Solution Viscosity Effects on the Heterogeneous Electron Transfer Kinetics of Ferrocenemethanol in Dimethyl Sulfoxide−Water Mixtures

Abstract

The electrochemical kinetics for the oxidation of ferrocenemethanol (FcCH 2 OH) over the whole composition range of dimethyl sulfoxide (DMSO)-water solutions of different viscosities (η) containing 50.0 mM (CH 3 ) 4 NClO 4 (TMAP) at a Pt microelectrode was studied using scanning electrochemical microscopy (SECM). The measured diffusion coefficient, D FcCH 2 OH , as well as the standard rate constant of the heterogeneous electron transfer, k 0 , as a function of solution composition, showed a minimum at about a DMSO molar fraction (x DMSO ) of 0.33, corresponding to the mixture with the maximum solution viscosity. The largest k 0 value found, 2.06 ( 0.31 cm s -1 in pure water (electrolyte) medium, was about 15 times larger than that obtained in the solution of x DMSO ) 0.33 (0.14 ( 0.02 cm s -1 ). A good linear correlation between ln k 0 and ln η was observed within the solution composition range of 0.10 e x DMSO e 0.60. An excellent linear correlation between ln k 0 and ln τ L , the longitudinal relaxation time, was also obtained with a slope equal to 1.0 when x DMSO ) 0-0.60. Unusually small rate constants found in the solutions of x DMSO g 0.70 were attributed to adsorption effects at the tip and the substrate electrode. The k 0 obtained for the present system was generally found to be inversely proportional to the viscosity of the solution and directly proportional to the diffusion coefficient of the electroactive species.

Delayed voltammetric with respect to amperometric electrochemical detection of concentration changes in microchannels

“…To investigate this possibility, we compared the responses of an electrode incorporated into a fluidic channel to variations in analyte concentration. The outer-sphere redox probe ferrocenemethanol (FcMeOH) 20,23,24 was used, to disentangle our observations from secondary mechanisms that are typical of inner-sphere reactions (adsorption, formation of chemical bonds, changes in chemical structure, etc. ), which may delay the response.…”

Electroreduction of peroxodisulfate on mercury in mixed water–carbohydrate media: The interplay of solvent effects and concentration-dependent structure of reaction layer

“…This type of mixed solvents was used earlier by a number of groups [9][10][11][12][13][14][15][16]. Despite of evident problems to interpret the data for solvent with so complex dielectric spectra (see discussion in Ref.…”

Cathodic pretreatment improves the resistance of boron-doped diamond electrodes to dopamine fouling

“…Initially cyclic voltammograms (CVs) for DA-unfouled electrodes were performed at cathodically and anodically prepared electrodes, for FcMeOH [10] and DA ( Figure 1B, C). The FcMeOH CVs for the anodic treatment show a slightly decreased current in comparison to the cathodic one, even though no significant differences are observed from the CV numerical characteristics (p=0.04 for ip and p=0.1 for ΔEp; Table 1).…”