The U.S. Department of Energy (DOE) is actively pursuing cheaper automotive fuel cells as part of its push for alternative energy solutions. Specifically, proton exchange membrane fuel cells—powered by hydrogen and the oxygen contained in air via a reduction-oxidation reaction—are seen to have the greatest potential for use in the auto industry.
In 2008, the system cost for automotive fuel cells was $95 per kilowatt. By 2015, the DOE wants to bring the cost down to $30, roughly the same as that of a gasoline engine. To achieve this target, the expensive platinum electrode catalysts—used in fuel cells since the 1960s—have been singled out for replacement.
A group from the University of Dayton recently discovered that nitrogen-doped carbon nanotubes could be the solution the DOE is seeking. The results, published in Science, show that electrodes containing vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) have much better electrocatalytic activity for the oxygen reduction reactions required to generate electricity in alkaline fuel cells. The VA-NCNTs also display long-term stability and are not susceptible to the carbon monoxide poisoning that can deactivate platinum catalysts. Most importantly, the carbon nanotube-based electrode can potentially be produced more cheaply than the platinum version.
Since reporting his group's results in February, Dr. Liming Dai has been working with a “major energy company” to test the viability of the VA-NCNT electrodes in an acidic fuel cell environment, and is looking at other applications in which nitrogen-doped carbon nanotubes can be used as efficient, cost-effective metal-free catalysts.
Carbon nanotube-based catalysts have already proven effective in a number of chemical conversions, one of which occurred at the Max Planck Society in Berlin. In this application, butane was converted into butadiene, a chemical used extensively by rubber and plastics manufacturers. Compared with the current metal oxide catalyst process, the reaction ran at a much lower temperature and required much less oxygen, making the process safer and more efficient.
Carbon Nanotubes Caught On Film The use of carbon nanotubes in consumer products and solar cells is set to increase this year, driven largely by advances in thin-film nanotechnology. With proprietary carbon nanotube synthesis, ink formulation and coating processes in place, Unidym is testing a number of applications for its thin, transparent, ultra-conductive carbon nanotube-coated plastic films. In October of last year, SAMSUNG used Unidym’s film to demonstrate a color display the size of a piece of paper, proving that carbon nanotube-based films are a viable alternative to indium-tin oxide-coated films currently used in displays. Electronics giant LG Display has also jumped on board, entering into an agreement with Unidym to develop a version of its carbon nanotube films for use in its displays.
Unidym is also positioned to play a major role in the development of thin-film solar cells, which replace the large wafers used in silicon cells with ultra-thin layers of light-absorbing material. Essential to this technology is a transparent layer of conductive film that acts as an electrode by collecting the current generated by the cells.