JP2008243776A - Solid polymer electrolyte fuel cell and membrane electrode assembly thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solution for improving cell performance of a solid polymer electrolyte fuel cell, and to enhance output density of a cell, specially, by improving the catalyst characteristics of an anode of a membrane electrode assembly. <P>SOLUTION: The membrane electrode assembly comprises a polymer electrolyte membrane 1, and an anode electrode 2 and a cathode electrode 3 formed on the surface of the polymer electrolyte membrane 1. The anode electrode 2 is formed of an inner-layer catalyst layer 2A and an outer-layer catalyst layer 2B, and respective catalysts included in the respective layers are different from each other. For example, a platinum/ruthenium alloy catalyst is used on the inner-layer catalyst layer 2A, and a platinum catalyst is used on the outer-layer catalyst layer 2B. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane / electrode assembly (hereinafter sometimes referred to as MEA) of a solid polymer electrolyte fuel cell. In this way, the cell performance is improved.

FIG. 5 shows an example of an MEA that is a reaction part of a solid polymer electrolyte fuel cell. In FIG. 5, the code | symbol 1 shows a polymer electrolyte membrane.
A membrane-like anode electrode 2 having a thickness of about 10 μm is joined to one surface of the polymer electrolyte membrane 1 and a membrane-like cathode electrode 3 having a thickness of about 10 μm is joined and integrated on the other surface. A diffusion layer made of carbon paper or the like (not shown) is provided on the surfaces of the anode electrode 2 and the cathode electrode 3 to form an MEA.

As the polymer electrolyte membrane 1, a film made of a perfluorosulfonic acid polymer having a thickness of about 30 to 70 μm is used.
The anode 2 and the cathode electrode 3 are made of polymer electrolyte solution made of ionomer, water, isopropanol, and the like, with supported catalyst particles in which platinum fine particles having a diameter of about 2 to 5 nm are supported on carbon particles having a diameter of several tens of nm. The catalyst dispersion is applied onto carbon paper or the like serving as a diffusion layer and dried.

The anode 2 and the cathode electrode 3 are joined to the polymer electrolyte membrane 1 by arranging the diffusion layers of the anode 2 and the cathode electrode 3 to be outside and joining them by thermocompression bonding or the like.
The amount of catalyst in the anode and cathode electrodes is about 1 to 3 mg / cm ^{2 because} of the relationship between the power density and cost. There is also a proposal that it can be reduced to about cm ² .

  Further, when reformed hydrogen, methanol, dimethyl ether (DME) or the like is used as the fuel, there is a risk of poisoning of the catalyst by carbon monoxide contained in these fuels. Platinum / ruthenium alloy catalysts are used.

The principle of operation of this solid polymer electrolyte fuel cell is as follows. Hydrogen supplied to the anode electrode 2 is converted into hydrogen ions by the catalytic reaction here, moves through the polymer electrolyte membrane 1, reaches the cathode electrode 3, and is supplied here by the catalytic reaction at the cathode electrode 3. It reacts with oxygen to become water. Electrons generated in the anode electrode 2 flow to an external circuit via a separator (not shown) and move to the cathode electrode 3.
When methanol, dimethyl ether or the like is used as the fuel, methanol or dimethyl ether or the like is directly oxidized by a catalytic reaction at the anode electrode 2 to generate carbon dioxide, hydrogen ions, electrons, and hydrogen ions are contained in the polymer electrolyte membrane 1. Is moved toward the cathode electrode 3.
Research and development for improving the cell performance such as the output density of such a solid polymer electrolyte fuel cell has been actively promoted, and many patent applications have been filed.
Japanese translation of PCT publication No. 2002-532833 Japanese translation of PCT publication No. 2003-502827 JP-A-9-27326 JP 2006-140134 A JP 2005-197195 A JP 2005-56583 A JP 2005-174620 A

  It is an object of the present invention to provide one solution for improving the cell performance of a solid polymer electrolyte fuel cell, and in particular, to improve the catalyst characteristics at the anode and cathode electrodes of the MEA to improve the cell output. The purpose is to increase the density.

To solve this problem,
The invention according to claim 1 is a membrane electrode assembly comprising a polymer electrolyte membrane and an anode and a cathode electrode formed on the surface of the polymer electrolyte membrane,
A membrane / electrode assembly for a solid polymer electrolyte fuel cell, wherein either one or both of the anode and cathode electrodes have a multilayer structure, and the catalysts contained in the respective layers are different from each other. .

