Suppression Effect of Small Organic Molecules on Oxygen Reduction Activity of Fe/N/C Catalysts

Abstract

Pyrolyzed Fe/N/C catalysts have high selectivity for catalyzing the oxygen reduction reaction (ORR) and exhibit no activity toward the electrooxidation of small organic molecules (SOMs). As such, their tolerance toward SOMs has rarely been questioned. Unexpectedly, we found that SOMs can greatly suppress the ORR activity of microporous-type Fe/N/C catalysts in alkaline medium. Such a suppression effect is strengthened as molecular polarity decreases or molecular weight increases and can be attributed to the blockage of micropore transport channels for ORR-related species by SOM adsorption. Interestingly, such a suppression effect by micropore filling disappears in the acidic medium. High tolerance to SOMs in acidic medium is attributed to the protonation of pyridinic-N, which increases the polarity of the micropore surrounding and inhibits the adsorption of low-polarity SOMs. This study is helpful to guide the synthesis of porous Fe/N/C electrocatalysts, especially when they are applied in an alkaline medium.