Potential-Induced Adsorption and Structuring of Water at the Pt(111) Electrode Surface in Contact with an Ionic Liquid.

Water adsorption is important in many fields from surface electrochemistry to electrocatalysis, where molecular-level information is much needed in order to gain a detailed understanding of the role of interfacial water. Here we report on water at Pt(111) surfaces in contact with an [EIMIM][BF4] ionic liquid, which was spectroscopically resolved by using in situ sum-frequency generation (SFG). O-H modes are used to study water adsorption and water structure as a function of electrode potential, while the analysis of C-H modes is used to infer orientational changes of [EMIM] cations at the interface. Different from the bulk where free water molecules are found, SFG spectra provide evidence that an interfacial layer with an extended network of hydrogen-bonded water molecules exists and grows with increasing absolute potential which is used to identify the potential of zero charge at +0.1 V SHE, where a pronounced minimum in O-H intensity is found.