Novel electrocatalyst for the oxygen reduction reaction in acidic media using electrochemically activated iron 2,6-bis(imino)-pyridyl complexes

Abstract

Electrochemically activated materials produced from iron 2,6-bis(imino)-pyridyl complexes were deposited onto a glassy carbon electrode from an acetonitrile solution containing 0.1 mol dm −3 tetrabutylammonium perchlorate and 0.002 mol dm −3 monomeric iron chelate by successively scanning the potential between −0.6 and 0.8 V vs. the Ag/Ag + reference electrode (RE). The electrocatalytic activity of the resultant material to the reduction of dioxygen molecules in aqueous sulfuric acid solution was studied by hydrodynamic voltammetry. It is found that although the material can dissolve in sulfuric acid solution, it is re-deposited on the electrode surface during cathodic polarization. The re-deposited material can efficiently catalyse the electrochemical reduction of molecular dioxygen through different pathways depending upon the structure of the ligands. The material produced from the iron chelate with 2,4,6-trimethylphenyl substituents allows only a two-electron reduction of dioxygen molecules, while the reduction of dioxygen on the material produced from the iron chelate with 2,6-biisopropylphenyl substituents follows the four-electron pathway to produce water. The latter material shows good stability and unusually high mass activity towards the oxygen reduction reaction in the acidic medium. Although the onset potential is quite low (−0.2 V vs. SCE), the material is a prospective candidate in power sources, oxygen sensors and some chemical processes. It is suggested that the active center for oxygen reduction is determined by the structure of the activated material.