Deep eutectic solvents (DESs) are innovative materials that ruled the research about new green media in the last two decades. Among them, metal-based deep eutectic solvents (MDESs) are formed by a mixture of a hydrogen bond donor (HBD) with a metal salt. In particular, those formed by choline chloride (ChCl) or urea with halide metal salts have shown promising results for what concerns their employment in a wide range of applications, such as electrolytes for electrochemical devices or solvents for catalysis, electrodepositions, chemical extractions and analysis. However, the structural properties that are at the base of the unique characteristics of these new media are still unknown for many of them. For these reasons, the purpose of this project is to study the structural arrangement of these new materials by means of a combined approach between X-ray absorption spectroscopy (XAS) and molecular dynamics (MD) simulations. Since the peculiar chemical-physical properties of these solvents seem to be enhanced upon the introduction of additional water, particular attention will be devoted to the study of their structural modifications upon water addition. Our aim is to trace a clear relationship between the microscopic structural arrangement of these new innovative materials and their unique macroscopic physical-chemical properties, hoping that this will help to find the optimum experimental conditions and favor the promotion of these more sustainable processes targeting such important technological sectors.
The main result of this project will be the possibility of linking the molecular structure, obtained by means of high-quality simulations and experimental data analysis, to observable and measurable "bulk" properties of MDESs. This project has the potential to provide an interpretative disentanglement of the rather complex physical-chemical properties of the materials that we have chosen to study. From the mere methodological point of view, the proposed objectives and the expected results are certainly appealing and, alone, should justify the need for such studies. It is, however, important to consider the added value provided to this project by the wide applicative horizon involving such kinds of innovative substances. For example, the knowledge of the metal ion speciation is of central importance for the application of MDESs as electrolytes in new electrochemical devices (e.g. batteries, supercapacitors, solar cells), since
the nature of the charged species formed by a metal ion in solution is directly related to its transference number and has a crucial influence on the working of electrochemical systems.[1,2] The employment of DESs in these devices is highly desirable since the purpose would be the substitution of the currently employed organic solvents, which are often highly volatile, flammable, and toxic, with non-volatile, non-flammable, and less toxic DESs. As regards MDESs applications in catalysis, here the catalytic species usually consist of the metal ion merely solvated by the eutectic components. Also here, we can understand how the knowledge about the nature of the catalytic species, i.e. of the metal ion coordination in solution, is of central importance to understand and eventually improve the catalytic process. For these reasons, we believe that the obtained results will allow finding a relationship between the structural arrangement and the unique physical-chemical properties that have been observed for these mixtures, hoping that this will help to find the optimum experimental conditions and favor the promotion of these more sustainable processes targeting such important technological sectors.
References.
1. M. Armand et al., Nat. Mater., 2009, 8, 621-629.
2. D. R. MacFarlane et al., Energy Environ. Sci., 2014, 7, 232-250.