reduction product crossover: Electrochemical Cell Applications.*

CO₂ reduction cells are one of the interesting techniques to cope with CO₂ emission issue. A typical CO₂ reduction cell consists of two cells separated by an ion exchange membrane (IEM). The major role of IEM is to prevent the transport of various CO₂ reduction products (formate, acetate, methanol, and ethanol). Therefore, it is necessary to tailor the membranes to block the transport of these products. Previously, to suppress CO₂ reduction product crossover we introduced a series of uncharged comonomers, acrylic acid (AA, n=0, where n is the number of PEG repeat units), hydroxyethyl methacrylate (HEMA, n=1), and poly(ethylene glycol) methacrylate (PEGMA, n=5), where we observed the crossover of carboxylates were significantly suppressed in PEGMA-containing films in co-diffusion. To further understand this, we prepared a series of PEGMA (n=9)- containing films and measured the permeabilities and solubilities of these films to carboxylates (formate and acetate) and alcohols (methanol and ethanol) in one- and two-component mixtures. In one-component permeation, we observed permeabilities to all solutes being increased with increasing PEGMA content (increased water volume fraction). However, emergent behavior was observed for the co-transport of carboxylates with alcohols. For instance, we observed the permeabilities to acetate in co-diffusion are decreased with increasing PEGMA content. This behavior motivates further investigation for rationally designing ion-exchange membranes.