New Strategies for Electrocatalysis at Polymer-Coated Electrodes. Reduction of Dioxygen by Cobalt Porphyrins Immobilized in Nafion Coatings on Graphite Electrodes

A new method for introducing porphyrin molecules into Nafion coatings on electrodes is described. The incorporated porphyrins are exceptionally stable and can readily be metallated while remaining in the coating. Coatings containing cobalt tetraphenylporphyrin (CoTPP) were prepared to exemplify the method, which is applicable to a variety of macrocyclic ligands possessing basic sites. The CoTPP in the Nafion coatings retained its ability to catalyze the electroreduction of dioxygen when the electrons were carried from the electrode to the almost immobile catalyst sites by Ru(NH₃)₆²⁺ ions also incorporated in the coating. The resulting separation of the catalytic and electron transport functions within such coatings is argued to have general virtues that may be exploited to extend the range of applicability of polymer-coated electrodes in electrocatalysis and to diagnose the mechanisms by which they operate.