JP6916124B2 - Fuel cell - Google Patents

Description

The present invention relates to a fuel cell, and more specifically, in a fuel cell in which the anode-side diffusion layer is made of a carbon-based material, power is generated in a state where the supply of fuel (mainly hydrogen) to the anode of some single cells is cut off. The present invention relates to a fuel cell capable of suppressing deterioration of the diffusion layer on the anode side even when it is continued.

The polymer electrolyte fuel cell includes an electrode (catalyst layer) containing a catalyst on both sides of the electrolyte membrane and a membrane-electrode-gas diffusion layer assembly (MEGA) to which a gas diffusion layer is bonded. ing. Further, current collectors (separators) provided with gas flow paths are arranged on both sides of MEGA. The polymer electrolyte fuel cell usually has a structure (fuel cell stack) in which a plurality of single cells composed of such MEGA and a current collector are stacked.

Each single cell in the fuel cell stack is electrically connected in series. When power is generated using such a fuel cell stack, only a part of the single cells may be in a state where the fuel supply is cut off (fuel shortage state). For example, if a part of the fuel gas flow path is blocked due to freezing at the time of low temperature start, only a part of the single cells will be in the fuel shortage state (hereinafter, the single cells in the fuel shortage state are referred to as "fuel shortage cells". Also called). If power generation is continued in this state, current will flow to the fuel-deficient cell with the remaining single cell as the power source. As a result, the anode potential of the fuel-deficient cell rises, and the oxidation reaction of the anode components other than the fuel (for example, carrier carbon for supporting the catalyst, water held in the single cell, etc.) proceeds. When the carrier carbon is oxidized in the fuel-deficient cell, the catalyst layer structure is destroyed and the cell performance is significantly deteriorated.

Therefore, in order to solve this problem, various proposals have been made conventionally.
For example, Patent Document 1 includes a first catalyst composition for electrochemically oxidizing a fuel and a second catalyst composition for generating oxygen from water (so-called water electrolysis catalyst). The anode is disclosed.
The document describes that when a water electrolysis catalyst is added to the anode, the electrolysis of water is promoted and the deterioration of the anode component is suppressed.

Further, Patent Document 2 discloses a method for increasing the amount of hydrophobic additives in the anode catalyst layer in a polymer electrolyte fuel cell having an anode composed of an anode base material / anode catalyst layer.
In the same document,
(A) By increasing the amount of the hydrophobic additive, the flow of water from the anode catalyst layer to the anode base material is reduced, and
(B) It is described that this increases the water content in the anode catalyst layer and suppresses the oxidation of the anode component.

Further, in Patent Document 3,
(A) The cathode-side catalyst layer contains a proton conductive substance and platinum powder or platinum alloy powder having no carbon carrier.
(B) The cathode side diffusion layer is made of a carbon base material, and
(C) A membrane electrode structure for a polymer electrolyte fuel cell in which a cathode isolation layer containing _{highly crystalline carbon nanofibers or Ti 4} O ₇ is provided between a cathode-side catalyst layer and a cathode-side diffusion layer is disclosed. Has been done.
In the same document,
(A) By not using a carbon carrier for the cathode side catalyst layer, the catalytic action is not deteriorated due to the corrosion of the carbon carrier, and
(B) It is described that the isolation layer suppresses the corrosion of the diffusion layer.

Further, in Patent Document 4,
_{(A) IrO 2} / TiO ₂ is added to the polytetrafluoroethylene (PTFE) dispersion to prepare a barrier layer ink.
(B) Barrier layer The ink is screen-printed on the side of the gas diffusion layer (GDL) covered with the microporous layer, and the coating film is dried to obtain a barrier layer having a thickness of about 2.5 to 3 μm on the GDL surface. Form (BL)
(C) A method for producing a barrier layer in which GDL coated with the barrier layer is heat-treated at 340 ° C. is disclosed.
In the same document,
(A) When a barrier layer is introduced between the catalyst layer and the gas diffusion layer, it shows very good performance in the accelerated corrosion test, and
(B) The thickness of the barrier layer after drying is preferably 1 to 100 μm.
Is described.

As described in Patent Documents 1 and 2, when a catalyst that promotes an oxygen generation reaction (OER) (so-called water electrolysis catalyst) is added to the anode, OER is preferentially replaced with carbon oxidation even when hydrogen is deficient. It occurs and the deterioration of the anode can be suppressed to some extent. However, it is necessary to use a material having a small amount of resources such as iridium oxide as the OER catalyst.

