Multicomponent transport of methanol and acetate in a series of crosslinked PEGDA-AMPS cation exchange membranes

Transport and Co-Transport of Carboxylate Ions and Ethanol in Anion Exchange Membranes

“…To rationalize this behavior, we conjecture the permeation of carboxylate salts to be dependent on the polyatomic carboxylate anions over the cations. Consequently, electrostatic attraction (i.e., counterion condensation [18]) between the bound quaternary ammonium (QA + ) and mobile carboxylate anions (OFm − and OAc − ) can be suppressed by co-permeation with EtOH (i.e., charge screening [29,30,32]); see Figure 1. As a result, the overall salt permeabilities of QA + -containing A8 and A12 are decreased in co-permeation with EtOH.…”

“…While the majority of ion exchange membranes (IEM [17][18][19][20]) designed for PEC-CRCs have focused on AEMs, one of the major drawbacks of AEMs for such devices is their high diffusibility for negatively charged CO 2 reduction products (OFm − and OAc − ). To avoid this issue, our group has performed a series of investigations to gain a fundamental understanding of cation exchange membranes (CEM [21][22][23][24]) for PEC-CRCs, such as how the presence of a series of charge-neutral comonomers (acrylic acid, hydroxyethyl methacrylate and poly(ethylene glycol) methacrylate (PEGMA) [25,26]) or how the presence of co-diffusing neutral CO 2 reduction products (alcohols) can act to impact and, in some cases, mitigate the permeation of CO 2 reduction products (carboxylates) [27][28][29][30][31][32]); see Figure 1A,D. In the case of Nafion ® 117 (a commercial CEM) and PEGDA-AMPS (a crosslinked CEM that we prepared by incorporating 2-acrylamido-2methyl-1-propanesulfonic acid (AMPS, sulfonate-containing ionomer) with a crosslinker, poly(ethylene glycol) diacrylate (PEGDA)), both OFm − and OAc − diffusivities were increased in co-diffusion with either MeOH or EtOH, where we conjectured a potential charge screening by co-diffusing alcohol [32].…”

“…However, those of PEGDA-AMPS/PEGMA were the same [28] or slightly decreased in co-diffusion with MeOH, where we conjectured a potential charge screening by long pendant chains. [28,30,32] with permission from Elsevier and Wiley.…”

“…Here, to further investigate multicomponent transport behavior [33] in IEMs, we perform an analogous investigation on a series of AEMs, Selemion ® AMVN (AMVN) and PEGDA-APTA (A8 and A12). AMVN is a commercial AEM and PEGDA-APTA is a crosslinked AEM that we prepare by incorporating (3-acrylamidopropyl) trimethylammonium chloride (APTA, QA + -containing ionomer) with a crosslinker, PEGDA [28,30,34,35]; see Figure 2. Moreover, we prepare and characterize a crosslinked PEGDA (A0) as an uncharged analog to exclude the effect of QA + from A8 and A12 for comparison.…”

“…In Figure 1A-C, the diffusion of the carboxylate anion by itself is depicted, where the mobile carboxylate anion experiences electrostatic repulsion from bound sulfonate in CEMs (Figure 1A) and electrostatic attraction from bound QA + in AEMs (Figure 1C) (ion-polymer interaction). In Figure 1D-F, the diffusion of carboxylates is assisted by co-diffusing alcohols (flux coupling; [38]) (ion-alcohol interaction), where the electrostatic interaction between bound charge groups and the mobile carboxylate anion is screened by the co-permeating alcohol (alcohol-polymer interaction, charge screening; [27,[29][30][31]; Figure 1D,F).…”