POTENTIAL ENHANCEMENT OF POLYIODIDE REDOX COUPLES VIA SOLUTION MODIFICATION

The stability and high reversibility of the polyiodide equilibrium results in a positive redox couple useful in fuel, battery, and photoelectrochemical 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 positive shift of polyiodide redox couples which can make polyiodide more attractive as a storage cathode is accomplished by a two-step solution modification process. Solution-phase iodide is bound by complexation with cadmium salts. Then the complexation product, unstable at neutral pH, is stabilized by acidification. The redox potential is increased 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.