The development of an all copper hybrid redox flow battery using deep eutectic solvents

•A novel redox flow battery based on a deep eutectic solvent is reported.•Favourable kinetics of the positive electrode reaction are shown.•The cell potential is 0.7 V.•Coulombic and energy efficiency are 95% and 62% respectively.•A separator based on jellifying the electrolyte using polyvinyl alcohol is reported.

The performance of a redox flow battery based on chlorocuprates dissolved in an ionic liquid analogue is reported at 50 °C. The kinetics of the positive electrode reaction at a graphite electrode are favourable with a heterogeneous rate constant, k0, of 9.5 × 10−4 cm s−1. Coulombic efficiency was typically 94% and independent of current density. The small cell potential of 0.75 V and slow mass transport result in energy efficiencies of only 52% and 62% at current densities of 10 and 7.5 mA/cm2 respectively. The successful development of a separator by jellifying the electrolyte using polyvinyl alcohol is reported.