JP2007335162A - Membrane catalyst layer assembly, membrane electrode assembly, and polymer-electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane catalyst layer assembly capable of restraining deterioration of a catalyst layer even if actuation and stop of a polymer-electrolyte fuel cell are repeated, and achieving the polymer-electrolyte fuel cell having excellent durability and performing sufficient battery performance. <P>SOLUTION: A degree of graphitization of conductive carbon powder in a cathode catalyst layer is set higher at a portion corresponding to a downstream side than at a portion corresponding to an upstream side of a cathode gas flow path. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a membrane catalyst layer assembly, a membrane electrode assembly, and a polymer electrolyte fuel cell.

A conventional polymer electrolyte fuel cell using a polymer electrolyte having cation (hydrogen ion) conductivity is an electrochemical reaction between a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air. Power and heat are generated simultaneously.
Here, FIG. 8 is a schematic cross-sectional view showing an example of the basic configuration of a unit cell mounted on a conventional polymer electrolyte fuel cell. FIG. 9 is a schematic cross-sectional view showing an example of a basic configuration of a membrane electrode assembly (MEA) mounted on the unit cell 101 shown in FIG. As shown in FIG. 9, the membrane / electrode assembly 110 is obtained by supporting a catalyst (for example, a platinum-based metal catalyst) on carbon powder on both surfaces of a polymer electrolyte membrane 111 that selectively transports hydrogen ions. A catalyst layer 112 including an electrode catalyst and a polymer electrolyte having hydrogen ion conductivity is formed. This is called a membrane catalyst layer assembly.

Currently, as the polymer electrolyte membrane 111, for example, a polymer electrolyte membrane made of perfluorocarbon sulfonic acid is used. A gas diffusion layer 113 having both air permeability and electronic conductivity is formed on the outer surface of the catalyst layer 112 using, for example, carbon paper subjected to water repellent treatment. The combination of the catalyst layer 112 and the gas diffusion layer 113 constitutes a gas diffusion electrode (anode or cathode) 114.
A conventional unit cell 101 includes a membrane electrode assembly 110, a gasket 115, and a pair of plate-like separators 116. The gasket 115 is disposed around the gas diffusion electrode with a polymer electrolyte membrane interposed therebetween in order to prevent leakage and mixing of the supplied fuel gas and oxidant gas to the outside. This gasket is pre-assembled integrally with the gas diffusion electrode and the polymer electrolyte membrane, and a combination of these is sometimes called a membrane electrode assembly.

A pair of separators 116 for mechanically fixing the membrane electrode assembly 110 is disposed outside the membrane electrode assembly 110. A reaction gas (fuel gas or oxidant gas) is supplied to the gas diffusion electrode at a portion of the separator 116 that comes into contact with the membrane electrode assembly 110, and an electrode reaction product and a gas containing an unreacted reaction gas are discharged from the reaction field. A gas flow path 117 for carrying away to the outside of the electrode and a cooling fluid flow path 118 for flowing a cooling fluid (for example, cooling water) for controlling the temperature of the polymer electrolyte fuel cell are formed.
Although the gas channel 117 and the cooling fluid channel 118 can be provided separately from the separator 116, a method of forming a gas channel by providing a groove on the surface of the separator is generally used.

Thus, the membrane electrode assembly 110 is fixed by the pair of separators 116, the fuel gas is supplied to the gas flow path 117 of one separator 116, and the oxidant gas is supplied to the gas flow path 117 of the other separator 116. Thus, an electromotive force of about 0.7 to 0.8 V can be generated by one unit cell 101 when a practical current density of several tens to several hundred mA / cm ² is applied. However, in general, when a polymer electrolyte fuel cell is used as a power source, a voltage of several volts to several hundred volts is required. Therefore, in actuality, the required number of unit cells 101 are connected in series. Use as a stack.

In order to supply the reaction gas to the gas flow path 117, the piping for supplying the reaction gas is branched into a number corresponding to the number of separators 116 used in the stack, and the branch destinations are directly connected to the gas on the separator 116. A manifold that is a member connected to the flow path 117 is required. In particular, a manifold of the type that is directly connected to the separator 116 from an external pipe that supplies the reaction gas is called an external manifold.
On the other hand, there is a so-called internal manifold having a simpler structure. The internal manifold is configured by a through hole provided in the separator 116 in which the gas flow path 117 is formed, and the reaction port is directly connected to the gas flow path 117 from the through hole by connecting the inlet / outlet of the gas flow path 117 to this hole. Can be supplied.

The gas diffusion layer 113 mainly has the following three functions. The first function is a function of diffusing the reaction gas in order to uniformly supply the reaction gas from the gas flow path 117 of the separator 116 located outside the gas diffusion layer 113 to the electrode catalyst in the catalyst layer 112. The second function is a function of quickly discharging water generated by the reaction in the catalyst layer 112 to the gas flow path 117.
The third function is a function of conducting electrons necessary for the reaction or generated electrons. That is, the gas diffusion layer 113 is required to have high reaction gas permeability, moisture exhaustability, and electronic conductivity.

  In general, the gas diffusion layer 113 is made of a porous carbon fine powder having an electron conductivity, a pore former, carbon paper, carbon cloth, or the like so as to have gas permeability. A conductive base material having a porous structure is used. In addition, in order to provide moisture drainage, a water-repellent polymer such as a fluororesin is dispersed in the gas diffusion layer 113, and in addition, carbon fibers are provided in order to provide electron conductivity. The gas diffusion layer 113 is also made of an electron conductive material such as metal fiber or carbon fine powder.

  Next, the catalyst layer 112 mainly has four functions. The first function is a function of supplying the reaction gas supplied from the gas diffusion layer 113 to the reaction site of the catalyst layer 112, and the second function is hydrogen ions or generation necessary for the reaction on the electrode catalyst. It is a function to conduct the generated hydrogen ions. The third function is a function of conducting electrons necessary for the reaction or the generated electrons, and the fourth function is a function of accelerating the electrode reaction by high catalyst performance and its wide reaction area. That is, the catalyst layer 112 needs high reaction gas permeability, hydrogen ion conductivity, electron conductivity, and catalyst performance.

  In general, the catalyst layer 112 has a porous structure and a gas channel using porous conductive carbon particles or a pore-forming material having electron conductivity in order to provide gas permeability. Is formed. In order to provide hydrogen ion permeability, a polymer electrolyte is dispersed in the vicinity of the electrode catalyst in the catalyst layer 112 to form a hydrogen ion network. Furthermore, in order to provide electron conductivity, an electron channel is formed by using an electron conductive material such as conductive carbon particles as a carrier for an electrode catalyst. Further, in order to improve the catalyst performance, an electrode catalyst obtained by supporting very fine metal catalyst particles having a particle diameter of several nanometers on conductive carbon particles is highly dispersed in the catalyst layer 112. Things have been done.

In order to put the polymer electrolyte fuel cell into practical use, it is important to improve the durability and life of the membrane catalyst layer assembly or the membrane electrode assembly including the membrane catalyst layer assembly, and various studies have been made.
Here, as one of the causes of deterioration in durability of the polymer electrolyte fuel cell having the above-described configuration, oxidation of conductive carbon particles that are catalyst carriers can be cited. Carbon powder, which is a catalyst support for a polymer electrolyte fuel cell, is electrochemically oxidized at around +0.2 V (vs. RHE) at 25 ° C., so that the potential on the cathode side is +0.7 to +0.8 V. In (vs. RHE), there is a concern that it is oxidized to CO ₂ and disappears.

