Methanol transport in Nafion investigated with a combination of theory, simulation, and experiment

Modeling the performance of selectively permeable polymer electrolyte membranes (PEMs) under realistic operating conditions is an unmet need in the renewable energy field. In particular, swelling and transport under non-steady-state conditions are rarely considered in simulation studies. This presentation will focus on methanol transport through Nafion(R) that is fully hydrated in liquid water, a situation that is applicable to membranes used in an aqueous phase solar fuels device for CO₂ reduction. Theoretical and experimental values are used to inform a parameter-free reaction-diffusion mechanistic scheme, including swelling, uptake, and desorption. The scheme is validated by simulating new experimental data for time-dependent methanol permeation and sorption in Nafion(R), measured using Fourier transform infrared (FTIR) spectroscopy, as well as literature studies using FTIR attenuated total reflectance spectroscopy. Good agreement is observed for both steady-state and non-steady-state conditions. Key phenomena controlling transport in this type of system are identified, and their implications for membrane design are discussed. This work builds towards a general framework for understanding and modeling transport through PEMs at the level of fundamental physical chemistry.