Ion-pair membrane based on methylated poly(4-vinylpyridinium) for high temperature proton exchange membrane fuel cells

This study presents ion-pair membranes based on commercially available poly(4-vinylpyridine) (PVPyr), which underwent a simple and quantitative N-methylation to form methylated poly(4-vinylpyridinium) (Me-PVPyr). The high charge density of Me-PVPyr resulted in brittleness, which precluded the formation of a mechanically stable polymer membrane. In order to overcome this issue, polybenzimidazole (F6PBI), a polymer with good film-forming properties and thermal stability, was blended with the Me-PVPyr. An optimized blend ratio of 7/3 wt. % (Me-PVPyr/F6PBI, Blend 7/3) demonstrated excellent proton conductivity of 409 mS cm -1 at 180°C under anhydrous conditions, surpassing that of commercially available PA-doped p PBI membranes being 366 mS cm -1 . Furthermore, the blend membranes demonstrated superior conductivity retention during thermal cycling between 80°C (50% RH) and 160°C (0% RH). In the fuel cell, the Blend 7/3 membrane reached a peak power density of 1.69 W cm -2 at 200°C with 2 bars of back pressure in H 2 /O 2 , outperforming commercial p PBI membranes under the same test conditions. An accelerated stress test (AST) involving thermal cycling between 80 and 160°C at a constant voltage (0.5V) demonstrated the superior durability of the blend membrane, which showed no performance decay over 100 cycles, in contrast to the significant decay of p PBI within 70 cycles. A post-mortem analysis of Blend 7/3 membrane electrode assembly (MEA) by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed a decrease in membrane thickness from 60 μm to 15 μm during the fuel cell operation, accompanied by minimal creeping of the membrane into the catalyst layers. • Efficient N-methylation of polyvinyl pyridine for ion-pair polymer conversion. • Mechanical stability: elongation at brake over 50% for all the membranes. • Superior conductivity of 400 mS cm -1 and conductivity retention under 80-160°C cycling. • Fue cell perfomance: 1.69 W cm −2 at 200 °C, H 2 /O 2 , 2 bars.