Further, as described in Patent Document 3, if an isolation layer is introduced between the cathode side catalyst layer and the cathode side diffusion layer, deterioration of the cathode side diffusion layer can be suppressed to some extent. However, the resistance to mass transfer due to the diffusion of oxygen in the air increases by the amount of the isolation layer. Therefore, in order to suppress the initial performance deterioration, it is necessary to take measures such as making the isolation layer extremely thin and using a member having high gas diffusivity.

Further, as described in Patent Document 4, when a barrier layer is formed on the surface of the gas diffusion layer using the barrier layer ink, deterioration of the gas diffusion layer can be suppressed to some extent. However, since the process of preparing the barrier layer ink and forming the layer controlled to the thickness of 100 μm or less is included, the production process becomes complicated.
Furthermore, there has been no conventional example in which a method capable of suppressing deterioration of the diffusion layer on the anode side has been proposed without using a material having a small amount of resources or an ink process.

International Publication No. 2001/015247 International Publication No. 2001/015255 Japanese Unexamined Patent Publication No. 2010-272347 Special Table 2016-514346

The problem to be solved by the present invention is that in a fuel cell in which the diffusion layer on the anode side is made of a material containing carbon, power generation is performed in a state where the supply of fuel (mainly hydrogen) to the fuel electrode of some single cells is cut off. The purpose is to suppress deterioration of the anode-side diffusion layer even if it is continued.
Another problem to be solved by the present invention is to suppress deterioration of the diffusion layer on the anode side without using a material having a small amount of resources or an ink process.

The fuel cell according to the present invention in order to solve the above problems has the following configurations.
(1) The fuel cell is
An electrolyte membrane containing a solid polymer electrolyte and
An anode-side catalyst layer provided on one surface of the electrolyte membrane,
A cathode-side catalyst layer provided on the other surface of the electrolyte membrane,
An anode-side diffusion layer provided outside the anode-side catalyst layer,
The cathode side diffusion layer provided outside the cathode side catalyst layer and
It is provided with an isolation layer provided only between the anode-side catalyst layer and the anode-side diffusion layer.
(2) The anode-side diffusion layer contains carbon.
(3) The isolation layer has an electron conduction resistance of 0.5 Ωcm ² or less and a proton conduction resistance of 500 Ωcm ² or more.
If the isolation layer contains carbon, the porosity needs to be less than 50%.

When the anode-side diffusion layer is in contact with the catalyst layer ionomer during the hydrogen-deficient operation, the potential of the diffusion layer at the contact portion rises to about 2 V or more. As a result, the deterioration of the diffusion layer on the anode side progresses. On the other hand, if an isolation layer having no proton conductivity is introduced between the anode-side catalyst layer and the anode-side diffusion layer, the potential increase of the diffusion layer is suppressed. As a result, deterioration of the diffusion layer on the anode side during hydrogen-deficient operation can be suppressed.

It is a schematic diagram of an ion exchange method. This is the initial IV performance of MEGA with the isolation layer introduced.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Fuel cell]
The fuel cell according to the present invention has the following configurations.
(1) The fuel cell is
An electrolyte membrane containing a solid polymer electrolyte and
An anode-side catalyst layer provided on one surface of the electrolyte membrane,
A cathode-side catalyst layer provided on the other surface of the electrolyte membrane,
An anode-side diffusion layer provided outside the anode-side catalyst layer,
The cathode side diffusion layer provided outside the cathode side catalyst layer and
It is provided with an isolation layer provided only between the anode-side catalyst layer and the anode-side diffusion layer.
(2) The anode-side diffusion layer contains carbon.
(3) The isolation layer has an electron conduction resistance of 0.5 Ωcm ² or less and a proton conduction resistance of 500 Ωcm ² or more.
If the isolation layer contains carbon, the porosity needs to be less than 50%.

[1.1. Electrolyte membrane]
In the present invention, the material of the electrolyte membrane is not particularly limited. The electrolyte membrane may be either a fluorine-based electrolyte or a hydrocarbon-based electrolyte. Further, the type of acid group of the electrolyte membrane is not particularly limited. Examples of the acid group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, a sulfonimide group and the like. The electrolyte membrane may contain only one of these acid groups, or may contain two or more of these acid groups.
Further, the electrolyte membrane may be composed of only the solid polymer electrolyte, or may be a composite of the solid polymer electrolyte and the reinforcing layer.

