Two‐Phase Tandem Catalysis With Interfacial Synergy in MoNi _x /Mo ₂ C Heterostructures for Stepwise Sulfur Conversion

ABSTRACT Lithium‐sulfur (Li‐S) batteries have attracted considerable attention as high‐energy storage systems, but are hindered by sluggish lithium polysulfide (LiPSs) redox kinetics and the shuttle effect. Although heterostructured catalysts can alleviate these issues by tailoring interfacial electronic structures, it remains difficult to precisely control the interfacial composition during synthesis, and the stepwise LiPSs conversion mechanism at such interfaces is not fully understood. Herein, we propose a facile synthesis strategy based on thermodynamic modulation for the directional growth of MoNi x /Mo 2 C heterostructures and elucidate their catalytic mechanism in Li‐S batteries. By tuning the Ni/Mo precursor mass ratio, a continuous and controllable evolution from a MoNi x solid solution to a MoNi x /Mo 2 C heterostructure is achieved, with MoNi x /Mo 2 C‐NCNFs exhibiting the optimal catalytic effect on LiPSs conversion. An initial discharge capacity as high as 1343.9 mAh g − 1 at 0.2 C was achieved with the MoNi x /Mo 2 C‐NCNFs separator. Combined experimental and theoretical analyses reveal that the charge redistribution induced at the heterointerface leads to an upward shift of the d‐band center, activating a “functional zoning and tandem catalysis” mechanism in which the phases and interface cooperatively accelerate stepwise LiPSs conversion. These findings clarify how interfacial electronic structures govern LiPSs conversion and provide practical guidelines for high‐performance catalysts.