Hematite and titania inverse opals and inverse photonic glass nanostructured films for solar energy conversion and water splitting -

Abstract

This thesis consists of three different studies. In one study, the photoelectrochemical effects of order vs disorder was investigated at monodispersed disordered inverse opal and ordered inverse opals with and without coupling to nc-TiO₂ film under front wall and back wall illumination. While inverse opals (600-i-TiO₂-o) show only slight enhancement at the red edge of stop band (660-680 nm), inverse glass (i-TiO₂-g) when not coupled to nc-TiO₂ showed significant enhancement (compared to the conventional nc-TiO₂) in the entire spectrum. The observed enhancement was attributed to multiple internal scattering in the film that leads to longer light-matter interaction. The gain was similarly observed under front wall illumination and back wall illumination. Coupling nc-TiO₂ to i-TiO₂-g film on the other hand failed to enhance energy conversion as in the case of nc-TiO₂-600-i-TiO₂-o. Internal scattering and back scattering at nc-TiO₂-i-TiO₂-g hindered light from reaching the nc-TiO₂ layer where most of the dye is adsorbed and resulted in lower enhancements at the red edge of the stop band. Photonic effects due to the presence of order are causing localization of light within the nc-TiO₂ coupled to 600-i-TiO₂-o and that this effect does not persist in the presence of significant disorder. In a second study, the effect of doping NiBi films with iron for catalyzing the oxygen evolution reaction was studied. Ni₄₀Fe₆₀Bi and Ni₆₀Fe₄₀Bi exhibited the highest turnover frequencies at high overpotentials whether anodized or non-anodized and hence had the highest catalytic activity, while the slightly doped Ni90Fe10Bi films had similar catalytic activity as NiBi films. To further confirm the catalytic effect of iron in Ni1-xFexBi films, Ni₄₀Fe₆₀Bi and Ni₆₀Fe₄₀Bi films were also compared with thin NiBi having similar amounts of Ni. The higher turnover f