Non-aqueous chromium acetylacetonate electrolyte for redox flow batteries

A single-metal redox flow battery employing chromium(III) acetylacetonate in tetraethylammonium tetrafluoroborate and acetonitrile has been investigated using electrochemical techniques. Cyclic voltammetry was used to evaluate electrode kinetics. Four redox couples were observed in the stable potential window. The CrII/CrIII, CrI/CrII, CrIII/CrIV and CrIV/CrV redox couples all appeared to be quasi-reversible, with the CrIII/CrIV couple exhibiting comparatively slow kinetics. A cell potential of 3.4 V was measured for the one-electron disproportionation of the neutral CrIII complex. The diffusion coefficient for chromium acetylacetonate in the supporting electrolyte solution was estimated to be in the range of 5.0–6.2 × 10−7 cm2 s−1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell, and coulombic and energy efficiencies of approximately 55% and 20%, respectively, were obtained.