WO2019167437A1

WO2019167437A1 - Fuel cell

Info

Publication number: WO2019167437A1
Application number: PCT/JP2019/000491
Authority: WO
Inventors: 千尋平岩; 奈保水原; 光靖小川; 博匡俵山; 孝浩東野; 真嶋　正利
Original assignee: 住友電気工業株式会社
Priority date: 2018-02-27
Filing date: 2019-01-10
Publication date: 2019-09-06
Also published as: JP2021068493A

Abstract

This fuel cell is provided with: a cell structure that includes a cathode, an anode, and a solid electrolyte layer provided between the cathode and the anode; a cathode-side separator that is opposed to the cathode; and an anode-side separator that is opposed to the anode, wherein the cell structure is held between the cathode-side separator and the anode-side separator, the cathode-side separator and the anode-side separator each have gas flow paths, a collector is provided between the anode-side separator and the anode and/or between the cathode-side separator and the cathode, the collector is a metal mesh formed from woven wire, and the wire has a corrosion resistant layer.

Description

Fuel cell

This disclosure relates to fuel cells. This application claims priority based on Japanese Patent Application No. 2018-032913, which is a Japanese patent application filed on February 27, 2018. All the descriptions described in the Japanese patent application are incorporated herein by reference.

A fuel cell is a device that generates electricity by an electrochemical reaction between a fuel gas such as hydrogen and air (oxygen), and has high power generation efficiency because it can directly convert chemical energy into electricity. Among them, a solid oxide fuel cell (hereinafter referred to as SOFC) having an operating temperature of 700 ° C. or higher, particularly about 800 ° C. to 1000 ° C. is considered promising because of its high reaction rate. SOFC uses MEA (Membrane Electrode Assembly, membrane-electrode assembly) in which an electrolyte layer containing a solid oxide is sandwiched between two electrodes formed of ceramics (sintered body). The All components of the MEA are solid and easy to handle.

As the solid electrolyte, a metal oxide having oxygen ion conductivity, such as yttrium-stabilized zirconia (YSZ) is used. The operating temperature of SOFC using oxygen ion conductive YSZ as an electrolyte is a high temperature of 750 ° C. to 1000 ° C. From the viewpoint of reducing the energy consumption required for heating and the selectivity of materials having high temperature resistance, development of SOFCs operating in the middle temperature range of 400 ° C to 600 ° C that can use inexpensive general-purpose stainless steel is underway. . Perovskite oxides such as BaCe _0.8 Y _0.2 O _2.9 (BCY) and BaZr _0.8 Y _0.2 O _2.9 (BZY) exhibit high proton conductivity in the middle temperature range. It is expected as a solid electrolyte for type fuel cells.

In a fuel cell, in order to obtain large electric power, a plurality of MEAs are usually stacked and an interconnector (separator) that separates fuel gas and air is disposed between the MEAs. The interconnector also has a current collecting function for taking out the generated current to the outside.

A fuel cell requires a gas flow path adjacent to the MEA in order to supply fuel gas or air to the MEA. In order to secure the gas flow path, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2007-250297), an expanded metal is disposed between the MEA and the interconnector. Patent Document 2 (International Publication No. 2003/12903 pamphlet) teaches a method of forming dimples serving as gas flow paths in an interconnector by etching or the like.

JP 2007-250297 A International Publication No. 2003/12903 Pamphlet

A fuel cell according to the present disclosure includes a cell structure including a cathode, an anode, and a solid electrolyte layer interposed between the cathode and the anode, a cathode-side separator facing the cathode, and an anode facing the anode A side separator, wherein the cell structure is sandwiched between the cathode side separator and the anode side separator, the cathode side separator and the anode side separator have gas flow paths, and the anode side separator and the anode Or at least one of the cathode side separator and the cathode is provided with a current collector, and the current collector is a metal mesh knitted with a wire, and the wire has a corrosion-resistant layer. Have.

FIG. 1 is a cross-sectional view schematically showing a configuration of a fuel cell according to an embodiment. FIG. 2 is a cross-sectional view schematically showing a cell structure included in the fuel cell of FIG. FIG. 3 is an SEM photograph of an example of a corrosion-resistant layer including a Ni—Sn layer. FIG. 4 is a graph showing a change with time in accordance with an increase in the number of operation of the voltage between the anode side separator and the cathode side separator of the fuel cell as a change in voltage decrease rate (deterioration rate). FIG. 5 is a graph showing a change with time in accordance with an increase in the number of operation times of the voltage between the anode side separator and the cathode side separator of the fuel cell as a change in voltage decrease rate (deterioration rate).

[Problems to be solved by this disclosure]
Electrons flowing to the cell are collected via a metallic material that contacts the anode and / or cathode. At this time, if there are few metal materials which contact an anode and / or a cathode, it will become difficult to flow an electron and resistance will become high. In the method of Patent Document 1, the expanded metal arranged for securing the gas flow path also plays a role as a current collector. However, since the expanded metal has a large hole diameter, the internal resistance during operation tends to be high.

The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a fuel cell with reduced internal resistance during operation.

[Effects of the present disclosure]
According to this indication, internal resistance at the time of operation of a fuel cell can be reduced.

