POLYOXOMETALLATES FOR USE AT ELEVATED TEMPERATURES AND PRESSURES

The present invention relates to 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 in 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 re-generated by reaction with the oxidant in a regeneration zone after such reduction at the cathode, the catholyte solution further comprising one or more vanadium species that result from the speciation of the polyoxometallate at an elevated temperature and/or pressure, wherein the polyoxometallate is represented by the formula: Xa[ZbMcOd] wherein X is selected from hydrogen, alkali metals, alkaline earth metals, ammonium, transition metal ions and combinations of two or more thereof; Z is selected from B, P, S, As, Si, Ge, Ni, Rh, Sn, Al, Cu, I, Br, F, Fe, Co, Cr, Zn, H2, Te, Mn and Se and combinations of two or more thereof; M comprises vanadium and optionally one or more of Mo, W, Nb, Ta, Mn, Fe, Co, Cr, Ni, Zn Rh, Ru, TI, Al, 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; d is from 1 to 180; X includes an amount of a non-hydrogen cation and the molar ratio of the non-hydrogen cation to vanadium is more than 0 and less than 1.