JP2009048896A - Membrane electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of an electrolyte membrane and improve output performance of a fuel cell. <P>SOLUTION: The unit cell 10 of a fuel cell is provided with an MEA 20, gas diffusion layers 120, 121, and separators 130, 140. The MEA 20 is provided with an electrolyte membrane 100, an intermediate part 110 which is formed on one face of the electrolyte membrane 100 and contains titanium (Ti), a cathode catalyst layer 102 arranged on the intermediate part 110, and anode catalyst layer 102 formed on the other face of the electrolyte membrane 100. Platinum ions (Pt<SP>2+</SP>, Pt<SP>4+</SP>) eluted from the cathode catalyst layer by continuous use of the fuel cell is bonded with titanium having high affinity with platinum in the intermediate part 110 before moving into the electrolyte membrane 100. The platinum ions captured by titanium in the intermediate layer 110 are precipitated again in the intermediate part 110 and become platinum particles (Pt). Thereby, movement of the platinum particles to the electrolyte membrane can be suppressed and deterioration of the membrane electrode assembly can be suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Fuel cells that generate electricity by a chemical reaction between hydrogen gas and oxidizing gas are used. The fuel cell uses, for example, a solid polymer electrolyte membrane having proton conductivity. A solid polymer fuel cell is composed of a membrane electrode assembly in which a cathode catalyst electrode layer and an anode catalyst electrode layer are disposed on both surfaces of an electrolyte membrane, and a separator disposed on both sides of the membrane electrode assembly. A plurality of single cells are stacked.

  The cathode electrode catalyst layer and the anode electrode catalyst layer are formed in a thin film using a carbon-supported catalyst in which a catalyst is supported on carbon particles. For example, platinum is used as the catalyst, and the catalyst promotes a chemical reaction in each electrode catalyst layer.

JP 2006-302578 A JP 2005-353591 A

However, when the fuel cell is operated for a long period of time, the platinum particles are dissolved to become platinum ions (Pt ^2+, Pt ⁴⁺ ) and move into the electrolyte membrane. In the electrolyte membrane, platinum ions react with hydrogen gas from the anode, are reduced, recrystallized into platinum particles (Pt), and precipitate in the electrolyte membrane. Since platinum deposited in the electrolyte membrane cannot participate in the electrode reaction, the output of the fuel cell is reduced. Further, there is a problem that the electrolyte membrane is decomposed and deteriorated by radicals generated from platinum in the electrolyte membrane.

  The present invention has been made in view of the above-described problems, and aims to suppress deterioration of an electrolyte membrane and improve output performance of a fuel cell.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the following aspects can be realized as application examples.

[Application Example 1]
The membrane electrode assembly includes a cathode electrode catalyst layer formed on the first surface of the electrolyte membrane, an anode electrode catalyst layer formed on a second surface different from the first surface of the electrolyte membrane, and a cathode electrode Among the catalyst layer and the anode electrode catalyst layer, an intermediate portion disposed between the electrode catalyst layer supporting platinum and the electrolyte membrane and formed using a material having an affinity for platinum, Prepare.

  According to the membrane electrode assembly of the first application example, it is possible to capture platinum particles eluted from the electrode catalyst layer in which the intermediate portion carries platinum. Therefore, the movement of platinum particles to the electrolyte membrane can be suppressed. Therefore, deterioration of the membrane electrode assembly can be suppressed.

  In the membrane electrode assembly of Application Example 1, the cathode electrode catalyst layer carries platinum, and the intermediate portion is disposed between the cathode electrode catalyst layer and the electrolyte membrane.

  According to the membrane electrode assembly of Application Example 1, since platinum particles eluted from the cathode electrode catalyst layer in which platinum is easily dissolved can be captured, deterioration of the membrane electrode assembly can be suppressed.

  In the membrane electrode assembly of Application Example 1, the intermediate portion is formed using a material having electrical conductivity.

  According to the membrane electrode assembly of Application Example 1, since the intermediate portion has electrical conductivity, the re-deposited platinum can contribute to the electrode reaction in the electrode catalyst layer supporting platinum through the intermediate portion. Therefore, it is possible to suppress a decrease in electrode reaction due to a decrease in platinum catalyst in the supported electrode catalyst layer supporting platinum.

