Catalytic Fe-xN Sites in Carbon Nanotubes

To reduce fuel cell cost, durable and inexpensive electrode catalysts need to be developed to replace precious metal materials, particularly for the electrocatalytic oxygen reduction at cathodes. In this study, we explored the structure and the energetics of Fe- x N ( x = 2,4) incorporated into carbon nanotubes and graphene using density functional theory to show that these structures are more stable than iron atoms on nanotubes and that pyridinic structures of Fe-4N are more favorable than pyrrolic structures. EXAFS spectra simulated from the optimized structures show good agreement with results of measurements obtained on arrays of aligned nanotubes doped with iron and nitrogen, which have demonstrated activity toward oxygen-reduction reactions.