Long-range influence of steps on water adsorption on clean and D-covered Pt surfaces

Abstract

We have examined water desorption from Pt(111) terraces of varying width and its dependence on precoverage by deuterium (D) with temperature programmed desorption studies. We observe distinct water desorption from (100) steps and (111) terraces, with steps providing adsorption sites with a higher binding energy than terraces. Preadsorption of D at the steps causes annihilation of water stabilization at the steps, while it also causes an initial stabilization of water on the (111) terraces. When the (111) terraces also become precovered with D, this water stabilization trend reverses on all surfaces. Destabilization continues for stepped surfaces containing up to 8-atom wide (111) terraces with a (100) step type and these become hydrophobic, in contrast to surfaces with a (110) step type and with the infinite (111) terrace. Our results illustrate how surface defects and a delicate balance between intermolecular forces and the adsorption energy govern hydrophobic vs. hydrophilic behavior, and that the influence of steps on the adsorption of water on nano-structured platinum surfaces has a very long-ranged character.

Double-Stranded Water on Stepped Platinum Surfaces

“…Instead of lines, nearly isoenergetic two-dimensional (2D) structures of tetragons, pentagons, hexagons, and heptagons extending across the step onto the terrace are favored. These structures qualitatively explain the absence of a distinct water desorption feature from (111) terrace sites on Pt(533) [24]. Only a high-temperature desorption peak with a lowtemperature shoulder is observed for water coverages up to a monolayer.…”

Initial stages of water solvation of stepped platinum surfaces

“…Intuitively, the water chain on the step edge can be viewed as an extended one-dimensional defect when comparing it to the regular hexagonal arrangement of water on the (111) terrace. This explains the absence of a fully developed (111)-like desorption feature observed in TPD experiments for the Pt(533) surface and the appearance of such a peak on the larger Pt(755) and (977) surfaces 22 . This means that the actual influence area of the step edge extends to at least one or two rows of platinum atoms onto the terrace (see figure 5a).…”

“…For instance, for hydrogen adsorption the Pt(533) surface can be considered to have a "wide" terrace with clear Pt(111)-like features, while for water adsorption the (111) features are absent 22,45 . For instance, for hydrogen adsorption the Pt(533) surface can be considered to have a "wide" terrace with clear Pt(111)-like features, while for water adsorption the (111) features are absent 22,45 .…”

“…A more recent publication 22 focused on the Pt(755) and Pt(977) surfaces, which have the same step type but an increased terrace width. Our group has previously carried out experimental work on this model surface in ultra-high-vacuum (UHV) 14 using temperature programmed desorption (TPD) measurements.…”

Thermodynamic properties of hydrogen–water adsorption at terraces and steps of Pt(111) vicinal surface electrodes

“…In this sense, results from temperature programmed desorption (TPD) experiments on Pt(111) and vicinal surfaces have shown that pre-adsorption of hydrogen, or deuterium, atoms on Pt(111) causes a stabilization of the adsorbed water on the electrode [37][38][39][40][41], together with a small decrease in the H2Oads coverage. Conversely, on {111} vicinal surfaces it weakens the H2O-metal bonding at {110} and {100} steps and, at high coverages, also at {111} terraces [37,[42][43][44]. In contrast, pre-adsorption of hydrogen on Pt(100) destabilizes the adsorbed water [45].…”