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

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 chrono-amperometry (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 CY,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 [HMPyrrr 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(.-). (C) 2011 Elsevier B.V. All rights reserved.