Ink Processing and its Influence on Particle Size Distribution, Ionomer Requirements and Electrode Properties in Polymer Electrolyte Membrane Fuel Cell and Electrolyzer Catalyst Coated Membranes

The processing of catalyst-coated membranes (CCM) is a major challenge in the production of efficient fuel cells and electrolyzers. In addition to the material properties and the formulation, the processing of the ink has a decisive effect on the crack pattern of the resulting electrodes. In this work, the influence of milling time in a ball mill on ink and electrode properties is investigated. Prolonged milling results in a reduction in large agglomerates, particularly. The pore diameter distribution of the membrane direct coatings exhibits a strong correlation with the particle size distribution (PSD) of the inks. With regard to the proportion of cracks, an optimum milling time exists. With very long milling time and thus small and narrow PSD, a continuous crack network is created. This phenomenon is explained by the large specific surface area of the dispersed particles and the distribution of the ionomer in the ink. Ionomer adsorbed to the particles is no longer available as a stress-absorbing binder during solidification. A higher ionomer to carbon ratio can compensate for small PSD, enabling low-crack coatings.