[Description of Embodiment]
In order to reduce internal resistance, the present inventors first considered a configuration in which a material having a main role of current collection and a material having a main role of gas diffusibility are separately arranged. For example, a metal material (current collector) having a current collecting function as a main role is arranged between the cell and the interconnector.

On the other hand, an SOFC operating at a high temperature of 700 ° C. to 1000 ° C. is exposed to a wide temperature change from room temperature to 1000 ° C. when it is repeatedly operated and stopped. For this reason, a high thermal shock resistance is required for the current collector disposed between the cell and the interconnector. Further, the current collector is preferably a material having excellent corrosion resistance in a high temperature environment.

Based on the above, earnest studies were repeated and the fuel cell of the present disclosure was completed. The contents of the embodiments of the present disclosure will be listed and described below.

(1) The fuel cell of the present disclosure is:
A cell structure including a cathode, an anode, and a solid electrolyte layer interposed between the cathode and the anode;
A cathode separator facing the cathode, and an anode separator facing the anode,
The cell structure is sandwiched between the cathode side separator and the anode side separator,
Each of the cathode side separator and the anode side separator has a gas flow path,
A current collector is provided between at least one of the anode side separator and the anode or between the cathode side separator and the cathode,
The current collector is a metal mesh knitted with wire,
The wire has a corrosion resistant layer.

The current collector composed of the metal mesh has high heat resistance and thermal shock resistance. Moreover, since the corrosion-resistant layer is formed in the wire which comprises a metal mesh, the said electrical power collector also has high oxidation resistance. Therefore, according to the fuel cell, the internal resistance during operation of the fuel cell is reduced. In particular, in the case of a high fuel utilization rate, an increase in internal resistance during operation is more effectively suppressed.

(2) The corrosion resistant layer preferably contains Ni and Sn. Thereby, a corrosion-resistant layer can be further excellent in heat resistance. Sn easily forms an alloy with the metal constituting the metal mesh, and easily forms a corrosion-resistant layer. Especially, the alloy of Ni and Sn can have high heat resistance and high corrosion resistance (oxidation resistance).

(3) It is preferable that the corrosion-resistant layer includes a first phase and a second phase having different concentrations of Sn with respect to Ni, and the concentration of Sn in the first phase is higher than the concentration of Sn in the second phase. Thereby, a corrosion-resistant layer can ensure corrosion resistance, heat resistance, and favorable electrical conductivity.

(4) In the fuel cell, the current collector can be provided between the anode separator and the anode. Hereinafter, the current collector provided between the anode-side separator and the anode is appropriately referred to as “anode-side current collector”. At the anode, a reaction of oxidizing a fuel such as hydrogen and releasing protons and electrons proceeds. The atmosphere around the anode and the anode-side current collector is basically a reducing atmosphere because it contains hydrogen gas. However, when operating at a high temperature and a high fuel utilization rate, the amount of water (water vapor) increases on the anode side, and the atmosphere around the anode-side current collector tends to be oxidizing.

For example, when a porous nickel sintered body or a metal mesh made of only nickel is used as the anode-side current collector, nickel is easily oxidized during operation at a high temperature and a high fuel utilization rate. Internal resistance tends to increase. On the other hand, since the metal mesh has a corrosion resistant layer, the oxidation resistance is improved. For this reason, by using a metal mesh for the anode side current collector, the metal mesh is hardly oxidized even during operation at a high temperature and a high fuel utilization rate, thereby suppressing an increase in internal resistance.

(5) In (4), the solid electrolyte layer may have oxygen ion conductivity. In this case, on the anode side, protons and oxide ions react to produce water. Therefore, the atmosphere around the anode-side current collector tends to be an oxidizing atmosphere. According to the present disclosure, an increase in internal resistance can be suppressed even in this case.

(6) In (4), the operating temperature of the fuel cell may be 800 ° C. or higher. At such a high temperature, the atmosphere around the anode-side current collector tends to be a highly oxidizing atmosphere, but according to the present disclosure, an increase in internal resistance can be suppressed even in this case.

(7) In (4), the fuel utilization rate may be 75% or more. With such a high fuel utilization rate, the atmosphere around the anode-side current collector tends to be a highly oxidizing atmosphere, but according to the present disclosure, an increase in internal resistance can be suppressed even in this case.

The fuel utilization rate refers to the ratio of the amount of fuel actually used for cell reaction out of the amount of fuel supplied to the fuel cell via the fuel flow path. The fuel utilization rate can be calculated based on the amount of current flowing through the fuel cell and the flow rate of the fuel gas supplied via the fuel flow path.

(8) In the fuel cell, the current collector can be provided between the cathode separator and the cathode. Hereinafter, the current collector provided between the cathode side separator and the cathode is appropriately referred to as a “cathode side current collector”. At the cathode, the oxidant (oxygen) introduced from the oxidant flow path is dissociated to generate oxide ions. For this reason, the periphery of the cathode and the cathode-side current collector is exposed to a high temperature and highly oxidizing atmosphere.

