Development of metal-based electrodes for non-aqueous redox flow batteries

The electrochemistry of a non-aqueous redox flow battery employing nickel and iron bipyridine in tetraethylammonium tetrafluoroborate and propylene carbonate has been investigated. Ni(0)/Ni(II) and Fe(II)/Fe(III) redox couples showed reversible reactions for negative and positive electrodes, respectively. Various metal electrodes (Pt, Ir, Ni, Cu, Mo, W, Nb, Co, and Ti) were evaluated for those couples using cyclic voltammetry. Based on the analysis of the cyclic voltammograms, the reactivity and kinetics for the electrochemical reaction of metal complexes were found to strongly depend on the type of metal electrodes. Among non-precious metals, Cu and Mo showed relatively better electrocatalytic activities as negative electrodes for the Ni(0)/Ni(II) redox couple and Ni was the best material as a positive electrode for the Fe(II)/Fe(III) redox couple in terms of electrochemical reactivity and reaction kinetics.