A catalyst-free preparation of conjugated poly iron-phthalocyanine and its superior oxygen reduction reaction activity

Although Fe-phthalocyanine (FePc) has undergone extensive chemical modifications to realize improved oxygen reduction reaction (ORR), its superior performance has yet to be demonstrated at a practical level. Herein, a conjugated poly-FePc was prepared via microwave-assisted polymerization of 1,2,4,5-tetracyanobenzene in presence of FeCl2. The characterization results of multiple spectroscopic techniques indicated that poly-FePc and monomeric FePc possessed similar structural features, proving that the polymerization process was successful. Further, the prepared poly-FePc was tested for ORR in 0.1 M KOH electrolyte and compared with the traditional 20% Pt/C and monomeric FePc catalysts. Poly-FePc was found to be the best ORR catalyst among studied electrocatalysts, displaying 258 and 40 mV positive shifts in half-wave potential compared with FePc and 20% Pt/C, respectively. The theoretical studies suggested that the large conjugation in poly-FePc down-shifted the energy of the dz(2)-orbital of Fe closer to the pi*-orbital of O-2 (as also supported by the anodic shift in Fe3+/Fe2+ redox potential after polymerization), which allowed for an optimal coupling between these orbitals and therefore followed the 4e- ORR pathway. This study found that adjusting the electronic structures of the active sites of electrocatalysts might have improved their performance.

Automated summary

A conjugated poly-FePc was prepared via microwave-assisted polymerization and exhibited superior catalytic performance for oxygen reduction reaction (ORR). It displayed positive shifts in half-wave potential compared to monomeric FePc and traditional 20% Pt/C catalysts. The study suggests that adjusting the electronic structures of active sites can improve the performance of electrocatalysts.