We report the electrochemical characterization of bis(trifluoromethylsulfonyl)imide (H[NTf(2))) and ferrocene in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(2)mim][NTf(2)]) 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[NTf(2)] and ferrocene at 298 K in [C(2)mim]NTf(2)]. 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.