Three-Dimensional Hierarchical NixCo1–xO/NiyCo2–yP@C Hybrids on Nickel Foam for Excellent Supercapacitors

Active materials and special structures of the electrode have decisive influence on the electrochemical properties of supercapacitors. Herein, three-dimensional (3D) hierarchical NixCo1–xO/NiyCo2–yP@C (denoted as NiCoOP@C) hybrids have been successfully prepared by a phosphorization treatment of hierarchical NixCo1–xO@C grown on nickel foam. The resulting NiCoOP@C hybrids exhibit an outstanding specific capacitance and cycle performance because they couple the merits of the superior cycling stability of NixCo1–xO, the high specific capacitance of NiyCo2–yP, the mechanical stability of carbon layer, and the 3D hierarchical structure. The specific capacitance of 2638 F g–1 can be obtained at the current density of 1 A g–1, and even at the current density of 20 A g–1, the NiCoOP@C electrode still possesses a specific capacitance of 1144 F g–1. After 3000 cycles at 10 A g–1, 84% of the initial specific capacitance is still remained. In addition, an asymmetric ultracapacitor (ASC) is assembled through using NiCoOP@C hybrids as anode and activated carbon as cathode. The as-prepared ASC obtains a maximum energy density of 39.4 Wh kg–1 at a power density of 394 W kg–1 and still holds 21 Wh kg–1 at 7500 W kg–1.