Voltammetry of Adhered Microparticles in Contact with Ionic Liquids: Principles and Applications

Abstract

Although many compounds possess a high thermodynamic level of solubility in ionic liquids, the rate of their dissolution in this type of media is frequently extremely slow. As a result, it can take several hours to prepare the solutions needed for electrochemical studies, even when the dissolution process is assisted by sonication or heating. Under these conditions, voltammetric studies with adhered microparticles are advantageous, allowing parameters such as formal potentials and electrode kinetics of electroactive species to be investigated without lengthy and tedious solution preparation. This chapter focuses on reviewing the attributes of voltammetry of adhered microparticles in contact with ionic liquids method for determining the thermodynamics and kinetic properties of electroactive species exhibiting a diverse range of electrode-reaction mechanisms. The conditions under which the adhered microparticle method gives voltammetric data analogous to that observed when working in the dissolved state are outlined, and the results obtained when applied to oxidation of ferrocene and its derivatives in a range of ionic liquids are surveyed. Additionally, quantitative measurements on electrode processes exhibiting more complex mechanisms, such as electron-transfer with a coupled first-order homogeneous process (oxidation of cis-[Mn-(CN)(CO)2{P(OPh)3} (Ph2PCH2PPh2)]) or with unstable reactants, intermediates, or products (polyoxometalate reduction in the “distillable ionic liquid” DIMCARB, which is largely composed of N,N-dimethylammonium, N′,N′-dimethylcarbamate and the corresponding N′,N′-dimethylcarbamic acid) and benzophenone reduction in “wet” 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide are considered. Use of a microchemical thin-layer configuration, which involves immersing a microparticle-modified electrode with a thin film of adhered hydrophobic ionic liquid into aqueous solution is considered, along with application of this technique to the reversible oxidation of trans-[Mn-(CN)(CO)2{P(OPh)3}(Ph2PCH2PPh2)]. In summary, the voltammetry of adhered microparticles is demonstrated to provide a powerful electroanalytical tool which has great versatility in ionic liquids, under conditions where conventional dissolved-state voltammetry is sometimes difficult or impractical.