Multicomponent transport of alcohols in Nafion 117 measured by in situ ATR FTIR spectroscopy

Proton exchange membranes are vital components for many applications including energy applications such as fuel cells and electrolyzers. Artificial photosynthesis devices are one type of fuel cell which converts CO2 into useful high-value products via catalytic reduction. In this, and other, applications the transport behavior of small molecules and ions through the polymeric membrane is critical. In this work, the transport behavior of the commercial cation exchange membrane Nafion® 117 is examined to four CO2 reduction products (methanol, ethanol, n-propanol, and acetone) and their complex mixtures. Here, we use in situ attenuated total reflectance Fourier-transform infrared (ATR FTIR) spectroscopy to characterize the co-transport behavior of complex solute mixtures without the need for aliquotic sampling and ex situ analysis. Methanol (MeOH), ethanol (EtOH), n-propanol (PrOH), and acetone (Ace) permeabilities are determined via a custom-built diffusion cell in single, double, triple and quadruple component aqueous permeability experiments. Overall, differences in solute transport behavior are observed across these complex mixtures. Importantly, the relative permeability (permselectivity) of Nafion® to solute pairs was found to vary by up to 60% when comparing the multicomponent selectivity to the single component selectivity for solute pairs. Changes in solute permeabilities are discussed in the context of measured solute solubilities and calculated solute diffusivities in Nafion® 117. The observed large changes in permeability and, consequently, permselectivity for multicomponent mixtures highlights the importance of directly investigating transport behavior for complex systems. [Display omitted] •In-situ spectroscopy determines Nafion 117 alcohol and alcohol mixture permeability.•Nafion 117 permselectivity vary from single solute to solute mixtures by up to 60%.•Solubility and diffusivity for each solute and binary solute mixtures determined.•Solubility and diffusivity changes cause permeability changes for solute mixtures.•Largest permselectivity changes driven by changes in diffusivity selectivity.