The interface between an electrode and a molten salt or ionic liquid is particularly topical - since the use of ionic liquids in electrochemical technologies is expanding rapidly. Macroscopic (current/voltage) data on such systems is often analysed by appeal to classical double-layer ideas yet the validity of these mean-field concepts, introduced to describe dilute electrolyte solutions, is undermined by the molecular scale information arising from novel types of experiment. New insights, linking the macroscopic and microscopic observations, arise from atomistic computer simulations, where strong correlation effects arising from the coulombic and short-range interactions between the ions and with the electrode surface are included, and also from emerging theories, in which the mean-field treatment is systematically extended.   A major challenge for simulation is to treat the interface and the interionic interactions at a sufficiently realistic level that the calculated quantities may be compared with the results of experiments on real materials. The methods underpinning recent simulations of electrochemical �double layer� capacitors (supercapacitors) will be described. Supercapacitors store energy at the electrolyte/electrode interface through reversible ion adsorption leading to higher charge/discharge rates and better cyclability compared to batteries; very high capacitances are achieved using porous electrodes [1]. The nature of the reorganisation of the molecular organisation at the interface in response to an applied potential is best studied at a planar interface, where simulation and experimental observation may be directly compared [2]. Recent work shows a link between peaks observed in the variation of the differential capacitance with potential and abrupt structural transitions resembling phase transitions.[1] C. Merlet et al.;  Nature Materials,  11 , 306-310 (2012).[2] D.T. Limmer et al.; Phys. Rev. Lett., 111 , 106102 (2013).

Ionic liquids at electrochemical interfaces

248th National Meeting (2014)

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