Phase behaviour and conductivity study of electrolytes in supercritical hydrofluorocarbons

Bartlett, Philip N., Cook, David C., George, Michael W., Ke, Jie, Levason, William, Reid, Gillian, Su, Wenta and Zhang, Wenjian (2011) Phase behaviour and conductivity study of electrolytes in supercritical hydrofluorocarbons. Physical Chemistry Chemical Physics, 13 (1), 190-198. (doi:10.1039/c0cp01202e). (PMID:21072413)

Abstract

The purpose of this work was to characterise supercritical hydrofluorocarbons (HFC) that can be used as solvents for electrodeposition. The phase behaviour of CHF3, CH2F2, and CH2FCF3 containing [NBun4][BF4], [NBun4][B{3,5-C6H3(CF3)2}4] and Na[B{3,5-C6H3(CF3)2}4] was studied and the conditions for forming a single supercritical phase established. Although all three HFCs are good solvents for [NBun4][BF4] the results show that the CH2F2 system has the lowest pr for dissolving a given amount of [NBun4][BF4]. The solubility of Na[B{3,5-C6H3(CF3)2}4] in CH2F2 was found to be unexpectedly high. Studies of the phase behaviour of CH2F2 containing [NBun4][BF4] and [Cu(CH3CN)4][BF4] showed that the copper complex was unstable in the absence of CH3CN. For CHF3, [Cu(hfac)2] was more soluble and more stable than [Cu(CH3CN)4][BF4] and only increased the phase-separation pressure by a moderate amount. Studies of the conductivity of [NBun4][B(C6F5)4], [NBun4][B{3,5-C6H3(CF3)2}4], [NRfBun3][B{3,5-C6H3(CF3)2}4] (Rf = (CH2)3C7F15), and Na[B{3,5-C6H3(CF3)2}4] were carried out in scCH2F2. The results show that these salts are more conducting than [NBun4][BF4] under the same conditions although the increase is much less significant than that reported in previous work in supercritical CO2 + CH3CN. Consequently, either [NBun4][BF4] or the corresponding BARF salts would be suitable background electrolytes for electrodeposition from scCH2F2

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Contributors

Author: Philip N. Bartlett

Author: William Levason

Author: Gillian Reid

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