Atomic Structure Modification of Fe‒N‒C Catalysts via Morphology Engineering of Graphene for Enhanced Conversion Kinetics of Lithium–Sulfur Batteries

Single-atom M‒N‒C catalysts have attracted tremendous attention for their application to electrocatalysis. Nitrogen-coordinated mononuclear metal moieties (MN_x moities) are bio-inspired active sites that are analogous to various metal-porphyrin cofactors. Given that the functions of metal-porphyrin cofactors are highly dependent on the local coordination environments around the mononuclear active site, engineering MN_x active sites in heterogeneous M‒N‒C catalysts would provide an additional degree of freedom for boosting their electrocatalytic activity. This work presents a local coordination structure modification of FeN₄ moieties via morphological engineering of graphene support. Introducing highly wrinkled structure in graphene matrix induces nonplanar distortion of FeN₄ moieties, resulting in the modification of electronic structure of mononuclear Fe. Electrochemical analysis combined with first-principles calculations reveal that enhanced electrocatalytic lithium polysulfide conversion, especially the Li₂S redox step, is attributed to the local structure modified FeN₄ active sites, while increased specific surface area also contributes to improved performance at low C-rates. Owing to the synergistic combination of atomic-level modified FeN₄ active sites and morphological advantage of graphene support, Fe‒N‒C catalysts with wrinkled graphene morphology show superior lithium–sulfur battery performance at both low and high C-rates (particularly 915.9 mAh g⁻¹ at 5 C) with promising cycling stability.