No abstract

Understanding multi‐component transport behavior through hydrated dense membranes is of interest for numerous applications. For the particular case of photoelectrochemical CO2 reduction cells (PEC‐CRC), it is important to understand the multi‐component transport behavior of CO2 electrochemical reduction products including mobile carboxylates (formate and acetate) and alcohols (methanol and ethanol) in the ion exchange membranes as one role of the membrane in these devices is to minimize the permeation of these CO2 reduction products to the anolyte as they often oxidize back to CO2. Cation exchange membranes (CEM) are promising candidates for such devices as they act to minimize the permeation of mobile anions, such as carboxylates. However, the design of new CEMs is necessary as the permeation of carboxylates often increases in co‐permeation with alcohols. Here, we investigate the transport behavior of carboxylates and alcohols in two types of CEMs (1) a crosslinked CEM was prepared by free‐radical copolymerization of a sulfonated monomer (AMPS) with a crosslinker (PEGDA), and (2) Nafion® 117. We observe an increase in both PEGDA‐AMPS and Nafion® 117 diffusivities to carboxylates in co‐diffusion with alcohols. We attribute this behavior to charge screening by co‐diffusing alcohol that reduces the electrostatic repulsion between bound sulfonates and mobile carboxylates.

Understanding multi-component transport behavior through hydrated dense membranes is of interest for numerous applications. For the particular case of photoelectrochemical CO2 reduction cells, it is important to understand the multi-component transport behavior of CO2 electrochemical reduction products including mobile formate, acetate and ethanol in the ion exchange membranes as one role of the membrane in these devices is to minimize the permeation of these products. Anion exchange membranes (AEM) have been employed in these and other electrochemical devices as they act to facilitate the transport of common electrolytes (i.e., bicarbonates). However, as they act to facilitate the transport of carboxylates as well, thereby reducing the overall performance, the design of new AEMs is necessary to improve device performance through the selective transport of the desired ion(s) or electrolyte(s). Here, we investigate the transport behavior of formate and acetate and their co-transport with ethanol in two types of AEMs: (1) a crosslinked AEM prepared by free-radical copolymerization of a monomer with a quaternary ammonium (QA) group and a crosslinker, and (2) Selemion® AMVN. We observe a decrease in diffusivities to carboxylates in co-diffusion. We attribute this behavior to charge screening by the co-diffusing alcohol, which reduces the electrostatic attraction between QAs and carboxylates.

No abstract

The properties of polymer materials are largely a result of the local and long-range order of polymer chains and systems of polymer chains. The ability to tune polymer chain architecture at the monomer and chain levels through controlled synthesis is therefore a powerful tool for manipulating its properties. Perhaps, the most widely used synthetic means to manipulate polymer properties is copolymerization, where more than one monomer is simultaneously polymerized. For living anionic copolymerization, the statistics of comonomer incorporation have long been known to be dependent on the solvent, temperature, and initiator. Here, we leverage solvent dependence in the anionic copolymerization of styrene and isoprene to tailor the compositional profile along the polymer chain. Copolymerization of styrene and isoprene is conducted with varied quantities of a polar modifier (triethylamine), and the conversion is monitored by in situ attenuated total reflectance Fourier transform infrared spectroscopy. Monomer conversion profiles are used to extract reactivity ratios as a metric for examining the change in the compositional drift as the solvent composition is varied. Increasing triethylamine content leads to a continuous flattening of the compositional profile from the extreme nearly pure diblock structure for synthesis in cyclohexane to an essentially flat compositional profile in 50/50 (vol./vol.) cyclohexane/triethylamine. The ability to continuously tune compositional drift, as shown here, between these two extremes is a powerful synthetic tool for preparing copolymers and block copolymers with tunable properties.