1The University of Western Australia, Crawley, Australia
Molecular Resolution Nanostructure and Dynamics of the Deep Eutectic Solvent – Graphite Interface as a Function of Potential
Rob Atkin,a* Justin S. Freeman,a Haile Mesfin Mamme,b,c Jon Ustarroz,b,d Gregory G. Warr,e Hua Li,a
aSchool of Molecular Sciences, The University of Western Australia, Perth, WA 6009, Australia.
bResearch Group Electrochemical and Surface Engineering (SURF), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium
cEenheid Algemene Chemie (ALGC),Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium
dChemistry of Surfaces, Interfaces and Nanomaterials (ChemSIN), Université Libre de Bruxelles, Boulevard du Triomphe 2, 1050 Brussels, Belgium
eSchool of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia.
* Corresponding author: firstname.lastname@example.org
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 nanostructure 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 we use in situ amplitude modulated atomic force microscopy (AM-AFM) complemented by MD simulations 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 (HOPG) 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 was 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.