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.