Novel platinum-based nanocrystals and their use as electrocatalysts for the oxygen reduction reaction

Abstract

Owing to the low operating temperature and high power density, polymer electrolyte membrane fuel cells (PEMFCs) are promising candidates to replace the conventional combustion engines in the automotive industry. The poor performance of Pt-based catalysts toward oxygen reduction still needs to be addressed to make PEMFCs viable for commercialization. To this end, it is essential to tailor the physicochemical properties of the catalytic nanocrystals involved, including the crystal facets, elemental composition, and structure. This dissertation includes a number of projects for the development of Pt-based electrocatalysts with markedly enhanced performance toward oxygen reduction. In the first project, I synthesize Pd@PtnL core−shell octahedra by depositing ultrathin Pt shells on octahedral nanocrystals made of a less expensive metal, such as Pd. This strategy presents a great opportunity to enhance both the activity and durability of the catalyst toward oxygen reduction while significantly reducing the Pt loading in a PEMFC. Theoretical calculations are also employed to understand the improvement in catalytic activity. In the second project, I further apply the Pt deposition method to passivate Pt−Ni alloy octahedral nanocrystals and improve their poor catalytic durability toward oxygen reduction. In this strategy, an ultrathin Pt shell effectively protects the Ni in the Pt−Ni alloy core from dissolution in a highly corrosive environment, greatly improving the catalytic durability. In the third project, I developed an advanced catalyst based upon Pt nanoframes with open faces and a hollow interior. The catalyst exhibits not only significantly increased catalytic surface area but also remarkably improved durability toward oxygen reduction. The strategies presented in this dissertation and the understanding of catalytically relevant physicochemical properties offer insights for the design of advanced fuel cell catalysts in the future, allowing for large-scale commercialization of PEMFCs.