Calcination/phosphorization of dual Ni/Co-MOF into NiCoP/C nanohybrid with enhanced electrochemical property for high energy density asymmetric supercapacitor

Abstract

Binary metal compounds have higher conductivity and richer redox reactions due to the co-existence and synergism of different transition metals. Besides, carbon in composite materials has the advantage of enhancing electronic conductivity to promote fast electron transmission. Herein, a series of NimPn/C, Ni2P/C, Co2P/C and NixCo2-xP/C nanohybrids with different Ni/Co molar ratios were synthesized by in-situ calcination/phosphorization of MOF precursors. These nanohybrid materials were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive spectrometer and electrochemical tests. The NiCoP/C material possesses a granular structure with NiCoP nanoparticles anchored in a large number of carbon. Taking advantage of the bimetallic synergism and carbon anchoring effect, the as-prepared NiCoP/C sample delivers the most prominent specific capacities of 775.7C g−1 at 1 A g−1, and 582.4C g−1 at 20 A g−1 (20-fold) with a superior rate capability of 75.1% retention, much superior to those of the corresponding NimPn/C, Ni2P/C, Co2P/C, other NixCo2-xP/C samples and various reported metal phosphide nanostructures/nanocomposites. Furthermore, the constructed NiCoP/C//activated carbon asymmetric supercapacitor can exhibit a high energy density of 47.6 Wh kg−1 at a power density of 798.9 W kg−1, which was superior to those previously reported of Ni/Co phosphide nanomaterials.