Characterization of Anion Exchange Membrane Using Dopamine Methacrylate for Reverse Electrodialysis

Introduction Reverse electrodialysis (RED) can be used to generate renewable energy from the mixing of water of two different salinities. Herein, we have focused on anion exchange membranes (AEMs) for RED, because these... [ view full abstract ]

Introduction Reverse electrodialysis (RED) can be used to generate renewable energy from the mixing of water of two different salinities. Herein, we have focused on anion exchange membranes (AEMs) for RED, because these significantly affect RED performance parameters such as power density and open circuit voltage. Particularly, dopamine methacrylate (DMA) was used as a supplementary monomer for introducing quaternary ammonium (QA) groups, because the addition reaction of catechol-bearing DMA binds amines. For membrane fabrication, we chose the pore-filling method. Method Microporous polyethylene (PE; porosity 40 vol.%, thickness 22 μm) was used as a substrate. The electrolyte for substrate filling (E4C1; 50% (w/v) in ethanol) comprised vinylbenzyl trimethyl ammonium chloride as the source of the anion exchange groups, ethylene glycol diacrylate as a cross-linker, and DMA (hereafter E4C1). The PE substrate was immersed in the E2C1 solution and cured by UV irradiation for 10 min. The resulting coating was removed and subsequently immersed in a diamine solution of piperazine (PI; 10 mM) or hexamethylenediamine (Hx; 10 mM) for 10 min at room temperature to induce the formation of the supplementary QA by binding with the DMA groups. The resulting membrane was characterized using thermogravimetric analysis (TGA), swelling degree, and area resistance. Results and Discussion TGA results showed two peaks at 174 and 208 °C for the treated membranes, which corresponded to the degradation of the QA groups. A single peak at 214 °C was observed in the sample before diamine treatment. Moreover, after PI and Hx treatment, the swelling degrees (%) were 23.4 and 12.2, respectively, and that of the control membrane (E4C1) before diamine treatment was 20.8. The area resistance of E4C1-PI and E2C1-Hx was 0.404 and 0.421 Ω·cm2, respectively. The change in the swelling degrees was attributed to the penetration of hydrated ions through the AEM, which consequently influenced the area resistance. Conclusions We successfully characterized the pore-filled AEM using DMA and diamine, and expect that E4C1-diamine membranes can be used as an alternative membrane for RED systems.