Comparison of a-Fe2O3 electrodes grown by direct plasma and thermal oxidation of iron for photoelectrochemical water splitting.
Date on Master's Thesis/Doctoral Dissertation
Sunkara, Mahendra K.
Ferric oxide; Electrodes
Iron oxide, Fe2O3, is a promising material for water splitting reaction using solar energy due to its stability and optimal bandgap of 2 eV. Even the recent efforts, however, using Fe2O3 thin film materials reported low efficiencies due to poor carrier transport within these films. A novel plasma oxidation method was used to synthesize arrays of a-Fe2O3 which are single crystal and have highly ordered oxygen vacancy planes. As one-dimensional nanostructures, these nanowires offer many other benefits to photoelectrochemical electrolysis, including high surface area, reduced charge carrier diffusion distance, and a preferential direction for charge diffusion. Furthermore, due to the ordered-oxygen vacancy planes in these nanowires, the high resistivity that has plagued this material may become a non-issue. The photoelectrochemical performance of these samples was compared to that of nanowire (and nanobelt) arrays grown by thermal oxidation of iron foils. Hematite samples grown by plasma oxidation were found to have considerably greater photoactivity than by thermal oxidation. This was attributed to the presence of a large (7.5 µm) mixed-phase interfacial layer in the latter, wherein the charge carriers are lost to recombination. Due to the fast growth process in plasma oxidation, the interfacial layer is much thinner (1 µm) and may in fact contain only hematite, rather than a mixed phase. Studies are currently underway to determine the interfacial layer composition. It is concluded that further studies of hematite for photoelectrochemical electrolysis should be performed using nanowire arrays grown by direct plasma oxidation.
Chernomordik, Boris David, "Comparison of a-Fe2O3 electrodes grown by direct plasma and thermal oxidation of iron for photoelectrochemical water splitting." (2009). Electronic Theses and Dissertations. Paper 240.