MOF-derived rose-like carbon-coated Ni-Co phosphide with phosphorus vacancies to enhance hydroxide-ion storage in hybrid supercapacitors
Honghong Cheng, Zhibiao Cui, Weijie Zheng, Dong Shu, Cong Liu, Yaotao Zeng, Jinyi Zheng, Jiayin Cui, Keyi Chen, Tao Meng
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.