On the other hand, for example, in Patent Document 1, when the crystallinity (graphitization degree) of carbon (conductive carbon particles) is increased, the corrosion resistance is increased. It has been proposed to use highly crystalline carbon (conductive carbon particles) for batteries.
JP 2005-209615 A

  However, as in the technique described in Patent Document 1, carbon having a high degree of graphitization has a small surface area, and a catalyst using this carbon (conductive carbon particles) as a support has noble metal catalyst particles such as a platinum catalyst on the support. In other words, the particle size of the noble metal catalyst particles was increased and the catalytic activity was lowered, so there was still room for improvement. That is, simply using an electrode catalyst that uses carbon (conductive carbon particles) having a high degree of graphitization as a carrier simply for the catalyst layer, the battery voltage decreases and sufficient battery voltage cannot be obtained. There is still room for improvement from the viewpoint of obtaining a fuel cell having sufficient durability while securing a voltage.

The present invention has been made in view of the above problems, and an object thereof is to provide a membrane / catalyst layer assembly capable of realizing a polymer electrolyte fuel cell having sufficient battery voltage and sufficient durability. .
The present invention also provides a membrane / electrode assembly that includes the membrane / catalyst layer assembly of the present invention and can realize a polymer electrolyte fuel cell having sufficient battery voltage and sufficient durability. Objective.
Furthermore, the present invention provides a polymer electrolyte fuel cell equipped with any one of the membrane catalyst layer assembly and the membrane electrode assembly of the present invention, and having sufficient battery voltage and sufficient durability. The purpose is to provide.

  Therefore, as a result of intensive studies to achieve the above object, the inventors of the present invention have a region in which oxidation of conductive carbon particles tends to proceed when viewed in the main surface of the catalyst layer of the membrane-catalyst layer assembly. It was found that there is a region where oxidation is difficult to proceed. Further, the present inventors have further conducted intensive research, and in the main surface of the catalyst layer of the membrane-catalyst layer assembly, conductive carbon particles are selected depending on the region where the oxidation of the conductive carbon particles tends to proceed and the region where the oxidation does not proceed easily. Changing the degree of graphitization of the particles is extremely effective in achieving the above-described object of the present invention, in which sufficient battery voltage is obtained while suppressing oxidation of the conductive carbon particles in the catalyst layer. The headline and the present invention were completed.

That is, a cathode gas flow path is formed in the cathode separator sandwiching the membrane electrode assembly, and the oxidant gas flows from upstream to downstream. The inventors have observed in detail the corrosion state of the conductive carbon particles (carbon) in the catalyst layer along the cathode gas flow path. There is almost no deterioration due to oxidation of the conductive carbon particles, and there is significant deterioration due to oxidation of the conductive carbon particles in the catalyst layer from the center of the cathode gas passage to the part of the cathode catalyst layer along the downstream. I understood. Therefore, in order to suppress the corrosion of the conductive carbon particles, the present inventors have found that the conductive carbon particles having high oxidation resistance, that is, the degree of graphitization, is not formed on the portion of the cathode catalyst layer along the downstream of the cathode gas flow path. Therefore, it was considered effective to use conductive carbon particles having a high particle size.
Here, although the reason why the conductive carbon particles are significantly corroded in the portion of the catalyst layer of the cathode along the downstream of the cathode gas flow path has not necessarily been clearly clarified, the present inventors have I think as follows.

  That is, when the fuel cell is started and stopped, the gas in the fuel cell is replaced (purged). At this time, the gas distribution in the portion of the catalyst layer of the cathode along the downstream portion of the cathode gas flow path is improper. It tends to be uniform, and the potential is locally high (high on the brass side), and it is considered that the oxidation of the conductive carbon particles easily proceeds. And from the viewpoint of sufficiently suppressing the progress of the oxidation of the conductive carbon particles, the inventors of the present invention have high oxidation resistance conductive carbon particles on the portion of the cathode catalyst layer along the downstream of the cathode gas flow path, that is, It was considered effective to use conductive carbon particles with a high degree of graphitization.

On the other hand, in the catalyst layer of the cathode along the cathode gas flow path, the oxidant gas is gradually consumed from the upstream toward the downstream, so that the oxidant gas (for example, as oxidant gas, If used, the concentration of oxygen) will decrease, the polarization will increase and the current will decrease. That is, in the cathode catalyst layer, current concentration occurs in a portion along the upstream side of the cathode gas flow path.
Then, the present inventors considered that it is effective to use a catalyst having higher activity in the part of the cathode catalyst layer along the upstream side of the cathode gas flow path where current concentrates. As such a highly active catalyst, it is preferable to use conductive carbon particles having a low graphitization degree and a large surface area. Such conductive fine particles having a large surface area can finely disperse electrocatalyst metal particles having a small particle size, and can obtain high activity.

Therefore, the present invention provides
A polymer electrolyte having an anode separator and a cathode separator that are arranged to face each other, and a membrane electrode assembly that is arranged between the anode separator and the cathode separator, wherein a cathode gas channel is formed on the inner surface of the cathode separator A membrane-catalyst layer assembly mounted on a fuel cell,
An anode catalyst layer and a cathode catalyst layer disposed to face each other;
A polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer;
Have
The cathode catalyst layer includes an electrode catalyst and conductive carbon particles serving as a support for the electrode catalyst.
Of the cathode catalyst layer, the degree of graphitization of the conductive carbon particles contained in the part corresponding to the upstream of the cathode gas flow path is the same as the degree of graphitization of the conductive carbon particles contained in the part corresponding to the downstream of the cathode gas flow path. Lower than,
A membrane catalyst layer assembly is provided.

  As described above, conductive carbon particles having a low graphitization degree are used in the catalyst layer portion corresponding to the upstream portion of the cathode gas flow path where high activity against electrode reaction is required and corrosion of the conductive carbon particles hardly occurs. Adopting a structure using conductive carbon particles having a high degree of graphitization in the catalyst layer portion corresponding to the downstream portion of the cathode gas flow path, where current concentration is less likely to occur and corrosion of the conductive carbon particles is likely to occur. As a result, the performance degradation of the catalyst layer (particularly, the deterioration of the electrode catalyst carrier, which has been a conventional problem) can be sufficiently suppressed.

Therefore, according to the present invention, it is possible to provide a membrane / catalyst layer assembly capable of realizing a polymer electrolyte fuel cell having sufficient battery voltage and sufficient durability.
Further, a membrane / catalyst layer assembly capable of realizing a polymer electrolyte fuel cell having sufficient battery voltage and sufficient durability can be obtained by configuring a membrane / electrode assembly on which the membrane / catalyst layer assembly of the present invention is mounted. Can be provided.
Furthermore, if any one of the membrane catalyst layer assembly of the present invention and the membrane electrode assembly equipped with the membrane catalyst layer assembly of the present invention is employed, sufficient battery voltage and sufficient durability can be obtained. A polymer electrolyte fuel cell can be provided.

Here, in the present invention, “the portion of the cathode catalyst layer corresponding to the upstream of the cathode gas flow path” means that the oxidant gas is applied to the cathode catalyst layer and the cathode catalyst layer in the laminate of MEA and separator. Paying attention to the cathode separator disposed for supply, when viewed from the substantially normal direction of the main surface of the cathode catalyst layer and the main surface of the cathode separator at the same time, the inner surface of the cathode separator in the cathode catalyst layer (that is, The portion corresponding to the upstream portion of the cathode gas flow path provided on the cathode catalyst layer side (the portion that appears to overlap substantially, and the portion around the portion that appears to overlap substantially, upstream of the cathode gas flow channel This refers to the part where the oxidant gas supplied from the part diffuses and the electrode reaction proceeds. The range of the part where the oxidant gas supplied from the upstream part of the cathode gas channel diffuses and the electrode reaction proceeds is as follows: the flow rate of the oxidant gas, the temperature of the oxidant gas, the pressure of the oxidant gas, the cathode gas flow It varies as appropriate depending on the shape of the channel, the cross-sectional area of the cathode gas channel, the component composition of the cathode catalyst layer, the thickness of the cathode catalyst layer, the porosity of the cathode catalyst layer, and the like.
The term “upstream of the cathode gas channel” generally refers to the inlet side of the cathode gas channel in the flow direction of the oxidant gas.