  The invention according to claim 2 is characterized in that in the anode electrode, a platinum / ruthenium alloy catalyst is used for one layer, and a platinum catalyst is used for the other layer. This is a membrane electrode assembly of a fuel cell.

The invention according to claim 3 is the membrane electrode of the solid polymer electrolyte fuel cell according to claim 2, wherein in the anode electrode, one layer is arranged on the inner side and the other layer is arranged on the outer side. It is a joined body.
The invention according to claim 4 is a polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 3.

  In general, in MEA, it is known that output characteristics peculiar to a catalyst can be obtained according to the type of catalyst contained in the anode or the cathode electrode. For this reason, if the anode or cathode electrode has a multilayer structure and the types of catalysts contained in the respective layers are different from each other, each layer exhibits different output characteristics. For this reason, the overall output characteristics of these output characteristics can be obtained for the entire anode or cathode electrode, and the cell characteristics can be improved.

FIG. 1 shows an example of the MEA of the present invention. The MEA of this example has the same structure as the MEA shown in FIG. 5 except that the anode electrode 2 has a two-layer structure.
That is, the anode electrode 2 formed on one surface of the polymer electrolyte membrane 1 is composed of an inner layer 2A and an outer layer 2B. Carbon paper forming a diffusion layer exists outside the outer layer 2B.

In the inner layer 2A, a platinum / ruthenium alloy catalyst is used as a catalyst, and in the outer layer 2B, a platinum catalyst is used as a catalyst.
As the platinum / ruthenium alloy catalyst, an alloy composed of 10 to 50 wt% platinum and the remaining ruthenium is used.
These platinum catalysts and platinum / ruthenium alloy catalysts are used as supported catalysts in which catalyst fine particles having a diameter of about 2 to 5 nm are supported on carbon particles having a diameter of several tens of nm, as in the past, and this supported catalyst is used as an ionomer or the like. Is dispersed in a polymer electrolyte solution, and this dispersion is applied onto carbon paper or the like serving as a diffusion layer and dried to form the inner layer 2A and the outer layer 2B.

Moreover, although the catalyst amount is the same as that of the conventional art, it is set to about 1 to 3 mg / cm ² from the relationship between the power density and the cost, but is not limited to this range. In reality, when dimethyl ether is used as a fuel, the platinum / ruthenium alloy catalyst is preferably 0.5 mg / cm ² or less and the platinum catalyst is about 1 mg / cm ² from the balance between cost and performance. preferable.

In the fuel cell provided with such an MEA, the output density is increased. In particular, when dimethyl ether or methanol is used as the fuel and the cell temperature is 80 ° C. or lower, the effect is increased.
In the case of a platinum catalyst, in the cell output characteristics, the voltage is inferior when the current is low, but power generation is possible up to a high current. On the other hand, the platinum / ruthenium alloy catalyst has the property that the voltage is high at a low current, but the voltage is suddenly reduced at a high current.

On the other hand, in the two-layer structure of the outer layer 2B containing the platinum catalyst and the inner layer 2A containing the platinum / ruthenium alloy catalyst, the effect of the platinum / ruthenium alloy catalyst is relatively large in the low current region, In the high current region, the effect of the platinum catalyst is relatively large.
For this reason, with such a two-layer structure, it is possible to generate power while maintaining a high voltage from a low current region to a high current region.

When dimethyl ether is used as a fuel, the same effect can be obtained even if a platinum catalyst is used for the inner layer and a platinum / ruthenium alloy catalyst is used for the outer layer.
Furthermore, in the above example, the anode electrode 2 has a two-layer structure, but three or more layers may be used, and different catalysts may be contained in each layer. Examples of such a catalyst include a platinum / chromium alloy catalyst, a platinum / nickel alloy catalyst, a platinum / cobalt alloy catalyst, and a platinum / iron alloy catalyst in addition to the above-described platinum catalyst and platinum / ruthenium alloy catalyst.
Also, the cathode electrode 3 has a multilayer structure, and the same effect can be obtained even if each layer contains different catalysts.

Specific examples are shown below.
Example 1
-Using supported catalyst particles (manufactured by Tanaka Kikinzoku Co., Ltd.) in which 50% by mass of platinum particles having an average particle size of 3 nm are supported on ketjen black having an average primary particle size of 30 nm, this supported catalyst particle and perfluorocarbon sulfonate ionomer are mixed with isopropanol. And a water dispersion (mass ratio 1: 2) to prepare a catalyst dispersion (1).

