Heterogeneous nanostructural ageing of fuel cell ionomer revealed by operando SAXS

Proton Exchange Membrane Fuel Cells (PEMFCs) represent one of the most interesting technologies for powering vehicles and small portable electronic devices in an eco-friendly way. Large scale implementation of PEMFCs requires to tailor novel resilient economically-viable materials with prolongated lifetimes. One key issue is the durablity of the ionomer membrane, which is responsible for the conduction of protons from anode to cathode. Here we report on the impact of ageing on the membrane structure by means of operando SAXS . By analyzing the most prominent features of the in-situ aged and pristine spectra at different relevant positions in the fuel cell, we could establish that structural ageing is highly heterogeneous and strongly dependent on the local conditions. The increase in current density produces a decrease in ionic nanodomain sizes in aged ionomer, due to continuous membrane drying, as in pristine materials. However, long term operation most dramatically affects the polymer organization into ...