Interaction of Ester-Functionalized Ionic Liquids with Atomically-Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability

Tao Xu; Tobias Waehler; Julia Vecchietti; Adrian Bonivardi; Tanja Bauer; Johannes Schwegler; Peter S Schulz; Peter Wasserscheid; Joerg Libuda

doi:10.1002/cphc.201700843

Interaction of Ester-Functionalized Ionic Liquids with Atomically-Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability

Chemphyschem. 2017 Dec 6;18(23):3443-3453. doi: 10.1002/cphc.201700843. Epub 2017 Oct 13.

Authors

Tao Xu¹, Tobias Waehler¹, Julia Vecchietti², Adrian Bonivardi², Tanja Bauer¹, Johannes Schwegler³, Peter S Schulz³, Peter Wasserscheid³, Joerg Libuda^{1

4}

Affiliations

¹ Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax: +49 9131 8527308.
² Instituto de Desarrollo Tecnológico para la Industria Química (INTEC), UNL-CONICET, Güemes 3450, 3000, Santa Fe, Argentina.
³ Lehrstuhl für Chemische Reaktionstechnik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058, Erlangen, Germany.
⁴ Erlangen Catalysis Resource Center and Interdisciplinary Center for Interface Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058, Erlangen, Germany.

PMID: 28898518
DOI: 10.1002/cphc.201700843

Abstract

Hybrid materials consisting of ionic liquid (ILs) films on supported oxides hold a great potential for applications in electronic and energy materials. In this work, we have performed surface science model studies scrutinizing the interaction of ester-functionalized ILs with atomically defined Co₃ O₄ (111) and CoO(100) surfaces. Both supports are prepared under ultra-high vacuum (UHV) conditions in form of thin films on Ir(100) single crystals. Subsequently, thin films of three ILs, 3-butyl-1-methyl imidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf₂ ]), 3-(4-methoxyl-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([MBMIM][NTf₂ ]), and 3-(4-isopropoxy-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([IPBMIM][NTf₂ ]), were deposited on these surfaces by physical vapor deposition (PVD). Time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) were applied to monitor in situ the adsorption, film growth, and thermally induced desorption. By TP-IRAS, we determined the multilayer desorption temperature of [BMIM][NTf₂ ] (360±5 K), [MBMIM][NTf₂ ] (380 K) and [IPBMIM][NTf₂ ] (380 K). Upon deposition below the multilayer desorption temperature, all three ILs physisorb on both cobalt oxide surfaces. However, strong orientation effects are observed in the first monolayer, where the [NTf₂ ]^- ion interacts with the surface through the SO₂ groups and the CF₃ groups point towards the vacuum. For the two functionalized ILs, the [MBMIM]⁺ and [IPBMIM]⁺ interact with the surface Co²⁺ ions of both surfaces via the CO group of their ester function. A very different behavior is found, if the ILs are deposited above the multilayer desorption temperature (400 K). While for [BMIM][NTf₂ ] and [MBMIM][NTf₂ ] a molecularly adsorbed monolayer film is formed, [IPBMIM][NTf₂ ] undergoes a chemical transformation on the CoO(100) surface. Here, the ester group is cleaved and the cation is chemically linked to the surface by formation of a surface carboxylate. The IL-derived species in the monolayer desorb at temperatures around 500 to 550 K.

Keywords: IRAS; chemical anchoring; cobalt oxide; ionic liquids; thermal stability.