Phase Modulation and Electrochemical Behavior of Fe₃Mo₃C/Mo₂C Composite Nanofibers as Supercapacitor Negative Electrodes

The advancement of negative electrode materials is essential for enhancing the performance of supercapacitors. Fe–Mo-based bimetallic carbide presents significant potential as a supercapacitor negative electrode material. In this study, Fe3Mo3C/Mo2C composite nanofiber was synthesized using the electrospinning method followed by high-temperature carbonization. As-prepared composite nanofibers consist of two phases: Mo2C nanoparticles embedded within the nanofiber and a block-like dispersion of the Fe3Mo3C phase. The Mo2C-dominated Mo2C/Fe3Mo3C-900 electrode shows an optimal specific capacitance of 354.9 F g–1 at 1 A g–1, notably exceeding that of the Fe3Mo3C-dominated Fe3Mo3C/Mo2C-900 electrode (253.2 F g–1). This advancement can be ascribed to the enhanced textural characteristics and lower resistance. The assembled NiCo2O4//Mo2C/Fe3Mo3C-900 device yields an energy density of 54.6 Wh kg–1 when the power density is 850 W kg–1. On the other hand, the NiCo2O4//Mo2C/Fe3Mo3C-900 ASC device retained 67% of its capacitance after 5000 charge–discharge cycles, underperforming that of the NiCo2O4//Fe3Mo3C/Mo2C-900 (78%). This suggests that composite nanofiber with Mo2C as the main phase exhibits superior specific capacitance, while the bimetallic carbide Fe3Mo3C presents higher conductivity, which further improves its electrochemical stability. In short, the as-designed Fe3Mo3C/Mo2C composite nanofibers present promising negative electrode features for energy storage applications.