Self-Reconstruction of Co/Co₂P Heterojunctions Confined in N-Doped Carbon Nanotubes for Zinc–Air Flow Batteries

The development of highly efficient, stable, and low-cost catalysts for oxygen reduction and evolution reactions (ORR and OER, respectively) is vital for rechargeable metal–air batteries and united regenerative fuel cells. Herein, we develop a facile strategy for fabricating the heterojunction Co/Co2P nanocrystals that are confined in bamboo-like N-doped carbon nanotubes (Co/Co2P@NCNTs) on a large scale. In particular, operando X-ray absorption spectroscopy and electrochemical measurements were conducted to investigate the dynamic structural evolution of the precatalyst during electrocatalytic operation. Active state self-reconstruction from the Co/Co2P heterojunctions into Co3+ octahedral site (Oh)-containing CoOx(OH)y active species is observed. Consequently, the high degree of graphitization of NCNTs with optimized N species and the completely triggered cross-linked CoOx(OH)y both contribute to the outstanding bifunctional ORR/OER activity (Egap = 0.68 V vs RHE) and durability. Meanwhile, the Co/Co2P@NCNTs as a precatalyst exhibits an ultralong cycling stability (cycling life of >1000 h) in rechargeable zinc–air flow batteries.