Hollow cobalt selenide nanospheres wrapped with reduced graphene oxide nanosheets as electrodes for hybrid supercapacitor

In this work, hollow CoSe2 nanospheres wrapped with reduced graphene oxide (rGO) nanosheets are fabricated through combining the self-templated method with the electrostatic self-assembled method followed by heat treatment. The experimental results indicate that rGO nanosheets can act as space separator and structural protector to reduce the aggregation and nanoparticle size of hollow CoSe2 nanospheres and meanwhile maintain their structural integrity. Density functional theory calculations indicate that the wrapping of rGO nanosheets not only increases the electrical conductivity but also reduces the adsorption energy of OH- at the CoSe2/rGO interface. Accordingly, hollow CoSe2/rGO nanocomposites yield specific capacities of 757C g-1 at 3 A/g and 552C g-1 at 20 A/g, as well as a capacity retention of 92 % over 5000 cycles at 10 A/g. When coupled with N -doped carbon nanotube-based negative electrode, the fabricated HSC device delivers an energy density of 50.1 W h kg-1 at 800 W kg-1 as well as maintains a capacity retention of 94 % after 5000 cycles. Our work offers a further understanding of the charge storage mechanism of hollow CoSe2/rGO nanocomposites and may be extended to develop other advanced nanostructured metal selenides/graphene electrodes.