In the present invention, “the portion of the cathode catalyst layer corresponding to the downstream of the cathode gas flow path” refers to supplying the oxidant gas to the cathode catalyst layer and the cathode catalyst layer in the laminate of MEA and separator. Focusing on the cathode separator disposed for the purpose, the inner surface of the cathode separator (that is, the cathode) of the cathode catalyst layer when viewed from the substantially normal direction of the main surface of the cathode catalyst layer and the main surface of the cathode separator simultaneously. The portion corresponding to the downstream portion of the cathode gas flow path provided on the catalyst layer side) (the portion that appears to overlap substantially and the portion around the portion that appears to overlap substantially and the downstream portion of the cathode gas flow passage The portion where the oxidant gas supplied from the gas diffuses and the electrode reaction proceeds). The range of the part where the oxidant gas supplied from the downstream part of the cathode gas channel diffuses and the electrode reaction proceeds is the range of the oxidant gas flow rate, the oxidant gas temperature, the oxidant gas pressure, the cathode gas flow. It varies as appropriate depending on the shape of the channel, the cross-sectional area of the cathode gas channel, the component composition of the cathode catalyst layer, the thickness of the cathode catalyst layer, the porosity of the cathode catalyst layer, and the like.
The term “downstream of the cathode gas passage” generally refers to the outlet side of the cathode gas passage in the flow direction of the oxidant gas.

  Further, from the viewpoint of obtaining the effects of the present invention more reliably, in the present invention, the “portion corresponding to the upstream of the cathode catalyst layer” means that one end of the total channel length of the cathode gas channel is the inlet and the other end. Is a portion facing a region having a position of 25% to 50% starting from the inlet, and “the portion corresponding to the downstream of the cathode catalyst layer” is the total length of the cathode gas channel. It is preferable that it is a part which opposes the area | region made into the position of 50%-75% by making one end of this into an exit and making the other end into the said outlet.

FIG. 7 illustrates preferred setting conditions for the “portion of the cathode catalyst layer corresponding to the upstream side of the cathode gas flow path” and the “portion of the cathode catalyst layer corresponding to the downstream side of the cathode gas flow path”. It becomes.
That is, FIG. 7 shows the “part of the cathode catalyst layer corresponding to the upstream of the cathode gas flow path” and “the part of the cathode catalyst layer corresponding to the downstream of the cathode gas flow path” in the present invention described above. It is explanatory drawing for demonstrating suitable setting conditions. FIG. 7 shows an upstream portion and a downstream portion of the cathode gas flow path. The “part of the cathode catalyst layer corresponding to the upstream side of the cathode gas flow path” is the part of the cathode catalyst layer that is disposed opposite to the upstream region R1 of the cathode gas flow path 170 shown in FIG. This is a portion around the portion facing the upstream region R1, and is a portion where the oxidant gas supplied from the upstream portion of the cathode gas channel diffuses and the electrode reaction proceeds.

In addition, the “part of the cathode catalyst layer corresponding to the downstream side of the cathode gas flow path” is the part of the cathode catalyst layer that is opposed to the downstream region R2 of the cathode gas flow path 170 shown in FIG. It is a part around the part arranged to face the downstream region R2, and is a part where the oxidant gas supplied from the downstream part of the cathode gas flow channel diffuses and the electrode reaction proceeds.
As shown in FIG. 7, the upstream region R1 of the cathode gas flow path 170 has an end of one end P1 of the total flow path length L1 of the cathode gas flow path 170 and the other end P2 as a base point of 25% to This is an area having a position of 50%. Further, the downstream region R2 of the cathode gas channel 170 has a position of 50% to 75% with the one end P3 of the total channel length L1 of the cathode gas channel 170 as the outlet and the other end P4 as the starting point. It is an area to do.

Here, the portion of the catalyst layer corresponding to the region R1 shown in FIG. 7 (“the portion of the cathode catalyst layer corresponding to the upstream of the cathode gas flow path”) and the portion of the catalyst layer corresponding to the region R2 (“cathode” Between the catalyst layer and the portion corresponding to the downstream of the cathode gas flow path)), a region of the catalyst layer containing conductive carbon particles having another degree of graphitization (hereinafter referred to as “the cathode catalyst layer, A portion corresponding to the middle flow of the cathode gas flow path ”).
In this case, from the viewpoint of more reliably obtaining the effects of the present invention, the degree of graphitization of the conductive carbon particles contained in the cathode catalyst layer portion corresponding to the middle flow of the cathode gas flow path is “the cathode gas in the cathode catalyst layer”. The degree of graphitization of the conductive carbon particles contained in the “part corresponding to the downstream of the flow path” is lower than the degree of graphitization of the conductive carbon particles contained in the “part of the cathode catalyst layer corresponding to the upstream of the cathode gas flow path”. It is preferable that the degree of graphitization is higher.

Furthermore, from the viewpoint of more reliably obtaining the effects of the present invention, the membrane catalyst layer assembly of the present invention includes a position where the portion corresponding to the upstream side of the cathode catalyst layer faces the inlet of the cathode gas flow path, The portion corresponding to the downstream of the cathode catalyst layer includes a position facing the outlet of the cathode gas flow path, and the area of the portion corresponding to the upstream of the main surface of the cathode catalyst layer is 25% to the total area of the main surface The area of the portion corresponding to the downstream of the main surface of the cathode catalyst layer is preferably 50% to 75% of the total area of the main surface.
In particular, when a gas flow path having a serpentine structure as shown in FIG. 4 is employed, the area of the portion corresponding to the upstream of the main surface of the cathode catalyst layer and the portion corresponding to the downstream of the main surface of the cathode catalyst layer. In some cases, the aspect of satisfying both the area condition and the condition described above with reference to FIG. 7 is more effective from the viewpoint of obtaining the effect of the present invention more reliably.

The present invention also provides:
A pair of gas diffusion layers disposed opposite to each other, and a membrane catalyst layer assembly disposed between the pair of gas diffusion layers,
The membrane catalyst layer assembly is the membrane catalyst layer assembly described above,
A membrane electrode assembly is provided.
As described above, since the membrane electrode assembly of the present invention includes the membrane catalyst layer assembly of the present invention described above, a polymer electrolyte fuel cell having sufficient battery voltage and sufficient durability is obtained. Can be realized.

Furthermore, the present invention provides
There is also provided a polymer electrolyte fuel cell comprising the membrane electrode assembly described above.
Thus, since the polymer electrolyte fuel cell of the present invention includes the membrane electrode assembly of the present invention described above, it has sufficient battery voltage and sufficient durability.

According to the present invention, it is possible to sufficiently suppress the oxidative deterioration of the conductive particles (carbon) as the catalyst carrier even when the operation and stop of the polymer electrolyte fuel cell are repeated, and to achieve sufficient battery voltage and sufficient durability. It is possible to provide a membrane / catalyst layer assembly capable of realizing a polymer electrolyte fuel cell.
Further, according to the present invention, there is provided a membrane electrode assembly capable of realizing a polymer electrolyte fuel cell having sufficient battery voltage and sufficient durability by mounting the membrane catalyst layer assembly of the present invention. Can be provided.
Further, according to the present invention, a polymer electrolyte fuel having sufficient battery voltage and sufficient durability by mounting any one of the membrane catalyst layer assembly and the membrane electrode assembly of the present invention. A battery can be provided.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description may be abbreviate | omitted.
FIG. 1 is a schematic cross-sectional view showing an example of a basic configuration of a unit cell mounted in a preferred embodiment of a polymer electrolyte fuel cell of the present invention. Note that the polymer electrolyte fuel cell (not shown) of this embodiment is composed of a single cell 1 shown in FIG. 1 or a stack obtained by stacking a plurality of single cells 1. May be.

