ZIF-Derived Porous CoNi<sub>2</sub>S<sub>4</sub> on Intercrosslinked Polypyrrole Tubes for High-Performance Asymmetric Supercapacitors
Xueyan Zhao, Qingxiang Ma, Kai Tao, Lei Han
Abstract
Bimetallic transition metal sulfide is considered to be an excellent cathode material for asymmetric supercapacitors (ASCs) because of its outstanding electrochemical activity and rich valences for the faradaic reactions. However, it usually shows a small specific surface area and sluggish reaction kinetics leading to poor energy storage capacity and unsatisfactory rate performance. Herein, a zeolitic imidazolate framework-67 (ZIF-67) dodecahedron is uniformly stringed on intercrosslinked polypyrrole (PPy) via an in situ synthesis, and the ZIF-67 is converted into NiCo layered double hydroxide (LDH) through an etching and coprecipitation process with Ni(NO3)2. The final porous nickel cobalt sulfide@PPy (NiCoS@PPy) is obtained after a solution sulfidation. The NiCoS@PPy electrode achieves an ultrahigh specific capacitance of 2316.6 and 1409.5 F g–1 at 1 and 10 A g–1, largely outperforming control NiCoS or NiCo-LDH@PPy. Furthermore, the fabricated ASC utilizing NiCoS @PPy as the cathode displays outstanding energy storage capability (34.4 Wh kg–1 at 799 W kg–1) and splendid cyclic life (retaining ∼84% initial capacitance after 8500 cycles). The excellent electrochemical performance makes the NiCoS@PPy electrode have prospective applications in electrochemical energy storage.