Proton-coupled electron transfer from an interfacial phenol monolayer

A tert-butyl protected phenol is covalently link to a mixed self-assembled monolayer on a gold or platinum electrode. The phenol reduction potential shows the expected pH-dependence of a one-electron, one-proton couple with a decrease in formal reduction potential of 59 ± 5 mV per pH. A titration of the phenol is observed with a pKa of 13.2 and the reduction potential for the phenolate is 0.11 V . NHE. The kinetic behavior of the proton-coupled oxidation deviates substantially from the commonly used models for a step-wise reaction that assume the proton transfer reactions are in equilibrium throughout the reaction. A novel model for step-wise proton-coupled reactions is presented that fully accounts for the pH dependent kinetics and allows the formal rate constants and the transfer coefficients to be determined. [Display omitted] •The pH-dependent mechanism of proton coupled redox reactions from a phenol monolayer is revealed.•A non-pre-equilibrium model (Steady-state model) accurately describes the kinetics of proton coupled redox reactions.•An approach to describe surface confined proton coupled electron transfer reactions with rate limiting proton transfer is presented.