Porous Electrode Substrate and Production Method Therefor

Provided is a porous electrode substrate capable of reducing a drop in electromotive force when used in a battery. This porous electrode substrate comprises a carbon fiber sheet wherein carbon fibers are bound by a binder. For dust of 0.3 μm or more in particle size， the dust generation amount per 1 m 2 of the porous electrode substrate is 120，000/m2 or less， as determined by the following method: dust particles in a gas obtained by suctioning at 47.2 mL/s for 40 minutes using a dust collecting hood having an opening of 500 mm×100 mm while traveling the sheet at a speed of 10 m/min from a position 200 mm below the sheet are used; the number of dust particles having a diameter within a predetermined range is measured by a particle counter; and the measured value is divided by 200 m2， which is a suction area， and the resulting value is defined as a dust generation amount per 1 m2.