Electrolytic cell, electrolysis tank, and method for producing hydrogen

Abstract

This electrolytic cell comprises an element provided with: an anode chamber provided with an anode; a cathode chamber provided with a cathode; a conductive partition wall provided between the anode chamber and the cathode chamber; and an outer frame that borders the conductive partition wall. The electrolytic cell is stacked with a gasket and a diaphragm interposed between cells. Sealing of an electrolytic solution is achieved by applying surface pressure between the gasket and the diaphragm and between the gasket and the outer frame. The contact ratio between the diaphragm and a first electrode, which is at least one of the anode and the cathode, is 15%-60%, and a region in which the local stress between the diaphragm and the first electrode is 0.1 MPa or more is 5% or less.

Description

Electrolytic cell, electrolytic bath, and method for producing hydrogen

[0001] The present invention relates to an electrolysis cell, an electrolyzer and a method for producing hydrogen.

[0002] In recent years, technologies such as wind power generation and solar power generation that utilize renewable energy sources such as wind and sunlight 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 has the property of being highly variable, as its output depends on weather conditions. As a result, it is not always possible to transport the electricity generated by renewable energy (hereinafter referred to as "variable power source") to the general power grid, raising concerns about social impacts such as imbalances in power supply and demand and instability in the power grid. It is also well known that imbalances between the power generated by renewable energy and the power demand occur not only throughout the day but also depending on the season.

[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 the generated 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, its potential use has expanded to include hydrogen stations for fuel cell vehicles (FCVs), smart communities, hydrogen power plants, etc. For this reason, there are high expectations for the development of technology to obtain particularly high-purity hydrogen from renewable energy sources.

[0006] Methods for electrolyzing water include solid polymer water electrolysis, high-temperature steam electrolysis, alkaline water electrolysis, etc. Among these, 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 inexpensive compared to other water electrolysis devices.

[0007] However, to adapt alkaline water electrolysis as a means of energy storage and transportation in the future, it is necessary to perform water electrolysis by efficiently and stably utilizing electric power, which has large fluctuations in output, as described above. When the supply and demand imbalance, particularly the supply of electric power from renewable energy sources, fluctuates significantly, the electric power supplied to the water electrolysis device also fluctuates. As a result, the current density per unit area of ​​the electrolytic cell fluctuates. With existing alkaline water electrolysis devices, there are concerns about a worsening of the electric power consumption rate for hydrogen production and an increase in the oxygen concentration in the generated hydrogen and / or hydrogen concentration in the oxygen, resulting in an increase in refining losses. Under these circumstances, the capacity of the water electrolysis device must be increased to be able to accept a wide range of currents, which increases capital investment and raises profitability concerns. Therefore, it is desirable for water electrolysis devices to be able to efficiently produce hydrogen over a wide range of current densities.

[0008] It is well known that, in alkaline water electrolysis, the electrolysis voltage must be kept low to achieve an improvement in the power consumption rate for hydrogen production. To this end, it is effective to employ, as an electrolysis cell structure, a structure known as a zero-gap structure, in which the gap between the diaphragm and the electrodes is substantially eliminated (see Patent Documents 1 and 2). In the zero-gap structure, generated gas is quickly released through pores in the electrodes to the side opposite the diaphragm, thereby reducing the distance between the electrodes and minimizing the occurrence of gas accumulation near the electrodes, thereby keeping the electrolysis voltage low. Therefore, the zero-gap structure is extremely effective in reducing the electrolysis voltage and is adopted in various electrolysis devices.

[0009] U.S. Patent No. 4,530,743, Japanese Patent Laid-Open Publication No. 59-173281

[0010] When a current flows through the electrodes, a pressure difference may occur between the anode chamber and the cathode chamber. The pressure difference presses the diaphragm against one of the electrodes.

[0011] In particular, when the supply of electricity from renewable energy sources fluctuates significantly, the power supplied to the water electrolysis apparatus also fluctuates. In such a power-fluctuating operation, the fluctuation in the differential pressure between the anode chamber and the cathode chamber may damage the diaphragm, potentially causing mixing of oxygen gas and hydrogen gas.

[0012] On the other hand, from the viewpoint of electrolysis efficiency, it is preferable to make the diaphragm thinner. A thinner diaphragm reduces voltage loss in a zero-gap structure and increases electrolysis efficiency. However, there is a concern that a thin membrane may break.

[0013] In view of the above circumstances, an object of the present invention is to provide an electrolytic cell, an electrolytic bath, and a method for producing hydrogen that achieve both high resistance to differential pressure fluctuations and high electrolysis efficiency.

[0014] An electrolytic cell as a first aspect of the present invention is: (1) an electrolytic cell including elements including an anode chamber equipped with an anode, a cathode chamber equipped with a cathode, a conductive partition wall provided between the anode chamber and the cathode chamber, and an outer frame that borders the conductive partition wall, wherein the electrolytic cells are stacked with a gasket and a diaphragm sandwiched therebetween, and sealing of the electrolytic solution is achieved by applying surface pressure between the gasket and the diaphragm and between the gasket and the outer frame, wherein a contact rate between the diaphragm and a first electrode that is at least one of the anode and the cathode is 15% or more and 60% or less, and a region between the diaphragm and the first electrode where a local stress is 0.1 MPa or more is 5% or less.

[0015] An electrolytic cell as one embodiment of the present invention is the electrolytic cell according to (1), wherein (2) the distance between the end of the first electrode on the outer frame side that is in contact with the diaphragm and the end of the first electrode that is closest to the first electrode and sandwiches the diaphragm between the gaskets is 7 mm or less.

[0016] An electrolytic cell according to one embodiment of the present invention is the electrolytic cell according to (1) or (2), wherein: (3) the first electrode includes, at least at one end thereof, an inclined portion inclined from another portion, and the inclined portion extends at an angle greater than 30° and not greater than 180° with respect to a surface of the diaphragm on the inclined portion side.

[0017] An electrolytic cell according to one embodiment of the present invention is the electrolytic cell according to any one of (1) to (3), wherein (4) the first electrode is the electrode having higher rigidity out of the anode and the cathode.

[0018] In one embodiment of the electrolytic cell of the present invention, (5) the bending rigidity of the first electrode is 10 kN·m２ The electrolytic cell according to any one of (1) to (4) above.

[0019] An electrolytic cell according to one embodiment of the present invention is the electrolytic cell according to any one of (1) to (5), wherein the first electrode has a catalyst layer formed of a nickel compound on a surface thereof.

[0020] An electrolytic cell according to one embodiment of the present invention is the electrolytic cell according to any one of (1) to (6), wherein (7) the diaphragm is a porous membrane.

[0021] An electrolytic cell according to one embodiment of the present invention is the electrolytic cell according to any one of (1) to (6), wherein (8) the diaphragm is an ion exchange membrane.

[0022] An electrolytic cell according to a second aspect of the present invention is (9) an electrolytic cell comprising the electrolytic cell according to any one of (1) to (8), wherein the electrolytic cells are stacked with the gasket and the diaphragm sandwiched therebetween, and surface pressure is applied between the gasket and the diaphragm and between the gasket and the outer frame to seal in the electrolytic solution.

[0023] An electrolytic cell according to a third aspect of the present invention is (10) an electrolytic cell including the electrolytic cell according to any one of (1) to (8), wherein the diaphragm divides the interior of the partition wall into an anode chamber and a cathode chamber.

[0024] A fourth aspect of the present invention provides a method for producing hydrogen using the electrolytic cell according to (11) (9), comprising the steps of bringing an electrolytic solution into contact with the anode and the cathode of the electrolytic cell, and passing a current through the anode and the cathode to generate hydrogen from the cathode.

[0025] According to the present invention, it is possible to provide an electrolytic cell, an electrolytic bath, and a method for producing hydrogen that achieve both high resistance to differential pressure fluctuations and high electrolysis efficiency.

