title: Photo-driven oxidation of water on α-Fe2O3 surfaces: an ab initio study.
abstract: Adopting the theoretical scheme developed by the Nørskov group [see, for example, Nørskov et al., J. Phys. Chem. B 108, 17886 (2004)], we conducted a density functional theory study of photo-driven oxidation processes of water on various terminations of the clean hematite (α-Fe2O3) (0001) surface, explicitly taking into account the strong correlation among the 3d states of iron through the Hubbard U parameter. Six best-known terminations, namely, Fe−Fe−O3− (we call S1), O−Fe−Fe−(S2), O2−Fe−Fe−(S3), O3−Fe−Fe− (S4), Fe−O3−Fe− (S5), and O−Fe−O3−(S6), are first exposed to water, the stability of resulting surfaces is investigated under photoelectrochemical conditions by considering different chemical reactions (and their reaction free energies) that lead to surfaces covered by O atoms or/and OH groups. Assuming that the water splitting reaction is driven by the redox potential for photogenerated holes with respect to the normal hydrogen electrode, UVB, at voltage larger than UVB, most 3-oxygen terminated substrates are stable. These results thus suggest that the surface, hydroxylated in the dark, should release protons under illumination. Considering the surface free energy of all the possible terminations shows that O3–S5 and O3–S1 are the most thermodynamically stable. While water oxidation process on the former requires an overpotential of 1.22 V, only 0.84 V is needed on the latter.
authors: The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy.
authors: Manh-Thuong
authors: MT
authors: Nguyen
authors: The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy.
authors: Nicola
authors: N
authors: Seriani
authors: CNR-IOM DEMOCRITOS, c/o SISSA, via Bonomea 265, 34136 Trieste, Italy.
authors: Simone
authors: S
authors: Piccinin
authors: The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy and CNR-IOM DEMOCRITOS Simulation Center, 34136 Trieste, Italy.
authors: Ralph
authors: R
authors: Gebauer