Efficient ether-free poly(p-terphenyl-isatin-dimethylfluorene) for proton exchange membrane water electrolysis

Proton exchange membrane (PEM) is an important component that affects the cost and cell performance of PEM water electrolysis (PEMWE). In this study, a series of ether-free poly( p -terphenyl-isatin- dimethylfluorene) (PID-x) polymers were synthesized by superacid-catalyzed Friedel-Crafts alkylation . The transparent PEMs of sulfonated poly( p -terphenyl-isatin- dimethylfluorene) (SPID-x) were prepared by the solution casting method. Introduction of dimethylfluorene groups enhances proton conductivity of PEMs while also preserving their high dimensional stability. The results indicate that the synthesized PID-x has excellent solubility in non-protic polar solvents . SPID-5, prepared with 5 % dimethylfluorene in the backbone structure exhibits a high conductivity of 0.176 S·cm −1 at 80 °C (compared to 0.155 S·cm −1 at 80 °C for Nafion115) and excellent dimensional stability, with a swelling ratio of only 10 % at 80 °C (compared to 20 % at 80 °C for Nafion115). In the water electrolysis cell performance test, SPID-25 achieved a current density of 167 mA·cm −2 at 2.5 V, outperforming the commercial Nafion 211 (151 mA·cm −2 ) at a similar membrane thickness. • PEMs of sulfonated poly( p -terphenyl-isatin-dimethylfluorene) were synthesized and prepared. • The solubility of polymers has been enhanced by introducing dimethylfluorene. • Proton conductivity and dimensional stability have been improved through the introduction of a rigid structure. • SPID-25 exhibited a higher current density than Nafion 212 for electrolyzed water.