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

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. Herein, a functionalized cerium oxide (CeO₂@Ph-PEI) induced by phosphate-grafted polyethyleneimine (Ph-PEI) was prepared and used as an antioxidant to modify the Nafion matrix to break the “trade-off” between durability and proton conductivity of PEMs. Owing to the electrostatic interactions between the amino groups on the surface of CeO₂@Ph-PEI and the sulfonate groups in the Nafion matrix, the microphase-separated structure of the PEM is strengthened and rapid channels for proton transport are constructed. As a result, the obtained CeO₂@Ph-PEI-based PEM exhibited a substantially reduced activation energy of 9.3 kJ mol⁻¹ and an outstanding proton conductivity up to 0.242 S cm⁻¹, enabling it to achieve a high power density of 1.337 W cm⁻² in a PEMFC single cell, almost 1.32 times higher than that of the unmodified CeO₂-based PEM. After 200 h of accelerated degradation testing, the CeO₂@Ph-PEI-based PEM demonstrated superior performance compared to the pristine and CeO₂-based PEMs, exhibiting an OCV decay rate of 0.32 mV h⁻¹, a maximum power density of 1.19 W cm⁻², an H₂ crossover current density of 2.12 mA cm⁻², and a thickness retention rate of 93.7%. 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.

Multifunctional CeO₂@Ph-PEI as free radical scavenger constructed a proton transport network within the PEM enabling rapid proton transfer, thus simultaneously improving proton conductivity and durability of PEM.