Abstract
Hematite is a promising and extensively investigated material for various photoelectrochemical (PEC) processes for energy conversion and storage, in particular for oxidation reactions. Thermal treatments during synthesis of hematite are found to affect the performance of hematite electrodes considerably. Herein, we present hematite thin films fabricated via one-step oxidation of Fe by rapid thermal processing (RTP). In particular, we investigate the effect of oxidation temperature on the PEC properties of hematite. Films prepared at 750 °C show the highest activity towards water oxidation. These films show the largest average grain size and the highest charge carrier density, as determined from electron microscopy and impedance spectroscopy analysis. We believe that the fast processing enabled by RTP makes this technique a preferred method for investigation of novel materials and architectures, potentially also on nanostructured electrodes, where retaining high surface area is crucial to maximize performance.
Highlights
Fe2O3 is synthesized in the laboratory using a wide range of chemical and physical processes
We retained the Fe2O3 thickness of 40 nm and investigated the effect of varying the oxidation temperature Tox in an rapid thermal processing (RTP) step on the physical and PEC properties of the fabricated electrodes
We presented RTP as convenient method to fabricate thin films of Fe2O3 in one-step oxidation of Fe. 40 nm thick Fe2O3 films oxidized at 750 °C delivered the maximum values of photocurrent density resulting from water oxidation
Summary
Fe2O3 is synthesized in the laboratory using a wide range of chemical and physical processes. A second annealing step is performed at temperatures up to 750 °C or 800 °C, in order to maximize performance[8] These heating steps are usually carried out in a tube or box furnace, a procedure that has the following disadvantages: (i) large temperature gradients, making temperature accuracy and control problematic; (ii) contamination from other materials, unless high purity dedicated furnaces are used; and (iii) relatively long ramp-up times. Ramp-up rates are normally of the order of 10 °C s−1, but can be as high as 400 °C s−1 This results in considerable time (and energy) savings as compared with tube/box furnace annealing. We have focused on characterizing the physical and electrochemical properties of Fe2O3 films oxidized at different temperatures. Our physical and electrochemical characterization of the electrodes indicates a strong correlation between properties such as grain size and majority charge carrier density and PEC performance
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