Combination of Acid-Base Electrolyte at Each Half-Cell with a Single Zeolite Membrane for Crossover Free and Possible Increased Energy Density in an All Aqueous Redox Flow Battery

Instead of an organic medium, a simple change in pH could lead to a high energy density redox flow battery (RFB). Besides, ion crossover and membrane optimization are problems that limit its commercialization. In this investigation, a zeolite-coated ceramic single membrane is adopted in an acid-base pH electrolyte combination for the vanadium (V4+/V3+)/sulfur (S42−/2S22−) (V/S) redox couple as a model system. First, the potential widening with a change in pH is explained by difference in OCP (open circuit potential) between the acid-acid and acid-base electrolyte combination that differs by 0.8 V. A 300 mV decrease in the V4+/V5+ redox peak potential and the 10 mV increase in the negative direction in the S42−/2S22− redox peak potential between acid-acid and acid-base electrolyte combination show the pH effect predominant in anodic half-cell than the cathodic half-cell. UV-visible analysis for the migration of vanadium and sulfur ions demonstrates no migration of vanadium and sulfur ions to each other half-cell via zeolite coated ceramic membrane. The current efficiency of 94%, voltage and energy efficiencies of 45%-50% are achieved under the given current density of 5 mA cm−2. In addition, the acid-base combination of V/S RFB system shows an energy density of 233.2 Wh l−1