Two-step oxygen reduction on spinel NiFe2O4 catalyst: Rechargeable, aqueous solution- and gel-based, Zn-air batteries

Electrocatalysts that lead to a four electron oxygen reduction reaction are generally proposed for metal-air batteries. Herein, we show that spinel NiFe2O4 catalyses oxygen reduction reaction by a two step process through stable peroxide species in aqueous medium. Further, it acts as an efficient bifunctional catalyst for oxygen reduction and oxygen evolution reactions with favourable rechargeable-battery characteristics. The kinetic parameters are deduced using electrochemical techniques. Rechargeable zinc-air batteries have been assembled using aqueous solution-as well as gel-based electrolytes and the battery characteristics are studied. (C) 2018 Elsevier Ltd. All rights reserved.