Strong coupled spinel oxide with N-rGO for high-efficiency ORR/OER bifunctional electrocatalyst of Zn-air batteries

The high cost, scarcity, and poor stability of precious-metal-based catalysts have hindered their extensive application in energy conversion and storage. This stimulates the search for earth-abundant alternatives to replace noble metal electrocatalysts. Hence, in this study, we investigate a novel and low-cost bifunctional electrocatalyst consisting of ZnCoMnO4 anchored on nitrogen-doped graphene oxide (ZnCoMnO4/N-rGO). Benefiting from the strong Co-N interaction in ZnCoMnO4 and the coupled conductive N-rGO, the catalysts exhibit high electrocatalytic activity. Moreover, density functional theory calculations support the dominant role of the strong Co-N electronic interaction, which leads to ZnCoMnO4/N-rGO having more favorable binding energies with O2 and H2O, resulting in fast reaction kinetics. The obtained ZnCoMnO4/N-rGO electrocatalyst exhibits superb bifunctional activity, with a half-wave potential of 0.83 V for the oxygen reduction reaction and a low onset potential of 1.57 V for the oxygen evolution reaction in 0.1 M KOH solution. Furthermore, a Zn-air battery driven by the ZnCoMnO4/N-rGO catalyst shows remarkable discharge/charge performance, with a power density of 138.52 mW cm−2 and long-term cycling stability for 48 h. This work provides a promising multifunctional electrocatalyst based on non-noble metals for the storage and conversion of renewable energy.