2 is a schematic cross-sectional view showing an example of the basic configuration of the membrane electrode assembly mounted on the unit cell 1 shown in FIG. 1, and FIG. 3 is mounted on the membrane electrode assembly 10 shown in FIG. It is a schematic sectional drawing which shows an example of the basic composition of a membrane catalyst layer assembly.
4 is a cross-sectional view taken along line XX in FIG. 1, that is, a front view of the cathode separator 16c in FIG. 1 as viewed from the cathode gas flow path 17c. 5 is a cross-sectional view taken along line YY in FIG. 1, that is, a front view of the anode separator 16a in FIG. 1 as viewed from the anode gas flow path 17a side.

First, the structural requirements of the cell 1 of this embodiment will be described.
As shown in FIG. 1, the unit cell 1 of the present embodiment mainly includes a membrane electrode assembly 10, a gasket 15, and a pair of plate-like cathode separator 16c and anode separator 16a, which will be described later. The gasket 15 is provided with a polymer electrolyte membrane for preventing leakage of the fuel gas supplied to the membrane electrode assembly 10 to the outside, preventing leakage of the oxidant gas to the outside, and preventing mixing of the fuel gas and the oxidant gas. 11 is arranged around the gas diffusion electrode in a state of sandwiching the outer extension portion.

  Further, as shown in FIG. 2, the membrane electrode assembly 10 includes a cathode catalyst layer 12c and an anode on both surfaces of a polymer electrolyte membrane 11 mainly composed of a polymer electrolyte having cation (hydrogen ion) conductivity. A catalyst layer 12a is disposed. The cathode catalyst layer 12c includes an electrode catalyst obtained by supporting a noble metal catalyst containing at least platinum on support particles (for example, conductive carbon particles such as graphite), a polymer electrolyte having hydrogen ion conductivity, and an anode. The catalyst layer 12a includes an electrode catalyst obtained by supporting a noble metal catalyst containing at least platinum on carrier particles (for example, conductive carbon particles such as graphite) and a polymer electrolyte having hydrogen ion conductivity. As shown in FIGS. 2 and 3, the polymer electrolyte membrane 11, the cathode catalyst layer 12 c, and the anode catalyst layer 12 a constitute a membrane catalyst layer assembly 20.

The present invention is characterized by the conductive carbon particles that are a simple substance of the catalyst contained in the cathode catalyst layer 12c, and the specific contents thereof will be described later.
As the polymer electrolyte constituting the polymer electrolyte membrane 11, a conventionally known polymer electrolyte having hydrogen ion conductivity can be used. For example, it is particularly preferable to use a polymer electrolyte having a sulfonic acid group.
As said polymer electrolyte, what has an average EW value of 900-1200 is preferable. When the average EW is 1200 or less, it is possible to suppress an increase in the resistance value of the polymer electrolyte membrane 11, and when the average EW value is 900 or more, swelling due to an increase in water content can be suppressed. This is preferable because the strength of the polymer electrolyte membrane 11 can be easily maintained.

The polymer electrolyte is preferably composed of a perfluorocarbon polymer. For example, CF ₂ ═CF— (OCF ₂ CFX) _m —O _p — (CF ₂ ) _n —SO ₃ H (M represents an integer of 0 to 3, n represents an integer of 1 to 12, p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group.) A copolymer containing a polymer unit based on the above and a polymer unit based on tetrafluoroethylene can be used.

Preferable examples of the fluorovinyl compound include compounds represented by the following formulas (1) to (3). However, in the following formula, q is an integer of 1 to 8, r is an integer of 1 to 8, and t is an integer of 1 to 3.
_{CF 2 = CFO (CF 2)} q -SO 3 H ··· (1)
_{CF 2 = CFOCF 2 CF (CF} 3) O (CF 2) r -SO 3 H ··· (2)
_{CF 2 = CF (OCF 2 CF} (CF 3)) t O (CF 2) 2 -SO 3 H ··· (3)
Specific examples of the polymer electrolyte include Nafion (trade name) manufactured by Du Pont, USA, and Flemion (trade name) manufactured by Asahi Glass Co., Ltd.

  Gas diffusion layers 13c and 13a having both air permeability and electronic conductivity are formed on the outer surfaces of the cathode catalyst layer 12c and the anode catalyst layer 12a, respectively, using, for example, water-repellent carbon paper. . A cathode (gas diffusion electrode) 14c is configured by a combination of the cathode catalyst layer 12c and the gas diffusion layer 13c, and an anode (gas diffusion electrode) 14a is configured by a combination of the anode catalyst layer 12a and the gas diffusion layer 13a.

  As shown in FIG. 1, a pair of conductive cathode separators 16c and anode separators 16a for mechanically fixing the membrane electrode assembly 10 are disposed outside the membrane electrode assembly 10. Yes. An oxidant gas is supplied to the cathode 14c to the portion (inner surface) of the cathode separator 16c that comes into contact with the membrane electrode assembly 10, and electrode reaction products, unreacted reaction gas, reaction product water, and the like are supplied to the outside of the unit cell 1. A cathode gas flow path 17c is formed in the anode separator 16a, and a fuel gas is supplied to the anode 14a to a portion (inner surface) of the anode separator 16a that is in contact with the membrane electrode assembly 10. An anode gas flow path 17a for carrying away the gas containing the reaction product to the outside of the unit cell 1 is formed. Further, cooling fluid flow paths 18c and 18a are formed on the outer surfaces of the cathode separator 16c and the anode separator 16a, respectively, for flowing a cooling fluid (for example, cooling water) for controlling the temperature of the fuel cell.

  In this way, the membrane electrode assembly 10 is fixed by the pair of cathode separator 16c and anode separator 16a, the oxidant gas is supplied to the cathode gas flow path 17c of the cathode separator 16c, and the anode gas flow path 17a of the anode separator 16a is supplied. If fuel gas is supplied, a certain amount of electromotive force can be generated by one single cell 1. However, in general, when a polymer electrolyte fuel cell is used as a power source, a voltage of several volts to several hundred volts is required. Therefore, in actuality, the number of cells 1 required as in this embodiment is required. Only the stack structure connected in series is adopted.

  In order to supply the reaction gas (oxidant gas and fuel gas) to the cathode gas channel 17c and the anode gas channel 17a, the number of pipes that supply the reaction gas corresponds to the number of separators to be used (for example, a single cell). A manifold that is a jig for branching directly to the separator. In particular, a type of manifold that is directly connected to a separator from an external pipe that supplies reaction gas is called an external manifold. On the other hand, there is a so-called internal manifold having a simpler structure. The internal manifold is composed of a through hole provided in the separator having the gas flow path, and the reaction port can be directly supplied to the gas flow path from the through hole by connecting the inlet / outlet of the gas flow path to the hole. it can. Any manifold may be employed in the present invention.

  Here, as shown in FIG. 4, the cathode separator 16c has a substantially rectangular shape, and has an oxidant gas inlet manifold hole 21, an oxidant gas outlet manifold hole 22, a fuel gas inlet manifold hole 23, and a fuel gas outlet manifold at the peripheral edge. A hole 24, a cooling fluid inlet manifold hole 25 and a cooling fluid outlet manifold hole 26 are provided. Note that a region P in FIG. 4 is a portion where the main surface of the cathode 14c (the cathode catalyst layer 12c and the cathode gas diffusion layer 13c) contacts.

In particular, a cathode gas flow path 17c that connects the oxidant gas inlet manifold hole 21 and the oxidant gas outlet manifold hole 22 is provided on the surface of the cathode separator 16c that contacts the cathode catalyst layer 12c. The cathode gas channel 17c has a so-called serpentine shape. More specifically, the cathode gas flow path 17c is constituted by a groove, and is substantially on the side of the four sides of the cathode separator 16c where the fuel gas outlet manifold hole 24 and the cooling fluid inlet manifold hole 25 are provided. It has nine straight portions 18c ₁ extending in the vertical direction and eight turn portions 18c ₂ connecting the adjacent immediately preceding portions 18c ₁ .

