Single-Atom Ni Anchored on α-MnO2 Nanorods as an Electrocatalyst for the Oxygen Evolution and Oxygen Reduction Reactions

Developing efficient MnO2-based bifunctional catalysts is a considerable challenge due to slow oxygen reduction reaction (ORR) kinetics and the limited activity of the oxygen evolution reaction (OER). Herein, an efficient bifunctional catalyst Ni/α-MnO2 is prepared by a straightforward solid-phase synthesis method, enabling the anchoring of Ni atoms onto the α-MnO2 surface. The electrochemically active surface area is significantly enhanced due to the generation of oxygen vacancies and presence of atomic Ni sites. After Ni decoration, the half-wave potential of the ORR is elevated to 0.82 V, while the overpotential for the OER is reduced to 366 mV, resulting in an exceptionally low overall oxygen overpotential (ΔE = 0.79 V). Density functional theory calculations reveal that the d-band center of Mn exhibits negative shifts, consequently lowering the energy barrier for the conversion of OOH* to O* in the ORR and that of OH* to O* in the OER. In a secondary zinc–air battery, a supreme power density of 290 mW cm–2 is acquired at a current density of 350 mA cm–2, surpassing the performance of pristine α-MnO2. This work offers valuable guidance for the development of high-performance MnO2-based bifunctional catalysts.