Control of Catechol and Hydroquinone Electron-Transfer Kinetics on Native and Modified Glassy Carbon Electrodes

The electrochemical oxidation of dopamine, 4-methylcatechol, dihydroxyphenylacetic acid, dihydroxyphenyl ethylene glycol, and hydroquinone was examined on several native and modified glassy carbon (GC) surfaces. Treatment of polished GC with pyridine yielded small ΔEp values for cyclic voltammetry of all systems studied, implying fast electron-transfer kinetics. Changes in surface oxide coverage had little effect on kinetics, nor did the charge of the catechol species or the solution pH. Small ΔEp values correlated with catechol adsorption, and surface pretreatments that decreased adsorption also increased ΔEp. Electron transfer from catechols was profoundly inhibited by a monolayer of nitrophenyl or (trifluoromethyl)phenyl (TFMP) groups on the GC surface, so that voltammetric waves were not observed. The ΔEp increased monotonically with surface coverage of TFMP groups. The results indicate that catechol adsorption to GC is required for fast electron transfer for the redox systems studied. Unlike Ru(NH3)6...