Kinetic Behavior of Catalytic Active Sites Connected with a Conducting Surface through Various Electronic Coupling

Abstract

Electrocatalytic model surfaces consisting of catalytically active local surface sites and conducting electrode were formed by layer-by-layer assembly of functional molecules. The strength of electronic coupling between the catalytic surface sites and the electrode was tuned by changing the length and structure of wire molecules. When cobalt(II)–tetraphenylporphyrin was employed as a model surface site, the induced activity for oxygen reduction reaction was critically dependent on the coupling strength through the wire molecules. The overall reaction kinetics was disentangled to contributions of the internal electron tunneling and the intermolecular electron transfer. In the weak coupling condition with nanometer separation between the porphyrin and electrode, the overall reaction rate was limited by coherent quantum tunneling rate inside the catalytic system. In the strong coupling condition with the closer separation, on the other hand, the activity of the catalytic sites was significantly suppressed, a...