Exploring the structure-property relationships in hydroxide-exchange membranes

junhua fig

In Junhua’s recent work, a series of poly(2,4-dimethyl-1,4-phenylene oxide) hydroxide-exchange membranes (HEMs) with cation strings of a well-defined number of cations (1 to 6 denoted as CS-1 to CS-6) and similar, high ion-exchange capacities are synthesized to investigate the effect of cation distribution on key hydroxide exchange membrane properties. As the number of cations on each string grows, the size of ionic clusters increases from 10 to 55 nm. Well-connected ion pathways and hydrophobic framework are observed for n = 4 and above. The enhanced phase segregation increases the hydroxide conductivity from CS-1 to CS-6 (30 to 65 mS cm-1) and suppresses the water uptake (from 143% to 62%). Moreover, molar hydroxide conductivities for CS-n membranes show two distinctive stages as n increases: ~23 S cm2 mol-1 for n = 3 or below; and ~34 cm2 mol-1 for n greater than or equal to 4.