POTENTIAL ENHANCEMENT OF POLYIODIDE REDOX COUPLES VIA SOLUTION MODIFICATION

The stability and high reversibility of the polyiodide equilibrium res ults in a positive redox couple useful in fuel, battery, and photoelec trochemical solar cells I- + I-2 reversible arrow I-3(-); I-3(-) + 2e( -) --> 3I(-); E(0.01 mI(2), 1 m Nal) = 298 mV vs. Ag/AgCl A further po sitive shift of polyiodide redox couples which can make polyiodide mor e attractive as a storage cathode is accomplished by a two-step soluti on modification process. Solution-phase iodide is bound by complexatio n with cadmium salts. Then the complexation product, unstable at neutr al pH, is stabilized by acidification. The redox potential is increase d while maintaining facile charge transfer and electrolyte stability. For example, redox potentials of 425, 430, or 440 mV are sustained in solutions of 0.01 mI(2), 1 m Nal, and 1 m Cd(NO3)(2) containing either 1 m H2SO4, 1 m HNO3, or 1 m HClO4, respectively.