Electrolytic cell and electrolytic device

Abstract

To provide an electrolytic cell and an electrolytic device which are capable of reducing temperature variations.SOLUTION: An electrolytic cell includes: a support having air permeability; and elements which include an electrolyte isolating two electrodes. Three or more elements are arranged side by side on the support. The plurality of elements are electrically connected in series. When the number of the elements is divided equally into three parts, and the elements are divided into a central portion and two end portions on both sides of the central portion in the direction in which the elements are arranged, an average of the area of the elements in at least one of the two end portions is smaller than an average of the area of the elements in the central portion.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrolytic cell and an electrolytic device in which an element part containing an electrolyte is arranged to separate two electrodes. [Background technology]

[0002] An electrolytic cell comprises a breathable support and an element section containing an electrolyte that separates two electrodes, with the element sections arranged side by side on the support, and electrolyzes fuel gas in the element section to which a voltage is applied, synthesizing energy carriers such as hydrogen and hydrocarbons (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-72892 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an electrolytic cell in which a voltage is applied to the element parts, heat dissipation from the center in the direction in which the element parts are arranged is less than that from the ends located on either side of the center. This means that the temperature in the center tends to rise, which poses the problem of temperature variations easily occurring that affect the durability of the electrolytic cell.

[0005] The present invention has been made to solve this problem, and has an object to provide an electrolytic cell and an electrolytic apparatus capable of reducing temperature variations. [Means for solving the problem]

[0006] A first aspect for achieving this object is an electrolytic cell comprising an air-permeable support and an element portion containing an electrolyte separating two electrodes, in which three or more element portions are arranged in a row on the support, and the plurality of element portions are electrically connected in series, wherein when the number of element portions is divided into thirds and the element portions are divided into a central portion and two end portions located on either side of the central portion in the direction in which the element portions are arranged, the average area of ​​the element portions at least at one of the two end portions is smaller than the average area of ​​the element portions in the central portion.

[0007] In a second embodiment, in the first embodiment, the average area of ​​the element portion at the two ends is smaller than the average area of ​​the element portion at the center.

[0008] A third aspect is the first or second aspect, wherein the average area of ​​the element portion at the end portion is 40% or more of the average area of ​​the element portion at the central portion.

[0009] In a fourth aspect, in any one of the first to third aspects, the average area of ​​the element portion at the end portion is 97% or less of the average area of ​​the element portion at the central portion.

[0010] A fifth aspect is an electrolysis device comprising an electrolysis cell according to any one of the first to fourth aspects, a power source that passes a current through a circuit connected to the electrodes, and an adjustment unit that adjusts the output of the power source, wherein the adjustment unit sets the average voltage of the central portion to a voltage lower than the thermal neutral point where heat absorption and heat generation are balanced in the electrolysis cell set to a predetermined temperature, and sets the average voltage of at least one end portion to a voltage higher than the thermal neutral point. Effect of the Invention

[0011] According to the present invention, when the number of element parts included in the electrolysis cell is divided into three equal parts, a central part and two end parts located on both sides of the central part in the stacking direction, the average area of ​​the element parts at the end parts is smaller than the average area of ​​the element parts at the central part. Since the element parts are connected in series, the same current flows through the end parts and the central part, and the current density of the element parts at the central part can be made smaller than the current density of the element parts at the end parts. Since the Joule heat at the central part can be made smaller than the Joule heat at the end parts, the temperature rise at the central part, which dissipates less heat than the end parts, can be reduced, and the temperature variation of the electrolysis cell can be reduced. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view of an electrolysis module in which electrolysis cells are arranged in one embodiment. [Diagram 2] FIG. 1 is a cross-sectional view of an electrolysis cell. [Diagram 3] 1 is a graph showing the current-voltage characteristics and heat generation characteristics of an electrolysis cell. [Figure 4] FIG. 2(a) is a schematic diagram of an electrolytic cell, and FIG. 2(b) is a schematic diagram of an electrolytic cell in a modified example. [Diagram 5] FIG. 1 is a block diagram of an electrolysis device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view of an electrolysis module 10 in which an electrolysis cell 20 is arranged in one embodiment. The electrolysis module 10 includes a cylindrical electrolysis cell 20 extending along an axis, a manifold 11 connected to one end of the electrolysis cell 20, a manifold 12 connected to the other end of the electrolysis cell 20, and a plurality of supports 13 that support the manifolds 11 and 12 together.

