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

Abstract

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.

Cations of Ionic Liquid Electrolytes Can Act as a Promoter for CO2 Electrocatalysis through Reactive Intermediates and Electrostatic Stabilization

“…Clearly, the choice of the anion, e.g., NTf 2 in this work as opposed to [BF 4 ] or [DCA] in previous works, , has also a major effect on the CO formation from CO 2 RR and can lead to substantially different CO coverages at moderately low cathodic potentials of −0.4 to −0.7 V. This can be related to the strong anion–water interaction that plays a key role in the water accumulation at the interface . Kobayashi et al demonstrated that for ILs with a high packing fraction and hydrophilicity, the infusion of water in the interfacial layer can be entropically favored, which was confirmed by in situ vibrational SFG spectroscopy of the Pt(111)/[EMIM]­[BF 4 ] interface, where the co-adsorption of water at the interface leads to an extended and hydrogen-bonded interfacial layer of water molecules . Clearly, the active C2 position at the imidazolium ring as discussed in the Introduction section is not the only factor that can lower the overpotential for CO formation as well as the onset for other CO 2 RR.…”

“…42 Kobayashi et al 43 demonstrated that for ILs with a high packing fraction and hydrophilicity, the infusion of water in the interfacial layer can be entropically favored, which was confirmed by in situ vibrational SFG spectroscopy of the Pt(111)/[EMIM][BF 4 ] interface, where the co-adsorption of water at the interface leads to an extended and hydrogen-bonded interfacial layer of water molecules. 44 Clearly, the active C2 position at the imidazolium ring as discussed in the Introduction section is In Figure 4a, we focus on the FT-IRAS spectra of Pt electrodes in a CO 2 -saturated [BMIM][NTf 2 ] electrolyte that contained 0.5 M H 2 O. After reaching −0.45 V during the cathodic potential sweep, a vibrational band in the carbonyl stretching region starts to rise at 1672 cm −1 and is accompanied by an absorption loss at 2343 cm −1 that can be attributed to a consumption of CO 2 due to ongoing CO 2 RR.…”

Electrical Double Layer Structure in Ionic Liquids and Its Importance for Supercapacitor, Battery, Sensing, and Lubrication Applications

“…SFG investigations of water in [C 2 mim][BF 4 ] at a Pt(111) surface revealed that the electrode potential causes free water molecules from the bulk to form a network of hydrogen-bonded water molecules at the interface (see Figure 2). 34 By using water electrosorption as a "reporter molecule", the authors determined the potential of zero charge (PZC) of Pt in the IL to be +0.1 V versus a standard hydrogen electrode (SHE). These diverse studies reveal the complicated behavior of water at the EDL in ILs, presumably caused by strong bonding interactions with the ions.…”

The Structure of the Electric Double Layer of the Protic Ionic Liquid [Dema][TfO] Analyzed by Atomic Force Spectroscopy

“…In many ionic liquids, it has been found that water leads to distortion and weakening of the interface structure [ 27 , 28 ]. This has been attributed to the preferential adsorption of water on the electrified electrode, as well as to the interaction between the H 2 O molecules and ions of the PIL via hydrogen bonds [ 29 ]. However, in some ionic liquids, the presence of water was found to be a prerequisite for the formation of a detectable structured interface layer [ 30 ].…”