  In the membrane electrode assembly of Application Example 1, the material includes at least one of platinum, titanium, iridium, and osmium.

  According to the membrane electrode assembly of Application Example 1, platinum, titanium, iridium, and osmium have high affinity with platinum, and thus can efficiently capture platinum ions eluted from the electrode catalyst layer supporting platinum.

  In the membrane / electrode assembly of Application Example 1, the intermediate portion is arranged in the form of dots on the electrolyte membrane or on the electrode catalyst layer supporting platinum.

  In the membrane / electrode assembly of Application Example 1, the intermediate portion is arranged in a striped pattern on the electrolyte membrane or on the electrode catalyst layer supporting platinum.

  In the membrane / electrode assembly of Application Example 1, the intermediate portion is arranged in a lattice shape on the electrolyte membrane or on the electrode catalyst layer supporting platinum.

  According to the membrane electrode assembly of Application Example 1, the second reprecipitation layer can capture platinum ions eluted from the anode electrode catalyst layer. Therefore, not only platinum ions eluted from the cathode electrode catalyst layer but also platinum ions eluted from the anode electrode catalyst layer can be prevented from moving into the electrolyte membrane. Therefore, deterioration of the electrolyte membrane can be suppressed.

[Application Example 2]
The fuel cell includes a cathode electrode catalyst layer formed on the first surface of the electrolyte membrane, an anode electrode catalyst layer formed on a second surface different from the first surface of the electrolyte membrane, a cathode electrode catalyst layer, Among the anode electrode catalyst layers, a membrane electrode assembly including an intermediate portion that is disposed between an electrode catalyst layer supporting platinum and an electrolyte membrane and formed using a material having an affinity for platinum; And a separator having a reaction gas channel for supplying a reaction gas used for power generation of the fuel cell to the membrane electrode assembly.

  According to the fuel cell of Application Example 2, the intermediate part can capture platinum ions eluted from the electrode catalyst layer supporting platinum. Therefore, the migration of the eluted platinum ions to the electrolyte membrane can be suppressed, and deterioration of the electrolyte membrane can be suppressed. Therefore, the power generation performance of the fuel cell can be improved.

  In the present invention, the various aspects described above can be applied by appropriately combining or omitting some of them.

A. Example:
A1. Fuel cell schematic configuration:
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a single cell of a fuel cell in an example. As shown in FIG. 1, the unit cell 10 of the fuel cell according to the embodiment includes a membrane electrode assembly 20 (MEA), gas diffusion layers 120 and 121 disposed on both sides of the membrane electrode assembly 20, and gas. A cathode side separator 130 and an anode side separator 140 sandwiching the diffusion layers 120 and 121 and the membrane electrode assembly 20 are provided. The MEA 20 includes an electrolyte membrane 100, an intermediate portion 110 formed on one surface of the electrolyte membrane 100, a cathode electrode catalyst layer disposed on the intermediate portion 110, and an anode formed on the other surface of the electrolyte membrane 100. An electrode catalyst layer 102 is provided. In the embodiment, the intermediate portion 110 corresponds to the “first intermediate layer” in the claims.

  The electrolyte membrane 100 is formed in a thin film shape by, for example, Nafion (registered trademark). The intermediate portion 110 is formed on the surface of the electrolyte membrane 100 on the cathode electrode catalyst layer 101 side. The intermediate part 110 uses titanium (Ti) and ionomer as materials.

  The cathode electrode catalyst layer 101 is formed in a thin film shape from a carbon carrier carrying a catalyst that promotes an electrochemical reaction, and an ionomer is dispersed in the platinum carrying carbon carrier. In the embodiment, platinum particles (Pt) are used as the supported catalyst. However, other than platinum, for example, a platinum alloy may be used.

  As in the cathode electrode catalyst layer 101, the anode electrode catalyst layer 102 has a platinum catalyst supported on carbon alone.

  The gas diffusion layers 120 and 121 are carbon porous bodies having a porosity of about 20%, and are formed of, for example, carbon cloth or carbon paper. The gas diffusion layers 120 and 121 are integrated with the MEA 20 by bonding. The gas diffusion layers 120 and 121 diffuse the reaction gas in the thickness direction.

