Three-dimensional core-shell NiCoP@NiCoP array on carbon cloth for high performance flexible asymmetric supercapacitor

Abstract

Transition metal phosphides (TMPs) have been received widespread research attention and developed as electrode materials for their superior electrical conductivity and excellent redox activity. In this work, self-supported three-dimensional hierarchical core-shell NiCoP@NiCoP@CC electrode has been fabricated by a two-step hydrothermal and a phosphorization method, in which NiCoP@NiCoP core-shell leaf-like arrays are directly grown on carbon cloth. The electrode integrates the advantages of the 1D core for “hyperchannel” of the electron transport, 2D shell on core for a short diffusion distance for the ions and also the charge carrier meanwhile improvement of cycle stability, and 3D networked substrate for flexibility. The as-fabricated electrode shows superior electrochemical performance and delivers a high specific capacity of 1125 C g−1 (312 mAh g−1) at 1 A g−1, and outstanding rate capability with 78.0% retention even at 10 A g−1 and still retain 808 C g−1 (224 mAh g−1) (71.8% retention) after 2000 cycles. In addition, the asymmetric supercapacitor has also been assembled for actual use by employing NiCoP@NiCoP electrode as the anode and the activated carbon (AC) as the cathode, which displays a voltage window of 1.5 V and a high energy density of 34.8 Wh kg−1 at a power density of 750.0 W kg−1. The results demonstrate feasibility of NiCoP@NiCoP core-shell array on carbon cloth as electrode material for high performance hybrid supercapacitor applications.