Synthesis and characteristics of a cross-linked DMSIP-co-HDO-co-MA ion-exchange membrane for redox flow battery applications

Novel ion-exchange membranes composed of dimethyl 5-sulfoisophthalate sodium salt (DMSIP), 1,6-hexanediol (HDO), isophthalic acid (IPA) and maleic anhydride (MA) were prepared by the synthesis of a DHIM oligomer and UV-cross-linking. The basic properties of the membranes were characterized, and a redox flow battery (RFB) test was conducted. The conversion and molecular weight of the DHIM oligomer decreased with increasing DMSIP contents; the maximum conversion and molecular weight values were 90.8% and 1335–1620 g/mol, respectively. The thermal stability of the cross-linked DHIM ion-exchange membrane was 370 °C. The water uptake and ion-exchange capacity increased as the DMSIP contents increased, and the maximum values were 43.1% and 1.23 meq/g. The minimum values for the electrical resistance and ion transport were 0.27 Ω cm2 and 0.998, respectively. Charge–discharge, voltage and energy efficiencies increased with the increasing extent of cross-linking, and their values were 90.81%, 79.92% and 71.52%, respectively. The minimum value of methanol permeability was lower than that of Nafion 117®, which indicates that the membrane has higher ion selectivity than Nafion 117®.