Photoelectrochemical Investigation of Water Splitting with Hematite Thin Film Electrodes
Thomas Hamann a
a Michigan State University, 411 Chemistry Building, Michigan State University, East Lansing, 4824, United States
Invited Speaker, Thomas Hamann, presentation 012
Publication date: 31st March 2013

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. Even with such idealized nanostructures, the internal conversion efficiencies are far from ideal. There have been many examples of improving the performance by the incorporation of dopant atoms in hematite, however the physical cause of the enhancement is not clear. A series of electrochemical, photoelectrochemical and impedance spectroscopy measurements were employed to elucidate the cause of the improved photoactivity of doped hematite thin films. This performance enhancement was determined to be a combination of improved bulk properties (hole collection length) and surface properties (water oxidation efficiency). In addition to bulk properties, the sub-optimal water oxidation efficiency at hematite electrodes constrains the overall water splitting efficiency. Recent results of elucidating the water oxidation mechanism at hematite surfaces will be discussed. In addition, results of adding catalysts to the hematite surface in order to improve the water oxidation efficiency will be presented.

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