Construction of NiCo2O4@MnO2 nanosheet arrays for high-performance supercapacitor: Highly cross-linked porous heterostructure and worthy electrochemical double-layer capacitance contribution

Abstract A highly cross-linked three-dimensional (3D) hierarchical porous NiCo 2 O 4 nanosheet@MnO 2 nanosheet arrays (NNAs) on Ni foam is fabricated by a facile and stepwise hydrothermal approach. The NiCo 2 O 4 @MnO 2 hybrid electrode demonstrates excellent electrochemical properties with high area capacitance of 5.3 F cm -2  at 1 mA cm −2 , tremendous rate performance (68.9% with current density increased to 20 mA cm −2 ), and outstanding cycling stability (90.1% capacitance retention over 5000 cycles at 20 mA cm −2 ). The intriguing performance is related to unique cross-linked porous heterostructure with open geometry that provides large surface areas and superb channels for the electrolyte penetration and ion diffusion. Besides, by analyzing non-faradaic capacitive current upon repeated potential cycling, this honor attributes to not only sufficient Faraday reactions, but also a worthy electrochemical double-layer capacitance (EDLC) contribution with an electrochemical surface area (ESA) value of 616 mF cm −2 (220 F g −1 with a mass loading of 2.8 mg cm −2 ), which approximates to that of porous carbon.