Synthesis and characterization of new proton-exchange membranes based on poly-1-vinyl-1,2,4-triazole doped with phenol-2,4-disulfonic acid

Poly-1-vinyl-1,2,4-triazole (PVT) was synthesized in isolated yield by free radical polymerization of 1-vinyl-1,2,4-triazole. The number average molecular weight and weight average molecular weight of the synthesized PVT, determined by gel permeation chromatography, was 88 567 and 153 309 Da, respectively. PVT had a unimodal molecular weight distribution with a polydispersity coefficient of 1.7. Mixing PVT with phenol-2,4-disulfonic acid (PDSA) in the presence of a polyvinyl alcohol cross-linked with oxalic acid produces proton exchange membranes having different PVT:PDSA ratios. The composition and structure of the membranes were established by elemental analysis, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance spectroscopy (NMR). FT-IR and 15N NMR studies have shown that the interaction of PVT with PDSA was accompanied by the formation of acid-base complexes due to proton transfer from PDSA to the triazole rings of PVT. Formation of acid-base complexes PVT-PDSA additionally stabilizes membranes and increases their thermal stability. The SEM study showed that the membrane surface was homogeneous. The properties of membranes, such as thermal and oxidative stability, ion-exchange capacity, proton conductivity, water uptake, and their mechanical properties, have been studied. The commercial membrane Nafion 212 was used as a comparison. The proton conductivity of membranes increases with an increase in the content of PDSA in their composition and for membranes 1-3 was 59.80, 7.30, 6.23 mS/cm, respectively. The activation energies for proton transfer across the membranes were 19.5, 21.6, and 38.2 kJ/mol for the membranes 1-3, respectively. Water uptake, ion-exchange capacity, and proton conductivity depend on the content of PDSA in the membrane. The membranes obtained were tested in a test cell of an ElectroChem hydrogen fuel cell (USA) at a temperature of 25°C with the supply of humidified hydrogen and air.