Effect of Potential on the Nanostructure Dynamics of Ethylammonium Nitrate at a Graphite Electrode

Abstract

AbstractVideo‐rate atomic force microscopy (AFM) is used to study the near‐surface nanostructure dynamics of the ionic liquid ethylammonium nitrate (EAN) at a highly oriented pyrolytic graphite (HOPG) electrode as a function of potential in real‐time for the first time. The effects of varying the surface potential and adding 10 wt% water on the nanostructure diffusion coefficient are probed. For both EAN and the 90 wt% EAN‐water mixture, disk‐like features ≈9 nm in diameter and 1 nm in height form above the Stern layer at all potentials. The nanostructure diffusion coefficient increases with potential (from OCP −0.5 V to OCP +0.5 V) and with added water. Nanostructure dynamics depends on both the magnitude and direction of the potential change. Upon switching the potential from OCP −0.5 V to OCP +0.5 V, a substantial increase in the diffusion coefficients is observed, likely due to the absence of solvophobic interactions between the nitrate (NO3−) anions and the ethylammonium (EA+) cations in the near‐surface region. When the potential is reversed, EA+ is attracted to the Stern layer to replace NO3−, but its movement is hindered by solvophobic attractions. The outcomes will aid applications, including electrochemical devices, catalysts, and lubricants.