Identification of Efficient Active Sites in Nitrogen-Doped\nCarbon Nanotubes for Oxygen Reduction Reaction

Abstract

Nitrogen-doped\ncarbon nanotubes (NCNTs) have demonstrated great\npromise as an electrocatalyst alternative to platinum for oxygen reduction\nreaction (ORR). However, there is much disagreement regarding which\nN doping sites are most desirable for the reaction. Here, we report\nan experimental and computational study to identify the efficient\nactive sites in NCNTs for ORR in alkaline media. In our experiments,\nwe synthesized NCNTs of similar overall N content (∼4.1%) and\ncarbon matrix but varying percentages of different types of N doping\nspecies. Our results reveal a positive correlation between ORR activity\nand the content of graphitic N doping. Furthermore, we performed density\nfunctional theory calculations to predict the free energy evolution\nof ORR on various N doping sites in NCNTs. Our computational results\nalso indicate that graphitic N doping sites exhibit higher thermodynamic\nlimiting potential for ORR than pyridinic N doping sites. Our combined\nexperimental and theoretical study concludes that graphitic N doping\nsites are more efficient for ORR than pyridinic N doping in NCNTs.