Integration of vanadium diphosphide with 2D cobalt phosphide architected as an extensible redox active positrode for alkaline supercapacitor

Abstract

Metal phosphides in the form of rationally constructed two-dimensional (2D) nanosheets hold significant promise as versatile materials for energy storage applications. This study introduces a novel hybrid supercapacitor electrode, composed of a binder-free vanadium phosphide integrated cobalt phosphide (VP@CP) on a nickel foam substrate. The fabrication process involves the hydrothermal growth of Co₂(OH)₂BDC (BDC- 1,4-benzenedicarboxylate) nanosheets on a Ni-foam substrate (CMF-Ni), followed by the deposition of VO₂ on CMF nanosheets (VO@CMF-Ni) using chronoamperometry and phosphorization of the VO@CMF-Ni to yield VP@CP-Ni nanosheets. Particularly, the density functional theory (DFT) results show that the VP₂ integrated Co₂P sample provides metallic behavior and low adsorption energy of OH⁻ ions, resulting in improved electrochemical redox process. These bimetallic phosphides exhibit outstanding properties, including enhanced pathways for rapid ion transport and storage, increased electronic conductivity, and expanded electroactive regions facilitating the faradaic charge storage process. Due to the presence of vanadium and cobalt coupled sites, the fabricated VP@CP-Ni electrode was able to attain a maximum areal capacity (C_AR) of 971 mA h cm⁻² at 6 mA cm⁻². Additionally, the fabricated hybrid device (HDC) exhibits an impressive specific energy (S_E) of 30.9 Wh kg⁻¹ at a specific power (S_P) of 1344 W kg⁻¹, and excellent cyclic durability. These remarkable results stimulate the exploration of such possible 2D VP@CP-Ni nanosheets with promising charge storage electrode capabilities to develop a future era of energy storage devices.