Structure–Property Relationships in Hydroxide‐Exchange Membranes with Cation Strings and High Ion‐Exchange Capacity. Issue 24 (2nd December 2015) - Wang, Junhua
Abstract: A series of poly(2, 4‐dimethyl‐1, 4‐phenylene oxide) hydroxide‐exchange membranes (HEMs) with cation strings containing a well‐defined number of cations (CS‐ n ) and similar, high ion‐exchange capacities are synthesized to investigate the effect of cation distribution on key HEM properties. As the number of cations on each string grows, the size of the ionic clusters increases from 10 to 55 nm. Well‐connected ion pathways and a hydrophobic framework are observed for n ≥4. 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 cm 2 mol −1 for n ≤3; and ∼34 cm 2 mol −1 for n ≥4. Abstract : String them along : The structure– property relationships of a series of hydroxide‐exchange membranes with cation strings containing a well‐defined number of cations and similar, high ion‐exchange capacities are compared. Together with long and flexible side chains, a high number of cations on each side chain leads to improved hydrophilic–hydrophobic phase separation that suppresses the water uptake and increases the conductivity and mechanical strength of the membranes.