N/O-co-doped Carbon Shell Structures Loaded with Iron Phthalocyanine for Oxygen Reduction Catalysis

Metal phthalocyanines (MPcs) have highly conjugated pi electron systems and metal atoms acting as active centers, and so exhibit excellent electrocatalytic performance during the oxygen reduction reaction (ORR). However, these complexes also tend to undergo aggregation and exhibit poor electrical conductivity and minimal durability, all of which hinder their large-scale industrial applications. In the present study, iron phthalocyanine (FePc) is applied to hollow carbon shells (HCSs) to generate an ORR catalyst containing single Fe atoms(HCS-O-FePc). The HCSs have numerous N/O-based surface functional groups that promote the formation of Fe-O bonds with the FePc held in an axial coordination position. These axial Fe-O bonds disrupt the electron symmetry in the plane of the FePc molecules, which facilitate electron transfer. 1100HCS-O-FePc exhibits an onset potential of 0.98 V (vs RHE), a half-wave potential of 0.91 V (vs RHE), an electron transfer number of 3.90, and durability better than that of a 20 % commercial Pt/C catalyst. Electrochemical impedance spectroscopy demonstrates that the ORR process over this material likely proceeds via a rapid 2+2 electron mechanism. This composite displays excellent oxygen reduction properties and is a promising alternative to Pt-based ORR catalysts.