SPEEK-co-PEK-x proton exchange membranes with controllable sulfonation degree for proton exchange membrane fuel cells

Sulfonated poly(ether ether ketone)-poly(ether ketone) (SPEEK-co-PEK-x) copolymers with controlled degree of sulfonation are synthesized by the polycondensation reaction of varying monomer ratios. Compared with the traditional homopolymer sulfonated poly(ether ether ketone) (H-SPEEK), the SPEEK-co-PEK-x copolymer membrane has a high degree of sulfonation and excellent proton conductivity. Meanwhile, it also has favorable mechanical properties and stability. This is attributed to the introduction of the -PEK- segment. The SPEEK-co-PEK-75 membrane exhibits the highest conductivity (0.285 S cm−1) at 80 °C, 100% RH and when tests at 80 °C with 80% RH, the SPEEK-co-PEK-75 membrane reaches 0.0587 S cm−1. In addition, the tensile strength of the SPEEK-co-PEK-75 membrane reaches 47.66 MPa at room temperature. Moreover, the study investigates the impact of key variables on the single-cell performance of SPEEK-co-PEK-x membranes. The measured peak power densities of the SPEEK-co-PEK-75 membrane are 212 mW cm−2 and 495 mW cm−2 at 70% RH and 100% RH, which are 1.3 times and 1.7 times higher than that of the Nafion 117 membrane, respectively. After the 80 h durability test at 80 °C and 80% RH, the voltage of the SPEEK-co-PEK-75 membrane only drops by 4.8%. The presence of the -PEK- segment results in a more compact and connected distribution of hydrophilic ion clusters in the SPEEK-co-PEK-X membrane. This adjustment greatly enhances the performance of the membrane, making it an excellent candidate for proton exchange membrane in H2/air fuel cells.