As the oxidation-resistant cathode-side current collector, for example, lanthanum strontium cobalt ferrite (LSCF), which is also used as a cathode material, is used. However, in this case, by repeating the operation at high temperature and the operation stop, the LSCF may be broken by a thermal shock, and the LSCF is likely to fall off, and the internal resistance is likely to increase accordingly. In contrast, the metal mesh has high heat resistance and thermal shock resistance, and has oxidation resistance by forming a corrosion-resistant layer on at least the surface layer of the metal mesh wire. For this reason, by using a metal mesh for the cathode current collector, it is possible to suppress an increase in internal resistance when the fuel cell is operated.

(9) In (8), the operating temperature of the fuel cell is preferably 700 ° C. or lower. In the case of the above operating conditions, it is easy to suppress an increase in internal resistance by using a metal mesh provided with at least a corrosion-resistant layer as a cathode current collector. Since the SOFC using the above-described materials having proton conductivity such as BCY and BZY as the solid electrolyte layer operates in the middle temperature range of 400 ° C. to 600 ° C., the above metal mesh is preferably used as the cathode side current collector. be able to. In an SOFC using another proton conductive solid electrolyte layer or an SOFC using an oxygen ion conductive solid electrolyte layer, when operating at 700 ° C. or lower, the metal mesh is used as the cathode current collector. Can be preferably used.

[Details of Embodiment of the Present Disclosure]
Specific examples of the embodiments of the present disclosure will be described below with reference to the drawings as appropriate. In addition, this indication is not limited to these illustrations, is shown by the attached claim, and it is intended that all the changes within the meaning and range equivalent to the claim are included.

(Metal mesh)
The metal mesh is formed by weaving a wire made of metal into a mesh, and the wire has a corrosion-resistant layer. Such a metal mesh may be processed into a mesh by braiding a wire in which a corrosion-resistant layer has been formed in advance, or after forming the wire into a mesh, a treatment for forming a corrosion-resistant layer on the mesh surface may be performed. . The formation of the corrosion resistant layer is preferably performed by plating. In addition, for example, vapor deposition, chemical vapor deposition (CVD), plasma CVD, sputtering, or other vapor phase methods, or metal paste may be applied. The plating process, the vapor deposition process, and the sputtering process can be performed by a known method according to the material of the corrosion-resistant layer.

As the wire metal constituting the mesh, for example, any metal or alloy material such as Cu, Fe, Ni, Ag, Zn, brass, ferrochrome (an alloy of Fe and Cr), stainless steel (SUS), or the like can be used. The metal constituting the mesh is selected in consideration of the affinity with the corrosion resistant layer. Especially, it is preferable to employ Ni in terms of low resistivity, heat resistance, and cost for use as a current collector.

The corrosion-resistant layer preferably contains Ni and Sn. This is because such a layer is excellent in both characteristics of corrosion resistance (oxidation resistance) and heat resistance. Especially, the alloy of Ni and Sn can have high corrosion resistance and high heat resistance. Therefore, an alloy layer of Ni and Sn (hereinafter referred to as “Ni—Sn layer” as appropriate) can be preferably employed as the corrosion resistant layer.

For example, an Ni—Sn layer is formed on the surface of the metal mesh by performing electrolytic plating using a plating solution containing stannous chloride, nickel chloride, and potassium pyrophosphate on the surface of the wire. be able to.

The Ni—Sn layer can be formed, for example, by plating a wire made of Ni with a Sn layer or a layer made of an alloy of Ni and Sn. That is, the surface of the Ni wire is coated with a Sn layer or a layer made of an alloy of Ni and Sn using a plating process or the like, and then heat-treated in a reducing atmosphere. As a result, Sn diffuses inside the wire, and the Ni—Sn layer can be changed from the surface layer of the wire to a region having a certain depth.

Specifically, for example, when the surface of a wire is covered with a Sn layer, first, an Sn plating layer is formed on the underlying Ni wire by an electrolytic plating process using a plating solution containing sulfuric acid and stannous sulfate. To do. Thereafter, Sn can be diffused into the Ni wire by heat treatment in a reducing atmosphere at 800 to 1000 ° C. From the viewpoint of easily forming the Ni—Sn alloy layer, it is preferable to employ Ni as the wire.

It is preferable that the corrosion-resistant layer includes a first phase and a second phase having different concentrations of Sn with respect to Ni, and the concentration of Sn in the first phase is higher than the concentration of Sn in the second phase. Such a configuration is easy when the corrosion-resistant layer is the above-described Ni—Si layer. According to this corrosion-resistant layer, corrosion resistance, corrosion resistance, heat resistance and good electrical conductivity can be ensured. The reason is as follows.

In the first phase, Ni and Sn are present in the form of an intermetallic compound (for example, Ni ₃ Sn). The second phase is a phase containing Ni as a main component, and it is considered that Sn is present in the form of a solid solution in Ni. Of the first phase and the second phase, the first phase that is the intermetallic compound phase has higher corrosion resistance than the second phase. On the other hand, the second phase has higher heat resistance and electrical conductivity than the first phase. For this reason, the corrosion-resistant layer having the first phase and the second phase can have corrosion resistance, heat resistance, and good electrical conductivity.

