Iron Phosphate–Carbon Nanofiber Composite for High-Performance Asymmetric Hybrid Supercapacitors

Abstract

A composite of iron phosphate (FeP) and carbon nanofibers (CNFs) was synthesized using a facile hydrothermal technique. The surface morphologies of the FeP and FeP–CNF nanocomposites were characterized through field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The crystallinity and functional groups of the materials were identified using X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, the binding energies and electronic bonding states of the FeP–CNF composites were analyzed using X-ray photoelectron spectroscopy. The electrochemical performance of FeP and FeP–CNF as active materials for supercapacitors was investigated by fabricating three- and two-electrode systems. Their performance was evaluated through cyclic voltammetry, galvanostatic charge–discharge measurements, and electrochemical impedance spectroscopy. Two-electrode asymmetric devices, FeP//AC and FeP–CNF//AC, were tested within a voltage range of 0–1.6 V using a 3 M KOH aqueous electrolyte. The maximum specific capacitances of the electrodes were 59.90 and 120.11 F/g at 1 A/g for FeP//AC and FeP–CNF//AC, respectively. Both asymmetric devices demonstrated excellent cycling stability and capacitance retention over 10,000 cycles at 5 A/g. The FeP–CNF-based asymmetric supercapacitor performed particularly well, underscoring its prospects for high-energy storage applications in advanced energy storage systems.