Three-Dimensional Hierarchical Ni_xCo_1–xO/Ni_yCo_2–yP@C Hybrids on Nickel Foam for Excellent Supercapacitors

Abstract

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.

Metal Phosphides and Phosphates‐based Electrodes for Electrochemical Supercapacitors

“…Through a similar procedure, interconnected 3D networks of Ni 2 P nanosheets are formed from Ni(OH) 2 nanosheets grown on nickel foam . Hierarchical 3D NiCoOP@C hybrids were successfully prepared by phosphorization treatment of Ni x Co 1−x O@C grown on nickel foam . In these hybrid‐type structures, carbon cloth and nickel foam are acting as the conducting substrates …”

“…Hierarchical 3D NiCoOP@C hybrids were successfully prepared by phosphorization treatment of Ni x Co 1−x O@C grown on nickel foam . In these hybrid‐type structures, carbon cloth and nickel foam are acting as the conducting substrates …”

“…As described above, transition metal phosphides, such as nickel and cobalt phosphides, exhibit varying electrochemical behavior, depending on the structural features that can be tuned by processing parameters . Their pseudocapacitance performance is closely related to the redox chemistry involved . To further improve their performance, there have been a number of research works that are performed in the integration of phosphide materials with one or more other types of active materials .…”

“…Their pseudocapacitance performance is closely related to the redox chemistry involved . To further improve their performance, there have been a number of research works that are performed in the integration of phosphide materials with one or more other types of active materials . These hybrid‐type electrode materials thus developed can be grouped into three categories, depending on the type of material integrated with metal phosphides: i) metal oxides/hydroxides, ii) graphene/carbon‐based materials, and iii) metals, respectively.…”

“…Similar to transition metal oxides/hydroxides and conducting polymers, some of which have been widely studied for the hybrid‐type electrode materials aiming for improved electrochemical performance . While considerable progress has been made with the carbon‐based materials, transition metal oxides/hydroxides, conducting polymers and their composites; several of the metal phosphides and phosphates would be better alternatives, when they are properly established …”