The higher the proportion of the first phase in the total of the first phase and the second phase in the corrosion resistant layer, the better the corrosion resistant layer. Therefore, in the Ni—Sn layer, the composition ratio of Ni and Sn is set so that the ratio of Sn contained in the Ni—Sn layer is 100% by mass based on the total amount of Ni and Sn. The content is preferably 4% by mass or more, and more preferably 5% by mass or more. On the other hand, the higher the proportion of the first phase, the relatively lower the proportion of the second phase, so there is a concern about the decrease in heat resistance and electrical conductivity. Therefore, from the viewpoint of maintaining high heat resistance and electrical conductivity, the ratio of Sn contained in the Ni—Sn layer is 15% by mass or less with the total amount of Ni and Sn contained in the Ni—Sn layer being 100% by mass. It is preferable that it is 10% by mass or less. When Sn is contained in the Ni—Sn layer at a composition ratio satisfying such a condition, the Ni—Sn layer has an intermetallic compound phase (first phase) containing Ni ₃ Sn as a main component and Ni as the main component. And two phases of the phase in which Sn is dissolved in Ni (second phase) are observed at an appropriate ratio. In this case, higher corrosion resistance, higher heat resistance, and better electrical conductivity can be ensured.

FIG. 3 shows an SEM photograph of the cross section of the Ni—Sn layer. FIG. 3 is a cross-sectional photograph of a porous metal body (Celmet) on which a Ni—Sn layer is formed. This Ni—Si layer is composed of the first phase and the second phase described above. However, the metal mesh having the Ni—Si alloy layer also shows the same composition distribution as in FIG. 3 at least in the surface layer.

As can be seen from FIG. 3, the Ni—Sn layer has two phases, a portion indicated as Location 1 (first phase) and a darker gray portion (second phase) that is blacker than Location 1 and indicated as Location 2. Is observed. In Location 1, Ni, Sn, and O (oxygen) were included in atomic fractions of 75 at%, 18 at%, and 7 at%, respectively. From this, it is considered that in Location 1, most of Ni and Sn are present in the form of the intermetallic compound Ni ₃ Sn. On the other hand, in Location 2, Ni, Sn, and O were contained in atomic fractions of 91 at%, 4 at%, and 5 at%, respectively. From this, it is considered that Sn is contained in a state of being dissolved in Ni in Location 2.

It is more preferable that all of the wires constituting the metal mesh are Ni—Sn layers. That is, the wire itself is more preferably an alloy of Ni and Sn. In this case, not only the surface of the wire but also the wire itself can have the various characteristics described above.

In addition, a metal mesh in which Co or Mn is coated as an anticorrosion layer on an Fe—Cr alloy may be used.

The mesh size (opening) of the metal mesh is, for example, a square with sides of 0.5 mm to 1 mm.

The metal mesh on which the above corrosion-resistant layer is formed is used for an anode-side current collector or a cathode-side current collector of a solid oxide fuel cell (SOFC).

(Fuel cell)
FIG. 1 schematically shows the configuration of a fuel cell (solid oxide fuel cell) according to an embodiment. The fuel cell 10 includes a cell structure 1. An example of a schematic cross-sectional view of the cell structure is shown in FIG. As shown in FIG. 2, the cell structure 1 includes a cathode 2, an anode 3, and a solid electrolyte layer 4 interposed therebetween. In the illustrated example, the anode 3 and the solid electrolyte layer 4 are integrated to form an electrolyte layer-electrode assembly 5.

In addition to the cell structure 1, the fuel cell 10 includes an oxidant channel 23 for supplying an oxidant to the cathode, a fuel channel 53 for supplying fuel to the anode, and a cathode, as shown in FIG. The side separator 22 and the anode side separator 52 are provided. In the example of FIG. 1, the oxidant flow path 23 is formed by the cathode side separator 22, and the fuel flow path 53 is formed by the anode side separator 52. That is, the oxidant channel 23 is a gas channel that the cathode-side separator 22 has, and the fuel channel 53 is a gas channel that the anode-side separator 52 has.

The cell structure 1 is sandwiched between the cathode side separator 22 and the anode side separator 52. The oxidant flow path 23 of the cathode side separator 22 is disposed to face the cathode 2 of the cell structure 1, and the fuel flow path 53 of the anode side separator 52 is disposed to face the anode 3. Hereinafter, the individual components of the fuel battery cell will be further described.

(Solid electrolyte layer)
As the solid electrolyte layer, a layer having proton conductivity or oxygen ion conductivity in a predetermined temperature range is used. A known material can be used for the solid electrolyte layer. Examples of the metal oxide having oxygen ion conductivity include yttrium-stabilized zirconia (YSZ). In this case, the SOFC using YSZ as the electrolyte must be operated at a high temperature of 750 ° C. to 1000 ° C.

Examples of the metal oxide having proton conductivity include perovskite oxides such as BaCe _0.8 Y _0.2 O _2.9 (BCY) and BaZr _0.8 Y _0.2 O _2.9 (BZY). Is mentioned. Since BCY and BZY exhibit high proton conductivity in the middle temperature range of 400 ° C. to 600 ° C., BCY and BZY can be used as a solid electrolyte layer of a medium temperature fuel cell. These metal oxides can be formed, for example, by sintering and used as a solid electrolyte layer.

