Oxygen electrode current collector for proton-conducting solid oxide electrochemical cells and proton-conducting solid oxide electrochemical cells

Abstract

We provide a low-cost oxygen electrode current collector that exhibits high electrical conductivity and can be used in proton-conducting solid oxide electrochemical cells. [Solution] The oxygen electrode current collector for a proton-conducting solid oxide electrochemical cell comprises a conductive substrate and a metal oxide film provided on the surface of the conductive substrate, which exhibits higher electrical conductivity than the electrical conductivity of the conductive substrate when exposed to water vapor in the operating environment of the proton-conducting solid oxide electrochemical cell.

Description

Technical Field

[0001] Embodiments of the present invention relate to an oxygen electrode current collector for a proton-conducting solid oxide type electrochemical cell and a proton-conducting solid oxide type electrochemical cell.

Background Art

[0002] As one of new energies, hydrogen can be mentioned. As a field of use of this hydrogen, a fuel cell that can convert chemical energy into electrical energy by electrochemically reacting hydrogen and oxygen has attracted attention. Since the fuel cell has high energy utilization efficiency, development is underway as a large-scale distributed power source, a household power source, and a mobile power source. Fuel cells are classified according to the temperature range and the types of materials and fuels used. When classified according to the electrolyte material used, it is divided into a solid polymer type, a phosphoric acid type, a molten carbonate type, and a solid oxide type. From the viewpoint of efficiency, the solid oxide type using a solid oxide electrolyte has attracted attention. Among solid oxide electrolytes, they are roughly classified into two types: oxide ion-conducting type and proton-conducting type depending on the ion conduction species. The temperature range in which the ionic conductivity becomes high differs depending on the ion conduction species, and it is 600 to 1000 ° C for oxide ion-conducting solid oxides and 400 to 600 ° C for proton-conducting solid oxides. Electrochemical cells using oxide ion-conducting solid oxides as electrolytes and electrochemical devices equipped with them have a problem that the constituent members become expensive because the operating temperature range is high. On the other hand, an electrochemical cell using a proton-conducting solid oxide as an electrolyte is expected to reduce the cost of the constituent members.

[0003] A proton-conducting solid oxide electrochemical cell stack is a stacked structure formed by stacking proton-conducting solid oxide electrochemical cells to increase capacity. The functions of the stack include supplying oxidizing and reducing gases to both electrodes of the proton-conducting solid oxide electrochemical cells and having conductive parts for conducting electricity. To achieve these functions, components other than the electrochemical cells of the cell stack include gasket sealing materials to prevent gas leakage to the outside, interconnects to isolate oxidizing and reducing gases without mixing them, and current collectors to maintain good contact between the proton-conducting solid oxide electrochemical cells and the conductive parts.

[0004] Current collectors include hydrogen electrode current collectors, which are positioned in contact with the hydrogen electrode of a proton-conducting solid oxide electrochemical cell, and oxygen electrode current collectors, which are positioned in contact with the oxygen electrode of a proton-conducting solid oxide electrochemical cell. Both hydrogen electrode current collectors and oxygen electrode current collectors have pores for gas passage, have electrical conductivity, and preferably have cushioning properties to reduce contact resistance between the proton-conducting solid oxide electrochemical cell and the current collector. Of the two types of current collectors, oxygen electrode current collectors in particular have the problem of high electrical resistance, such as contact resistance. As an example of application to electrochemical cells in a temperature range slightly higher than the operating temperature range of the proton-conducting solid oxide electrochemical cell, an example is known in which a columnar conductive path is formed between the electrochemical cell and the interconnector. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-121160 [Patent Document 2] Japanese Patent Publication No. 2019-121567 [Patent Document 3] Japanese Patent Publication No. 2015-060643 [Patent Document 4] Japanese Patent Publication No. 2007-234590 [Patent Document 5] Japanese Patent Publication No. 2002-298861 [Non-patent literature]

[0006] [Non-Patent Document 1] Hiromichi Arai, "Humidity Sensor," Electrochemistry, The Electrochemical Society of Japan, Vol. 50, No. 1, 1982, pp. 38-45. [Overview of the project] [Problems that the invention aims to solve]

[0007] Hydrogen electrode current collectors are less susceptible to oxidation under operating conditions because reducing gases such as hydrogen flow through them during electrochemical cell operation, resulting in a wide range of candidate materials. On the other hand, oxygen electrode current collectors are more susceptible to oxidation under operating conditions because oxidizing gases flow through them during electrochemical cell operation, and the operating environment is high-temperature. Metals that are less susceptible to oxidation under operating conditions include silver (Ag), gold (Au), and platinum (Pt), but these are all expensive precious metals. Using such precious metals to manufacture current collectors increases the cost of the current collector.

