Achieving Complete Conversion from Nickel Foam to Nickel Sulfide Foam for a Freestanding Hybrid‐Supercapacitor Electrode

Abstract We present a unique, one‐step, hydrothermal process to prepare nickel sulfide (Ni 3 S 2 ) foam by a simple and direct conversion from nickel foam, which contributes both as a scaffold for the reaction and as reactant. The Ni 3 S 2 foam exhibits remarkable mechanical stability, retaining the structural integrity of the foam and excellent crystallinity even after ultrasonication at 200 W for 30 mins. We document the transformation of the nickel foam template into a Ni 3 S 2 foam, highlighting the role of synthesis duration on the phase evolution and unique morphology of Ni 3 S 2 . PXRD and SEM analyses reveal a complete transformation after 24 hours from the nickel foam to a pure Ni 3 S 2 foam, which has a highly porous and interconnected ultra‐thin nanosheet architecture. This significantly enhances the surface area and provides many electrochemical reaction sites. In a three‐electrode cell, the capacity of the Ni 3 S 2 foam electrode is 3.9 C cm −2 at 8 mA cm −2 , which is higher than previous reports for Ni 3 S 2 . In a hybrid supercapacitor device, the Ni 3 S 2 foam demonstrates significant increase in capacitance through 500 cycles and the capacitance plateaus after 2000 cycles. Even after 8500 continued charge‐discharge cycles, the device exhibits excellent cycle stability indicating improvement with age.