Intrinsically Functionalized Fe/C₃N₄ Nanotubes Display pH-Dependent Oxygen Reduction Overpotentials

The oxygen reduction reaction (ORR) has been studied for decades due to its importance in fuel cells or batteries. Carbon-based materials decorated with few metal active sites are one of the options to replace and reduce the use of Pt metals. Here, we demonstrate the ORR on various intrinsically functionalized Fe/C₃N₄ nanotubes by density functional theory (DFT) calculations in both acidic and alkaline media. Most of the alkaline overpotentials are similar regardless of functionalization and are generally lower than those in the acidic media. On the other hand, systems with the intrinsically functionalized O₂ can dramatically and significantly lower the overpotentials in acidic media. Our results are consistent with the experimental data reported at different pH values and may correlate with the better performance observed in a higher O₂ extent environment in solution. This study provides experimentalists with a microscopic understanding of the different operating conditions of the ORR.