Potential-Induced Ordering Transition of the Adsorbed Layer at the Ionic Liquid/Electrified Metal Interface

Abstract

The potential-driven ordering transition of a LiCl layer adsorbed on the (100) surface of a metallic aluminum electrode is studied by molecular dynamics simulations. The transition causes a sharp peak in the potential dependence of the differential capacitance of the interface. This result is in qualitative agreement with recently reported experimental work on the interface between a room temperature ionic liquid and a well-defined Au(100) surface. In the LiCl/Al simulations, the transition occurs when the interaction model includes the induction of dipoles on the ions of the liquid by their mutual interaction and their interaction with the electrode surface as well as the polarization of the metal by the charges and dipoles on the ions ("image" interactions). When the electrode or ion polarization effects are not included, the transition is no longer observed. The interaction between the induced charges on the metal atoms and the induced dipoles on the ions creates an additional screening, which stabilizes the formation of a crystalline layer at the anode. When the crystallographic plane of the metal is changed to (110) instead of (100), the two first adsorbed layer are crystalline on both the anode and the cathode, but the structure is different: the crystal is formed through an epitaxial mechanism to adapt to the electrode surface structure. In the case of the (110) crystallographic plane, the charging of the adsorbed layer occurs through the formation of nonstoichiometric crystalline layers.

Nanostructure of the Ionic Liquid–Graphite Stern Layer

“…29 Appling a surface potential induces a re-ordering of the normal Stern layer structure to compensate the interfacial charge; the surface is enriched in anions at positive potentials and vice-versa. [29][30][31][32][33][34] This behaviour has been theoretically validated with several important computational studies modelling the ILelectrode interface. [30][31][32][33][34][35][36][37] In a landmark 2011 paper Bazant et al 38 predicted the potential dependant normal distribution of ions with focus on overscreening and crowding of ions at electrode interfaces.…”

Poly(a)morphic portrait of the electrical double layer in ionic liquids

“…Charge/voltage driven structural transitions in the electrical double layer (EDL) in ionic liquids (ILs) have recently attracted large interest in experimental [1,2,3,4,5,6], theoretical [7] and computational [8,9,10,11,12,13,14] communities due to the importance of this subject for a variety of IL applications [15,16].…”

Capacitive Energy Storage: Current and Future Challenges

“…60 As a common trend, the atomistic MD simulations on atomically flat, metallic electrode surfaces showed only a weak dependence of DC versus the applied potential (∆U) in the range of potentials where the electrode surface is not saturated with ions (i.e., within ∆U 4-5V). 110 126 and calculations based on restricted primitive model 127 showed that when the interactions between electrode-electrolyte were treated as polarizable 126 , a strong peak in DC is generated at lower voltages. Another possible mechanism that has been suggested to explain the sharp peaks in DC near PZC is related to a strong ion pairing that dissociates upon a small increase in the electrode potential.…”