogen generation efficiency (Nm 3 / h) can be realized.

[0082] In the method for operating the electrolysis apparatus of this embodiment, it is preferable to measure the potential Ec of the cathode using a reference electrode and control the value of the potential Ec of the cathode. By measuring the potential Ec of the cathode using a reference electrode and controlling the value of the potential Ec of the cathode, it becomes easy to accurately control the potential Ec of the cathode in a potential region more negative than the reversible hydrogen electrode (RHE), and it becomes easy to avoid an unintended increase in the potential Ec of the cathode.

[0083] In the method for operating the electrolysis apparatus of this embodiment, it is preferable to use a current value as an input value and change the current value to control the potential Ec of the cathode. By using a current value as an input value and changing the current value to control the potential Ec of the cathode, it becomes easier to accurately control the potential Ec of the cathode and to easily avoid an unintended increase in the potential Ec of the cathode.

[0084] The method for operating the electrolysis apparatus of this embodiment is preferably a method for operating an electrolysis apparatus for alkaline water electrolysis. Methods for water electrolysis include solid polymer water electrolysis, high-temperature steam electrolysis, and alkaline water electrolysis. Among these, alkaline water electrolysis is particularly advantageous because it has been industrially used for several decades or more, can be carried out on a large scale, and is less expensive than other water electrolysis apparatuses. Furthermore, the method for operating the electrolysis apparatus of this embodiment can suppress metal deposition on the cathode without shutting down the system, and can also dissolve and remove metal deposited on the cathode, even in alkaline water electrolysis.

[0085] In the method for operating the electrolysis apparatus of this embodiment, the conditions such as the power supplied to the electrolytic cell, the current density, and the time for which current is applied are not particularly limited. By controlling the cathode potential Ec in a potential region that is more negative than that of a reversible hydrogen electrode (RHE), conditions can be appropriately selected that can suppress the adhesion of substances that increase the cathode potential Ec in the negative direction to the cathode and can remove substances that increase the cathode potential Ec in the negative direction from the cathode. [Example]

[0086] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0087] Example 1 -cathode- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a 10.0 cm × 10.0 cm piece. The piece was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using an electronic balance ATX224 manufactured by Shimadzu Corporation. Next, a dinitrodiammine platinum nitric acid solution (Tanaka Precious Metals, Pt concentration: 100 g / L) and water were mixed so that the Pt concentration became 12.5 g / L, to prepare a Pt coating liquid.

[0088] --Dip coating process-- The conductive substrate after heating and firing was immersed in a tray containing a Pt coating solution, then pulled out, and the coating solution remaining in the mesh of the conductive substrate was blown off using an air blower (dip method).

[0089] --Precursor layer formation process-- The conductive substrate that had been subjected to the coating step was dried at 60° C. for 10 minutes to form a precursor layer.

[0090] --Firing process-- The conductive substrate on which the precursor layer had been formed was heated and baked in a muffle furnace at 500° C. for 10 minutes to pyrolyze the precursor layer.

[0091] This cycle of dip coating, precursor layer formation, and firing was repeated 17 times, followed by post-firing at 500° C. for 1 hour in an air atmosphere to produce a cathode. The weight of the cathode was measured using an electronic balance, and the weight of the catalytic layer was assumed to be the weight of PtO contained in the catalytic layer. The difference between this weight and the weight of the conductive substrate before the catalytic layer was formed was divided by the area of ​​10.0 cm × 10.0 cm to calculate the weight of the Pt catalytic layer per unit area, which was 6.0 g / m 2 It was.

[0092] -Cathode potential Ec relative to the reversible hydrogen electrode (RHE)- The potential Ec was measured by the three-electrode method using a potentiogalvanostat PARSTAT MC 1000 manufactured by Princeton Applied Research as follows. The cathode prepared as described above was cut into an 18 mm × 17 mm piece and fixed to a PTFE-coated nickel rod with a nickel screw. A platinum mesh was used as the counter electrode, and the electrolyte was a 90°C sodium hydroxide solution adjusted to a pH of 14.5. Iron (III) nitrate nonahydrate was added to the electrolyte to adjust the iron ion concentration to 1.0 mg / L. A silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The cathode potential measured against this silver-silver chloride (Ag / AgCl) glass electrode was used to calculate the potential Ec of the cathode relative to the reversible hydrogen electrode (RHE).

[0093] -Cathode overvoltage- At the cathode potential Ec obtained by the above method, the ohmic loss that could not be completely eliminated even using the three-electrode method was measured by the AC impedance method, and the measured ohmic loss was subtracted from the absolute value of the cathode potential to calculate the cathode overvoltage.

