Award Date

2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry

Advisor 1

Clemens Heske, Committee Chair

First Committee Member

Dennis Lindle

Second Committee Member

Dong-Chan Lee,

Graduate Faculty Representative

Adam Simon

Number of Pages

137

Abstract

One of the main barriers to commercialization of polymer electrolyte membrane fuel cells systems is cost, which is largely due to the need of platinum (Pt)-containing catalysts. In this thesis we investigate bimetallic systems consisting of a base metal (copper) and a noble metal (palladium) that, as an alloy on the nanoscale, mimic the electronic properties that make Pt desirable as a catalyst.

We present a detailed investigation of the electronic structure of carbon-supported Pd/Cu nanoparticle catalysts, model bilayer thin film systems, alloys, and various metal reference samples. We have investigated the valence band structure of the catalysts using a combination of X-ray photoelectron spectroscopy (XPS) and UV photoelectron spectroscopy (UPS). We have studied the approach of modifying the d-band structure by fabricating and characterizing bilayer thin film systems (Cu/Pd and Pd/Cu). Furthermore, we have investigated carbon-supported bimetallic nanoparticles, fabricated at Argonne National Lab by colloidal and impregnation techniques.

Our experiments show that it is important to consider the entire d-band structure for describing the electronic structure of the catalyst and demonstrate how the alloy formation leads to new spectral contributions to the valence band density of states (as compared to simple superpositions of Cu and Pd contributions). Furthermore, our results shed light on the degradation processes of the catalysts under highly acidic conditions (as in the real fuel cell environment).

The results provide fundamental insights into the tailoring of the electronic structure of Pd/Cu bimetallic systems and help to develop approaches to improve the performance of Pd/Cu-based nanoparticle catalysts in polymer electrolyte membrane fuel cells.

Keywords

Alloys; Bimetallic; Catalysts; Crystal lattices; Crystal structures; Electrical properties; Electronic structures; Nanoparticles; Palladium-copper (Pd/Cu); Polymer electrolyte membranes (PEM); Polymer electrolyte membrane fuel cells (PEMFC); Thin film systems

Disciplines

Metallurgy | Nanoscience and Nanotechnology | Physical Chemistry | Power and Energy

Language

English


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