  The cathode side separator 130 and the anode side separator 140 are made of a conductive metal material such as stainless steel, titanium, or a titanium alloy. The cathode separator 130 is formed with a flow path 132 for supplying an oxidizing gas to the membrane electrode assembly 20. The anode-side separator 140 is formed with a flow path 142 for supplying fuel gas to the membrane electrode assembly 20.

  FIG. 2 is an explanatory diagram illustrating the detailed configuration of the intermediate unit 110 in the embodiment. 2A is a plan view illustrating the electrolyte membrane, and FIG. 2B is a cross-sectional view illustrating the AA cross section of FIG. 2A. As shown in FIG. 2A and FIG. 2B, the intermediate portion 110 is formed in a stripe shape so that titanium (Ti) is arranged on the electrolyte membrane 100 at a predetermined interval. . The thickness of the electrolyte membrane 100 is, for example, 50 nm, and the thickness of the intermediate portion 110 is, for example, 100 nm or less, more preferably 50 nm or less. The thickness of the electrolyte membrane 100 is preferably 20 nm to 50 nm. Further, the coverage of the intermediate portion 110 with respect to the electrolyte membrane 100 is, for example, about 30%. As the thickness and coverage of the intermediate portion 110 increase, the proton conduction distance from the electrolyte membrane 100 to the cathode electrode catalyst layer 101 increases, and the adhesion between the ionomer in the cathode electrode catalyst layer 101 and the electrolyte membrane decreases. As a result, proton conductivity from the electrolyte membrane 100 to the cathode electrode catalyst layer 101 may be inhibited. Therefore, the above values are preferable for the thickness and coverage of the intermediate portion 110.

Titanium constituting the intermediate portion 110 (Ti) are platinum ions (Pt ^2+, Pt ⁴⁺⁾ eluting from the cathode electrode catalyst layer 101 combines with, the electrolyte membrane 100 of platinum ions (Pt ^2+, Pt ⁴⁺⁾ Suppresses intrusions. In an embodiment, it referred to titanium (Ti) and platinum ions (Pt ^2+, Pt ⁴⁺⁾ the binding of the capture of titanium (Ti) with platinum ions (Pt ^2+, Pt ^4+), and also.

A2. About platinum ion capture:
FIG. 3 is a schematic diagram illustrating capture of platinum ions (Pt ^2+, Pt ⁴⁺ ) ions by titanium (Ti) in the example. FIG. 3 is an enlarged view of a circle X portion of FIG.

When the fuel cell is operated for a long time, as shown in FIG. 3A, platinum supported on the cathode electrode catalyst layer 101 is dissolved and platinum ions (Pt ^2+, Pt ⁴⁺ ) are eluted.

Titanium (Ti) constituting the intermediate layer 110 has a high affinity with platinum (Pt), and thus was found to easily bind to platinum (Pt). For this reason, the eluted platinum ions (Pt ^2+, Pt ⁴⁺ ), as shown in FIG. 3 (b), move into the electrolyte membrane 100 before the titanium having high affinity with platinum in the intermediate portion 110. Join.

As shown in FIG. 3C ^, platinum ions (Pt ^2+, Pt ⁴⁺ ) bonded to titanium are caused by hydrogen gas (H ₂ ) moving from the anode electrode catalyst layer 102 or electrochemically. Reduced. Thereby, in the intermediate part 110, platinum (Pt) is deposited again. Titanium (Ti) contained in the intermediate part 110 has electronic conductivity in the operating environment (high potential and low pH) of the cathode electrode catalyst layer 101 of the fuel cell, and the ionomer contained in the intermediate part 110 is Proton conductivity. Therefore, platinum deposited in the intermediate part 110 can participate in the power generation reaction on the spot.

A3. Production method:
FIG. 4 is a flowchart illustrating the manufacturing process of the membrane electrode assembly in the example. First, the intermediate portion 110 is formed on one surface of the electrolyte membrane 100 (step S10). Specifically, the electrolyte membrane is fixed to the substrate holder, a striped metal mask with an aperture ratio of about 30% is adhered to one surface of the electrolyte membrane, and titanium is attached to the electrolyte membrane from above the metal mask by DC sputtering. Let Titanium adheres only to the opening portion of the metal mask, and a striped intermediate portion 110 is formed.