  On the other hand, as shown in FIG. 5, the anode separator 16a has a substantially rectangular shape, and has an oxidant gas inlet manifold hole 21, an oxidant gas outlet manifold hole 22, a fuel gas inlet manifold hole 23, and a fuel gas outlet manifold hole at the peripheral edge. 24, a cooling fluid inlet manifold hole 25 and a cooling fluid outlet manifold hole 26 are provided. Note that a region Q in FIG. 5 is a portion where the main surface of the anode 14a (the anode catalyst layer 12a and the anode gas diffusion layer 13a) is in contact.

In particular, an anode gas flow path 17 a that communicates the fuel gas inlet manifold hole 23 and the fuel gas outlet manifold hole 24 is provided on the surface of the anode separator 16 a that contacts the anode catalyst layer 12 a. The anode gas channel 17a has a so-called serpentine shape. More specifically, the anode gas flow path 17a is constituted by a groove, and is approximately on the side of the four sides of the anode separator 16a where the fuel gas outlet manifold hole 24 and the cooling fluid inlet manifold hole 25 are provided. It has nine straight portions 18a ₁ extending in the vertical direction and eight turn portions 18a ₂ connecting the adjacent immediately preceding portions 18a ₁ .

The materials of the cathode separator 16c and the anode separator 16a as described above are not particularly limited, and those known in the art can be used, such as metal, carbon, and a mixed material of graphite and resin. Is mentioned.
Further, the materials of the cathode gas diffusion layer 13c and the anode gas diffusion layer 13a are not particularly limited, and those known in the art can be used, and examples thereof include carbon cloth and carbon paper.

  Next, as described above, the cathode catalyst layer 12c is formed by an electrode catalyst composed of carrier particles (conductive carbon particles) carrying a noble metal catalyst containing at least platinum, and a polymer electrolyte having hydrogen ion conductivity. The anode catalyst layer 12a is formed by an electrode catalyst composed of carrier particles (conductive carbon particles) carrying a noble metal catalyst containing at least platinum, and a polymer electrolyte having hydrogen ion conductivity.

This embodiment, as shown in FIG. 6, of the cathode catalyst layer 12c, graphitization degree of the conductive carbon particles contained in the portion 12c ₁ corresponding to the upstream of the cathode gas passage 17c is, the cathode gas passage 17c It is characterized by being lower than the degree of graphitization of the conductive carbon particles contained in the portion 12c ₂ corresponding to the downstream side. 6 is a cross-sectional view taken along the line ZZ in FIG. 1 (in the unit cell 1 shown in FIG. 1, the polymer electrolyte membrane 11, the anode catalyst layer 12a, the anode gas diffusion layer 13a, the gasket 15 and the anode separator 16a are removed, and the cathode It is the figure seen from the catalyst layer 12c side. That is, FIG. 6 shows the positional relationship between the cathode catalyst layer 12c and the cathode gas flow path 17c in the cathode separator 16c.

This embodiment corresponds to the graphitization degree G ₁ of the conductive carbon particles contained in the portion 12c ₁ corresponding to the upstream of the cathode gas flow path 17c in the cathode catalyst layer 12c and the downstream of the cathode gas flow path 17c. The graphitization degree G ₂ of the conductive carbon particles contained in the portion 12c ₂ satisfies the following relational expression (1). In the anode catalyst layer 12a, the graphitization degree of the conductive carbon particles may be substantially uniform over the entire main surface of the anode catalyst layer 12a.
Relational expression: G ₁ <G ₂ (1)

The portion 12c ₁ corresponding to the upstream of the cathode catalyst layer 12c has a total flow length of 25 with one end out of the total flow length of the cathode gas flow channel 17c and the other end as the origin. The portion 12c _{2 that} is opposed to the region having a position of 50% to 50% (position indicated by reference numeral 29 in FIG. 6) and that corresponds to the downstream side of the cathode catalyst layer 12c is the total flow of the cathode gas channel 17c. One part of the path length is the part facing the region of 50% to 75% (position indicated by reference numeral 31 in FIG. 6) with the outlet 30 as one end and the outlet 30 of the entire flow path as the starting point. is there.

The portion 12c ₁ corresponding to the upstream of the cathode catalyst layer 12c is 25% or more of the total flow path length with one end of the total flow path length of the cathode gas flow path 17c and the other end as the starting point. If it is a portion facing the region at the position of 50%, a current having a low oxidation resistance and a high activity in the portion 12c ₁ corresponding to the upstream where current (for example, a current that is almost half of the entire current) is likely to concentrate. It is possible to more surely realize a polymer electrolyte fuel cell that can cause the presence of conductive carbon particles, has high activity, and exhibits sufficient battery performance.

Further, the portion 12c ₂ corresponding to the downstream side of the cathode catalyst layer 12c has an outlet 30 as one end of the total channel length of the cathode gas channel 17c and the outlet 30 as the starting point of the other channel length as the other end. % if a portion opposed to the area in 75% of the positions, the portion 12c ₂ which corresponds to the downstream fuel cell start due to stop uneven gas conductive carbon particles due to the distribution is degraded Conductive carbon particles with high oxidation resistance and low activity can be present more reliably, more reliably a polymer electrolyte fuel cell with suppressed catalyst deterioration, durability and sufficient battery performance Can be realized.

In other words, the portion 12c ₁ corresponding to the upstream of the cathode catalyst layer 12c includes a position (a position indicated by reference numeral 28a in FIG. 6) facing the inlet 28 of the cathode gas flow path 17c. The portion 12c ₂ corresponding to the downstream includes a position (a position indicated by reference numeral 30a in FIG. 6) facing the outlet 30 of the cathode gas flow path 17c, and corresponds to the upstream of the main surface of the cathode catalyst layer 12c. The area of the portion 12c ₁ is 25% to 50% of the total area of the main surface, and the area of the portion 12c ₂ corresponding to the downstream of the main surface of the cathode catalyst layer 12c is 50% to the total area of the main surface. 75%.

Similarly to the above, if the area of the portion 12c ₁ corresponding to the upstream of the main surface of the cathode catalyst layer 12c is 25% to 50% of the total area of the main surface, the current (for example, approximately half of the entire current). The conductive carbon particles having low oxidation resistance and high activity can more surely be present in the portion 12c ₁ corresponding to the upstream where the current) tends to concentrate, and has high activity and sufficient battery performance. Thus, a polymer electrolyte fuel cell can be realized more reliably.

Further, if the area of the portion 12c ₂ corresponding to the downstream side of the main surface of the cathode catalyst layer 12c is 50% to 75% of the total area of the main surface, the gas distribution is uneven due to the start / stop of the fuel cell. As a result, the conductive carbon particles having high oxidation resistance and low activity can be more surely present in the portion 12c ₂ corresponding to the downstream where the conductive carbon particles are deteriorated, and the deterioration of the catalyst is suppressed and the durability is improved. And a polymer electrolyte fuel cell that exhibits sufficient battery performance.

Further, as a modification of the present embodiment, the degree of graphitization of the conductive carbon particles of the cathode catalyst layer 12c from the position facing the inlet 28 of the cathode gas flow path 17c (position indicated by reference numeral 28a in FIG. 6) from the cathode. You may increase (inclination) over the position (position shown by the code | symbol 30a in FIG. 6) facing the exit 30 of the gas flow path 17c.
Here, “the degree of graphitization of the conductive carbon particles in the cathode catalyst layer 12c increases (inclines) from a position facing the inlet 28 of the cathode gas channel 17c to a position facing the outlet 30 of the cathode gas channel 17c. The state of “being on” assumes that the cathode catalyst layer 18c is composed of two or more regions (a plurality of regions) from the upstream side to the downstream side of the cathode gas flow channel 17c. The graphitization degree of the conductive carbon particles in the most downstream region located is finally larger than the graphitization degree of the conductive carbon particles in the most upstream region located at the other end of the cathode catalyst layer 18c, When the regions are viewed as a whole, the degree of graphitization of the conductive carbon particles in each region is roughly increased from the most upstream region to the most downstream region of the cathode gas channel 17c.

