Catalytic Reactions on the Open-Edge Sites of Nitrogen-Doped Carbon Nanotubes as Cathode Catalyst for Hydrogen Fuel Cells

Abstract

Recent experimental reports proposed that pyridinic-type sites on the open edges of carbon nanotubes (CNTs) may contribute to the high catalytic activity for oxygen reduction reaction (ORR) on nitrogen-doped CNTs (N-CNTs). Herein, we performed first-principles spin-polarized density functional theory calculations to examine the catalytic steps for ORR and water formation reaction (WFR) on the open edges of N-CNTs. For half-N doping on the open edge of CNTs (HN-CNTs), O2 and OOH can be chemisorbed and partially reduced on the C–N bridge site without an energy barrier. The subsequent WFR for reduced O2/OOH with ambient H+ and additional electrons can be finished without energy barrier for the formation of two H2O molecules. The second H2O molecule needs an energy of ∼0.49 eV to be desorbed from the catalytic site, which completes an electrocatalytic reaction cycle on the cathode catalyst for hydrogen fuel cells (HFCs). For H-saturated open-edge sites of HN-CNT, ORR and WFR can also be completed energeticall...