Proton-exchange membrane fuel cells convert chemical energy into electricity using an electrochemical cell and could be used as portable power sources with high energy densities. At the anode of these devices, the fuel (usually hydrogen) is broken down into protons and electrons using a catalyst. The protons then travel through the membrane to the cathode, whereas the electrons are forced to travel round an external circuit to reach the cathode. At the cathode, the protons and electrons react with oxygen to produce water with the help of another catalyst, which is typically composed of platinum nanoparticles dispersed across a carbon support. These nanoparticles can, however, degrade over time, compromising the performance of the fuel cell.
Xueliang Sun and colleagues at the University of Western Ontario and General Motors Research and Design Center have now developed a fuel cell catalyst that is both active and durable. The catalyst is comprised of single-crystal platinum nanostructures that have a star-like shape, each with several nanowire arms. Compared with a commercial platinum nanoparticle catalyst, the new catalyst is three times more active for the oxygen reduction reaction (as occurs at the cathode of the fuel cell). Furthermore, in accelerated durability tests the nanoparticles of the commercial catalyst significantly increased in size, reducing the active surface area of the catalyst, whereas the star-shaped nanostructures were relatively unaffected.