Researchers at Western University have deposited clusters of platinum as small as a single atom on sheets of graphene. The structures could improve catalysis in fuel cells and automotive catalytic converters.
Direct methanol fuel cells (DMFCs) generate electricity by oxidizing methanol and could be used in portable power applications such as laptops and mobile phones. Current DMFC catalysts are made of platinum supported on particles of carbon with diameters of about 30 nanometres (nm). “The advantage of graphene is its very high electrical conductivity, combined with very high surface area,” says project lead Andy (Xueliang) Sun, who holds the Canada Research Chair in Development of Nanomaterials for Clean Energy at Western. Using chemical reduction of graphite, his team created sheets of graphene that were about 500 to 1000 nanometres across, but only one atom thick.
The platinum was added via atomic layer deposition: graphene was functionalized with hydroxyl (OH) groups by reaction with water, then exposed to (methylcyclopentadienyl)-trimethylplatinum (MeCpPtMe3), which is converted to elemental platinum by decomposition. The material was characterized using X-ray light from the Canadian Light Source (CLS) in Saskatoon. “Platinum is a good catalyst because it has unoccupied high-energy orbitals in the outer shell where you can put electrons,” says Tsun-Kong Sham, who holds the Canada Research Chair in Nanomaterials and Synchrotron Radiation at Western. “It turns out there’s a correlation between the availability of these states to the performance.”
In a paper published in Scientific Reports, the team showed that the platinum-graphene catalysts oxidized methanol at rates 10 times higher than the current industry standard. “This approach can work for pure platinum, but also platinum alloys, palladium and really any noble metal,” says Sun. “I think it’s very promising.”