Density functional theory study on the adsorption and decomposition of H ₂ O on clean and oxygen-modified Pd (1 0 0) surface

Based on density functional theory together with periodic slab models, the adsorption and the corresponding dehydrogenation reaction of H ₂ O on clean and oxygen modified Pd (1 0 0) have been investigated. The preferential sites for H ₂ O, OH, O, and H were obtained on the surfaces. According to the optimized structural and energetic properties, it was found that H ₂ O prefers to adsorb on the top site with weak adsorption energy (physisorption), whereas O and H atoms are prone to adsorb on the hollow site and OH occupies the bridge site. In addition, this work identified the optimum configurations for the relevant co-adsorption groups. The results confirmed that co-adsorption tends to weaken the adsorbate-substrate interaction due to the existence of oxygen atom, and that the OH group, O and H atoms are less stable on oxygen-covered Pd (1 0 0) surface than on the clean surface. Finally, the transition states and related barrier energies were ascertained to analyze the dehydrogenation mechanism of H ₂ O. Water decomposition was found favorable on O-covered Pd (1 0 0) surface (0.49 eV), in agreement with the experimental observations. This result indicated that the joining of O _ads could reduce the barrier energy and facilitate the decomposition of H ₂ O. Besides, the distinct differences over Pd (1 1 1) and Pd (1 0 0) surface implied that water decomposition over Pd-based catalysts is a structure-sensitive reaction.