Hierarchical CoO@CoS nanowall structures assembled by many nanosheets for high performance asymmetric supercapacitors.

Herein, we report hierarchical CoO@CoS nanowalls assembled by many nanosheets. The as-synthesized products are characterized in detail using various characterization methods. They can be directly used as supercapacitor electrodes with excellent electrochemical performance due to the synergy effect between CoO and CoS. Furthermore, a flexible asymmetric supercapacitor is fabricated by using the as-synthesized CoO@CoS structures as the cathode and the active carbon as the anode, which reveals a specific capacitance of 266.6 mF cm at a current density of 4 mA cm. In addition, the supercapacitor shows an excellent capacity retention rate of 86.5% after 10 000 cycles at a current density of 10 mA cm. Finally, three supercapacitor devices connected in series can light a blue LED lamp for 5 min.