Homologous NiCoP/CoP hetero-nanosheets supported on N-doped carbon nanotubes for high-rate hybrid supercapacitors

Abstract

Rational design of highly active electrode materials made of low-cost and earth-abundant transition metal phosphides is essential to boost the energy density and overall performance of electrochemical capacitors. In this work, homologous 3D NiCoP/CoP hetero-nanosheets network supported on N-doped carbon nanotubes are synthesized through one-step phosphorization of nickel cobalt hydroxide. The synergistic effects between NiCoP and CoP in the heterointerface are studied systematically through tuning the molar ratio of original Ni/Co. As a result, the optimized N-CNTs@NiCoP/CoP (with the Ni/Co ratio of 1:2) reveals a remarkable specific capacity of 152 mAh g−1 at 1 A g−1 and a superior rate capability with a capacity retention of 61% even at 30 A g−1. A hybrid supercapacitor assembled with N-CNTs@NiCoP/CoP cathode and ZIF-67-derived porous carbon anode exhibits a high energy density of 45.5 Wh kg−1 at power density of 784 W kg−1 and excellent stability of 87% retention after 10,000 cycles at 12 A g−1. Such excellent electrochemical performance of N-CNTs@NiCoP/CoP is mainly ascribed to the strong synergistic effect between NiCoP and CoP in their heterojunctions, enlarged surface area and active sites due to the 3D nanosheets network and conductive N-CNTs support.