Roles of functionalized nanoparticles in the performance improvement of proton-exchange membranes used in low- and intermediate-temperature hydrogen fuel cells: A review

A variety of nanoparticles (NPs) (e.g., SiO 2 , TiO 2 , CeO 2 , Co 3 O 4 , etc.) and their functionalized counterparts have been intensively investigated for improving the electrochemical and mechanical durability of polymer -based proton -exchange membranes (PEMs) for use in low- and intermediate -temperature fuel cells. This study is to conduct a comprehensive review on the roles of functionalized NPs in the performance enhancement of PEMs including proton conductivity, gas crossover resistance, electrochemical and mechanical durability, etc. A brief historical review of PEM fuel cell (PEMFC) technology is made. Typical types of NPs and their functionalization techniques are retrospected and their roles in the performance improvement of PEMs are compared in detail. Consequently, the opportunities and challenges to develop high-performance functionalized NPs for use in PEMs and PEMFCs are prospected and justi fied.