Dual Hybrid Effect Endowing Nickel–Cobalt Sulfides with Enhanced Cycling Stability for Asymmetrical Supercapacitors

The construction and optimization of electrode materials with a stable structure have received great attention to realize high-performance supercapacitors. Herein, we present the fabrication of nickel–cobalt sulfide (NiCo)9S8 nanoparticles protected by NiCo-based oxyhydroxides coupled with nitrogen and sulfur codoped graphene substrates (N, S-doped G) via an ethylenediamine (EDA)-mediated assembly and electrochemical oxidation strategy, named O-(NiCo)9S8/N, S-doped G. It was found that the (NiCo)9S8 nanoparticles coated by the metal oxyhydroxide shell are tightly encapsulated into N, S-doped G frameworks, yielding a unique dual hybrid effect to achieve ample heterojunctions/interfaces and robust architecture, which is conducive to enhance electroactivity and cycling stability. As a proof-of-concept application, the as-fabricated O-(NiCo)9S8/N, S-doped G as the electrode for the supercapacitor achieves a high specific capacity of 1247 F g–1, that is, 166 mA h g–1 at 0.5 A g–1 and a superior rate capability of 89% at 20 A g–1. Further, the asymmetric supercapacitor made of the O-(NiCo)9S8/N, S-doped G//activated carbon along with a high mass loading of about 6 mg cm–2 exhibits an ultralong cycling stability of 70% after 20,000 cycles and a high charge storage capability of 50.8 W h kg–1 at 400 W kg–1, which is much better than those of the other comparative electrode materials.