Co2P-Assisted Atomic Co–N4 Active Sites with a Tailored Electronic Structure Enabling Efficient ORR/OER for Rechargeable Zn–Air Batteries

Oxygen reduction and evolution reactions (ORR and OER, respectively) are vital steps for metal–air batteries, which are plagued by their sluggish kinetics. It is still a challenge to develop highly effective and low-cost non-noble-metal-based electrocatalysts. Herein, a simple and reliable method was reported to synthesize a Co2P-assisted Co single-atom (Co–N4 centers) electrocatalyst (Co2P/Co-NC) via evaporative drying and pyrolysis processes. The Co2P nanoparticles and Co–N4 centers are uniformly distributed on the nitrogen-doped carbon matrix. Notably, Co2P/Co-NC showed excellent activities in both ORR (initial potential, 1.01 V; half-wave potential, 0.88 V) and OER (overpotential, 369 mV at 10 mA cm–2). The above results were comparable to those of commercial catalysts (such as Pt/C and RuO2). Based on the experimental and theoretical analyses, the impressive activity can be ascribed to the tailored electronic structure of Co–N4 centers by the adjacent Co2P, enabling the electron transfer from the Co atom to the neighboring C atoms, leading to a downshift of the d-band center, and improved reaction kinetics were achieved. The assembled Zn–air batteries using Co2P/Co-NC as the air cathode showed a peak power density of 187 mW cm–2 and long-life cycling stability for 140 h at 5 mA cm–2. This work may pave a promising avenue to design hybrid bifunctional electrocatalysts for highly efficient ORR/OER.