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

Electrochemical generation of superoxide ion (O2-) 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 O2- was not stable in the IL based on pyridinium cation, [HPPy]⁺. While a stable O2- was electrochemically generated in [MOPMPip]⁺ and [HMPyrr]⁺ based ILs. CV and CA techniques were used to determine the diffusion coefficients of O₂ 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 O₂ 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 O2.