In Situ Probing of Ion Ordering at an Electrified Ionic Liquid/Au Interface

Charge transport at the interface of electrodes and ionic liquids is critical for the use of the latter as electrolytes. A room‐temperature ionic liquid, 1‐ethyl‐2,3‐dimethylimidazolium bis(trifluoromethanesulfonyl)imide (EMMIM TFSI), is investigated in situ under applied bias voltage with a novel method using low‐energy electron and photoemission electron microscopy. Changes in photoelectron yield as a function of bias applied to electrodes provide a direct measure of the dynamics of ion reconfiguration and electrostatic responses of the EMMIM TFSI. Long‐range and correlated ionic reconfigurations that occur near the electrodes are found to be a function of temperature and thickness, which, in turn, relate to ionic mobility and different configurations for out‐of‐plane ordering near the electrode interfaces, with a critical transition in ion mobility for films thicker than three monolayers.