Dresden 2020 – scientific programme

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O: Fachverband Oberflächenphysik

O 84: Poster Session - Solid-Liquid Interfaces: Reactions and Electrochemisty

O 84.7: Poster

Wednesday, March 18, 2020, 18:15–20:00, P2/EG

Sum-Frequency Generation Spectroscopy of Water at [EMIM][BF4]/Platinum Electrolyte/Electrode interfaces — •Andre Kemna and Björn Braunschweig — Institute of Physical Chemistry, WWU Münster, 48149 Münster, Germany

In room-temperature ionic liquids (RTIL), the presence of water can heavily influence reactions at the electrode/electrolyte interface. In case of CO2 reduction reactions, water influences the catalysis of CO2 substantially. In order to gain a detailed molecular-level understanding, in situ studies of the interfacial water structure as a function of electrode potential are desirable. Using vibrational sum-frequency generation (SFG), we have now revealed the presence and structure of water at platinum interfaces in contact with a RTIL and as a function of electrode potential. At the [EMIM][BF4]/Pt interface, the addition of water leads first to negligible O-H contributions to the SFG spectra at open circuit potentials, but to broad bands at 3200 and 3450 cm^-1 when the potential control is established. These bands are attributable to O-H stretching bands from hydrogen bonded interfacial molecules. Because the SFG intensity of the O-H bands increases during a cathodic sweep of the electrode potential, we propose that the interfacial layer of [EMIM][BF4] in contact with a Pt electrode can be enriched with water molecules at low electrode potentials. In order to investigate the interaction of water at RTIL interfaces in more detail, we have applied SFG to the liquid/gas interface as an easily accessible model system. Here we demonstrate that the enrichment of water at RTIL interfaces strongly depends on the chemical identity of the cation.