Recent Advances in the Application of Covalent Organic Framework–Based Ionic Conductors in Proton Exchange Membrane Fuel Cells

Covalent organic frameworks (COFs), known for their tunable porosity and functional versatility, have demonstrated exceptional ionic conductivity in proton exchange membrane fuel cells (PEMFCs). This review summarizes recent advancements in COF-based materials for PEMFC applications, emphasizing their roles as intrinsic proton conductors, host matrices for proton carriers, and additives in composite ionomers/membranes. Key strategies such as pore engineering, functional group modification, and hybrid designs with polymers are analyzed to highlight their influence on proton conductivity and mechanical stability. Recent developments reveal that functionalized COFs can achieve proton conductivities exceeding 0.89 S cm⁻¹ at 90 °C under 100% relative humidity (RH), comparable to commercial Nafion membranes. Additionally, COF-modified ionomers applied to catalyst layers have enabled fuel cells to achieve peak power densities 1.6 times higher than those without COF incorporation. Despite these advancements, challenges persist in terms of membrane durability, scalability, and performance under low humidity or high-temperature conditions. Future research should prioritize structural optimization, interfacial compatibility, and cost-effective synthesis methods to fully realize the potential of COFs in next-generation PEMFCs. This review underscores the transformative potential of COFs in addressing the critical limitations of traditional proton-conducting materials, paving the way for innovative solutions in fuel cell technology.