[0026] Fig. 3 is a diagram showing an example of the configuration of an electrolytic cell according to the present embodiment. Fig. 4 is a cross-sectional view of the electrolytic cell shown in Fig. 1. Fig. 5 is a partially enlarged view showing the ends of a gasket and an electrode shown in Fig. 2. Fig. 6 is a partially enlarged view showing the ends of a gasket and an electrode in another embodiment. Fig. 7 is a flowchart showing an example of a method for producing hydrogen using the electrolytic cell according to the present embodiment.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0028] [Electrolytic Cell] The electrolytic cell 50 may generate oxygen from the anode 2a side and hydrogen from the cathode 2c side by electrolysis of water using an electrolyte based on the supplied power. The electrolytic cell 50 may be electrically connected to a rectifier. The rectifier may apply a predetermined DC voltage determined by a control device between the anode terminal and the cathode terminal of the electrolytic cell 50, thereby controlling the operation and stop of the electrolytic cell 50. The electrolytic cell 50 may be a bipolar electrolytic cell. The electrolytic cell 50 may include a plurality of electrolytic cells 65 (see FIG. 1 ). Details of the configurations of the electrolytic cell 50 and the electrolytic cells 65 will be described later.

[0029] The electrolyte is an alkaline aqueous solution in which an alkali salt is dissolved, such as an aqueous NaOH solution or an aqueous KOH solution. The concentration of the alkali salt is determined taking into consideration ionic conductivity, kinetic viscosity, freezing at low temperatures, and the like. Furthermore, if the concentration of the alkali salt in the electrolyte is too high, the electrolyte may crystallize, increasing electrical resistance and deteriorating electrolytic performance, which may interfere with the operation of the electrolytic cell. From the above viewpoints, the concentration of the alkali salt is preferably 5 to 50 mass %, more preferably 10 to 40 mass %.

[0030] An example of the configuration of the electrolytic cell 50 according to this embodiment will be described in detail with reference to FIGS. 1 and 2. FIG.

[0031] In the electrolytic cell 50, a plurality of bipolar elements 60 are disposed between an anode terminal element (anode terminal) 51a and a cathode terminal element (cathode terminal) 51c. The anode terminal element 51a and the cathode terminal element 51c are electrically connected to a rectifier. The anode terminal element 51a is electrically connected to the anode 2a located at the leftmost end in FIG. 1, and the cathode terminal element 51c is electrically connected to the cathode 2c located at the rightmost end in FIG. 1. Current flows from the anode terminal element 51a through the cathode 2c and anode 2a included in the plurality of bipolar elements 60 toward the cathode terminal element 51c.

[0032] The electrolytic cell 50 is arranged in the following order from left to right in Fig. 1 : a fast head 51g1, an insulating plate 51i1, an anode terminal element 51a, a set of an anode side gasket portion 7a, a diaphragm 4, a cathode side gasket portion 7c, and multiple bipolar elements 60, a cathode terminal element 51c, an insulating plate 51i2, and a loose head 51g2. The multiple bipolar elements 60 are arranged so that the cathode 2c faces the anode terminal element 51a and the anode 2a faces the cathode terminal element 51c. The electrolytic cell 50 is integrated by being clamped together with tie rods 51r. A hydraulic cylinder or the like may be used as the clamping mechanism. The electrolytic cell 50 can be arranged from either the anode 2a side or the cathode 2c side, and the above order is not limited to this.

[0033] The electrolytic cell 50, which is a bipolar electrolytic cell, can reduce the current of the power supply compared to a monopolar electrolytic cell, and can produce large amounts of compounds, predetermined substances, etc. in a short period of time. Therefore, from an industrial perspective, using a bipolar electrolytic cell can reduce costs more than using a monopolar electrolytic cell.

[0034] [Bipolar Element] The bipolar element 60 includes 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. One surface of the bipolar element 60 serves as the anode 2a, and the other surface serves as the cathode 2c.

[0035] The number of bipolar elements 60 is not particularly limited, and they may be repeatedly arranged in the number required for the designed production volume, but the number is preferably 50 to 500, and more preferably 100 to 300.

[0036] When the number of bipolar elements 60 is small, the adverse effects of leakage current on gas purity are mitigated. Furthermore, when the number of bipolar elements 60 is large, it becomes difficult to uniformly distribute the electrolyte to each electrolytic cell 65. Furthermore, when the number of bipolar elements 60 is too large, it becomes difficult to manufacture the electrolytic cell 50. When a large number of bipolar elements 60 with poor manufacturing accuracy are stacked, the sealing surface pressure in the electrolytic cell 50 becomes uneven, making electrolyte and gas leakage more likely to occur. Therefore, by ensuring that the number of bipolar elements 60 satisfies the above-mentioned range, self-discharge that occurs when power supply is stopped can be reduced, and the electrical control system can be stabilized. Furthermore, it is possible to store power with high efficiency, such as by reducing pump power and leakage current.

[0037] 1 and 2 , the electrolytic cell 65 includes a partition wall 1, an anode chamber 5a, and an anode 2a included in one adjacent bipolar element 60, and a cathode 2c, a cathode chamber 5c, and a partition wall 1 included in the other adjacent bipolar element 60, an outer frame 3, a diaphragm 4, and a gasket 7. The cathode chamber 5c includes a current collector 2r and a conductive elastic body 2e. The electrolytic cell 65 may include a baffle plate between the anode 2a and the partition wall 1.

[0038] The temperature of the electrolytic solution inside the electrolytic cell 65 is preferably 40°C or higher, and more preferably 80°C or higher. The temperature of the electrolytic solution inside the electrolytic cell 65 is preferably 110°C or lower, and more preferably 95°C or lower. Ensuring that the temperature of the electrolytic solution inside the electrolytic cell 65 satisfies this range effectively prevents thermal deterioration of various components included in the alkaline water electrolysis system while maintaining high electrolysis efficiency.

[0039] The upper limit of the current density applied to the electrolytic cell 65 is 15 kA / m ２] or less, and 10 [kA / m ２ In particular, when a variable power supply is used, such as in an alkaline water electrolysis system, it is preferable that the upper limit of the current density be in the above range.

[0040] The internal pressure of the electrolytic cell 65 is preferably 3 kPa to 1000 kPa, and more preferably 3 kPa to 300 kPa.

[0041] -Partition Wall- The partition wall 1 is provided between the anode chamber 5a and the cathode chamber 5c. The partition wall 1 may have two surfaces, one in contact with the anode chamber 5a and the other in contact with the cathode chamber 5c. The partition wall 1 may have a structure that is impermeable to the electrolytic solution.

[0042] The partition wall 1 is preferably formed of a conductive material. Examples of the conductive material include nickel, a nickel alloy, mild steel, and a nickel alloy plated with nickel. When the partition wall 1 is formed of a conductive material, a uniform supply of power can be achieved. It is particularly preferable that the material of the partition wall 1 that comes into contact with the electrolyte is formed of nickel. This can improve alkali resistance, heat resistance, and the like.

[0043] Ribs 1r1 and 1r2 are formed on the inner surface of the partition wall 1. In the anode chamber 5a, the rib 1r1 protrudes toward the anode 2a. The tip of the rib 1r1 is welded to the anode 2a. In the cathode chamber 5c, the rib 1r2 protrudes toward the current collector 2r. The rib 1r2 is welded to the current collector 2r. The ribs 1r1 and 1r2 support the anode 2a and the current collector 2r and form a conductive path between the anode 2a and the current collector 2r and the partition wall 1. Furthermore, the presence of the ribs 1r1 and 1r2 allows for the formation of a suitable flow path with low pressure loss for the electrolyte or the generated gas. Furthermore, the rib 1r1 promotes stirring of the electrolyte by the generated gas, thereby homogenizing the temperature distribution due to heat generated locally in the electrolytic cell 50. This prevents damage to components such as the diaphragm 4 caused by local temperature increases inside the electrolytic cell 50.

[0044] The partition wall 1 may have a through hole communicating with the anode chamber 5a and a through hole communicating with the cathode chamber 5c formed in a portion extending perpendicular to the diaphragm 4 (in the left-right direction in FIG. 2 ). The electrolytic solution flows into the anode chamber 5a through the through hole communicating with the anode chamber 5a. The electrolytic solution flows out of the anode chamber 5a and the cathode chamber 5c through the respective through holes.

[0045] The shape of the partition wall 1 is not particularly limited, but is preferably a plate shape having a predetermined thickness. The partition wall 1 may have, for example, a rectangular, circular, or elliptical shape in plan view, and if it is a rectangular shape, the corners may be rounded.

[0046] 1 , the outer frame 3 is provided along the outer edge of the partition wall 1 so as to surround the partition wall 1. The shape of the outer frame 3 is not particularly limited as long as it can surround the partition wall 1, but it is preferable that the outer frame 3 has an inner surface that is aligned in the vertical direction with respect to the plane of the partition wall 1 and extends along the periphery of the partition wall 1. It is preferable that the outer frame 3 is set appropriately in accordance with the shape of the partition wall 1 in a plan view.

