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 (EMImBF 4 ) 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 3d 5/2 in situ XPS signal, collected in a 5 wt % EMImBr solution at an EMImBF 4 –vacuum interface, enabled the detection of the start of the electrooxidation process of the Br - anion to Br 3- anion and thereafter to the Br 2 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 3d 5/2 photoelectrons.