Extraordinary Hydrogen Evolution and Oxidation Reaction Activity from Carbon Nanotubes

Abstract

The hydrogen evolution reaction, 2H+ + 2e- -> H2, has utility in the electrochemical production of hydrogen from water and is perhaps the most studied reaction in all of electrochemistry. Its converse, the hydrogen oxidation reaction, H2 -> 2H+ + 2e-, is the half cell reaction occurring in hydrogen fuel cells, which, by direct conversion of chemical to electrical energy avoids the Carnot efficiency limits intrinsic to heat pumps. These reactions are central to any realization of a hydrogen economy. Various forms of carbon have been used for decades as the precious metal catalyst support in these reactions. Here we report the unexpected result that single wall carbon nanotubes (SWNTs), can be activated by a simple process to exhibit an activity for these reactions, in acidic and pH neutral electrolytes, that exceeds that of all known non-precious metal catalysts. We have labored to exclude conventional metals as the source of this activity and concluded that it is due to the SWNTs themselves.