[0047] The outer frame 3 is preferably formed of an electrically conductive material, such as nickel, a nickel alloy, mild steel, a nickel alloy, etc. From the viewpoint of alkali resistance and heat resistance, the outer frame 3 is preferably formed of nickel, a nickel alloy, mild steel, or a nickel alloy that is plated with nickel.

[0048] -Electrodes- The anode 2a is provided in the anode chamber 5a. The cathode 2c is provided in the cathode chamber 5c. The anode 2a and cathode 2c belonging to one electrolytic cell 65 are electrically connected to each other. The cathode 2c is also electrically connected to the current collector 2r via the conductive elastic body 2e.

[0049] To integrate the cathode 2c, the current collector 2r, and the conductive elastic body 2e, the cathode 2c may include an inclined portion 2ct1, a folded portion 2ct2, and a returned portion 2cr at at least one end (both in the embodiment shown in FIG. 2 ). The inclined portion 2ct1 may cover the end of the conductive elastic body 2e. The inclined portion 2ct1 may be inclined from a contact portion of the inclined portion 2ct1 that contacts the diaphragm 4. As shown in FIG. 2 , a bend may exist between the inclined portion 2ct1 and the contact portion. The folded portion 2ct2 may cover the end of the current collector 2r. The folded portion 2ct2 may be in contact with the partition wall 1. The returned portion 2cr may cover at least a portion of the side surface of the current collector 2r opposite to the diaphragm 4.

[0050] Electrode 2 is preferably a porous body in order to increase the surface area available for water electrolysis and to efficiently remove gas generated by water electrolysis from the surface of electrode 2. Examples of porous bodies include plain woven mesh, punched metal, expanded metal, and metal foam.

[0051] The electrode 2 may be the substrate itself, but preferably has a highly reactive catalyst layer on the surface of the substrate.

[0052] The substrate is preferably made of a material such as mild steel, stainless steel, nickel, or a nickel-based alloy, in view of its resistance to the environment in which it is used.

[0053] The catalytic layer of the anode 2a is preferably formed of a material with high oxygen generation ability and good durability. Examples of such materials include nickel, cobalt, iron, and platinum group elements. The anode 2a may have a catalytic layer formed of a nickel compound on its surface. The surface of the catalytic layer of the anode 2a may contain nickel metal crystals and have pores formed thereon. Furthermore, examples of materials for achieving desired catalytic activity, durability, etc. include simple metals such as palladium, iridium, platinum, gold, ruthenium, rhodium, cerium, nickel, cobalt, tungsten, iron, molybdenum, silver, copper, zirconium, titanium, hafnium, and lanthanides; compounds such as oxides; composite oxides or alloys composed of multiple metal elements; or mixtures thereof; and carbon materials such as graphene.

[0054] The catalytic layer of the cathode 2c is preferably formed of a material with high hydrogen generation ability, and examples of such materials include nickel, cobalt, iron, and platinum group elements. Furthermore, the cathode 2c may have a catalytic layer formed of a nickel compound on its surface. The surface of the catalytic layer of the cathode 2c may contain nickel metal crystals and have pores formed thereon. Examples of materials for achieving desired catalytic activity, durability, and the like include simple metals, compounds such as oxides, composite oxides or alloys composed of multiple metal elements, and mixtures thereof. Specifically, examples of the catalyst include Raney nickel, Raney alloys formed from a combination of multiple materials such as nickel and aluminum, or nickel and tin; porous coatings prepared by plasma spraying using nickel compounds or cobalt compounds as raw materials; alloys or composite compounds of nickel with an element selected from cobalt, iron, molybdenum, silver, copper, etc.; platinum group metals or oxides such as platinum or ruthenium, which have high hydrogen generating capacity, and mixtures of these platinum group metals or oxides with compounds of other platinum group elements such as iridium and palladium, or compounds of rare earth metals such as lanthanum or cerium; and carbon materials such as graphene. To achieve high catalytic activity and durability, multiple catalyst layers formed from the above materials may be stacked, or multiple materials may be mixed within a catalyst layer. Furthermore, to improve durability and adhesion to the substrate, organic substances such as polymeric materials may be included in the material.

[0055] The electrolysis voltage largely depends on the performance of the electrode 2. Reducing the electrolysis voltage can reduce energy consumption in an alkaline water electrolysis system. The electrolysis voltage includes not only the theoretically required voltage for water electrolysis, but also the overvoltage of the anode reaction (oxygen generation), the overvoltage of the cathode reaction (hydrogen generation), and the voltage due to the inter-electrode distance between the anode 2a and the cathode 2c. Here, overvoltage refers to a voltage that needs to be applied in excess of the theoretical decomposition potential when a certain current is passed. The electrolysis voltage can be reduced by lowering the overvoltage.

[0056] The electrode 2 preferably has properties such as high electrical conductivity, high oxygen generating ability or hydrogen generating ability, and high wettability of the electrolyte on the surface of the electrode 2. When the electrode 2 has such properties, the above-mentioned overvoltage can be reduced. Furthermore, the electrode 2 preferably has properties that make it less susceptible to corrosion of the substrate and catalyst layer, shedding of the catalyst layer, dissolution in the electrolyte, adhesion of inclusions to the diaphragm 4, etc., even when supplied with unstable power such as renewable energy.

[0057] The present invention is particularly effective in suppressing damage to the diaphragm 4 in an electrode 2 having a porous structure in the catalyst layer. This is because, when the catalyst layer has a porous structure, the diaphragm is easily damaged by friction caused by pressure fluctuations. On the other hand, the degree of damage due to friction is reduced when the contact rate between the diaphragm 4 and the first electrode, which is at least one of the anode 2a and the cathode 2c, is 15% or more and 60% or less, and the region where the local stress between the diaphragm 4 and the first electrode is 0.1 MPa or more is 5% or less. The maximum value of the local stress is preferably 1 MPa or less, more preferably 0.75 MPa or less, and even more preferably 0.5 MPa or less. Furthermore, the region where the local stress is 0.5 MPa or more is preferably 1% or less, and the region where the local stress is 1 MPa or more is preferably 0.3% or less.

[0058] - Current Collector - The current collector 2r transmits electricity to the conductive elastic body 2e and the electrode 2, supports the load received from the conductive elastic body 2e and the electrode 2, and allows gas generated from the electrode 2 to pass through to the partition wall 1 side without hindrance.

[0059] The current collector 2r preferably has a shape such as an expanded metal or a punched perforated plate. The current collector 2r preferably has an aperture ratio that satisfies a range in which hydrogen gas generated from the cathode 2c can be easily extracted to the partition wall 1 side. If the aperture ratio is too large, problems such as a decrease in the strength of the current collector 2r or a decrease in conductivity to the conductive elastic body 2e are likely to occur, while if the aperture ratio is too small, gas escape becomes poor. Therefore, the aperture ratio of the current collector 2r is preferably set appropriately taking these problems into consideration.

[0060] From the viewpoints of electrical conductivity and alkali resistance, the current collector 2r is preferably formed from a material such as nickel, a nickel alloy, stainless steel, mild steel, etc. From the viewpoint of corrosion resistance, the current collector 2r is preferably formed by plating nickel on nickel, mild steel, or a stainless steel-nickel alloy.

[0061] A current collector may be provided not only in the cathode chamber 5 c but also in the anode chamber 5 a. The current collector may be made of the same material and have the same structure as the current collector provided in the cathode chamber 5 c. Alternatively, the anode 2 a itself may function as a current collector.

[0062] -Conductive Elastic Body- The conductive elastic body 2e is provided between the current collector 2r and the cathode 2c, and is in contact with the current collector 2r and the electrode 2. The conductive elastic body 2e has the function of bringing the diaphragm 4 and the electrode 2 into close contact with each other by evenly applying an appropriate pressure to the electrode 2 without damaging the diaphragm 4.

[0063] It is preferable that the conductive elastic body 2e has conductivity with respect to the electrode 2, but does not hinder the diffusion of the gas generated from the electrode 2. If the conductive elastic body 2e were to hinder the diffusion of the gas, the electrical resistance would increase and the area of ​​the electrode 2 used for the electrolysis of water would decrease, resulting in a decrease in the efficiency of electrolysis.

