In-Plane Electronic Metal-Support Interaction Enables Efficient Sulfur Catalysis on Ni Single-Atom Catalysts

The nonspin-polarized state electron occupancy of the Ni in the conventional NiN₄ coordination site cannot form an effective Ni-S bond with lithium polysulfides, failing to elucidate the intrinsic origin of the experimentally observed high catalytic activity of the single Ni catalyst (SANi) arising from Ni-S interactions. Accordingly, a deep understanding of the true effective catalytically active sites is essential for the rational design of single-atom catalysts (SACs) for lithium sulfur batteries (LSBs). Herein, we constructed and evaluated a series of Ni-N-C coordination models that represent the diverse local environments likely formed during catalyst synthesis to identify the true catalytically active sites. Density functional theory calculations show that in-plane electronic metal-support interaction emerging from specific Ni-N-C coordination configurations can activate Ni-S bond formation by inducing spin-polarized delocalization of Ni d electrons and constructing an electron-relay channel. Seven coordination configurations were found to form effective Ni-S bonds, providing a plausible explanation for the efficient Ni-S coupling observed in SANi. Among them, a low-coordination NiN₂ site was identified as the most active center for catalyzing sulfur redox reactions, owing to its optimal anchoring capability and low redox reaction barrier. Our results open new avenues for fundamentally understanding the role of metal coordination in governing the catalytic performance of SACs for LSBs.