Hydrogen Bonding in MixedOH+H2OOverlayers on Pt(111)

Abstract

The stability of OH on Pt(111) has been investigated to determine the role of hydrogen bonding in stabilizing the overlayer. We find that the optimal structure is a mixed ($\mathrm{O}\mathrm{H}+{\mathrm{H}}_{2}\mathrm{O}$) phase, confirming recent density-functional theory predictions. The reaction $\mathrm{O}+3{\mathrm{H}}_{2}\mathrm{O}$ forms a hexagonal $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$-($\mathrm{O}\mathrm{H}+{\mathrm{H}}_{2}\mathrm{O}$) lattice with a weak ($3\ifmmode\times\else\texttimes\fi{}3$) superstructure, caused by ordering of the hydrogen bonds. The mixed overlayer can accommodate a range of ${\mathrm{H}}_{2}\mathrm{O}/\mathrm{O}\mathrm{H}$ compositions but becomes less stable as the ${\mathrm{H}}_{2}\mathrm{O}$ content is reduced, causing defects in the hydrogen-bonding network that lift the ($3\ifmmode\times\else\texttimes\fi{}3$) superstructure and destabilize the overlayer.