Microscopy Studies of the Catalyst Inks for PEM Fuel Cells

The microstructure of the catalyst layer in proton exchange membrane fuel cell (PEMFC) is one of the key factors that may determine fuel cell performance. The ink preparation, including dispersion solvent, mixing time, and mixing power, is among the less studied parameters that would influence the ionomer distribution on the catalyst surface and the continuity of the carbon network. In this work, novel characterization approaches have been used to investigate the effect of the Pt/C catalyst ink preparation conditions on the morphology and structures of the catalyst layer. Microscopy analysis revealed that longer mixing time led to better electrode structures than shorter mixing time. The longer mixing time enabled superior continuity of the ionomer network and high porosity in the cathode layer that contributes to improved proton conductivity and mass transport. This has been reflected in performance and durability tests, where the electrode made from 5-day catalyst ink displayed improved performance compared to the one from 3-day ink. Durability studies showed 26% and 43% loss of initial mass activity for 5 days and 3 days mixing, respectively. In addition, the catalyst layer prepared with ethylene glycol as the dispersion solvent showed better durability than water/1-propanol based solution. The effect of the ink mixing power as another considerable factor on the resulting catalyst layer morphology will be investigated. This work will provide an insight into the better electrode design to maximize the performance of PEM fuel cells.