Main-Chain Densely Sulfonated Poly(phenylquinoxaline) PEMs: Achieving High Power Density in DMFCs via Microphase methodology

A series of sulfonic acid groups densely on main chain in random (R-SPPQs) and multiblock (MB-SPPQs) form polyphenylquinoline proton exchange membranes (PEMs) with acid-base ion crosslinking were synthesized. The relationship between membrane selectivity of proton conductivity ( σ )/methanol permeability ( P MeOH ) and microstructure is investigated. R-SPPQs PEMs benefit from acid-base ion crosslinking. Ion exchange capacity (IEC) changing from 1.73 to 2.40 meq g -1 , P MeOH increases from 1.89 × 10 -7 to 3.15 × 10 -7 cm 2 s -1 , approximately 1/10 that of NR212. R-SPPQ-5 shows the highest relative membrane selectivity (RS) of 5.5. Its maximum power density ( W max ) of 100 mW cm -2 exceeds that of NR212 (70 mW cm -2 ). Low repetitive structural units of MB-SPPQ-0505 with unconnected hydrophilic microphase-separation structure exhibit promoted σ of 103 mS cm -1 at 60 o C, outperforming R-SPPQ-4 with similar IEC by 45%. The P MeOH value of 4.7 ×10 -7 cm 2 s -1 represents a 66% increase over that of R-SPPQ-4, with a slight decrease in RS to 4.4. Its W max is 103 mW cm -2 . This stems from the combination of low internal resistance and low P MeOH . There’s no significant attenuation in battery performance in the 50-hour durability test, indicating promising potential application prospects in direct methanol fuel cells. Increased repetitive structural units of MB-SPPQ-1010 with interconnected microphase-separated structure, resulting in a further 17% increase in σ than MB-SPPQ-0505 at 60 o C. Whereas P MeOH is elevated to 10.4 × 10 -7 cm 2 s -1 , resulting in a decrease in RS to 2.7. Its W max drops to 65 mW cm -2 .