TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The redox fuel cell further comprises a regeneration zone which is separate from the cathode so that in use oxidant does not come into contact with the cathode but instead regenerates the redox couple in the regeneration zone. The separator is microporous. The porous separator is polyolefinic. The catholyte comprises at least one transition metal. The redox couple comprises a polyoxometalate that is a Keggin-type polyoxometalate. The catholyte solution comprises at least 0.075 M polyoxometalate. The catholyte comprises a polyoxometalate of formula (Xa(ZbMcOd)) (I).X = H, alkali metals, alkaline earth metals, ammonium and/or alkyl ammonium;Z = B, P, S, As, Si, Ge, Ni, Rh, Sn, Al, Cu, I, Br, F, Fe, Co, Cr, Zn, H2, Te, Mn and/or Se;M = W, V (both preferred), Mo, Nb, Ta, Mn, Fe, Co, Cr, Ni, Zn, Rh, Ru, Ti, Al, Ga, In and/or other metals of 1st, 2nd and 3rd transition metal series and the lanthanide series;a = number of X necessary to charge balance the (ZbMcOd) anion;b = 0-20, preferably 0-5;c = 1-40, preferably 5-30; andd = 1-180.The counterion for the redox couple comprises at least one divalent ion that is calcium, magnesium, manganese, iron, cobalt, nickel, copper, zinc, strontium, barium, beryllium, chromium, cadmium, mercury, tin and/or other suitable ions from the 2nd and 3rd transition series or from the lanthanides. The catholyte comprises a redox mediator which is at least partially reduced at the cathode in operation of the cell, and at least partially regenerated by, optionally indirect, reaction with the oxidant after such reduction at the cathode, where the catholyte solution comprises a complexed multidentate N-donor ligand as the redox mediator and/or as a redox catalyst catalyzing the regeneration of the mediator. The complexed multidentate N-donor ligand is a complexed multidentate macrocyclic N- donor ligand. The multidentate N-donor ligand comprises at least one heterocyclic substituent comprising pyrrole, imidazole, 1,2,3-triazole, 1,2,4-triazole, pyrazole, pyridazine, pyrimidine, pyrazine, indole, tetrazole, quinoline, isoquinoline, or alkyl, alkenyl, aryl, cycloalkyl, alkaryl, alkenaryl, aralkyl or aralkenyl groups substituted with at least one of the heterocyclic groups. The redox couple comprises a ferrocene species of formula (II).X1, Y1 = H, or functional groups comprising halo, hydroxy, amino, protonated amino, imino, nitro, cyano, acyl, acyloxy, sulfate, sulfonyl, sulfinyl, alkylamino, protonated alkylamino, quaternary alkylammonium, carboxy, carboxylic acid, ester, ether, amido, sulfonate, sulfonic acid, sulfonamide, phosphonic acid, phosphonate, phosphonic acid, phosphate, alkylsulfonyl, arylsulfonyl, alkoxycarbonyl, alkylsulfinyl, arylsulfinyl, alkylthio, arylthio, alkyl, alkoxy, oxyester, oxyamido, aryl, arylamino, aryloxy, heterocycloalkyl, heteroaryl, (2-5C)alkenyl, (2-5C)alkynyl, azido phenylsulfonyloxy or amino acid conjugates of formula (-CO-W1-OH) (a1), or alkyl, alkenyl, aryl, cycloalkyl, alkaryl, alkenaryl, aralkyl or aralkenyl groups substituted with at least one of the functional groups; andW1 = amino acid.The catholyte comprises a ferrocene species having at least one bridging unit of formula (-A1-(B1)n-C1-) (III) between the cyclopentadienyl rings.A1-(B1)n-C1 = divalent heteroannular bridging group; andn = 1-8.The catholyte comprises a ferrocene species of formula (IV) and substituted 9H-carbazole compound of formula (V).X2, Y2 = electron withdrawing substituent;R, R1 = spacer group;n, m = 1- 10; eitherX3 = H, or functional groups comprising halo, hydroxy, amino, protonated amino, imino, nitro, cyano, acyl, acyloxy, sulfate, sulfonyl, sulfinyl, alkyamino, protonated alkylamino, quaternary alkylammonium, carboxy, carboxylic acid, ester, ether, amido, sulfonate, sulfonic