Photocatalytic Water Oxidation at the GaN (101̅0)−Water Interface

Abstract

Domen has observed that the GaN/ZnO semiconductor alloy serves, in the presence of a sacrificial electron scavenger, as a photocatalyst for solar water oxidation, producing H+ and O2 at the aqueous/semiconductor interface. With a suitable cocatalyst, the same solar photoexcitation process also generates H2 from H+. The active sites, mechanisms, and reaction intermediates are not known. This paper describes atomistic modeling and proposes a sequence of intermediate steps for the water oxidation process at a pure GaN/water interface. Pure GaN is known to be photocatalytically active but only in the UV region, because the semiconductor band gap is 3.4 eV, outside the visible region of the spectrum. However, it serves as an appropriate model system in the absence of more detailed information. A flat (1010) nonpolar surface is chosen to model an active site. Ab initio molecular dynamics simulations examine the fully solvated aqueous interface at ambient temperature. An appropriate cluster model, that includes...