According to standard contact porosimetry data, treatment of electrospun pyropolymer mats based on pyrolyzed polyacrylonitrile and polybenzimidazole (PBI) nanofibers with a mixture of sulfuric and nitric acids causes a drastic increase in the specific surface area of macro- and mesopores and complete disappearance of micropores. Acid treatment is followed by hydrophilization of pores with radiir< 10 nm. Taken altogether, these effects lead to higher performance of the membrane-electrode assembly of a high-temperature polymer electrolyte membrane fuel cell based on PBI membrane with the cathode made of the platinized acid-treated material.