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 16 122 W kg(-1) as well as an exceptional capacitance retention of 92.1% after 10 000 cycles.