[0064] The configuration of the conductive elastic body 2e is not particularly limited and may be a known configuration. For example, the conductive elastic body 2e may be a cushion mat made of woven nickel wire with a wire diameter of about 0.05 mm to 0.5 mm and corrugated.

[0065] - Diaphragm - The diaphragm 4 separates the anode chamber 5a containing the anode 2a from the cathode chamber 5c containing the cathode 2c. As shown in FIG. 1 , the diaphragm 4 is provided 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. The diaphragm 4 is ion permeable and separates hydrogen gas from oxygen gas while conducting ions. The diaphragm 4 may be an ion exchange membrane having ion exchange capacity, a porous membrane permeable to an electrolyte, or the like. The diaphragm 4 preferably has low gas permeability, high ionic conductivity, low electronic conductivity, and high strength.

[0066] --Porous membrane-- Porous membranes have a structure that allows electrolyte to pass through the membrane, with multiple fine through-holes. Ion conduction occurs when electrolyte penetrates the porous membrane, so control of the porous structure, such as pore size, porosity, and hydrophilicity, is extremely important. Meanwhile, it is also necessary to prevent the passage of not only electrolyte but also generated gas, i.e., to have gas barrier properties. Control of the porous structure is also important from this perspective.

[0067] The porous membrane has a plurality of fine through-holes, and examples thereof include a polymer porous membrane, an inorganic porous membrane, a woven fabric, and a nonwoven fabric. These can be produced by known techniques. Examples of methods for producing a polymer porous membrane include a phase inversion method (microphase separation method), an extraction method, a stretching method, and a wet gel stretching method.

[0068] ---Polymer Materials---Examples of polymer materials include polysulfone, polyethersulfone, polyphenylsulfone, polyvinylidene fluoride, polycarbonate, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polytetrafluoroethylene, perfluorosulfonic acid, perfluorocarboxylic acid, polyethylene, polypropylene, polyphenylene sulfide, polyparaphenylene benzobisoxazole, polyketone, polyimide, polyetherimide, etc. Among these, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, and polytetrafluoroethylene are preferred, and polysulfone is more preferred. These may be used alone or in combination of two or more.

[0069] Since the porous membrane exhibits ionic conductivity by the penetration of the electrolyte solution, it is preferable that the porous structure, such as the pore size, porosity, and hydrophilicity, be appropriately controlled. By appropriately controlling the porous structure of the porous membrane, not only the electrolyte solution can be permeated but also the barrier property against the generated gas can be improved.

[0070] It is preferable to control the pore size of the porous membrane in order to obtain appropriate membrane properties such as separation ability and strength. Furthermore, when used in alkaline water electrolysis, it is preferable to control the pore size of the porous membrane from the viewpoint of preventing mixing of oxygen gas generated from the anode and hydrogen gas generated from the cathode and reducing voltage loss during electrolysis. The larger the average pore size of the porous membrane, the greater the amount of permeation through the porous membrane per unit area. In particular, the ion permeability of the porous membrane during electrolysis tends to be improved, making it easier to reduce voltage loss. Furthermore, the larger the average pore size of the porous membrane, the smaller the contact surface area with alkaline water, which tends to suppress polymer degradation. On the other hand, the smaller the average pore size of the porous membrane, the higher the separation accuracy of the porous membrane, which tends to improve the gas barrier properties of the porous membrane during electrolysis. Furthermore, when hydrophilic inorganic particles with small particle sizes, as described below, are supported on the porous membrane, they can be firmly held without falling off. This allows the high holding ability of the hydrophilic inorganic particles to be imparted, and the effect can be maintained over a long period of time.

[0071] From these viewpoints, the porous membrane preferably has an average pore size in the range of 0.1 to 1.0 μm. When the pore size is in this range, the porous membrane can achieve both excellent gas barrier properties and high ion permeability. The pore size of the porous membrane is preferably controlled in the temperature range in which it is actually used. Therefore, for example, when the porous membrane is used as the diaphragm 4 in an environment of 90°C, it is preferable that the pore size satisfy the above range at 90°C. The porous membrane more preferably has an average pore size of 0.1 to 0.5 μm, which is a range in which the porous membrane can achieve even better gas barrier properties and high ion permeability as a diaphragm for alkaline water electrolysis.

[0072] The average pore size of the porous membrane can be measured by the following method. The average pore size of the porous membrane refers to the average water permeation pore size measured by the following method using an integrity tester ("Sartocheck Junior BP-Plus" manufactured by Sartorius Stedim Japan). First, the porous membrane, including the core material, is cut to a predetermined size and used as a sample. This sample is placed in an arbitrary pressure-resistant container, and the container is filled with pure water. Next, the pressure-resistant container is held in a thermostatic chamber set to a predetermined temperature, and measurement is started once the inside of the pressure-resistant container has reached the predetermined temperature. When measurement begins, the upper surface of the sample is pressurized with nitrogen, and the pressure and permeation flow rate when pure water permeates from the lower surface of the sample are recorded. The average water permeation pore size can be determined from the following Hagen-Poiseuille equation using the gradient between pressure and water permeation flow rate at pressures of 10 kPa to 30 kPa. Average water permeable pore size (m) = {32ηLμ0 / (εP)}0.5, where η is the viscosity of water (Pa·s), L is the thickness of the porous membrane (m), μ0 is the apparent flow velocity, and μ0 (m / s) = flow rate (m ３ / s) / flow path area (m ２ ) where ε is the porosity and P is the pressure (Pa).

[0073] For alkaline water electrolysis diaphragms, it is preferable to control the porosity of the porous membrane from the viewpoints of gas barrier properties, maintaining hydrophilicity, preventing a decrease in ion permeability due to bubble adhesion, and obtaining stable electrolysis performance (low voltage loss, etc.) for a long period of time. From the viewpoint of achieving both high levels of gas barrier properties and low voltage loss, the lower limit of the porosity of the porous membrane is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more. The upper limit of the porosity is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 55% or less. When the porosity of the porous membrane is equal to or less than the above upper limit, ions can easily permeate through the membrane, and voltage loss across the membrane can be suppressed.

[0074] The porosity of the porous membrane refers to the open porosity determined by Archimedes' method, and can be determined by the following formula: Porosity P (%) = ρ / (1 + ρ) × 100, where ρ = (W3 - W1) / (W3 - W2), W1 is the dry mass (g) of the porous membrane, W2 is the mass (g) of the porous membrane in water, and W3 is the mass (g) of the porous membrane saturated with water.

[0075] To measure the porosity, a porous membrane washed with pure water is cut into three pieces measuring 3 cm x 3 cm to be used as measurement samples. First, W2 and W3 of the sample are measured. Then, the porous membrane is left to dry for 12 hours or more in a dryer set at 50 ° C, and W1 is measured. Then, the porosity is calculated from the values ​​of W1, W2, and W3. The porosity of the three samples is calculated, and their arithmetic average value is taken as the porosity P.

[0076] The thickness of the porous membrane is not particularly limited, but is preferably 100 to 700 μm, more preferably 100 to 600 μm, and even more preferably 200 to 600 μm. When the thickness of the porous membrane is equal to or greater than the above lower limit, it is less likely to break when pierced or the like, and is less likely to short-circuit between electrodes. In addition, the gas barrier properties are improved. When the thickness is equal to or less than the above upper limit, voltage loss is less likely to increase. In addition, the influence of variations in the thickness of the porous membrane is reduced. When the thickness of the diaphragm is 100 μm or more, it is less likely to break when pierced or the like, and is less likely to short-circuit between electrodes. In addition, the gas barrier properties are improved. When the thickness is 600 μm or less, voltage loss is less likely to increase. In addition, the influence of variations in the thickness of the porous membrane is reduced. When the thickness of the porous membrane is 250 μm or more, even better gas barrier properties are obtained, and the strength of the porous membrane against impact is further improved. From this viewpoint, the lower limit of the thickness of the porous membrane is more preferably 300 μm or more, more preferably 350 μm or more, and even more preferably 400 μm or more.On the other hand, if the thickness of the porous membrane is 700 μm or less, the ion permeability is less likely to be hindered by the resistance of the electrolyte contained in the pores during operation, and more excellent ion permeability can be maintained.From this viewpoint, the upper limit of the thickness of the porous membrane is more preferably 600 μm or less, even more preferably 550 μm or less, and even more preferably 500 μm or less.