acid, sulfonamide, phosphonic acid, phosphonate, phosphate, alkylsulfonyl, arylsulfonyl, alkoxycarbonyl, alkylsulfinyl, arylsulfinyl, alkylthio, arylthio, alkyl, alkoxy, oxyester, oxyamido, aryl, fused-aryl, arylamino, aryloxy, heterocycloalkyl, heteroaryl, fused-heteroaryl, (2-5C)alkenyl, (2-5C)alkynyl, azido phenylsulfonyloxy and/or amino acid, preferably substituted phenyl moiety of formula (VI); andR1-R8 = H, halo, hydroxy, amino, protonated amino, imino, nitro, cyano, acyl, acyloxy, sulfate, sulfonyl, sulfinyl, alkyamino, protonated alkylamino, quaternary alkylammonium, carboxy, carboxylic acid, ester, ether, amido, sulfonate, sulfonic acid, sulfonamide, phosphonic acid, phosphonate, phosphate, alkylsulfonyl, arylsulfonyl, alkoxycarbonyl, alkylsulfinyl, arylsulfinyl, alkylthio, arylthio, alkyl, alkoxy, oxyester, oxyamido, aryl, fused-aryl, arylamino, aryloxy, heterocycloalkyl, heteroaryl, fused-heteroaryl, (2-5C)alkenyl, (2-5C)alkynyl, azido phenylsulfonyloxy and/or amino acid; andR9-R13 = H, or functional groups comprising halo, hydroxy, amino, protonated amino, imino, nitro, cyano, acyl, acyloxy, sulfate, sulfonyl, sulfinyl, alkyamino, protonated alkylamino, quaternary alkylammonium, carboxy, carboxylic acid, ester, ether, amido, sulfonate, sulfonic acid, sulfonamide, phosphonic acid, phosphonate, phosphate, alkylsulfonyl, arylsulfonyl, alkoxycarbonyl, alkylsulfinyl, arylsulfinyl, alkylthio, arylthio, alkyl, alkoxy, oxyester, oxyamido, aryl, fused-aryl, arylamino, aryloxy, heterocycloalkyl, heteroaryl, fused-heteroaryl, (2-5C)alkenyl, (2-5C)alkynyl, azido phenylsulfonyloxy and/or (a1); orR1X3, R5X3, R1R2, R2R3, R3R4, R4R8, R8R7, R7R6, R6R5 = optionally substituted ring structure; orR9R1 and/or R13R5 = linking group comprising O, N, S, imino, sulfonyl, sulfinyl, alkylamino, protonated alkylamino, quaternary alkylammonium, carbonyl, ester, ether, amido, sulfonamide, phosphonate, phosphate, alkysulfonyl, alkenylsulfonyl, arylsulfonyl, alkylsulfinyl, alkenylsulfinyl, arysulfinyl, alkylthio, alkenylthio, arylthio, oxyester, oxyamido, aryl, cycloalkyl, heteroaryl, (2-5C)alkyl, (2-5C)alkenyl, (2-5C)alkynyl, or amino acid;Sp = optionally spacer group; andL = optional presence of a linking bond or group between the two neighboring aromatic rings of the structure, which is optionally substituted ring structure with one or both of R4 and R8, where at least one substituent group of the structure is a charge-modifying substituent.The anode region of the cell is supplied with an alcoholic fuel, the redox potential of the redox couple is 0.01-0.6 V different from the potential of oxygen and the redox couple and/or the concentration of the redox couple in the catholyte solution are selected so that the current density generated by the cell in operation is substantially unaffected by the oxidation of alcoholic fuel due to crossover of the alcoholic fuel from the anode region of the cell to the cathode region of the cell across the porous separator. The cathode region is supplied in use with a liquid low molecular weight fuel, where at least some of the liquid low molecular weight fuel in use crosses the porous separator to supply the anode region with liquid low molecular weight fuel. The volume of catholyte solution in the regeneration zone is 25-90% of the total combined volume of catholyte solution in the regeneration zone and the cathode chambers. The redox fuel cell comprises a regeneration zone with: droplet formation means or atomization means for the catholyte; and means to separate catholyte after regeneration. The cathode electrode comprises a porous skeletal medium. The redox fuel cell further comprises means for contacting the redox catalyst and/or mediator couple with the oxidant to generate a foam comprising oxidized catalyst and/or mediator couple.