Engineering Co–N–C active sites with non-traditional nitrogen coordination to enhance oxygen electrocatalysis for liquid/flexible Zn–air batteries

Overcoming the challenges of high cost and poor durability associated with the use of precious metal catalysts in Zn–air batteries, metal–nitrogen–carbon (M–N–C) has emerged as one of the promising alternatives for their good oxygen reduction reaction and oxygen evolution reaction properties, low price and simple preparation process. However, the quantity of M–N–C active sites formed through the conventional method of the metal elements and N co-doped graphene is quite limited, leading to a significant discrepancy between the battery performance and the theoretical values. Herein, we propose a non-traditional nitrogen coordination method to achieve the increase of Co–N–C active sites by retaining N atoms, accompanied by the generation of Co nanoparticles. Benefiting from the synergistic effect of Co–N–C sites and Co nanoparticles, the g-C₃N₄–Co_0.6 shows a higher limiting current density (4.81 mA cm⁻²) and a lower ΔE (0.90 V), and the assembled liquid Zn–air battery (LZAB) has a higher power density (77.69 mW cm⁻²) and an excellent specific capacity (723.05 mAh g⁻¹). In addition, the assembled flexible Zn–air battery (FZAB) has a significant power density (29.71 mW cm⁻²) as well as good mechanical flexibility and cycle stability. This work provides insights into improving electrochemical performance from the perspective of constructing active sites.