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.