Glassy carbon electrodes modified with supramolecular assemblies generated by π-stacking of Cobalt (II) octaethylporphyrins. A 4 electrons-dioxygen reduction reaction occurring at positive potentials

A new method of modifying previously oxidized glassy carbon electrode (GCE) using commercial cobalt (II) porphyrin is proposed. This novel assembly presents a significant improvement in terms of electroactivity towards the oxygen reduction reaction (ORR), as compared to other reported systems. The device reduces molecular oxygen at positive potentials involving 4 electrons, as corroborated by kinetic studies. In addition, a 46 mV per decade Tafel slope was obtained, evidencing that the ORR mechanism would involve a chemical step following the first electron transfer, or, the rate determining step would be the transfer of a second electron. Concomitant to this, studies with different metalloporphirins were accomplished in order to compare the central metal ion effect. Morphological studies conducted using Atomic Force Microscopy (AFM) consistent with the proposed modification based on the structural changes found on the GCE surface, as well as to the obtained differences of roughness parameters (Rq values). Finally, it was demonstrated that this new system is better, in terms of electroactivity, than previously reported arrays. (C) 2015 Elsevier Ltd. All rights reserved.