Thermodynamics of Hydrogen Adsorption and Incorporation at the ZnO(10(1)over-bar0) Surface

Hydrogen, as a surface adsorbate and a bulk impurity, plays an important role in determining the electronic and catalytic properties of zinc oxide, but the nature of the interaction between these two species remains poorly understood. In this work we study the thermodynamics of hydrogen adsorption on zinc oxides (10 (1) over bar0)) surface. We find that the adsorption of hydrogen on the oxygen sites only, as observed in several previous experiments, is metastable and consider the thermodynamics of exchange of hydrogen between surface and bulk as an explanatory mechanism. We propose that the hydrogen termination of zinc oxide at room temperature is strongly dependent on the hydrogen concentration of the interior and thus that surface reactions involving hydrogen may proceed in an unreliable way depending on the history of the sample, particularly for ZnO in nanostructures.