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 (OH+H2O) phase, confirming recent density-functional theory predictions. The reaction O+3H(2)O forms a hexagonal (sqrt[3]xsqrt[3])R30 degrees -(OH+H2O) lattice with a weak (3x3) superstructure, caused by ordering of the hydrogen bonds. The mixed overlayer can accommodate a range of H(2)O/OH compositions but becomes less stable as the H2O content is reduced, causing defects in the hydrogen-bonding network that lift the (3 x 3) superstructure and destabilize the overlayer.

The structure of mixed H2O–OH monolayer films on Ru(0001)

“…This is in accordance with previous findings summarized in the so-called 2D water rules 32,33 and also with results for the extended H-bonded mixed H 2 O / OH phases on Pt͑111͒. [6][7][8][9][10][11][12] The oxygen atoms in the H 2 O and OH molecules are nearly coplanar, with a small corrugation of approximately 0.2 Å, which can reach a value of 0.5 Å at the edges. In a separate study of the water structures formed on Pd and Ru at temperatures below 140 K, we observed that individual water molecules are often attached to the edges of single hexamers or clusters containing several hexagons.…”

“…It also shows that the layer has a domain structure with narrow dimensions in one direction. [3][4][5] This is in contrast to the extended twodimensional ͑2D͒ hydrogen ͑H͒-bonding network formed on Pt͑111͒ [6][7][8][9][10][11][12] and with similar models on Ru͑0001͒ put forward based on theoretical modeling. 1,2 The detailed structure of the stable H 2 O -OH phase on Ru͑0001͒ remains unclear to date.…”

“…16 In the so-called bifunctional mechanism, 17 the proposed lower activation barrier for water dissociation on Ru sites compared to Pt sites facilitates the generation of OH ads which reduces the CO coverage by oxidation to CO 2 . 17,18 Compared to the large body of work accumulated on the water-Pt interface and the mixed H 2 O -OH intermediate phases involved in the reaction H 2 +O 2 → H 2 O, and water splitting reactions for H 2 production, [6][7][8][9][10][11][12][19][20][21] very little is known about the local structure and chemical properties of the mixed H 2 O -OH phase on Ru. Establishing the nature of this phase has become increasingly relevant in view of reports that a low coverage of Pt islands on Ru-surfaces is more electrocatalytically active than the Pt/Ru alloy surface.…”

Water clustering on nanostructured iron oxide films

“…A similar effect has been observed in mixed OH/H 2 O monolayers on Pt(111) (OH in this case referring to a distinct molecule coadsorbed with water), where very stable, ordered hexagonal structures form at a 1:1 (OH:H 2 O) ratio as a result of alternating H-bond donor (H 2 O) and acceptor (OH) molecules 47,48 . Such a tendency towards donor/acceptor ordering is expected to occur as a general feature of water adsorption on hydroxylated oxide surfaces, to the extent this is compatible with the geometric features of the specific surface.…”

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…In the H 2 O*/HO* superstructure, half of the water molecules lie in a plane approximately parallel to the surface, and the other water molecules lie in a plane perpendicular to the surface with one hydrogen atom pointing away from the surface. 61,[206][207][208][209][210] …”