Activity, Selectivity, and Anion-Exchange Membrane Fuel Cell Performance of Virtually Metal-Free Nitrogen-Doped Carbon Nanotube Electrodes for Oxygen Reduction Reaction

Virtually metal-free, aligned nitrogen-doped carbon nanotubes (N-CNTs) are prepared by an alumina template technique and characterized using XRD, Raman spectroscopy, SEM, and XPS. Highly uniform and aligned nanotubes are identified from SEM. The surface nitrogen concentration in the N-CNTs is estimated to be similar to 8.0 at.%. Electrocatalytic oxygen reduction reaction (ORR) activity in alkali media is investigated by rotating disk electrode (RDE) voltammetry and compared with commercial Pt/C (E-TEK). RDE measurements indicated the comparable ORR activity of nitrogen-doped carbon nanotubes with Pt/C. Kinetic analysis reveals that the ORR on nitrogen-doped carbon nanotubes follows the four-electron pathway leading to water. Moreover, during the ORR, nitrogen-doped carbon nanotubes exhibited substantially higher ethanol tolerance than Pt/C. A maximum power density of 37 and 62 mW/cm(2) is observed with N-CNT and Pt/C cathodes, respectively, under anion-exchange membrane fuel cell conditions. Durability measurements performed under fuel cell operating conditions for 30 h indicate the good stability of the catalysts.