Carbon-Encased Mixed-Metal Selenide Rooted with Carbon Nanotubes for High-Performance Hybrid Supercapacitors

Transition metal-based compounds with high theoretical capacitance and low cost represent one class of promising electrode materials for high-performance supercapacitors. However, their low intrinsic electrical conductivity impedes their capacitive effect and further limits their practical application. Rational regulation of their composition and structure is, therefore, necessary to achieve a high electrode performance. Herein, a well-designed carbon-encased mixed-metal selenide rooted with carbon nanotubes (Ni-Co-Se@C-CNT) was derived from nickel-cobalt bimetallic organic frameworks. Due to the unique porous structure, the synergistic effect of bimetal selenides and the in situ growth of carbon nanotubes, the composite exhibits good electrical conductivity, high structural stability and abundant redox active sites. Benefitting from these merits, the Ni-Co-Se@C-CNT exhibited a high specific capacity of 554.1 C g^-1 (1108.2 F g^-1) at 1 A g^-1 and a superior cycling performance, i.e., 96.4% of the initial capacity was retained after 5000 cycles at 10 A g^-1. Furthermore, a hybrid supercapacitor assembled with Ni-Co-Se@C-CNT cathode and activated carbon (AC) anode shows a superior energy density of 38.2 Wh kg^-1 at 1602.1 W kg^-1.