Work function, carrier type, and conductivity of nitrogen-doped single-walled carbon nanotube catalysts prepared by annealing via defluorination for efficient oxygen reduction reaction

Pyridinic and graphitic nitrogen atoms can be doped into carbon nanomaterials to create intrinsic structural defects and improve catalytic activity for the oxygen reduction reaction (ORR). An understanding of the relationship between the electronic properties and ORR activity of nitrogen-doped carbon nanomaterials could help design catalysts with better ORR performance. Here we report on the synthesis of nitrogen-doped single-walled carbon nanotubes (SWCNTs) by a combination of defluorination-assisted nanotube-substitution reaction and high-temperature annealing treatment using edge-free highly crystalline SWCNTs. The electronic properties of the prepared samples, such as the work function, carrier type, and conductivity were measured and correlated with their ORR activity in an acid electrolyte. Graphitic nitrogen-rich SWCNTs with n-type carrier, low work function, and high conductivity exhibited efficient ORR activity. The work function, carrier type, conductivity, and O₂ dissociative adsorption sites are dependent on both the species/number of doping nitrogen atoms and the structural defects. The tuning of these two structural factors is necessary for achieving high ORR activity.