Nanostructured hematite photoelectrochemical electrodes prepared by the low temperature thermal oxidation of iron

We report on a facile low temperature method for the preparation of high surface area, nanostructured alpha-Fe(2)O(3) (hematite) thin films and their application as photoelectrochemical (PEC) water splitting electrodes. The hematite films are fabricated by thermal oxidation in air of DC sputter deposited iron films at temperatures as low as 255 degrees C. This method results in films with a higher surface area than typically obtained by directly sputtering alpha-Fe(2)O(3). It is shown that beyond a minimum iron thickness, alpha-Fe(2)O(3) nanowires result upon thermal treatment in atmospheric conditions. Structural and optical characteristics of the resulting films are analyzed. The oxidation process is studied in detail and correlated to the photoelectrical properties. The Fe films oxidize in stages via Fe-oxide layers of increasing oxidation states. Resulting photoelectrochemical performance of fully oxidized films is a balance between optical absorption and charge collection, which varies with film thickness. The optimum film achieved a net photocurrent density of 0.18 mA/cm(2) in 1 M NaOH at 1.23 V vs. RHE under simulated AM 1.5 sunlight, amongst the highest values reported for undoped hematite films produced at low temperature. (C) 2011 Elsevier B.V. All rights reserved.