Highly conductive quaternary ammonium-containing cross-linked poly(vinyl pyrrolidone) for high-temperature PEM fuel cells with high-performance

Poly(vinyl pyrrolidone) (PVP)-based high-temperature polymer electrolyte membranes (HT-PEMs) doped with phosphoric acid (PA) present an attractive prospect for high-temperature fuel cell. However, its proton conductivities and mechanical properties are inversely dependent on PVP content in membranes. Herein, chloromethyl-polysulfone is used as a polymeric crosslinker to fabricate cross-linked PVP. The effects of chloromethylation degree of polysulfone on PVP cross-linking degree, free volume and other parameters are studied. The quaternary amine groups introduced by cross-linking reaction enhances PA adsorption and retention capacity of membrane. The increased molar free volume created by polymeric crosslinker can accommodate more PA storage and reduce the polymer main chain plasticization. Thus, the mechanical properties of membranes are maintained. When compared to uncross-linked C-PVP-0/PA, the cross-linked C-PVP-13.7%/PA exhibits improved mechanical strength with increasement of 140% (4.5 MPa) and enhanced proton conductivity with increasement of 119% (120.0 mS cm⁻¹@160 °C). Also, these superior characteristics allow a significantly enhanced H₂–O₂ fuel cell performance with the membrane of 724.9 mW cm⁻² @160 °C, which has increasement of 50% in comparison with that of the C-PVP-0%/PA membrane, and excellent durability. These praiseworthy results suggest that the cross-linked membrane within moderately molar free volume is potential to act as HT-PEMs materials for real-world applications.