Mitigation of Mechanical Membrane Degradation in Fuel Cells by Controlling Electrode Morphology: A 4D In Situ Structural Characterization

Abstract

Mechanical degradation is a critical mechanism responsible for the operational failure of fuel cell membranes. In addition to the membrane’s intrinsic durability, component interactions play a crucial role in this degradation process. This work investigates the interaction and associated impact of electrode morphology on membrane failure under pure mechanical degradation conditions by utilizing 4D in situ visualization by X-ray computed tomography. Using periodic identical-location imaging, membrane damage progression is monitored and compared for electrodes with high and low initial crack density. Membrane fracture is found to be significantly curtailed through minimization of ab initio crack density in the cathode catalyst layer. Hydration-dehydration cycles, however, still introduce early electrode cracking which, as an intermediate step, exclusively governs the subsequent initiation and propagation of membrane cracks. Two distinct membrane failure mechanisms are identified that are characterized by: (i) permanent buckling deformation of the catalyst coated membrane; and (ii) direct membrane fracture from electrode cracks without buckling. The buckling phenomenon is found to be strongly influenced by the microstructure of the gas diffusion media and has a dominant contribution towards the overall frequency and scale of membrane fracture. Additionally, the effect of hydration on the in situ size and geometry of fracture features is demonstrated.