Investigation of the influence of coating and drying methods of catalytic inks on the structure of resulting electrodes for Proton Exchange Membrane Fuel Cells

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 was 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.