Sulfur Vacancy‐Enrichment Boosts the Proton Storage Sites in Mesoporous Cobalt Sulfide‐Carbon Nanofiber Composites for High‐Performance Supercapacitor Devices

Abstract Transition metal sulfides are promising electrode materials for supercapacitor devices, but their practical applications are limited due to critical challenges, such as poor redox active sites, low specific surface area, particle agglomeration during charging‐discharging cycles, and low conductivity. To address these limitations, an innovative strategy of sulfur vacancy (S _vac )‐enrichment that boosts the proton storage sites in high surface area, mesoporous cobalt sulfide‐carbon nanofiber (Co ₃ S ₄ /CNF) composites is presented. Controlled calcination of electrospun PVP‐CoS fibers induces the phase transformation of hexagonal CoS to spinel Co ₃ S _4, comprising abundant S _vac to serve as proton storage sites, as evidenced from the potential of zero charge (E _pzc ) analysis. It augments ion transport channels and redox active sites for enhanced surface adsorption, leading to an excellent performance for supercapacitive charge‐storage devices delivering a high specific capacitance of 1092 F g ⁻¹ at 10 A g ⁻¹ and excellent cycling stability. Asymmetric supercapacitor device utilizing Co ₃ S ₄ /CNF achieves an energy density of 104 Wh kg ⁻¹ at a power density of 1053 W kg ⁻¹ , retaining 95.7% of its performance over 10,000 cycles.