Maxime Gondrexon
Systèmes Moléculaires et nanoMatériaux pour l'Énergie et la Santé (SyMMES)/ STEP Team
UMR 5819
CEA-CNRS-UGA-Grenoble-INP
The proton exchange membrane fuel cell (PEMFC) is a device for converting chemical energy into electricity. It could play a part in decarbonising various sectors, such as heavy transport (road, rail and sea). However, it requires high performance and durability (more than 25,000 hours by 2030) if it is to be widely deployed. Its properties are closely linked to those of the membrane which is at the heart of the cell. To achieve the performance and durability targets set for 2030, operating temperatures higher than 100°C are targetted. However, the membranes currently used are perfluorinated membranes of the Nafion® type, which do not allow PEMFC to be used at these temperatures (fall in thermomechanical properties and conductivity at around 80-90°C). They also pose environmental and public health problems because they contain fluorine. Alternative membranes are therefore proposed, such as sulfonated poly (ether ether ketone) aromatic membranes (sPEEK). However, these membranes are less chemically stable and it is necessary to improve this property. In this purpose, this thesis looks at a way of improving the chemical stability of commercial sPEEK membranes via a hybridization route using Sol-Gel chemistry. A first study investigated the effects of hydroalcoholic pretreatments applied to a commercial sPEEK membrane, improving its mechanical cohesion in water at 80°C, a necessary condition for its use in a PEMFC. This improvement was associated with morphological changes in the membrane. Next, SG precursors with promising antioxidant functions were synthesized by a simple and efficient route: thiol-ene chemistry. Two commercial membranes were then prepared using some of these SG precursors. However, against all expectations, ex-situ accelerated ageing tests revealed that this hybridization route may have no effect on the chemical stability of the material, or even a prodegradant effect, depending on the host membrane. To understand these unexpected effects, morphological studies were carried out in direct space (AFM) and reciprocal space (CV-SANS). Hypotheses linking the chemical durability and morphology of hybrid membranes are finally proposed.