Oxygen Reduction at Cobalt Phthalocyanine Modified Au(111) Electrodes

Abstract

Au(111) substrates were modified with cobalt phthalocyanine (CoPc) monolayers. Formation of the adsorbed layer was confirmed by in situ electrochemical scanning tunneling microscopy (STM) while its electrochemical activity was monitored by cyclic voltammetry (CV). The adsorbed molecules have demonstrated a noticeable electrocatalytic activity toward the reduction of oxygen. Significant changes in the STM features of the adsorbed molecules were observed when the measurements were performed in the presence of ca. 1 atm of oxygen at low overpotentials. The reported features were attributed to changes in the electronic structure of the molecule when it forms an intermediate during oxygen reduction. Geometries of two of the possible intermediates, HOOCoPc and O2CoPc, were optimized by density functional theoretical (DFT) method. Frontier orbitals of the hydroperoxo intermediate have electronic density similar to the STM features reported here, which could support that we are probing a reaction intermediate during the O2 reduction process.