Temperature-Dependent Ordering Phenomena of a Polyiodide System in a Redox-Active Ionic Liquid

Abstract

Iodine added to iodide-based ionic liquids leads to dramatic changes of their physical properties which may have implications for technological applications. Here we study the phase diagram of 1-methyl-3-propylimidazolium iodide, the temperature versus iodine (I 2 ) concentration. Above a threshold I 2 concentration of 3.9 M, polyiodides are found to be the major determinant of the thermodynamic properties, where nucleation occurs at reduced temperatures leading to a crystalline phase followed by a nematic phase. At the highest concentrations and for increasing temperatures a phonon mode develops which gives indication of mesophases with both improved orientational order of the polyiodide chains and a degree of positional order close to melting. These novel results are important for the fundamental understanding of the physical properties in molten salts and for applications where ionic liquids are used as charge-transporting media such as in batteries and dye-sensitized solar cells.

Molten‐Salt‐Assisted CsPbI3 Perovskite Crystallization for Nearly 20%‐Efficiency Solar Cells

“…[24][25][26][27][28] The MS melts can exhibit homogeneous heat and mass transfer to carry out chemical transformation even at low temperature. [24,29] MS methods have been widely used in industrial production. For example, they are regarded as ideal reactors for the closed Th-U cycle due to their lower fissile inventory [30] and are applied in lignite pyrolysis to affect the products.…”

Methylammonium Polyiodides in Perovskite Photovoltaics: From Fundamentals to Applications

“…In fact, a liquid state of RPM at room temperature is not unique itself if considering the whole class of plolyiodides. However, it was previously thought that only polyiodides with large organic cations such as aromatic (e.g., imidazolium) (Thorsmølle et al, 2012;Fei et al, 2015), trialkylsulfonium [e.g., (Et) 3 S + ] ( Bengtsson et al, 1991), or tetraalkylammonium [e.g., (Oc) 4 N + ] ( Stegemann et al, 1992;Wang et al, 2014;Yushina et al, 2014) are able to generate liquid phases of such polyiodides at room temperature (Bengtsson et al, 1991;Stegemann et al, 1992;Thorsmølle et al, 2012). Conversely, CsI 3 has a melting point over 130 • C (Topol, 1968).…”

Glyme–Li salt equimolar molten solvates with iodide/triiodide redox anions

“…35,36 Likewise, room temperature ionic liquids with polyiodide [I m ] (1# m # 8) can be formed upon the addition of I 2 to imidazolium iodide salts. 37,38 The thermal stability of the solvates was studied using isothermal TGA at 100 C, as shown in Fig. 1 (Fig.…”