(351d) Comonomer Effects on Co-Permeation of Methanol and Acetate in Cation Exchange Membranes

Co-permeation in a hydrated dense membrane is crucial in many applications from energy conversion (i.e. photoelectrochemical CO₂ reduction cells) to liquid separation (i.e. pervaporation cells). One of the major challenges of CO₂ reduction cells is to design an ion exchange membrane that minimize the permeation of CO₂ reduction products (i.e. methanol and acetate). Previously, the transport behavior of Nafion® 117 and crosslinked PEGDA-AMPS cation exchange membranes to methanol and sodium acetate was investigated and distinct changes in permeabilities of membranes to sodium acetate was observed in co-permeation with methanol. To further investigate this co-permeation behavior, we modified PEGDA-AMPS structure by varying negatively-charged AMPS content with three different charge-neutral comonomers, acrylic acid (AA, n = 0), 2-hydroxylethyl methacrylate (HEMA, n = 1), and poly(ethylene glycol) methacrylate (PEGMA, n = 5). While the permeability to sodium acetate in co-permeation with methanol was increased for membranes with shorter comonomers, PEGDA-AA-AMPS and PEGDA-HEMA-AMPS, it was consistent for PEGDA-PEGMA-AMPS membranes. From these experiments, we deduce that charge-neutral molecules, both moving (e.g. methanol) and membrane-bound (e.g. ethylene glycol), can interfere with the electrostatic repulsion during ionic transport in ion exchange membranes and this shielding of electrostatic repulsion leads to variance in transport behavior.