Date of Award

2015

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Biao Zhou

Second Advisor

Stephan H Eichhorn

Keywords

catalyst, fuel cell, membrane

Rights

CC-BY-NC-ND

Abstract

Polymer electrolyte membrane fuel cell (PEMFC) is regarded as a promising technology for both automotive and stationary applications. Two significant challenges that hamper its commercialization are its high cost and insufficient durability. Catalyst layer (the region where fuel and oxidant convert to products) has a vital importance to be able to mitigate the above challenges. This dissertation reports a systematic study of using niobium (Nb)-doped titanium dioxide nanofibers as a corrosion-resistance catalyst support for PEMFCs, along with the study on the control of physical and electrochemical properties to create durable and still active platinum catalysts, and a new strategy to optimize ionomer phase (Nafion) loadings in the catalyst layers. It also proposed a simple wet coating process of Nb-doped titanium dioxide (TiO2) sols onto carbon papers to protect the interface between gas diffusion backing layer and catalyst layer for unitized regenerative fuel cell applications. Oxidative treatment and dip coating of carbon paper with Nb-doped TiO2 sol was shown to increase the corrosion resistance of carbon paper at the interface between catalyst layer and gas diffusion backing layer (Chapter 2). Anatase phase Nb-doped TiO2 nanofibers were synthesized by using the upscalable method of electrospinning to find a more durable alternative catalyst support, to substitute not corrosion resistant pure carbon-based catalyst supports (Chapter 3). More electronically conductive and high surface area rutile phase Nb-doped TiO2 nanofibers were synthesized through embedding carbon in between rutile crystallites using an innovative strategy called “in-situ reductive embedment (ISRE)” (Chapter 4). However, the ORR mass activities of the Pt catalysts that were supported by carbon-embedded Nb-doped TiO2 nanofibers were still slightly lower than pure carbon black based Pt catalysts. Instead, electronically more conductive and high surface area catalyst supports were synthesized by physically mixing of commercial carbon blacks with carbon-embedded Nb-doped TiO2 nanofibers (Chapter 5) and the effect of catalyst layer preparation method on the distribution of catalyst layer components has been investigated (Chapter 6).

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