Reduced Graphene Oxide Nanosheet-Wrapped Hollow Cobalt Selenide Nanocubes as Electrodes for Supercapacitors

Transition-metal selenides (TMSs) as electrode materials for supercapacitors (SCs) are suffering from low rate capacities and poor cyclic stability due to their easy aggregation and structural instability over charge/discharge cycles. Herein, reduced graphene oxide (rGO) nanosheet-wrapped hollow cobalt selenide (CoSe₂) nanocubes are synthesized using a sacrificial-template method combined with a selenization treatment. In such nanocomposites, hollow CoSe₂ nanocubes with porous shells are featured by abundant electroactive sites, easy ion diffusion, and enough buffering space. More importantly, the wrapping of rGO nanosheets around hollow CoSe₂ nanocubes not only endows the nanocomposites with higher electrical conductivity but also restrains the aggregation of hollow CoSe₂ nanocubes as well as maintains the structural stability during cycles. Consequently, the synthesized hollow CoSe₂@rGO nanocomposites demonstrate a specific capacity of up to 856 C g^–1 at 2 A g^–1, 76% capacity retention at 20 A g^–1, and 95% capacity retention over 5000 cycles at 10 A g^–1. Moreover, an asymmetric supercapacitor cell with hollow CoSe₂@rGO nanocomposites as the positive electrode achieves an energy density of 53.0 W h kg^–1 at a power density of 800 W kg^–1, suggesting a great potential for their practical applications. This work showcases a feasible approach to engineer hollow TMS–graphene nanocomposites as electrode materials for SCs.