Hydrophobic alkylphosphonium ionic liquid for electrochemistry at ultramicroelectrodes and micro liquid|liquid interfaces

• Published in: Electrochimica acta Vol. 62; pp. 8 - 18
• Main Authors: Stockmann, Tom J., Zhang, Jing, Wren, J. Clara, Ding, Zhifeng
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.02.2012; Elsevier
• Subjects: Anions; Cations; Chemical vapor synthesis; Chemistry; Electrochemistry; Electron transfer; Exact sciences and technology; General and physical chemistry; Hydrophobicity; Information technology; Ion transfer; Ionic liquids; Melting points; Micro liquid|liquid interfaces; Miscellaneous; Properties of electrolytes: conductivity; Rate constants; Room temperature ionic liquid (RTIL); Study of interfaces; Ultramicroelectrode; Electron transfer; Room temperature ionic liquid (RTIL); Micro liquid|liquid interfaces; Ultramicroelectrode; Ion transfer; Electrode electrolyte interface; Metallocene; Ionic liquid; Transport process; Cyclic voltammetry; Redox couple; Platinum; Liquid liquid interface; Interface two immiscible electrolyte solution; Charge transfer; Electrical properties; Electrolyte solution; Ionic conductivity; Theoretical study; Hydrophobic compound; Transition metal; Experimental study; Non miscible liquid; Ferrocene; Room temperature
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2011.10.087

[Display omitted] ► A hydrophobic room temperature ionic liquid (RTIL) was prepared and characterized. ► Ferrocene oxidation reaction in the RTIL was investigated at an ultramicroelectrode. ► The RTIL demonstrates a wide polarized potential window at the water|IL interface. ► Galvani transfer potentials of several IT reactions at the interface were determined. ► CVs at the ultramicroelectrode and at the micro water|IL interface were simulated. Combining a large asymmetric alkylphosphonium cation, trihexyltetradecylphosphonium, with the tetrakis(pentafluorophenyl)borate anion affords a very hydrophobic room temperature ionic liquid (RTIL) possessing a melting point below room temperature. The viscosity and conductivity of this RTIL have been measured along with cyclic voltammetry (CV) of the ferrocene/ferrocenium redox couple at an ultramicroelectrode from 25 to 90 °C. The RTIL demonstrates a polarized potential window (PPW) at the water|IL interface as large as 0.8 V; indicating the large hydrophobicity of its component ions. Simple ion transfer (IT), at the micro water|IL interface (25 μm in diameter) housed at the tip of a micropipette was calibrated using the tetraphenylarsonium tetraphenylborate TATB assumption. The Galvani transfer potentials of several IT reactions at the interface were determined. It was discovered that large peak-to-peak separation in CVs obtained at the solid–liquid and liquid–liquid junction was mainly due to the slow electron transfer (ET) and IT kinetics. This is confirmed by overlapping experimental and theoretical CVs obtained from finite element analysis simulations. Standard rate constants ( k°) of 5 × 10 −4 cm s −1 were garnered at these interfaces.