  Second, an electrode catalyst layer is formed (step S12). Specifically, platinum-supporting carbon is produced by supporting 50% by weight of platinum particles on a carbon support. In the production of the cathode electrode catalyst layer, the produced platinum-supported carbon and ionomer (manufactured by DuPont) are mixed at a weight ratio of 3: 4 and dispersed in an ethanol / water mixed solvent to produce a catalyst ink, and a sheet The catalyst ink is applied to the surface of the electrode formed in a shape and dried. In the production of the anode electrode catalyst layer 102, the produced platinum-supported carbon and ionomer (DuPont) are mixed at a weight ratio of 1: 1 and dispersed in an ethanol / water mixed solvent to produce a catalyst ink. The catalyst ink is applied to the surface of the substrate and dried.

  Third, the electrolyte membrane 100 on which the intermediate portion 110 is formed and the electrode catalyst layers 101 and 102 are joined (step S14). Specifically, the cathode electrode catalyst layer 101 is disposed on the side of the electrolyte membrane 100 where the intermediate portion 110 is formed, the anode electrode catalyst layer 102 is disposed on the other side of the electrolyte membrane 100, and the electrolyte is formed by thermocompression bonding. The membrane 100 is joined to the cathode electrode catalyst layer 101 and the anode electrode catalyst layer 102. In this way, a membrane electrode assembly is produced.

A4. Performance evaluation of membrane electrode assembly:
FIG. 5 is a graph showing the performance evaluation of the membrane electrode assembly in the example. In the performance evaluation graph 300, the vertical axis represents the output voltage V of the fuel cell. The performance evaluation graph 300 shows a fuel cell in which a fuel gas having a pressure of 1.5 atm, a temperature of 80 ° C. and a dew point of 80 ° C. is supplied to the anode electrode catalyst layer 102, and a pressure of 1.5 atm to the cathode electrode catalyst layer 101. The result of having performed output measurement after supplying air with a temperature of 80 ° C. and a dew point of 75 ° C. and performing a potential cycle test of 0.2 to 1.0 V for 5000 cycles is shown. In the graph 300, a bar graph 310 indicates an output voltage before the potential cycle test of the membrane electrode assembly 20 including the intermediate portion 110, and a bar graph 320 indicates a membrane electrode assembly that does not include the intermediate portion 110 (hereinafter, referred to as “the potential of the membrane electrode assembly 20”). In the examples, the output voltage before the potential cycle test of the comparative example is shown. Moreover, the bar graph 311 shows the output voltage after the potential cycle test of the membrane electrode assembly 20 including the intermediate part 110, and the bar graph 321 shows the output voltage after the potential cycle test of the comparative example.

  Before the potential cycle test, as indicated by the bar graph 310 and the bar graph 320, the output voltage of the membrane electrode assembly 20 and the output voltage of the comparative example are substantially the same P1. On the other hand, after the potential cycle test, as shown by the bar graph 311, the output voltage of the membrane electrode assembly 20 decreases from P1 to P2 (about 5%), and as shown by the bar graph 312, the output voltage of the comparative example. Decreases from P1 to P3 (about 20%). That is, the output decrease of the membrane electrode assembly 20 including the intermediate portion 110 is suppressed as compared with the comparative example not including the intermediate portion 110.

  In addition, when the cross section of the membrane electrode assembly 20 and the comparative example after the potential cycle test was observed with an electron microscope, in the comparative example, many deposits of platinum (Pt) were observed in the electrolyte membrane 100, whereas In the membrane electrode assembly 20, platinum (Pt) precipitates were hardly observed in the electrolyte membrane 100. Furthermore, platinum (Pt) was detected from the intermediate part 110 of the membrane electrode assembly 20.

  According to the embodiment described above, the intermediate part 110 made of titanium having high affinity with platinum can be provided in the membrane electrode assembly 20 between the electrolyte membrane 100 and the cathode electrode catalyst layer 101. The intermediate part can capture the platinum eluted from the cathode electrode catalyst layer 101 by the operation of the fuel cell for a long time before it moves into the electrolyte membrane. Therefore, platinum deposition from the catalyst layer to the electrolyte membrane can be suppressed, and deterioration / damage of the electrolyte membrane can be suppressed.

