JP2012079572A - Forming method for convexoconcave membrane electrode assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct an unevenness processing to a membrane electrode assembly (MEA) while keeping a uniform interface structure of a polymer electrolyte membrane 14 and a catalyst layer 13.SOLUTION: In this forming method, a uniform interface structure of a polymer electrolyte membrane 14 and a catalyst layer 13 is kept by conducting an unevenness processing simultaneously to the MEA with a membrane electrode assembly which is applied with the catalyst layer 13 in advance on a cathode side of the polymer electrolyte membrane 14, a pitch L, a metal mold 11 made based on a dimension of width W and height H of a convexoconcave structure, and a mold support 18.

Description

  The present invention relates to a method for producing a membrane electrode assembly for a fuel cell and a fuel cell using the membrane electrode assembly for a fuel cell.

  Solid polymer fuel cells using polymer electrolyte membranes are expected to be one of highly efficient power generation methods due to the remarkable improvement in performance due to the recent development of electrolyte and catalyst technology. In order to obtain a high-efficiency polymer electrolyte fuel cell, a chemical reaction occurs at an interface in a membrane electrode assembly (MEA), that is, an interface between a solid polymer membrane and a catalyst layer containing a metal catalyst such as platinum. The transport of chemical substances involved, such as oxygen, protons and water, is considered very important. For example, as one of attempts to devise this interface structure, a method of forming irregularities on the surface of a polymer electrolyte membrane has been reported (for example, Non-Patent Document 1). When the concavo-convex structure is formed, the area of the interface in the MEA is improved, and the material transport speed at the interface is also improved, so that it is expected that the power generation efficiency of the fuel cell is improved. In order to improve the current voltage output characteristics of the fuel cell by the uneven structure on the surface of the polymer electrolyte membrane, it is considered that the narrower the pitch (period) of the uneven structure and the greater the difference in height of the uneven structure, the more suitable.

  As a method for forming such a concavo-convex structure, a method for forming a concavo-convex structure on the film surface by a chemical or mechanical polishing method disclosed in Patent Document 1, or a concave hole disclosed in Patent Document 2 is used. A method of casting an electrolyte on a mold having a film and forming a film has been reported.

JP-A-9-320616 JP 2005-53198 A

J. et al. Am. Chem. Soc. , 2006, 128, 12963

  However, in the conventional configuration, when the concavo-convex structure is miniaturized, some difficulties occur in the MEA manufacturing process. The scale that means the miniaturization here is typically that the pitch of the concavo-convex structure is on the order of micrometers or less. For example, when the height difference of the concavo-convex structure with respect to the pitch is increased, the mechanical strength of the convex portion is weakened and may be broken or fall down. The uneven structure is greatly disturbed, and the design concept of the uneven structure cannot be reflected in the improvement of the current-voltage characteristics. There is also a problem with uniformity at the interface within the MEA. For example, in a conventional method in which an uneven structure is applied to a polymer electrolyte membrane and a catalyst layer is applied on the surface thereof to create an MEA interface, it is difficult to apply the catalyst layer to the recess. There was a problem that it was difficult to create an MEA having a uniform interface.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide an MEA manufacturing method in a fuel cell having a polymer electrolyte having a concavo-convex structure.

  In order to solve the above-described conventional problems, the method for forming a concavo-convex MEA according to the present invention includes a metal mold and mold receiver defined by the pitch L, the height H and the width W of the concavo-convex structure, and a polymer electrolyte membrane. An MEA having a catalyst layer applied to the surface is used. The MEA heated to near the glass transition temperature of the polymer electrolyte membrane is pressure-bonded to the mold, and the uneven structure is processed on the entire MEA.

  With this configuration, an MEA having an ideal sub-microstructure can be created at the interface between the polymer electrolyte membrane and the catalyst layer.

According to the method for forming a concavo-convex catalyst layer of the present invention, in the current-voltage power generation characteristics of the solid polymer fuel cell, the output voltage can be improved by 3 to 5% in the range where the current is 250 mA / cm ² or less. .

Schematic diagram of the formation method of the uneven catalyst layer in Embodiment 1 of the present invention The graph which shows the current-voltage (L = 10) output characteristic in Embodiment 1 of this invention The graph which shows the pitch dependence of the voltage output in Embodiment 1 of this invention

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic diagram of a method for forming an uneven catalyst layer in Embodiment 1 of the present invention.

  In FIG. 1, a metal mold 11 is formed by convex processing on the surface of a metal film with dimensions of pitch L, convex structure width W and height H. The mold receiver 18 is obtained by processing a metal film into a hole-shaped recess with dimensions of a pitch W concave structure having a width W and a height H. The metal mold 11 and the mold receiver 18 can be formed by photolithography or electroforming. As the material, a transition metal that exhibits ductility even under high pressure and is easily processed is suitable, and typically Ni or the like is easily used. A water repellent film 12 is applied to the surfaces of the mold 11 and the mold receiver 18. This water-repellent treatment facilitates separation of the mold 11 and mold receiver 18 after hot pressing from the catalyst layer 13 or the polymer electrolyte membrane 14.

  In order to simultaneously process the catalyst layer 13 and the polymer electrolyte membrane 14 by the method for forming an uneven catalyst layer according to the present invention, the catalyst layer is formed on the both sides of the cathode side of the polymer electrolyte membrane 14 in advance by a spray coating method or the like. The MEA is applied in a thickness and generally used widely. After sufficient moisture is contained in this MEA, it is slowly heated to 140 ° C. near the glass transition temperature of the polymer electrolyte membrane. When the MEA is inserted between the mold 11 and the mold receiver 18 and hot pressing is performed, the MEA can be subjected to uneven processing.

Example 1
FIG. 2 is a current-voltage output characteristic diagram according to Embodiment 1 of the present invention. A curve 21 is a current-voltage output characteristic in the first embodiment. The mold dimensions are pitch L = 10 μm, width W = 5 μm, and height H = 5 μm. A curve 22 is a current-voltage output characteristic in Comparative Example 1. In the comparative example 1, MEA before performing uneven | corrugated processing was used. Other configurations are the same as those of the first embodiment.

In FIG. 2, it can be seen that the output voltage is improved by 3% to 5% when the current is in the range of 250 mA / cm ² or less. In order to clarify the effect of the unevenness processing on the current-voltage output characteristics, the pitch L was decreased from 10 μm to 2 μm. The ratio of pitch L to width W was fixed at 2: 1. The results are shown in FIG. It can be seen that the effect of improving the output voltage becomes more prominent when the pitch L is reduced and the unevenness processing is refined.

  The MEA according to the present invention has a submicrometer uneven structure on both surfaces of a membrane electrode assembly and is useful as a membrane electrode assembly for a fuel cell.

11 Metal mold 12 Water repellent film 13 Catalyst layer 14 Polymer electrolyte film 15 Pitch (L)
16 Uneven structure width (W)
17 Uneven structure height (H)
18 Mold Receiver 21 Current-Voltage Output Characteristics in Embodiment 1 22 Current-Voltage Output Characteristics in Comparative Example 1

Claims (2)

Metal mold and mold receiver defined by pitch L, height H and width W of the concavo-convex structure,
A membrane electrode assembly (MEA) having a catalyst layer applied to the surface of the polymer electrolyte membrane;
A method for producing an MEA, wherein a membrane electrode assembly heated to near the glass transition temperature of a polymer electrolyte membrane is pressure-bonded to a mold to process a concavo-convex structure on the entire MEA.   The method for producing MEA, wherein the mold and the mold receiver satisfy a pitch 2 ≦ L ≦ 10 μm of the concavo-convex structure.

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