Heteroatom-Mediated Electronic Modulation of FeX4/Graphene Electrocatalysts for Enhanced ORR Performance

Abstract

Understanding how coordination environments govern both the stability and catalytic performance of single-atom catalysts remains a central challenge in electrocatalysis. Herein, we systematically investigate FeX4 moieties (X = N, O, P, S) embedded in graphene (FeX4/Gr) using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations to establish a unified descriptor-based framework for oxygen reduction reaction (ORR) catalysis under acidic conditions. We show that heteroatom identity critically modulates Fe–X bonding, electron localization, charge transfer, and electrostatic confinement, which collectively determine the stability of Fe active sites and their resistance to aggregation. Among the investigated systems, FeN4/Gr exhibits the strongest structural stability, characterized by short Fe–N bonds (∼1.91 Å), high charge transfer (1.063 e), and pronounced electron localization, resulting in robust Fe anchoring. These features translate directly into optimal catalytic behavior, where FeN4/Gr efficiently activates O2 via end-on adsorption, with significant charge transfer (1.563 e) and a low energy barrier (0.564 eV) for the rate-determining OOH* formation step. In contrast, FeO4/Gr promotes strong side-on adsorption (−3.574 eV), facilitating O–O bond activation but leading to stronger intermediate binding and a higher reaction barrier. FeP4/Gr and FeS4/Gr exhibit weakened Fe–X coordination, reduced electronic coupling, and inferior catalytic performance, with FeS4/Gr showing the highest energy barrier (1.085 eV). As a result, the ORR activity follows the trend FeN4/Gr > FeO4/Gr > FeP4/Gr > FeS4/Gr, reflecting a fundamental balance between structural stability and adsorption energetics. Importantly, we demonstrate that the heteroatom acts as an active electronic modulator rather than a passive ligand, governing both Fe anchoring and catalytic reactivity. This work establishes a direct correlation among coordination chemistry, electronic structure, and ORR performance, providing a predictive strategy for designing high-performance, nonprecious single-atom catalysts.