Electronic structure regulation of carbon atoms from wood for enhancing Zn–air battery performances†

The oxygen reduction reaction (ORR) is a crucial process in zinc–air batteries (ZABs), but its sluggish kinetics impedes the widespread application of ZABs. Herein, balsa wood-derived carbon embedded with nitrogen and sulfur atoms was proposed as a metal-free carbon electrocatalyst to enhance the ORR kinetics process for ZABs. Wood carbonization/activation and N, S co-doping were simultaneously achieved in a one-step high-temperature pyrolysis, resulting in the formation of N, S-doped carbonized wood (NSCW-900). The resultant NSCW-900 showed well-aligned microchannels/hierarchical pores, large specific surface area and good wettability, increasing activation sites and improving reaction kinetics. The introduction of N and S atoms modified the electronic structure of the neighbouring carbon atoms, enabling a redistribution of charge for enhancing the intrinsic catalytic activity. Numerous graphitic nitrogen, pyridinic nitrogen and thiophene sulphur sites were exposed adequately, providing good electronic conductivity and facilitating the mass transfer of reactants. The NSCW-900 showed a high half-wave potential of 0.832 V vs. the reversible hydrogen electrode (RHE) and a high onset potential of 0.93 V (vs. RHE), along with excellent methanol tolerance and long-term stability. The assembled rechargeable liquid ZABs exhibited a maximum output power density of 149 mW cm⁻², with a low voltage gap of 0.87 V over a prolonged 125-hour cycling. This work provides a novel carbon-based ORR electrocatalyst via utilizing balsa wood nanostructures and regulating the electronic structure of carbon atoms, facilitating the development of next-generation energy storage devices.