In Situ Construction of MnO₂-Co₃O₄ Nanosheet Heterojunctions on Co@NCNT Surfaces for Oxygen Evolution

Electrocatalytic water splitting is still circuitous and controversial because of the lack of highly active electrocatalysts to decrease the overpotential. Herein, we report a feasible method for constructing heterojunctions of MnO₂-Co₃O₄ nanosheets on Co@NCNT support surfaces (MnO₂-Co₃O₄/Co@NCNT) by spontaneous redox reactions. Experimental results indicate that Co embedded in Co@NCNT can be used as the carbon support and anchoring sites for heterojunctions, thus exposing a large number of active sites, adjusting the surface electronic structure, changing the OER rate-determining step of the catalyst, and reducing the reaction energy barrier. Besides, the in situ formation of MnO₂-Co₃O₄ nanosheets on Co@NCNT inhibits the loss and aggregation of the catalyst, leading to robust structural stability. Therefore, the synergistic effects of these factors provide multi-functional active sites to enhance the intrinsic activity and achieve maximum catalytic performances. To deliver a current density of 10 mA cm^-2, the catalyst of MnO₂-Co₃O₄/Co@NCNT achieves an overpotential (η) of 303 mV in 1.0 M KOH media for OER. This simple redox strategy can be easily extended to prepare other ultrathin transition-metal oxide heterojunctions, which could be applied not only for water splitting but also for other energy conversion and storage technologies.