[0014] A plurality of electrolytic cells 20 (ten in this embodiment) are connected to the manifold 11, and fuel gas is supplied to each of the electrolytic cells 20 from the manifold 11. Examples of fuel gas include water vapor, carbon dioxide, and a mixture of these. A plurality of electrolytic cells 20 are connected to the manifold 12, and used fuel gas that has passed through each of the electrolytic cells 20 is supplied to the manifold 12. Sealing materials (not shown) that prevent leakage of fuel gas are arranged between the manifold 11 and the electrolytic cells 20, and between the manifold 12 and the electrolytic cells 20. The heat insulating material 14 reduces heat transferred from the electrolytic cells 20 to the manifolds 11 and 12.

[0015] One or more electrolysis modules 10 are disposed, for example, in a container (not shown) that houses the electrolysis module 10. A fuel gas flows inside the electrolysis cell 20 connected to the manifolds 11, 12, and an oxidant gas flows outside (inside the container) the electrolysis cell 20. Examples of the oxidant gas include air and oxygen.

[0016] The electrolysis cell 20 is a cylindrical horizontal stripe type solid oxide electrolysis cell. The electrolysis cell 20 includes a plurality of (three or more) element units 21 that electrolyze a fuel gas. The number of element units 21 provided in one electrolysis cell 20 is, for example, about 30 to 100 depending on the required output, but for ease of illustration, an electrolysis cell 20 provided with eight element units 21 is shown.

[0017] FIG. 2 is a cross-sectional view including the axis C of the electrolytic cell 20. FIG. 2 illustrates a portion of the electrolytic cell 20 on one side of the axis C. The axis C of the electrolytic cell 20 connects the manifold 11 and the manifold 12. The electrolytic cell 20 includes a cylindrical support 22 having gas permeability, and an element unit 21 is provided on the outer surface of the support 22. The element unit 21 includes, in this order from the outer surface of the support 22, a fuel electrode 23, an electrolyte 24, and a cathode 25. In FIG. 2, the thickness of the element unit 21 is exaggerated. The element units 21 are aligned along the axis C of the cylindrical support 22.

[0018] The support 22 is a member having no electronic conductivity, and an example of the material is stabilized zirconia. Examples of stabilizers for stabilized zirconia include CaO and MgO. Examples of the material for the fuel electrode 23 include a material containing a catalyst containing Ni and zirconia with Y dissolved therein, and a material containing a catalyst containing Ni and ceria with Gd dissolved therein. Examples of the catalyst include Ni, Ni-based alloys, and cermets that are composites (sintered bodies) of NiO and oxides (solid electrolytes).

[0019] The material of the electrolyte 24 is a solid oxide, and examples thereof include stabilized zirconia, ceria-based solid solution, and a solid solution of one or more selected from stabilized zirconia and ceria-based solid solution and alumina. Examples of stabilizers for stabilized zirconia include CaO, MgO, YO, ScO, and YbO. Examples of elements dissolved in ceria in the ceria-based solid solution include Gd, Sm, and Y.

[0020] The material of the cathode 25 is a perovskite oxide called La 1-X Sr X MnO 3-δ ,La 1-X Sr X Chief of Staff 3-δ ,La 1-X Sr X Co 1-Y Fe Y O 3-δ ,Pr 1-X Sr X MnO 3-δ Examples are given below.

[0021] The interconnector 26 connects the air electrode 25 and the fuel electrode 23 of the adjacent element units 21. The material of the interconnector 26 is conductive La 1-X Sr X TiO 3-δ The element sections 21 are connected in series by the interconnectors 26.

