Morphological engineering of 3D hollow urchin-like MnO2 spheres as bifunctional oxygen electrocatalyst for zinc-air batteries

Abstract

Favorable stability and cost-efficient bifunctional catalysts are highly desirable for rechargeable zinc-air batteries. α-MnO2 has been considered a promising candidate with moderate electrochemical performance. Morphological engineering offers a feasible approach to further optimize the intrinsic and specific activities of α-MnO2. Herein, three-dimensional hollow Urchin-like α-MnO2 microspheres (denoted as the hollow α-MnO2) were successfully prepared by a facile hydrothermal reaction. The unique structure endows α-MnO2 with abundant accessible active sites and enhanced intrinsic activity. Profited from surface reconstruction, abundant oxygen vacancies were created and maintained high activity during electrocatalytic processes. As a result, the hollow α-MnO2 displays excellent oxygen reduction reaction activity with the half-wave potential at 0.80 V versus reversible hydrogen electrode (vs RHE), oxygen evolution reaction with an overpotential of 465 mV to reach the current density of 10 mA·cm−2, and remarkable rechargeable zinc-air battery performance with an open-circuit voltage of 1.48 V and a higher power density of 110.9 mW cm−2 at 0.64 V (vs zinc).