A detailed TPD study of H2O and pre-adsorbed O on the stepped Pt(553) surface

Water molecules desorbing from the bare Pt(553) surface desorb in a three peak structure, associated with, respectively, desorption from step and terrace sites and the water multilayer. Upon pre-covering the step sites with O ad we mainly observe OH formation on step sites. When terrace sites are also pre-covered with O ad , OH terrace formation is favored over OH step formation, presumably because OH formed at terrace sites is more easily incorporated in a hydrogen bonded network of OH/H 2 O. This is a gradual process: with increasing O less OH step is formed. Thus, in spite of the fact that OH at step sites has a higher binding energy than OH at terrace sites, the possibility of the formation of OH at terrace sites actually inhibits the formation of OH at step sites, leaving O step as the most stable water dissociation product on the step. Upon co-adsorption of O ad and H 2 O on Pt(553), the amount of OH terrace increases with increasing O at the expense of OH step .