Synthesis of Co3O4 nanosheets via electrodeposition followed by ozone treatment and their application to high-performance supercapacitors

► Thin film of Co(OH)2 nanosheets is converted to Co3O4 by UV-ozone treatment. ► Synthesis of Co3O4 film is done at low temperature on flexible substrate. ► The specific capacitance of the film after UV-ozone treatment reaches 1033.3 F g−1. ► The capacitance is more than 10 times higher than the film before the treatment. ► Still 77% of specific capacitance remains after 3000 cycles of charge/discharge.