Modified Electrodes with Adsorbed Porphine Complexes on Modified Covalent Surfaces. Effect of the Covalent Bond on the Electrocatalytic Activity

In this work, glassy carbon (GC) electrodes were modified with different species covalently bonded to the surface, being allowed to act as bridge molecules, for the posterior modification by adsorption of the azamacrocyclic complexes of transition metals. The bridge molecules that were studied were isonicotinic acid (GC-AL), 4-aminobenzoic acid (GC-PABA), 4-aminopyridin (GC-4AP) and the glassy carbon own functional groups obtained from its oxidation (GC-Ox). The modification was done through different methods that included the controlled-potential electrolysis in presence of the species, and electrochemical in-situ generation of the specie that was able for bonding.
Once this procedure was probed versus the redox couple Fe(CN)₆^3-/ Fe(CN)₆^2-, its electrocatalytic activity was studied versus oxygen reduction. It was found that the more active system, in comparison to the bare GC electrode, was the one that was obtained with the own GC functional groups (GC-Ox) (Figure 1A). Then, after the electrode was modified, the physical adsorption of the octaethyl porphine of M(II) complex (Figure 1B) was done, where M=Co, Cu, Zn, Ru and Fe. The modification process with the porphine was done by adsorption of monomer multilayers and by reflux, in order to obtain ordered systems with directional complex columns due to the different bridge molecules, as said before. It was found that the activity versus  oxygen electroreduction was notoriously increased when the Co(II) complex is used, which shows a potential shift and a current increment. The figure 1C shows this behavior for the system modified with GC-Ox, as a covalent electrode. In this case, the Fe complex gets a better response in terms of current, but the potential shift is better accomplished with the Co(II) complex (GC-Ox-Co).

Acknowledgements: To Fondecyt project Nº 1120049