Superior Oxygen Electrocatalysis on Nickel Indium Thiospinels for Rechargeable Zn-Air Batteries

Developing active bifunctional oxygen catalysts to eliminate/reduce the reliance on precious-metal-based ones in metal-air batteries is nowadays of great importance. Here, we report the synthesis of nickel indium thiospinel nanosheets supported on carbon nanofibers (denoted as NiIn₂S₄/CNFs) via a facile in situ solvothermal growth process and, for the first time, demonstrate its superior bifunctional oxygen electrocatalytic performances as a precatalyst. Electrocatalytic experiments show that NiIn₂S₄/CNFs not only exhibits a positive half-wave potential of 0.81 V for the oxygen reduction reaction (ORR) but also delivers a lower overpotential of 0.39 V for the oxygen evolution reaction (OER) at 10 mA cm^-2, outperforming those of monometallic Ni or In sulfides. Theoretical calculations confirm that the (220) and (111) plane in NiIn₂S₄ are selectively active to the ORR and OER, respectively. Apart from the intrinsic nature of NiIn₂S₄, the superior OER activity of NiIn₂S₄/CNFs is also related to the oxide/hydroxide species in-situ-formed on NiIn₂S₄ surface under the OER condition. Moreover, the developed NiIn₂S₄/CNFs pre-catalyst is demonstrated to be an efficient air-cathode for Zn-air batteries. This work brings a new perspective for designing various ternary thiospinels for energy conversion and storage.