Hematite has long been considered a potential candidate for photocatalytic water splitting because of its favourable valence band edge, reasonably low band gap, high stability and low cost. Unfortunately, only very poor conversion efficiencies have been achieved, which is generally attributed to a short minority carrier collection length. In principle, the short collection length can be overcome through nanostructuring the electrode. Thin films represent ideal model systems of nanostructured electrodes which allow for detailed mechanistic investigations. We utilize atomic layer deposition (ALD) to make conformal thin film hematite electrodes with controllable thickness for this purpose. Films less than 20 nm thick, however, are plagued by a dead layer near the substrate contact. We found that the dead layer can be alleviated by the incorporation of dopant atoms in the hematite film or by alteration of the contacting substrate. In both cases significantly improved water oxidation efficiency was observed, however the cause of the improvement was distinct. A series of photoelectrochemical and spectroscopic measurements were employed to elucidate the cause of the improved photoactivity of these hematite thin films. This performance enhancement was determined to be a combination of improved bulk properties which improved charge separation and surface properties which improved the water oxidation efficiency. In addition, recent results of the effect of adding water oxidation catalysts to the hematite surface as well as alternative metal oxide films will be presented.

Photoelectrochemical investigation of solar energy storage via water splitting with metal oxide electrodes

247th National Meeting (2014)

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