First Principles Calculation of CO and H₂ Adsorption on Strained Pt Surface

Abstract

First principles calculations are carried out to analyze adsorption of CO and H₂ molecules on a Pt (111) surface and the effect of surface strain on the adsorption energy. A CO molecule is more adsorptive on the Pt (111) surface than a H₂ molecule under an ordinary condition. Surface expansion enhances CO poisoning on a Pt (111) surface. On the contrary, a compressive strain reduces adsorptive strength of a CO molecule. Similar tendency is also found in adsorption of a H₂ molecule on the bridge, fcc-hollow, and hcp-hollow sites. However, H₂ adsorption on the top site is less affected by the strain. As a consequence, the difference of adsorption energies between CO and H₂ molecules becomes smaller when compressive strain is introduced into the Pt (111) surface. Based on thermodynamics, surface coverage ratio is quantitatively evaluated with taking into account the effect of surface strain and partial pressure of gas phase. It is revealed that compressive strain improves probability of H₂ adsorption on Pt surface.