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

Video-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 approximate to 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. Using video-rate atomic force microscopy (AFM) the real-time dynamics of ethylammonium nitrate (EAN) near-surface nanostructures on a graphite electrode as a function of potential is revealed for the first time. Disk-like bilayer features persist above the Stern layer. The dynamics of the structures varies with electrode potential. These insights have relevance for diverse applications including electrochemical devices, catalysts, and lubricants.image

Automated summary

This study uses video-rate AFM to investigate the dynamics of near-surface nanostructures of an ionic liquid on a graphite electrode in real-time. The diffusion coefficient of the nanostructures is influenced by both the potential and the presence of water. The results are important for various applications including electrochemical devices, catalysts, and lubricants.