Production method of electrode catalyst, electrode catalyst, composition for forming gas diffusion electrode, gas diffusion electrode, membrane-electrode assembly (mea), and fuel cell stack

Abstract

Provided is a production method of an electrode catalyst that can reduce the content of chlorine species reliably and sufficiently through a simple operation, even when using an electrode catalyst precursor containing a high concentration of chlorine (Cl) species as a raw material of the electrode catalyst. The production method of the electrode catalyst has a core-shell structure including a core part formed on a support and a shell part formed to cover at least a part of a surface of the core part. The production method includes a first step (1) of preparing a first liquid with an electrode catalyst precursor (I) being dispersed in ultrapure water by adding the electrode catalyst precursor (I) to the ultrapure water, the electrode catalyst precursor (I) being produced using a material containing chlorine (Cl) species, and exhibiting a chlorine (Cl) species concentration not lower than a first chlorine (Cl) species concentration when measured by X-ray fluorescence (XRF) spectroscopy; and a second step (2) of preparing a second liquid by dispersing an electrode catalyst precursor (II), the electrode catalyst precursor (II) being obtained by filtrating and washing the electrode catalyst precursor (I) contained in the first liquid with ultrapure water, and then performing washing until an electric conductivity ρ of a filtrate has become a first value or lower.