[0022] When the positive electrode of a power supply (not shown) is connected to the air electrode 25 and the negative electrode of the power supply is connected to the fuel electrode 23, electrons begin to flow toward the fuel electrode 23. The fuel gas that has passed through the support 22 is reduced at the fuel electrode 23. Since electrons are lost at the air electrode 25, oxide ions that have moved to the air electrode 25 via the electrolyte 24 are oxidized at the air electrode 25. As a result, energy carriers such as hydrogen and hydrocarbons are synthesized in the electrolysis cell 20.

[0023] 3 is a graph showing the current-voltage characteristics and heat generation characteristics of the electrolysis cell 20. Since the electrolysis of water vapor, carbon dioxide, and the like contained in the fuel gas is an endothermic reaction, the temperature of the element unit 21 (the temperature of the exhaust gas entering the manifold 12) decreases with an increase in current density compared to the temperature at the open circuit voltage of the element unit 21 at which current begins to flow (the average voltage of the element unit 21 when the current density is 0). When the current density increases further, the temperature of the element unit 21 begins to rise due to Joule heat, and reaches a thermal neutral point N where the heat absorption and heat generation are balanced.

[0024] At the thermal neutral point N, the electrolytic cell 20 neither generates nor absorbs heat, but when the current density of the element unit 21 becomes lower than the current density of the element unit 21 at the thermal neutral point N, heat absorption becomes predominant in the electrolytic cell 20, and the temperature decreases. When the current density of the element unit 21 becomes higher than the current density of the element unit 21 at the thermal neutral point N, heat generation becomes predominant in the electrolytic cell 20, and the temperature increases.

[0025] Returning to FIG. 1, the electrolytic cell 20 has element parts 21 arranged in the longitudinal direction of the support 22 (see FIG. 2). The electrolytic cell 20 is used in a state where the element parts 21 reach their operating temperature (for example, about 700°C). The element parts 21 dissipate more heat the closer they are to the manifolds 11, 12 (closer to the ends in the direction in which the element parts 21 are arranged), so their temperature is more likely to drop, and the element parts 21 dissipate less heat the farther they are from the manifolds 11, 12 (closer to the center in the direction in which the element parts 21 are arranged), so their temperature is more likely to rise. If any part of the electrolytic cell 20 has a higher temperature than necessary, the durability of the electrolytic cell 20 may be reduced.

[0026] FIG. 4(a) is a schematic diagram of an electrolytic cell 20 in which the element portion 21 of the electrolytic cell 20 is represented by lines (the same applies to FIG. 4(b) and FIG. 5). The length of the lines in the diagram indicates the size of the area of ​​the element portion 21. The area of ​​the element portion 21 refers to the area of ​​the portion where the electrolyte 24 (see FIG. 2), the fuel electrode 23, and the air electrode 25 overlap. The area of ​​the element portion 21 can be changed, for example, by changing the area of ​​the fuel electrode 23 or the air electrode 25. The positions of the lines in the diagram indicate the positions of the element portion 21 arranged on the support 22. In FIG. 4(a), an electrolytic cell 20 in which eight element portions 21 are arranged on the support 22 is illustrated as a set of eight lines.

[0027] The central portion 30 is a portion located in the center in the stacking direction when the number of element portions 21 included in the electrolytic cell 20 is divided into thirds and the element portions 21 are divided into three. The end portions 31 and 32 are portions located on both sides of the central portion 30 when the number of element portions 21 included in the electrolytic cell 20 is divided into thirds and the element portions 21 are divided into three. In this embodiment, the end portion 31 is located near the manifold 12 (see FIG. 1 ), and the end portion 32 is located near the manifold 11.

[0028] The method of dividing the number of element portions 21 into thirds and dividing the central portion 30 and the end portions 31 and 32 differs depending on whether the number of element portions 21 is a multiple of 3 or not. When the number of element portions 21 is a multiple of 3, the number of element portions 21 included in the central portion 30, the number of element portions 21 included in the end portions 31, and the number of element portions 21 included in the end portions 32 are equal.

[0029] When the number of element portions 21 is not a multiple of three, the number of element portions 21 is divided by three to obtain a quotient and a remainder, and then the remainder is allocated to the central portion 30 or the ends 31 and 32 so that the number of element portions 21 included in the end portion 31 is equal to the number of element portions 21 included in the end portion 32. The reason why the number of element portions 21 included in the end portion 31 is equal to the number of element portions 21 included in the end portion 32 is to fairly evaluate the areas of the element portions 21 included in the ends 31 and 32.

