Thermodynamics of Hydrogen Adsorption and Incorporation at the ZnO(101̅0) Surface

Abstract

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 oxide’s (100)) 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.

Morphology of Zinc Oxide Nanoparticles and Nanowires: Role of Surface and Edge Energies

“…Termination with some other chemical species (for instance in solution-based processes) may change the relative surface energies of the (100) and (110) surfaces, changing the Wulff-optimal shape from. It should be noted, however, that the bonding behavior of the (110) and (100) surfaces is very similar; for instance the adsorption energy of hydrogen on the (100) versus the (110) form is found to differ by only 0.03 eV/atom . Further work may be able to better predict whether adsorbates may stabilize one facet over another.…”

“…We ignore the temperature-dependent vibrational terms in the energy of formation. Vibrational terms were recently shown to be insignificant even for the energetics of hydrogenterminated ZnO surfaces, 20 and should be even less so for the bare surfaces where hydrogen is not present.…”

Single Molecular Reaction of Water on a ZnO Surface

“…Very recently, we report that the preadsorbed H atoms on the ZnO(101̅0) surface can significantly promote the heterolytic adsorption of H 2 . , In principle, the HO (s) species produced via water dissociation have no difference from those obtained from the direct adsorption of atomic hydrogen. , To verify the effects of the water dissociation over the adsorption of H 2 , we first dissociate the water molecules with tip pulsing and then examined the same molecules after in situ exposing to H 2 . Figure a presents the original ZnO(101̅0) covered with preadsorbed M-H 2 O.…”

Solvent assisted evolution and growth mechanism of zero to three dimensional ZnO nanostructures for dye sensitized solar cell applications

“…The figure indicate that all the particles exhibit a preferential growth along [100] direction of ZnO. The ZnO crystal growth in the plane (100) is less compared to other planes and for ZnO wurtzite structure, (100) nonpolar surface has the lowest surface energy and better stablility 8 , 14 , 16 , 31 , 32 . Upon variation of all these growth parameters, the ZnO nanodots were found to prefer the growth in a significantly stable (100) surface.…”