Nitrogen-Doped Co₃ O₄ Mesoporous Nanowire Arrays as an Additive-Free Air-Cathode for Flexible Solid-State Zinc-Air Batteries

The kinetically sluggish rate of oxygen reduction reaction (ORR) on the cathode side is one of the main bottlenecks of zinc-air batteries (ZABs), and thus the search for an efficient and cost-effective catalyst for ORR is highly pursued. Co₃ O₄ has received ever-growing interest as a promising ORR catalyst due to the unique advantages of low-cost, earth abundance and decent catalytic activity. However, owing to the poor conductivity as a result of its semiconducting nature, the ORR activity of the Co₃ O₄ catalyst is still far below the expectation. Herein, we report a controllable N-doping strategy to significantly improve the catalytic activity of Co₃ O₄ for ORR and demonstrate these N doped Co₃ O₄ nanowires as an additive-free air-cathode for flexible solid-state zinc-air batteries. The results of experiments and DFT calculations reveal that the catalytic activity is promoted by the N dopant through a combined set of factors, including enhanced electronic conductivity, increased O₂ adsorption strength and improved reaction kinetics. Finally, the assembly of all-solid-state ZABs based on the optimized cathode exhibit a high volumetric capacity of 98.1 mAh cm^-3 and outstanding flexibility. The demonstration of such flexible ZABs provides valuable insights that point the way to the redesign of emerging portable electronics.