[1.2. Catalyst layer]
The anode-side catalyst layer and the cathode-side catalyst layer are portions that serve as reaction fields for electrode reactions, respectively, and are bonded to both sides of the electrolyte membrane. The catalyst layer includes an electrode catalyst or an electrode catalyst supported on a carrier, and a catalyst layer ionoma that covers the periphery thereof. In the present invention, the materials of the electrode catalyst, the catalyst layer ionomer and the carrier are not particularly limited. Examples of the electrode catalyst include platinum, platinum alloys, palladium, ruthenium, rhodium and the like, or alloys thereof.

[1.3. Diffusion layer]
The anode-side diffusion layer and the cathode-side diffusion layer are joined to the outside of the anode-side catalyst layer and the cathode-side catalyst layer, respectively. The diffusion layer is for supplying and receiving electrons to and from the electrode and at the same time supplying the reaction gas to the electrode. Generally, carbon paper, carbon cloth, or the like is used for the diffusion layer. Further, in order to enhance water repellency, a gas diffusion layer obtained by coating the surface of carbon paper or the like with a mixture (water repellent layer) of a water-repellent polymer powder such as polytetrafluoroethylene and carbon powder is used. You may.
In the present invention, at least the anode-side diffusion layer is made of a material containing carbon. The material of the cathode side diffusion layer is not particularly limited.

[1.4. Isolation layer]
[1.4.1. Definition]
The "isolating layer" refers to a layer inserted between the anode-side diffusion layer and the anode-side catalyst layer in order to isolate the anode-side diffusion layer from the catalyst layer ionoma. Deterioration of the anode-side diffusion layer during hydrogen-deficient operation occurs when the anode-side diffusion layer and the catalyst layer ionomer come into contact with each other and the anode-side diffusion layer becomes high potential. Therefore, if an isolation layer is inserted between the anode-side diffusion layer and the anode-side catalyst layer, it is possible to prevent the anode-side diffusion layer from becoming high potential during hydrogen-deficient operation.
In the present invention, the isolation layer is not inserted between the cathode side diffusion layer and the cathode side catalyst layer. This is because the deterioration of the diffusion layer can occur on the cathode side as well, but the abnormal potential of the cathode is about 1.5 V, and the deterioration of the diffusion layer is not remarkable at this potential.

[1.4.2. Isolation layer characteristics]
[A. Electron conduction resistance]
During the operation of the fuel cell, it is necessary to transfer electrons between the anode-side catalyst layer and the anode-side diffusion layer. Therefore, the isolation layer needs to have a low electron conduction resistance. In order to suppress the deterioration of battery performance, the electron conduction resistance of the isolation layer needs to be ^{0.5 Ωcm 2 or less.} The electron conduction resistance is preferably 0.3 Ωcm ² or less, more preferably 0.1 Ωcm ² or less.

[B. Proton conduction resistance]
Deterioration of the anode-side diffusion layer occurs due to contact between the anode-side catalyst layer and the catalyst layer ionomer during hydrogen-deficient operation. Therefore, the isolation layer needs to have a high proton conduction resistance. In order to suppress the deterioration of the diffusion layer on the anode side, the proton conduction resistance of the isolation layer needs to be ^{500 Ωcm 2 or more.} The proton conduction resistance is preferably 750 Ωcm ² or more, more preferably 1000 Ω cm ² or more.

[C. Gas permeability]
During the operation of the fuel cell, the hydrogen gas supplied to the anode flow path moves from the anode-side diffusion layer to the anode-side catalyst layer. Therefore, the isolation layer may be at least permeable to hydrogen gas. Since the fuel introduced into the anode is a gas having a hydrogen concentration of 100%, hydrogen is supplied to the vicinity of the catalyst by convection (mass movement) rather than diffusion. Therefore, even if the isolation layer is made thicker or a member having low diffusivity is used as the isolation layer, the mass transfer resistance hardly increases.
[D. Porosity]
When the isolation layer contains carbon, the isolation layer itself can be oxidatively deteriorated due to a high potential. However, when the porosity of the isolation layer itself is less than 50%, the effect on the performance of oxidative deterioration is small.

