Edge atomic Fe sites decorated porous graphitic carbon as an efficient bifunctional oxygen catalyst for Zinc-air batteries

Abstract

The development of advanced bifunctional oxygen electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) is critical to the practical application of zinc-air batteries (ZABs). Herein, a silica-assisted method is reported to integrate numerous accessible edge Fe-Nx sites into porous graphitic carbon (named Fe-N-G) for achieving highly active and robust oxygen electrocatalysis. Silica facilitates the formation of edge Fe-Nx sites and dense graphitic domains in carbon by inhibiting iron aggregation. The purification process creates a well-developed mass transfer channel for Fe-N-G. Consequently, Fe-N-G delivers a half-wave potential of 0.859 V in ORR and an overpotential of 344 mV at 10 mA cm−2 in OER. During long-term operation, the graphitic layers protect edge Fe-Nx sites from demetallation in ORR and synergize with FeOOH species endowing Fe-N-G with enhanced OER activity. Density functional theory calculations reveal that the edge Fe-Nx site is superior to the in-plane Fe-Nx site in terms of OH* dissociation in ORR and OOH* formation in OER. The constructed ZAB based on Fe-N-G cathode shows a higher peak power density of 133 mW cm−2 and more stable cycling performance than Pt/C + RuO2 counterparts. This work provides a novel strategy to obtain high-efficiency bifunctional oxygen electrocatalysts through space mediation.