Optimizing nanostructure and constructing heterostructure via Mo/W incorporation to improve electrochemical properties of NiCoP for hybrid supercapacitors

Transition metal phosphides (TMPs) are promising battery-type electrodes for hybrid supercapacitors (HSCs) due to their high electrical conductivity and electrochemical activity. Constructing TMPs with fast kinetics and stable structure is requisite to realize high-performance HSCs but remains a challenge. Herein, we incorporate Mo (or W) into NiCoP to form Ni-Co-Mo-P (or Ni-Co-W-P) heterostructures with a unique three-dimensional (3D) open morphology and modified electronic structure. Electrochemical analyses and density functional theory (DFT) calculations reveal that the incorporation of Mo/W enables NiCoP with optimized nanostructure, high conductivity, abundant reaction active sites and enhanced reaction kinetics. As a result, the designed Ni-Co-Mo-P heterostructure delivers a high areal capacity of 4.08 C cm−2 (703 C g−1) at 2 mA cm−2 and 3.25 C cm−2 at 30 mA cm−2 with a good cycling stability, superior to those of NiCoP and Ni-Co-W-P counterparts. The practical feasibility of the Ni-Co-Mo-P heterostructure is further demonstrated by an energy conversion and storage system consisting of commercial solar cell and Ni-Co-Mo-P//activated carbon (AC) device, which could obtain a high energy density of 53.3 W h kg−1 at a power density of 800 W kg−1. All-solid-state Ni-Co-Mo-P//AC device further illustrates the superior flexibility and makes a strong candidate for wearable energy storage electronics.