  In the membrane electrode assembly of the example, the intermediate part has electrical conductivity and proton conductivity, and thus the platinum deposited in the intermediate part 110 can participate in the power generation reaction on the spot. Accordingly, since platinum eluted from the cathode electrode catalyst layer 101 can also participate in the power generation reaction, the power generation efficiency of the fuel cell can be improved.

B. Variations:
(1) In the above-described embodiment, an intermediate portion made of titanium is disposed only between the electrolyte membrane 100 and the cathode electrode catalyst layer 101. For example, the electrolyte membrane 100 and the anode electrode catalyst layer 102 are An intermediate portion may be disposed only between them, or an intermediate portion may be disposed between both electrode catalyst layers and the electrolyte membrane. It suffices if there is an intermediate portion between the electrode catalyst layer supporting platinum and the electrolyte membrane, and when both electrode catalyst layers are electrode catalyst layers supporting platinum, at least of the anode electrode catalyst layer and the cathode electrode catalyst layer. The intermediate portion may be disposed only on one side, or the intermediate portion may be disposed on both sides.

  FIG. 6 is a cross-sectional view illustrating a single cell of the fuel cell in Modification Example (1). As shown in FIG. 6, an intermediate portion 111 is disposed between the electrolyte membrane 100 and the anode electrode catalyst layer 102. The intermediate portion 111 is made of titanium (Ti), like the intermediate portion 110, and is formed in stripes so that the titanium (Ti) is arranged on the electrolyte membrane 100 at a predetermined interval. . The coverage of the intermediate portion 110 with respect to the electrolyte membrane 100 is, for example, about 30%. The intermediate portion 110 corresponds to a “second intermediate portion” in the claims.

Also in the anode electrode catalyst layer 102, when the fuel cell is operated for a long period of time as in the case of the cathode electrode catalyst layer 101, platinum (Pt) as a supported catalyst dissolves and platinum ions (Pt ^2+, Pt ⁴⁺ ) Elutes. A part of platinum ions (Pt ^2+, Pt ⁴⁺ ) is reduced and deposited by hydrogen gas in the anode electrode catalyst layer 102 to become platinum. That is, a part of platinum ions (Pt ^2+, Pt ⁴⁺ ) eluted in the anode electrode catalyst layer 102 is reprecipitated in the anode electrode catalyst layer 102. The remaining part of platinum ions (Pt ^2+, Pt ⁴⁺ ) moves toward the electrolyte membrane 100.

According to the membrane electrode assembly of this modification, titanium having a high affinity with platinum not only between the electrolyte membrane 100 and the cathode electrode catalyst layer 101 but also between the electrolyte membrane 100 and the anode electrode catalyst layer 102. Can be placed. Therefore, platinum ions (Pt ^2+, Pt ⁴⁺ ) eluted in the cathode electrode catalyst layer 101 and the anode electrode catalyst layer 102 can be captured before moving into the electrolyte membrane 100. Therefore, reprecipitation of platinum in the electrolyte membrane 100 can be suppressed, and damage to the electrolyte membrane 100 can be suppressed.

(2) In the above-described embodiment, the intermediate portion is arranged in a stripe shape on the electrolyte membrane 100, but may be arranged in a dot shape on the electrolyte membrane 100, for example.

  FIG. 7 is a plan view illustrating an electrolyte membrane in Modification Example (2). As shown in FIG. 6, the intermediate part 110 a is arranged in a dot shape on the electrolyte membrane 100. The coverage of the intermediate portion 110a with respect to the electrolyte membrane 100 is, for example, about 30%. The intermediate portion 110a can be easily formed by various methods such as sputtering.

(3) Moreover, the intermediate part 110b may be arrange | positioned on the electrolyte membrane 100 at the grid | lattice form. FIG. 8 is a plan view illustrating an electrolyte membrane in a modified example. As shown in FIG. 8, the intermediate part 110 b is arranged on the electrolyte membrane 100 in a lattice shape. For example, the intermediate portion 110b may be formed by a sputtering method using a lattice-like 0 metal mask. The coverage of the intermediate portion 110b with respect to the electrolyte membrane 100 is, for example, about 30%.

