Oxygen coordination engineering in Fe–N–O–graphene single-atom catalysts for enhanced bifunctional oxygen electrocatalysis

Abstract

Developing efficient, durable, and low-cost bifunctional electrocatalysts is essential for renewable energy conversion. In this study, density functional theory (DFT) calculations are employed to systematically investigate Fe–N–O coordination structures anchored on graphene (Fe–N–O–gra), aiming to elucidate the structure–electronic–activity relationship in Fe-based single-atom catalysts. Among seven representative configurations, FeN₃O exhibits the highest structural stability, optimal orbital hybridization, and the largest charge transfer, thereby effectively facilitating O₂ activation. FeN₃O exhibits a longer Fe–O bond and weaker electronic coupling during *OH adsorption, which moderates intermediate binding in a step-specific way—facilitating *OH desorption in the ORR and stabilizing *OOH formation in the OER. This balance leads to exceptionally low overpotentials of 0.41 V for the ORR and 0.55 V for the OER, outperforming other configurations. Furthermore, a volcano plot constructed based on adsorption energy scaling relations identifies the *OH adsorption free energy as an effective descriptor of bifunctional catalytic activity, with FeN₃O located near the apex of the plot. These findings highlight the critical role of oxygen coordination in tuning the electronic structure and catalytic performance of Fe single-atom catalysts and provide theoretical guidance for the rational design of next-generation non-precious metal electrocatalysts.