CoS spheres for high-rate electrochemical capacitive energy storage application

Sphere-like CoS nanostructures are synthesized in water/ethylene glycol mixed solvents by simple hydrothermal technique using l-cysteine amino acid as a source of sulfur. The results obtained by BET and BJH methods reveal that the CoS has mesoporous bimodal pore distribution in the range of 2–23 nm with a dominant peak around 12.4 nm and a small peak at 2.4 nm. The electrochemical experiments demonstrate that CoS has a high-rate capability for capacitor applications. The reduction of the specific capacitance is very marginal by about 13% of the available capacitance of 363 F g−1 when the scan rate is increased by 10 times. Even at very high frequency of 10 Hz, it retains the specific capacitance value of 150 F g−1, which confirms its higher power capability. Furthermore, during the cycling process, the Coulombic efficiency is better than 90% demonstrating excellent reversibility of CoS electrode.