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Water Dissociation and Further Hydroxylation of Perfect and Defective Polar ZnO Model Surfaces
journal contribution
posted on 2018-08-07, 00:00 authored by Mathilde Iachella, Jérémy Cure, Mehdi Djafari Rouhani, Yves Chabal, Carole Rossi, Alain EstèveZnO
is a high-band gap semiconductor material important for microelectronic
and catalytic applications, such as water splitting among others.
Although the nonpolar face of ZnO has been well-studied, its polar
faces (Zn- and O-terminated) are less studied because of intrinsic
difficulties to the model. Here, we combine density functional theory
calculations and analytical modelling to determine the thermodynamics
of the water molecule interaction with perfect ZnO polar model surfaces,
(0001) and (0001̅) surfaces (p-Zn and p-O). Defects (oxygen
vacancies, pits, and missing oxygen rows) are also investigated. Adsorption,
dissociation, surface migration, and agglomeration are considered.
We find that H2O preferentially adsorbs and dissociates
on Zn atoms on p-Zn and at defects on p-O. At room temperature, water
is found to spontaneously dissociate, except for p-O, in which dissociation
is endothermic. After dissociation, the resulting protons either bind
to surface oxygen atoms or to zinc atoms to form hydrides. Migration
of H and OH is limited on p-Zn with moderate barriers and absent on
p-O. Interestingly, further agglomeration or islanding of OH species
is inhibited by repulsive OH–OH electrostatic forces. Consequently,
although polar surfaces are highly reactive with water, they cannot
sustain high OH coverages, unless highly defective. This limitation
is one obstacle to ZnO catalytic activity, pointing to the need to
tune temperature and pressure conditions.
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dissociationOH coveragesagglomerationwater molecule interactiontheory calculationsZn atomsform hydridesnonpolar facewater Dissociationpressure conditionswater splittinghigh-band gap semiconductor materialsurface migrationtune temperaturemodel surfacesoxygen rowsDefective Polar ZnO Model Surfaces ZnOH 2 Osurface oxygen atomsp-ZnOH speciesoxygen vacanciesroom temperaturezinc atomsp-O
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