[0077] ---Hydrophilic inorganic particles---The porous membrane preferably contains hydrophilic inorganic particles in order to exhibit high ion permeability and high gas barrier properties. The hydrophilic inorganic particles may be attached to the surface of the porous membrane, or may be partially embedded in the polymer material that constitutes the porous membrane. Furthermore, when the hydrophilic inorganic particles are encapsulated in the voids of the porous membrane, they are less likely to detach from the porous membrane, allowing the performance of the porous membrane to be maintained for a long period of time.

[0078] Examples of hydrophilic inorganic particles include at least one inorganic substance selected from the group consisting of oxides or hydroxides of zirconium, bismuth, and cerium, oxides of Group IV elements of the periodic table, nitrides of Group IV elements of the periodic table, and carbides of Group IV elements of the periodic table. Among these, from the viewpoint of chemical stability, oxides of zirconium, bismuth, and cerium and oxides of Group IV elements of the periodic table are more preferred, oxides of zirconium, bismuth, and cerium are even more preferred, and zirconium oxide is even more preferred.

[0079] The hydrophilic inorganic particles are preferably in the form of fine particles.

[0080] --Porous Support-- When a porous membrane is used as a diaphragm, the porous membrane may be used together with a porous support. Preferably, the porous membrane has a structure in which the porous support is embedded, and more preferably, the porous membrane is laminated on both sides of the porous support. Alternatively, the porous membrane may have a structure in which the porous membrane is laminated symmetrically on both sides of the porous support.

[0081] Examples of the porous support include mesh, porous membrane, nonwoven fabric, woven fabric, and composite fabric containing a nonwoven fabric and a woven fabric contained within the nonwoven fabric. These may be used alone or in combination of two or more. More preferred embodiments of the porous support include, for example, a mesh substrate made of polyphenylene sulfide monofilament, or a composite fabric containing a nonwoven fabric and a woven fabric contained within the nonwoven fabric.

[0082] --Ion Exchange Membrane-- Ion exchange membranes include cation exchange membranes, which selectively allow cations to pass through, and anion exchange membranes, which 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.

[0083] Examples of fluorine-containing ion exchange membranes include those that have the function of selectively permeating ions generated during electrolysis and contain a fluorine-containing polymer having an ion exchange group. The fluorine-containing polymer having an ion exchange group as used herein refers to a fluorine-containing polymer having an ion exchange group or an ion exchange group precursor that can be converted to an ion exchange group by hydrolysis. Examples include polymers that have a fluorinated hydrocarbon main chain, have functional groups that can be converted to ion exchange groups by hydrolysis or the like as pendant side chains, and are melt-processable.

[0084] The molecular weight of the fluorine-containing copolymer having ion exchange groups is not particularly limited, but the melt flow index (MFI) measured in accordance with ASTM: D1238 (measurement conditions: temperature 270°C, load 2160 g) is preferably 0.05 to 50 (g / 10 min), more preferably 0.1 to 30 (g / 10 min).

[0085] Examples of the ion exchange group of the ion exchange membrane include cation exchange groups such as sulfonic acid groups, carboxylic acid groups and phosphate groups, and anion exchange groups such as quaternary ammonium groups.

[0086] Ion exchange membranes can be endowed with excellent ion exchange capacity and hydrophilicity by adjusting the equivalent mass (EW) of the ion exchange groups. Furthermore, they can be controlled to have a large number of smaller clusters (microscopic portions where ion exchange groups coordinate and / or adsorb water molecules), which tends to improve alkali resistance and ion selective permeability. This equivalent mass (EW) can be measured by salt-substituting the ion exchange membrane and back-titrating the resulting solution with an alkaline or acid solution. The equivalent mass (EW) can be adjusted by the copolymerization ratio of the raw material monomers, the selection of the monomer species, etc. The equivalent mass (EW) of the ion exchange membrane is preferably 300 or more from the viewpoints of hydrophilicity and water resistance of the membrane, and is preferably 1300 or less from the viewpoints of hydrophilicity and ion exchange capacity.

[0087] The thickness of the ion exchange membrane is not particularly limited, but is preferably in the range of 5 to 300 μm from the viewpoint of ion permeability and strength.

[0088] The ion exchange membrane may be subjected to a surface treatment to improve the hydrophilicity of the surface, such as by coating with hydrophilic inorganic particles such as zirconium oxide or by providing the surface with fine irregularities.

[0089] From the viewpoint of membrane strength, the ion exchange membrane is preferably used together with a reinforcing material. Examples of the reinforcing material include, but are not limited to, general nonwoven fabrics, woven fabrics, and porous membranes made of various materials. In this case, the porous membrane is not particularly limited, but is preferably a PTFE-based membrane that has been stretched and made porous. In the bipolar zero-gap electrolytic cell for water electrolysis of this embodiment, any of these membranes can be used without limitation.

[0090] - Electrode Chamber - The electrode chamber 5 allows the electrolyte to pass through and is defined by the partition wall 1, outer frame 3, diaphragm 4, etc. The range defined by the electrode chamber 5 varies depending on the structure of the outer frame 3 provided at the outer end of the partition wall 1. The electrode chamber 5 is provided, at the boundary with the outer frame 3, with an electrolyte inlet for introducing the electrolyte into the electrode chamber 5 and an electrolyte outlet for discharging the electrolyte from the electrode chamber 5.

[0091] The electrode chamber 5 may be provided with a baffle plate for adjusting the gas-liquid ratio inside the electrolytic cell 50. The electrode chamber 5 may also be provided with an internal distributor for uniformly distributing the electrolytic solution on the surface of the electrode 2 inside the electrolytic cell 50. The electrode chamber 5 may also be provided with protrusions (ribs 1r1, 1r2, etc.) for creating Karman vortices inside the electrolytic cell 50 to uniformize the concentration and temperature of the electrolytic solution or to promote degassing of gas adhering to the electrode 2 and diaphragm 4.

[0092] The electrolytic cell 65 includes an element including an anode chamber 5a equipped with an anode 2a, a cathode chamber 5c equipped with a cathode 2c, a conductive partition wall 1 provided between the anode chamber 5a and the cathode chamber 5c, and an outer frame 3 that frames the conductive partition wall 1. The electrolytic cells 65 are stacked with a gasket 7 and a diaphragm 4 sandwiched therebetween. The electrolytic solution is sealed by applying surface pressure between the gasket 7 and the diaphragm 4 and between the gasket 7 and the outer frame 3.

[0093] As described above, the ribs 1r1 and 1r2 are formed on the inner surface of the partition wall 1. In the anode chamber 5a, the rib 1r1 protruding toward the anode 2a is welded to the anode 2a. In the cathode chamber 5c, the rib 1r2 protruding toward the current collector 2r is welded to the current collector 2r. The cathode 2c is disposed between the current collector 2r and the diaphragm 4 with the conductive elastic body 2e interposed therebetween. In this embodiment, the diaphragm 4 is in contact with the anode 2a and the cathode 2c.

[0094] When a current flows through the anode 2 a and the cathode 2 c, a pressure difference may occur between the anode chamber 5 a and the cathode chamber 5 c. The pressure difference presses the diaphragm 4 against one of the electrodes. This pressure may damage the diaphragm 4.

[0095] The pressure in the cathode chamber 5c is higher than the pressure in the anode chamber 5a because the amount of hydrogen generated from the cathode 2c is greater than the amount of oxygen generated from the anode 2a and because oxygen is prevented from being mixed into the hydrogen to improve the quality of the hydrogen. Therefore, the diaphragm 4 is often pressed against the anode 2a. From the viewpoint of more effectively reducing damage to the diaphragm 4, the first electrode, which is at least one of the anode 2a and the cathode 2c that contacts the diaphragm 4, is preferably the anode 2a.

[0096] - Zero Gap Structure - A gasket 7 is placed in the opening of the partition wall 1. The gasket 7 has the function of preventing leakage of the electrolyte and generated gas to the outside of the electrolytic cell 50, and preventing gas mixing between the anode chamber 5a and the cathode chamber 5c. The inner surface of the gasket 7 (the surface that contacts the diaphragm 4) is placed on the same plane as the inner surface of the partition wall 1. By sandwiching the diaphragm 4 between two gaskets 7, the diaphragm 4 can be stacked (supported) between adjacent bipolar elements 60. Surface pressure is applied between the gasket 7 and the diaphragm 4 and between the gasket 7 and the outer frame 3, thereby achieving sealing of the electrolyte. The gaskets 7 are preferably provided on both edge portions of the diaphragm 4.

