Enhanced reaction kinetics of an aqueous Zn–Fe hybrid flow battery by optimizing the supporting electrolytes

Abstract Redox flow batteries attract ever growing interest over the past decades in stationary energy storage. Iron and zinc species have been widely studied as active species for redox flow batteries. In this paper, the redox behavior of iron species has been tested in aqueous ionic liquid solutions. 1-butyl-3-methylimidazolium chloride (BMImCl) is found to be most effective to regulate the redox activity of iron species. While in the anolyte, the standard rate constant of zinc plating/stripping can be promoted by one order up to 1.44 × 10−4 cm s−1, when aqueous NH4Cl is used as supporting electrolyte. Kinetic analysis is further conducted on the iron and zinc species in the corresponding supporting electrolytes. By using an anion exchange membrane, an aqueous Zn–Fe hybrid flow battery showed a high energy efficiency of 80% at 20 mA cm−2, making it an alternative for flow battery application.