Catalyst for electrode, composition for forming gas diffusion electrode, gas diffusion electrode, membrane-electrode junction, and fuel cell stack
Provided is a catalyst for electrode that has excellent catalytic activity and that is capable of contributing toward lower PEFC costs. This catalyst for electrode includes: a hollow carbon support having nanopores with a pore diameter of 1 to 20 nm; and a plurality of catalyst particles supported on the support. The catalyst particles are supported both inside and outside the nanopores of the support, are composed of (zerovalent) Pt, and when analysis of the particle size distribution of the catalyst particles is performed using three-dimensional, reconstructed images obtained through STEM-based electron tomography measurement, the percentage of catalyst particles supported inside the nanopores is 50% or more.
1 . A catalyst for an electrode which includes a conductive hollow carbon carrier having nanopores of a pore size of 1 to 20 nm, and a plurality of catalyst particles supported on the carrier, wherein
the catalyst particles are composed of Pt (0 valent),
each catalyst particle is supported on either inside of a nanopore and outside a nanopore of the carrier,
a ratio of the catalyst particles supported inside the nanopore is 50% or more when an analysis of a particle size distribution of the catalyst particles is performed by using a three-dimensional reconstructed image obtained by an electron beam tomography measurement using STEM (scanning transmission electron microscopy), and
the catalyst satisfies the condition of following equation (1), when an analysis of a particle size distribution of the catalyst particles is performed by using a three dimensional reconstructed image obtained by an electron beam tomography measurement using STEM:
( D 10/ D 20)≤0.75 (1)
wherein, in above equation (1),
D10 indicates the arithmetic mean value of the sphere-equivalent diameter of the catalyst particles supported on the inside of the nanopores of the carrier, and
D20 indicates the arithmetic mean value of the sphere-equivalent diameter of the catalyst particles supported on the outside of the nanopores of the carrier.
2 . The catalyst for an electrode according to claim 1 , wherein the ratio of the catalyst particles supported inside the nanopore is 70% or more when an analysis of a particle size distribution of the catalyst particles is performed by using a three dimensional reconstructed image obtained by an electron beam tomography measurement using STEM.
3 . The catalyst for an electrode according to claim 1 , which further satisfies simultaneously the conditions of following equation (2) and equation (3) in addition to the condition of equation (1), when the analysis of the particle size distribution of the catalyst particles is performed by using three-dimensional reconstructed images obtained by electron beam tomography measurement with STEM:
D 1≤ D 2 (2)
( N 1/ N 2)>2.0 (3)
wherein, in equation (2) and equation (3),
D1 indicates a sphere equivalent diameter of particles exhibiting a maximum frequency among the catalyst particles supported inside the nanopores of the carrier,
D2 indicates a sphere equivalent diameter of particles exhibiting a maximum frequency among the catalyst particles supported outside the nanopores of the carrier,
N1 indicates a frequency of particles exhibiting a maximum frequency among the catalyst particles supported inside the nanopores of the carrier,
N2 indicates a frequency of particles exhibiting a maximum frequency among the catalyst particles supported outside the nanopores of the carrier.
4 . The catalyst for an electrode according to claim 1 , wherein at least a part of the surface of the catalyst particles is covered with a Pt oxide film.
5 . The catalyst for an electrode according to claim 1 , wherein the hollow carbon carrier has a BET specific surface area (nitrogen adsorption specific surface area) of 200 to 1500 m 2 /g.
6 . A powder of a catalyst for an electrode, which contains 10 wt % or more of the catalyst for an electrode according to claim 1 .
7 . A composition for forming a gas diffusion electrode, which contains the catalyst for an electrode according to claim 1 .
8 . A gas diffusion electrode, which contains the catalyst for an electrode according to claim 1 .
9 . A membrane-electrode assembly (MEA), which comprises the gas diffusion electrode according to claim 8 .
10 . A fuel cell stack, which comprises the membrane-electrode assembly (MEA) of claim 9 .