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

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 16122 W kg^-1 as well as an exceptional capacitance retention of 92.1% after 10000 cycles.