Effect of the structural parameters of commercial carbon supports on the oxygen reduction reaction activity of iron phthalocyanine

Iron phthalocyanine (FePc)—a molecular catalyst—has attracted attention for the oxygen reduction reaction (ORR) in fuel cells and other applications. Supporting FePc on carbon materials enhances the ORR activity. However, factors influencing its ORR activity remain unclear owing to limited data on carbon supports. To further improve the ORR catalytic performance of the Fe–N4 structure, this study systematically investigated the structural parameters of carbon supports that influence the ORR activity of FePc. Compared to bulk FePc powder, the ORR activity was higher for all the carbon-supported FePc catalysts. The ORR current correlated with the amount of electrochemically responsible FePc, determined by cyclic voltammetry, rather than with the total loaded FePc. The amount of electrochemically responsible FePc also increased with carbon layer size. Furthermore, the onset potential for the ORR varied with carbon support, with Ketjenblack (KB) showcasing the highest value. Transmission electron microscopy and small-angle X-ray scattering measurements revealed a hollow spherical structure for KB (the average diameter = 44.8 nm). X-ray absorption fine structure analysis showed that the KB-supported FePc was curved. Thus, our study provides insights into the key influencing factors of carbon support that enhance the ORR activity of FePc.