Indiana University-Purdue University Indianapolis (IUPUI) / There are three parts in this work centered on the catalyst layer of Polymer
Electrolyte Fuel Cell (PEFC) in this thesis. The first part is for making best MEA
structure. One of the major aims of this investigation is to understand the micro-structural
organization of ionomer particles and Pt/C aggregates dispersed in a catalyst ink. The
dispersion of Nafion® ionomer particles and Pt/C catalyst aggregates in liquid media was
studied using ultra small angle x-ray scattering (USAXS) and cryogenic TEM
technologies. A systematic approach was taken to study the dispersion of each
component (i.e. ionomer particles and Pt/C aggregates) first, then the combination, last
the catalyst ink. A multiple curve fitting was used to extract the particle size, size
distribution and geometry from scattering data. The results suggests that the particle size,
size distribution and geometry of each system are not uniform, rather, vary significantly.
The results also indicate that interaction among components (i.e. ionomer particles and
Pt/C aggregates) exists. The cryogenic TEM, by which the size and geometry of particles
in a liquid can be directly observed, was used to validate the scattering results, which
shows the excellent agreement. Based on this study, a methodology of analyzing
dispersion of Pt/C particles, Nafion® particles in a catalyst ink has been developed and
can serve as a powerful tool for making a desired catalyst ink which is a critical step for
making rational designed MEA.
The carbon corrosion process is the second part of the thesis. The carbon corrosion
process of low–surface-area Pt/XC72 and high-surface-area Pt/BP2000 was investigated
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using an developed accelerated durability testing (ADT) method under simulated fuel cell
conditions (a Rotating Disk Electrode (RDE) approach). Compared with the complex
MEA system, this innovated approach using RDE can simply focus on carbon corrosion
process and avoid the use of MEA in which many degradation/corrosion processes
simultaneously occur. It was observed that different carbon corrosion processes resulted
in different performance (electrochemical active surface area, mass activity and double
layer capacity) decay of catalysts. The corrosion process was studied using TEM. It was
found that in the case of Pt/XC72, major corrosion occurred at the center of the Pt/XC72
particle, with some minor corrosion on the surface of the carbon particle removing some
amorphous carbon black filaments, while in the case of Pt/BP2000, the corrosion started
on the surface. The understanding of carbon corrosion process provides the guidance for
making high corrosion resistance catalysts to increase the durability performance of
PEFC.
Based on the second work, XC72 carbon blacks were etched using steam under
different time and used as a new high corrosion resistance catalysts support for the
oxygen reduction reaction. TEM results show that the center part of the XC72 particle
was more easily etched away. XRD results show that the 002 and 10 peaks of the XC72
based samples are initially sharp, but then broaden during the corrosion process. TEM
results of Pt particles show that the steam etching can improve dispersion uniformity of
Pt nanoparticles on the surface of carbon support and reduce the Pt particles size.
Electrochemical characterization results show that the mass activity of etched carbon
black for 1 hour was 1.3 and 34 times greater than that of the carbon blacks etched for 3h
and that of carbon blacks non-ecthed. ECSA of the carbon blacks was also significantly
increased after etching. MEA test showed after 45 hours testing, the performance MEA
with steam etching 1 hour XC72 based catalyst decreases much less than the MEA with
commercial catalyst. Clearly, steam etching is a simple and efficient method to increase
the performance and durability of the fuel cells catalysts.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/2217 |
| Date | 27 July 2010 |
| Creators | Xu, Fan |
| Contributors | Xie, Jian, Chen, Jie, Petrache, Horia |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
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