Corn stigma-modulated helical carbonaceous nanotubes for stable and efficient oxygen reduction and evolution reactions in rechargeable Zn-air batteries

Developing cost-effective bifunctional electrocatalysts for oxygen reduction and evolution reactions (ORR/OER) is crucial for rechargeable Zn-air batteries. Herein, we synthesize a novel catalyst comprising helical carbonaceous nanotubes encapsulating cobalt nanoparticles, using corn stigma agricultural waste, melamine and cobalt chloride as precursors. The curved surface of helical carbonaceous nanotubes promotes metal ion dispersion and charge separation within the carbon lattice. Applying strain engineering to these curved structures further tunes the electronic configuration of the active centers, boosting electrocatalytic performance. The as-prepared catalyst demonstrates remarkable electrocatalytic performance, achieving a high ORR half-wave potential of 0.869 V with minimal degradation (10 mV shift after 5000 CV cycles), along with a low OER overpotential of 350 mV at 10 mA cm −2 . In liquid Zn-air batteries, the catalyst delivers a peak power density of 214.8 mW cm −2 and stable operation for over 390 h at 10 mA cm −2 with negligible voltage decay. Moreover, the corresponding flexible wearable Zn-air battery demonstrates excellent foldability and cyclic stability. These results highlight a promising strategy for designing durable, high-efficiency electrocatalysts for metal-air energy systems.