Ionic Liquid Ordering at an Oxide Surface.

Michael Wagstaffe,Mark J Jackman,Karen L Syres,Andrew G Thomas,Alexander Generalov

doi:10.1002/cphc.201600774

Abstract

The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near‐edge X‐ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyte–electrode and dye‐sensitized solar cells. The initial interaction involves degradation of the [BF4]− anion, resulting in incorporation of F into O vacancies in the anatase surface. At low coverages, [C4C1Im][BF4] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO2 surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost.

Highlights

The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy
The measured binding energies and peak assignments in this work are in good agreement with those reported by Foelske-Schmitz et al.[30] and Villar-Garcia et al.,[29] though we observe a 0.4 eV shift to higher binding energy in all core level spectra, most likely a result of the different methods used to calibrate the binding energy scale
The components arising from C1, C2 and C3 are shifted by 0.3 eV to lower binding energies relative to the thick film

Summary

Introduction

The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The measured binding energies and peak assignments in this work are in good agreement with those reported by Foelske-Schmitz et al.[30] and Villar-Garcia et al.,[29] though we observe a 0.4 eV shift to higher binding energy in all core level spectra, most likely a result of the different methods used to calibrate the binding energy scale (described in S.1).

Results

Conclusion