Date of Award

10-22-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Tansel Karabacak

Abstract

Polymer electrolyte membrane fuel cell (PEMFC) is one of the most attractive technologies for clean, renewable energy in the twenty-first century. It has many advantages in terms of zero carbon emission, quiet operation mode, high power density, higher efficiency than Carnot engines, and it requires less warm-up & fast start-up time. However, oxygen reduction reaction (ORR) activity and stability are still significant issues for the next generation PEMFCs to increase its usage. In this study, we developed a new design of stacked core-shell nanorod array and self-supported composition graded Pt:Ni nanorod array electrocatalyst to improve ORR kinetics and catalyst stability. For this purpose, in the first design, we fabricated a two-layer stacked core-shell nanorod structure, where each layer is composed of a tungsten carbide (WC) core and a platinum-nickel (Pt-Ni) alloy shell. We used a combination of glancing angle deposition (GLAD) and high-pressure sputtering deposition (HIPS) methods to grow the WC core nanorods and Pt-Ni shell, respectively, utilizing a magnetron sputtering unit. This process was repeated two times to obtain longer stacked core-shell nanorods. In the second design, Pt:Ni composition on each stack was changed to take advantage of different properties in the same structure. In a third design, without using any support material, gradient-alloy-ratio Pt:Ni nanorod electrocatalyst were fabricated using a simultaneously opposing-glancing angle deposition technique (SO-GLAD). We investigated the ORR activity and stability of three different Pt:Ni ratios for stacked core-shell and self-supported nanorod array electrocatalysts. Cyclic voltammetry (CV) and rotating disk electrode (RDE) methods were used for electrochemical characterizations. A 0.1 M HClO4 solution was chosen as the electrolyte solution. The morphological and crystallographic analysis was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Pt mass loading values were measured using quartz crystal microbalance (QCM).

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