Improved performance of poly(vinyl pyrrolidone)/phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)/graphitic carbon nitride nanocomposite membranes for high temperature proton exchange membrane fuel cells

To achieve desirable performance of a polymer electrolyte membrane with higher proton conduction and better mechanical strength is a challenging work in the development of the phosphoric acid (PA) doped solid-state membrane for high temperature proton exchange membrane fuel cells. Firstly, phosphonated poly(2,6-dimethyl-1,4-phenylene oxide) (pPPO) was prepared by the bromination and phosphonation of poly(2,6-dimethyl-1,4-phenylene oxide). Afterward, a series of poly(vinyl pyrrolidone)–phosphonated poly(2,6-dimethyl-1,4-phenylene oxide) (PVP/pPPO) blend membranes and poly(vinyl pyrrolidone)–phosphonated poly(2,6-dimethyl-1,4-phenylene oxide)–graphitic carbon nitride (PVP/pPPO/g-C3N4) nanocomposite membranes were prepared by a solution casting method. The PA uptake, volume swelling ratio, and proton conductivity of the PVP/pPPO blend membrane increased with increasing PVP content. But PA molecules drastically reduced the mechanical strength of the PVP/pPPO blend membrane. The incorporation of g-C3N4 improved the proton conduction and mechanical properties of the nanocomposite membrane due to the proton hopped sites provided by NH2 and the interaction of g-C3N4 and polymer chains. A higher proton conductivity of 74.4 mS cm−1 and a higher power density of 294 mW cm−2 at 180 °C without additional humidifying were observed for the PA doped PVP/pPPO nanocomposite membrane containing 5 wt% g-C3N4. The results show the PVP/pPPO nanocomposite membrane as a potential polymer electrolyte membrane for high temperature fuel cells.