Electrocatalytic oxidation of nitrite to nitrate mediated by Fe(III) poly-3-aminophenyl porphyrin grown on five different electrode surfaces

Conducting poly-tetrakis(3-aminophenyl) porphyrin-Fe(III) chloride films are prepared by electropolymerization of the complex on five different electrode surfaces: highly oriented pyrolytic graphite (HOPG), glassy carbon (GC), transparent electrode modified with tin oxide doped with indium (ITO), polycrystalline gold (Au(pc)) and monocrystalline An(111). The electrocatalytic behaviors of the polymer film-modified electrodes in the nitrite electrooxidation reaction were investigated. The results show that three of the five modified electrodes, HOPG, GC and ITO, have catalytic effect toward the oxidation of nitrite to nitrate. According to the shift of the potential, the activity shows the following order: HOPG approximate to ITO > GC. However, the activity measured as the increase in current between modified and unmodified electrode in the presence of nitrite at a fixed potential shows the following order: ITO >> HOPE > GC. In the case of Au(111) there is a current enhancement when the electrode is covered with the polymer film, but the foot of the oxidation wave appears at more positive potential. For Au(pc) the response in both current or potential is the same whether the electrode is modified or not. On the other hand, after a few cycles in the presence of nitrite, gold-modified electrodes (mono and polycrystalline) lose their activity. In the cases of HOPG, GC and ITO, the modified electrodes are stable and reproducible systems for the electrooxidation of nitrite. (c) 2007 Elsevier B.V. All rights reserved.