Formation of three-dimensional hierarchical pompon-like cobalt phosphide hollow microspheres for asymmetric supercapacitor with improved energy density

A novel three-dimensional (3D) hierarchical pompon-like CoP hollow microspheres are prepared via a hydrothermal method combined with a subsequent phosphatization treatment. These hollow microspheres present a high specific surface area of roughly 24.6 m ² g ⁻¹ , and a plausible mechanism for their growth is also proposed. The as-obtained materials display an enhanced specific capacitance of 449.4 F g ⁻¹ at 1 A g ⁻¹ benefited from its unique 3D hierarchical pompon-like hollow structure with a large surface area and high utilization of active materials. Moreover, an asymmetric supercapacitor employing the as-synthesized CoP as the positive electrode and actived carbon (AC) as the negative electrode were successfully assembled, which delivered a high energy density of 22.2 Wh kg ⁻¹ at power density of 374.9 W kg ⁻¹ with a good cycling performance (80.9% capacitance retention after 3000 cycles). As a practical application test, a unit of three serially-connected ASCs was charged for 15 s and supplied power to, (a) a light emitting diode (LED) and (b) a small LED display screen, each of which worked for more than 35 min and 1 min, respectively. The above results demonstrate that the 3D hierarchical pompon-like CoP hollow microspheres are a promising electrode material for supercapacitor applications.