Insights into Co-Catalytic Single-Atom-Support Interactions for Boosting Sulfur Reduction Electrocatalysis

The use of single-atom catalysts (SACs) with abundant electrocatalytic centers has been identified as the most desirable strategy to inhibit the shuttle effect in lithium-sulfur batteries. However, the co-contribution from SAC and its support via their interactions for accelerating the sulfur reduction reactions (SRR) has so far received little attention, since the underlying mechanism remains elusive. Herein, guided by density functional theory calculations, Cobalt-SACs supported on a graphitic carbon nitride substrate (Co-GCN), are selected to elucidate the co-catalytic role in enhancing the SRR. The inherent high charge polarity of GCN, combined with its unique tri-s-triazine structure, offers multiple binding sites for lithium polysulfides (LiPSs) through Li-N bonds, as well as N/C-coordinated frameworks for anchoring Co-SACs. This structural configuration further amplifies the interaction with LiPSs via Co-S bonds. Consequently, both Co-SACs and GCN actively participate in sulfur reduction electrocatalysis by binding LiPS intermediates, lowering the conversion energy barrier of SRR. Benefitting from such unique synergy, the battery demonstrates outstanding rate performance (718.9 mAh g^-1 at 5.0 C) and yields a high areal capacity of up to 13.8 mAh cm^-2 (1584.3 mAh g^-1) under a high areal sulfur loading of 8.7 mg cm^-2 but a low electrolyte/sulfur ratio of 5.0 μL mg^-1.