  For example, it may be in a state where the degree of graphitization of the conductive carbon particles continuously and monotonously increases from the most upstream region to the most downstream region. When the cathode catalyst layer 12c is composed of three or more regions, for example, among the regions disposed between the most upstream region and the most downstream region, conductive carbon particles in some adjacent regions. The graphitization degree may take the same value. Furthermore, when comparing the graphitization degree of the conductive carbon particles of some adjacent regions among the regions arranged between the most upstream region and the most downstream region, the region located on the side of the most downstream region The graphitization degree of the conductive carbon particles may be smaller than the graphitization degree of the conductive carbon particles in the region located on the most upstream region side.

  As the conductive carbon particles having different degrees of graphitization, at least two kinds of conductive carbon particles having different degrees of graphitization may be used. If the degree of graphitization can be increased from upstream to downstream of the cathode gas flow path, 3 More than one kind of conductive carbon particles may be used. In addition, the boundary of the region where the conductive carbon particles change may be continuous or discontinuous, and the mixture ratio of the two types of conductive carbon particles is gradually changed for each region. It may be (gradient).

As the conductive carbon particles having a high degree of graphitization, for example, acetylene black and natural graphite can be used, and as the conductive carbon particles having a low degree of graphitization, for example, ketjen black, vulcan black and activated carbon can be used. Can do.
Examples of the method for measuring the degree of graphitization of the conductive carbon particles include a method using a Raman spectrum. The graphitization degree can be evaluated using the half-value width of the peak of the absorption band appearing in the vicinity of 1580 cm ⁻¹ in the Raman spectrum as an index. When the half width is 75 cm ⁻¹ or less, the degree of graphitization is high, the resistance to oxidation is strong, and deterioration can be suppressed. On the other hand, if the half width is 80 cm ⁻¹ or more, the degree of graphitization is low and the surface area is large, so that the resistance to oxidation tends to be low. However, the electrode catalyst can be highly dispersed, and a highly active catalyst region can be obtained. It is done.

Therefore, in the present embodiment, the half width of the peak of 1580 cm ⁻¹ measured by the Raman spectroscopy of the conductive carbon particles is 80 cm ⁻¹ or more in the portion corresponding to the upstream of the cathode gas flow path 17 c, and the cathode gas It is preferably 75 cm ⁻¹ or less at a portion corresponding to the downstream side of the flow path 17c.

Next, an example of a method for manufacturing the fuel cell according to the present embodiment as described above will be described.
First, in order to produce the membrane / catalyst layer assembly 20 of the present embodiment shown in FIG. 3, for example, a commercially available polymer electrolyte membrane 11 is used, and the cathode catalyst layer 12c and the anode catalyst layer 12a are disposed on both sides thereof, respectively. . The cathode catalyst layer 12c and the anode catalyst layer 12a can be formed with catalyst layer forming ink. The ink for forming a catalyst layer includes at least an electrode catalyst made of conductive carbon particles that are carrier particles carrying a noble metal catalyst, the polymer electrolyte, and a dispersion medium.

As the dispersion medium used for preparing the ink for forming the catalyst layer, it is preferable to use a liquid containing alcohol that can dissolve or disperse the polymer electrolyte (including a dispersion state in which the polymer electrolyte is partially dissolved).
The dispersion medium preferably contains at least one of water, methanol, propanol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butyl alcohol. These water and alcohol may be used alone or in combination of two or more. The alcohol is particularly preferably a straight chain having one OH group in the molecule, and ethanol is particularly preferable. This alcohol includes those having an ether bond such as ethylene glycol monomethyl ether.

  The ink for forming the catalyst layer preferably has a solid content concentration of 0.1 to 20% by mass. When the solid content concentration is 0.1% by mass or more, a catalyst layer having a predetermined thickness can be formed without repeating spraying or coating many times in preparing the catalyst layer by spraying or coating the catalyst layer forming ink. Can be obtained and production efficiency is improved. Moreover, the viscosity of a liquid mixture can be moderately adjusted as solid content concentration is 20 mass% or less, and a catalyst layer can be made uniform. The solid content concentration is particularly preferably 1 to 10% by mass.

  Moreover, it is preferable to prepare the ink for forming the catalyst layer so that the mass ratio of the electrode catalyst to the polymer electrolyte is 50:50 to 85:15 in terms of solid content. Thereby, the polymer electrolyte can efficiently coat the noble metal catalyst, and when the membrane electrode assembly 10 is produced, the three-phase interface can be increased. When the mass ratio is 50:50 or more, the pores of the conductive carbon particles as the carrier particles are not easily crushed by the polymer electrolyte, a reaction field can be secured, and the performance as a polymer electrolyte fuel cell can be further improved. It can be surely secured. Further, when the mass ratio is 85:15 or less, the coating of the electrode catalyst with the polymer electrolyte can be made more reliable, and the performance as the polymer electrolyte fuel cell can be more reliably ensured. it can. It is particularly preferable that the mass ratio of the electrode catalyst and the polymer electrolyte is adjusted to be 60:40 to 80:20.

The ink for forming the catalyst layer can be prepared based on a conventionally known method. Specifically, a method using a stirrer such as a homogenizer or a homomixer, a method using high-speed rotation such as using a high-speed rotating jet flow method, or a high-pressure emulsifying apparatus or the like is used to push the dispersion from a narrow part. The method of giving a shearing force to a dispersion liquid by taking out is mentioned.
When the cathode catalyst layer 12c and the anode catalyst layer 12a are formed using the catalyst layer forming ink, the catalyst layer 12c and the anode catalyst layer 12a are formed on the support sheet. Specifically, the catalyst layer forming ink is applied to the support sheet by spraying or coating, and the catalyst layer forming ink on the support sheet is dried to dry the catalyst layer on the support sheet. What is necessary is just to form 12c and the anode catalyst layer 12a.

  Here, the cathode gas diffusion electrode 14c and the anode gas diffusion layer 14a may be manufactured using only the cathode catalyst layer 12c or the anode catalyst layer 12a obtained by peeling from the support sheet as a product (gas diffusion electrodes 14c and 14a). Alternatively, a product in which the cathode catalyst layer 12c or the anode catalyst layer 12a is formed on the support sheet so as to be peelable may be manufactured as a product. As this support sheet, as will be described later, a synthetic resin sheet having no solubility in the mixed solution for forming the catalyst layer, a laminate film having a structure in which a layer made of a synthetic resin, a layer made of a metal is laminated, Examples thereof include metallic sheets, ceramic sheets, inorganic organic composite sheets, and polymer electrolyte membranes.

As a coating method of the mixed liquid when forming the cathode catalyst layer 12c or the anode catalyst layer 12a, a method using an applicator, a bar coater, a die coater, a spray, a screen printing method, a gravure printing method, or the like is applied. Can do.
The thicknesses of the cathode catalyst layer 12c and the anode catalyst layer 12a are preferably independently 3 to 50 μm. When the thickness is 3 μm or more, it is easy to form a uniform catalyst layer, a certain amount of catalyst can be secured and durability can be kept moderately preferable, and when the thickness is 50 μm or less, it is supplied. The reaction gas is preferable because it easily diffuses in the catalyst layer and allows the reaction to proceed easily. From the viewpoint of obtaining the effects of the present invention more reliably, the thickness of the cathode catalyst layer 12c and the anode catalyst layer 12a is particularly preferably 5 to 30 μm.

