Phase behaviour and conductivity study on multi-component mixtures for electrodeposition in supercritical fluids

Philip N. Bartlett; David C. Cook; Michael W. George; Jie Ke; William Levason; Gillian Reid; Wenta Su; Wenjian Zhang

doi:10.1039/b918981e

Phase behaviour and conductivity study on multi-component mixtures for electrodeposition in supercritical fluids

Philip N. Bartlett, David C. Cook, Michael W. George, Jie Ke, William Levason, Gillian Reid, Wenta Su, Wenjian Zhang

Research output: Journal Publication › Article › peer-review

25 Citations (Scopus)

Abstract

Electrochemistry in supercritical CO₂ (scCO₂) is difficult because the very low dielectric constant of the fluid restricts the solubility of ionic species and the conductivity of dissolved electrolytes. To overcome this problem to allow us to carry out electrodeposition at macroelectrodes from scCO₂ we have investigated the use of co-solvents and modified electrolyte salts chosen to increase their solubility and dissociation in the supercritical fluid. Here we report results of phase behaviour studies for mixtures of CO₂ with [NBuⁿ ₄][BF₄] and either methanol (CH₃OH) or acetonitrile (CH₃CN) as the co-solvent. These show that the solubility of [NBuⁿ₄][BF₄] is approximately 5 times larger when CH₃CN is the co-solvent rather than CH ₃OH. Consequently the phase behaviour of the ternary of CO ₂-[NBuⁿ₄][BF₄]-CH₃CN was studied in greater detail over a range of compositions. To enhance the conductivity of scCO₂-CH₃CN a range of electrolyte salts was synthesised in which the [NBuⁿ₄]⁺ and/or [BF₄]^- ion were replaced by different derivatives. Results for the phase behaviour and conductivity of these modified electrolyte salts in scCO₂-CH₃CN are reported for several different compositions. We find that increasing the degree of fluorination and size of the ions increases the solubility of the electrolyte salt in scCO ₂-CH₃CN. Of the 11 electrolytes investigated [NBu ⁿ₄][B{3,5-C₆H₃(CF₃) ₂}₄] appears the most suitable for use in scCO ₂-CH₃CN with a molar conductivity of 22-26 S cm ² mol^-1 and a maximum measured conductivity of ∼3 mS cm^-1 for 0.07 M [NBuⁿ₄][B{3,5-C ₆H₃(CF₃)₂}₄] dissolved in scCO₂-CH₃CN (molar ratio CH₃CN: CO₂ ≈ 0.12) at 20 MPa and 328.15 K. This is an order of magnitude improvement over similar results for the [NBuⁿ₄][BF₄] parent. Studies of the conductance as a function of the electrolyte concentration suggest that triple ions make an important contribution to the conductivity of the supercritical fluid.

Original language	English
Pages (from-to)	492-501
Number of pages	10
Journal	Physical Chemistry Chemical Physics
Volume	12
Issue number	2
DOIs	https://doi.org/10.1039/b918981e
Publication status	Published - 2010
Externally published	Yes

ASJC Scopus subject areas

General Physics and Astronomy
Physical and Theoretical Chemistry

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@article{e15272d07cfe403894c44a14164c9bca,

title = "Phase behaviour and conductivity study on multi-component mixtures for electrodeposition in supercritical fluids",

abstract = "Electrochemistry in supercritical CO2 (scCO2) is difficult because the very low dielectric constant of the fluid restricts the solubility of ionic species and the conductivity of dissolved electrolytes. To overcome this problem to allow us to carry out electrodeposition at macroelectrodes from scCO2 we have investigated the use of co-solvents and modified electrolyte salts chosen to increase their solubility and dissociation in the supercritical fluid. Here we report results of phase behaviour studies for mixtures of CO2 with [NBun 4][BF4] and either methanol (CH3OH) or acetonitrile (CH3CN) as the co-solvent. These show that the solubility of [NBun4][BF4] is approximately 5 times larger when CH3CN is the co-solvent rather than CH 3OH. Consequently the phase behaviour of the ternary of CO 2-[NBun4][BF4]-CH3CN was studied in greater detail over a range of compositions. To enhance the conductivity of scCO2-CH3CN a range of electrolyte salts was synthesised in which the [NBun4]+ and/or [BF4]- ion were replaced by different derivatives. Results for the phase behaviour and conductivity of these modified electrolyte salts in scCO2-CH3CN are reported for several different compositions. We find that increasing the degree of fluorination and size of the ions increases the solubility of the electrolyte salt in scCO 2-CH3CN. Of the 11 electrolytes investigated [NBu n4][B{3,5-C6H3(CF3) 2}4] appears the most suitable for use in scCO 2-CH3CN with a molar conductivity of 22-26 S cm 2 mol-1 and a maximum measured conductivity of ∼3 mS cm-1 for 0.07 M [NBun4][B{3,5-C 6H3(CF3)2}4] dissolved in scCO2-CH3CN (molar ratio CH3CN: CO2 ≈ 0.12) at 20 MPa and 328.15 K. This is an order of magnitude improvement over similar results for the [NBun4][BF4] parent. Studies of the conductance as a function of the electrolyte concentration suggest that triple ions make an important contribution to the conductivity of the supercritical fluid.",

author = "Bartlett, {Philip N.} and Cook, {David C.} and George, {Michael W.} and Jie Ke and William Levason and Gillian Reid and Wenta Su and Wenjian Zhang",

year = "2010",

doi = "10.1039/b918981e",

language = "English",

volume = "12",

pages = "492--501",

journal = "Physical Chemistry Chemical Physics",

issn = "1463-9076",

publisher = "Royal Society of Chemistry",

number = "2",

}

TY - JOUR

T1 - Phase behaviour and conductivity study on multi-component mixtures for electrodeposition in supercritical fluids

AU - Bartlett, Philip N.

