Phosphate-grafted polyethyleneimine-induced multifunctional cerium oxide as an antioxidant for simultaneously enhancing the proton conductivity and durability of proton exchange membranes

Abstract

Abstract Free radical attack on Proton exchange membranes (PEM) is detrimental to the long-term durability of proton exchange membrane fuel cells (PEMFCs), and although state-of-the-art cerium-based antioxidants defend against free radical attack, potentially impairing the proton conductivity of PEM limits their more comprehensive application. To break the "trade-off" between the durability and proton conductivity of PEM, a functionalized cerium oxide (CeO2@Ph-PEI) composite with a synergistic enhancement of durability and proton conductivity has been synthesized induced by phosphate-grafted polyethyleneimine (Ph-PEI). Owing to the strong adsorption of phosphate groups on transition metal hydroxides/oxides, Ph-PEI was firmly anchored on the particle surface during the transition from sol-gel to oxide, which suppressed the further aggregation of CeO2 nanoparticles and thus retained abundant active sites for free radical scavenging. Moreover, due to the extra proton transport sites in the anchored Ph-PEI functional shells, the hybrid membrane fabricated with CeO2@Ph-PEI as the antioxidant additive exhibited a high proton conductivity up to 0.242 S cm− 1, which was approximately 1.32 times higher than that of the unmodified CeO2-based hybrid membrane. Consequently, CeO2@Ph-PEI-based PEMs exhibited an OCV decay rate of 0.32 mV h− 1, a maximum power density of 1.19 W cm− 2, an H2 crossover value of 2.12 mA cm− 2, and thickness retention (93.7%) after 200 hours of accelerated degradation testing. This strategy synergistically improves the proton conductivity of PEMs and the lifetime of PEMFCs through CeO2 functionalization, providing a promising solution for next-generation fuel cell-based energy storage techniques.