NH4F-modulated 3D NiCoP nanosheet arrays for ultrahigh-energy-density supercapacitors with long-Term Cyclability

Transition metal phosphides are regarded as ideal electrode materials for high energy density supercapacitors due to their high theoretical specific capacitance and multi-electron redox properties, but they still face challenges such as low utilization of active sites, high resistance to ion diffusion, and structural collapse during cycling. In this study, we propose a three-dimensional nickel-cobalt phosphide nanosheet array design strategy based on ammonium fluoride (NH 4 F) modulation, and vertically aligned three-dimensional porous nickel-cobalt-phosphide nanosheet arrays (F5–NiCoP/NF) were constructed in-situ on nickel foam substrates by a template-free hydrothermal-phosphorization two-step method. Its superior electrochemical performance stems from bimetallic synergy and the high conductivity of the phosphide. Vertical nanosheet arrays build a three-dimensional conductive network to reduce ion diffusion resistance, and abundant pores significantly accelerate charge transport and expose abundant electroactive sites. Notably, this approach simultaneously simplifies the preparation process and reduces the cost. Benefitted from these merits, the F5–NiCoP/NF electrode achieves a high specific capacitance of 3244 F g −1 at a current density of 1 A g −1 , a capacity retention of 75.69 % at a high multiplicity of 10 A g −1 , and retains 81.44 % of its initial capacity after 10,000 cycles. The assembled asymmetric supercapacitor F5–NiCoP/NF//AC exhibits an energy density of 48.37 Wh kg −1 and a power density of 800.04 W kg −1 .