Freeze-thaw integrity of modified Nafion membranes: Microstructure and MEA performance

Integrity of Nafion membranes in freeze-thaw cycles is an important factor which should be considered when developing proton exchange membrane fuel cells (PEMFC) for the wide range of operating temperatures. Freezing of the Nafion membrane swollen in water leads to desorption of free water/ice on the membrane surface, which causes delamination of catalyst layer, and changes in membrane microstructure. To increase Nafion stability, in situ sol-gel modification with silica nanoparticles was carried out. Morphological changes of pristine and modified membranes during freeze-thaw cycles were investigated by small angle X-ray scattering (SAXS), in addition water uptake and proton conductivity were determined. Stabilization of the structure of ionic domains due to the introduction of silica nanoparticles into the membrane was shown. The observed changes can be attributed to a decrease in the intensity of water sorption-desorption processes and stabilization of ionic domains by modifier nanoparticles. The MEAs fabricated using modified membranes demonstrated enhanced stability during freeze-thaw cycling. • Freeze-thaw cycles affect proton exchange membrane microstructure; • Incorporation of silica nanoparticles increased the stability of the Nafion structure; • The use of modifier in the membrane prevents MEA degradation during F/T cycling