Construction of a High-Performance Three-Dimensional Structured NiCo2O4@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@NiCo2O4@PPy), consisting of a polypyrrole (PPy) thin film shell and spinel NiCo2O4 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@NiCo2O4@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.