NOVELTY - Washing process of fuel cell involves forming platinum chloride complex ion by impregnating chloride ionic solution which contains chloride ion supply substance into electrolytic membrane and adjusting the electric potential (VPt) to 0.75-1.2 V (vs. SHE) to precipitate the platinum chloride complex ion on electrolytic membrane in the presence of oxidizing agent, removing platinum complex ion by outflow removal from electrolytic membrane and washing chloride ion from electrolytic membrane.    USE - Washing process of fuel cell consists of membrane electrode assembly provided with anode electrode, which contains platinum particles, on a surface of electrolytic membrane and cathode electrode, which contains platinum particles, provided on the other surface of electrolytic membrane (claimed).    ADVANTAGE - Production of hydrogen peroxide in an electrolytic membrane is suppressed which also suppresses electrolytic membrane deterioration and fuel cell durability is improved.    DETAILED DESCRIPTION - Washing process of fuel cell consists of membrane electrode assembly provided with anode electrode, which contains platinum particles, on a surface of electrolytic membrane and cathode electrode, which contains platinum particles, provided on the other surface of electrolytic membrane involves forming platinum chloride complex ion by impregnating chloride ionic solution which contains chloride ion supply substance into electrolytic membrane and adjusting the electric potential (VPt) to 0.75-1.2 V (vs. SHE) to precipitate the platinum chloride complex ion on electrolytic membrane in the presence of oxidizing agent, removing platinum complex ion by outflow removal from electrolytic membrane and washing chloride ion from electrolytic membrane.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional structural diagram of single cell for fuel cells.    Electrolytic membrane (1)    Fuel electrode (2)    Oxidizing agent electrode (3)    Fuel electrode side catalyst layer (4a)    Oxidizing agent electrode side catalyst layer (4b)    Fuel electrode side gas diffusion layer (5a)    Oxidizing agent electrode side gas diffusion layer (5b)