Alessandra SERVA1, Roxanne BERTHIN1, Camille BACON1, Mathieu SALANNE1,2
1Sorbonne Université, CNRS, Laboratoire PHENIX, Paris, France
2Institut Universitaire de France, Paris, France
Over the past decade a classical molecular dynamics code that allows to simulate electrochemical cells, i.e. systems where a constant electrical potential is applied to the electrode materials, has been developed in our group. The main improvement with respect to conventional molecular dynamics code was the use of realistic models for electrified nanoporous carbon electrodes for supercapacitors. However, this was made at the expense of the electrolyte description, often represented with a coarse-grained model. Recently, we have introduced new models for the electrolytes, in which all the atoms are represented explicitly and polarization effects can be included, allowing for the simulation of electrochemical systems with improved accuracy.
In this talk, I will first show some results obtained on a well-known electrolyte, namely the EMIM-TFSI ionic liquid, either pure or dissolved in acetonitrile, confined between planar or nanoporous carbon-based electrodes. An example of the system is shown in Figure 1a. Then, I will move to the case of biredox ionic liquids, a recent class of electrolytes where both the cation and the anion of the ionic liquid are functionalized with redox-active moieties. As shown in Figure 1b, the investigated system is composed of the cation EMIM+ functionalized by TEMPO, while the anion TFSI- is grafted with an anthraquinone (AQ) group. Recent experimental studies on these systems have shown a significant increase in the capacitance compared to common ionic liquids, due to redox processes. Yet the charging mechanisms is not completely elucidated, in particular the interplay between redox reactions and confinement effects remains to be understood. By studying the structure of the liquid, both in the bulk and confined in pores with various widths, we show that the TEMPO moieties tend to aggregate and the AQ groups to form stacked arrangements, percolating through the whole liquid. This result provides an interesting lead for shedding light on the charging mechanisms of these systems.
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