Sulfur‐Vacancy Defect Engineering in Nickel Sulfide via Starch Templating for High‐Performance Supercapacitors

Abstract Material morphology and defect structure are of paramount importance to high‐performance supercapacitor development. In this study, a starch‐assisted synthesis approach for preparing sulfur vacancy (Sv)‐enriched NiS electrode materials was proposed. First, Ni(OH) 2 was prepared by the co‐precipitation method, then annealed to convert it into NiO, and then NiO was transformed into NiS by hydrothermal sulfurization. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) confirm that starch addition markedly improves NiS dispersion and forms a high concentration of Sv. The optimized NiS‐3 (the sample obtained using 3 g of starch) electrode delivered an specific capacitance ( C s ) of 2034 F g −1 (276.85 mAh g −1 ) at a current density of 1 A g −1 , which far exceeded that of the nonstarch‐assisted synthesized NiS electrodes (1226 F g −1 ), owing to the enhanced material conductivity and synergistic redox activity of the Ni 3+ /Ni 2+ induced by Sv. The gel‐type hybrid supercapacitor (HSC) (NiS‐3//activated carbon (AC)) delivered an energy density of 15.8 Wh kg −1 at a power density of 750 W kg −1 , and it still retained 69.15% capacitance at a current density of 3 A g −1 after 5000 cycles. This work provides a promising synthesis route to transition metal sulfides for energy storage.