Self-templated formation of hierarchical hollow β-MnO2 microspheres with enhanced oxygen reduction activities

Herein, hierarchical hollow β-MnO2 microspheres assembled by nanorod subunits are facilely fabricated using a one-step hydrothermal approach, which serve as electrocatalyst for oxygen reduction reaction (ORR). The influences of the reaction temperature and H2SO4 concentration on the crystalline phase and morphology of products are studied. Impressively, detailed characterizations reveal that the hollow β-MnO2 microspheres can be formed through a self-templated process by phase transformation, in which solid γ-MnO2 microspheres are first generated and then convert to hollow β-MnO2 microspheres. Owing to their unique hollow shape and robust O2 adsorption ability, the hollow β-MnO2 microspheres show superior ORR performance (a more positive half-wave potential of ~ 0.69 V, a larger limiting current density of 5.04 mA cm−1, and better stability) compared with commercial β-MnO2 particles. The insights afforded in this study offer positive guidance for the rational design of hollow Mn-based materials.