[1.4.3. Specific example of isolation layer]
In the present invention, specifically, as the isolation layer,
(A) A porous metal layer inserted between the anode-side catalyst layer and the anode-side diffusion layer,
(B) There is an ion exchange layer formed on the surface layer portion of the anode side catalyst layer on the anode side diffusion layer side.
The isolation layer may be either a porous metal layer or an ion exchange layer, or may be both.
As another concrete example,
(C) A method of removing 90% or more of the sulfonic acid groups of ionomer contained in the surface layer portion on the diffusion layer side of the catalyst layer on the anode side instead of ion exchange.
(D) A method of using a conductive oxide porous body such as non-stoichiometric titanium oxide instead of the porous metal can be considered.
The isolation layer may consist of any one of these, or may be used in combination of two or more as long as physically possible.

[A. Porous metal layer]
The “porous metal layer” refers to a porous layer inserted between the anode-side catalyst layer and the anode-side diffusion layer, which contains a metal and does not contain a proton conductor.

[A. 1. 1. thickness]
The thickness of the porous metal layer affects the durability of the anode-side diffusion layer. If the thickness of the porous metal layer becomes too thin, the protons easily permeate through the electron conductor layer. When protons reach the anode-side diffusion layer during hydrogen-deficient operation, the anode-side diffusion layer is likely to deteriorate. Therefore, the thickness of the porous metal layer is preferably 100 μm or more. The thickness of the porous metal layer is preferably 125 μm or more, more preferably 150 μm or more.
On the other hand, even if the thickness of the porous metal layer is made thicker than necessary, there is no difference in the effect and there is no actual benefit. Therefore, the thickness of the porous metal layer is preferably 500 μm or less. The thickness of the porous metal layer is preferably 475 μm or less, more preferably 450 μm or less.

[A. 2. Material and structure]
The porous metal layer is inserted between the anode-side catalyst layer and the anode-side diffusion layer. Therefore, the porous metal layer preferably has high corrosion resistance in a fuel cell environment (that is, in a strongly acidic environment) and appropriate gas permeability. The material and structure of the porous metal layer are not particularly limited as long as they perform such a function.
As a material of the porous metal layer, for example,
(A) Precious metals (Au, Ag, Pt, Pd, Rh, Ir, Ru, Os),
(B) Ti or
(C) Noble metal or alloy containing Ti (for example, PtTi alloy, PtSn alloy, IrRu alloy)
and so on.
The structure of the porous metal layer includes, for example, a metal mesh, a metal foam, an aggregate of nanoparticles or submicron particles, and the like.

[B. Ion exchange layer]
The "ion exchange layer" refers to a layer obtained by ion-exchange the protons of the acid groups of the catalyst layer ionoma contained in the anode-side catalyst layer with cations other than protons. The ion exchange layer is formed only on the surface layer portion of the anode side catalyst layer on the anode side diffusion layer side.

[B. 1. 1. Ion exchange rate]
The "ion exchange rate" refers to the ratio of the number of moles of acid groups ion-exchanged with a cation to the total number of moles of acid groups contained in the ion exchange layer.
The ion exchange rate of the ion exchange layer affects the durability of the diffusion layer on the anode side. If the ion exchange rate is too low, protons are likely to be conducted to the diffusion layer on the anode side. Therefore, the ion exchange rate is preferably 90% or more. The ion exchange rate is preferably 92% or more, more preferably 94% or more.

[B. 2. thickness]
The thickness of the ion exchange layer affects the durability and battery performance of the diffusion layer on the anode side. If the thickness of the ion exchange layer is too thin, the diffusion of protons cannot be sufficiently suppressed. Therefore, the thickness of the ion exchange layer is preferably 10% or more of the thickness of the anode-side catalyst layer. The thickness of the ion exchange layer is preferably 15% or more, more preferably 20% or more of the thickness of the anode-side catalyst layer.
On the other hand, if the thickness of the ion exchange layer becomes too thick, the battery performance deteriorates. Therefore, the thickness of the ion exchange layer is preferably 50% or less of the thickness of the anode-side catalyst layer. The thickness of the ion exchange layer is preferably 45% or less, more preferably 40% or less of the thickness of the anode-side catalyst layer.

