Investigating drying conditions of screen-printed platinum-free fuel cell cathode layers
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Examensarbete för masterexamen
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Renewable energy sources are becoming more significant in a society where sustainable
development is becoming more crucial. Efficient ways to store and convert energy are
therefore essential for the success implementation of the new sources. One part of the puzzle
is hydrogen fuel cell technology. A challenge, however, is to develop a hydrogen fuel cell that
is both cost-effective and high performing. The anode and cathode of the fuel cell are
separated by a membrane, and together they are the heart of the fuel cell. The cathode side has
been the focus of this study, specifically how to create a suitable coating with as minimal
resistance as feasible. There are various alternative deposition procedures that may be
employed; however, screen printing was used in this dissertation. The aim of this thesis is to
investigating drying conditions of screen-printed platinum-free fuel cell cathode layers and
minimize the ohmic resistance caused by the defects in the deposited layer. In addition, a
valid resistance measurement strategy needs to be implemented and integrated during the
characterization step without negatively affecting the eventual use of the membrane in fuel
cell testing. The work process was divided into broad testing, reproducibility, and
characterization. The samples were analyzed by microscopy techniques, profilometry and
resistance measurements.
From the broad testing experiments, it could be concluded that the drying environment and
time had an influence on the formation of cracks in the plane. The best possible settings found
in this study were 24 hours in ethanol followed by 24 hours in slow drying air. In addition, a
decreased in-plane electrical resistance could be obtained by increasing the thickness of the
deposition layer. The reproducibility experiments concluded the properties of the ink also had
a significant impact on resistance. Higher mass-% of dry matter resulted in increased
viscosity, which aided the screen-printing process by enabling more ink to remain on the
sample, resulting in a thicker deposit layer and fewer fractures. In the characterization and
fuel cell experiments, tests were performed to evaluate the substrate selection closer. In
general, all samples dried in air performed slightly better compared to the ones dried in a
saturated environment. Possible explanations for achieving these results can be the structure
of the substrate. Printing on a porous material, a portion of the ink may penetrate the substrate
rather than staying on the surface as a coating. In these circumstances, the drying process
benefits from a faster drying period to reduce the loss of active catalyst. Another possibility is
to use a microporous sublayer as a membrane to prevent ink from entering the substrate. The
third substrate evaluated, Nafion membrane, proved to be extremely fragile. Fuel cell
experiments suggest that Nafion dried in air performs better, but since several samples
collapsed, a controlled drying technique would be preferable. Future prospects include further
optimizing the correct ink in relation to the right environment and substrate choice, increase
the knowledge about Nafion membrane and how to increase the adhesion strength and
investigate how the mesh marks impact the substrates.
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Platinum-free fuel cell, screen printing, cathode layers, drying environment, resistance measurements