A carbon sheet， a gas-diffusion-electrode base material， and a fuel cell

The present invention addresses the problem of providing a gas diffusion electrode substrate which is excellent in suppressing reduction of power generation performance at high current density and can suppress fracturing or structural breakage during conveyance， and which can be stably produced. The present invention is: a porous carbon sheet including at least carbon fibers， the carbon sheet having a thickness of 30-95 ??m， a gas permeation resistance of 0.5-8.8 Pa， and a tensile strength of 5-50 N/cm; and a gas diffusion electrode substrate having a microporous layer including at least an electroconductive filler on at least one surface of a porous carbon sheet including at least carbon fibers， the thickness of a large-pore part being 3-60 ??m when the gas diffusion electrode substrate is divided into a small-pore part and a large-pore part in the thickness direction thereof. The present invention addresses the problem of providing a gas diffusion electrode substrate which is excellent in suppressing reduction of power generation performance at high current density and can suppress fracturing or structural breakage during conveyance， and which can be stably produced. The present invention is: a porous carbon sheet including at least carbon fibers， the carbon sheet having a thickness of 30-95 ??m， a gas permeation resistance of 0.5-8.8 Pa， and a tensile strength of 5-50 N/cm; and a gas diffusion electrode substrate having a microporous layer including at least an electroconductive filler on at least one surface of a porous carbon sheet including at least carbon fibers， the thickness of a large-pore part being 3-60 ??m when the gas diffusion electrode substrate is divided into a small-pore part and a large-pore part in the thickness direction thereof.