Decoration of CeO2 nanoparticles radical scavengers with innovative anchoring groups in Aquivion®- based Proton Exchange Membranes

Hydrogen economy is considered the best alternative to the current fossil fuel-based energy production system; which is arguably the main cause of climate change. It involves the employment of green hydrogen, produced form renewable energies, in fuel cells to sustain today’s massive energy demand. The most prominent technology in this field, are Proton Exchange Membranes Fuel Cells (PEMFCs); which are based chiefly on perfluorosulfonated polymers such as Nafion® and Aquivion®. One of the main factors hindering a wider diffusion of these devices is related to their limited durability, especially in heavy-duty applications where longer lifetimes are required. This is caused by the reaction between various radical species and the ionomer, that result in the disruption of either the backbone or the lateral chains of the polymer. Currently the best strategy to improve the long-term stability of MEAs (Membrane Electrode Assembly) for PEMFC, is to add some fillers that act as a scavenger for radical species; and the most promising one are ceria nanoparticles. They have been added in the ionomer present in the catalyst layer and, more recently, are being dispersed directly in the membranes; both approaches lead to an improvement of the MEA’s lifetime. Either way, however, the nanoparticles tend to migrate, over time, under working conditions; thus, they progressively lose their effectiveness. The decoration of the surface of the NPs with organic pendants, that act as anchoring groups, is amongst the innovative strategies pursued to hinder this phenomenon. Our work is devoted to the synthesis of CeO2 NPs decorated with perfluorinated short chain alkanes ; that anchor them in the hydrophobic domain of the Aquivion® membranes they are dispersed into. This innovative approach is aimed at the improvement of the membrane’s lifetime, without meaningful performances reduction, while also enhancing the mechanical resistance of the ionomer (the decorated nanoparticles act as physical cross-linker). The synthesis is accompanied by a thorough characterization both of the nanoparticles and the resulting composite membrane, through thermal (DSC, TGA), mechanical (DMA, tensile strength), morphological (SEM, XRD) and spectroscopical (IR, ss-NMR) analysis, as well as with electrochemical performance tests. In addition to these, accelerated durability test, such as the well-known Fenton-test and an innovative time domain NMR, are used to investigate the effect of these scavengers on the membrane’s lifetime.