Advisor(s)

Sanjeev Mukerjee (1960-)

Contributor(s)

David E. (David Edward) Budil, Max Diem, Eugene S. Smotkin, Graham B. Jones

Date of Award

2007

Date Accepted

12-2007

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Arts and Sciences. Department of Chemistry and Chemical Biology.

Keywords

Chemistry, Oxygen reduction reaction

Subject Categories

Electrocatalysis, Catalysts, Porphyrins, Fuel cells

Disciplines

Chemistry

Abstract

Cathodic oxygen reduction reaction (ORR) is an important chemical process for a variety of industries and applications. It serves not only as a major component of state of the art low temperature polymer exchange membrane fuel cells (PEMFCs), but is also harnessed for the chlorine-generation industry. Of the noble metals, platinum exhibits unparalleled activity and efficiency. However, in addition to also being particularly susceptible to poisoning via an array of chemicals, platinum is a rare, expensive noble metal. These stability and economic issues are primarily responsible for keeping consumers from reaping the benefits of the clean energy afforded by PEMFCs for transportation applications. Because of these issues, a vast worldwide research effort is underway to identify and synthesize cheaper electrocatalysts to replace Pt-based materials. Perhaps the most viable candidates include transition metal-based chalcogenides (e.g. MxSy or MxSey, where M = Ru, Co, Fe, etc), and pyrolyzed organometallic complexes (e.g. Co or Fe-based porphyrins). The scope of this research has been to utilize X-ray absorption spectroscopy (XAS), in combination with electrochemical characterization, to not only identify the active sites of such electrocatalysts, but also to define the specific adsorption pathways of adsorbed species. Removing the ambiguities in the structure/property relationships of these materials will allow for tailored synthesis of cheaper electrocatalysts for a variety of applications. XAS is a core-level, element-specific spectroscopy which allows for in situ electrochemical measurements. Further, XAS is inherently a short range order technique, and is therefore ideally suited for the study of nanoscopic electrocatalyst particles. Arising from the judicious application of the novel ""delta mu"" technique of XAS analysis, a full characterization of chalcogenide and Co-based porphyrin systems will be presented. These results represent the first time that direct spectroscopic observation of oxygen adsorption on the surface of these materials has been achieved. In addition, these techniques have been extended to Osmium-based hydrogel mediators for a laccase-based biofuel cell cathode, and these preliminary results represent the first time that in situ XAS has been utilized on a biofuel cell system.

Document Type

Dissertation

Rights Information

Copyright 2008

Rights Holder

Joseph M. Ziegelbauer


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