Temperature Induced Diffusion of Sn and Si in Hematite and Implications for Photocatalytic Water Splitting Applications
(English)Manuscript (preprint) (Other academic)
The performance of Hematite (α-Fe2O3) for the water oxidation step in solar hydrogen production is dependent upon annealing of the material. In this study, these effects are investigated in terms of temperature induced diffusion of Sn and Si from the substrate into thin films of hematite by using hard X-ray photoelectron spectroscopy (HAXPES). Here, HAXPES is used for the first time to characterize a buried interface between a conducting substrate and a nanostructured thin film overlayer by diffusion upon annealing. This process is prototypical for the large class of photoelectrochemical devices that uses indium and fluorine doped tin oxide as substrates where the device is subsequently annealed. Indeed, we observe that: diffusion of Sn and Si is significant, already at 550 °C; the photocatalytic efficiency of the hematite films increased, from low values to 0.23 mA/cm2; annealing in air preserves the hematite phase, while annealing in vacuum induces a phase transition into magnetite, which impairs the photocatalytic performance. The increase in efficiency is explained in terms of an improvement of the quantum efficiency of the oxygen evolution reaction accompanied by a slight improvement in charge carrier transport.
HAXPES, diffusion, hematite, PEC, water splitting
IdentifiersURN: urn:nbn:se:uu:diva-232946OAI: oai:DiVA.org:uu-232946DiVA: diva2:750277