[0008] The problem that this invention aims to solve is to provide a low-cost oxygen electrode current collector that exhibits high electrical conductivity and can be used in proton-conducting solid oxide electrochemical cells. [Means for solving the problem]

[0009] The oxygen electrode current collector for a proton-conducting solid oxide electrochemical cell of this embodiment comprises a conductive substrate and a metal oxide film provided on the surface of the conductive substrate, which exhibits higher electrical conductivity than the electrical conductivity of the conductive substrate when exposed to water vapor in the operating environment of the proton-conducting solid oxide electrochemical cell. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an example of the structure of an electrochemical cell stack. [Figure 2]It is a schematic diagram showing a structural example of an oxygen electrode current collector. [Figure 3] It is a schematic diagram showing a structural example of an oxygen electrode current collector. [Figure 4] It is a schematic diagram showing a structural example of an oxygen electrode current collector. [Figure 5] It is a schematic diagram for explaining an evaluation method of electrical characteristics in an embodiment. [Figure 6] It is a schematic diagram for explaining an evaluation method of electrical characteristics in an embodiment. [Figure 7] It is a diagram showing the results of electrical resistance measurement.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described with reference to the drawings. In each of the embodiments shown below, substantially the same constituent parts are denoted by the same reference numerals, and the description thereof may be partially omitted. The drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thicknesses of each part, etc. may be different from the actual ones.

[0012] In this specification, "connect" includes not only directly connecting but also indirectly connecting unless otherwise specified.

[0013] FIG. 1 is a schematic diagram showing a structural example of an electrochemical cell stack. FIG. 1 shows an electrochemical cell stack 10. The electrochemical cell stack 10 is a proton-conducting solid oxide type electrochemical cell stack.

[0014] The electrochemical cell stack 10 includes an electrochemical cell 11, a current collector 16, a current collector 17, and an interconnector 18. The electrochemical cell 11 is a proton-conducting solid oxide type electrochemical cell. Fig. 1 shows a structure in which two electrochemical cells 11 are stacked via an interconnector 18. However, the number of stacked electrochemical cells 11 is not particularly limited, and it may have a structure in which three or more electrochemical cells 11 are stacked. When stacking three or more electrochemical cells 11, an interconnector 18 is disposed between each adjacent pair of electrochemical cells 11, and each electrochemical cell 11 is electrically connected by the interconnector 18. By stacking a plurality of electrochemical cells 11, the capacity of the electrochemical cell stack 10 can be increased.

[0015] The electrochemical cell 11 includes an electrode 13 that functions as a hydrogen electrode (fuel electrode), an electrode 14 that functions as an oxygen electrode (air electrode), and a solid oxide electrolyte 15 disposed between the electrode 13 and the electrode 14.

[0016] The electrode 13 and the electrode 14 are each formed of a porous electric conductor. The solid oxide electrolyte 15 is made of a proton-conducting oxide and is an ion conductor that does not conduct electricity.

[0017] The current collector 16 is a hydrogen electrode current collector for a proton-conducting solid oxide type electrochemical cell. The current collector 16 is disposed between the electrode 13 and the interconnector 18.

[0018] The current collector 17 is an oxygen electrode current collector for a proton-conducting solid oxide type electrochemical cell. The current collector 17 is disposed between the electrode 14 and the interconnector 18.

[0019] The current collector 16 and the current collector 17 are porous, and can improve the electrical connection between the electrochemical cell 11 and the interconnector 18 while allowing the reaction gas to pass through.

