Molecular Degradation of Iron Phthalocyanine during the Oxygen Reduction Reaction in Acidic Media

Abstract

Molecular iron phthalocyanine (FePc) possesses an FeN4 active site structure similar to practical pyrolyzed Fe/N/C catalysts for the acidic oxygen reduction reaction (ORR), making it an ideal model system to derive the degradation mechanism of such catalysts. However, the degradation mechanism of FePc during the acidic ORR has been largely unclear to date. Herein, five most likely degradation factors affecting FePc-based ORR activity are individually investigated and compared. The attack by free radicals is found to be the main reason for the instability of FePc. Assisted by the combination of several spectroscopic methods, we successfully identify the degradation products and then propose a full structural evolution of molecular FePc degradation. Finally, high similarity in the decay mechanism between molecular FePc and practical Fe/N/C catalysts was present. This study provides a clear picture of the currently missing degradation mechanism of molecular FePc during acidic ORR, which will assist future investigations on the performance degradation of practical Fe/N/C catalysts.

Influence of Carbon Nanotube Support on Electrochemical Nitrate Reduction Catalyzed by Cobalt Phthalocyanine Molecules

“…The first band is a weak band located at ∼594 cm −1 and is associated with Co−N stretching. 25,26 The second band is the most intense in the spectra, located at ∼1531 cm −1 , and is assigned to a vibration involving the movement of atoms in the C−N−C bridge bonds between the isoindole units. 27−30 Both bands are present in the CoPc hybrid structures.…”

Low-cost transition metal–nitrogen–carbon electrocatalysts for the oxygen reduction reaction: operating conditions from aqueous electrolytes to fuel cells

“…[92][93][94][95][96][97][98][99] By utilizing such molecular model catalysts, it is possible to track changes at the active site with clarity. For example, Wan et al 100 employed iron phthalocyanine (FePc) as a molecular-model catalyst to elucidate the degradation products and structural evolution pathways on FePc. Despite their well-dened structure, the ORR activity of these molecularmodel catalysts lags signicantly behind that of practical catalysts.…”

Identification and Understanding of Active Sites of Non‐Noble Iron‐Nitrogen‐Carbon Catalysts for Oxygen Reduction Electrocatalysis

“…[ 140,141 ] For example, Wan et al. [ 142 ] clearly revealed the degradation products and the corresponding structural evolution pathways of FePc molecule by in situ Raman spectroscopy. The degradation mechanism between molecular FePc and practical Fe‐N‐C catalysts was highly similar, and free radical attack was the main cause for the instability of FePc in acidic media.…”

“…Raman and infrared (IR) spectroscopy techniques, can be used to distinguish structural information of molecules and further identify the key reaction intermediates and dynamic process on active sites. [140,141] For example, Wan et al [142] clearly revealed the degradation products and the corresponding structural evolution pathways of FePc molecule by in situ Raman spectroscopy. The degradation mechanism between molecular FePc and practical Fe-N-C catalysts was highly similar, and free radical attack was the main cause for the instability of FePc in acidic media.…”