[B. 3. 3. Cation]
In order to suppress the diffusion of protons from the anode-side catalyst layer to the anode-side diffusion layer, the higher the water repellency of the ion exchange layer, the better. For that purpose, the higher the water repellency of the cation contained in the ion exchange layer, the better.
Further, in order to maintain the durability of the diffusion layer on the anode side for a long period of time, it is preferable that the cation is hard to elute from the ion exchange layer. For that purpose, the larger the molecular weight of the cation contained in the ion exchange layer, the better.

Examples of cations that satisfy such conditions include, for example.
(A) Tetraalkylammonium ions containing an alkyl group having 3 or more carbon atoms (for example, tetrabutylammonium ion, tetrapropylammonium ion, etc.),
(B) Complex ions (for example, hexaamminecobalt ions, hexaammine ruthenium ions, etc.)
and so on.
The ion exchange layer may contain any one of these cations, or may contain two or more cations.

[2. Fuel cell manufacturing method]
The membrane-electrode-gas diffusion layer conjugate (MEGA) can be produced by superimposing a catalyst layer and a diffusion layer on both sides of a solid polymer electrolyte and hot-pressing them, respectively. The fuel cell is usually used in the state of a stack in which a plurality of such MEGAs are stacked.
MEGA in which the isolation layer is made of a porous metal layer can be produced, for example, by inserting a porous metal layer between the anode-side catalyst layer and the anode-side diffusion layer and hot-pressing.

Further, in MEGA in which the isolation layer is an ion exchange layer, as shown in FIG. 1, after producing a membrane-electrode assembly (MEA) containing no diffusion layer, the anode side of the MEA is subjected to an ion exchange solution (for example, tetra). It can be produced by contacting it with an aqueous solution of butylammonium) and then joining a diffusion layer. By optimizing the temperature of the solution, the treatment time, etc. at the time of ion exchange, the thickness of the ion exchange layer and the ion exchange rate can be controlled.

[3. Action]
When the anode-side diffusion layer is in contact with the catalyst layer ionomer during the hydrogen-deficient operation, the potential of the diffusion layer at the contact portion rises to about 2 V or more. As a result, the deterioration of the diffusion layer on the anode side progresses. On the other hand, if an isolation layer having no proton conductivity is introduced between the anode-side catalyst layer and the anode-side diffusion layer, the potential increase of the diffusion layer is suppressed. As a result, deterioration of the diffusion layer on the anode side during hydrogen-deficient operation can be suppressed.
When carbon is used as the carrier in the catalyst layer, the carrier carbon may deteriorate even if this method is used, but by suppressing the deterioration of the diffusion layer, the cell due to hydrogen deficiency operation Performance degradation is significantly reduced.

If a partial hydrogen deficiency occurs when starting and stopping, an abnormally high potential also occurs on the cathode side. Therefore, it is considered that a means for introducing an isolation layer between the catalyst layer on the cathode side and the diffusion layer is also effective. However, even if the isolation layer is introduced on the cathode side, it is not as effective as when it is introduced on the anode side. It is considered that this is because the abnormal potential of the cathode is about 1.5 V, and the deterioration of the diffusion layer is originally not remarkable at this potential.

Further, when the isolation layer is introduced between the catalyst layer and the diffusion layer, the moving distance of the reactant becomes long. Therefore, when the isolation layer is introduced on the cathode side, the resistance to mass transfer due to the diffusion of oxygen in the air increases. Therefore, in order to prevent the initial performance deterioration, it is necessary to make the isolation layer very thin and use a member having high diffusivity.
On the other hand, when the isolation layer is introduced on the anode side, the concentration of hydrogen as a reactant is 100%, so hydrogen is supplied to the vicinity of the catalyst by convection (mass movement) instead of diffusion. Therefore, even when the isolation layer is thickened or a member having low diffusivity is used as the isolation layer, the mass transfer resistance hardly increases. Therefore, by introducing the isolation layer only on the anode side, it is possible to suppress the deterioration of the diffusion layer while suppressing the initial performance deterioration without any special measures.

