Series-Connected Tetracation Partially Cross-Linked Anion Exchange Membranes: Insight towards Consequences of Alkyl Spacer Length

Abstract

To systematically study how the length of alkyl spacers between cationic head groups in a cross-link impacts the performance of a multication anion exchange membrane (AEM), a series of cross-linkers with varied chain lengths of alkyl spacers between cations from 3-methylene (−CH 2 −) 3 to 10-methylene (−CH 2 −) 10 groups are prepared. Specifically, a series of partially cross-linked poly(phenylene oxide)-based AEMs with seriesconnected tetracations along with a monocation pristine membrane with a pendent hexyl chain is synthesized. The highest ionic conductivity of 17.33 mS cm −1 at 30 °C in water is realized for a partially cross-linked membrane having series-connected tetracations with butyl spacer between cations (AEM-Q5-C4). On the contrary, decreased water uptake and ionic conductivities are observed when the alkyl spacer chain is lengthened from the butyl to decyl group between cations while keeping the same degree of functionalization. Comparatively, high limiting current density (5.29 mA cm −2 ) for AEM-Q5-C4 membrane offers a broad window to achieve fast brackish water electrodialysis (ED) at higher applied potential/current. When being applied to electrodialysis, relatively higher NaCl removal percentage of 94.13% and energy efficiency of 82.01% and comparatively low energy consumption of 1.11 kWh kg −1 are obtained for AEM-Q5-C4 membrane among all prepared membranes tested for ED application. This work thus highlights the suitability of a partially cross-linked motif (AEM-Q5-C4) for brackish water electrodialysis.

Aliphatic Anion Exchange Ionomers with Long Spacers and No Ether Links by Ziegler–Natta Polymerization: Properties and Alkaline Stability

“…The second broad peak between 130 • C and more than 200 • C corresponding to 12% of the sample mass can be attributed to the two amines present in the ionomer. Similar decomposition temperatures were reported in various references [71,72].…”

“…The second broad peak between 130 °C and more than 200 °C corresponding to 12% of the sample mass can be attributed to the two amines present in the ionomer. Similar decomposition temperatures were reported in various references [71,72]. The second peak observed in the Figure 7b from 210 °C to 310 °C can be attributed to the thermal degradation of benzyl chloride moieties [73], it corresponds to about 30%.…”

Improving the conductivity and dimensional stability of anion exchange membranes by grafting of quaternized dendrons

“…The motivation of this work is to gain fundamental insights into the introduction of quaternized dendrons on the conductivity of AEMs. Consequently, the commercially available and widely studied AEM matrix of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) 12,21,[37][38][39][40][41][42][43] was used as the polymer backbones in this work, although PPO may not be stable enough under harsh alkaline environments. 44 Meanwhile, alkyl QA groups without beta-hydrogen atoms were chose as the cationic groups due to the excellent alkaline stability.…”