TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The catalyst redox species is selected from ligated transition metal complexes and/or polyoxometallate species. The transition metal in the transition metal complexes are selected from manganese (II-V), iron (I-IV), copper (I-III), cobalt (I-III), nickel (I-III), chromium (II-VII), titanium (II-IV), tungsten (IV-VI), vanadium (II-V) and molybdenum (II-VI). The catalyst redox species comprises a multidentate N-donor ligand. The N-donor ligand comprises at least one pyridine substituents. The catalyst redox species is an iron complex of N4Py, pydien, trilen or its derivatives.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The modified ferrocene species is of formula (I). The catholyte is acidic or alkali. The ferrocene is non-ionic or anionic in its oxidized form. The ferrocene is non-ionic or cationic in its reduced form. The modified ferrocene species is present in the catholyte at a concentration of at least 0.0001 (preferably at least 0.005, especially at least 0.001 M). The catholyte additionally comprises a catalyst redox species.X and Y1=H or T1 (preferably H, F, CHO, COCH3, COCH2CH3, COCH2CH2COOH, COOH, (COOH)2, NH2, NH3+, N(CH2)2, NH(CH3)2+, N(CH3)3+, N(CH2CH3)2, NH(CH2CH3)+, N(CH2CH3)3+, CH2N(CH3)2, CH2NH(CH3)2+, CH2N(CH3)3+, OH, CH2OH, CH(OH)CH3, OSO3-, SO3-, CH2SO3-, CH2OSO3-, PO(OH)2 or OPO(OH)2);T1=halogen, hydroxy, amino, protonated amino, imino, nitro, cyano, acyl, acyloxy, sulphate, sulphonyl, sulphinyl, alkylamino, protonated alkylamino, quaternary alkylammonium, carboxy, carboxylic acid, ester, ether, amido, sulphonate, sulphonic acid, sulphonamide, phosphonic acid, phosphonate, phosphonic acid, phosphate, alkylsulphonyl, arylsulphonyl, alkoxycarbonyl, alkylsulphinyl, arylsulphinyl, alkylthio, arylthio, alkyl, alkoxy, oxyester, oxyamido, aryl, arylamino, aryloxy, heterocycloalkyl, heteroaryl, 2-5C alkenyl, 2-5C alkynyl, azido phenylsulphonyloxy or amino acid conjugates of formula -CO-W1-OH;W1=alkyl, alkenyl, aryl, cycloalkyl, alkaryl alkenaryl, aralkyl, aralkenyl (all substituted with T1) or amino acid (preferably -CO-Gly-OH, -CO-Glu-OH or -CO-Asp-OH).    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The ion selective polymer electrode membrane is cation and/or proton selective. The ion selective polymer electrode membrane is anion selective. The ion selective polymer electrode membrane is a bi-membrane.