Synthesis of Co ₃O ₄ nanosheets via electrodeposition followed by ozone treatment and their application to high-performance supercapacitors

A thin film of Co ₃O ₄ nanosheets is electrodeposited on a flexible Ti substrate by a one-step potentiostatic method, followed by an UV-ozone treatment for 30 min. The films before and after the UV-ozone treatment are characterized with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The film is composed of Co(OH) ₂ before UV-ozone treatment, and of Co ₃O ₄ after the treatment. The morphologies of both films are examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The obtained films are composed of nanosheets, and there is no change in their sheet-like morphology before and after the UV-ozone treatment. When applied for a supercapacitor, the Co ₃O ₄ modified Ti electrode (Co ₃O ₄/Ti) shows a far higher capacitance than that of the Co(OH) ₂ modified Ti electrode. The electrodeposition time and NaOH concentration in the electrolyte are optimized. A remarkably high specific capacitance of 1033.3 F g ^-1 is obtained for the Co ₃O ₄ thin film at a charge-discharge current density of 2.5 A g ^-1. The long-term stability data shows that there is still 77% of specific capacitance remaining after 3000 repeated charge-discharge cycles. The high specific capacitance and long-term stability suggest the potential use of Co ₃O ₄/Ti for making a flexible supercapacitor.