TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred System: The fuel cell has several single cells (2) equipped with a membrane-electrode assembly (3), and an antioxidant supply system for supplying antioxidant to fuel cell and for contacting the supplied antioxidant with electrode. The membrane electrode assembly has a solid-polymer-electrolyte membrane clamped between air electrode (5) and fuel electrode (6), air electrode side separator arranged at air electrode side of membrane-electrode assembly, and fuel-electrode side separator arranged at the surface of fuel-electrode side of membrane-electrode assembly. The air electrode side separator constitutes an air flow path between membrane-electrode assemblies, and fuel electrode side separator constitutes a fuel gas flow path between membrane-electrode assemblies. The antioxidant supply system has an antioxidant solution tank sealed with antioxidant solution, wave-sending pump for supplying antioxidant solution to the fuel electrode, and antioxidant solution pipe line, which connects the wave-sending pump and fuel gas flow path. The antioxidant is continuously supplied in the form of aqueous solution.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The antioxidant is hydrocarbon-type compound comprising carbon, oxygen, nitrogen and hydrogen. The hydrolyzed substance obtained by hydrolyzing oxidant of the antioxidant is chemically stable. The antioxidant has reversible oxidation-reduction ability. The antioxidant contains compound which has oxidation-reduction property. The compound which has oxidation-reduction property is nitrogen-containing compound of formula (I), imide compound of formula (II), or imide compound of formula (III). The imide compound of formula (III) is preferably of formula (IVa). The imide compound of formula (II) is a compound preferably of formula (V), more preferably of formula (VIa). The compound of formula (VIa) is N-hydroxy glutaric acid imide, N-hydroxy-1,8-naphthalene dicarboxylic acid imide, N-hydroxy-1,8-decalin dicarboxylic acid imide, N,N'-dihydroxy-1,8:4,5-naphthalene tetracarboxylic acid imide, N,N'-dihydroxy-1,8:4,5-decalin tetracarboxylic acid imide and N,N',N"-trihydroxy isocyanuric acid. The nitrogen-containing compound of formula (I) is preferably of formula (VII). The nitrogen-containing compound of formula (VII), is preferably of formula (XII). The imide compound of formula (III) is chosen from N-hydroxy succinic acid imide, N-hydroxy maleic acid imide, N-hydroxy hexahydro phthallic imide, N,N'-dihydroxy cyclohexane tetracarboxylic acid imide, N-hydroxy phthalimide, N-hydroxy tetrabromo phthalic imide, N-hydroxy tetrachlorophthalic acid imide, N-hydroxy HET-acid imide, N-hydroxy himic acid imide, N-hydroxy trimellitic acid imide, N,N'-dihydroxy pyromellitic acid imide and N,N'-dihydroxy naphthalene tetracarboxylic acid imide.R1,R2=arbitrary substituents, and are optionally coupled to form double bond, aromatic ring or non-aromatic ring;Y1=5-12 membered aromatic or non-aromatic ring having double bond;R3,R4=H, halogen, alkyl, aryl, cycloalkyl, hydroxyl, alkoxyl, carboxyl, alkoxycarbonyl or acyl, where R3 and R4 are optionally coupled to form double bond, aromatic ring or non-aromatic ring, preferably 5-12 membered aromatic or non-aromatic ring, are R3 and R4 are coupled to form cycloalkane, cycloalkene, crosslinked-type hydrocarbon ring, aromatic ring or their substitution products;X=oxygen atom or hydroxyl group;R13,R14=alkyl or (un)substituted alkyl;andZ=alkyl in which a portion is substituted by arbitrary groups and remaining portions are in chain, cyclic or branched form, aryl in which a portion is substituted by arbitrary groups, alkoxy, carboxyl, alkoxy carbonyl, cyano, hydroxyl, nitro, amino or H.R13 and R14 are optionally coupled to form ring containing oxygen and nitrogen. Alkyl and aryl groups of Z optionally contain oxygen and nitrogen atom.In formula (IVa),R3,R4=H, halogen, alkyl, hydroxyl, alkoxyl, carboxyl, alkoxycarbonyl, acyl, nitro, cyano or amino;andm=1-3In formula (V),R1-R6=H, halogen, alkyl, aryl, cycloalkyl, hydroxyl, alkoxy, carboxyl, substituted oxycarbonyl, acyl or acyloxy.R1-R6 are optionally coupled to form aromatic or non-aromatic ring having double bond.In formula (VIa),R7-R12=H, alkyl, hydroxyl, alkoxyl, carboxyl, alkoxycarbonyl, acyl, nitro, cyano or amino.Preferred Property: The oxidation-reduction potential of the compound which has oxidation-reduction property, is 0.68-2.85 V, preferably 0.68-1 V.