@article{Zhang2023, 
author = {Zelei Zhang and Atsushi Kitada and Kazuhiro Fukami and Kuniaki Murase},
title = {Annealing, solvation, and mirror-plating effects in phosphonium chloroaluminate ionic liquids},
year = {2023},
journal = {Nano Research},
volume = {16},
number = {2},
pages = {3348-3357},
keywords = {electrodeposition, physicochemical property, ionic liquid, ab initio calculation},
url = {https://www.sciopen.com/article/10.1007/s12274-022-4999-6},
doi = {10.1007/s12274-022-4999-6},
abstract = {The physicochemical properties of a specific ionic liquid (IL) are naturally considered to be constant at a given temperature. However, a series of eutectic melts of trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14]Cl) with aluminum chloride (AlCl3) is an exception. The viscosity of Al2Cl7−-dominated [P6,6,6,14]Cl–AlCl3 ILs (i.e., AlCl3 mole fraction x = 0.60–0.67) gradually increased as a function of annealing. Annealing also influenced the ultraviolet–visible spectra, nuclear magnetic resonance spectra, and the glass transition temperature of the ILs. Such annealing-induced variations in physicochemical properties were not observed in the AlCl4−- and Cl−-dominated ILs. In particular, the ionic conductivities of the ILs (x = 0.60–0.67) were strongly decoupled from their viscosities during annealing. Ab initio calculations revealed the bending of the long tetradecyl chains in [P6,6,6,14]+ coupled with Al2Cl7−, while neither Cl− nor AlCl4− caused bending. In general, [P6,6,6,14]+-based ILs are recognized as sponge-like structures that consist of nano-scale polar and non-polar domains. We propose a gradual structurization process in Al2Cl7−-dominated ILs to account for their unusual physicochemical properties. Moreover, the addition of tetradecane, solvated in the non-polar domains of the ILs, substantially reduced the viscosity of the structured IL with x = 0.67. Mirror Al electroplating is possible without a brightener, using the x = 0.67 ILs, regardless of annealing or the admixture of tetradecane.}
}