Highly porous oxygen-doped NiCoP immobilized in reduced graphene oxide for supercapacitive energy storage

Transition metal phosphides (TMPs) have received extensive research attention as an electrode material for supercapacitors. Current application of TMPs as electrodes is restricted by their limited electrochemical reaction activity and electrical conductivity. Herein, we report an effective strategy for fabricating highly porous oxygen doped NiCo-phosphides (O–NiCoP) immobilized in reduced graphene oxide network (O–NiCoP@rGO). The control of phosphorization degree is studied in this paper. Abundant interior and surface channels are created in O–NiCoP particles, leading to easy electrolyte infiltration and facilitated redox reaction kinetics. In addition, the rGO nanosheets functioned in providing continuous electron pathways and buffering interior stress of the electrode during redox reactions. The Density functional theory (DFT) calculations further reveals that the band gap can be eliminated during phosphorization, and the charge accumulation can be produced at the interface gap between graphene and O–NiCoP (001) plane after the introduction of graphene. The O–NiCoP@rGO electrode demonstrates superior capacitive performance with a remarkable capacitance of 1663.2 F g−1 at 1 A g−1 and high capacitance retention of 89.3% after 5000 cycles at 5 A g−1. Asymmetrical supercapacitors (ASCs) are also prepared demonstrating a high energy density of 21 Wh·kg−1 at a power density of 775 W kg−1 and predominant cycling performance (91.0% capacity retention after 5000 cycles at 2 A g−1). The ASCs are used to light up LED bulbs and a mobile phone, further demonstrating its superior performance. The O–NiCoP@rGO was demonstrated as an electrode material for supercapacitors. Synergistic effect was exhibited from its porous structure, lattice defects and the highly conductive rGO network, which provided more active sites and greatly improved electron transportation. Density functional theory (DFT) calculations proved that phosphorization and rGO incorporation can induce favorable electronic structures with zero band gap and electron accumulation. [Display omitted] •The samples with different electrochemical properties were obtained by controlling the doping of O in NiCoP by phosphorization.•Close connection between O-NiCoP and rGO to increase conductivity and enhanced electron transport rate.•It is proved by Density functional theory (DFT) calculations that phosphating and introducing rGO can eliminate band gap and accumulate charge.