Carbon nanotube material could lower cost of fuel cells

Platinum is a well-established catalyst but it costs more than $1,000 (£645) an ounce, which is a limiting factor for applications such as fuel cells that rely on the metal.

In a search for an inexpensive alternative, a team including researchers from the US Department of Energy’s Oak Ridge National Laboratory (ORNL) turned to carbon, one of the most abundant elements.

Led by Stanford University’s Hongjie Dai, the team developed a multi-walled carbon nanotube complex that consists of cylindrical sheets of carbon.

According to ORNL, once the outer wall of the complex was partially unzipped with the addition of ammonia, the material was found to exhibit catalytic properties comparable to platinum.

Although the researchers suspected that the complex’s properties were due to added nitrogen and iron impurities, they couldn’t verify the material’s chemical behaviour until ORNL microscopists imaged it at an atomic level.

‘With conventional transmission electron microscopy, it is hard to identify elements,’ said team member Juan-Carlos Idrobo of ORNL. ‘Using a combination of imaging and spectroscopy in our scanning transmission electron microscope, the identification of the elements is straightforward because the intensity of the nanoscale images tells you which element it is. The brighter the intensity, the heavier the element. Spectroscopy can then identify the specific element.’

ORNL microscopic analysis confirmed that the nitrogen and iron elements were incorporated into the carbon structure, causing the observed catalytic properties similar to those of platinum.

The next step for the team is to understand the relationship between the nitrogen and iron to determine whether the elements work together or independently.