Platinum alloy nanoparticles: Composition, shape, structure and electrocatalytic property.

摘要

With the increasing environmental concern and accelerated depletion of fossil fuel, there are renewed research interests in the development of new technology using alternative energy sources, most noticeably those fuels that can be utilized by proton exchange membrane fuel cells (PEMFCs). Platinum has been widely used as electrocatalyst in PEMFCs because of its outstanding catalytic property over others metals. While platinum is often essential to ensure outstanding catalytic properties, cost, activity and durability are still some of the key issues that have hindered its real world applications. Exploration of highly efficient and durable electrocatalysts with low Pt content is pivotal in advancing the fuel cell technology. Studies have demonstrated that both d-band electrons and surface geometric structure can greatly affect the activity of catalysts and can be optimized by tailoring their composition and shape and overall structure. The cost issue can be addressed in part by improving the specific activity and durability of the catalysts and by reducing the amount of platinum used.;In this thesis I present my studies on the synthesis, characterization and electrochemical study of platinum alloy nanoparticles. A series of Pt-on-Metal (M=Ag, Au, Cu, Pd) heterogeneous nanostructures have been prepared and their electrocatalytic properties have been tested. The Pt-on-Pd catalyst exhibited both enhanced activity and much improved stability in oxygen reduction reaction (ORR). We have been able to make other platinum alloy nanostructures from these Pt-on-M nanoparticles. Pt-Au bimetallic nanoparticles produced by thermal treatment were much more active than Pt in catalyzing formic acid oxidation reaction (FAOR). Platinum hollow nanospheres and cubic nanoboxes were obtained by an electrochemical approach and exhibited significant improvement in ORR and methanol oxidation reaction (MOR) activities. Study on novel platinum nanoalloys with composition in their bulk miscibility gap and their electrocatalytic property has resulted in the synthesis of PtAg alloy nanoparticles with a wide range of composition. An electrochemical method has been developed for the preparation of heterogeneous PtAg alloy catalysts with low-Pt content cores and Pt-rich surfaces. The optimal PtAg catalyst not only can have much improved activity but also show limited degradation in FAOR. A generic chemical dealloying method has also been developed for making tiny metal nanoparticles with their size down to 1 nm. Their catalytic activity has been demonstrated using p-nitrophenol reduction as the model reaction.