Hierarchical nanohoneycomb-like CoMoO4–MnO2 core–shell and Fe2O3 nanosheet arrays on 3D graphene foam with excellent supercapacitive performance

Abstract

Recently, graphene-based three-dimensional (3D) architectures have attracted a lot of attention because of their multifunctional properties. In this paper, we report on hierarchical nanohoneycomb-like CoMoO₄–MnO₂ core–shell and Fe₂O₃ nanosheet arrays on 3D graphene foam (GF) and explore their use as a binder-free electrode in supercapacitor applications. The GF was prepared by solution casting on a Ni foam scaffold. The nanohoneycomb-like CoMoO₄–MnO₂ core–shell nanosheet arrays were prepared by a hydrothermal method under optimized conditions. The unique core–shell network provides efficient space and a short diffusion length for faradaic reactions. The as-synthesized CoMoO₄–MnO₂@GF hybrid electrode exhibits excellent areal and specific capacitances of 8.01 F cm⁻² and 2666.7 F g⁻¹, respectively, at a current density of 3 mA cm⁻². In addition, Fe₂O₃@GF was also prepared using a hydrothermal process followed by hydrogen treatment. Under optimized conditions Fe₂O₃@GF exhibits a high areal capacitance of 1.26 (572.7 F g⁻¹) F cm⁻². The asymmetric supercapacitor (ASC) assembled from CoMoO₄–MnO₂@GF as the positive electrode and Fe₂O₃@GF as the negative electrode delivers an excellent specific capacitance of 237 F g⁻¹ and a high rate capability of 61%. Moreover, the as-fabricated ASC also exhibits an ultra-high energy density of 84.4 W h kg⁻¹ and an outstanding power density of 16 122 W kg⁻¹ as well as an exceptional capacitance retention of 92.1% after 10 000 cycles.