Porous electrode substrate, method for producing the same, precursor sheet, membrane electrode assembly, and polymer electrolyte fuel cell

Abstract

The provision of a porous electrode substrate that has large sheet strength, low production costs, high handling properties, high thickness precision and surface smoothness, and sufficient gas permeability and electrical conductivity. A porous electrode substrate including a three-dimensional entangled structure including short carbon fibers (A) dispersed in a three-dimensional structure, joined together via three-dimensional mesh-like carbon fibers (B). A method for producing a porous electrode substrate, including a step (1) of producing a precursor sheet including short carbon fibers (A), and short carbon fiber precursors (b) and/or fibrillar carbon fiber precursors (b') dispersed in a two-dimensional plane; a step (2) of subjecting the precursor sheet to entanglement treatment; and a step (3) of subjecting this sheet to carbonization treatment at 1000° C. or higher. It is preferable to include a step (4) of subjecting the sheet to hot press forming at lower than 200° C. between step (2) and step 3), and to further include a step (5) of subjecting the sheet after hot press forming to oxidation treatment at 200° C. or higher and lower than 300° C. between step (4) and step (3).