Investigation of catalyst structure and dispersion methodology on PEMFC catalytic inks and resulting electrodes

Examensarbete för masterexamen
Master's Thesis
Materials chemistry (MPMCN), MSc
Ulberstad, Emma
The demand for green energy increases every year, pushing the development of sus tainable energy sources. Proton exchange membrane fuel cells (PEMFCs) are a promising technology for renewable energy conversion due to their clean emissions and high energy-conversion efficiency. The electrodes are a core part of PEMFCs, containing the catalyst at which the electrochemical reactions occur, where hydro gen and oxygen are converted to water and energy. To enhance cost efficiency, performance and durability of PEMFCs, it is essential to better understand the complex and partly unknown properties of the electrode and optimize the electrode production process. There is a need to better understand the dispersion method of the catalyst ink that makes up the electrode because it is one of the major factors determining the electrode properties. The effect of catalyst ink materials, dispersion technique and parameters on the catalyst ink microstructure were studied using rhe ological measurements and light microscope imaging of the electrodes. Dispersion by ultrasonication at higher vibrational amplitude showed an increase in viscosity and less visible agglomerates on the electrode surface as compared to lower amplitudes. A continuous decrease in apparent agglomerate size and abundance was found with increasing ultrasonic energy input. The results also showed a partly unexpected rhe ological trend where highly dispersed inks exhibit poorer rheological properties, such as low viscosity and elastic modulus for the applied coating method as compared to less dispersed inks. Ultrasonication and bead-milling dispersion method resulted in inks with different rheological properties. The investigation showed that rheology and microscopy are able to only partly capture the complex characteristics of the agglomerated structures and complimenting techniques like e.g. SEM and DLS can help further investigation. With this work, an optimization of the ink dispersion process was achieved and further insight into the dispersion parameters allowed to establish dispersion design rules, e.g. regarding the ultrasonic power and energy input, and to further elucidate the interdependency between ink components and dispersion methodology.
proton exchange membrane fuel cell, catalyst, rheology, catalyst layer.
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