Lawrence Berkeley National Laboratory

Anion exchange membranes (AEMs) play an essential role in artificial photosynthesis devices, which photoelectrochemically convert CO2 and water into useful products. AEMs allow the transport of charge carriers between electrodes while minimizing the transport of CO2 reduction products (e.g., ethanol). Fundamental transport studies in AEMs relevant to artificial photosynthesis are uncommon. Herein, we describe the preparation of an imidazolium-functionalized poly(phenylene oxide) membrane. Membrane transport properties were controlled by systematic variation of the degree of imidazolium functionalization, which induced changes in the membrane water volume fraction. Ethanol permeability and ionic conductivity increased with the membrane water volume fraction. Consequently, the membranes with a relatively high ionic conductivity exhibited a relatively high ethanol permeability, presenting a trade-off in the transport properties desirable for artificial photosynthesis applications. This work seeks to enable the optimization of AEMs for artificial photosynthesis through the systematic study of membrane structure (water volume fraction) and its relevance to alcohol transport and electrolyte ion conductivity.