Interrelation between Ink Viscoelasticity And Crack Structure of Fuel Cell Microporous Layers

Abstract

Cracks in the microporous layers of fuel cells greatly affect their performance. It is essential to understand the viscoelasticity of ink, the key precursor during MPL fabrication, to gain insights into crack formation and control. This work has comprehensively investigated ink rheology with different solid content and the resulting MPL crack structure from a theoretical and practical level. The network microstructure strength of the ink is evaluated by rheological measurements, and the interrelation between ink viscoelasticity and two distinct crack configurations is established. The detailed SEM characterization shows that an appropriate ink cohesive energy produces more intersected cracks within the MPL, while lower or higher cohesive energy is prone to unpenetrated and interlayer cracks. Applying high shear rates associated with the coating process (∼ 500 s-1), it could be indicated that a lower variation of cohesive energy promotes a homogeneous PTFE distribution. Combining the ink viscoelasticity and crack structure, the moderate solid (5 wt.% - 7 wt.%) ink would be the optimal formulation for the desired MPL porous structure.

Keywords: Microporous layer, Crack, Ink Viscoelasticity, Cohesive energy, Solid content