Construction of a High-Performance Three-Dimensional Structured NiCo 2 O 4 @PPy Nanosheet Array Free-Standing Electrode for a Hybrid Supercapacitor

Asymmetric supercapacitors (ASCs) with free-standing electrodes have attracted extensive attention due to enhanced power density, high energy density, long-term stability, and low inner resistance. Herein, a three-dimensional (3D) hierarchical nanosheet array electrode (CC@NiCo 2 O 4 @PPy), consisting of a polypyrrole (PPy) thin film shell and spinel NiCo 2 O 4 as the core, was prepared on carbon cloth (CC) via a simple two-step electrodeposition. Since the protection of the highly conductive pseudocapacitive PPy shell, the integrated electrode delivers an enhanced specific capacitance (1687.2 F g –1 or 257.8 mAh g –1 at 1 A g –1 ) and a high cycling stability (91.9% capacitance retention after 10,000 cycles at 10 A g –1 ). We further demonstrate the ASC based on CC@NiCo 2 O 4 @PPy/6 M KOH/active carbon, which can be cycled over 10,000 times with 80% retention at 4 A g –1 . Moreover, the prepared ASCs present a favorable rate capability with high energy densities of 46.5 and 31 Wh kg –1 at power densities of 725 and 7246 W kg –1, respectively. Our work provides a viable approach to construct a hierarchical 3D structure under ambient conditions and opens possibilities for adopting it in hybrid supercapacitors.