When the solid electrolyte layer has proton conductivity, the solid electrolyte layer 4 moves protons generated at the anode 3 to the cathode 2. When the solid electrolyte layer has oxygen ion conductivity, the solid electrolyte layer 4 moves oxide ions generated at the cathode 2 to the anode 3.

The thickness of the solid electrolyte layer is, for example, 1 μm to 50 μm, preferably 3 μm to 20 μm. When the thickness of the solid electrolyte layer is in such a range, it is preferable in that the resistance of the solid electrolyte layer can be kept low.

The solid electrolyte layer forms a cell structure together with the cathode and the anode and can be incorporated into the fuel cell. In the cell structure, the solid electrolyte layer is sandwiched between the cathode and the anode, and one main surface of the solid electrolyte layer is in contact with the anode, and the other main surface is in contact with the cathode.

(Cathode)
The cathode has a porous structure. When a proton conductive solid electrolyte layer is used, a reaction (oxygen reduction reaction) between protons conducted through the solid electrolyte layer and oxide ions proceeds at the cathode. Oxide ions are generated when the oxidant (oxygen) introduced from the oxidant flow path is dissociated.

A known material can be used as the cathode material. As the cathode material, for example, a compound containing lanthanum and having a perovskite structure (ferrite, manganite, and / or cobaltite, etc.) is preferable, and among these compounds, a compound further containing strontium is more preferable. Specifically, lanthanum strontium cobalt ferrite (LSCF, La _1-x1 Sr _x1 Fe _1-y1 Co _y1 O _3-δ1 , 0 <x1 <1, 0 <y1 <1, δ1 is the amount of oxygen deficiency), Lanthanum strontium manganite (LSM, La _1-x2 Sr _x2 MnO _3-δ1 , 0 <x2 <1, δ1 is oxygen deficiency), lanthanum strontium cobaltite (LSC, La _1-x3 Sr _x3 CoO _3-δ1 , 0 <x3 ≦ 1, and δ1 is the amount of oxygen deficiency). From the viewpoint of promoting the reaction between protons and oxide ions, the cathode may contain a catalyst such as Pt. When a catalyst is included, the cathode can be formed by mixing the catalyst and the above materials and sintering.

The cathode can be formed, for example, by sintering raw materials of the above materials. If necessary, a binder, an additive, and / or a dispersion medium may be used together with the raw material.

The thickness of the cathode is not particularly limited, but can be appropriately determined from 5 μm to 2 mm, for example, and may be about 5 μm to 40 μm.

(anode)
The anode has a porous structure. In the anode, a reaction (oxidation reaction of fuel) that oxidizes fuel such as hydrogen introduced from the fuel flow path and releases protons and electrons proceeds. When an oxygen ion conductive solid electrolyte layer is used, a reaction (oxygen reduction reaction) between oxide ions and protons conducted through the solid electrolyte layer proceeds at the anode.

A known material can be used as the material for the anode. For example, when a proton conductive solid electrolyte layer is used as the anode material, nickel oxide (NiO) as a catalyst component and proton conductors (yttrium oxide (Y ₂ O ₃ ), BCY, BZY constituting the solid electrolyte layer) Etc.) and the like. When an oxygen ion conductive solid electrolyte layer is used, a composite oxide of nickel oxide (NiO) that is a catalyst and an electronic conductor component and an oxygen ion conductor (YSZ or the like) that constitutes the solid electrolyte layer can be used. .

The anode can be formed, for example, by sintering raw materials. For example, the anode can be formed by sintering a mixture of NiO powder and proton conductor powder.

The thickness of the anode can be appropriately determined from 10 μm to 2 mm, for example, and may be 100 μm to 600 μm.

1 and 2, the thickness of the anode 3 is larger than that of the cathode 2, and the anode 3 functions as a support for supporting the solid electrolyte layer 4 (and thus the cell structure 1). Note that the thickness of the anode 3 is not necessarily larger than that of the cathode 2. For example, the thickness of the anode 3 may be approximately the same as the thickness of the cathode 2.

In the illustrated example, the anode and the solid electrolyte layer are integrated. However, the present invention is not limited to this, and the cathode and the solid electrolyte layer are integrated to form an electrolyte layer-electrode assembly. May be.

The oxidant flow path 23 has an oxidant inlet into which the oxidant flows and an oxidant discharge port through which water generated by the reaction, unused oxidant, and the like are discharged (both not shown). Examples of the oxidizing agent include a gas containing oxygen. The fuel flow path 53 has a fuel gas inlet through which fuel gas flows, and a fuel gas outlet through which unused fuel, H ₂ O, N ₂ , CO _{2 and the} like generated by the reaction are discharged (all not shown). ). Examples of the fuel gas include gas containing gas such as hydrogen, methane, ammonia, carbon monoxide.

(Current collector)
The fuel cell 10 includes a cathode-side current collector 21 disposed between the cathode 2 and the cathode-side separator 22, and an anode-side current collector 51 disposed between the anode 3 and the anode-side separator 52. You may prepare. In addition to the current collecting function, the cathode-side current collector 21 functions to diffuse and supply the oxidant gas introduced from the oxidant flow path 23 to the cathode 2. In addition to the current collecting function, the anode current collector 51 functions to diffuse and supply the fuel gas introduced from the fuel flow path 53 to the anode 3. Therefore, each current collector is preferably a structure having sufficient air permeability.

