3-Aminopropyltriethoxysilane interfacial modification for enhanced aging resistance of polydimethylsiloxane-based fluorine-free microporous layers in proton exchange membrane fuel cells

Polydimethylsiloxane (PDMS) is a promising fluorine-free hydrophobic material for proton exchange membrane fuel cell (PEMFC) microporous layers (MPLs) owing to its low surface energy, environmental compatibility, and low-temperature curing. However, weak adhesion between low-loading PDMS and carbon materials limits the structural stability, especially under hydrothermal and oxidative conditions. Here, 3-aminopropyltriethoxysilane (APTES) is used to modify carbon black and enhance the carbon-PDMS interfacial interaction. An APTES-modified 5 wt% PDMS-MPL is compared with unmodified 5 wt% PDMS-MPL and conventional 20 wt% polytetrafluoroethylene (PTFE)-MPL. Hot-water and Fenton oxidative aging, combined with microstructural, pore, hydrophobicity, X-ray photoelectron spectroscopy (XPS), and single-cell electrochemical analyses, are used to evaluate aging-induced degradation and transport evolution. APTES modification reduces the ultrasonic mass loss rate from 11.67% to 5.17%, indicating improved interfacial stability. After aging, the modified MPL maintains a more stable pore structure and hydrophobicity and shows a mass-transfer resistance of 0.194 Ω cm 2 after Fenton aging. In contrast, unmodified PDMS-MPL exhibits polymer migration, local delamination, and oxidation, whereas PTFE-MPL retains a relatively stable pore structure but shows stronger high-current mass-transport limitations. These results demonstrate that APTES interfacial modification improves the structural stability and aging resistance of low-loading fluorine-free PDMS-based MPLs.