TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The multidentate N-donor ligand is non-polymeric molecule containing up to 8 nitrogen atoms capable of coordinating to a transition metal center. The ligand coordinates through the nitrogen atom(s). The ligand comprises 3-6, preferably 5-6 nitrogen atoms capable of coordinating to the transition metal center. The N-donor ligand has the structure of formula: Z-(B')b-N((A)a-X)-(C')c-Y'(I), preferably of formula: (R4)-CH2-N(C(R1)(R2)(R3))-CH2-R5 (II) or R1-N(R2)(CH2)n-N(R3)R4 (III).X1,Y',Z=N-containing heterocyclic group (optionally substituted by alkyl, aryl, alkenyl, alkynyl, amine, protonated amine, quaternary amine, sulfate, sulfonate, sulfonate, sulfonic acid, sulfonic acid, phosphate, phosphonate, phosphonic acid, carboxylate, carboxylic acid and/or halide);A,B',C'=spacer elements chosen from optionally branched chain alkyl, alkenyl, aryl, cycloalkyl, alkaryl, aralkyl and/or aralkenyl;a-c=0-5, preferably 1-3;R1-R5=organic groups containing N donor atom, chosen from optionally substituted heterocyclic group;andn=1-10, preferably 1-3, or 2.The N-donor ligand is chosen from tris-(1-methyl-1H-imidazol-2-yl methyl)-amine, tris-(2-pyrazin-2-yl-ethyl)-amine, (1-methyl-1H-imidazol-2-yl methyl)-pyrazin-2-ylmethyl-pyrazin-1-ylmethyl-amine, (1-methyl-1H-imidazol-2-yl methyl)-bis-pyridin-2-yl methyl-amine, bis-(1-methyl-1H-imidazol-2-yl methyl)-pyridin-2-yl methyl-amine, (dipyrazin-2-yl-methyl)-bis-pyrazin-2-yl methyl-amine, (bis-(1-methyl-1H-imidazol-2-yl)-methyl)-bis(1-methyl-1H-imidazol-2-yl methyl)-amine, N,N,N',N'-tetrakis-(1-methyl-1H-imidazol-2-yl methyl)-ethane-1,2-diamine, N,N,N',N'-tetrakis-(2-methyl-2H-(1,2,4)triazol-3-yl methyl)-ethane-1,2-diamine, N,N,N',N'-tetrakis-pyrazin-2-yl methyl-ethane-1,2-diamine, N-(1-methyl-1H-imidazol-2-ylmethyl)-N'-pyrazin-2-yl methyl-N,N'-bis-pyridin-2-yl methyl-ethane-1,2-diamine, N-methyl-N,N',N'-tris-(1-methyl-1H-imidazol-2-yl methyl)-ethane-1,2-diamine, N-methyl-N,N',N'-tris-(2-methyl-2H-(1,2,4)triazol-3-yl methyl)-ethane-1,2-diamine, N-methyl-N,N',N'-tris-pyrazin-2-yl methyl-ethane-1,2-diamine or N-methyl-N'-(1-methyl-1H-imidazol-2-yl methyl)-N,N'-bis-pyridin-2-ylmethyl-ethane-1,2-diamine. The catholyte solution comprises redox mediator and complexed multidentate N-donor ligand as redox catalyst, or complexed multidentate N-donor ligand as redox mediator and a further material as redox catalyst. The operation of the fuel cell reduces the oxidant in the catholyte solution by the redox catalyst. The oxidized redox catalyst partially oxidizes the mediator to regenerate the mediator after its reduction at the cathode. The catholyte solution is an aqueous solution. The catholyte is acidic when the ion selective polymer electrolyte membrane is cation selective membrane, and the catholyte is alkaline when the polymer membrane is anion selective membrane. Alternately, the ion selective polymer electrolyte membrane is a bi-membrane. The redox mediator comprises a modified ferrocene species.