(2lb) Influence of Neutral Comonomer Side Chain Length on Transport and Co-Transport of Carboxylates and Alcohols in PEGDA-Based Membranes

CO₂ emission being a leading cause of rapid climate change, has been a global concern for researchers. CO₂ reduction cells are one of the innovative CO₂ utilization techniques to cope with this issue. A typical CO₂ reduction cell consists of two reaction cells separated by an ion-exchange membrane (IEM). One role of the IEM is to prevent the transport of various CO₂ reduction products (formate, acetate, methanol, and ethanol), such that it is necessary to design membranes to mitigate the transport of these products. Previously, we observed a significant crossover of carboxylates in co-diffusion with alcohol in cation exchange membranes (CEM), where we conjectured the carboxylate transport was increased due to charge screening by the co-diffusing alcohol. To suppress this behavior we introduced uncharged comonomers, acrylic acid (AA, n=0, where n is the number of PEG units), hydroxyethyl methacrylate (HEMA, n=1), and poly(ethylene glycol) methacrylate (PEGMA, n=5), where we observed the crossover of carboxylates was significantly suppressed in PEGMA-containing films in co-transport. To further understand this effect of long, charge-neutral comonomers on co-diffusion, 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 and calculate the diffusivities using the solution-diffusion relationship. In one-component permeation, we observed permeabilities to all solutes is increased with increasing PEGMA content (increased water volume fraction). However, emergent behavior was observed for co-transport of carboxylates with alcohols. For instance, permeabilities to both acetate (with methanol or ethanol) and methanol (with acetate or formate) are decreased with increasing PEGMA content. This type of behavior motivates further investigation of multicomponent transport effects.