|The new Pd nanoparticles outperform commercially available versions. Credit: ACS. Click to enlarge.|
Chemists at Brown University have developed palladium (Pd) nanoparticles for use as fuel cell catalysts with about 40% greater active surface area than commercially available palladium particles, and the nanoparticles remain intact four times longer. A paper on their work was published online 12 March in the Journal of the American Chemical Society.
Palladium has been under investigation as an alternative to platinum for use in fuel cells; palladium is more abundant and less expensive. However, researchers have had difficulties in creating palladium nanoparticles with enough active surface area to make catalysis efficient in fuel cells while preventing particles from clumping together during the chemical processes that convert a fuel source to electricity. The two Brown University researchers found a way to overcome those challenges.
This approach is very novel. It works. It’s two times as active, meaning you need half the energy to catalyze. And it’s four times as stable.—Vismadeb Mazumder, a graduate student who joined chemistry professor Shouheng Sun on the paper
Mazumder and Sun created palladium nanoparticles 4.5 nanometers in size. They attached the nanoparticles to a carbon platform at the anode end of a direct formic acid (CH2O2) fuel cell. They used weak binding amino ligands to keep the palladium nanoparticles separate and at the same size as they’re attached to the carbon platform. By keeping the particles separate and uniform in size, they increased the available surface area on the platform and raised the efficiency of the fuel cell reaction.
The oleylamine-coated Pd nanoparticles are readily “cleaned” with a 99% acetic acid wash, without jeopardizing the integrity of the separated palladium nanoparticles. This is an important step, Mazumder emphasized, because previous attempts to remove binding ingredients have caused the particles to lose their rigid sizes and clump together, which gums up the reaction.
The Brown team said in experiments lasting 12 hours, their catalysts lost 16% of its surface area, compared to a 64-percent loss in surface area in commercial catalysts.
The Brown scientists now are looking at various palladium-based catalysts with enhanced activity and stability for future fuel cell applications. The research was funded by the Division of Materials Research of the National Science Foundation and a Brown seed fund.
Vismadeb Mazumder and Shouheng Sun (2009) Oleylamine-Mediated Synthesis of Pd Nanoparticles for Catalytic Formic Acid Oxidation. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja9004915