[0097] The material of the gasket 7 is not particularly limited, and may be selected from known rubber materials or resin materials having insulating properties. Specific examples of the rubber or resin material include rubber materials such as 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-perfluoroalkylvinyl ether 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, it is particularly preferable to select ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) from the viewpoint of elastic modulus and alkali resistance.

[0098] —Contact rate between diaphragm and first electrode— In the present disclosure, the contact rate between the diaphragm 4 and the first electrode, which is at least one of the anode 2a and the cathode 2c that contacts the diaphragm 4, is 15% or more. With this configuration, the force that the diaphragm 4 receives from the first electrode is dispersed over a wide area of ​​the diaphragm 4. As a result, the contact pressure that the diaphragm 4 receives from the first electrode, i.e., local stress, is reduced. From the viewpoint of further reducing damage to the diaphragm 4, the contact rate between the diaphragm 4 and the first electrode is preferably 18% or more. The contact rate is more preferably 20% or more.

[0099] The contact rate between the diaphragm 4 and the first electrode, which is at least one of the anode 2a and the cathode 2c in contact with the diaphragm 4, is preferably 60% or less, more preferably 50% or less, from the viewpoint of promoting defoaming at the interface between the electrode and the membrane. The contact rate is further preferably 40% or less.

[0100] In this specification and claims, the contact ratio between the diaphragm and the first electrode refers to the area ratio of the region of the first electrode that is in contact with the diaphragm to the region of the diaphragm to which a load is applied. The contact ratio is measured in a state in which the diaphragm and the first electrode overlap and are supported.

[0101] A method for designing the contact rate between the diaphragm 4 and the first electrode will be described below. As described above, in a configuration in which the first electrode (electrode 2) is porous, the contact rate can be increased or decreased by increasing or decreasing the porosity of the first electrode. Furthermore, the contact rate can be increased by flattening the first electrode. By flattening the first electrode, the vicinity of the edges of the holes in the first electrode is formed flat along, for example, the extension direction of the first electrode. As a result, the surface of the diaphragm 4 and the vicinity of the edges of the holes in the first electrode come into surface contact, thereby increasing the contact rate.

[0102] - Local stress between diaphragm and first electrode - In the present disclosure, the region between the diaphragm 4 and the first electrode where the local stress is 0.1 MPa or more is 5% or less. Such a local stress distribution is achieved by a configuration in which the diaphragm 4 and the first electrode are in contact with each other over a relatively large area. Due to such a local stress distribution, when a differential pressure fluctuation occurs between the anode chamber 5a and the cathode chamber 5c, the force applied to the diaphragm 4 is dispersed, and the maximum stress of the diaphragm 4 can be reduced. As a result, damage to the diaphragm 4 can be reduced. The proportion of such a region is more preferably 4% or less, and even more preferably 3% or less.

[0103] —Distance between the contact end of the diaphragm and the electrode, and the contact end of the diaphragm and the gasket— Here, a gap is provided between the first electrode and the gasket, taking into consideration the manufacturing tolerances of the first electrode, the electrolysis frame, and the gasket. On the other hand, if the gap is too large, the diaphragm 4 may enter the gap and be significantly deformed, potentially damaging the diaphragm 4. Furthermore, a small gap not only contributes to expanding the area in the electrolytic cell where the contact rate between the diaphragm 4 and the first electrode and the local stress fall within preferred ranges, but also increases the effective electrode area, potentially reducing the voltage required to produce the same amount of gas, and is therefore important from the perspective of achieving the effects of the present invention over a wider range.

[0104] 2 to 4 illustrate a case where the first electrode is the anode 2a. However, the present invention is not limited to this. As shown in FIGS. 2 to 4, the distance d between the outermost end 2a1, where the anode 2a and the diaphragm 4 are in contact with each other, and the end 7f, where the diaphragm 4 is sandwiched between the gasket 7 and is closest to the first electrode, is preferably 7 mm or less. This configuration of the electrolytic cell 65 can reduce damage to the diaphragm 4. The distance d is more preferably 5 mm or less, and even more preferably 3 mm or less. Furthermore, if the distance d is too small, the end 2a1 and the gasket 7 may come into contact with each other, causing the gasket 7 to ride up on the end 2a1, potentially damaging the diaphragm 4. This risk increases particularly when the gasket 7 is widened. From this perspective, the distance d is preferably 0.5 mm or more, and more preferably 1 mm or more.

[0105] The first electrode may include an inclined portion 2 at at least one end (both in the embodiment shown in FIG. 2 ) that is inclined from the other portions. The inclined portion 2 at may extend at an inclination angle θ greater than 30° and less than or equal to 180° with respect to the surface of the diaphragm 4 on the inclined portion 2 at side. The inclined portion 2 at may have an arc shape as shown in FIG. 3 . The portion between the inclined portion 2 at and the other portions may be bent as shown in FIG. 4 . From the viewpoint of reducing the distance d described above, the inclination angle θ is preferably 60° or greater and 120° or less, more preferably 80° or greater and 100° or less, and even more preferably 87° or greater and 93° or less.

[0106] - Bending rigidity of the first electrode - The electrode in the other electrode chamber, which has a lower pressure than the other electrode chamber, is subjected to a pressure difference. If the electrode is deformed by the pressure difference, the zero-gap structure cannot be achieved, the contact resistance increases, and the electrolysis efficiency decreases. Therefore, it is important to have an electrolysis cell structure in which the rigidity of the electrode in the electrode chamber, which is subjected to a lower pressure difference, is increased. From this perspective, it is preferable that the first electrode is the electrode with the higher rigidity between the anode and the cathode. In addition, the bending rigidity of the first electrode is 10 kN mm ２ The lowest bending stiffness of the first electrode in any bending direction is preferably 10 kN mm or more. ２It is most preferable that the bending rigidity in the direction perpendicular to the rib is 10 kN mm or more. ２ or more. With this configuration, deformation of the first electrode is reduced when the first electrode is pressed by the diaphragm 4. Therefore, when the diaphragm 4 presses the first electrode due to a pressure difference between the anode chamber 5a and the cathode chamber 5c, deformation of the first electrode and the diaphragm 4 can be reduced. From the viewpoint of further reducing deformation of the first electrode and the diaphragm 4, the bending rigidity of the first electrode is set to 20 kN mm ２ The bending rigidity of the first electrode is preferably 40 kN mm or more. ２ More preferably, it is equal to or greater than this.

[0107] [Circulation Pump] The circulation pump circulates the electrolytic solution through the electrolytic cell 50. The configuration of the circulation pump is not particularly limited, and may be, for example, a rotary pump, a gear pump, a tube pump, or the like. When a tube pump is used as the circulation pump, chemical resistance can be improved and the electrolysis system can be made smaller.

[0108] Although one example of the configuration of the electrolytic cell 50 and the electrolytic cell 65 has been described in detail above, the electrolytic cell 50 and the electrolytic cell 65 are not limited to the above configuration. For example, the electrolytic cell 50 may include, in addition to the above-described components, a header, which is a pipe for distributing or collecting the electrolyte. More specifically, the electrolytic cell 50 includes, in a lower part of the outer frame 3 located at the edge of the partition wall 1, an anode inlet header for introducing the electrolyte into the anode chamber 5a and a cathode inlet header for introducing the electrolyte into the cathode chamber 5c. Similarly, the electrolytic cell 50 includes, in an upper part of the outer frame 3 located at the edge of the partition wall 1, an anode outlet header for discharging the electrode solution from the anode chamber 5a and a cathode outlet header for discharging the electrolyte from the cathode chamber 5c.

[0109] Representative examples of the arrangement of headers attached to the electrolytic cell 50 include an internal header type and an external header type. From the viewpoint of reducing leakage current, which is related to electrolysis efficiency and gas quality, the external header type is preferred, and from the viewpoint of reducing the size of the electrolytic cell itself, the internal header type is preferred.

[0110] <Method of Operating Alkaline Water Electrolysis System> With reference to FIG. 5 , an example of a method for producing hydrogen using the electrolytic cell 50 according to this embodiment will be described.