[0020] In the electrochemical cell 11, air, oxygen, and water vapor flow as gases towards the electrode 14 side, contributing to the electrochemical reaction. The current collector 17 is permeable and can supply gases such as air, oxygen, and water vapor to the electrode 14. Similarly, across the interconnector 18, nitrogen and hydrogen flow to the electrode 13 side of the electrochemical cell 11 via a permeable current collector 16, causing an electrochemical reaction. When the electrochemical cell stack 10 is used as an electrochemical cell such as an SOEC applying high-temperature steam electrolysis, water vapor is supplied to the electrode 13, which serves as the hydrogen electrode.

[0021] Figures 2, 3, and 4 are schematic diagrams showing examples of the structure of an oxygen electrode current collector. Figures 2, 3, and 4 show examples of the structure of current collector 17.

[0022] The current collector 17 comprises a conductive substrate 171 and a metal oxide film 172. The current collector 17 exhibits high electrical conductivity in the operating environment of the electrochemical cell 11 by coating the surface of the conductive substrate 171 with a metal oxide that improves electrical conductivity under a high-temperature water vapor atmosphere. The operating temperature of the electrochemical cell 11 is, for example, 300°C to 800°C, preferably 400°C to 700°C. The water vapor concentration in the water vapor atmosphere of the operating environment of the electrochemical cell 11 is, for example, 50% by volume to 99% by volume, preferably 80% by volume to 95% by volume.

[0023] The conductive substrate 171 is a porous conductor through which gases such as water vapor can pass. The shape of the conductive substrate 171 is not particularly limited. Examples of conductive substrates 171 include porous bodies with uniformly distributed pores, such as sponges; laminates formed by stacking multiple members having multiple openings, such as meshes; and fibrous bodies formed by weaving multiple fibers together. The conductive substrate 171 is provided between the electrode 13 and the interconnector 18. The conductive substrate 171 is, for example, porous and can improve the electrical connection between the electrochemical cell 11 and the interconnector 18 while allowing reaction gases to pass through. Examples of materials for the conductive substrate 171 include metallic materials such as silver, gold, and platinum.

[0024] The metal oxide film 172 has a surface that exhibits higher electrical conductivity than the conductive substrate 171 when exposed to water vapor in the operating environment of a proton-conducting solid oxide electrochemical cell. The reason why the metal oxide film 172 exhibits high electrical conductivity in a high-temperature water vapor atmosphere is that current flows more easily through the surface of the metal oxide film 172 in a water vapor atmosphere. Some metal oxides are known to have the property that their electrical resistance decreases at room temperature, such as 25°C, and at high humidity. For example, chromium oxide (Cr2O3) 、 Metal oxides such as iron oxide (Fe2O3), tin oxide (SnO2), zinc oxide (ZnO), aluminum oxide (Al2O3), and titanium oxide (TiO2) are used as humidity-sensing elements in hygrometers because their electrical resistance is highly dependent on humidity. For example, Fe2O3·K2O has an electrical resistance of 10 when the relative humidity is changed from 0% to 80%. 7 Ω to 10 2 It is known that the conductivity can decrease to Ω. When a metal oxide is left in a water vapor atmosphere, hydroxyl groups are formed on the surface, and water molecules are adsorbed onto the surface by the bonding of these hydroxyl groups with water molecules. The adsorbed water can improve the electrical conductivity of the surface. Therefore, even a metal oxide, which is an insulator, can exhibit high electrical conductivity on its surface. If the conductive substrate 171 is a fibrous material, the metal oxide film 172 may be provided on the surface of each fiber of the fibrous material.

[0025] The current collector 17 is operated by applying a load and pressing it against the electrochemical cell 11 to reduce the electrical contact resistance. Since the electrochemical cell 11 is fragile, it is preferable that the current collector 17 has cushioning properties that allow it to deform under load. From the viewpoint of electrical resistance and cost, it is preferable that the current collector 17 is made of a single material, but it may be made of multiple materials for reasons such as improving cushioning properties.

