Dynamical Response of the Electric Double Layer Structure of the DEME-TFSI Ionic Liquid to Potential Changes Observed by Time-Resolved X-ray Reflectivity

The interface between the N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) ionic liquid and a gold (111) surface was investigated with time-resolved X-ray reflectivity in order to clarify the dynamics of structural changes of the electric double layer after changing the electrode potential. In the experiment, the potential was switched repeatedly between +1.5 V and −1.5 V every 2 s or every 0.3 s, while measuring the specular X-ray reflectivity. When the potential was switched every 2 s, the time dependence of the reflectivity was different from that of the accumulated charge. This indicates structural relaxation processes that occur on a slower time scale than the acummulation of the charge at the electric double layer.When the potential was switched every 0.3 s, on the other hand, the reflectivity changes followed the evolution of the charge of the electric double layer within the experimental precision, indicating that slow relaxation processes without charge transfer do not contribute significantly to structural changes at this time scale.