Cerium-polysulfide redox flow battery with possible high energy density enabled by MFI-Zeolite membrane working with acid-base electrolytes

A pH change can enable high-energy-density RFB (redox flow battery) in an aqueous medium. Nevertheless, a membrane to prevent the ion crossover is needed. This study adopted cerium and polysulfide in an acid-base combined electrolyte with an MFI-Zeolite membrane as a separator. The increased potential with pH change is described by the OCP (open circuit potential) difference, which varies by 0.8 V for the combination of acid-acid and acid-base electrolyte. A decrease of 350 mV at the redox peak potential of Ce³⁺/Ce⁴⁺ and a 10 mV negative potential shift for S₄²⁻/2S₂²⁻ highlights the pH effect between the combination of acid-acid and acid-base electrolyte indicates the influence of pH leading in half-cell of anodic than the opposite cathodic side. The UV–visible spectral analysis for Ce³⁺ and S₄²⁻ ions displacement shows that cerium and sulfur ions do not migrate to each other half-cell through an MFI-Zeolite membrane. As a result, the current efficiency of 94%, voltage, and energy efficiency of 40%–43% were attained at a current density of 10 mA cm⁻². Moreover, the acid-base composition of the Ce/S system showed an energy density of 378.3 Wh l ⁻¹.