[0111] In step S101, the electrolytic solution is brought into contact with the anode 2a and the cathode 2c of the electrolytic cell 50. An example of the procedure for flowing the electrolytic solution into the electrolytic cell 50 is as follows: A circulation pump connected to the electrolytic cell 50 is driven. The driving conditions of the circulation pump, such as the rotation speed, are controlled by a control device based on the flow rate of the electrolytic solution measured by a flow meter.

[0112] In step S102, a current flows between the anode 2a and the cathode 2c, and hydrogen is generated from the cathode 2c. Specifically, a rectifier applies a predetermined DC voltage between the anode 2a and the cathode 2c, causing a current to flow between the anode 2a and the cathode 2c. As a result, water in the electrolyte is electrolyzed, and hydrogen is generated from the cathode 2c side and oxygen is generated from the anode 2a side.

[0113] Although the above-described embodiments have been described as typical examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present disclosure. Therefore, the present invention should not be interpreted as being limited by the above-described embodiments, and various modifications and alterations are possible without departing from the scope of the claims. For example, multiple building blocks shown in the configuration diagrams of the embodiments can be combined into one, or a single building block can be divided. Furthermore, multiple steps shown in the flowcharts of the embodiments can be combined into one, or a single step can be divided.

[0114] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0115] [Contact Ratio Between Diaphragm and First Electrode] Pressure-sensitive paper (Prescale LW, manufactured by Fujifilm) that changes color depending on pressure and an anode serving as the first electrode were placed on top of each other and clamped in a circular jig with a diameter of 100 mm using an autograph (AG-XPlus, manufactured by Shimadzu Corporation) and compressed for 5 minutes with a load of 7850 N. After compression, the pressure-sensitive paper was removed from the autograph, and the color-developed area ratio (the ratio of the colored area to the area where the load was applied) was measured. The aperture ratio of the first electrode is expressed as the sum of the area of ​​the multiple through holes relative to the area of ​​the side surface of the first electrode. Even if the aperture ratio of the first electrode is the same, the contact ratio between the diaphragm and the first electrode may differ. For example, when the aperture ratio is 35%, the contact ratio may be 10% or 40%. The aperture ratio and contact ratio may differ depending on whether the first electrode is flattened or whether the first electrode has a catalyst layer.

[0116] [Local Stress Between Diaphragm and First Electrode] A 100 mm square jig was prepared by stacking the rib, current collector, conductive elastic body, cathode, pressure-sensitive paper, diaphragm, pressure-sensitive paper, anode, and rib from bottom to top in this order. The jig was clamped in an autograph (AG-XPlus, manufactured by Shimadzu Corporation), and the conductive elastic body was compressed to a thickness of 1 mm and clamped for 5 minutes. After clamping, the pressure-sensitive paper was removed from the autograph, and the proportion of the area where the local stress was 0.1 MPa or more relative to the area where the load was applied was measured. The pressure-sensitive paper was analyzed using a pressure image analysis system FPD-8010J manufactured by Fujifilm. In Table 1, described below, "0.1% or less" indicates that the measurement result was smaller than the lower limit of measurement or the measurement error range. By placing the pressure-sensitive paper through the diaphragm, as in this system, it is possible to measure the local stress between the diaphragm and each electrode (first electrode) in the anode chamber and the cathode chamber.

[0117] The anode was different in each example and comparative example. Fujifilm Prescale LW was used as the pressure-sensitive paper. A commercially available porous membrane for water electrolysis ("Zirfon Perl UTP500" manufactured by Agfa) was used as the diaphragm. A plain-woven mesh-type porous electrode made of 0.15 mm diameter nickel fine wires woven into 40 meshes was used as the cathode. A conductive cushion mat made of 0.15 mm nickel wires woven into a corrugated fabric was used as the conductive elastic body. A nickel expand metal with a mesh center-to-center distance in the long direction (LW) of 4.5 mm, a mesh center-to-center distance in the short direction (SW) of 3 mm, and a thickness of 1.2 mm was used as the current collector.

[0118] [Differential Pressure Fluctuation Resistance] In a small test device with a zero-gap structure and an electrode area of ​​approximately 65 mm (length) x 69 mm (width), the differential pressure between the anode chamber and the cathode chamber was repeatedly varied from 0 kPa to 80 kPa approximately 100 times per hour.

[0119] The number of pressure swings (number of fluctuations) at which diaphragm damage was observed was evaluated based on the state of diaphragm damage after the pressure swing test.

[0120] Here, a first test and a second test were carried out. In the first test, pressure swings of 10,000 or more were carried out on Examples 1 to 7 and Comparative Example 1 (in which the diaphragm was an ion exchange membrane composed of a PTFE core material and a fluorine-based sodium sulfonate polymer EW950 having a thickness of 100 μm). After the test, the appearance of the diaphragm was observed and graded as AAA if there was very little deformation, AA if there was slight deformation, A if there was little deformation, B if there was moderate deformation, and C if there was contact marks or significant deformation. The results are shown in Table 1. In the second test, pressure swings of 10,000 or less were carried out on Examples 8 to 11 and Comparative Example 2 to 5 (in which the diaphragm was a commercially available porous membrane for water electrolysis ("Zirfon Perl UTP500", manufactured by Agfa)). However, if a gas leak was observed in the gas leak test, the test was terminated after that number of swings. After the test, the appearance of the diaphragm was observed and a Z was given if numerous or deep cracks were found, a Y if there was a medium amount of deformation or cracking, an X if there was only a small amount of deformation or cracking, an XX if there was only slight deformation or cracking, and an XXX if there was only slight deformation or cracking. The results are shown in Table 2.

[0121] The anode and diaphragm were different in each Example and Comparative Example. A plain-woven mesh porous electrode made of 0.15 mm diameter nickel fine wire woven into 40 meshes was used as the cathode. A conductive cushion mat made of 0.15 mm nickel wire woven into a fabric and then corrugated was used as the conductive elastic body. Nickel expand metal with a mesh center-to-center distance in the long direction (LW) of 4.5 mm, a mesh center-to-center distance in the short direction (SW) of 3 mm, and a thickness of 1.2 mm was used as the current collector.

[0122] [Electrolysis Efficiency] Electrolysis tests were carried out using a small test device with a zero-gap structure, measuring approximately 59 mm (length) x 49 mm (width). The electrolyte temperature was 90°C and the current density was 6 kA / m. ２An alkaline water electrolysis test was performed by passing a current at 1.5 V. After the test, the average value of the voltage across the electrolytic cell was calculated for each Example and Comparative Example, and this was designated as the cell voltage (V). The results are shown in Tables 1 and 2. Table 1 shows the voltage difference when the cell voltage (2.17 V) of Comparative Example 1 is used as the reference. That is, in each Example and Comparative Example, the cell potential difference is the difference between the cell voltage obtained by the experiment and the cell voltage of Comparative Example 1. Table 2 shows the voltage difference when the cell voltage (1.97 V) of Comparative Example 3 is used as the reference. That is, in each Example and Comparative Example, the cell potential difference is the difference between the cell voltage obtained by the experiment and the cell voltage of Comparative Example 3. When the electrolysis efficiency is improved compared to Comparative Examples 1 and 3, it is indicated as "-" and when it is worsened, it is indicated as "+". The electrolysis efficiency can be calculated using the following formula. In Tables 1 and 2, the electrolysis efficiency is expressed as the cell voltage. That is, the electrolysis efficiency and the cell voltage are proportional. Electrolysis efficiency = cell voltage × 2.39

[0123] The anode and diaphragm were different in each example and comparative example. A plain-woven mesh-type porous electrode (with a catalyst layer) made of 0.15 mm diameter nickel fine wire woven into 40 meshes was used as the cathode. A conductive cushion mat made of 0.15 mm nickel wire woven into a fabric and then corrugated was used as the conductive elastic body. A nickel expand metal was used as the current collector, with a mesh center-to-center distance in the long direction (LW) of 4.5 mm, a mesh center-to-center distance in the short direction (SW) of 3 mm, and a thickness of 1.2 mm. An aqueous NaOH solution or an aqueous KOH solution was used as the electrolyte. The smaller measured value of these electrolytes was used to determine the electrolysis efficiency.