[0094] -Electrolysis at potential 1 and potential 2- The cathode potential Ec measured as above was controlled using a potentiogalvanostat to be potential 1: -0.12 [V] vs RHE, and electrolysis was carried out for 8 hours. Immediately thereafter, the cathode potential Ec was controlled to be potential 2: -0.040 [V] vs RHE, electrolysis was carried out for 2 hours, and then the cathode potential Ec was returned to potential 1: -0.12 [V] vs RHE, and this electrolysis cycle was repeated.

[0095] Example 2 Electrolysis was carried out under the same conditions as in Example 1, except that the potential 2 was set to −0.070 [V] vs. RHE.

[0096] Example 3 Electrolysis was carried out under the same conditions as in Example 1, except that the electrolyte temperature was set to 70°C.

[0097] Example 4 Electrolysis was carried out under the same conditions as in Example 1, except that the electrolyte temperature was set to 100°C.

[0098] Example 5 Electrolysis was carried out under the same conditions as in Example 1, except that the iron ion concentration in the electrolyte was set to 0.25 mg / L.

[0099] Example 6 Electrolysis was carried out under the same conditions as in Example 1, except that the iron ion concentration in the electrolyte was set to 10 mg / L.

[0100] Example 7 Electrolysis was carried out under the same conditions as in Example 1, except that the electrolysis time at potential 2 was changed to 1.2 hours.

[0101] Example 8 Electrolysis was carried out under the same conditions as in Example 1, except that the electrolysis time at potential 2 was changed to 4 hours.

[0102] Example 9 Electrolysis was carried out under the same conditions as in Example 1, except that nickel (II) nitrate hexahydrate was added so that the nickel ion concentration in the electrolytic solution became 1.0 mg / L.

[0103] Example 10 Electrolysis was carried out under the same conditions as in Example 1, except that iron (III) nitrate nonahydrate and nickel (II) nitrate hexahydrate were not added to the electrolytic solution.

[0104] Example 11 Electrolysis was carried out under the same conditions as in Example 1, except that nickel (II) nitrate hexahydrate was added so that the nickel ion concentration in the electrolyte was 1.0 mg / L, and iron (III) nitrate nonahydrate was not added.

[0105] Example 12 Electrolysis was performed under the same conditions as in Example 1, except that there was no electrolysis at potential 1. In Example 12, electrolysis was performed from the beginning under one potential condition in which the cathode potential Ec was potential 2: −0.040 [V] vs. RHE.

[0106] Example 13 Electrolysis was carried out under the same conditions as in Example 1, except that the iron ion concentration in the electrolyte was set to 0.10 mg / L.

[0107] Example 14 Electrolysis was carried out under the same conditions as in Example 1, except that the electrolysis time at potential 2 was changed to 0.8 hours.

[0108] Example 15 The electrolyte used was a sodium hydroxide aqueous solution adjusted to a pH of 13. Under these conditions, Ed was −0.028 [V] vs. RHE, so potential 2 was controlled to be −0.025 [V] vs. RHE. Electrolysis was performed under the same conditions as in Example 1.

[0109] Example 16 Electrolysis was carried out under the same conditions as in Example 1, except that the electrolyte temperature was set to 60°C.

[0110] (Comparative Example 1) Electrolysis was carried out under the same conditions as in Example 1, except that electrolysis at Potential 2 was not performed. In Comparative Example 1, electrolysis was carried out from the beginning under a single potential condition in which the cathode potential Ec was Potential 1: −0.12 [V] vs. RHE.

[0111] (Comparative Example 2) Except for setting potential 2 to −0.090 [V] vs. RHE, electrolysis was carried out under the same conditions as in Example 1. In Comparative Example 2, the cathode potential Ec at potential 2 did not satisfy Ed≦Ec<0.

[0112] (Comparative Example 3) Electrolysis was performed under the same conditions as in Example 1, except that electrolysis at potential 2 was not performed and electrolysis was performed under the following reverse current cycle evaluation conditions. In Comparative Example 3, electrolysis was performed from the beginning under one potential condition in which the cathode potential Ec was potential 1: −0.12 [V] vs. RHE, and an oxidation current was applied to the cathode according to the following reverse current cycle conditions.

[0113] (Reverse current cycle evaluation) A reverse current cycle was carried out to simulate the reverse current that flows through each cell after electrolysis has stopped in a bipolar electrolytic cell. The current density was set at -6 kA / m as a pretreatment for the cathode. 2 After applying a reduction current of +15A / m for 5 hours, immediately after applying a reduction current of +15A / m without measuring the open circuit voltage. 2 An oxidation current of +1.22 V vs. RHE was applied. The cathode potential gradually increased from the hydrogen generation potential to a more noble potential. When the cathode potential reached +1.22 V vs. RHE, the cathode potential Ec was immediately controlled to -0.12 V vs. RHE without any open circuit voltage measurements, and a reduction current was applied for 1 minute. This set of oxidation current and reduction current for 1 minute constituted a reverse current cycle, and this reverse current cycle was repeated.

