Method for producing electrode catalyst, and electrode catalyst
Provided is a method with which it is possible to easily produce an electrode catalyst having excellent catalytic performance such as kinetically controlled current density. The method involves: a dispersion liquid preparation step of preparing a dispersion liquid by mixing (i) at least one type of solvent selected from the group consisting of sulfoxide compounds and amide compounds, (ii) a catalyst carrier powder constituted by a metal oxide, (iii) a platinum compound, (iv) a transition metal compound, and (v) an aromatic compound including a carboxyl group; and a loading step of heating the dispersion liquid to thereby load a platinum alloy of platinum and a transition metal on a surface of the catalyst carrier powder.
1. A method for producing an electrode catalyst in which a platinum alloy of platinum and a transition metal is loaded on a tin oxide carrier, comprising:
a dispersion liquid preparation step of preparing a dispersion liquid by mixing (i) at least one type of solvent selected from the group consisting of sulfoxide compounds and amide compounds, (ii) a catalyst carrier powder comprising a tin oxide, (iii) a platinum compound, and (iv) a transition metal compound; and
a loading step of heating the dispersion liquid to thereby load a platinum alloy of platinum and a transition metal on a surface of the catalyst carrier powder, wherein a heating temperature in said loading step is below 160° C.;
wherein said at least one type of solvent is present in said dispersion liquid in an amount of 30 to 99.9 mass % of a total mass of said dispersion liquid.
2. The method for producing an electrode catalyst according to claim 1 , wherein said heating temperature in the loading step is at least 120° C.
3. The method for producing an electrode catalyst according to claim 1 , wherein said at least one type of solvent is selected from the group consisting of dimethylsulfoxide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, N,N-dimethylformamide, N-methylformamide, N,N-diethylformamide, N-ethylformamide, N,N-dimethylacetamide, and N,N-diethylacetamide.
4. An electrode catalyst in which a platinum alloy of platinum and a transition metal is loaded on a tin oxide carrier including tungsten, wherein:
in a diffraction pattern obtained by subjecting the electrode catalyst to an X-ray diffraction measurement, a diffraction angle 2θ at a peak of a (200) plane of the platinum alloy is from 46.5° to 48.0°;
a metallization rate of Sn, as defined by equation (1) below, in an analysis region on the electrode catalyst's surface and a vicinity of the surface as measured by X-ray photoelectron spectroscopy is 3.5% or less:
metallization rate of Sn (%)=R Sn-metal /(R Sn-metal +R Sn-oxide )×100 (Eq. 1),
wherein R Sn-metal is an area that Sn metal occupies in a spectrum ascribable to the Sn 3d 5/2 orbit as measured by X-ray photoelectron spectroscopy, and
R Sn-oxide is an area that Sn oxide occupies in a spectrum ascribable to the Sn 3d 5/2 orbit as measured by X-ray photoelectron spectroscopy; and
the transition metal is at least one member selected from the group consisting of nickel, cobalt, iron, chromium, titanium, vanadium, manganese, copper, zinc and scandium; and
wherein a molar ratio of platinum to said transition metal in said platinum alloy is at least 2.09 and at most 10.
5. The electrode catalyst according to claim 4 , wherein the diffraction angle 2θ at the peak of the (200) plane of the platinum alloy is from 46.8° to 47.7°.
6. The electrode catalyst according to claim 4 , wherein the transition metal is nickel, cobalt, iron, or chromium.
7. The electrode catalyst according to claim 4 , wherein the tin oxide carrier further comprises fluorine.