Dual-crosslinked sulfonated poly (ether ether ketone) membranes with isophthalic acids for enhanced proton exchange membrane fuel cells

Abstract

To facilitate the practical application of hydrocarbon-based proton exchange membranes (PEMs) in proton exchange membrane fuel cells (PEMFCs), it is imperative to address and mitigate their significant humidity dependence, including proton conductivity and membrane stability. Herein, crosslinked sulfonated poly(ether ether ketone) (SPEEK) membranes with sulfonated isophthalic acid (SIPA) and isophthalic acid (IPA) as crosslinkers are investigated for realizing robust and high-performance PEMFCs. Through chemical reduction and subsequent crosslinking reactions, dual-crosslinked SPEEK (dc-SPEEK) membranes are synthesized with optimized SIPA and IPA ratios. The dc-SPEEK membranes demonstrate enhanced proton conductivity, water uptake, and membrane stability compared to non-crosslinked SPEEK and single-crosslinked SPEEK membranes. Morphological analysis reveals a well-developed phase separation in dc-SPEEK, which enables effective proton transport, resulting in superior proton conductivity of 278.8 and 8.9 mS cm⁻¹ at relative humidity 100 % and 50 %, respectively. Additionally, membrane electrode assemblies fabricated with dc-SPEEK exhibit significantly higher current and power densities of 287.03 mW cm⁻² compared to other membranes, highlighting their potential for practical fuel cell applications. Overall, the results underscore the importance of crosslinking strategies in improving the performance and durability of PEMs for PEMFCs.