Optimizing the supercapacitive performance via encasing MOF-derived hollow (Ni,Co)Se2 nanocubes into reduced graphene oxide

For achieving the long cycle and high capacity of supercapacitive materials, the emphasis lies in ameliorating conductivity, regulating phase content and constructing porous structure. In such case, we synthesize a hierarchical hollow (Ni,Co)Se-2 nanocubes@reduced graphene oxide (rGO) via the procedures of co-precipitation, selenation and rGO coating treatments. The hollow structure and ultra-thin nanosheets are conducive to rapid OH- diffusion. The tailored Ni: Co ratio, coupled with weak-electronegativity Se, is beneficial to adjusting the electronic structure of hybrid structure. Meanwhile, the existing porous rGO is not only served as conducive network to improve conductivity, but also acted as the structure protector and space separator to maintain structural integrality. Benefiting from such merits in the content and morphology, the (Ni,Co)Se-2@rGO electrode is featured with specific capacity (649.1C g(-1) at 1 A g(-1)), ultrahigh rate performance (75.5% at 20 A g(-1)) together with outstanding cycling stability (90.5% retention after 5000 times charge/discharge at 10 A g(-1)). Moreover, the resulting (Ni,Co)Se-2@rGO//activated carbon (AC) hybrid supercapacitor (HSC) achieves high energy density of 52.6 Wh kg(-1) at 803.4 W kg(-1) and remarkable cycling lifespan (similar to 100% retention over 10,000 cycles), further eliciting the tremendous potentiality of such (Ni,Co)Se-2@rGO material.