A membrane-free, aqueous/nonaqueous hybrid redox flow battery

Abstract

While membrane-free batteries have been successfully demonstrated in static batteries, membrane-free batteries in authentic flow modes with high energy capacity and high cyclability are rarely reported. Here, we present a biphasic flow battery with high capacity employing organic compound in organic phase and zinc in aqueous phase. Under ambient flow testing conditions, a capacity retention of 94.5% is obtained over 190 charging/discharging cycles with a Coulombic efficiency of > 99% at a current density of 8.54 mA cm−2. Self-discharge at full state-of-charge of the membrane-free RFB is negligible (potential drop = 0.78 mV h−1). DFT calculation and operando UV-visible and FT-IR spectroscopies are performed to probe minor side reactions during cycling and monitor the water content in the organic electrolyte in real time. The successful demonstration of the prototypical membrane-free battery under flow conditions, together with the developed operando spectroscopic techniques, will open a new avenue towards detailed mechanistic studies and practical applications of redox flow batteries for cost-effective energy storage.