Supercapacitors incorporating hollow cobalt sulfide hexagonal nanosheets

We have prepared hollow cobalt sulfide (CoS) hexagonal nanosheets (HNSs) from Co(NO₃)₂ and thioacetamide in the presence of poly(vinylpyrrolidone) (PVP) at 100°C under alkaline condition. The as-prepared hollow CoS HNSs have an average edge length ca. 110 ± 27 nm and an outer shell of 16 ± 4 nm in thickness from 500 counts. The CoS HNSs are deposited onto transparent fluorine-doped tin oxide (FTO) substrates through a drop-dry process to prepare two types of supercapacitors (SCs); high rate and large per-area capacitance. The electrolyte used in this study is KOH_(aq). The CoS HNSs (8 μg cm^-2) electrodes exhibit excellent capacity properties, including high energy density (13.2 h kg ^-1), power density (17.5 kW kg^-1), energy deliverable efficiency (81.3-85.3%), and stable cycle life (over 10,000 cycles) at a high discharge current density of 64.6 A g^-1. With their fast charging and discharging rates (<3 s), the CoS HNSs show characteristics of high-rate SCs. The CoS HNS SCs having high mass loading (9.7 mg cm^-2) provide high per-area capacitance of 1.35 F cm^-2 and per-mass capacitance of 138 F g^-1, respectively, showing characteristics of SCs with large per-area capacitance. Our results have demonstrated the potential of the CoS HNS electrodes hold great practical potential in many fields such as automobile and computer industries.