A new catalyst design utilizing metal nanoparticles and graphene may lead to longer lasting fuel cells, according to a recently published article in the Journal of the American Chemical Society, whose first author, Dr. Rong Kou, is a Senior Scientist at EC Power. The article, titled “Stabilization of Electrocatalytic Metal Nanoparticles at Metal-Metal Oxide-Graphene Triple Junction Points”, can be found in the journal’s March 2 issue (J. Am. Chem. Soc. 2011, 133, 2541–2547).
A great potential benefit of using catalyst nanoparticles as opposed to more commonly used larger particles, is that the nanoparticles yield a much larger surface area for the same amount of catalyst material. The electrochemical reactions that take place in fuel cells (and many other catalytic devices) take place on the surface of the catalyst. Therefore, for a given catalyst surface area required for a high-performing fuel cell, using nanoparticles as opposed to larger particles means the use of significantly less catalyst material. Because fuel cells and other catalytic devices frequently employ expensive catalyst materials such as platinum, the nanoparticles can lead to a considerable reduction in cost.
Directly incorporating catalyst nanoparticles in fuel cell electrodes is not the catch-all solution, however. One serious issue with directly using catalyst nanoparticles is that their small size causes them to be unstable, fusing together, thereby eliminating their potential surface area benefits. In fuel cells, this leads to accelerated degradation of electrodes, and a shortened cell life.
The work of Dr. Kou and her colleagues directly addresses this catalyst nanoparticle degradation issue. The paper elaborates on a new method developed to deposit metal oxides and metal nanoparticles on graphene (a form of solid carbon with special properties), forming stable metal-metal oxide-graphene triple junctions. The supported catalyst structure was developed by synthesis of indium tin oxide (ITO) nanocrystals directly on functionalized graphene sheets, followed by the deposition of platinum nanoparticles. The result is a unique triple-junction structure (Pt-ITO-graphene), for which experiments and density functional theory show the platinum particles to be more stable than they are in their native form. This enhanced stability should lead to less fusing of the platinum catalyst nanoparticles, and ultimately a longer-lasting fuel cell.
The new catalyst design has already shown promising results for oxygen reduction, which is the reaction that occurs in a hydrogen polymer electrolyte fuel cell cathode (the type of fuel cell widely being developed for automobiles). The approach is general enough, however, to have benefits for wide-ranging catalyst design, far beyond just the fuel cell application. You can read more about the work in R&D Magazine: http://www.rdmag.com/News/2011/02/Materials-Nanotechnology-Paperweight-For-Platinum/.