Proton exchange membrane fuel cells, also known as polymer electrolyte membrane fuel cells (PEMFCs), offer a way to power future emission-free vehicles, by providing stationary and portable power sources. However, the high cost and low durability of platinum catalysts are two major challenges hindering their commercialization. Researchers from the University of Western Ontario, and General Motors Research and Development Center have now discovered a new catalyst, platinum nanostars, that could make fuel cells more cost-effective and stable. [S. H. Sun et al., Angew Chem Int Ed (2011) 50, 422].

Pt is the most effective catalyst for fuel (usually hydrogen) oxidation at the anode and oxygen reduction reaction (ORR) at the cathode. The ORR is considerably slower than the oxidation of H2, and requires more catalyst. But Pt is expensive and relatively rare, and so has pushed up the price of fuel cells. At present, the most widely used cathode catalysts consist of fine particles of Pt supported on carbon black supports. In contrast to Pt nanoparticles, one-dimensional structures of Pt, such as nanowires, exhibit additional advantages associated with their anisotropy and unique structure.

Star-like single-crystal platinum nanostructures were produced, each with several nanowire arms with diameters of ~4 nm on carbon black. The carbon supported star-like Pt nanostructures (star-like PtNW/C) were synthesized in an environmentally friendly process, which does not require high temperatures, organic solvents, surfactants or complicated electrochemical deposition apparatus, by reducing a Pt precursor (H2PtCl6) with formic acid (HCOOH) in aqueous solution at room temperature.

The star-like PtNW/C showed greatly improved activity and durability compared to a state-of-the-art commercial catalyst made of Pt nanoparticles on carbon. More interestingly, the durability can be further improved by eliminating the carbon support.

The key reason this strategy works relies on the combination of a multi-armed network structure and the one-dimensional shape of the arms. This helps the activity and durability. In addition, the few surface defects and the preferential exposure of certain crystal facets further improves the activity. The increased activity and durability means that the amount of Pt needed on an electrode can be reduced, which could significantly lower the cost and increase the durability of PEMFCs.

Source: Materials Today