In Situ X-ray Photoelectron Spectroscopic and Electrochemical Studies of the Bromide Anions Dissolved in 1-Ethyl-3-Methyl Imidazolium Tetrafluoroborate

Abstract

Influence of electrode potential on the electrochemical behavior of a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) solution containing 5 wt % 1-ethyl-3-methylimidazolium bromide (EMImBr) has been investigated using electrochemical and synchrotron-initiated high-resolution in situ X-ray photoelectron spectroscopy (XPS) methods. Observation of the Br 3d5/2 in situ XPS signal, collected in a 5 wt % EMImBr solution at an EMImBF4⁻vacuum interface, enabled the detection of the start of the electrooxidation process of the Br− anion to Br3− anion and thereafter to the Br2 at the micro-mesoporous carbon electrode, polarized continuously at the high fixed positive potentials. A new photoelectron peak, corresponding to B⁻O bond formation in the B 1s in situ XPS spectra at E ≤ −1.17 V, parallel to the start of the electroreduction of the residual water at the micro-mesoporous carbon electrode, was observed and is discussed. The electroreduction of the residual water caused a reduction in the absolute value of binding energy vs. potential plot slope twice to ca. dBE dE−1 = −0.5 eV V−1 at E ≤ −1.17 V for C 1s, N 1s, B 1s, F 1s, and Br 3d5/2 photoelectrons.

Keywords

• room temperature ionic liquids
• in situ X-ray photoelectron spectroscopy
• binding energies
• cyclic voltammetry
• electrochemical impedance spectroscopy
• micro-mesoporous carbon electrode
• supercapacitor materials