In the present embodiment, the metal mesh having the above-mentioned corrosion-resistant layer can be used as the anode-side current collector 51. The metal mesh has sufficient heat resistance and oxidation resistance even when the operating temperature is 800 ° C. or higher, particularly when exposed to a high-temperature oxidizing atmosphere in which the fuel utilization rate is 75% or higher. . Of course, there is no problem in using the metal mesh as the anode-side current collector 51 even under conditions where the operating temperature is less than 800 ° C. or the fuel utilization rate is less than 75%. In this case, the upper limit value of the operating temperature is not particularly limited, but can be set to 920 ° C. from the viewpoint of the stability of the first phase that is the intermetallic compound phase. The upper limit value of the fuel utilization rate is theoretically 100%.

When the operating temperature of the fuel cell 10 is less than 800 ° C. or the fuel utilization rate is less than 75%, the anode-side current collector 51 may be, for example, silver, silver alloy, nickel, nickel alloy in addition to the metal mesh It is also possible to use a metal porous body containing a metal, a metal mesh (without a corrosion-resistant layer), a punching metal, an expanded metal, or the like. Especially, a metal porous body is preferable at the point of lightweight property or air permeability. In particular, a porous metal body having a three-dimensional network structure is preferable. The three-dimensional network structure refers to a structure in which rod-like or fibrous metals constituting a metal porous body are three-dimensionally connected to form a network. For example, a sponge-like structure or a nonwoven fabric-like structure can be mentioned.

The metal porous body can be formed, for example, by coating a resin porous body having continuous voids with the metal as described above. When the internal resin is removed after the metal coating process, a cavity is formed inside the skeleton of the metal porous body, and the metal becomes hollow. As a commercially available metal porous body having such a structure, nickel “Celmet” manufactured by Sumitomo Electric Industries, Ltd. can be used.

Since the cathode-side current collector 21 is exposed to an oxidizing atmosphere higher than that of the anode side, a material having higher oxidation resistance than the anode-side current collector 51 is desired. In general, for example, a material obtained by processing LSCF, which is a material constituting the cathode, into a paste form can be used. However, when the operating temperature of the fuel cell 10 is 700 ° C. or lower, particularly when the fuel utilization rate is 75% or lower, the metal mesh having the above-mentioned corrosion resistant layer is preferably used as the cathode current collector 21. Can do. A metal mesh having a corrosion-resistant layer has higher thermal shock resistance than LSCF. In this case, the lower limit of the operating temperature is not particularly limited, but can be 300 ° C. from the viewpoint of the activity of the catalyst. The lower limit value of the fuel utilization rate is not particularly limited, but can be 10% from the viewpoint of appropriate utilization.

(Separator)
When a fuel cell is configured by stacking a plurality of cell structures, for example, the cell structure 1, the cathode side separator 22, and the anode side separator 52 are stacked as a unit. The plurality of cell structures 1 may be connected in series by, for example, a separator having gas channels (oxidant channels and fuel channels) on both surfaces.

Examples of the material of the separator include heat-resistant alloys such as stainless steel, nickel-base alloy, and chromium-base alloy. Of these, stainless steel is preferable because it is inexpensive. In a proton conductive solid oxide fuel cell (PCFC), since the operating temperature is about 400 ° C. to 600 ° C., stainless steel can be used as a separator material. In the case of an SOFC that operates at a high temperature of about 800 ° C. or more, such as when an oxygen ion conductive solid electrolyte is used, a nickel-based alloy, a chromium-based alloy, or the like is used as a separator material.

The fuel cell can be manufactured by a known method except that the above cell structure is used.

<Appendix>
The above description includes embodiments described below.
(Appendix 1)
A cell structure including a cathode, an anode, and a solid electrolyte layer interposed between the cathode and the anode;
An oxidant flow path for supplying an oxidant to the cathode,
A fuel flow path for supplying fuel to the anode,
An anode separator, and
A cathode side separator,
A current collector is provided between the anode separator and the anode, or at least one of the cathode separator and the cathode,
The current collector is a metal mesh in which a wire is knitted, and includes a corrosion-resistant layer on at least a surface layer of the wire.

Hereinafter, the present embodiment will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[Example 1]
A fuel cell using YSZ as a solid electrolyte layer was prepared and evaluated as follows.

(1) Preparation of metal mesh Ni mesh (made by Taiyo Wire Mesh, mesh opening 0.5 mm) is immersed in a plating solution containing stannous sulfate, sulfuric acid, cresolsulfonic acid, gelatin, and β-naphthol, and electrolytic plating treatment is performed. went. Thereafter, heat treatment was performed in a hydrogen atmosphere at 1000 ° C. for 2 hours. As a result, a metal mesh (Ni—Sn mesh) X1 provided with a Ni—Sn layer was obtained.

