JP2003217598A - Electrode material for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode material for a fuel cell, which scarcely causes deterioration of cell performance by carbon monoxide. <P>SOLUTION: The electrode material for a fuel cell is composed of a pyrochlore type oxide represented by A<SB>2-</SB>XB<SB>2-</SB>YO<SB>7-</SB>Z, (wherein, A=Pb, B=Ir, 0≤X≤0.2, 0≤Y≤0.2, and 0≤Z≤0.5). <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a fuel cell electrode material, which is a pyrochlore type oxide having a catalytic action, and is composed of A _{2 -XB 2 -Y 7-. Z} (where A = Pb, B = Ir, 0 ≦ X ≦ 0.2, 0 ≦ Y ≦ 0.2, 0 ≦ Z ≦ 0.
It relates to a fuel cell electrode material having the composition of 5). [0002] As an electrode catalyst of a polymer electrolyte fuel cell,
Generally, a platinum-based catalyst is used. The platinum-based catalyst is characterized by exhibiting high catalytic activity and cell performance in the cathode reaction H ₂ → 2H ⁺ + 2e ⁻ and the anode reaction 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O of the fuel cell. [0003] However, when hydrogen extracted from hydrocarbons or the like using a reforming reaction is used as a fuel for a fuel cell, platinum, which is a cathode-side electrode catalyst, is affected by carbon monoxide contained in the fuel. It is poisoned, catalyst activity is reduced, and battery performance is reduced. In order to suppress the decrease in platinum activity due to carbon monoxide, an electrode catalyst using a platinum-ruthenium alloy has been proposed, for example, as disclosed in JP-A-2000-3712. This catalyst is characterized in that even if carbon monoxide is contained in the fuel in an amount equal to or less than the allowable concentration, it exhibits the same cell performance as that in the case where carbon monoxide is not contained. [0005] However, in order to reduce the carbon monoxide concentration in the fuel to an allowable concentration or less, a device for reducing the carbon monoxide concentration to a predetermined concentration is provided in the fuel reformer. Is required. Further, when a fuel containing carbon monoxide at a permissible concentration or more is supplied, there is a problem that the cell performance is reduced. Accordingly, the present invention provides a fuel cell electrode material in which the performance of the fuel cell is hardly degraded by carbon monoxide in order to solve the above problems. [0007] Means for Solving the Problems A fuel cell electrode material of the present _{invention, A 2-X B 2-} Y O 7-Z ( where A = Pb, B = Ir
0 ≦ X ≦ 0.2, 0 ≦ Y ≦ 0.2, 0 ≦ Z ≦ 0.2.
It is a pyrochlore type oxide represented by 5). DETAILED DESCRIPTION OF THE INVENTION As a raw material of a pyrochlore type oxide used in the present invention, lead chloride and iridium chloride hexahydrate were used. These were dissolved in an aqueous solution of caustic soda, and a precipitate was obtained by a coprecipitation method in which oxygen gas was bubbled for 24 hours while heating to 75 ° C. The precipitate is dried at 120 ° C. for 12 hours,
After pulverized in a mortar, washed with water, dried at 120 ° C. for 12 hours, and pulverized in a mortar. The obtained powder is dried in air for 8 hours.
Firing at 00 ° C. or 380 ° C. for 2 hours, Pb ₂ Ir ₂ O
A pyrochlore type oxide of _6.5 was obtained. The oxide calcined at 800 ° C. has a particle size of about 20 nm, and at 380 ° C., a particle size of about 5 n
m. The electrode material using the pyrochlore type oxide comprises a reaction layer 1 and a gas diffusion layer 2 as shown in FIG. As a reaction layer material, a hydrophobic carbon black, polytetrafluoroethylene, and a pyrochlore-type oxide synthesized earlier were added to a butanol aqueous solution in a weight ratio of oxide: hydrophobic carbon black: PTFE = 40: 28: 32. It is obtained by mixing for 1 hour, filtering and drying. The gas diffusion layer material is obtained by adding and mixing polytetrafluoroethylene and hydrophilic carbon black in a weight ratio of 4: 6 in an aqueous butanol solution, followed by filtration and drying. 380 ° C., 60 MPa together with the copper mesh plate 3 using this gas diffusion layer material as a current collector
And hot pressed to form a gas diffusion layer 2. The reaction layer 1 and the gas diffusion layer 2 are
By hot-breathing and joining at 60 ° C. and 60 ° C., a fuel cell electrode material as shown in FIG. 1 is obtained. Comparative Example In order to compare the present invention with the prior art, an electrode material using platinum was prepared. The reaction layer material was prepared by mixing a hydrophobic carbon black and an ammonium chloroplatinate solution in a butanol aqueous solution (carbon: PT = 10: 1; mass ratio). Furthermore, it is obtained by adding polytetrafluoroethylene (carbon: PTFE = 2: 1; mass ratio), mixing for 1 hour, filtering and drying. A reaction layer made of platinum and a gas diffusion layer produced by the same method as described above were hot-pressed at 370 ° C. and 60 MPa to obtain an electrode material for comparison with the present invention. The electrode material obtained by the above method was attached to a known electrochemical measuring device, and the electrode performance of the electrode material was confirmed. In this electrochemical measurement device, an electrode material was placed in a water tank filled with a 2N aqueous sulfuric acid solution to form a test electrode. Hydrogen or hydrogen containing carbon monoxide can be externally supplied to the test electrode. Further, a platinum electrode was provided as a counter electrode and a hydrogen electrode was provided as a reference electrode in 2N sulfuric acid. Using the above measuring device, the electrode performance of the fuel cell electrode material (potential difference from hydrogen electrode at 50 ° C.
The current density at 0 mV (mA / cm ² ) was measured. Table 1 shows the results. [Table 1] From Table 1, at 50 ° C., when hydrogen containing 100 ppm of carbon monoxide was used as the fuel, the electrode material using the pyrochlore-type oxide of the present invention fired at 380 ° C., compared to the electrode material using platinum, It was found that the current density was small at a potential difference of 200 mV from the hydrogen electrode serving as the reference electrode. From this, it was found that the electrode material using the pyrochlore type oxide of the present invention did not cause much deterioration in battery performance due to carbon monoxide. As described above, according to the present invention, in a fuel containing carbon monoxide, battery performance is improved as compared with a conventional electrode material using platinum as a material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view showing a structure of an electrode material according to the present invention. [Description of Signs] 1 ... Reaction layer 2 ... Gas diffusion layer 3 ... Copper mesh plate

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Yoshitaka Uchida             Fukuoka Prefecture Fukuoka City Minami-ku Shiobara 2-1-1 47             State Electric Power Company Research Institute (72) Inventor Keigo Tsujimoto             Fukuoka Prefecture Fukuoka City Minami-ku Shiobara 2-1-1 47             State Electric Power Co., Inc. F-term (reference) 5H018 EE02 EE13 HH00                 5H026 AA06 BB01 EE13 HH00

Claims (1)

[Claims 1] _{A 2-X B 2-Y} O 7-Z ( where A = Pb,
B = Ir, 0 ≦ X ≦ 0.2, 0 ≦ Y ≦ 0.2, 0 ≦
An electrode material for a fuel cell, which is a pyrochlore type oxide represented by the following formula: Z ≦ 0.5).