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 Co4S3 nanorod arrays in situ on flexible carbon cloth substrates. Benefited from the larger specific surface area of nanoarrays, the binder-free Co4S3 electrode demonstrates a higher specific capacity of 1.97 F cm-2 at a current density of 2 mA cm-2, while the Co3O4 electrode has a capacity of only 0.07 F cm-2 at the same current density. Surprisingly, at a high scan rate of 200 mV s-1, the synthesized Co4S3 electrode still maintains almost 100% of its initial capacitance after 5000 cycles. Moreover, when using the prepared Co4S3 and MnO2 electrode as the anode and cathode, the fabricated flexible supercapacitor obtains a high volumetric energy density of 0.87 mW h cm-3 (power density of 0.78 W cm-3) and a peak power density of 0.89 W cm-3 (energy density of 0.50 mW h cm-3). The excellent electrochemical properties imply that there is a large market for the prepared materials in flexible energy storage devices.