Nanoconfinement of Ionic Liquid into Porous Carbon Electrodes

Abstract

Planar electrochemical double-layer capacitors (supercapacitors) are strategic elements for the realization of miniaturized autonomous devices requiring energy storage and conversion capabilities. In particular, supercapacitors fabricated with nanoporous carbon electrodes and ionic liquids as electrolytes are very promising for a wide range of applications. The understanding and control of the interactions of the ionic liquid with the porous carbon interface is both practically and fundamentally interesting, because of the effects of surface confinement on the structural and functional properties of the ionic liquid. In particular, the role of the morphology in the ionic liquid confinement has attracted huge interest in many disciplines. Here we report direct experimental evidence of the solid-like structuring of confined 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl) imide ([Bmim]­[NTf2]), which extends several tens of nanometers from the interface of nanoporous carbon thin films. These solid-like structures coexist with a huge amount of ionic liquid in its bulk phase. The presence of a solid-like phase occurring at the interface affects the double-layer organization of the ionic liquid at the electrified interface of nanoporous carbon based planar supercapacitors. Our results suggest the presence of the solid-like structured ionic liquid domains not only on the upper carbon thin film interface but also into the bulk of the nanoporous matrix.

Nanostructure Determines the Wettability of Gold Surfaces by Ionic Liquid Ultrathin Films

“…If the wetting of the walls matrix by the ionic liquid in its solid-phase is favored compared to the wetting by the ionic liquid in the liquid-phase, the phase transition in confining conditions may occur at highest temperature than in bulk conditions. As it has been demonstrated for nanostructured oxidized silicon surface (Borghi et al, 2019b) and nanostructured carbon surface (Borghi et al, 2021), the nanostructure does not prevent the formation of ordered ionic liquid structures, which maintain their solid-like behavior.…”

“…In fact, the elemental building blocks (atoms deposited by thermal evaporation or clusters deposited by SCBD) that constitute the gold thin films provide different structural properties to the layers (Mirigliano et al, 2019;Mirigliano et al, 2020). Interestingly, the formation of extended solid-like domains of ionic liquids, similar to those observed in Refs (Bovio et al, 2009;Galluzzi et al, 2018a;Borghi et al, 2019b, Borghi et al, 2021Borghi and Podestà, 2020), were demonstrated, with more relevance on the evaporated gold thin film, where the liquid phase wets less the surface.…”

“…The formation of solid-like ionic liquid terraces on flat (mica, amorphous silica, and oxidized silicon) (Bovio et al, 2009;Galluzzi et al, 2018a) and nanostructured thin films (Borghi et al, 2019b;Borghi et al, 2021) has been extensively reported in literature. IL thin film patches and droplets coexist on the surface, in condition of surface confinement, as described in Ref.…”

“…Borghi and Podestà (2020). Here, the term solid-like refers to changes of many structural and functional properties of the ionic liquid which form multi-layered micrometer-wide terraces, characterized by a 0.6 nm (Bovio et al, 2009;Ballone et al, 2012) fundamental step, which extend from the surface up to several tens or even hundreds of nanometers (Bovio et al, 2009;Galluzzi et al, 2018b;Borghi et al, 2019b;Borghi et al, 2021). These structures are rigid, characterized by an apparent Young Modulus of the order of 1 GPa (Galluzzi et al, 2018a;Borghi et al, 2019b;Borghi et al, 2021), and possess electrical insulating character (Galluzzi et al, 2018b).…”

Computational study of halogen-halogen interactions in polyhalide ionic liquids

“…Room temperature ionic liquids (ILs) are completely composed of ions with melting points below 100°C [1][2][3]. These non-volatile liquids have several unique properties, such as excellent thermal stability, high ionic conductivity, and low combustibility, which are being explored as environmentally benign solvents [4][5][6][7]. In addition, ILs have also been described as "designer solvents" with characteristics that can be tuned to meet specific requirements for a particular application [8,9].…”