Comprehensive characterization and electrochemical performance of Fe-doped Co3O4 nanoparticles for energy storage applications

This study investigates the structural, spectroscopic, and electrochemical properties of Fe-doped cobalt oxide nanoparticles (Fe-doped Co3O4 Nps). X-ray diffraction (XRD) analysis reveals that the Fe-doped samples have a spinel cubic Co3O4 structure with peaks corresponding to (220), (311), (400), (511), and (400) reflection planes. Fourier-transform infrared (FTIR) analysis shows that the major peaks correspond to Co2+ and Co3+ vibrations in the spinel Co3O4 crystal structure, and their positions shift with the increase in Fe doping concentration. X-ray photoelectron spectroscopy (XPS) studies confirm the presence of Co2+ and Co3+ in the Co 2p spectrum and identify Fe3+ and Fe2+ in the Fe 2p spectrum. Scanning electron microscopy (SEM) reveals the surface morphology of the Fe-doped Co3O4 Nps, showing hexagonal/granular structures with varying pore sizes. High-resolution transmission electron microscopy (HR-TEM) analysis confirms the nanocrystalline nature of the Fe-doped Co3O4 Nps. Energy-dispersive X-ray spectroscopy (EDAX) elemental analysis confirms the presence of Co, O, and Fe in the doped samples. Fe-doped Co3O4 nanoparticles were characterized through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopic analysis (EIS). The CV curves displayed consistent electrochemical behavior with observed redox peaks, confirming pseudocapacitive nature. Increasing scan rates led to higher current responses and minor peak position shifts. The Fe-doped Co3O4 nanoparticles exhibit a specific capacity of 253 C/g at a current density of 1.5 A/g, and they maintain 95% of their initial specific capacity after undergoing 1500 cycles. Specific capacity increased with higher Fe doping concentrations, attributed to electron injection and ion diffusion enhancement. GCD profiles showed nonlinear plateau regions, indicating pseudocapacitive behavior, with longer discharge curves for Fe-doped samples, demonstrating superior specific capacity. Electrochemical impedance spectroscopy revealed disrupted ion transport paths. Cyclic stability tests showed good capacity retention for all samples, with the 7 wt% Fe-doped Co3O4 sample exhibiting the highest capacity and cyclic stability, making it suitable for pseudo-capacitor applications.