Rationally designed mesoporous carbon-supported Ni–NiWO₄@NiS nanostructure for the fabrication of hybrid supercapacitor of long-term cycling stability

Abstract

Rational design and synthesis of nanostructured functional materials are of considerable interest for energy storage applications. We demonstrate a facile synthesis of N- and S-doped mesoporous carbon-supported Ni–NiWO₄@NiS nanostructure (Ni–NiWO₄@NiS/NS-C) for the fabrication of high-performance hybrid supercapacitor. The synthesis of Ni–NiWO₄@NiS/NS-C involves the initial room temperature precipitation of NiWO₄ over the cotton fabric, subsequent thermal annealing of the cotton fabric, and sulfidation. The doping of carbon framework with nitrogen and sulfur, and the sulfidation of nickel are hydrothermally achieved in single step. The hydrothermal process significantly enhances the surface area (2.5 times). The voltammetric analysis indicates that the diffusion-controlled process predominantly contributes to the capacitive performance of the materials. Hybrid supercapacitor device is fabricated with the as-synthesized Ni–NiWO₄@NiS/NS-C material and it delivers an energy density of 43.68 W h kg⁻¹ at the power density of 0.85 kW kg⁻¹. The hybrid device has long cycling stability for >20,000 consecutive charge-discharge cycles with 34% enhancement in the initial capacity after 20,000 cycles. The potential cycling-induced phase transformation of the Ni–NiWO₄@NiS to K₄NiW₆O₂₁ and NiOOH enhances the overall performance of the hybrid device. Flexible and non-flexible solid-state hybrid devices are fabricated. The flexible device retains its initial capacity even after repeated bending at different angles.