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, OHterrace formation is favored over OHstep formation, presumably because OH formed at terrace sites is more easily incorporated in a hydrogen bonded network of OH/H2O. This is a gradual process: with increasing theta(O) less OHstep 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.