(2) Production of Cell Structure NiO was mixed with YSZ powder, which is a solid solution of ZrO ₂ and Y ₂ O ₃ , so as to contain 70% by volume of NiO (catalyst raw material), and pulverized and kneaded by a ball mill. The ratio (atomic composition ratio) between Zr and Y in YSZ was 90:10. A slurry containing the obtained mixture (55% by volume) and a binder (PVB resin, 45% by volume) was processed into a 1.0 mm thick sheet by a doctor blade method to obtain an anode precursor sheet. . Similarly, a slurry containing the YSZ powder (55% by volume) and the binder (PVB resin, 45% by volume) is processed into a sheet having a thickness of 12 μm by a doctor blade method, and a precursor sheet for a solid electrolyte layer Got.

These precursor sheets were stacked and laminated to obtain a laminate having a total thickness of about 1.0 mm. Next, the obtained laminate was heated in the atmosphere at 600 ° C. for 1 hour to remove the binder. Subsequently, co-sintering was performed by performing a heat treatment at 1300 ° C. for 2 hours in an oxygen atmosphere to form a composite of the anode and the solid electrolyte layer.

Subsequently, on the surface of the solid electrolyte layer, a powder of LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ ) as a cathode material, an organic solvent (butyl carbitol acetate), The cell structure was produced by screen-printing the LSCF paste mixed with and firing at 1000 ° C. for 2 hours in an oxygen atmosphere. The thickness of the cathode was 10 μm.

(3) Fabrication of fuel cell A stainless steel anode-side separator having the above-mentioned metal mesh X1 laminated as an anode current collector on the surface of the anode of the cell structure obtained above, and further having a gas flow path Were laminated. On the other hand, a stainless steel cathode-side separator having a gas flow path was laminated on the surface of the cathode to produce a fuel cell Y1 similar to FIG. One end of the lead wire was joined to each of the anode side separator and the cathode side separator. The other end of each lead wire was pulled out of the fuel cell and connected to a measuring instrument so that the current value and voltage value between the lead wires could be measured.

(4) Evaluation of internal resistance The operating temperature was 900 ° C., hydrogen was supplied as a fuel gas to the anode of the produced fuel cell at 0.3 L / min, and air was supplied to the cathode at 1.0 L / min. Each lead wire was connected to an electronic load device, and the current and voltage flowing between the anode side separator and the cathode side separator were measured. At this time, the electronic load device was set so that the current flowing between the anode side separator and the cathode side separator would be 32 A so that the fuel utilization rate would be 75%.

After operating the fuel cell for 100 hours, the operation was stopped and the fuel cell was cooled to room temperature. The stopped state of the fuel cell was maintained for 10 hours. Thereafter, the fuel cell was operated again for 100 hours under the same conditions as described above.

The operation and stop of the fuel cell are repeated 10 times, and the deterioration rate A from the initial voltage (V0) of the voltage (V1) between the anode side separator and the cathode side separator immediately before the end of the operation of each fuel cell is completed. = (V0-V1) / V0 was obtained.

The voltage V1 is expressed as V1 = E−rI, where E is the electromotive force generated in the fuel cell, r is the internal resistance generated in the current collector, and I is the current between the anode side separator and the cathode side separator. Can do. Therefore, when the current I is constant, the voltage V1 decreases and the deterioration rate A increases as the internal resistance r increases.

[Comparative Example 1]
A fuel cell using an Ni metal mesh X2 in which a corrosion-resistant layer was not formed as an anode current collector was produced in the same manner as in Example 1 to obtain a fuel cell Y2. The deterioration rate of the fuel cell Y2 was evaluated in the same manner as in Example 1.

[Example 2]
(1) Fabrication of fuel cell In fabrication of the fuel cell Y1, a Ni metal mesh on which no corrosion-resistant layer is formed is laminated as an anode current collector on the surface of the anode of the cell structure. A stainless steel anode-side separator was laminated. On the other hand, a metal mesh X1 having a corrosion-resistant layer was laminated as a cathode current collector on the surface of the cathode, and a stainless steel cathode side separator having a gas flow path was further laminated. Except for this, a fuel cell Y3 was obtained in the same manner as the fuel cell Y1 of Example 1.

(2) Evaluation of internal resistance With an operating temperature of 700 ° C., hydrogen was supplied as a fuel gas to the anode of the produced fuel cell at 0.3 L / min, and air was supplied to the cathode at 1.0 L / min. The lead wire was connected to an electronic load device, and the current and voltage flowing between the side separator and the cathode side separator were measured. At this time, the electronic load device was set so that the current flowing between the anode side separator and the cathode side separator would be 32 A so that the fuel utilization rate would be 75%.

In the same manner as in Example 1, the operation and stop of the fuel cell were repeated, and the voltage deterioration rate A = (V0−V1) / V0 between the anode side separator and the cathode side separator was obtained.

[Comparative Example 2]
A fuel cell using a Ni metal mesh X2 on which no corrosion-resistant layer was formed as a cathode current collector was produced in the same manner as in Example 2 to obtain a fuel cell Y4. The deterioration rate of the fuel cell Y4 was evaluated in the same manner as in Example 2.

