Ring any bells? The differential capacitance curve of Au(100) in neat [BMI]BF(4) (BMI = 1-butyl-3-methylimidazolium) ionic liquid has a bell-shaped feature (see picture). The adsorption of BMI(+) shows a disorder-order transition and depends on the structure of the surface. Ordered adsorption in a micelle-like structure stabilizes the underlying Au surface.

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Oberflächlich betrachtet: Die differenzielle Kapazität von Au(100) in der ionischen Flüssigkeit [BMI]BF4 (BMI=1‐Butyl‐3‐methylimidazolium) als Funktion des elektrostatischen Potentials nimmt einen glockenförmigen Verlauf (siehe Bild). Die Adsorption von BMI+ geht von einem ungeordneten in einen geordneten Prozess über und hängt von der Struktur der Oberfläche ab. Die geordnete Adsorption zu einer micellartigen Struktur stabilisiert die darunter befindliche Au‐Oberfläche.magnified image

In supercapacitors based on ionic liquid electrolytes, small amounts of absorbed water could potentially reduce the electrochemical window of electrolytes and cause performance degradation. The same would take place if ionic liquids are used as solvents for electrocatalysis involving the dissolved molecular species. In this work, we carry out molecular dynamics simulations, with gold and carbon electrodes in typical ionic liquids, hydrophobic and hydrophilic, to study electrosorption of water. We investigate the effects of hydrophobicity/hydrophilicity of ionic liquids and electrodes on interfacial distribution of ions and electrosorbed water. Results reveal that using hydrophilic ionic liquids would help to keep water molecules away from the negatively charged electrodes, even at large electrode polarizations. This conclusion is supported by electrochemical cyclic voltammetry measurements on gold and carbon electrodes in contact with humid ionic liquids. Thereby, our findings suggest potential mechanisms for protection of electrodes from water electrosorption.

High quality AFM force curves are presented with detailed potential dependent layering behaviors of the ionic liquid molecules, from which charged interior and neutral exterior layers are distinguished. The electric double layer is confined within the interior layers of one to two molecular size within the potential range of up to 1 V negative of the PZC.