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 electro-catalysts. 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.