(Examples 1 to 3 and Comparative Examples 1 to 3)
[1. Preparation of sample]
When power generation is continued in a state where the supply of fuel (mainly hydrogen) is cut off in some cells of the fuel cell stack, the remaining cells become the power source, and it is one of the constituent materials at the anode of the fuel shortage cell. There is a problem that oxidation (COR) of a certain carbon occurs and the cell performance is significantly deteriorated. One of the deterioration modes is the deterioration of the diffusion layer at the portion in contact with the ionomer.
On the other hand, it is conceivable to have an anode structure in which an electron conductive layer (isolation layer) that does not contain ionomer and does not significantly deteriorate the performance even when exposed to a high potential is provided between the catalyst layer and the diffusion layer. However, Reference 1 suggests that protons may be conducted in the range of 200 to 300 nm even in the absence of ionomer. Therefore, it is important that the isolation layer is sufficiently thicker or hydrophobic. Therefore, the following samples were prepared.
[Reference 1] Electrochimica Acta, 146 (2014) 194

[1.1. Examples 1-2]
A MEGA having a Pt mesh (thickness 150 μm, Example 1) or a Ti mesh (thickness 350 μm, Example 2) inserted between the catalyst layer on the anode side and the diffusion layer was prepared.

[1.2. Example 3]
As shown in FIG. 1, by bringing the anode side of MEA into contact with the tetrabutylammonium aqueous solution, the protons in the catalyst layer ionoma on the outside (diffusion layer side) of the anode side catalyst layer were exchanged with tetrabutylammonium ions. The pH in the aqueous solution changes due to the protons released by ion exchange. By measuring it, the thickness of the ion exchange layer can be estimated. As a result, it was found that ion exchange was carried out in a region having a thickness of 30% of the thickness of the catalyst layer. However, the thickness of the tetrabutylammonium ion was estimated on the assumption that it does not move after being bound to the acid group.
After ion exchange, diffusion layers were bonded to both sides of the catalyst layer to obtain MEGA.

[1.3. Comparative Examples 1-2]
A MEGA having a Pt mesh (thickness 150 μm, Comparative Example 1) or a Ti mesh (thickness 350 μm, Comparative Example 2) inserted between the catalyst layer on the cathode side and the diffusion layer was prepared.
[1.4. Comparative Example 3]
MEGA was prepared without inserting a metal mesh or performing an ion exchange treatment.

[2. Test method]
[2.1. Hydrogen shortage operation mock test]
The following endurance test was imposed, simulating that hydrogen deficiency operation occurs intermittently. Nitrogen was passed through the anode and hydrogen was passed through the cathode, and the potential cycle was carried out 450 times, using the cathode as a reference electrode and holding the potential of the anode for 10 s at 0 V and 10 s at 2.35 V. The cell temperature was 5 ° C., and the dew point of the supplied gas was 35 ° C. This upper limit potential assumes the ultimate potential of the anode when the current is controlled at 0.2 to 1.2 A / cm ^{2 in a hydrogen-deficient environment (see Reference 2).}
[Reference 2] ECS Transactions, 80 (8) 535-542 (2017)

[2.2. Partial hydrogen deficiency mock test at start / stop]
The following endurance test was imposed, simulating an abnormal cathode potential rise (see Reference 3) due to the generation of reverse current when starting and stopping. Hydrogen was passed through the anode and nitrogen was passed through the cathode, and the potential cycle of holding the cathode potential at 0 V for 10 s and 1.5 V for 10 s was performed 450 times with the anode as the reference electrode. The cell temperature was 33 ° C., and the dew point of the supplied gas was 32 ° C. This upper limit potential assumes the maximum cathode potential at the time of starting and stopping (see Reference 3).
[Reference 3] Electrochimical and Solid-State Letters, 8 (6) A273-A276 (2005)

[2.3. Initial performance]
The initial IV performance of MEGA was evaluated.

[3. result]
[3.1. Hydrogen deficiency operation mock test and partial hydrogen deficiency mock test at start / stop]
Table 1 shows the performance maintenance rate of the cells after the endurance test simulating hydrogen shortage operation and start / stop for each sample. The "performance maintenance rate" refers to the ratio of the current value in IV performance at a predetermined voltage of 0.6 V or more before and after the durability test. From Table 1, the following can be seen.