AU - Cook, David C.

AU - George, Michael W.

AU - Ke, Jie

AU - Levason, William

AU - Reid, Gillian

AU - Su, Wenta

AU - Zhang, Wenjian

PY - 2010

Y1 - 2010

N2 - Electrochemistry in supercritical CO2 (scCO2) is difficult because the very low dielectric constant of the fluid restricts the solubility of ionic species and the conductivity of dissolved electrolytes. To overcome this problem to allow us to carry out electrodeposition at macroelectrodes from scCO2 we have investigated the use of co-solvents and modified electrolyte salts chosen to increase their solubility and dissociation in the supercritical fluid. Here we report results of phase behaviour studies for mixtures of CO2 with [NBun 4][BF4] and either methanol (CH3OH) or acetonitrile (CH3CN) as the co-solvent. These show that the solubility of [NBun4][BF4] is approximately 5 times larger when CH3CN is the co-solvent rather than CH 3OH. Consequently the phase behaviour of the ternary of CO 2-[NBun4][BF4]-CH3CN was studied in greater detail over a range of compositions. To enhance the conductivity of scCO2-CH3CN a range of electrolyte salts was synthesised in which the [NBun4]+ and/or [BF4]- ion were replaced by different derivatives. Results for the phase behaviour and conductivity of these modified electrolyte salts in scCO2-CH3CN are reported for several different compositions. We find that increasing the degree of fluorination and size of the ions increases the solubility of the electrolyte salt in scCO 2-CH3CN. Of the 11 electrolytes investigated [NBu n4][B{3,5-C6H3(CF3) 2}4] appears the most suitable for use in scCO 2-CH3CN with a molar conductivity of 22-26 S cm 2 mol-1 and a maximum measured conductivity of ∼3 mS cm-1 for 0.07 M [NBun4][B{3,5-C 6H3(CF3)2}4] dissolved in scCO2-CH3CN (molar ratio CH3CN: CO2 ≈ 0.12) at 20 MPa and 328.15 K. This is an order of magnitude improvement over similar results for the [NBun4][BF4] parent. Studies of the conductance as a function of the electrolyte concentration suggest that triple ions make an important contribution to the conductivity of the supercritical fluid.

AB - Electrochemistry in supercritical CO2 (scCO2) is difficult because the very low dielectric constant of the fluid restricts the solubility of ionic species and the conductivity of dissolved electrolytes. To overcome this problem to allow us to carry out electrodeposition at macroelectrodes from scCO2 we have investigated the use of co-solvents and modified electrolyte salts chosen to increase their solubility and dissociation in the supercritical fluid. Here we report results of phase behaviour studies for mixtures of CO2 with [NBun 4][BF4] and either methanol (CH3OH) or acetonitrile (CH3CN) as the co-solvent. These show that the solubility of [NBun4][BF4] is approximately 5 times larger when CH3CN is the co-solvent rather than CH 3OH. Consequently the phase behaviour of the ternary of CO 2-[NBun4][BF4]-CH3CN was studied in greater detail over a range of compositions. To enhance the conductivity of scCO2-CH3CN a range of electrolyte salts was synthesised in which the [NBun4]+ and/or [BF4]- ion were replaced by different derivatives. Results for the phase behaviour and conductivity of these modified electrolyte salts in scCO2-CH3CN are reported for several different compositions. We find that increasing the degree of fluorination and size of the ions increases the solubility of the electrolyte salt in scCO 2-CH3CN. Of the 11 electrolytes investigated [NBu n4][B{3,5-C6H3(CF3) 2}4] appears the most suitable for use in scCO 2-CH3CN with a molar conductivity of 22-26 S cm 2 mol-1 and a maximum measured conductivity of ∼3 mS cm-1 for 0.07 M [NBun4][B{3,5-C 6H3(CF3)2}4] dissolved in scCO2-CH3CN (molar ratio CH3CN: CO2 ≈ 0.12) at 20 MPa and 328.15 K. This is an order of magnitude improvement over similar results for the [NBun4][BF4] parent. Studies of the conductance as a function of the electrolyte concentration suggest that triple ions make an important contribution to the conductivity of the supercritical fluid.

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U2 - 10.1039/b918981e

DO - 10.1039/b918981e

M3 - Article

C2 - 20023827

AN - SCOPUS:74249088055

SN - 1463-9076

VL - 12

SP - 492

EP - 501

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

IS - 2

ER -

Phase behaviour and conductivity study on multi-component mixtures for electrodeposition in supercritical fluids

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