[Comparative Example 3]
In the production of the fuel cell Y3 of Example 2, instead of laminating the metal mesh X1 as the cathode current collector between the cathode and the cathode-side separator, the amount of LSCF paste formed on the surface of the solid electrolyte layer was increased, The cathode was thicker than the fuel cell Y3. Except for this, a fuel cell Y5 was produced in the same manner as in Example 2.

In the fuel cell Y5, by increasing the thickness of the cathode, a part of the cathode material located on the cathode side separator functions as a cathode current collector. The thickness of the fired cathode was 50 μm. In this case, the LSCF layer having a thickness of 40 μm on the side in contact with the cathode side separator corresponds to the cathode current collector. The deterioration rate of the fuel cell Y5 was evaluated in the same manner as in Example 2.

FIG. 4 shows the change with time of the voltage V1 for each operation in the fuel cells Y1 and Y2 as the change with time of the deterioration rate A = (V0−V1) / V0 (%) from the initial voltage V0. FIG. 5 shows the change over time of the voltage V1 for each operation frequency in the fuel cells Y3, Y4 and Y5 as the change over time of the deterioration rate A = (V0−V1) / V0 (%) from the initial voltage V0.

As shown in FIG. 4, in the fuel cell Y2, the internal resistance increases greatly as the cumulative operation time becomes longer. This is because the operating temperature of the fuel cell is high (900 ° C.), and the fuel cell is operated at a high fuel utilization rate, so the area around the anode and the anode current collector is locally in an oxidizing atmosphere, This is probably because the surface of the Ni mesh used as the anode current collector was oxidized and the resistance increased. On the other hand, in the fuel cell Y1, an increase in internal resistance is suppressed even during a long cumulative operation. This is probably because the Ni—Sn mesh provided with the corrosion-resistant layer is used, so that the corrosion resistance and oxidation resistance are high, and the current collector is suppressed from being oxidized.

The fuel cells Y1 and Y2 after the evaluation were disassembled, the anode current collector was taken out, and the surface was observed. In the fuel cell Y2, the Ni metal mesh X2 was oxidized to form nickel oxide. However, in the fuel cell Y1, oxidation of nickel in the mesh X1 was not observed.

As shown in FIG. 5, in the fuel cells Y4 and Y5, the internal resistance increases greatly as the cumulative operation time becomes longer. This is probably because the fuel cell Y4 has an oxidizing atmosphere around the cathode and the cathode current collector, so that the surface of the Ni mesh used as the cathode current collector was oxidized and the resistance increased. Regarding the fuel cell Y5, it is considered that a part of the LSCF functioning as the cathode current collector was broken and dropped due to thermal shock as the operation and the stop were repeated.

In contrast, in the fuel cell Y3, the increase in internal resistance is suppressed even during long-term cumulative operation. This is presumably because the metal mesh has a thermal shock resistance and is a Ni—Sn mesh provided with a corrosion resistant layer, so that the corrosion resistant layer suppresses oxidation of Ni.

The fuel cells Y3 and Y4 after the evaluation were disassembled, the cathode current collector was taken out, and the surface was observed. In the fuel cell Y4, the surface of the Ni metal mesh X2 was oxidized to form nickel oxide. However, in the fuel cell Y3, oxidation of nickel in the metal mesh X1 was not observed. Moreover, when the fuel cell Y5 after the evaluation was disassembled and the cell structure was taken out and observed, a part of the LSCF constituting the cathode was dropped from the cell structure.

The fuel cell according to the present embodiment is suitable for use in SOFC and can realize SOFC with low internal resistance during operation.

1: cell structure, 2: cathode, 3: anode, 4: solid electrolyte layer, 5: electrolyte layer-electrode assembly, 10: fuel cell, 21, 51: current collector, 22, 52: separator, 23: Oxidant channel, 53: fuel channel.

Claims

A cell structure including a cathode, an anode, and a solid electrolyte layer interposed between the cathode and the anode;
A cathode side separator facing the cathode, and an anode side separator facing the anode,
The cell structure is sandwiched between the cathode side separator and the anode side separator,
The cathode side separator and the anode side separator each have a gas flow path,
A current collector is provided between the anode separator and the anode, or at least one of the cathode separator and the cathode,
The current collector is a metal mesh knitted with wire,
The fuel cell, wherein the wire has a corrosion-resistant layer.
The fuel cell according to claim 1, wherein the corrosion-resistant layer contains Ni and Sn.
The corrosion-resistant layer includes a first phase and a second phase having different concentrations of Sn with respect to Ni,
The fuel cell according to claim 2, wherein the concentration of Sn in the first phase is higher than the concentration of Sn in the second phase.
The fuel cell according to any one of claims 1 to 3, wherein the current collector is provided between the anode-side separator and the anode.
The fuel cell according to claim 4, wherein the solid electrolyte layer has oxygen ion conductivity.
The fuel cell according to claim 4 or 5, wherein an operating temperature of the fuel cell is 800 ° C or higher.
The fuel cell according to any one of claims 4 to 6, wherein a fuel utilization rate of the fuel cell is 75% or more.
The fuel cell according to any one of claims 1 to 3, wherein the current collector is provided between the cathode separator and the cathode.
The fuel cell according to claim 8, wherein an operating temperature of the fuel cell is 700 ° C or lower.