Co-precipitation-derived nanocrystalline FeS with enhanced electrochemical performance for supercapacitor electrodes and FeS//Cu energy storage devices

In this study, nanocrystalline FeS was prepared using a facile and easily scalable co-precipitation method and investigated for its performance as supercapacitor electrode. Phase pure hexagonal FeS was found by XRD analysis of synthesized FeS and the average crystallite size was calculated as 25.67 nm. Presence of characteristic Fe-S bonding was confirmed using FTIR spectrum and Fe/S states in FeS lattice was analyzed by XPS. Field-emission SEM analysis revealed that it possessed a porous, highly interconnected porous morphology comprising closely packed quasi-spherical nanoparticles and EDAX spectrum confirmed its composition and purity. In three-electrode configurations with 6 M KOH electrolyte, it displayed good battery-type faradaic activity with a high specific capacitance of 270 F g−1 at 4 A g−1. Charge storage mechanism was studied and from anodic and cathodic b values of 0.55 and 0.47, respectively, it was concluded that storage mechanism is diffusion controlled. EIS measurements showed that the electrodes have good charge transfer property and effective ion diffusion due to their highly porous structure. The FeS electrodes exhibited about 60% retention of their initial capacitance over 10,000 charge–discharge cycles. An FeS//Cu full-cell device fabricated with FeS electrodes provided stable operating potential of ~1.61 V and showed 75% capacitance retention after 10,000 cycles at 18 A g−1. Overall, co-precipitation synthesis of nanostructured FeS showed excellent electrochemical performance with fast charge transfer and good long cycle performance.