Chromium redox couples for application to redox flow batteries

Both anodic and cathodic chromium-EDTA (ethylenediaminetetra-acetate) complex redox processes have been studied using cyclic voltammetry. Their potential use in a redox battery has been evaluated by comparing the charge and discharge performance of a simple redox battery employing several redox couples including the conventional Fe-Cr redox couples. The cyclic voltammetry experiments suggested that oxidation of Cr(III)-EDTA formed Cr(V)-EDTA rather than a hexavalent chromium species. It was found that the kinetics of the Cr(III)-EDTA/Cr(II)-EDTA redox reaction are fast at a graphite rod electrode, whereas the Cr(V)-EDTA/Cr(III)-EDTA redox reaction is relatively slow. In spite of the slow kinetics, the battery employing solely these chromium-EDTA based redox couples provided higher energy output and longer life than the conventional Fe-Cr redox system. (C) 2002 Elsevier Science Ltd. All rights reserved.