Affiliation: | 1. School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, 6009 Australia;2. Research Group Electrochemical and Surface Engineering (SURF), Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels, 1050 Belgium
Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels, 1050 Belgium;3. Research Group Electrochemical and Surface Engineering (SURF), Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels, 1050 Belgium
Chemistry of Surfaces, Interfaces and Nanomaterials (ChemSIN), Université Libre de Bruxelles, Boulevard du Triomphe 2, Brussels, 1050 Belgium;4. School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, New South Wales, 2006 Australia;5. School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, 6009 Australia
Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, Western Australia, 6009 Australia |
Abstract: | Interest in deep eutectic solvents (DESs), particularly for electrochemical applications, has boomed in the past decade because they are more versatile than conventional electrolyte solutions and are low cost, renewable, and non-toxic. The molecular scale lateral nanostructures as a function of potential at the solid–liquid interface—critical design parameters for the use of DESs as electrochemical solvents—are yet to be revealed. In this work, in situ amplitude modulated atomic force microscopy complemented by molecular dynamics simulations is used to probe the Stern and near-surface layers of the archetypal and by far most studied DES, 1:2 choline chloride:urea (reline), at the highly orientated pyrolytic graphite surface as a function of potential, to reveal highly ordered lateral nanostructures with unprecedented molecular resolution. This detail allows identification of choline, chloride, and urea in the Stern layer on graphite, and in some cases their orientations. Images obtained after the potential is switched from negative to positive show the dynamics of the Stern layer response, revealing that several minutes are required to reach equilibrium. These results provide valuable insight into the nanostructure and dynamics of DESs at the solid–liquid interface, with implications for the rational design of DESs for interfacial applications. |