NiCoP nanoparticle-decorated carbon nanosheet arrays assembled on nickel nanowires for volumetric energy-dense supercapacitors

Abstract

Transitional metal phosphide Ni_xCo_yP has been considered a promising capacitor electrode material due to its high specific capacity. However, the inferior electronic conductivity and structure instability of Ni_xCo_yP severely restrict its applications. Designing effective structures is challenging to simultaneously optimize the conductivity and stability of Ni_xCo_yP. Herein, a hierarchical structure of film electrodes based on NiCoP nanoparticle-decorated carbon nanosheet arrays assembled on nickel nanowires (Ni@C–NiCoP) were demonstrated for volumetric energy-dense supercapacitors by assembling C nanosheets loaded with phosphide nanoparticles on Ni nanowires film. The porous carbon nanosheets array in situ assembled on Ni wires could provide high structural stability as well as enhanced ion diffusibility. Simultaneously, NiCoP nanoparticles could remain unpulverized and improved the utilization ratio under the protection of carbon nanosheets. Density functional theory calculations indicate that the interfaces of NiCoP and carbon could transmit charges sufficiently near the Fermi energy level, which was attributed to the hybridization between C 2p and Co 3d orbitals. The as-fabricated Ni@C–NiCoP film electrode could deliver a high volumetric capacity of 751 C cm⁻³ at 0.5 A cm⁻³ and retain 481 C cm⁻³ at a high rate of 5 A cm⁻³. Moreover, the as-assembled hybrid supercapacitor (graphene/carbon//Ni@C–NiCoP) exhibited a high volumetric capacitance of 161 F cm⁻³ at 0.5 A cm⁻³, together with a superior energy density of 49.6 mW h cm⁻³ and a power density of 3823.6 mW cm⁻³. Remarkably, high capacitance retention of 89% was achieved after 10 000 cycles at 4 A cm⁻³. The concept of hierarchical electrode design can pave the road to engineer high-performance electrode materials for energy storage and catalysis.