Innovative ceria nanoparticles decoration for composite Aquivion® proton exchange membranes with improved lifetime

Almost all the energy we consume is produced from fossil fuels with the subsequent production of CO2 that is the main cause of the ongoing climate crisis. The most promising alternative is a hydrogen-based circular economy where green H2 is produced in renewable electricity-powered water electrolyzers, and electrochemically combined with oxygen to power all our everyday activities in fuel cells. The only commercially available technology in this field are of proton exchange membrane fuel cell (PEMFC) where the ion conducting membrane is based on a perfluorosulfonated polymer (e.g. Nafion® and Aquivion®). The main limit of this technology is related to the relatively low lifetime of the device caused by the degradation of the polymeric chains [1] caused by radical species (•OH •OOH) created, as byproducts of the complicated oxygen reduction reaction, at the cathode. The best strategy to improve the device’s lifetime is the introduction of radical scavenger species in the membrane electrode assembly (MEA). The most promising radical scavengers are cerium oxide nanoparticles embedded either in the polymeric membrane [2], or in the catalyst layer [3]. To improve the compatibility between the inorganic filler and the organic polymeric matrix we synthesized CeO2 NPs decorated with a perfluoroalkyl chain trough a silanization process of the nanoparticles surface (figure1). This is expected to increase the compatibility of the filler with the membrane thus allowing for higher scavenger loads without significant losses in conductivity: the perfluorinated pendant on the oxide NP is expected to anchor it in the hydrophobic domain of the membrane; thus, hopefully, not disrupting the delicate ionic channel network. Furthermore, the decoration is expected to reduce the migration effect that have been highlighted in long-term studies [4] of composite MEAs and improve the mechanical properties of the membrane acting as a physical cross-linker between different polymeric chains. Both the decorated NPs and the composite membrane have been characterized with thermal analysis (TGA, DSC), mechanical measurements (DMA, tensile strength) morphological studies (XRD and SEM) and spectroscopies (IR, ss-NMR). The resulting membranes were also electrochemically characterized with IEC and conductivity measurements as well as with Fenton for durability assessment. References [1] Ren et al. Prog. Energy Combust. Sci. 2020, 80, 100859 [2] Cong Tinh et al. J. Membr. SCI 2020, 613, 118517 [3] D’Urso et al. J. Power Sources 2014, 272, 753 [4] Baker et al. J. Electrochem. Soc. 2016,163, F1023