Regenerative fuel cell with catholyte comprising a polyoxometalate and a vanadium (iv) - compound

A redox fuel cell comprising an anode and a cathode separated by an ion selective polymer electrolyte membrane;

• means for supplying a fuel to the anode region of the cell;
• means for supplying an oxidant to the cathode region of the cell;
• means for providing an electrical circuit between the anode and the cathode;
• a non-volatile catholyte solution flowing fluid communication with the cathode, the catholyte solution comprising a polyoxometallate redox couple being at least partially reduced at the cathode in operation of the cell, and at least partially regenerated by reaction with the oxidant after such reduction at the cathode, the catholyte solution comprising at least about 0.075M of the said polyoxometallate, wherein the polyoxometallate is represented by the formula:
• Xa[ZbMcOd]
• wherein:
• X is selected from hydrogen, alkali metals, alkaline earth metals, ammonium or alkyl ammonium and combinations of two or more thereof;
• Z is selected from B, P, S, As, Si, Ge, Ni, Rh, Sn, M, Cu, I, Br, F, Fe, Co, Cr, Zn, H2, Te, Mn and Se and combinations of two or more thereof;
• M comprises at least one V atom, and M is a metal selected from Mo, W, V, Nb, Ta, Mn, Fe, Co, Cr, Ni, Zn Rh, Ru, Tl, M, Ga, In and other metals selected from the 1st, 2nd and 3rd transition metal series and the lanthanide series and combinations of two or more thereof;
• a is a number of X necessary to charge balance the [ZbMcOd] anion;
• b is from 0 to 20;
• c is from 1 to 40;
• and
• d is from 1 to 180,
• the catholyte further comprising a vanadium(IV) compound.