Synthesis and nanostructure-activity correlation of multimetallic catalysts for oxygen reduction reaction in fuel cells

Nanomaterials have found diverse applications in areas such as catalysis, chemical/bio sensing, microelectronics and medical diagnostics. The application in fuel cell catalysis is often hampered by the lack of clear correlation between nanostructural parameters and the electrocatalytic properties. This dissertation work focuses on the fundamental understanding of factors governing the nanostructural parameters (size, composition, shape, phase, etc) of multimetallic alloy nanoparticles and electrocatalytic activities for oxygen reduction reaction in fuel cells. Examples of bimetallic/trimetallic nanoparticles studied include bimetallic AuPt and trimetallic PtNiCo, PtVCo, PtNiFe nanoparticles with controllable sizes and compositions. Carbon-supported catalysts prepared from these nanoparticles have been demonstrated to exhibit enhanced electrocatalytic activity for oxygen reduction reaction. To gain fundamental insights into the electrocatalytic activity of the bimetallic and trimetallic alloy nanoparticle catalysts in fuel cell reactions, an array of analytical techniques have been utilized for the characterization of the structures and properties. The results have allowed us to establish the correlation between the nanostructural parameters and the electrocalytic properties. One example involves AuPt/C catalysts with electrocatalytic activity highly dependent on nanoscale alloying structures. Another example involves PtNiCo/C catalysts with electrocatalytic activity dependent on the nanoscale lattice strain structures. The nanoscale alloying and strain structures are shown to be controllable by a combination of nanoengineered synthesis and thermal activation parameters for a variety of different multimetallic nanoparticle catalysts. The establishment of the correlation between the nanoscale alloying or strain structures with the electrocatalytic activity has provided new fundamental insights for the design of multimetallic alloy catalysts with high activity, improved stability, and low cost. Implications of the findings to nanoengineering of active and robust alloy catalysts for the ultimate application in fuel cells will also be discussed.