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

Area of Science:

• Electrochemistry
• Supercritical Fluids
• Materials Science

Background:

• Electrochemistry in supercritical CO(2) (scCO(2)) faces challenges due to low dielectric constant, limiting ion solubility and electrolyte conductivity.
• This hinders applications like electrodeposition in scCO(2).

Purpose of the Study:

• To enhance ion solubility and conductivity in scCO(2) for electrodeposition.
• To investigate co-solvents and modified electrolyte salts for improved electrochemical performance.

Main Methods:

• Phase behavior studies of CO(2) with [NBu(n)(4)][BF(4)] and co-solvents (methanol, acetonitrile).
• Synthesis and characterization of modified electrolyte salts with varying ion structures.
• Measurement of conductivity and phase behavior of electrolytes in scCO(2)-acetonitrile mixtures.

Main Results:

• Acetonitrile significantly increased [NBu(n)(4)][BF(4)] solubility compared to methanol.
• Increased ion fluorination and size enhanced electrolyte solubility in scCO(2)-acetonitrile.
• [NBu(n)(4)][B{3,5-C(6)H(3)(CF(3))(2)}(4)] exhibited high molar conductivity (22-26 S cm(2) mol(-1)) and maximum conductivity (3 mS cm(-1)), an order of magnitude improvement over the parent salt.

Conclusions:

• Co-solvents and specifically designed electrolyte salts can overcome conductivity limitations in scCO(2) electrochemistry.
• Modified electrolyte salts, particularly highly fluorinated ones, are promising for enabling electrodeposition in scCO(2).
• Triple ions contribute significantly to the conductivity of these supercritical fluid electrolytes.