Synergistic Catalysis of Cobalt Tetroxide and Bamboo-Shaped Carbon Nanotubes Doped with Nitrogen for Oxygen Reduction in Zn-Air Batteries

Zinc-air batteries (ZABs) have been considered as one of the most emerging systems for energy conversion and storage. However, the preparation of highly efficient oxygen reduction reaction (ORR) catalysts on an air cathode is still faced with significant challenges. Herein, we report a secondary nitrogen source strategy for fine-tuning the active center, which provides a carbon-based hierarchical porous catalyst (termed Co₃O₄@N/CNT-1000) for highly efficient ORR activity (E_1/2 = 0.87 V, J_L = 5.32 mA cm^-2, and E_onset = 1.021 V) and excellent stability. Controlled experiments demonstrate that such high activity derives from the synergistic effect of cobalt tetroxide and bamboo-shaped carbon nanotubes doped with nitrogen, prepared by the pyrolysis of a two-dimensional metal-organic framework nanosheet (termed NTU-70) and melamine. Furthermore, the ZAB assembled with Co₃O₄@N/CNT-1000 displays high specific capacity (854 mA h g^-1_Zn) and power density (179 mW cm^-2), excellent long-term cycling (330 h), and durable charging/discharging ability.