[0030] For example, when the remainder when the number of element portions 21 is divided by 3 is 1, the number of element portions 21 included in end portion 31 and the number of element portions 21 included in end portion 32 are each set to the quotient, and the number of element portions 21 included in central portion 30 is set to the quotient plus the remainder, 1. When the remainder when the number of element portions 21 is divided by 3 is 2, the number of element portions 21 included in central portion 30 is set to the quotient, and the number of element portions 21 included in end portion 31 and the number of element portions 21 included in end portion 32 are each set to the quotient plus 1.

[0031] 4(a) has eight element portions 21, so when eight is divided by three the quotient is two with a remainder of two. Therefore, the number of element portions 21 included in the central portion 30 is two, and the numbers of element portions 21 included in the end portions 31 and 32 are each three. The first three element portions 21 from the end are included in the end portions 31 and 32, and the two element portions 21 on the inside of the end portions 31 and 32 are included in the central portion 30.

[0032] In the electrolytic cell 20, the average area of ​​the element portions 21 at at least one of the ends 31, 32 is smaller than the average area of ​​the element portions 21 in the central portion 30. The area of ​​the element portions 21 at the end 31 of the electrolytic cell 20 gradually increases toward the central portion 30, and the area of ​​the element portions 21 at the end 32 also gradually increases toward the central portion 30. The areas of the element portions 21 in the central portion 30 are equal to each other. In this embodiment, the average area of ​​the element portions 21 at both the end portions 31, 32 is smaller than the average area of ​​the element portions 21 in the central portion 30.

[0033] Fig. 4(b) is a schematic diagram of an electrolytic cell 33 in a modified example. In Fig. 4(b), the electrolytic cell 33 in which six element portions 21 are arranged is illustrated as a set of six line segments. Since the number of element portions 21 is a multiple of three, the number of element portions 21 included in the central portion 30, the end portion 31, and the end portion 32 is two.

[0034] In the electrolytic cell 33, the average area of ​​the element portions 21 at the ends 31, 32 is smaller than the average area of ​​the element portions 21 at the central portion 30. The area of ​​the element portions 21 at the end 31 of the electrolytic cell 33 is smaller closer to the central portion 30, and the area of ​​the element portions 21 at the end 32 is also smaller closer to the central portion 30. The areas of the element portions 21 at the central portion 30 are equal to each other. In this embodiment, the average area of ​​the element portions 21 at both the ends 31, 32 is smaller than the average area of ​​the element portions 21 at the central portion 30.

[0035] Returning to FIG. 4(a), the explanation will be given. Since the element parts 21 of the electrolysis cell 20 are electrically connected in series, the same current flows through the element parts 21. Since the average area of ​​the element parts 21 at the ends 31, 32 is smaller than the average area of ​​the element parts 21 at the central part 30, the current density of the element parts 21 at the central part 30 is lower than the current density of the element parts 21 at the ends 31, 32. As a result, the temperature of the central part 30, which dissipates less heat and is more likely to rise in temperature than the ends 31, 32, can be reduced. This reduces the temperature variation between the ends 31, 32 and the central part 30. Since overheating of the central part 30 can be reduced, the durability of the electrolysis cell 20 can be ensured.

[0036] It is preferable that the average area of ​​the element portion 21 in at least one of the ends 31, 32 is 40% or more of the average area of ​​the element portion 21 in the central portion 30, because this can prevent the current density of the element portion 21 in at least one of the ends 31, 32 from becoming excessively large and reduce deterioration of the element portion 21 in at least one of the ends 31, 32. Furthermore, it is preferable that the average area of ​​the element portion 21 in at least one of the ends 31, 32 is 97% or less of the average area of ​​the element portion 21 in the central portion 30, because this can differentiate between heat generation of the element portion 21 in at least one of the ends 31, 32 and heat generation of the element portion 21 in the central portion 30.