(1) In the case of the hydrogen deficiency operation simulated test, the cell performance maintenance rate is improved in all the examples as compared with the comparative example 3 (blank) in which the treatment is not performed. This is because the deterioration of the diffusion layer is suppressed by introducing the isolation layer between the catalyst layer and the diffusion layer. When the temperature is low (5 ° C.) as in this test, the deterioration of the carrier carbon in the catalyst layer is originally small. Therefore, by protecting the diffusion layer, the performance maintenance rate of the cell is dramatically improved. From the above, according to the present invention, it is possible to suppress performance deterioration during hydrogen-deficient operation.
(2) On the other hand, in the case of the start / stop simulation test, as shown in Comparative Example 1 and Comparative Example 2, even if the isolation layer is provided on the cathode side exposed to a high potential, compared with Comparative Example 3 (blank), Performance maintenance rate has not improved. This is because, under the conditions of a temperature of 33 ° C. and a potential of 1.5 V, the deterioration of the diffusion layer is not remarkable from the beginning, and the performance deterioration is mainly due to the deterioration of the carrier in the catalyst layer, and this deterioration is caused by providing the isolation layer. This is because it cannot be suppressed.

[3.2. Initial performance]
FIG. 2 shows the initial IV performance of MEGA with the isolation layer introduced. From FIG. 2, it can be seen that the initial performance is significantly lower when the isolation layer is provided on the cathode side (Comparative Example 1) than when the isolation layer is provided on the anode side (Example 1). This is because if the isolation layer is provided on the cathode, the resistance to mass transfer due to the diffusion of oxygen in the supply gas (air) increases. From the above, it was found that it is desirable to insert the isolation layer only on the anode side.

(Examples 4 to 6, Comparative Example 4)
[1. Test method]
In the case of an ion exchange layer, the isolation layer is often thin. Therefore, in order to reliably suppress the conduction of protons to the diffusion layer, the cation used for ion exchange is preferably an ion having high water repellency. Therefore, in order to evaluate the water repellency of the cations, the electrolyte membrane was ion-exchanged with various cations to evaluate the water content.

A proton type Nafion (registered trademark) membrane was used as the electrolyte membrane. As the cation, tetrabutylammonium ion (Example 4), tetrapropylammonium ion (Example 5), or hexaammine cobalt ion (Example 6) was used. For comparison, an untreated electrolyte membrane (Comparative Example 4) was subjected to the test.

[2. result]
Table 2 shows the water content of various electrolyte membranes. From Table 2, it can be seen that the ion exchange-treated membranes of Examples 4 to 6 all have a lower water content than the untreated membranes. There is a correlation between the water content and the proton conductivity, and the lower the water content, the more difficult it is to conduct protons. It was found that the cations used in Examples 4 to 6 had high water repellency and were suitable as cations constituting the ion exchange layer.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The fuel cell according to the present invention can be used as an in-vehicle power source, a stationary generator, or the like.

Claims (7)

A fuel cell with the following configuration.
(1) The fuel cell is
An electrolyte membrane containing a solid polymer electrolyte and
An anode-side catalyst layer provided on one surface of the electrolyte membrane,
A cathode-side catalyst layer provided on the other surface of the electrolyte membrane,
An anode-side diffusion layer provided outside the anode-side catalyst layer,
The cathode side diffusion layer provided outside the cathode side catalyst layer and
It is provided with an isolation layer provided only between the anode-side catalyst layer and the anode-side diffusion layer.
(2) The anode-side diffusion layer contains carbon.
(3) The isolation layer has an electron conduction resistance of 0.5 Ωcm ² or less and a proton conduction resistance of 500 Ωcm ² or more. The fuel cell according to claim 1, wherein the isolation layer contains carbon and has a porosity of less than 50%. The isolation layer is composed of a porous metal layer inserted between the anode-side catalyst layer and the anode-side diffusion layer.
The fuel cell according to claim 1 or 2, wherein the thickness of the porous metal layer is 100 μm or more and 500 μm or less. The fuel cell according to claim 3, wherein the porous metal layer is made of a noble metal, Ti, or an alloy containing the noble metal or Ti. The isolation layer is composed of an ion exchange layer formed on the surface layer portion of the anode-side catalyst layer on the anode-side diffusion layer side.
The fuel cell according to any one of claims 1 to 4, wherein the ion exchange layer is a layer in which 90% or more of the protons of the acid group of the catalyst layer ionomer are ion-exchanged with cations other than the protons. The fuel cell according to claim 5, wherein the thickness of the ion exchange layer is 10% or more and 50% or less of the thickness of the anode-side catalyst layer. The fuel cell according to claim 5 or 6, wherein the cation is a tetraalkylammonium ion containing an alkyl group having 3 or more carbon atoms or a complex ion.

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