Background Information

The need for highly active fuel cell catalyst materials is clear, but the stability of these materials is still in question.   Nanoparticles are essential for fuel cell catalysts due to their high surface areas, allowing maximum utilization of the precious catalyst. Over long periods of time, however, platinum and platinum-ruthenium alloy catalysts undergo dissolution and ripening processes that cause the catalyst surface to be modified.  Since heterogeneous catalysis deals directly with surface chemistry, stability is of the utmost importance.

Intermetallic nanoparticles, such as PtBi and PtPb, are inherently more stable than an alloy such as Pt-Ru because the atoms are linked by an ordered crystal structure.  An alloy is a solid-solution where there is little preference for ordered of atoms, allowing atom migration over time.  An ordered intermetallic holds atoms in place by high enthalpy of mixing, leading to a more stable catalyst material.

My Research

Although industry is actively using Pt and Pt-Ru as anode fuel cell catalysts, dissolution and morphology changes cause breakdowns over time.  This is not predicted by bulk models where the pH and potential are both very low, yet it occurs, most likely due to property changes on the nanoscale.  My work looks at how these dissolution processes take place at the Pt anode and if intermetallics can help mitigate these processes.  I am studying this through a combination of rotating ring-disk electrode voltammetry and characterization.  Using pXRD, HRTEM, SEM, and ICP, the fate of nanoparticles over time can be studied, hopefully leading to a mechanism for dissolution.

I am also interested in the synthesis of intermetallic nanoparticles using confined geometries.  Restraining nanoparticle formation to a very small space, such is in a micelle, may help coerce the formation of homogeneous particles.  Differences in thermodynamics and kinetics between reducing species frequently cause heterogeneity in elemental composition in a bulk phase reduction.  Confined geometries may lead to not only single phase crystallites, but small unagglomerated nanoparticles as well.