A Comparison of Electron Transfer Kinetics of Three Common Carbon Electrode Surfaces in Acetonitrile and in Room Temperature Ionic Liquid 1-Butyl-3-Methylimidiazonium Hexafluorophosphate: Correlation to Surface Structure and the Limit of the Diffusion Domain Approximation

We report the comparison of electron transfer kinetic parameters of the ferrocene redox couple in both acetonitrile and in room temperature ionic liquid (RTIL) 1-butyl-3-methylimidiazonium hexafluorophosphate ([C(4)min] [PF6]) using edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG) and glassy carbon (GC) electrodes. Each electrode Surface was characterized using SEM and AFM and the surface morphology was analyzed in terms of surface heterogeneity including the distribution of edge plane defects. The experimental data were modeled using both one and two dimensional simulations to correlate the electron transfer parameters obtained with the different surface Structure of each electrode. Furthermore, we show that the diffusion domain approximation (commonly used to accurately simulate electron transfer kinetics at graphitic Surfaces) breaks down when a BPPG electrode is used in RTIL and demonstrate the near impossibility of assigning rate constant to the basal plane surface.