A Band-Matching Descriptor Breaks Scaling Relations for Sulfur Electrocatalysts

A predictive descriptor is crucial for the rational design of catalysts that enable fast and reversible sulfur redox in lithium–sulfur (Li–S) batteries. Although several descriptors have been proposed, most remain constrained by the conventional adsorption–activity trade-off and the associated volcano-type behavior. Here, we uncover that the catalytic activity of widely used transition-metal sulfides is dictated by the d/p band-matching ratio between metal centers and surface sulfur atoms, thereby going beyond this limitation. By tuning the band-matching ratio, which modulates the interaction between lithium polysulfides and the catalyst surface, a linear correlation with the overpotentials of both sulfur reduction and evolution reactions is established, accelerating the sulfur conversion kinetics. NbS2, with a band-matching ratio of 99.2%, delivers a minimal bifunctional overpotential of 0.70 V (the sum of sulfur reduction reaction (SRR) and sulfur evolution reaction (SER) overpotentials), 4-fold lower than that of WS2 (2.85 V, with a band-matching ratio of 46.0%). The Li–S battery that delivers a high initial areal capacity of 10.98 mAh cm–2 with the NbS2 catalyst exhibits an exceptionally high retention of 90.29% after 100 cycles, surpassing most of the reports. This work establishes band matching as a general principle for sulfur electrocatalysis, providing a predictive design rule that transcends classical scaling relations for metal–sulfur batteries.