Catalytic electroreduction of molecular oxygen at glassy carbon electrodes with immobilized iron porphyrins containing zero, one, or four amino groups

Reduction of oxygen at glassy carbon (GC) electrodes modified with iron tetraphenyloprphyrin derivatives (FeTPPs) having zero, one, or four amino groups was studied by several electrochemical methods. The number of prophyrin layers required to attain four-electron reduction in water were ca. 8, 5, and 2 for FeTTPs containing zero, one and four amino groups, respectively, indicating that the functional group does influence O₂ reduction. Moreover, the rate constants governing the reaction of the catalysts with oxygen were larger for FeTTPs with more amino groups. Ellipsometry on the modified GCs suggested that the porphyrin molecules are nearly stratified on the GC surface and therefore that the interdistance of the porphyrin plane is not a signficant factor affecting the four-electron reduction of oxygen.