A mild reduction of Co-doped MnO2 to create abundant oxygen vacancies and active sites for enhanced oxygen evolution reaction.

Efficient and non-precious-metal-based catalysts (e.g., manganese-based oxides) for the oxygen evolution reaction (OER) remain a substantial challenge. Creation of oxygen vacancies of manganese-based oxides with the aim to enhance their intrinsic activities is rarely reported, and there is a critical requirement for a mild and facile synthesis strategy to create abundant oxygen vacancies on manganese-based oxides. Herein, Co-doped MnO2 nanowires were reduced by NaBH4 solution at room temperature; then, MnCo2O4.5 nanosheets with abundant oxygen vacancies and active sites were formed on the surface of Co-doped MnO2 nanowires. Benefiting from the reduction strategy, the fabricated hierarchical Co-doped-MnO2@MnCo2O4.5 nanowire/nanosheet nanocomposites exhibit higher catalytic activity (an overpotential of 250 mV at a current density of 10 mA cm−2 in 1.0 M KOH solution) than pristine Co-doped MnO2 nanowires. The calculated TOF of Co-doped-MnO2@MnCo2O4.5 is 0.034 s−1 at the overpotential of 300 mV, which is 136-fold higher than that of Co-doped-MnO2. The excellent OER performance was attributed to the synergistic advantages of abundant oxygen vacancies and active sites over the hierarchical nanowire-nanosheet architectures.