Ion transport is a core function of energy conversion and storage devices like fuel cells and batteries. Nafion and sulfonated polysulfone (SPSf) are widely recognized as leading fluorocarbon and hydrocarbon-based ionomers, respectively, for proton transport in proton exchange membrane fuel cells (PEMFCs). Due to environmental concerns and the perfluorinated nature of Nafion, hydrocarbon-based alternatives are more desirable. However, SPSf exhibit significantly lower proton transport in sub-micron-thick films at catalyst–electrode interfaces, despite performing comparably to Nafion in bulk membranes. This limitation arises from unfavorable chain orientation near the substrate, which restricts ionomer–water mobility and hinders proton transport. To overcome this, we applied an interfacial engineering strategy by functionalizing electrodes with 3-aminopropyltriethoxysilane (APTES) before depositing SPSf films. APTES altered ionomer-substrate interactions, promoting favorable chain alignment and enhancing conductivity. Electrochemical impedance spectroscopy revealed a tenfold increase in proton conductivity, while confocal laser scanning microscopy confirmed a reduced low-conductivity interfacial region. These results demonstrate that interfacial engineering can mitigate substrate-induced conductivity losses, advancing hydrocarbon ionomers as viable, eco-friendlier alternatives to perfluorinated ionomers in PEMFCs.
