Facile hydrothermal synthesis of cobaltosic sulfide nanorods for high performance supercapacitors.

With high reactivity, electrical conductivity, theoretical specific capacitance and well redox reversibility, transition metal sulfides are considered as a promising anode material for supercapacitors. Hence, we designed a simple two-step hydrothermal process to grow CoS nanorod arrays on flexible carbon cloth substrates. Benefited from the larger specific surface area of nanoarrays, the binder-free CoS electrode demonstrates a higher specific capacity of 1.97 F cm at a current density of 2 mA cm, while the CoO electrode has a capacity of only 0.07 F cm at the same current density. Surprisingly, at a high scan rate of 200 mV s, the synthesized CoS electrode still maintains almost 100% of its initial capacitance after 5000 cycles. Moreover, when using the prepared CoS and MnO electrode as the anode and cathode, the fabricated flexible supercapacitor obtains a high volumetric energy density of 0.87 mW h cm (power density of 0.78 W cm) and a peak power density of 0.89 W cm (energy density of 0.50 mW h cm). The excellent electrochemical properties imply that there is a large market for the prepared materials in flexible energy storage devices.