Co/CoO hetero-nanoparticles incorporated into lignin-derived carbon nanofibers as a self-supported bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

The large-scale application of rechargeable Zn-air batteries (ZABs) necessitates the development of high- efficiency and cost-effective bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, the density functional theory calculations were performed to reveal the charge redistribution induced by the Co/CoO heterojunction integrating with N-doped carbon, which could optimize the d-band center, thereby accelerating O2 transformed into OOH* in the ORR and the conversion of O* into OOH* in OER. Guided by theoretical calculations, Co/CoO hetero-nanoparticles-decorated lignin-derived N-doped porous carbon nanofibers (Co-LCFs-800) were synthesized to use as an advanced self-supported bifunctional oxygen electrocatalyst. Consequently, Co-LCFs-800 shows a half-wave potential of 0.834 V in ORR and an overpotential of 354 mV at 10 mA cm- 2 in OER. The Co-LCFs-800-based liquid ZABs afford an admirable performance with a large specific capacity of 780.8 mAh g- 1, and the Co-LCFs-800-based solid-state ZABs exhibit satisfactory mechanical flexibility and cycling stability. The results suggest that the integration of hetero-nanoparticles into carbon nanofibers holds promise for oxygen cathode in ZABs.