Interaction between Ionic Liquids and a Pt(111) Surface Probed by Coadsorbed CO as a Test Molecule

We used temperature-programmed infrared reflection absorption spectroscopy (TP-IRAS) to study the desorption behavior of CO on Pt(111) coadsorbed with four kinds of ionic liquids (ILs), namely 1-butyl-1-methyl-pyrrolidinium-bis(trifluoromethyl-sulfonyl)imide ([C(4)C(1)Pyr][NTf2]), 1-ethyl-3-methyl-imidazolium-bis(trifluoromethyl-sulfonyl)imide ([C(2)C(1)Im][NTf2]), 1- butyl-1-methyl-pyrrolidinium- trifluoro-methane-sulfonate ([C(4)C(1)Pyr][OTf]), and 1-butyl-1-methyl-pyrrolidinium-hexafluorophosphate ([C(4)C(1)Pyr][PF6]). We found that CO desorbs earlier from a Pt(111) surface with coadsorbed ILs than without. In addition, the CO desorption temperature varies between different types of coadsorbed ILs, which follows the order: [C(4)C(1)Pyr][PF6] (365 K) > [C(4)C(1)Pyr][NTf2] (362 K) > [C(2)C(1)Im][NTf2] (352 K) > [C(4)C(1)Pyr][OTf] (348 K). We ascribe the difference in CO desorption temperature to the different interaction strength between ILs and the Pt(111) surface. A stronger IL-Pt(111) interaction leads to a lower CO desorption temperature. We suggest that TP-IRAS experiments of CO coadsorbed with ILs can be a useful method to aid the characterization of the interaction strength between ILs and metal surfaces such as Pt(111).

Automated summary

In this study, TP-IRAS was used to investigate the desorption behavior of CO on Pt(111) coadsorbed with four different ionic liquids (ILs). It was found that CO desorbs earlier from the surface with ILs compared to without. The desorption temperature of CO varied among different ILs, with higher IL-Pt(111) interaction leading to lower desorption temperature.