Electrocatalytic Four-Electron Reduction of Dioxygen by Electrochemically Deposited Poly{[meso-tetrakis(2-thienyl)porphyrinato]cobalt(II)}

Poly {[meso-tetrakis(2-thienyl)porphyrinato]Co(II)} (pCoTTP) was deposited onto a glassy carbon electrode (GCE) through electrochemical polymerization of [meso-tetrakis(2-thienyl)porphyrinato]Co(II). Both cyclic voltammetry and the rotating disk electrode (ROE) techniques were employed to investigate the kinetics and mechanism of the oxygen reduction reaction (ORR) by the pCoTTP-modified electrode. In comparison to a bare GCE or an electrode containing the nonmetalated polymer analogue, poly[meso-tetrakis(2-thienyl)porphyrin] (pTTP), the pCoTTP-modified electrode shows a significant electrocatalytic enhancement of the ORR as reflected in a current increase and peak potential shift to a lower reduction potential. Koutecky-Levich plots suggest a four-electron process for oxygen reduction in acidic, neutral and basic solutions using the pCoTTP-modified electrode, as opposed of the two-electron process that is usually observed for monomeric cobalt porphyrins. The electrocatalytic stability of the pCoTTP layer and its excellent tolerance toward the poisoning by methanol is demonstrated, highlighting this electrode as a promising precious metal-free electrode material for oxygen reductions in, for instance, fuel cells.