Proton exchange membranes based on sulfonated poly(arylene ether ketone) containing triazole group for enhanced proton conductivity

Sulfonated poly(arylene ether ketone) (SPAEK) containing carboxylic acid groups at the pendant position was synthesized. The proton conductivity was enhanced over a wide range of humidity by grafting 1H-1,2,3-triazole (TRI), a heterocyclic protogenic reagent, on SPAEK via the pendant carboxylic acid. The proton conductivity, water uptake, and thermal and mechanical stability of the TRI-grafted SPAEK membranes (SPAEK-TRI) were measured and compared against those of a commercial Nafion® 117 membrane. The proton conductivity increased as the degree of sulfonation (DS) increased, and this effect was further enhanced by the introduction of TRI. The SPAEK-TRI membrane with 40% DS (SPAEK40-TRI) exhibited an even higher proton conductivity than Nafion® 117 over the entire range of relative humidity (RH). The SPAEK40-TRI membrane exhibited a tensile strength of 16.52 MPa, which was similar to that of Nafion® 117, and all of the membranes prepared in this study were thermally stable at up to 200 °C. The ion cluster dimensions for SPAEK40-TRI and SPAEK50-TRI were of 4.52 nm and 4.91 nm, respectively, which are larger than that of Nafion® 117, 3.36 nm. This difference is attributed to the higher water uptake in the SPAEK-TRI membranes than Nafion® 117.