Comparative study of electropolymerized cobalt porphyrin and phthalocyanine based films for the electrochemical activation of thiols

We present a comparative study of the behavior of electrodes modified with electropolymerized cobalt porphyrins and cobalt phthalocyanine films towards the electro-oxidation of 2-mercaptoethanol (2-ME). First, we report here on the electrochemical formation of the complex-based films and their characterization by cyclic voltammetry and electrochemical quartz microbalance measurements. The obtained results clearly show that the accessibility to the redox centers within the electropolymerized films is limited to the external layers. In particular, this report focuses on the effect of polymer film thickness on the thiol electro-oxidation reaction. However, the electrocatalytic activity of the porphyrin-modified electrode depends on the film thickness, in contrast to the phthalocyanine-based ones: the greater the thickness the lower is the activation of the thiol in terms of current and of oxidation potential. This can be explained by the lower electronic conductivity of electropolymerized porphyrin films compared to the phthalocyanine-based ones, and the probable intervention of the Co-III form of the deposited complexes.