Palladium is far cheaper than the currently widely used platinum, and it is more abundant. However, researchers have struggled to create Pd nanoparticles with enough active surface area to make catalysis efficient in fuel cells, while preventing particles from clumping together during the power-generating electrochemical processes. But two Brown University chemists have now found a way to overcome those challenges.
In a paper in the online edition of the Journal of the American Chemical Society, the team report that they have produced Pd nanoparticles with about 40% greater surface area than commercially available Pd particles. These catalysts also remain intact four times longer than ones that are currently available.
Chemistry professor Shouheng Sun and graduate student Vismadeb Mazumder created Pd nanoparticles 4.5 nm in size. They attached the nanoparticles to a carbon platform at the anode end of a direct formic acid fuel cell. The researchers then did something new: they used weak binding amino ligands to keep the Pd nanoparticles separate at the same size as they are 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 ligands can also be ‘washed’ from the carbon platform without jeopardizing the integrity of the separated Pd nanoparticles. This is an important step, emphasizes Mazumder, because previous attempts to remove binding ingredients have caused the particles to lose their rigid sizes and clump together, which interferes with the reaction.
According to the Brown University team, in experiments lasting 12 h their catalyst lost 16% of its surface area, compared with a 64% loss which can occur with commercial catalysts. The scientists are now are looking at various Pd-based catalysts with enhanced activity and stability for future fuel cell applications.