Molecular electrocatalysis of oxygen reduction by iron(II) phthalocyanine at the liquid/liquid interface

• ORR catalyzed by iron(II) phthalocyanine was studied at the liquid/liquid interface.
• The catalytic O2 reduction mainly produces H2O with only minority of H2O2 (less than 5%).
• The reaction possibly involves a hydroperoxo intermediate.

Liquid/liquid interface electrochemistry has manifested itself as a good approach to study oxygen reduction reaction (ORR) and ORR catalyzed by various catalysts. In this work, we investigated the ORR catalyzed by iron(II) phthalocyanine (FePc), which has a structure similarity to the heme group of O2-binding proteins and reducing enzymes, at the polarized water/1,2-dichloroethane interface. Using the four-electrode cyclic voltammetry and the shake-flask biphasic reaction under chemically controlled polarization, it was demonstrated that FePc could catalyze the molecular oxygen reduction by lipophilic electron donors, such as 1,1′-dimethylferrocene (DFc) or tetrathiafulvalene (TTF), at the heterogeneous phase boundary. The overall process essentially can be equivalent to an interfacial proton transfer coupled ORR, which proceeds preferentially via a four electron reduction pathway to produce mainly H2O with only minority of H2O2 (less than 5%). The catalytic activity of FePc was compared with all previously studied porphyrins and phthalocyanines. The reaction mechanism was also analyzed, in which a hydroperoxo intermediate was probably involved.

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