Electrochemistry of Hydrogen in the Room Temperature Ionic Liquid 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide: Dissolved Hydrogen Lubricates Diffusional Transport

We report the electrochemical characterization of bis(trifluoromethylsulfonyl)imide (H[NTf2)) and ferrocene in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf2]) in the presence of dissolved hydrogen (H-2). Chronoamperometric measurements in the presence of varying levels of H-2 were used to determine the diffusion coefficient of H[NTf2] and ferrocene at 298 K in [C(2)mim]NTf2]. Upon saturation with H-2 at 298 K, these were found to increase from 2.5 (+/- 0.1) x 10(-11) m(2) s(-1) and 4.7 (+/- 0.1) x 10(-11) m(2) s(-1) to 2.8 (+/- 0.1) x 10(-11) and 5.1 (+/- 0.1) x 10(-11) m(2) s(-1), respectively. It is believed that the physiochemical changes correspond to the H-2 occupying the interstices and therefore resulting in a change in the permittivity of the space between ions of the RTIL, resulting in diminished Coulombic interactions and a net reduction in the RTILs viscosity. Even more significant changes were observed at 308 K, despite the dissolved H-2 concentration being lower (4.4 mM H-2 at 298 K, 4.0 mM H-2 at 308 K). Arrhenius plots of the diffusion coefficient of ferrocene in the RTIL displayed a decrease in the diffusion activation energy from 29.5 kJ mol(-1) in the absence of H-2 to 20.5 kJ morl(-1) upon saturation with H-2. The activation energy of diffusion of H-2 was also determined in an RTIL for the first time (13.7 kJ mol(-1)), and deviation of the mass transport of the small H-2 molecule from the Stokes-Einstein relationship was confirmed.