Thermal oxidation synthesis of crystalline iron-oxide nanowires on low-cost steel substrates for solar water splitting

Iron-oxide and in particular its crystallographic phase hematite ( α -Fe₂O₃) is a promising candidate for non-toxic, earth abundant and low cost photo-anodes in the field of photo-electrochemical water splitting. We report here on the synthesis of α -Fe₂O₃ nanowires by thermal oxidation of low-cost steel substrates. Nanowires grown in this manner exhibit often a blade-like shape but can also possess a wire-like geometry partly decorated at their tip with an iron-rich ellipsoidal head consisting also of crystalline iron-oxide. We show furthermore that these ellipsoidal heads represent suitable growth sites leading in some cases to an additional growth of so-called antenna nanowires. Besides nanowires also nanoflakes were frequently observed at the surface. We discuss the influence of the oxidation temperature and other synthesis parameters as well as dispute the current growth models. Finally, we show that our α -Fe₂O₃ nanostructures on steel are also photo-electrochemically active supporting in principle their use as photo-anode material. (paper)