Boron-induced phase-transition and selenium vacancy to enhance supercapacitive performance of cobalt diselenide

The phase-transition engineering has shown great potential in designing high-performance energy storage and catalytic materials. Herein, we report the phase transition and selenium vacancy induced by the trace boron doping into CoSe2, realizing an enhancement of the performance of supercapacitor. The trace amounts of boron doping (∼ 0.07 wt%) induce the phase-transition from cubic to orthorhombic structures and trigger selenium vacancies in orthorhombic cobalt diselenide (o-CoSe2). The doped defective cobalt diselenide (o-CoSe2−x/B) exhibits a high specific capacity of 376.3 mA h g−1 at a current density of 1 A g−1, which is much larger than that of the undoped cubic cobalt diselenide (211.3 mA h g−1) and annealed cubic cobalt diselenide (208.3 mA h g−1). A hybrid supercapacitor assembled using o-CoSe2−x/B and activated carbon delivers a high energy density of 102.5 W h kg−1 at a power density of 850.4 W kg−1 and maintains an energy density of 34.0 W h kg−1 at 16,767.1 W kg−1. In addition, the device possesses an excellent cycling stability that remains 83.5 % of the initial capacitance after 25,000 cycles at a current density of 10 A g−1. These results demonstrate that the boron is a new efficient dopant that can dramatically improve the supercapacitor performance of CoSe2 through the structural phase transition and defect engineering.