O2 reduction on a Au film electrode in an ionic liquid in the absence and presence of Mg2+ ions: Product formation and adlayer dynamics

Aiming at a detailed understanding of the interaction between an ionic liquid, O2, and electrodes in Mg-air batteries, we performed a combined differential electrochemical mass spectrometry and in situ infrared spectroscopy model study on the interaction between the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP-TFSI) and a gold film electrode in the presence and absence of O2 and Mg2+ ions in the potential range relevant for the oxygen reduction reaction (ORR) and evolution reaction. Detailed information on the dynamic exchange of adsorbed ions, on the stability/decomposition of the ionic liquid, and on the activity/selectivity/reversibility of the ORR is derived from measurements performed under potentiodynamic and potentiostatic conditions. In neat BMP-TFSI, we find the dynamics of the potential induced exchange of adsorbed ions to depend significantly on the exchange direction. In the presence of O2, the anions formed in the ORR distinctly affect the adsorptio...