[0026] The current collector 17 preferably has a structure that facilitates electrical conductivity on its surface because the surface of the metal oxide film 172 has high electrical conductivity. The current collector 17 preferably has a large area in the direction perpendicular to the surface (upper or lower surface) of each layer of the electrochemical cell 11 (for example, in the thickness direction of the electrochemical cell 11), and preferably the surface of the conductive substrate 171 perpendicular to the surface of the electrochemical cell 11 is coated with a metal oxide film 172 that improves conductivity. The surface of the current collector 17 perpendicular to the surface (upper or lower surface) of each layer of the electrochemical cell 11 is preferably continuous from the electrochemical cell 11 to the interconnector 18, but even if it is not continuous, a high effect can be obtained. The surface length of the metal oxide film 172 may be greater than the thickness of the conductive substrate 171, and if it is 15 times or less the thickness of the conductive substrate 171, a sufficient effect of improving the electrical conductivity of the surface of the metal oxide film 172 in the high-temperature water vapor atmosphere of the operating environment of the electrochemical cell 11 can be obtained. The thickness of the conductive substrate 171 represents the shortest distance of the conductive path passing through the conductive member 171. The surface length of the metal oxide film 172 can be defined, for example, by the shortest distance of the conductive path across the surface of the metal oxide film 172, from the interface (contact surface) between the metal oxide film 172 and the electrode 14 to the interface (contact surface) between the metal oxide film 172 and the interconnector 18. In other words, the surface length of the metal oxide film 172 can be defined, for example, by the shortest distance of the conductive path across the surface of the metal oxide film 172, from the first surface of the current collector 17 that can contact the electrode 14 to the second surface of the current collector 17 that can contact the interconnector 18.

[0027] The metal oxide film 172 preferably contains a metal oxide comprising at least one metal element selected from the group consisting of aluminum, zirconium, zinc, chromium, cobalt, magnesium, iron, titanium, nickel, copper, lead, vanadium, tungsten, cerium, and niobium. The metal oxide film 172 is preferably formed using a metal oxide that has high electrical conductivity on its surface in a water vapor atmosphere. Examples of such metal oxides include aluminum oxide, zirconium oxide, zinc chromium oxide, cobalt oxide, magnesium oxide, iron oxide, titanium oxide, nickel oxide, copper oxide, zinc oxide, vanadium oxide, tungsten oxide, cerium oxide, and niobium oxide. The metal oxide may also be a composite oxide such as cobalt nickel oxide. These metal oxides are a group of oxides that exhibit surface electrical conductivity at room temperature, such as 25°C, and in an atmosphere with a high water vapor concentration. It is also useful to add additive elements to these oxides according to the temperature and atmosphere. Examples of added elements include adding elements in combination with the metal elements shown above, or adding compounds (including oxides and salts) containing elements such as alkali metals (Li, Na, K, Rb, Cs, Fr) and alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra). In some cases, multiple metal groups may be selected.

[0028] The metal oxide film 172 may be formed on the surface of the bulk conductive substrate 171, as shown in Figure 2. Figure 2 shows an example in which the metal oxide film 172 is formed on the side surface 171a of the conductive substrate 171, but is not limited to this, and the metal oxide film 172 may be formed not only on the side surface 171a of the conductive substrate 171, but also on at least one surface of the upper surface 171b facing or in contact with the interconnector 18, or the lower surface 171c facing or in contact with the electrode 14. The metal oxide film 172 may extend continuously from the interconnector 18 to the electrode 14 to connect the interconnector 18 and the electrode 14.

[0029] The metal oxide film 172 may be formed continuously along the surface of the pores S formed in the porous conductive substrate 171, as shown in Figure 3. Figure 3 shows an example in which the metal oxide film 172 is formed continuously on the side surface 171a of the conductive substrate 171 and the inner wall surface of the pores S of the conductive substrate 171, but is not limited to this, and each metal oxide film 172 may be formed not only on the side surface 171a and the inner wall surface of the pores S of each conductive substrate 171, but also on at least one surface of the upper surface 171b facing or in contact with the interconnector 18 and the lower surface 171c facing or in contact with the electrode 14. The metal oxide film 172 may extend continuously from the interconnector 18 to the electrode 14 to connect the interconnector 18 and the electrode 14. By forming the metal oxide film 172 on the inner wall surface of the pores S, the surface area of ​​the metal oxide film 172 can be increased, and the electrical conductivity of the surface of the metal oxide film 172 can be improved.