(4) In the above-described embodiment, the intermediate portion 110 is formed using titanium (Ti) as a material. For example, in addition to titanium (Ti), platinum (Pt), iridium (Ir), osmium (Os) Alternatively, titanium oxide (TiO ₂ ) or the like may be used. The material of the intermediate portion 110 may be any material having affinity with the catalyst supported on the cathode electrode catalyst layer 101 and the anode electrode catalyst layer 102, and preferably having electrical conductivity. Furthermore, it is preferable to have corrosion resistance at the fuel cell operating potential.

(5) In the above-described embodiment, the intermediate portion 110 is formed on the electrolyte membrane 100 by sputtering or the like, but may be formed on the cathode electrode catalyst layer 101, for example.

  Although various embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to these embodiments and can take various configurations without departing from the spirit of the present invention.

Sectional drawing which illustrates schematic structure of the single cell of the fuel cell in an Example. Explanatory drawing which illustrates about the detailed structure of the intermediate part in an Example. The schematic diagram explaining the capture of the platinum ion by the titanium in an Example. The flowchart which illustrates the manufacturing process of the membrane electrode assembly in an Example. The graph which shows the performance evaluation of the membrane electrode assembly in an Example. Sectional drawing which illustrates the single cell of the fuel cell in a modification. The top view which illustrates the electrolyte membrane in a modification. The top view which illustrates the electrolyte membrane in a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Membrane electrode assembly 100 ... Electrolyte membrane 101 ... Cathode electrode catalyst layer 102 ... Anode electrode catalyst layer 110 ... Intermediate part 111 ... Intermediate part 120 ... Gas diffusion layer 130 ... Cathode side separator 132 ... Flow path 140 ... Anode-side separator 142 ... flow path 300 ... performance evaluation graph

Claims (8)

A membrane electrode assembly,
An electrolyte membrane having proton conductivity;
A cathode electrode catalyst layer formed on the first surface of the electrolyte membrane;
An anode electrode catalyst layer formed on a second surface different from the first surface of the electrolyte membrane;
Of the cathode electrode catalyst layer and the anode electrode catalyst layer, an intermediate layer that is disposed between the electrode catalyst layer supporting platinum and the electrolyte membrane and is formed using a material having an affinity for platinum. A membrane electrode assembly. The membrane electrode assembly according to claim 1,
The cathode electrode catalyst layer carries platinum,
The intermediate part is a membrane / electrode assembly disposed between the cathode electrode catalyst layer and the electrolyte membrane. The membrane electrode assembly according to claim 1,
The said intermediate part is a membrane electrode assembly formed using the material which has electrical conductivity. The membrane electrode assembly according to claim 3, wherein
The material is a membrane electrode assembly including at least one of platinum, titanium, iridium, and osmium. A membrane electrode assembly according to any one of claims 1 to 4,
The said intermediate part is a membrane electrode assembly arrange | positioned at the dot form on the electrode catalyst layer which carry | supported the said electrolyte membrane or the said platinum. A membrane electrode assembly according to any one of claims 1 to 4,
The said intermediate part is a membrane electrode assembly arrange | positioned on the said electrolyte membrane or the electrode catalyst layer which carry | supported the said platinum at stripe form. A membrane electrode assembly according to any one of claims 1 to 4,
The said intermediate part is a membrane electrode assembly arrange | positioned on the said electrolyte membrane or the electrode catalyst layer which carry | supported the said platinum in the shape of a grid | lattice. A fuel cell,
A cathode electrode catalyst layer formed on the first surface of the electrolyte membrane; an anode electrode catalyst layer formed on a second surface different from the first surface of the electrolyte membrane; the cathode electrode catalyst layer; Among the anode electrode catalyst layers, a membrane electrode provided between an electrode catalyst layer carrying platinum and the electrolyte membrane, and an intermediate portion formed using a material having an affinity for platinum A joined body;
And a separator having a reaction gas flow path for supplying a reaction gas used for power generation of the fuel cell to the membrane electrode assembly.

Images