Experimental and theoretical study of the activity of substituted metallophthalocyanines for nitrite electro-oxidation

The electrocatalytic activity of various metallophthalocyanines (M-Pc) adsorbed on an ordinary pyrolytic graphite electrode for the oxidation of nitrite has been investigated in aqueous phosphate buffer solution (pH 7.3). A comparison of Pcs of different metals, shows that the activity is influenced by the nature of the central metal but not very significantly. However, the effect of substituents on the periphery of the Pc ligand is more pronounced. Electron-donor substituents of the Pc ligand enhance this activity. At a density functional theoretical level, we found that the calculated condensed Fukui function, associated to a nucleophilic attack, gives a reasonable explanation for the location of the reaction site in the case of the set of M-Pcs. Indeed, for Cr-Pc, Mn-Pc, Fe-Pc, and Co-Pc, the Fukui function predicts that the preferred reactive sites are located on the central metal whereas for Ni-Pc, Cu-Pc, and Zn-Pc it predicts that the reactive sites are located on the ligand, in agreement with the experimental trends observed. (C) 2003 The Electrochemical Society.