Tailoring MoP/Rh2P-embedded BNFS-doped carbon nanofibers for supercapacitors via DFT-guided electronic and ion adsorption engineering

Enhancing electrochemical performance through synergistic redox activity and improved electronic conductivity is crucial for high-efficiency supercapacitors. To achieve this, a dual metal phosphide-integrated, heteroatom-doped carbon nanofiber composite (MoP/Rh₂P@BNFS–CNF) was synthesized via electrospinning followed by in situ phosphidation. The integration of B, N, F and S heteroatoms using ionic liquids, combined with embedded MoP and Rh₂P nanoparticles, resulted in a highly porous and conductive nanostructure with an average fiber diameter of 362 nm and nanoparticle sizes ranging from 10 to 20 nm. Structural and surface analyses confirmed uniform heteroatom doping and successful phosphide formation. The optimized composite exhibited a high surface area (1050.11 m² g⁻¹), superior wettability (contact angle: 3.79^o), and exceptional electrochemical performance, delivering specific capacitance of 937.5 F g⁻¹ (CV) and 548 C g⁻¹ (GCD) at 1 A g⁻¹. It also demonstrated excellent rate capability, 97.1 % capacitance retention over 5000 cycles, and the lowest R_s (0.86 Ω) and R_ct (1.01 Ω) among the tested electrodes. Density functional theory (DFT) calculations confirmed its metallic nature with no bandgap, high electronic density near the Fermi level, and strong K⁺ adsorption (62 sites), validating the composite's excellent conductivity and electrochemical stability. The assembled asymmetric supercapacitor device (ASD) achieved a wide voltage window (0–1.8 V), a high energy density of 27.5 Wh kg⁻¹, a power density of 9000 W kg⁻¹, and 97.3 % capacitance retention over 10,000 cycles. These results demonstrate the potential of MoP/Rh₂P@BNFS–CNF as a next-generation electrode for high-performance energy storage applications.