Structure–Water–Transport Coupling in Anion-Conducting Polyelectrolytes and Hydrogen Crossover in PEMWE

Ion transport in hydrated polymers is governed by how water uptake couples to charge pathways under mechanical constraints. This dissertation develops a unified, multiscale picture of that coupling in hydrocarbon polynorbornene (PNB)–based anion-conducting polyelectrolytes, integrating in-situ thin-film experiments with modeling and molecular simulation, and connecting the insights to membrane-relevant contexts. Chapter 1 motivates fluorine-free, hydrocarbon ionomers, frames open questions about water–conductivity relationships in polyelectrolyte thin films and membranes, and outlines design levers spanning ion-exchange capacity (IEC) and molecular architecture. Chapter 2 details an in-situ platform synchronizing humidity-programmed ellipsometry and quartz-crystal microbalance with interdigitated-electrode impedance (EIS), plus modeling: a Coupled Layers Model (CLM) linking lattice-gas water sorption to a random-resistor ion network, and molecular dynamics to resolve architecture–transport connections. In Chapter 3 (vinyl-addition PNB thin films), experiments and CLM reveal an IEC-independent master relation between ionic conductivity and water content. Water absorbed beyond the first hydration shell sets an effective IEC (the hydrated, current-carrying fraction of charges), which controls the joint percolation of the water hydrogen-bond and charge networks—explaining the collapse of conductivity vs. water uptake (or volume fraction) but not vs. hydration number λ. Chapter 4 (ROMP-PNB thin films with C2/C4/C6 side-chain spacers) shows that longer spacers enhance domain definition and water structuring (boosting ion mobility) while diluting local charge density—yielding non-monotonic trade-offs in swelling, hydration, and conductivity. Experiments and MD rationalize how side-chain architecture governs mesoscale morphology and transport. Chapter 5 quantifies hydrogen crossover in proton-exchange-membrane water electrolyzers (PEMWEs) and evaluates recombination layers (Pt, PtO₂, Au) and placement, clarifying durability and proximity trade-offs relative to the anode. Together, these studies provide mechanistic and design principles linking molecular architecture, water uptake, percolation, and ionic transport in anion-conducting polyelectrolytes, and establish an in-situ measurement framework that enables future, systematic extensions toward membrane-level studies.