From the cathode catalyst layer 12c and the anode catalyst layer 12a obtained as described above, the membrane catalyst layer assembly 20, the cathode gas diffusion electrode 14c, the anode gas diffusion electrode 14a, the membrane electrode assembly 10 and the unit cell 1 (polymer) An electrolyte fuel cell is manufactured.
At that time, when the polymer electrolyte membrane 11 is used as the support sheet, the cathode catalyst layer 12c and the anode catalyst layer 12a are formed on both surfaces thereof, and thereafter, the whole is made of carbon paper, carbon cloth, carbon felt or the like. It may be sandwiched between the gas diffusion layers 13c and 13a and bonded by a known technique such as hot pressing. When forming the cathode catalyst layer 12c, first, a catalyst layer using carbon having a high degree of graphitization is formed on a corresponding portion of the film, and then a catalyst layer using carbon having a low degree of graphitization is formed. Alternatively, the catalyst layer is formed through the reverse process. Specifically, for example, the first catalyst layer is formed on the corresponding portion of the film by using a spray, and the second catalyst layer is formed on the corresponding portion by replacing the catalyst layer paint.

  Further, when the cathode catalyst layer 12c and the anode catalyst layer 12a are formed on the support sheet, the support sheet with the cathode catalyst layer 12c and the support sheet with the anode catalyst layer 12a are brought into contact with the polymer electrolyte membrane 11. The cathode catalyst layer 12c and the anode catalyst layer 12a may be transferred by peeling the support sheet and bonded by a known technique. In this case as well, when forming the cathode catalyst layer, a support having a catalyst layer of carbon having a high degree of graphitization and a catalyst layer having a low degree of carbon is prepared, and the catalyst layer cut to the appropriate size is applied to the corresponding part of the membrane. And may be transferred by a known method.

  Further, when the unit cell shown in FIG. 1 is manufactured using the membrane electrode assembly 10, the gasket 15, the cathode separator 16c, and the anode separator 16a may be used and manufactured by a method known in the art. As described above, the polymer electrolyte fuel cell of the present invention may be constituted by a stack obtained by stacking a plurality of unit cells 1.

As mentioned above, although one Embodiment of this invention was described in detail, this invention is not limited to the said embodiment.
For example, the case where serpentine-shaped gas flow paths are used as the cathode gas flow path 17c and the anode gas flow path 18c has been described. However, the number of straight portions and turn portions to be configured is not limited to the above embodiment, It is also possible to appropriately change the design of the shape as long as the effects of the invention are not impaired.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

<< Comparative Example 1 >>
In this comparative example, a unit cell having the same configuration as that shown in FIG. 1 was prepared except that the cathode catalyst layer was configured as follows. For the cathode catalyst, only acetylene black was used as conductive carbon particles as a support. Half-width of the absorption peak of 1580 cm ^-1 in the Raman spectrum of the conductive carbon particles was 43cm ^-1.
First, a solution containing a polymer electrolyte (Nafion solution manufactured by Aldrich) was cast on a polypropylene support sheet and dried to obtain a 40 μm polymer electrolyte membrane.

  Further, acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., particle size 35 nm) was mixed with an aqueous dispersion of polytetrafluoroethylene (PTFE) (D-1 manufactured by Daikin Industries, Ltd.) and dried. A water repellent treatment ink containing 20% by mass of PTFE as a mass was prepared. This water-repellent treatment ink is applied and impregnated on a carbon cloth (Carbon GF-20-31E manufactured by Nippon Carbon Co., Ltd.) serving as a base material for the gas diffusion layer, and is heated at 300 ° C. using a hot air dryer. And a gas diffusion layer (about 200 μm) was formed.

Next, a commercially available 50 mass% acetylene black-supported platinum catalyst (manufactured by E-TEK) was added to a polymer electrolyte dispersion (Aldrich, USA) so that the mass ratio of the electrode catalyst to the polymer electrolyte was 1: 1. And a catalyst layer forming ink was prepared. The obtained ink for forming a catalyst layer was applied to two support sheets (made of polypropylene) to form two catalyst layers (a cathode catalyst layer and an anode catalyst layer). The amount of electrode catalyst (platinum) supported per cm ² was 0.4 mg in the cathode catalyst layer and 0.3 mg in the anode catalyst layer.

The gas diffusion layer, the cathode catalyst layer, and the anode catalyst layer obtained as described above were joined to both surfaces of the polymer electrolyte membrane by hot pressing to produce a membrane electrode assembly A having the structure shown in FIG.
Next, a rubber gasket plate (sealing material) was joined to the outer periphery of the polymer electrolyte membrane of the membrane electrode assembly A to form manifold holes for fuel gas and oxidant gas flow.

  On the other hand, an electrically conductive plate made of a graphite plate impregnated with a phenol resin, having an outer dimension of 10 cm × 10 cm × 1.3 mm, and having a gas flow path having a width of 0.9 mm and a depth of 0.7 mm. A cathode separator and an anode separator were prepared. The shapes of the cathode separator and the anode separator were as shown in FIGS. 4 and 5, respectively. Using these two separators, an anode separator in which a cathode separator 16c formed with a cathode gas channel 17c is formed on one surface of the membrane electrode assembly A and an anode gas channel 17a is formed on the other surface. 16a was overlaid to obtain a single cell.

A stainless steel current collector plate, an insulating plate made of an electrically insulating material, and an end plate were arranged at both ends of the unit cell, and the whole was fixed with a fastening rod. The fastening pressure at this time was 10 kgf / cm ² per separator area. In this way, a polymer electrolyte fuel cell A composed of single cells was produced.

<< Comparative Example 2 >>
Membrane electrode assembly B was obtained in the same manner as in Comparative Example 1, except that a catalyst (manufactured by Tanaka Kikinzoku Kogyo) in which the conductive carbon particles in the cathode catalyst layer 12c were ketjen black was used. Further, using this membrane electrode assembly B, a polymer electrolyte fuel cell B was produced in the same manner as in Example 1.

Example 1
Total flow length portion 12c ₁ corresponding to the upstream of the cathode gas passage 17c, one end of the total flow path length of the cathode gas channel 17c and the inlet 28 and the other end from the inlet 28 of the cathode catalyst layer 12c It was set to a portion facing the region of 33% position.
Further, the portion 12c ₂ of the cathode catalyst layer 12c corresponding to the downstream side of the cathode gas channel 17c has one end of the total channel length of the cathode gas channel 17c as the outlet 30 and the other end as the total channel length. It set to the part which opposes the area | region made into 67% of positions from the exit 30. FIG.
The area of the portion 12c ₁ corresponding to the upstream of the main surface of the cathode catalyst layer 12c was 33% of the total area of the main surface.
Furthermore, the area of the portion 12c ₂ corresponding to the downstream of the main surface of the cathode catalyst layer 12c was 67% of the total area of the main surface.

Then, in the portion 12c ₁ corresponding to the upstream, ketjen black having a low graphitization degree is used as the conductive carbon particles, and in the portion 12c ₂ corresponding to the downstream, acetylene black having a high graphitization degree is used as the conductive fine particles. A membrane / electrode assembly C of the present invention was obtained in the same manner as in Comparative Example 1 except that the catalyst used as the carrier was used. Further, using this membrane electrode assembly C, a polymer electrolyte fuel cell C of the present invention was produced in the same manner as in Comparative Example 1.

