Tungstophosphoric acid-doped sulfonated poly(arylene ether nitriles) composite membranes with improved proton conductivity and excellent long-term stability

Abstract A series of composite membranes based on sulfonated poly(arylene ether nitriles) (SPEN) with embedded tungstophosphoric acid (TPA) were prepared. The effect of TPA concentration on morphology, structure, thermal stability, mechanical strength, ion-exchange capacity and proton conductivity of SPEN-TPA composite membranes was studied in detailed. SEM images indicated the TPA were uniformly distributed throughout the SPEN membranes matrix, which is due to the hydrogen bonding networks and the electrostatic interactions in the composites. The existence of hydrogen bonds was also confirmed by FTIR. Benefiting from these, the composite membranes showed higher IEC, mechanical strength, and higher water uptake compared to pristine SPEN. The proton conductivity of the SPEN-TPA composite membranes were dominated by the TPA concentration. The proton conductivity of SPEN-50TPA achieved the highest value of 0.107 S/cm at 80 °C, which is 4.4 times as high as that of pristine SPEN. Moreover, it also showed excellent long-term stability, as the TPA did not show any leakage after 120 h at 80 °C. Furthermore, activation energy of proton conductivity imply coexistence of Grotthuss and vehicle mechanisms in the composite membranes. These results indicate that SPEN-TPA composite membrane have great potential as proton exchange membrane with high performance.