[0037] 5 is a block diagram of the electrolysis device 40. The electrolysis device 40 includes the electrolysis cell 20, a power supply 41 that supplies current to the element section 21 of the electrolysis cell 20, and an adjustment section 43 that adjusts the output of the power supply 41. An ammeter 42 that measures the current flowing through the circuit is disposed in a circuit connected to the power supply 41. The power supply 41 outputs a unipolar pulsating current, pulse, or direct current to the circuit.

[0038] The electrolysis device 40 is equipped with a thermometer 44 that detects the temperature of the electrolytic cell 20. The thermometer 44 is disposed near the manifold 12 (see FIG. 1 ) and detects the temperature of the exhaust gas entering the manifold 12 as a representative value of the temperature of the electrolytic cell 20. However, this is not limited to this, and it is of course possible to dispose the thermometer 44 in a location other than the manifold 12 and detect a representative value of the temperature of the electrolytic cell 20.

[0039] The electrolysis device 40 includes a heater (not shown) that heats the electrolytic cell 20. There are no limitations on the heater as long as it can heat the electrolytic cell 20. Examples of the heater include a heater that heats the electrolytic cell 20 by heating the fuel gas or oxidant gas supplied to the electrolytic cell 20, and a heater that is disposed in a furnace that houses the electrolytic cell 20 in order to heat the electrolytic cell 20 from around the electrolytic cell 20.

[0040] The adjustment unit 43 includes a CPU, a ROM, a RAM, and a backup RAM (none of which are shown). The adjustment unit 43 acquires the current detected by the ammeter 42, and adjusts the output of the power source 41 so that the average temperature of the element unit 21 (the temperature of the electrolytic cell 20) becomes a temperature equivalent to the thermal neutral point N (see FIG. 3). Since the area of ​​the element unit 21 is known, the current to be passed through the electrolytic cell 20 in order to make the average temperature of the element unit 21 become a temperature equivalent to the thermal neutral point N is determined in advance. The adjustment unit 43 adjusts the output of the power source 41 so that the current detected by the ammeter 42 becomes equal to the previously determined current.

[0041] Instead of the adjustment unit 43 adjusting the output of the power source 41 so that the current detected by the ammeter 42 is equal to the pre-determined current, the adjustment unit 43 may obtain the temperature detected by the thermometer 44 and adjust the output of the power source 41 so that the average temperature of the element unit 21 (the temperature of the electrolytic cell 20) becomes a temperature equivalent to the thermal neutral point N. The adjustment unit 43 may use both of these.

[0042] In the electrolytic cell 20, the average area of ​​the element portions 21 included in the end portions 31, 32 is smaller than the average area of ​​the element portions 21 included in the central portion 30. Therefore, when a current flows through the electrolytic cell 20 such that the average temperature of the element portions 21 becomes a temperature corresponding to the thermal neutral point N, the average voltage of the element portions 21 included in the central portion 30 becomes lower than the voltage corresponding to the thermal neutral point N. In addition, the average voltage of the element portions 21 included in the end portions 31, 32 becomes higher than the voltage corresponding to the thermal neutral point N.

[0043] As a result, the temperature of the element portion 21 included in the central portion 30 becomes lower than the temperature corresponding to the thermal neutral point N, and the temperature of the element portion 21 included in the end portions 31 and 32 becomes higher than the temperature corresponding to the thermal neutral point N. This allows the activation overvoltage of the end portions 31 and 32 to be lower than the activation overvoltage of the central portion 30. As a result, the end portions 31 and 32 can synthesize energy carriers more efficiently than the central portion 30 with respect to the energy input from the power source 41 to the electrolysis cell 20. Furthermore, since the temperature of the element portion 21 included in the central portion 30 is lower than the temperature corresponding to the thermal neutral point N, even if the heat dissipation of the central portion 30 is less than the heat dissipation of the end portions 31 and 32, the temperature variation between the central portion 30 and the end portions 31 and 32 can be reduced. This allows the deterioration of the durability of the electrolysis cell 20 caused by a part of the electrolysis cell 20 becoming high temperature to be reduced.

