Date of Graduation

8-2013

Document Type

Thesis

Degree Name

Master of Science in Chemistry (MS)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor

Jingyi Chen

Committee Member

Colin Heyes

Second Committee Member

Ingrid Fritsch

Abstract

Platinum and Pt alloys are among the most important heterogeneous catalysts for many organic reactions and electrochemical reactions associated with the fuel cell technologies. How to reduce Pt usage while maintaining the performance of the catalysts becomes a subject for intensive research in materials chemistry. For heterogeneous catalysis, the catalytic reactivity and selectivity are strongly correlated with different crystallographic facets exposed on the surface. The facets with high-index planes whose Miller indices with at one is larger than unity are generally more active than those with low-index planes (e.g., {100}, {111}, and {110}). Tuning the morphology of the nanoparticles to expose more high-index planes on the surface can improve the catalytic activity of the nanoparticles. As compared to isotropic nanoparticles, the branched nanostructures are the promising morphology that can improve both the activity and stability of the catalysts. In this work, a two-step polyol synthesis has been developed to synthesize the branched nanostructures of Pt at high-yield. This two-step process involves a slow reduction using ethylene glycol in the presence of oxidative etchants, following by a fast reduction using ascorbic acid. The slow reduction kinetics facilitates the formation of cubooctahedral single-crystal seeds while the fast reduction kinetics allows for the overgrowth of nanocrystals along the {111} facets in a short period of time, resulting in the branched nanostructures. By co-reducing Pt and Cu precursors, this approach has been demonstrated to synthesize the Pt-Cu dendritic nanostructures for the first time. The catalytic activity of these Pt and Pt-Cu nanostructures has been studied for MOR. It was found that Pt branched nanostructures reduced the CO-poisoning as compared to the Pt/C and the dendritic Pt-Cu nanostructures showed both enhanced resistance of CO-poisoning and improved efficiency of

ethanol oxidation.

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