Date of Award

9-22-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Tansel Karabacak

Abstract

Polymer electrolyte membrane fuel cell (PEMFC) technology has gained significant attention as an alternative power source, especially for automotive applications due to PEMFCs’ high energy conversion efficiency, low operating temperature and being environment-friendly compared to the other types of fuel cells. However, sluggish kinetics of oxygen reduction reaction (ORR) on the cathode requires a high loading of platinum (Pt), which increases the cost of the fuel cell. In addition, dissolution and agglomeration of Pt nanoparticles and oxidation of the carbon support are among the major factors that cause electrode degradation and performance loss. Therefore, it is essential to develop a high performance, durable, and low-cost electrocatalyst without a need for any support material. Extended surfaces such as nanostructured thin films with controlled microstructures are good candidates for non-conventional catalysts due to their high surface to volume ratio and no need for a support material. The goal of this dissertation was to develop self-supported nanocolumnar Pt and Pt-Ni alloy electrocatalysts with controlled microstructure and to investigate their electrochemical activity and stability for PEMFCs. Self-supported nano-columnar structured electrocatalyst thin films with controlled size, microstructure, and composition were produced by utilizing high pressure sputtering (HIPS). HIPS is a simple physical vapor deposition method that is scalable and easily applicable to industrial sputter deposition systems. This work involved fundamental studies investigating the growth process during HIPS that leads to desired nanostructure geometries for enhanced ORR activity, stability, and most effective utilization of the Pt atoms. Electrochemical characterization of the catalysts was performed using cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements. We developed a new sample preparation approach for benchtop CV and RDE tests that would better mimic the morphology of HIPS films in an actual PEMFC. Morphological characterization was conducted by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In addition, proof-of-concept membrane electrode assembly (MEA) fabrication and PEMFC tests were performed through a collaborative work with UTRC.

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