Influence of membrane type and molecular weight distribution on the degradation of PBI-based HTPEM fuel cells

• Detailed degradation study of membrane electrode assemblies of high temperature polymer electrolyte membrane fuel cells.
• Influence of different membrane concepts on lifetime was tested.
• Molecular weight distributions as well as the strengthening type have a major influence on the degradation behavior.
• Durability was enhanced by a higher amount of interactions between the polymer chains.
• PBI redistribution is proposed as new degradation mechanism for HTPEM-FC.

The degradation of high-temperature proton exchange membrane fuel cells with phosphoric acid-doped polybenzimidazole (PBI) based membranes is one of the key challenges for early commercialization. The aim of this work is to analyze the influence of different reinforcement strategies on the performance and degradation of PBI-based membranes. The effects on the membranes were analyzed by polarization curves, long term operation under constant load, electrochemical impedance spectroscopy, in-situ cyclic voltammetry and electron microscopy techniques. The results show that the molecular weight distribution of the PBI and the different types of reinforcement have a distinct influence on the poisoning of the cathode layer and the mass transport resistance of the cathode microporous layer. The reasons are discussed in detail and a new degradation mechanism is proposed. A significant reduction of the degradation was obtained by enhancing the interactions between the PBI polymer chains via cross-linking.