Preparation and characterization of crosslinked poly(vinylimidazolium) anion exchange membranes for artificial photosynthesis

Abstract

The dependence of small molecule transport on the water content of ion exchange materials frustrates the development of membranes with both high ionic conductivity and low alcohol permeability for artificial photosynthesis devices.

Transport of Neutral and Charged Solutes in Imidazolium-Functionalized Poly(phenylene oxide) Membranes for Artificial Photosynthesis

“…This result can be explained by the solvation of greater numbers of charged moieties present in more highly-functionalized materials, and corroborates results reported for other ion exchange materials. 22,23,33,37 Additionally, membranes in the bicarbonate form generally sorbed more water than those of the same degree of functionalization in the bromide form,…”

“…Such a relationship has been observed for small solutes (e.g., simple salts and small organic molecules) in other dilute or semi-dilute (i.e., highly hydrated) charged polymers. 22,37,68 To provide a point of comparison with a commercial membrane frequently employed in artificial photosynthesis devices, Selemion AMV is included in Figure 4. Selemion AMV, in both the bicarbonate and bromide forms, exhibited a relatively low ethanol permeability that was comparable to an ImPPO-χ material with a similarly low water volume fraction.…”

“…35 Within the family of ImPPO-χ materials prepared herein, conductivity depended exponentially on inverse water volume fraction ( Figure 6), in agreement with the free volume theory and other studies of AEMs. 22,23,61,62 These results suggest that changes in the structure of the membrane (specifically the free volume available for solute transport) impacted the conductivity of the membrane to a greater degree than changes in ion concentration or size. The bicarbonate and bromide forms of the Selemion AMV membrane exhibited ionic conductivities similar to that expected for ImPPO-χ membranes of the same water volume fraction, as demonstrated in Figure 6 by their proximity to the regression of the ImPPO-χ results.…”

“…[23][24][25] Relatively few studies have explicitly investigated the selectivity/permeability trade-off as it pertains to artificial photosynthesis device performance; however, such studies would contribute to the development of devices that are commercially viable. 14,22 Despite widespread usage, commercial availability, and multiple reviews of AEMs, a comprehensive understanding of how AEM structure correlates with transport phenomena has not been realized. 19,20,[26][27][28][29][30][31] While the market availability of these materials has made them popular in (photo)electrochemical CO2R studies, the proprietary nature of these materials makes it difficult to ascertain a detailed understanding of how membrane chemistry and structure affect device performance vis-à-vis water, electrolyte ion, and CO2R product transport.…”

“…While several studies have correlated salt transport to AEM structural and chemical properties, few studies have explored uncharged solute (e.g., alcohol) transport through AEMs. 22,23,31,[33][34][35][36][37] More studies are needed to understand the complexity of transport through diverse membrane materials in a range of applications, including artificial photosynthesis. 4,14 Imidazolium-functionalized poly(phenylene oxide)-based membranes offer a platform that enables explicit study of membrane structure and transport properties within the context of artificial photosynthesis.…”