Fuel cells

1. A redox fuel cell comprising:

an anode region comprising an anode and a cathode region comprising a cathode, said regions being separated by an ion selective polymer electrolyte membrane;

a fuel passage through which fuel is supplied to the anode region of the cell;

an oxidant inlet that supplies an oxidant to the cathode region of the cell;

an electrical circuit between the anode and the cathode; and

a catholyte solution flowing in fluid communication with the cathode, the catholyte solution comprising a modified ferrocene species, the modified ferrocene species being at least partially reduced at the cathode in operation of the cell, and at least partially re-generated by reaction with the oxidant isolated from the anode region after said reduction at the cathode.

2. A redox fuel cell according to claim 1 wherein the modified ferrocene species is represented by the formula:

wherein:

X and Y are independently selected from the group consisting of hydrogen and functional groups comprising 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, (C 2 -C 5 )alkenyl, (C 2 -C 5 )alkynyl, azido phenylsulphonyloxy or amino acid conjugates having the formula —CO—W—OH, where W is an amino acid, and from alkyl, alkenyl, aryl, cycloalkyl, alkaryl alkenaryl, aralkyl, aralkenyl groups substituted with one or more of the aforesaid functional groups.

3. A redox fuel cell according to claim 2 , wherein X and Y are independently selected from the group consisting of hydrogen and functional groups comprising, halogen, hydroxy, amino, protonated amino, imino, acyl, sulphate, alkylamino, protonated alkylamino, quaternary alkylammonium, carboxy, carboxylic acid, ester, oxyester, alkoxy, sulphonyl, sulphinyl, alkylsulphonyl, sulphonic acid, sulphonamide, phosphonic acid, phosphonate, phosphate, amido, oxyamido, or amino acid conjugates having the formula —CO—W—OH, where W is an amino acid, and from alkyl, alkenyl, aryl, cycloalkyl, alkaryl alkenaryl, aralkenyl groups substituted with one or more of the aforesaid functional groups.

4. A redox fuel cell according to claim 2 wherein X and Y are independently selected from the group consisting of hydrogen and from functional groups comprising —F, —CHO, —COCH 3 , —COCH 2 CH 3 , —COCH 2 CH 2 COOH, —COOH, —(COOH) 2 , —NH 2 , —NH 3 + , —N(CH 3 ) 2 , —NH(CH 3 ) 2 + , —N(CH 3 ) 3 + , —N(CH 2 CH 3 ) 2 , —NH(CH 2 CH 3 ) + , —N(CH 2 CH 3 ) 3 + , —CH 2 N(CH 3 ) 2 , —CH 2 NH(CH 3 ) 2 + , —CH 2 N(CH 3 ) 3 + , —OH, —CH 2 OH, —CH(OH)CH 3 , —OSO 3 − , —SO 3 − , —CH 2 SO 3 − , —CH 2 OSO 3 − , —PO(OH) 2 , —OPO(OH) 2 , —CO-Gly-OH, —CO-Glu-OH or —CO-Asp-OH, and from alkyl, alkenyl, aryl, cycloalkyl, alkaryl alkenaryl, aralkyl, aralkenyl groups substituted with one or more of the aforesaid functional groups.

5. A redox fuel cell according to claim 1 wherein the ion selective polymer electrode membrane is cation and/or proton selective.

6. A redox fuel cell according to claim 5 wherein the catholyte solution is acidic.

7. A redox fuel cell according to claim 5 wherein the ferrocene is non-ionic or anionic in its oxidized form.

8. A redox fuel cell according to claim 1 wherein the ion selective polymer electrode membrane is anion selective.

9. A redox fuel cell according to claim 8 wherein the catholyte solution is alkali.

10. A redox fuel cell according to claim 8 wherein the ferrocene is non-ionic or cationic in its reduced form.

11. A redox fuel cell according to claim 1 wherein the ion selective polymer electrode membrane is a bi-membrane.

12. A redox fuel cell according to claim 1 wherein the modified ferrocene species is present in the catholyte solution at a concentration of at least 0.0001 M.

13. A redox fuel cell according to claim 1 wherein the modified ferrocene species is present in the catholyte solution at a concentration of at least 0.005M.

14. A redox fuel cell according to claim 1 wherein the modified ferrocene species is present in the catholyte solution at a concentration of at least 0.001 M.

15. A redox fuel cell according to claim 1 wherein the catholyte solution additionally comprises a catalyst redox species.

16. A redox fuel cell according to claim 15 wherein the catalyst redox species is selected from the group consisting of ligated transition metal complexes, polyoxometallate species, and combinations thereof.

17. A redox fuel cell according to claim 16 wherein the transition metal(s) in the transition metal complexes are selected from the group consisting of 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).

18. A redox fuel cell according to claim 15 wherein the catalyst redox species comprises a multidentate N-donor ligand.

19. A redox fuel cell according to claim 18 wherein the N-donor ligand comprises one or more pyridine substituents.

20. A redox fuel cell according to claim 18 wherein the catalyst redox species is selected from the group consisting of iron complexes of N4Py (N,N-bis(pyridine-2-yl-methyl)-bis(pyridine-2-yl)methylamine) and derivatives thereof, pydien (1,9-bis(2-pyridyl)-2,5,8-triazanonane) and derivatives thereof, trilen (N-methyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine) and derivatives thereof, and tpen (N,N′,N′,N′-Tetrakis(2-pyridylmethyl)ethane-1,2-diamine) and derivatives thereof.