The art of balance: Engineering of structure defects and electrical conductivity of α-MnO2 for oxygen reduction reaction

Highlights: • Three α-MnO₂ samples were fabricated under different temperature. • α-MnO₂-80 exhibits the best ORR performance among three samples. • A balance in defect and electrical conductivity leads to the optimized ORR activity. Manganese dioxides have emerged as promising candidates for catalyzing oxygen reduction reaction (ORR). To promote ORR activity, intensive effort has been made to engineer manganese dioxides with either abundant defects or high electrical conductivity. In this work, a balance in engineering between defects and electrical conductivity in controllable engineering of α-MnO₂ is successfully demonstrated. By controlling the reaction temperature (60, 80, and 140 °C), three-dimensional (3D) dandelion-like α-MnO₂ microspheres were synthesized with different degrees of defects and electrical conductivities. The α-MnO₂ with either more defects or higher electrical conductivity should possess better ORR performance. However, with increasing synthesis temperature, the defects in the as-prepared samples decreased, while the electrical conductivity increased. Therefore, the preparation α-MnO₂ at 60 °C or 140 °C for the best ORR performance remains unclear. As determined by electrochemical measurement, the α-MnO₂ prepared at 80 °C with moderate defects and electrical conductivity exhibits superior ORR performance with a potential of 0.79 V at a current density of −3 mA cm⁻², which is considered outstanding for manganese oxides. This work shed new light on the strategy to simultaneously regulate the defect and electrical conductivity, and a balance between them should produce an effective catalyst for ORR.