・ Supported catalyst particles (manufactured by Tanaka Kikinzoku Co., Ltd.) in which platinum / ruthenium alloy particles having an average particle size of 3 nm (27% by mass of platinum and 13% by mass of ruthenium) are loaded on 50% by mass of ketjen black having an average primary particle size of 30 nm. Using this supported catalyst particle and perfluorocarbonsulfonic acid ionomer in a dispersion medium of isopropanol and water, a catalyst dispersion liquid (2) was prepared.

On the polytetrafluoroethylene sheet | seat used as a release paper, the said catalyst dispersion liquid was apply | coated several times using the doctor blade, and it dried and produced the 10-micrometer-thick film-form thing. This membrane was transferred to the surface of a perfluorocarbon sulfonic acid polymer sheet to be a polymer electrolyte membrane having a thickness of 50 μm to obtain a laminate.
Next, carbon paper (Toray Industries, Inc .: TGP-H-060) serving as a diffusion layer was superposed on the surface of this laminate and joined by hot pressing.

The MEA produced in this way was sandwiched between carbon separators to form a cell. The separator has a structure in which a flow path through which fuel and oxidant flow is engraved.
This cell produced three types by using the said catalyst dispersion liquid (1)-(2).
Cell 1: A film-like material composed of the catalyst dispersion (1) is transferred to both surfaces of the polymer electrolyte membrane, and the anode and cathode electrodes contain a platinum catalyst.
Cell 2: The membrane-like material comprising the catalyst dispersion (1) is transferred to one surface of the polymer electrolyte membrane to form a cathode electrode containing a platinum catalyst, and the membrane-like material comprising the catalyst dispersion (2) is used as the other An anode electrode containing a platinum / ruthenium alloy catalyst transferred onto the surface.

Cell 3: A membrane comprising the catalyst dispersion (1) is transferred to one surface of the polymer electrolyte membrane to form a cathode electrode containing a platinum catalyst, and the catalyst dispersion (1) and the catalyst dispersion (2) A two-layered film-like material consisting of 2 is transferred to the other surface to form a two-layered anode electrode composed of a platinum / ruthenium alloy catalyst layer and a platinum catalyst layer.
The power density of these three types of cells was measured. The measurement was performed by changing the cell temperature, fuel type, and catalyst usage.

2 shows the output density when the cell temperature is 80 ° C., dimethyl ether is used as the fuel, and the catalyst amount is 2 mg / cm ² .
In the graph of FIG. 2, the curve A shows the characteristics of the cell 3 of the present invention, the curve B shows the characteristics of the cell 2, and the curve C shows the characteristics of the cell 1.

FIG. 3 shows the power density when the cell temperature is 25 ° C., methanol is used as the fuel, and the amount of catalyst is 1 mg / cm ² .
In the graph of FIG. 3, the curve A shows the characteristics of the cell 3 of the present invention, the curve B shows the characteristics of the cell 2, and the curve C shows the characteristics of the cell 1.

4 shows the output density when the cell temperature is 50 ° C., methanol is used as the fuel, and the amount of catalyst is 1 mg / cm ² .
In the graph of FIG. 4, the curve A shows the characteristics of the cell 3 of the present invention, the curve B shows the characteristics of the cell 2, and the curve C shows the characteristics of the cell 1.

  As is apparent from the graphs of FIGS. 2 to 4, it can be seen that the output density of the cell 3 having the two-layer structure corresponding to the present invention is improved.

It is a schematic sectional drawing which shows an example of MEA of this invention. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example. It is a graph which shows the result of an Example. It is a schematic sectional drawing which shows the conventional MEA.

Explanation of symbols

1 ·· Polymer electrolyte membrane, 2 ·· Anode electrode, 2A ·· Inner catalyst layer, 2B ·· Outer catalyst layer, 3 ·· Cathode electrode

Claims (4)

A membrane electrode assembly comprising a polymer electrolyte membrane and an anode and a cathode formed on the surface of the polymer electrolyte membrane,
One or both of the anode and cathode electrodes have a multilayer structure, and the catalyst contained in each layer is different from each other, and the membrane electrode assembly of a solid polymer electrolyte fuel cell,   2. The membrane / electrode assembly of a polymer electrolyte fuel cell according to claim 1, wherein a platinum / ruthenium alloy catalyst is used in one layer and a platinum catalyst is used in the other layer in the anode electrode. .   3. The membrane electrode assembly for a solid polymer electrolyte fuel cell according to claim 2, wherein in the anode electrode, one layer is disposed on the inner side and the other layer is disposed on the outer side.   A solid polymer electrolyte fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 3.

Images