Edge plane pyrolytic graphite electrode covalently modified with 2-anthraquinonyl groups: theory and experiment.

An edge plane pyrolitic graphite (EPPG) electrode was modified by electrochemical reduction of anthraquinone-2-diazonium tetrafluoroborate (AQ2-N(2)(+)BF(4)(-)), giving an EPPG-AQ2-modified electrode of a surface coverage below a monolayer. Cyclic voltammograms simulated using Marcus-Hush theory for 2e(-) process assuming a uniform surface gave unrealistically low values of reorganisation energies, λ, for both electron transfer steps. Subsequently, two models of surface inhomogeneity based on Marcus-Hush theory were investigated: a distribution of formal potentials, E', and a distribution of electron tunneling distances, r(0). The simulation of cyclic voltammograms involving the distribution of formal potentials showed a better fit than the simulation with the distribution of tunneling distances. Importantly the reorganization energies used for the simulation of E' distribution were similar to the literature values for adsorbed species.