[0114] [Sample evaluation method] <Effect of suppressing rise in cathode overvoltage> Electrolysis at potential 1 and potential 2 described in each example and comparative example was repeated alternately, and the current density was −6 kA / m 2 The electrolysis time until the cathode overvoltage reached 150 mV in each example was used as an index of the effect of suppressing the rise in the cathode overvoltage, and was evaluated according to the following criteria: 2 Since the initial cathode overvoltage in is 100 mV, the longer the time until the cathode overvoltage reaches 150 mV, the greater the effect of suppressing the rise in the cathode overvoltage. A: More than 70 hours B: 40 hours or more but less than 70 hours C: 20 hours or more but less than 40 hours D: Less than 20 hours

[0115] <Recovery effect of cathode overvoltage> Electrolysis at potential 2 removes cathode deposits that increase the cathode overvoltage, reducing the value of the cathode overvoltage. The cathode overvoltage recovery width was calculated by subtracting the cathode overvoltage at the end of the holding time at potential 2 from the cathode overvoltage at the start of the holding time under the conditions of each example and comparative example. Operation at potential 1 and the subsequent operation at potential 2 constitute one cycle, and 100 cycles of operation were performed. The average value of the cathode overvoltage recovery width obtained by operation at each potential 2 was used as an index of the cathode overvoltage recovery effect and evaluated according to the following criteria. A higher value indicates a higher cathode overvoltage recovery effect. A: 40mV or more B: 20mV or more and less than 40mV C: 10mV or more and less than 20mV D: Less than 10mV

[0116] <Hydrogen generation efficiency [L / h]> The total amount of hydrogen generated up to 1000 hours of operation at potential 1 and potential 2 was divided by the operation time to obtain an index of hydrogen generation efficiency, which was evaluated according to the following criteria. A higher value indicates a higher efficiency of hydrogen generation. A: 0.55L / h or more B: 0.20L / h or more and less than 0.55L / h C: Less than 0.20 L / h

[0117] <Remaining cathode platinum> When the combined operating time at potential 1 and potential 2 reached 1,500 hours, the cathode was removed, washed with pure water, and thoroughly dried at 50°C before measuring the platinum XRF (X-ray fluorescence). The remaining amount of platinum component before and after electrolysis was calculated from the difference with the platinum XRF of the test cathode before evaluation. The XRF measurement was performed using a Thermo Scientific Niton XL5, as follows: An 18 mm x 17 mm test cathode was placed on the top of a hollow polypropylene box (50 mm deep). A Niton XL5 was placed in contact with the cathode so that the X-ray irradiation port was positioned at the center, and XRF measurement was performed for 20 seconds to measure the platinum weight percentage of the test cathode. A: 70% or more B: 30% or more but less than 70% C: Less than 30%

[0118] [Table 1]

[0119] [Table 2]

[0120] [Table 3]

[0121] In all of Comparative Examples 1 to 3, the evaluation result for the effect of suppressing an increase in cathode overvoltage was D, whereas in all of Examples 1 to 16, the results were A to C. In addition, in Comparative Example 2, the evaluation result of the cathode overvoltage recovery effect was D, whereas in Examples 1 to 9, 11, and 13 to 15, the results were A to C. Furthermore, in Comparative Example 3, the evaluation result of the remaining Pt amount in the cathode was C, whereas in Examples 1 to 16, the result was A. This indicates that by controlling the cathode potential Ec within the range of Ed≦Ec<0, the increase in cathode overvoltage can be suppressed and recovered without causing the Pt cathode to wear out or fall off.

[0122] In Examples 10 and 11, the evaluation results of the cathode overvoltage recovery effect were D and C, respectively, whereas in Example 1 it was A. This indicates that the effect of recovering the cathode overvoltage by controlling the cathode potential Ec within the range of Ed≦Ec<0 is achieved by the presence of metal ions in the electrolyte, and that it is more preferable that the metal ions are iron ions.

[0123] In Example 12, the hydrogen generation efficiency [Nm 3 / h] was evaluated as C, whereas Example 1 was evaluated as A. From this, it can be seen that the hydrogen generation efficiency [Nm 3 / h] while suppressing and recovering the increase in cathode overvoltage. [Potential 1] Ec <Ed [Potential 2] Ed≦Ed<0

[0124] In Example 13, the evaluation result of the recovery effect of the cathode overvoltage was C, whereas in Examples 1 and 5, the result was B. This indicates that in order to maximize the effect of recovering the cathodic overvoltage, it is preferable that the iron ion concentration in the electrolyte is 0.20 mg / L or more.

