Active materials and special structures of the electrode have decisive influence on the electrochemical properties of supercapacitors. Herein, three-dimensional (3D) hierarchical NiCoO/NiCoP@C (denoted as NiCoOP@C) hybrids have been successfully prepared by a phosphorization treatment of hierarchical NiCoO@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 NiCoO, the high specific capacitance of NiCoP, the mechanical stability of carbon layer, and the 3D hierarchical structure. The specific capacitance of 2638 F g can be obtained at the current density of 1 A g, and even at the current density of 20 A g, the NiCoOP@C electrode still possesses a specific capacitance of 1144 F g. After 3000 cycles at 10 A g, 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 at a power density of 394 W kg and still holds 21 Wh kg at 7500 W kg.

Recently, transition metal-based nanomaterials have played a key role in the applications of supercapacitors. In this study, nickel phosphide (Ni-P) was simply combined with NiCo LDH via facile phosphorization of Ni foam and subsequent electrodeposition to form core-shell nanorod arrays on the Ni foam; the Ni-P@NiCo LDH was then directly used for a pseudocapacitive electrode. Owing to the splendid synergistic effect between Ni-P and NiCo LDH nanosheets as well as the hierarchical structure of 1D nanorods, 2D nanosheets, and 3D Ni foam, the hybrid electrode exhibited significantly enhanced electrochemical performances. The Ni-P@NiCo LDH electrode showed a high specific capacitance of 12.9 F cm at 5 mA cm (3470.5 F g at a current density of 1.3 A g) that remained as high as 6.4 F cm at a high current density of 100 mA cm (1700 F g at 27 A g) and excellent cycling stability (96% capacity retention after 10 000 cycles at 40 mA cm). Furthermore, the asymmetric supercapacitors (ASCs) were assembled using Ni-P@NiCo LDH as a positive electrode and activated carbon (AC) as a negative electrode. The obtained ASCs delivered remarkable energy density and power density as well as good cycling performance. The enhanced electrochemical activities open a new avenue for the development of supercapacitors.

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