MOF-derived rose-like carbon-coated Ni-Co phosphide with phosphorus vacancies to enhance hydroxide-ion storage in hybrid supercapacitors

Abstract

The low structural stability and sluggish charge-transfer kinetics of transition metal phosphides (TMPs) hinder their application in hybrid supercapacitors. The realization of advanced OH- storage critically depends on the delicate TMP designs, particularly their chemical composition and structure. Herein, a synergistic engineering approach based on metal-organic framework (MOF)-derived C-coated bimetallic phosphides and P vacancies (Pv) was proposed. Using a Ni-Co-based MOF, a one-step high-temperature carbonization and phosphidation method was employed as the precursor to prepare a rose-like Ni1-xCoxP composite (Ni1-xCoₓP@NC), comprising a N-doped carbon (NC) coating and Pv. Physical characterization and theoretical calculations indicated that the open structure with porous Ni1-xCoxP@NC nanosheets originating from high-temperature pyrolysis of Ni-Co-based MOF provides abundant redox-active sites, and the NC layer offers excellent mechanical support for persistent electron/OH- transfer. The bimetallic phosphides, surface Pv, and NC coating synergistically enhance the electrical conductivity of TMPs, reduce the energy barriers for OH- adsorption, and accelerate charge-transfer kinetics. The prepared Ni1-xCoxP @NC electrode possessing an open architecture exhibits a high specific capacitance (2,108 F g-1 at 1 A g-1) and excellent rate capability (1,710 F g-1 at 10 A g-1). Furthermore, the assembled active carbon//Ni1-xCoxP P@NC hybrid supercapacitor demonstrates an energy density of 37.7 Wh kg-1 at a power density of 750 W kg-1. Our study presents a promising strategy for modifying TMP electrodes to realize efficient and stable OH- storage in hybrid supercapacitors.