[0125] In Example 14, the evaluation result of the recovery effect of the cathode overvoltage was C, whereas in Examples 1 and 7, the result was B. From this, it was found that in order to enhance the effect of recovering the cathodic overvoltage, it is preferable that the holding time at potential 2 is 1.0 hour or more. [Industrial Applicability]

[0126] According to the method for operating an electrolytic apparatus of the present invention, it is possible to dissolve and remove metal deposited on the cathode while suppressing metal deposition on the cathode without shutting down the apparatus. [Explanation of symbols]

[0127] 1: Bulkhead 2: Electrode 2a:Anode 2c: Cathode 2e: Conductive elastic body 2r: Current collector 3: Outer frame 4: Diaphragm 5: Electrode chamber 5a:Anode chamber 5c: Cathode chamber 6: Rib (rectifier plate) 7: Gasket 50: Electrolytic cell (dipolar electrolytic cell) 51g: Fast head, loose head 51i: Insulating plate 51a: Anode terminal element 51c: Cathode terminal element 51r: Tie rod 60: Multi-pole element 65: Electrolytic cell 70: Electrolyzer 71: Liquid transfer pump 72: Gas-liquid separation tank 74: Rectifier 75: Oxygen concentration meter 76: Hydrogen concentration meter 77:Flow meter 78: Pressure gauge 79:Heat exchanger 80: Pressure control valve Z: Zero gap structure

Claims

1. A method for operating an electrolysis apparatus comprising an anode chamber having an anode and a cathode chamber having a cathode, the anode chamber and the cathode chamber being separated from each other by a diaphragm, the method comprising the steps of: the anode chamber and the cathode chamber are filled with an electrolyte; A method for operating an electrolysis device, characterized in that the potential Ec of the cathode is controlled in a potential region more negative than a reversible hydrogen electrode (RHE), thereby suppressing adhesion of substances that increase the potential Ec of the cathode in a negative direction to the cathode and removing substances that increase the potential Ec of the cathode in a negative direction from the cathode.

2. 2. The method for operating an electrolytic device according to claim 1, wherein the electrolytic solution contains metal ions that are reduced by energizing the electrolytic device and deposited on the surface of the cathode.

3. 3. The method for operating an electrolytic apparatus according to claim 2, wherein the metal ions are iron ions.

4. The method for operating an electrolysis apparatus according to any one of claims 1 to 3, wherein the potential Ec of the cathode alternately satisfies the ranges of [potential 1] and [potential 2] shown in the following formula, where the values ​​of [potential 1] and [potential 2] are expressed as potential [V] vs RHE relative to RHE. [Potential 1] Ec<Ed [Potential 2] Ed≦Ec<0 [V] Ed:-9.9×10 －５ ×(pH-log １０ [M])×T+0.61 [V] pH: pH of the electrolyte [M]: metal ion concentration in the electrolyte [mol / L] T: absolute temperature of the electrolyte [K]

5. The method for operating an electrolysis apparatus according to any one of claims 1 to 3, wherein the potential Ec of the cathode alternately satisfies [Potential 1'] and [Potential 2'] shown in the following formula, where the values ​​of [Potential 1'] and [Potential 2'] are expressed as potential [V] vs RHE relative to RHE. [Potential 1'] Ec<-0.082[V] [Potential 2'] -0.082[V]≦Ec<0[V]

6. 5. The method for operating an electrolysis apparatus according to claim 4, wherein the electrolyte contains 0.20 mg / L or more of iron ions.

7. 5. The method for operating an electrolytic apparatus according to claim 4, wherein the potential Ec of the cathode is maintained at the [potential 2] for one hour or more.

8. 5. The method for operating an electrolysis apparatus according to claim 4, wherein the pH of the electrolytic solution is 14 or higher.

9. 5. The method for operating an electrolysis apparatus according to claim 4, wherein the temperature of the electrolytic solution is 70°C or higher.

10. 5. The method of claim 4, wherein the electrolytic device includes a system for removing metal ions from the electrolyte.

11. 5. The method for operating an electrolytic apparatus according to claim 4, further comprising measuring the potential Ec of the cathode using a reference electrode and controlling the value of the potential Ec of the cathode.

12. 5. The method for operating an electrolysis apparatus according to claim 4, wherein a current value is used as an input value, and the potential Ec of the cathode is controlled by changing the current value.

13. A method for operating the electrolysis apparatus according to claim 4 for alkaline water electrolysis.

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