Electrochemical study of the reduction of aromatic radical cations at a zinc oxide electrode

Abstract

The reduction of radical cations of rubrene, tri- p-tolylamine, and 9, 10-diphenylanthracene, which exhibit different electronic excited state energies, was studied at a ZnO electrode by voltammetric and capacity measurements. The current—voltage curves obtained for the three systems do not differ significantly, indicating that the electrode kinetics are not affected substantially by the involvement of excited states during electron transfer. The kinetics are rather controlled by irreversible electron transfer via surface states of which the existence has been confirmed by the capacity experiments. The energy of the surface states was estimated to be approx. 0.6 eV below the conduction band, and the rate constant k irr for the irreversible transitions has been determined to be 10 −1 cm s −1. From the change in the flat band potential on the generation of radical cations, it is concluded that the presence of the latter causes a change in the potential drop across the Helmholtz layer.