Structure-Property Relationships in Crosslinked Polymer Membranes: Understanding Methanol-Carboxylate Co-Transport

Abstract

Ion exchange membranes (IEMs) are essential components in numerous devices that require selective transport. Fuel cell devices such as photoelectrochemical CO2 reduction cells (PECCRC) require membranes that suppress product transport such as methanol, formate, and acetate to operate at maximum efficiency. Developing membrane structure-physicochemical-transport property relationships to elucidate the factors influencing product (solute) transport is thereby critical for the design and fabrication of next generation membranes. To address this need, this dissertation utilizes crosslinked poly(ethylene glycol) diacrylate (PEGDA) based polymer membranes with charge-containing and neutral monomers as a tunable model polymer membrane system to investigate structure-property relationships. Both IEMs and neutral membranes were prepared to (i) investigate methanol-carboxylate individual and co-transport behavior at varied membrane composition, (ii) correlate physicochemical properties such as water uptake and fixed charge concentration with their impact on solute transport, and (iii) elucidate the factors influencing thermodynamic sorption/partition and kinetic diffusion behavior. Carboxylate co-permeabilities with methanol are found to decrease at certain membrane compositions and the presence of loosely bound intermediate water affects solute permeabilities. Additionally, ionic conductivities increase and solute permeabilities decrease for membranes with higher charge content, lower crosslinker chain length and similar water uptake. Moreover, solute permeabilities are highly dependent on kinetic diffusion compared to thermodynamic partitioning in these series of membranes. Understanding from these results help to propose and develop new membranes with improved properties towards various applications.