(355d) High Performance Blend Membranes Based on Poly(arylene ether sulfone) and Poly(styrene-isobutylene-styrene) for Direct Methanol Fuel Cell Applications

Fuel Cells have emerged as an alternative to fossil fuel-based energy production, due to its high efficiency and environmentally benign nature. Nafion^® has been the standard proton exchange membrane (PEM) of choice for decades. Despite Nafion^®’s high proton conductivity, issues related to water management, cost, and processability, limit its performance and further commercial expansion. This work pursues PEM’s capable of enhancing the proton conductivity, while having the ability to operate at high temperatures. The objective of this study is to evaluate an alternative copolymer for Direct Methanol Fuel Cells (DMFC)s based on poly(arylene ether sulfones) using two sulfonation reagents. The copolymers were synthetized by a coupling reaction between decafluorobiphenyl (DFBP) end capped non sulfonated poly(arylene ether sulfone) (BPS0) and sulfonated poly(arylene ether sulfone) (BPS100). The reactive behavior of DFBP facilitates the low temperature coupling reaction (below 105 °C). Membrane’s performance was analyzed in function of the sulfonation reagents and blends with poly(styrene-isobutylene-styrene) (SIBS) at different sulfonation levels. A materials characterization study (e.g., FTIR, TGA and SAXS) was performed to analyze the presence of the ionic domains, phase segregation and interaction among ionic domains. Ion exchange capacity (IEC), methanol permeability and water absorption capabilities were also studied to identify possible effects that enhance the desired DMFC properties. Results suggest a phase segregation between hydrophobic and hydrophilic domains for IEC’s below 1 meq/g, and low water absorption, with no significative difference among sulfonation reactants, while having excellent thermal stability (over 600⁰C, >60%). The polymer blends of copolymers with sulfonated poly(styrene-isobutylene-styrene) (SIBS) provided more elastomeric behavior as well as a significant increment in proton conductivity (0.13 S/cm at 50°C) due to the synergistic effect of the sulfonic domains, the arylene ethers and the sulfone.