Master thesis presentation Sandeep Jayaprakash Nair, MPAEM

Abstract:

In the decal transfer process of making catalyst electrode coatings for Proton Exchange Membrane
Fuel Cells (PEMFCs), understanding the coating and drying parts of the process is important to get desired final electrode structures. Coating and drying are also important manufacturing steps and
must be optimized for this as well. The structural evolution during drying from ink microstructure to
the electrode microstructure yields the resulting pore structure at a micro scale, and at a larger
length scale the crack morphology. To achieve the desired structures, we need to make both a well dispersed catalyst ink with good interaction of components and provide favorable drying conditions.

In this study, different solvent combinations and dry weights in ink, and different drying conditions
of temperature and vapor pressures were explored. Qualitative inspection of digital microscope
images of the electrodes were used to analyze dried structure and cracks. Critical Crack Thickness
(CCT), the height up to which a coating can inhibit cracks well, and the maximum catalyst loading in
each setting was monitored. Results showed that 1-propanol rich solvent matrix with water gave the
least cracks and highest CCTs in comparison to ethanol and tert-butanol for the studied catalyst and
ionomer. Higher temperatures did not have a strong impact on crack morphology or CCT for the
same ink recipes but reduced the drying time. Higher vapor pressure of alcohol above the wet ink
coating led to slower drying and enabled higher CCTs. The experiments enabled us to achieve coatings with a loading of 0.7(mg/cm2) and a CCT of 250 microns, robust to higher temperature drying conditions, which was not possible before with recipes described by suppliers. The results
here are promising for making high performance electrodes in-house and has set a foundation for future work on fuel cells for a variety of applications, helping the green energy transition.

Examiner: Björn Wickman
Supervisor: Felix Ernst
Opponent: Anupama Surendran