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A First-Principles Study on the Role of an Al2O3 Overlayer on Fe2O3 for Water Splitting

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journal contribution
posted on 04.12.2015, 00:00 by Ofer Neufeld, Natav Yatom, Maytal Caspary Toroker
Understanding the role of an overlayer material on a catalyst is crucial for improving catalytic activity. Iron­(III) oxide (α-Fe2O3) is a widely studied catalyst commonly used for solar water splitting. Recently, the water splitting efficiency with α-Fe2O3 was enhanced by deposition of an α-Al2O3 overlayer. In order to understand the origin of this improvement, we perform first-principles calculations with density functional theory + U on the α-Fe2O3(0001) surface with an α-Al2O3 surface overlayer. We find catalysis is unfavorable directly over α-Al2O3 and rather takes place over α-Fe2O3 exposed areas. In agreement with experiment, we find that α-Al2O3 coverage decreases the overpotential required for water oxidation on α-Fe2O3. We explain this improvement through the decrease in the work function of α-Fe2O3 upon α-Al2O3 coverage that aids in extracting electrons during the water oxidation reaction. We suggest that selecting an overlayer with a smaller work function than that of the catalyst as a strategy for future development of better catalysts.