Non-noble metal oxygen reduction electrocatalysts based on carbon nanotubes with controlled nitrogen contents

Nitrogen-doped carbon nanotubes (CNx) were prepared via a floating catalyst chemical vapor deposition method using precursors consisting of ferrocene and melamine to control the nitrogen content. Structure, morphology and composition of all CNx catalysts were characterized by SEM, TEM, and XPS. These results indicated that the surface nitrogen content (up to 7.7 at.%) increases with the increase of melamine used. Electrochemical methods were used to study the correlation between surface structure and the activity of oxygen reduction reaction (ORR) in acid and alkaline solutions. Electrochemical data indicated that the higher the nitrogen content is, the higher the oxygen reduction activity. Especially, the results from the rotating ring disk electrode technique demonstrated that CNx (7.7%) has similar ORR activity and selectivity with commercial Pt/C in alkaline solution.