Master thesis presentation Emma Ulberstad, MPMCN

Abstract:
The demand for green energy increases every year, pushing the development of sustainable 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 hydrogen 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 rheological 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 rheological trend where highly dispersed inks 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 is 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.

Password: 726502

Examiner: Björn Wickman

Supervisor: Felix Ernst

Opponent: Axel lind