[0030] The metal oxide film 172 may be formed discontinuously along the surface containing pores S formed on the porous conductive substrate 171, as shown in Figure 4. Figure 4 shows an example in which the metal oxide film 172 is formed discontinuously on the side surface and the inner wall surface of the pores S of the conductive substrate 171, but is not limited to this. The metal oxide film 172 may be formed not only on the side surface and pores S of the conductive substrate 171, but also on at least one surface of the upper surface 171b facing the interconnector 18 and the lower surface 171c facing the electrode 14. The pores S may be formed on at least one surface of the upper surface 171b and the lower surface 171c. The metal oxide film 172 may extend continuously from the interconnector 18 to the electrode 14 to connect the interconnector 18 and the electrode 14. By forming the metal oxide film 172 on each surface of the pores S, the surface area of ​​the metal oxide film 172 can be increased, and the electrical conductivity of the surface can be improved.

[0031] The thickness of the metal oxide film 172 is less than or equal to the thickness of the conductive substrate 171. The thickness of the conductive substrate 171 is preferably, for example, 1 mm or more and 300 mm or less. The thickness of the conductive substrate 171 can be defined, for example, by the distance from the electrode 14 to the interconnector 18 (the height of the space occupied by the conductive member 171). The thickness of the metal oxide film 172 should be such that it exhibits electrical conductivity on the surface under a water vapor atmosphere, and is preferably, for example, 1 nm or more. Since metal oxides are harder and more brittle than metals, in order to provide cushioning, it is preferable that the thickness of the conductive substrate 171 be 50% or more of the thickness ratio of the current collector 17. In terms of the coverage of the metal oxide film 172 on the conductive substrate 171, sufficient performance can be expected even if the metal oxide film 172 is detached, as long as it is continuous. Furthermore, it is thought that the effective current-carrying area will be increased by improving the electrical conductivity of the surface, so it is preferable that the coverage rate of the metal oxide film 172 on the conductive substrate 171 be 10% or more and 100% or less. The coverage rate is calculated by (surface area of ​​metal oxide film 172 / surface area of ​​conductive substrate 171) × 100.

[0032] Various parameters, such as the thickness of the conductive substrate 171 and the metal oxide film 172, can be confirmed, for example, by observing the cross-section of the conductive substrate 171 and the metal oxide film 172 in the thickness direction using a device such as a scanning electron microscope (SEM).

[0033] The metal oxide film 172 may be formed using an oxide with low bulk electrical conductivity, such as aluminum oxide, or it may be formed using an oxide that exhibits electrical conductivity in the operating environment, such as spinel oxide or perovskite-type oxide. For example, spinel-type oxides are preferred because they readily exhibit electronic conductivity at high temperatures, and the high electrical conductivity of the material itself contributes to electrical conductivity at the surface. The metal oxide film 172 is not limited to crystalline and may be amorphous.

[0034] The metal oxide film 172 can be formed by oxidizing the metal film in situ after its formation, or by directly depositing the oxide film onto the surface of the conductive substrate 171. Examples of film formation methods include vacuum deposition, ion plating, sputtering, pulsed laser volumetric deposition, cold spraying, thermal spraying, electrodeposition, electroless plating, rolling, spin coating, dip coating, sol-gel method, doctor blade method, screen printing, and aerosol deposition. It is also effective to use a metal that can form the desired metal oxide film 172 at high temperatures. [Examples]

[0035] Samples were prepared by forming a metal oxide film on the surface of a conductive substrate, and the differences in electrical properties due to differences in environmental atmosphere were evaluated. Figures 5 and 6 are schematic diagrams illustrating the method for evaluating electrical properties in the examples. Figure 5 schematically shows an example of the structure of the test specimen 100. Figure 6 schematically shows an example of the configuration of the measurement system 110 for electrical resistance measurement.

[0036] (Comparative Example 1) A sample 101 having a CoNi oxide film was prepared by forming a 5 μm thick CoNi plating film on the entire surface of a stainless steel plate with a diameter of 14 mm and a thickness of 0.5 mm, and oxidizing the CoNi plating film by exposing it to air at 700°C for 10 hours. Subsequently, 10 mm diameter Pt electrodes 102 were formed on both sides of the sample 101, and the electrical resistance of the sample 101 was measured using a four-terminal method with a probe 103 connected to the Pt electrodes 102, a voltmeter V, and an ammeter A in an air atmosphere at 700°C.

