Bamboo-Modulated Helical Carbon Nanotubes for Rechargeable Zn-Air Battery

The high-performance and sustainable electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for rechargeable Zn-air batteries (ZABs). In this paper, a natural all-components bamboo is provided as the carbon source, and melamine and cobalt chloride are provided as the nitrogen and cobalt sources, respectively. As a result, the unique helical carbon nanotubes (HCNTs) encapsulated cobalt nanoparticles are prepared, which are acted as ORR/OER electrocatalysts to improve ZABs performance. The resultant HCNTs contribute to high ORR/OER activities via exposing more CoN sites, providing excellent electron conductivity, and facilitating mass transfer of the reactant. The HCNTs assembled rechargeable liquid ZABs showed a maximum output power density of 226 mW cm-2 and a low voltage gap of 0.85 V for 330 h cycles. The flexible all-solid-state ZABs achieved the maximum power density with 59.4 mW cm-2 and charge-discharge cycles over 25 h. The density functional theory (DFT) calculations reveal that the increase of CoN at HCNTs effectively regulates the electronic structure of Co, optimizing the binding affinity of oxygen intermediates and resulting in the low ORR/OER overpotentials. This work paves the way for transforming renewable bamboo biomass into versatile electrocatalysts, which boosts the development of next-generation energy storage and conversion devices. Bamboo-derived helical carbon nanotubes containing numerous CoN sites are proposed as advanced ORR/OER electrocatalysts to enhance Zn-air batteries performances.image