Defects in Nanotubes Could Halve Energy Required for Hydrogen Production

29 September 2005

A water molecule interacts with a carbon nanostructure.

Scientists at North Carolina State University have modeled a nanoscale method for extracting hydrogen from water that should require only half the energy of current hydrogen production methods.

The researchers discovered that defects in carbon nanotubes make it easier to disassociate water molecules and thus to extract hydrogen.

The scientists, led by NC State Department of Physics professor Dr. Marco Buongiorno-Nardelli and Dr. Keith Gubbins, W.H. Clark Distinguished University Professor of Chemical and Biomolecular Engineering, published their results in the 30 Sep edition of Physical Review Letters.

Buongiorno-Nardelli’s team discovered that naturally occurring defects in the nanotubes can increase the rate of a chemical reaction, because the atoms that form the defective nanotubes are essentially incomplete, thus making them more reactive.

Normally, when you talk about chemical reactions in carbon nanotubes, you’re imagining that these reactions are happening in perfectly formed nanostructures. But the reality is that these structures have defects—places where the carbon atom network is broken. And these defects can influence the chemical reaction.

—Prof. Buongiorno-Nardelli

When the team began running computer models to simulate what would happen if they used the defective nanostructures to break water molecules, it found that you could reduce the energy necessary by factor of two. To put it in another context, rather than having to heat water to 2,000º C to disassociate the molecules, you could achieve the same result at less than 1,000º if done over defective sites in graphene or nanotubes.

We studied water for many months and ran many different calculations, and we ended up showing that if you want to break a water molecule, you spend a lot less energy if you do it on this defective carbon material than if you do it by simply heating the molecule until it breaks.

This approach currently remains theoretical. The NCSU researchers hope to collaborate with other scientists to design and construct a nanoscale chemical reactor that embodies the principle.

Resources:

• “Dissociation of Water on Defective Carbon Substrates,”, published 30 Sep 2005, in Physical Review Letters