Rational Construction of Hollow Core-Branch CoSe2 Nanoarrays for High-Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution.

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core-branch CoSe2 nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe2 in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core-branch CoSe2 has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe2 delivers a high specific capacitance of 759.5 F g-1 at 1 mA cm-2 , which is much larger than that of CoO nanocones (319.5 F g-1 ). In addition, the CoSe2 electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge-discharge cycles at 5 mA cm-2 . An asymmetric supercapacitor using the CoSe2 as cathode and an N-doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg-1 at a power density of 1914.7 W kg-1 , and maintains 24.9 Wh kg-1 when power density increased to 7354.8 W kg-1 . Moreover, the CoSe2 electrode also exhibits better oxygen evolution reaction activity than that of CoO.