Fabrication of Assembled FeS₂ Nanosheet and Application for High-Performance Supercapacitor Electrodes

To overcome the low-energy-density limitation of supercapacitors, we aimed to achieve a material with a high specific capacitance by manipulating the nanostructure of FeS₂, which comprises the most abundant and affordable elements. In this study, nanosheet-assembled FeS₂ (NSA-FeS₂) was fabricated using a novel method. Sub-micron droplets of sulfur particles stabilized with polyvinylpyrrolidone were formed in silicone oil medium, and Fe(CO)₅ was absorbed and reacted on the surface to form core-shell particles, ES/[Fe], with a sulfur core and an iron-containing outer shell. The high temperature treatment of ES/[Fe] produced NSA-FeS₂, in which pyrite FeS₂ nanosheets grew and were partially interconnected. In a three-electrode system, the as-prepared NSA-FeS₂ and NSA-FeS₂/polyaniline (PANI) composites exhibited specific capacitances of 763 and 976 Fg^-1, respectively, at a current density of 0.5 Ag^-1, with corresponding capacitance retentions of 93 and 96% after 3000 charge-discharge cycles. The capacitance retention of the NSA-FeS₂/PANI composites was 49% when the current density was increased from 0.5 to 5 Ag^-1. Notably, the obtained specific capacitances exhibited the highest values in pure FeS₂ and FeS₂-based composites, indicating the significant potential for the utilization of iron sulfide in pseudocapacitive electrode materials.