[0124] [Distance between the contact end of the diaphragm and the electrode and the contact end of the diaphragm and the gasket] The test was conducted by changing the distance between the end of the first electrode on the outer frame side that contacts the diaphragm and the end of the gasket that sandwiches the diaphragm and is closest to the first electrode. The distance was measured with a vernier caliper or a ruler. If design drawings are available, it can be assumed that the product was manufactured at the angle specified on the drawings.

[0125] [Angle of inclined portion relative to the surface of the diaphragm] The anode as the first electrode includes inclined portions at both ends that are inclined from the other portions. Tests were conducted by changing the angle of the inclined portions relative to the surface of the diaphragm on the inclined portion side. Referring to Figure 3, the flat surface of the electrode in the cross section is used as a reference, and the angle θ between this flat surface and the straight portion of the electrode end is measured with an angle measuring device. If design drawings are available, it is assumed that the electrode is manufactured at the angle specified on the drawings.

[0126] [Anode catalyst layer] In Table 1 described later, when "Yes" is displayed, the anode as the first electrode has a catalyst layer formed of a nickel compound on the surface. When "No" is displayed, no catalyst layer is present on the surface of the anode.

[0127] [Bending Rigidity of First Electrode] Tests were conducted by changing the bending rigidity of the anode as the first electrode. Specifically, a compression test was conducted using a three-point bending tester. The three-point bending tester was an autograph (AG-XPlus, manufactured by Shimadzu Corporation). A stress-strain diagram (horizontal axis: strain ε [%], vertical axis: stress σ [MPa]) was drawn, and the slope (i.e., Young's modulus E [MPa]) in the elastic region (strain ε in the range of 0.1 to 0.4%) was calculated. Thereafter, the second moment of area I was calculated from the test piece thickness h [mm] and test piece width b [mm], and the bending rigidity EI [N mm ２ ] was calculated.

[0128] The test piece width b was 25 mm. The distance between supports L during the bending test was 50 mm. The test piece thickness h varied depending on the type of test piece, and in this case was either 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, or 2.0 mm. The compression speed was 2 mm / min.

[0129] More specifically, the distance between the supports during the bending test is L [mm]. The load applied to the center of the test piece from the three-point bending tester is P [N]. The stress σ generated in the test piece is expressed by the following formula.

[0130] If the deflection of the test piece is w [mm], then from the beam calculation formula for the case of simply supported at both ends and concentrated load, By transforming this formula, This becomes:

[0131] From Hooke's law, σ=Eε. Transforming this equation, Substituting the formulas 1 and 3 into σ and E on the right-hand side, we get This becomes:

[0132] The flexural modulus (Young's modulus) E is expressed by the following formula: σ １ is the strain ε １ = 0.1%. ２ is the strain ε ２ = 0.4%.

[0133]

[0134] A comparison of Examples 1 to 7 with Comparative Example 1, and a comparison of Examples 8 to 11 with Comparative Examples 2 to 5, showed that when the contact rate between the diaphragm and the first electrode was 15% or more and 60% or less, and the region in which the local stress between the diaphragm and the first electrode was 0.1 MPa or more was 5% or less, the electrolysis efficiency corresponding to the cell voltage difference was maintained at the same level or higher, while the resistance to differential pressure fluctuations was improved. The contact rate and the aperture rate differ when performing electrolysis in a zero-gap cell, and therefore it is better to define the aperture rate in terms of the contact rate. It is sometimes asserted that "if the aperture rate is too small, gas becomes difficult to separate from the electrode, resulting in a deterioration in electrolysis efficiency." However, in reality, in a zero-gap cell, gas generated on the electrode surface is desorbed from the interface between the electrode and the diaphragm, and therefore the contact rate between the electrode and the diaphragm is important.

[0135] A comparison of Examples 1-3 and 7 with Examples 5-6, and a comparison of Examples 8-9 and 11 with Example 10, showed that the resistance to differential pressure fluctuations was further improved when the distance between the end of the first electrode on the outer frame side that is in contact with the diaphragm and the end of the first electrode that is closest to the first electrode and sandwiches the diaphragm between the gaskets was 7 mm or less. A distance of 5 mm or less is more preferable.

[0136] A comparison of Examples 1 to 3 and 7 with Examples 4 to 6, and a comparison of Examples 8 to 9 and 11 with Example 10, showed that the resistance to differential pressure fluctuations was further improved when the first electrode included, at least at one end thereof, an inclined portion that was inclined from the other portion, and the inclined portion extended at an angle greater than 30° and not greater than 180°, particularly 90°, with respect to the surface of the diaphragm facing the inclined portion.

[0137] A comparison of Examples 1, 2, and 5 with Examples 3, 4, 6, and 7 and Comparative Example 1, and a comparison of Example 8 with Examples 9 to 11 and Comparative Examples 2 to 5, all showed that the electrolysis efficiency was improved when the anode serving as the first electrode had a catalytic layer formed of a nickel compound on the surface.

[0138] The electrolytic cell of this embodiment can provide an electrolytic cell, electrolytic cell, and hydrogen production method that achieve both high resistance to differential pressure fluctuations and high electrolysis efficiency. The electrolytic cell of this embodiment can be used, for example, as an electrolytic cell for alkaline water electrolysis. The present invention can provide an electrolytic cell, electrolytic cell, and hydrogen production method that achieve both high resistance to differential pressure fluctuations and high electrolysis efficiency.

[0139] REFERENCE SIGNS LIST 1 Partition wall 1r1, 1r2 Rib 2 Electrode 2a Anode 2a1 End 2at Inclined portion 2c Cathode 2ct1 Inclined portion 2ct2 Folded portion 2cr Folded portion 2e Conductive elastic body 2r Current collector 3 Outer frame 4 Diaphragm 5 Electrode chamber 5a Anode chamber 5c Cathode chamber 7 Gasket 7f End 7a Anode side gasket portion 7c Cathode side gasket portion 50 Electrolytic cell 51a Anode terminal element 51c Cathode terminal element 51g1 Fast head 51g2 Loose head 51i1 Insulating plate 51i2 Insulating plate 51r Tie rod system 60 Bipolar element 65 Electrolytic cell

Claims

1. An electrolytic cell including elements each including an anode chamber equipped with an anode, a cathode chamber equipped with a cathode, a conductive partition wall provided between the anode chamber and the cathode chamber, and an outer frame that borders the conductive partition wall, wherein the electrolytic cells are stacked with a gasket and a diaphragm sandwiched between them, and an electrolytic solution is sealed by applying surface pressure between the gasket and the diaphragm and between the gasket and the outer frame, the contact rate between the diaphragm and a first electrode that is at least one of the anode and the cathode is 15% or more and 60% or less, and the area between the diaphragm and the first electrode where the local stress is 0.1 MPa or more is 5% or less.

2. The electrolytic cell according to claim 1, wherein the distance between the end of the first electrode on the outer frame side that is in contact with the diaphragm and the end of the first electrode that is closest to the first electrode and sandwiches the diaphragm between the gaskets is 7 mm or less.

3. The electrolytic cell according to claim 1 or 2, wherein the first electrode includes an inclined portion at at least one end thereof that is inclined from the other portion, and the inclined portion extends at an angle greater than 30° and not greater than 180° relative to the surface of the diaphragm on the inclined portion side.

4. The electrolytic cell according to claim 1 or 2, wherein the first electrode is the electrode having the greater rigidity of the anode and the cathode.

5. The bending rigidity of the first electrode is 10 kN mm ２ The electrolytic cell according to claim 1 or 2, wherein:

6. The electrolytic cell according to claim 1 or 2, wherein the first electrode has a catalyst layer formed of a nickel compound on the surface thereof.

7. The electrolytic cell according to claim 1 or 2, wherein the diaphragm is a porous membrane.

8. The electrolytic cell according to claim 1 or 2, wherein the diaphragm is an ion exchange membrane.

9. An electrolytic cell comprising the electrolytic cell according to claim 1 or 2, wherein the electrolytic cells are stacked with the gasket and the diaphragm sandwiched between them, and surface pressure is applied between the gasket and the diaphragm and between the gasket and the outer frame to seal in the electrolyte.

10. An electrolytic cell comprising the electrolytic cell according to claim 1 or 2, wherein the diaphragm divides the interior of the partition wall into an anode chamber and a cathode chamber.

11. A method for producing hydrogen using the electrolytic cell according to claim 9, comprising the steps of: bringing an electrolyte into contact with the anode and the cathode of the electrolytic cell; and passing a current through the anode and the cathode to generate hydrogen from the cathode.

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