Hierarchical Co 3 O 4 @Co 9 S 8 nanowall structures assembled by many nanosheets for high performance asymmetric supercapacitors.

Herein, we report hierarchical Co 3 O 4 @Co 9 S 8 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 Co 3 O 4 and Co 9 S 8 . Furthermore, a flexible asymmetric supercapacitor is fabricated by using the as-synthesized Co 3 O 4 @Co 9 S 8 structures as the cathode and the active carbon as the anode, which reveals a specific capacitance of 266.6 mF cm -2 at a current density of 4 mA cm -2 . 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 -2 . Finally, three supercapacitor devices connected in series can light a blue LED lamp for 5 min.