[0037] (Example 1) A sample 101 having a CoNi oxide film was prepared by forming a 5 μm thick CoNi plating film on the entire surface of a 14 mm diameter x 0.5 mm thickness stainless steel plate and oxidizing the CoNi plating film by exposing it to air at 700°C for 10 hours. Subsequently, 10 mm diameter Pt electrodes 102 were formed on both sides of sample 101, and the electrical resistance of sample 101 was measured using a four-terminal method with a probe 103 connected to the Pt electrodes 102, a voltmeter V, and an ammeter A in an atmosphere of 700°C air mixed with 50 volume% water vapor.

[0038] Figure 7 shows the results of electrical resistance measurements for Comparative Example 1 and Example 1. The electrical resistance of Example 1 is a relative value with the electrical resistance of Comparative Example 1 set to 1. From Figure 7, it can be seen that CoNi metal oxide can significantly reduce the electrical resistance of sample 101 in an atmosphere containing water vapor, as in Example 1. Furthermore, it was confirmed that the metal oxide film in sample 101 is a spinel-type oxide.

[0039] From the above, it can be said that coating the surface of a conductive substrate with a metal oxide having high surface electrical conductivity, such as CoNi oxide, as the oxygen electrode current collector of a proton-conducting solid oxide electrochemical cell operated under a high-concentration water vapor atmosphere is useful from the viewpoint of reducing the electrical resistance of the electrochemical stack. Furthermore, in this embodiment, it is shown that the electrical resistance is lower between the Pt electrodes 102 through the conductive path 101B (dotted line in Figure 5) on the surface of the CoNi plating film with a surface length of 8.5 mm passing through the edge of the sample 101 than through the conductive path 101A (dashed line in Figure 5) passing through a bulk stainless steel plate with a thickness of 0.5 mm. Also, from Figure 7, it can be seen that the electrical resistance of Example 1 is about 1 / 15 of the electrical resistance of Comparative Example 1, indicating that if the surface length of the metal oxide film 172 (shortest distance of conductive path 101B) is 15 times or less than the thickness of the conductive substrate 171 (shortest distance of conductive path 101A), then surface electron conduction works favorably.

[0040] Although several embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0041] 10...Electrochemical cell stack, 11...Electrochemical cell, 13...Electrode, 14...Electrode, 15...Solid oxide electrolyte, 16...Current collector, 17...Current collector, 18...Interconnector, 100...Test specimen, 101...Sample, 101A...Conductive path, 101B...Conductive path, 102...Pt electrode, 103...Probe, 110...Measurement system, 171...Conductive substrate, 171a...Side view, 171b...Top view, 171c...Bottom view, 172...Metal oxide film.

Claims

1. An oxygen electrode current collector for a proton-conducting solid oxide electrochemical cell, Conductive substrate and A metal oxide film provided on the surface of the conductive substrate, having a surface that exhibits higher electrical conductivity than the electrical conductivity of the conductive substrate when exposed to water vapor under the operating environment of the proton-conducting solid oxide electrochemical cell, A current collector equipped with the following features.

2. The aforementioned current collector is A first surface that can come into contact with the oxygen electrode of the electrochemical cell, A second surface that can contact the interconnector, It is equipped with, The aforementioned metal oxide film is Extending continuously along the surface of the conductive substrate from the first surface to the second surface, The current collector according to claim 1.

3. The coverage rate of the metal oxide film on the conductive substrate is 10% or more. The current collector according to claim 1.

4. The thickness of the metal oxide film is 1 nm or more. The current collector according to claim 1.

5. The thickness of the metal oxide film is less than or equal to the thickness of the conductive substrate. The current collector according to claim 1.

6. The metal oxide film comprises a metal oxide containing at least one metal element selected from the group consisting of aluminum, zirconium, zinc, chromium, cobalt, magnesium, iron, titanium, nickel, copper, lead, vanadium, tungsten, cerium, and niobium. The current collector according to claim 1.

7. The aforementioned metal oxide is a spinel-type oxide or a perovskite-type oxide. The current collector according to claim 6.

8. The shortest distance from the first surface to the second surface of the metal oxide film is 15 times or less the thickness of the conductive substrate. The current collector according to claim 2.

9. The conductive substrate is a porous body having pores, The metal oxide film is provided on the inner wall surface of the pore, The current collector according to claim 1.

10. A current collector comprising the current collector described in claim 1, Proton-conducting solid oxide electrochemical cell.

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