Water Co‐Adsorption in Ultrathin Films of Ionic Liquids on Pt(111)

The influence of pre‐adsorbed water (D 2 O) on the growth, adsorption, orientation, and thermal behavior of two ionic liquids (ILs) on Pt(111) was studied within the SCILL (solid catalyst with ionic liquid layer) concept. Nonfunctionalized [C 1 C 1 Im][Tf 2 N] and nitrile‐functionalized [C 3 CNC 1 Im][Tf 2 N] were deposited at ∼100 K onto clean Pt(111) or onto single‐layer and multilayer crystalline (CI) or amorphous (ASW) D 2 O films and analyzed at various temperatures by angle‐resolved X‐ray photoelectron spectroscopy (ARXPS). On both clean and D 2 O‐covered Pt(111), the ILs initially grow in a 2D layer‐by‐layer mode, forming a closed wetting layer at ≈ 0.5 ML IL coverage, followed by moderate 3D growth above 0.8–1.0 ML. At 100 K, the ILs partially displace D 2 O from the Pt surface, yielding co‐adsorption structures where IL contacts Pt(111) directly and is also located in a second layer. [Tf 2 N] − anions adsorb in cis‐configuration with oxygen atoms toward the surface, while the cations adopt mixed parallel and tilted orientations. Heating to 130 K induces rearrangement, increasing direct IL–Pt(111) contact by favoring parallel cation alignment. Co‐adsorbed D 2 O remains but desorbs at ≈10 K lower temperature, indicating weaker binding to Pt. The similar interfacial behavior of both ILs shows that the nitrile group does not significantly influence adsorption geometry or thermal stability.