[0044] Since the electrolysis device 40 performs electrolysis near the current density of the element section 21 corresponding to the thermal neutral point N, the temperature of the element section 21 can be maintained even with little new energy input. Therefore, the electrolysis efficiency can be ensured. Furthermore, the durability of the element section 21 can be improved because the temperature change of the element section 21 can be reduced.

[0045] The present invention has been described above based on an embodiment, but the present invention is in no way limited to the above embodiment, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention without departing from the spirit of the present invention.

[0046] In the embodiment, the electrolytic cell 20 in which eight element parts 21 are stacked and the electrolytic cell 33 in which six element parts 21 are stacked are described, but the present invention is not necessarily limited to this. The number of element parts 21 is appropriately set according to the required characteristics of the electrolytic cell. However, since the number of element parts 21 is divided into three equal parts to partition the element parts 21 into three parts, the number of element parts 21 is three or more.

[0047] The size relationship of the areas of the element portions 21 at the ends 31, 32 and at the central portion 30 described in the embodiment is merely an example. It is sufficient that the average area of ​​the element portions 21 included in the end portion 31 and the average area of ​​the element portions 21 included in the end portion 32 are set to be larger than the average area of ​​the element portions 21 included in the central portion 30.

[0048] Although not explained in the embodiment, when the average area of ​​the element portions 21 at one of the ends 31, 32 is smaller than the average area of ​​the element portions 21 at the central portion 30, the average area of ​​the element portions 21 at the other of the ends 31, 32 may be the same as the average area of ​​the element portions 21 at the central portion 30 or may be larger than the average area of ​​the element portions 21 at the central portion 30.

[0049] In the embodiment, the electrolytic cells 20 and 33 have a cylindrical horizontal stripe cell design having a cylindrical support 22, but this is only an example, and the shape of the support 22 is not limited to a cylindrical shape. Other shapes of the support 22 include a flattened cylindrical shape obtained by flattening a cylinder, and a flat plate shape having a cavity. The electrolytic cells 20 and 33 may be configured such that the horizontal stripe element units 21 arranged side by side on the support 22 are connected in series.

[0050] In the embodiment, the electrolyte 24 having oxide ion conductivity is used, but the present invention is not necessarily limited to this. It is of course possible to use an electrolyte 24 having proton conductivity under the operating conditions of the element section 21. Examples of substances that exhibit proton conductivity under the operating conditions of the element section 21 include perovskite-type oxides such as BaZrO3 in which the B site is substituted with trivalent metal ions such as Y or In, pyrochlore-type oxides, and phosphates. [Explanation of symbols]

[0051] 20,33 Electrolysis cell 21 Element section 22 Support 23 Fuel electrode (electrode) 24 Electrolytes 25 Air pole (electrode) 30 Central part 31,32 End 40 Electrolyzer 41 Power supply 43 Adjustment part

Claims

1. A breathable support; an element portion including an electrolyte separating the two electrodes; An electrolysis cell in which three or more of the element units are arranged side by side on the support, and a plurality of the element units are electrically connected in series, An electrolytic cell in which, when the number of element portions is divided into thirds and the element portions are partitioned into a central portion and two end portions located on either side of the central portion in the direction in which the element portions are arranged, the average area of ​​the element portions in at least one of the two end portions is smaller than the average area of ​​the element portions in the central portion.

2. 2. The electrolysis cell according to claim 1, wherein an average area of ​​the element portions at the two ends is smaller than an average area of ​​the element portions at the central portion.

3. 3. The electrolysis cell according to claim 1, wherein an average area of ​​the element portions at the end portions is 40% or more of an average area of ​​the element portions at the central portion.

4. 3. The electrolytic cell according to claim 1, wherein an average area of ​​the element portions at the end portions is 97% or less of an average area of ​​the element portions at the central portion.

5. The electrolytic cell according to claim 1 or 2; A power source that applies a current to a circuit connected to the electrodes; An adjustment unit that adjusts the output of the power source, The adjustment unit sets the average voltage of the central portion to a voltage lower than a thermal neutral point where heat absorption and heat generation are balanced in the electrolytic cell, which is set to a predetermined temperature, and sets the average voltage of at least one of the ends to a voltage higher than the thermal neutral point.

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