Probing the Role of Pore Architecture of Carbon Support in the Stability of Iron Phthalocyanine during Oxygen Reduction

Emerging carbon-based molecular catalysts with a single metal active center possess attractive oxygen electroreduction performance comparable with that of commercial Pt/C catalysts. Nonetheless, the relative instability curtails their widespread industrial application. Research has started to clarify the mechanisms behind the degradation of the active site itself. However, the impact of the carbon support on the catalyst stability remains not fully understood. Here, we employed carbon supports with distinct pore structures (e.g., Ketjen black, carbon nanotube) to load iron phthalocyanine (FePc), which serves as a model single metal active center. The resulting catalysts exhibited markedly divergent stability with current density decreases of 63% and 34% over 10 h of amperometric I-t test, respectively. By integrating in situ electrochemical impedance spectroscopy (EIS) with distribution of relaxation times (DRT) analysis to dissect degradation pathways, we have found that variations in pore structures decisively impact the wetting behavior and mass transfer efficiency within the microenvironment around the catalytic sites, thus greatly influencing stability. Our insights provide a new viewpoint and strategic approach for designing carbon-based catalysts with highly a stable single metal active site.