Spherical α-MnO2 Supported on N-KB as Efficient Electrocatalyst for Oxygen Reduction in Al–Air Battery

Traditional noble metal platinum (Pt) is regarded as a bifunctional oxygen catalyst due to its highly catalytic efficiency, but its commercial availability and application is often restricted by high cost. Herein, a cheap and effective catalyst mixed with α-MnO2 and nitrogen-doped Ketjenblack (N-KB) (denoted as MnO2-SM150-0.5) is examined as a potential electrocatalyst in oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). This α-MnO2 is prepared by redox reaction between K2S2O8 and MnSO4 in acid conditions with a facile hydrothermal process (named the SM method). As a result, MnO2-SM150-0.5 exhibits a good catalytic performance for ORR in alkaline solution, and this result is comparable to a Pt/C catalyst. Moreover, this catalyst also shows superior durability and methanol tolerance compared with a Pt/C catalyst. It also displays a discharge voltage (~1.28 V) at a discharge density of 50 mA cm−2 in homemade Al–air batteries that is higher than commercial 20% Pt/C (~1.19 V). The superior electrocatalytic performance of MnO2-SM150-0.5 could be attributed to its higher Mn3+/Mn4+ ratio and the synergistic effect between MnO2 and the nitrogen-doped KB. This study provides a novel strategy for the preparation of an MnO2-based composite electrocatalyst.