PLASMA TREATED MESOPOROUS TiO\u3csub\u3e2\u3c/sub\u3e THIN FILMS FOR ENERGY STORAGE APPLICATIONS

Mesoporous TiO2 films treated with N2/argon plasma or H2 plasma were studied for use in photoelectrochemical water splitting and electrochemical supercapacitors, respectively. Cubic-ordered mesoporous thin films were prepared by a templated sol-gel method. UV-Vis absorbance spectra indicated that nitrogen plasma treatment significantly reduced the band gap of the TiO2. XPS analysis showed that nitrogen atoms are incorporated into substitutional sites, rather than interstitial. Photocatalytic activity of nitrogen-doped TiO2 films was evaluated by chronoamperometry and linear sweep voltammetry. Compared to pristine TiO2, plasma-treated films showed remarkable photocurrent enhancement (up to 240 times) in both ultraviolet and visible light. XPS of hydrogen plasma-treated films (H-TiO2) showed an increase of Ti3+ content. Electrochemical characterization of the films was performed using both aqueous and organic electrolytes. The capacitance of plasma-treated films was 300 and 176 times higher than the pristine film in aqueous and organic electrolytes, respectively. When subjected to long-term cycling, the H-TiO2 film demonstrated better stability in organic electrolyte versus aqueous electrolyte. This thesis suggests that plasma-treatment of transition metal oxides is a promising strategy to enable the efficient incorporation of nitrogen atoms and oxygen vacancies into metal oxide nanostructures, leading to superior visible-light driven photoelectrochemical hydrogen production and electrochemical capacitance