Synthesis and characterization of nanocatalytic systems for energy applications

Fuel Cells with their excellent energy conversion efficiency and very low emissions have been the focus of research for addressing ever-increasing energy needs. Proton exchange membrane fuel cells (PEMFCs) in particular, have shown tremendous potential towards becoming an alternative energy source for transportation and portable power applications. Despite the recent advances in fuel cell technology, challenges persist in making these energy systems affordable, practically viable and competitive. Some of the challenges in this context are enhancement of activity, durability and reducing the cost of the catalysts for fuel cells. The dissertation was focused on developing an understanding of nanocatalyst parameters like morphology, size, support and elemental composition with respect to their effect on electrochemical activity and utilizing it to engineer catalysts for addressing these challenges.

In the presented research a Dimethylformamide based surfactant free synthesis method for controlled fabrication of nano-sized catalysts was developed. Sub 10 nm Platinum nanoparticles with well faceted morphologies were synthesized. Precise shape control of platinum nanoparticles from truncated octahedron to cubes was demonstrated through control of synthesis parameters like solvent water concentration, reaction temperature and time. The synthesis route was further advanced for tuning of shape, size and composition of bimetallic PtNi nanoparticles by development of an in-situ strategy for carbon source addition. The PtNi nanoparticles on carbon black demonstrated a 12 fold enhancement of activity over the commercial Pt catalysts and displayed excellent durability, retaining their shape and activity under electrochemical cycling. Other nanocatalysts that were generated by extension of the synthetic approach include platinum nanoparticles on carbon supports, multi-twinned icosahedral palladium nanoparticles on carbon supports and a series of bi/tri-metallic alloy nanoparticle-graphene composites.