Electrochemical reduction of dioxygen in Bis (trifluoromethylsulfonyl) imide based ionic liquids

Abstract

Electrochemical generation of superoxide ion ( O 2 - ) has been investigated in three room temperature ionic liquids (ILs), based on bis (trifluoromethylsulfonyl) imide anion, [N(Tf) 2] −, comprising the following cations N-(3-Hydroxypropyl)pyridinium, [HPPy] +, 1-(3-methoxypropyl)-1-methylpiperidinium, [MOPMPip] +, and 1-hexyl-1-methyl-pyrrolidinium, [HMPyrr] +. Cyclic voltammetry (CV) and chronoamperometry (CA) techniques were used for the analysis of the the electrochemical process. It was found that the generated O 2 - was not stable in the IL based on pyridinium cation, [HPPy] +. While a stable O 2 - was electrochemically generated in [MOPMPip] + and [HMPyrr] + based ILs. CV and CA techniques were used to determine the diffusion coefficients of O 2 and solubility of oxygen in the studied ILs as a function of temperature. The diffusional activation energies were then determined. It was found that [HMPyrr] + based IL, in general, has higher diffusion coefficient and solubility of O 2 and less diffusional activation energy than [MOPMPip] + based IL. For our best knowledge, this is the first time piperidinium based ILs has been used for the electrochemical generation of O 2 - .