Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction

The large- scale practical application of fuel cells will be difficult to realize if the expensive platinum- based electrocatalysts for oxygen reduction reactions ( ORRs) cannot be replaced by other efficient, low- cost, and stable electrodes. Here, we report that vertically aligned nitrogen- containing carbon nanotubes ( VA- NCNTs) can act as a metal- free electrode with a much better electrocatalytic activity, long- term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air- saturated 0.1 molar potassium hydroxide, we observed a steady- state output potential of - 80 millivolts and a current density of 4.1 milliamps per square centimeter at - 0.22 volts, compared with - 85 millivolts and 1.1 milliamps per square centimeter at - 0.20 volts for a platinum- carbon electrode. The incorporation of electron- accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four- electron pathway for the ORR on VA- NCNTs with a superb performance.