Microstructure and macroscopic rheology of microporous layer nanoinks for PEM fuel cells

[Display omitted] •Two different CB/PTFE interaction modes, covering and bridging, are revealed.•Effect of PTFE loading and solvent composition on ink microstructure is clarified.•The correlation between ink rheology and microstructure is established.•The mechanism leading to the cracks in microporous layers is elucidated.•The optimal formulation for a uniform ink dispersion is proposed. The microporous layer (MPL) is of significance to the PEM fuel cell performance and durability through water management. It is essential to gain insights into the MPL nanoink, a critical state determining the resulting MPL porous structure and function. In this work, a comprehensive investigation of ink microstructure and rheology with different PTFE loadings and solvent compositions has been conducted from a theoretical and practical level. Two different CB/PTFE interaction modes (i.e., covering and bridging) were revealed and the latter dominates with increasing PTFE loading. It was found a PTFE loading of 30% produces homogeneous ink dispersion and best stability. Besides, larger aggregates were found with increased IPA/water ratio using cryo-SEM. Furthermore, rheological measurements revealed that less shear-thinning indicates stable inks. Combining the ink preparation and slot-die coating processes, an optimal formulation of 30% PTFE loading and 1/2 IPA/water weight ratio was proposed for a uniform ink dispersion.