Advisor(s)

Eugene S. Smotkin

Contributor(s)

Sanjeev Mukerjee (1960-), Max Diem

Date of Award

2011

Date Accepted

4-2011

Degree Grantor

Northeastern University

Degree Level

M.S.

Degree Name

Master of Science

Department or Academic Unit

College of Science. Department of Chemistry and Chemical Biology.

Keywords

chemistry, density function theory, fuel cells, infrared spectroscopy, ion exchange membrane, nafion

Subject Categories

Ion-permeable membranes, Proton exchange membrane fuel cells, Ionomers

Disciplines

Chemical Engineering

Abstract

Infrared Spectroscopy (IR) and density functional theory (DFT) calculations were used to study Nafion, a sulfonated tetrafluoroethylene ionomer used as the electrolyte material of choice for polymer electrolyte membrane fuel cells (PEMFCs). A methodology is described for assignment of infrared peaks in terms of mechanically coupled internal coordinates of near neighbor functional groups.

This work demonstrates (chapter 2- 4) the use of ionomer functional group internal coordinate coupling analysis to assign two key Nafion peaks formerly assigned as the sulfonate symmetric stretch (1056 cm 1) and a COC (A) vibrational mode (971 cm 1). The experiments and theory complement each other to show that the dominate motions of the 1056 cm 1 and 971 cm 1 modes are attributed to the COC (A) and the sulfonate stretch respectively, exactly reverse of the convention used for decades. The salient point is that both peaks result from mechanically coupled internal coordinates of both functional groups. This explains why the 1056 cm 1 and 971 cm 1 peaks shift together with changes in the sulfonate group environment (i.e., ion exchange or membrane dehydration). The assignments, correlated with extensive literature data, and new data showing both peaks vanishing upon rigorous dehydration (i.e. conversion of a C3V deprotonated -SO3- to a C1 -SO3H) of the membrane, were based on the correlation of observed IR peaks with animations of mechanically coupled internal coordinates obtained by DFT calculations. Further, the above methodology was augmented with polarization modulated infrared reflection-adsorption spectroscopy (PM-IRRAS) to elucidate the Nafion ionomers functional groups that participate in self-assembly of Nafion onto Pt surfaces. A model for Nafion adsorption onto Pt shows that the Nafion side-chain sulfonate and CF3 co-adsorbates are structural components of the Nafion-Pt interface. The DFT-spectroscopy method of assigning peaks in terms of mechanically coupled internal coordinates was augmented with ion-exchange-induced shifts for extensive assignments of Nafion IR peaks (explicit and deconvoluted).

Chapter 5 focuses on the durability of the membrane electrode assembly (MEAs) in direct methanol fuel cells (DMFCs). The MEA catalyst-polymer interfacial region was examined for degradation modes.

Document Type

Master's Thesis

Rights Holder

Dunesh Kumari


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Additional Files

SupplementaryMaterial_DuneshKumari_2011.pdf (217 kB)
Movies_SupplementaryMaterial_DuneshKumari_2011.zip (51247 kB)

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