Construction of a Janus MnO2-NiFe Electrode via Selective Electrodeposition Strategy as a High-Performance Bifunctional Electrocatalyst for Rechargeable Zinc-Air Batteries.

MnO2 has been considered as the most promising bifunctional electrocatalyst toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Despite their highly active ORR performance, the OER catalytic activity of MnO2 species is still far from satisfying. Herein, for the first time, highly active OER catalytic NiFe layered double hydroxides (NiFe LDHs) are combined with MnO2 via a selective electrodeposition method to form a Janus electrode in which the MnO2 and NiFe LDHs are in situ grown on two sides of a porous nickel foam (MnO2-NiFe/Ni). The MnO2-NiFe/Ni electrode exhibits excellent bifunctional catalytic activity and stability for both ORR and OER compared to bare MnO2 on account of the rational design of the Janus bifunctional configuration separating OER and ORR active materials. Moreover, such a Janus MnO2-NiFe air electrode endows the zinc-air battery with better cycling stability and energy efficiency than the bare MnO2 electrode. Our work demonstrates a novel Janus electrode configuration to design high-performance electrocatalysts for energy storage and conversion applications.