Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Bimetallic Nanoparticles for Advanced Energy Conversion Technologies(2015) Sims, Christopher; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The increased demand for a more sustainable energy infrastructure has spurred the development of innovative energy conversion processes and devices, such as the proton exchange membrane fuel cell (PEMFC). PEMFCs are highly regarded as a clean alternative energy technology for various applications, such as motor vehicles or power generators. Factors limiting their commercial viability include the poisoning of the hydrogen oxidation reaction (HOR) electrocatalyst at the anode by carbon monoxide (CO), an impurity in the H2 fuel feedstocks derived from hydrocarbons, and the high expense and inefficiency of the oxygen reduction reaction (ORR) electrocatalyst at the cathode. The research described in this dissertation entails the synthesis and characterization of new bimetallic nanoparticle (NP) catalysts with controlled sizes, compositions, and architectures. By varying the NPs' compositions, structures, and electronic environments, we aimed to elucidate the physical and chemical relationships that govern their ability to catalyze chemical reactions pertinent to PEMFC operation. The ongoing research and development of these NP-based catalytic systems is essential to realizing the viability of this energy conversion technology. We describe the development of a simple method for synthesizing monometallic and bimetallic NPs supported on various reduced graphene oxide (rGO) supports. Electrochemical studies illustrate how the chemical nature of the rGO support impacts the catalytic behavior of the NP catalysts through unique metal-support interactions that differ depending on the elemental composition of the NP substrate. In another study, we present the synthesis and characterization of CoxPty NPs with alloy and intermetallic architectures and describe how their inherent characteristics impact their catalytic activities for electrochemical reactions. CoxPty NPs with alloy architectures were found to have improved CO tolerance compared to their intermetallic counterparts, while the performance of the CoxPty NPs for ORR catalysis was shown to be highly dependent on the NPs' crystal structure. Finally, we present the synthesis and characterization of various bimetallic core-shell NPs. Preliminary data for CO oxidation and PrOx catalysis demonstrated how subsurface metals modify the electronic structure of Ni and enhances its catalytic performance for CO oxidation and the PrOx reaction.Item Synthesis, Characterization and Catalytic Properties of Bimetallic Nanoparticles(2009) Dylla, Anthony Greg; Walker, Robert A; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Due to the ever-increasing desire for catalysts that possess high activities and selectivities for industrially relevant reactions, much effort is being spent on the synthesis of mono and bimetallic nanoparticles with tunable characteristics such as size, shape and bimetallic composition. Understanding how these characteristics influence catalytic performance is the key to rationally designing catalysts for a specific reaction. While significant breakthroughs have been made, particularly in the area of monometallic nanoparticles with regard to shape and size, relating the bimetallic structure, i.e., core@shell or alloy to a specific reactivity remains a difficult task. Work presented in this thesis describes the synthesis, characterization and catalytic properties of mono and bimetallic nanoparticles. Our efforts were motivated by the desire to understand the relationships that exist between metallic nanoparticle structure and their function as catalysts. This work also seeks to better understand the dynamic changes a nanoparticle's structure undergoes during typical catalytic operating conditions. Our approach is to use a wide array of analytical tools including optical methods, electron microscopy, XRD and mass spectrometry to provide an interlocking description of nanoparticle structure, function and durability. We show how the polymer coatings and degraded carbonaceous deposits affect propene hydrogenation catalytic activity of Pt nanoparticles. We also present a unique view of the interplay between thermodynamic and kinetic variables that control bimetallic nanoparticle alloy structures by looking at ordered and disordered PdCu alloy nanoparticles as a function of particle size. In another study we show that Ru@Pt and PtRu alloy nanoparticle catalysts have similar surface structures under oxidizing conditions but completely different surface structures under reducing conditions as probed by vibrational spectroscopy. These differences and similarities in surface composition correlate very well to their catalytic activity for CO oxidation under oxidizing and reducing environments, respectively. Finally, we present the synthesis and characterization of Cu@Pt nanoparticles with a particular focus on the core@shell formation mechanism. We also show how dramatic changes in the surface electronic structure of Cu versus Cu@Pt nanoparticles can affect their ability to transform light into heat by using Raman spectroscopy to observe graphite formation on the surface of these nanoparticles.