[Evaluation test]
(1) Air purge test Using polymer electrolyte fuel cells A to C consisting of unit cells including membrane electrode assemblies A to C, power generation is carried out at a current density of 0.5 A / cm ² for 12 hours to be fully active After the conversion, the voltage (initial voltage) in a state where power was generated at 0.16 A / cm ² was recorded.
Next, power generation and stop were repeated in a pattern as shown below, and the difference between the power generation voltage after 1000 cycles and the initial voltage was measured.
That is, power generation is performed for 20 minutes (Step 1), power generation is stopped, N ₂ purge is performed for both the anode and cathode for 10 minutes, the N ₂ purge is stopped, the stack is sealed for 17 minutes, and only N ₂ purge is performed for the cathode. After the cathode N ₂ purge is stopped, the stack is sealed for 5 minutes, the hydrogen supply to the anode and the air supply to the cathode are started simultaneously, the supply is continued for 3 minutes, and the power generation in step 1 is performed again. The pattern was repeated.
Also, the cross section of the membrane electrode assembly before and after the measurement was observed with an electron microscope. The cathode catalyst layer had a thickness of 1 cm from the upper part of the catalyst layer as the upstream side, the middle part of the catalyst layer as the middle stream side, and the lower part of the catalyst layer as the downstream side The measurement was made at three points, 1 cm to 1 cm, and the changes were compared.
These results are shown in Table 1.

From the results shown in Table 1, according to the polymer electrolyte fuel cell of the present invention, deterioration due to carbon oxidation can be efficiently suppressed in 1000 power generation-stop tests, so that the voltage drop is suppressed to within 1%. can do. Further, the power generation voltage can be secured at 780 mV or more from the initial stage to after deterioration, and high power generation efficiency can be maintained from the initial stage of power generation to after deterioration of durability.
Moreover, when the voltage of Example 1 is simply calculated from the area ratio of the catalyst from the results of Comparative Example 1 and Comparative Example 2, it becomes 785 mV, but the result of Example 1 exceeds that, and the current is concentrated. The effect of arranging a highly active catalyst on the upstream side appears.

  The membrane-catalyst layer assembly of the present invention has excellent durability and suppresses the deterioration of the cathode, particularly when the catalyst-supported carbon of the cathode is used for a polymer electrolyte fuel cell. It is possible to realize a polymer electrolyte fuel cell capable of maintaining sufficient battery performance. Therefore, the present invention can be suitably used for high durability of a fuel cell using a polymer electrolyte membrane, particularly a stationary cogeneration system and an electric vehicle.

It is a schematic sectional drawing which shows an example of the basic composition of the single cell mounted in suitable one Embodiment of the polymer electrolyte fuel cell of this invention. It is a schematic sectional drawing which shows an example of the basic composition of the membrane electrode assembly mounted in the single battery 1 shown in FIG. It is a schematic longitudinal cross-sectional view which shows an example of the basic composition of the membrane catalyst layer assembly mounted in the membrane electrode assembly 10 shown in FIG. FIG. 2 is a cross-sectional view taken along line XX in FIG. 1, that is, a front view of the cathode separator 16c in FIG. 1 viewed from the cathode gas flow path 17c side. FIG. 2 is a cross-sectional view taken along line YY in FIG. 1, that is, a front view of the anode separator 16a in FIG. 1 viewed from the anode gas flow path 17a side. 1 is a cross-sectional view taken along the line ZZ in FIG. 1 (in the unit cell 1 shown in FIG. 1, the polymer electrolyte membrane 11, the anode catalyst layer 12a, the anode gas diffusion layer 13a, the gasket 15 and the anode separator 16a are removed, and the cathode catalyst layer 12c side Figure) Preferred setting conditions of “a portion of the cathode catalyst layer corresponding to the upstream of the cathode gas flow path” and “a portion of the cathode catalyst layer corresponding to the downstream of the cathode gas flow path” will be described. It is explanatory drawing for. It is a schematic sectional drawing which shows an example of the basic composition of the unit cell mounted in suitable one Embodiment of the conventional polymer electrolyte fuel cell. It is a schematic sectional drawing which shows an example of the basic composition of the membrane electrode assembly mounted in the single battery 101 shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,101 ... Single cell, 11, 111 ... Polymer electrolyte membrane, 12c ... Cathode catalyst layer, 12a ... Anode catalyst layer, 13c ... Cathode gas diffusion layer, 13a ... Anode Gas diffusion layer, 14c ... cathode, 14a ... anode, 15 ... gasket, 16c ... cathode separator, 16a ... anode separator, 17c ... cathode gas flow path, 17a ... anode Gas flow path, 18c, 18a ... Cooling fluid flow path, 21 ... Oxidant gas inlet manifold hole, 22 ... Oxidant gas outlet manifold hole, 23 ... Fuel gas inlet manifold hole, 24 ... Fuel gas outlet manifold hole, 25 ... cooling fluid inlet manifold hole, 26 ... cooling fluid outlet manifold hole, 112 ... catalyst layer, 113 ... Gas diffusion layer, 114 ... gas diffusion electrode, 115 ... gasket, 116 ... separator, 117 ... gas flow channel, 118 ... cooling fluid channel.

Claims (8)

An anode separator and a cathode separator, which are disposed to face each other, and a membrane electrode assembly disposed between the anode separator and the cathode separator, and a cathode gas flow path is formed on the inner surface of the cathode separator. A membrane catalyst layer assembly mounted on a polymer electrolyte fuel cell,
An anode catalyst layer and a cathode catalyst layer disposed to face each other;
A polymer electrolyte membrane disposed between the anode catalyst layer and the cathode catalyst layer;
Have
The cathode catalyst layer includes an electrode catalyst and conductive carbon particles serving as a support for the electrode catalyst,
Of the cathode catalyst layer, the conductive carbon particles contained in the portion corresponding to the downstream of the cathode gas flow path, the degree of graphitization of the conductive carbon particles included in the portion corresponding to the upstream of the cathode gas flow path Lower than the graphitization degree of
A membrane / catalyst layer assembly characterized by the above. The portion corresponding to the upstream of the cathode catalyst layer is 25% to 50% of the total flow path length with one end of the total flow path length of the cathode gas flow path as the inlet and the other end as the base point. It is a part facing the area to be
The portion corresponding to the downstream of the cathode catalyst layer is 50% to 75% of the total flow path length with one end of the total flow path length of the cathode gas flow path as the outlet and the other end as the origin. The part facing the area
The membrane-catalyst layer assembly according to claim 1. The portion corresponding to the upstream of the cathode catalyst layer includes a position facing the inlet of the cathode gas flow path, and the portion corresponding to the downstream of the cathode catalyst layer faces the outlet of the cathode gas flow path. Including location,
The area of the portion corresponding to the upstream of the main surface of the cathode catalyst layer is 25% to 50% of the total area of the main surface, and the area of the portion corresponding to the downstream of the main surface of the cathode catalyst layer is 50% to 75% of the total area of the main surface,
The membrane catalyst layer assembly according to claim 1 or 2, wherein The degree of graphitization of the conductive carbon particles of the cathode catalyst layer increases from a position facing the inlet of the cathode gas flow path to a position facing the outlet of the cathode gas flow path;
The membrane / catalyst layer assembly according to any one of claims 1 to 3. The specific surface area of the conductive carbon particles decreases from a position facing the inlet of the cathode gas flow path to a position facing the outlet of the cathode gas flow path;
The membrane catalyst layer assembly according to any one of claims 1 to 4. The half width of the peak at 1580 cm ⁻¹ measured by Raman spectroscopy of the conductive carbon particles is
80 cm ⁻¹ or more in the portion corresponding to the upstream of the cathode gas flow path, and 75 cm ⁻¹ or less in the portion corresponding to the downstream of the cathode gas flow path,
The membrane catalyst layer assembly according to any one of claims 1 to 5, wherein: A pair of gas diffusion layers disposed opposite to each other, and a membrane catalyst layer assembly disposed between the pair of gas diffusion layers,
The membrane catalyst layer assembly is the membrane catalyst layer assembly according to any one of claims 1 to 6,
A membrane electrode assembly characterized by the above. Comprising the membrane electrode assembly according to claim 7;
A polymer electrolyte fuel cell.

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