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You searched for +publisher:"University of Texas – Austin" +contributor:("Nakashima, Naotoshi"). One record found.

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University of Texas – Austin

1. Rasouli, SomayeSadat. Degradation mechanisms of Pt and Pt alloy nanocatalysts in proton exchange membrane fuel cells.

Degree: PhD, Materials Science and Engineering, 2018, University of Texas – Austin

The goal of this PhD research is to fundamentally understand the degradation mechanisms and durability issues of Pt and Pt-alloy nanocatalysts in the cathode of proton exchange membrane fuel cells (PEMFCs). The primary tool for this research has been state-of-the-art transmission electron microscopy, including aberration-corrected TEM/STEM, in-situ TEM heating, 3D tomography, and Energy Dispersive Spectroscopy (EDS). In order to reveal the degradation mechanisms of nanocatalysts, both indirect and direct TEM methods were used. In the first part of this research, we performed post-mortem transmission electron microscopy (TEM) on the membrane electrode assembly (MEA) of PEMFCs. Using a thorough composition and morphological analysis of the catalysts after fuel cell cycling, we showed that the mechanisms proposed in the literature do not fully explain the degradation of the nanocatalysts. Accordingly, new mechanisms were proposed, namely: 1- Modified Ostwald ripening until adjacent particles make contact with each other and coalesce, 2-preferential deposition of single atoms and atomic clusters between two or more particles and consequently bridging between them. To evaluate these proposed mechanisms mentioned above, the second part of this work focused on determining the behavior of Pt and Pt-alloy nanoparticles during different stages of fuel cell cycling. The first challenge was to find a way to ensure that I was observing the exact same nanoparticles during the various stages of cycling. To accomplish this, we developed an experimental setup which replicates on a TEM grid the effect of voltage cycling on the cathode of an MEA. Using this approach, it was possible to track the behavior of a single nanoparticle at different stages of voltage cycling on the nano-atomic scale. Through these direct observations, we demonstrated that due to carbon corrosion the defects appear at the carbon/nanoparticle interface, which in turn result in particle migration and consequently coalescence. We also revealed the mass transfer mechanisms during the coalescence of nanoparticles. In addition, we revisited the commonly held view on the mechanism of particle dissolution and deposition. Thus, during the later stages of cycling, when the concentration of dissoluble Pt reaches a critical amount, single atoms and atomic clusters appear on the carbon support, which consequently move toward other particles and re-deposit on their surface. This dissolution happens preferentially at the corners and steps of the nanoparticle, while re-deposition occurs on {111} type planes. Contrary to the literature, it turned out that re-deposition is not necessarily an isotropic process as atomic clusters can deposit between two or more particles and bridge them. Furthermore, we investigated the atomic surface evolution and phase segregation of Pt3Co and PtNi nanoparticles under the effect of voltage through advanced spectroscopy technique such as EDS. While it is generally accepted in the literature that larger particles grow at the expense of smaller… Advisors/Committee Members: Ferreira, Paulo J. (Paulo Jorge) (advisor), Manthiram, Arumugam (committee member), Yu, Guihua (committee member), Nakashima, Naotoshi (committee member), Higashida, Kenji (committee member), Kongkanand, Anusorn (committee member).

Subjects/Keywords: Fuel cells; Catalysts; Pt; Pt alloys; Electron microscopy

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APA (6th Edition):

Rasouli, S. (2018). Degradation mechanisms of Pt and Pt alloy nanocatalysts in proton exchange membrane fuel cells. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/63334

Chicago Manual of Style (16th Edition):

Rasouli, SomayeSadat. “Degradation mechanisms of Pt and Pt alloy nanocatalysts in proton exchange membrane fuel cells.” 2018. Doctoral Dissertation, University of Texas – Austin. Accessed January 17, 2020. http://hdl.handle.net/2152/63334.

MLA Handbook (7th Edition):

Rasouli, SomayeSadat. “Degradation mechanisms of Pt and Pt alloy nanocatalysts in proton exchange membrane fuel cells.” 2018. Web. 17 Jan 2020.

Vancouver:

Rasouli S. Degradation mechanisms of Pt and Pt alloy nanocatalysts in proton exchange membrane fuel cells. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2018. [cited 2020 Jan 17]. Available from: http://hdl.handle.net/2152/63334.

Council of Science Editors:

Rasouli S. Degradation mechanisms of Pt and Pt alloy nanocatalysts in proton exchange membrane fuel cells. [Doctoral Dissertation]. University of Texas – Austin; 2018. Available from: http://hdl.handle.net/2152/63334

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