Solvothermal coating of NiCoP on foam h-BN/EG substrates with sea urchin-like structure and supercapacitor application

In this study, a binder-free cauliflower-like NiCoP nanostructure is synthesized on expanded graphite (EG) paper through a sequential solvothermal, phosphorization, and electrolysis process.The hierarchical nanostructure promotes a highly rough and porous surface morphology, which, together with its intrinsic composition, enables superhydrophobic behavior. Surface wettability and structural properties were characterized in detail by contact angle measurements, SEM, and XPS analyses. Electrochemical tests revealed an excellent areal capacitance of 5.96 F cm⁻² at 1 mA cm⁻² and outstanding cycling stability, retaining 113.1% of its initial capacitance after 6000 charge–discharge cycles. Moreover, a CR2032-type asymmetric supercapacitor is assembled using NiCoP@EG as the positive and AC@EG as the negative electrode. The device delivers 848 mF cm⁻² at 1 mA cm⁻², along with a high energy density of 231.1 μWh cm⁻² at a power density of 8946.2 μW cm⁻², indicating outstanding rate capability. These findings highlight the synergistic advantages of combining morphology engineered NiCoP with a binder-free EG platform, offering a promising route toward high performance microscale energy storage systems.