Microstructure formation mechanism of catalyst layer and its effect on fuel cell performance: Effect of dispersion medium composition

The solvent composition affects the resulting CL microstructure and electrochemical properties through the catalyst ink characteristics and ink drying process, leading to variations in cell performance. The design of the catalyst layer (CL) offers a feasible way to realize the commercialization of proton exchange membrane fuel cells (PEMFCs). An in-depth understanding of catalyst inks is critical to achieving the optimal CL structure and cell performance. In this work, the effects of the solvent evaporation process during ink drying on the formation of the CL microstructure are particularly considered to reveal the structure–property correlations among the catalyst ink, drying process, CL microstructure and fuel cell performance. An increase in the alcohol content of the catalyst ink increases the amount of free ionomers while allowing the ionomer backbone to be more stretched in the dispersion medium. The higher alcohol content contributes to rapid solvent evaporation and thus inhibits the formation of coffee rings; as a result, a more developed ionomer network with a denser pore structure is obtained. Therefore, the alcohol-rich electrode exhibits better proton conduction capability, but higher oxygen transport resistance. For complex fuel cell operating conditions, a catalyst ink formulation with 50 wt% alcohol content is preferred due to its proper ionomer and pore size distribution, providing satisfactory fuel cell performance.