Influence of Solvent on the Ionomer Morphological Evolution at IrO ₂ /TiO ₂ Electrocatalytic Surface in Proton Exchange Membrane Water Electrolyzers

Precious metal catalysts constitute a significant portion of the costs associated with proton exchange membrane water electrolyzers (PEMWEs). However, the utilization efficiency of these catalysts remains relatively low within the conventional catalyst layer. Thus, optimizing the microstructure of the catalyst layer is crucial for the commercialization of PEMWEs. This work explores the influence of solvent properties on the ionomer morphology evolution, aiming to elucidate the formation mechanism of the anode catalyst layer (ACL) structure in PEMWE. It demonstrates that ACL prepared by an isopropyl alcohol-water (IPA-aq) solvent mixture forms a cross-linked ionomer network, primarily due to the low dielectric constant (ε) of the solvent. Molecular dynamics (MD) simulations reveal that ionomer chains adopt extended conformations in a low ε environment with weak catalyst surface adsorption, which contributes to the ionomer network formation. Additionally, the drying process induces further ionomer extension in the low ε solvent, strengthening the cross-linked ionomer network. Electrochemical characterization shows that ACLs processed with IPA-aq achieve superior performance (1.655 V at 1 A/cm²) with suppressed mass transfer decay (Δη_mt = 0.096 V). These insights provide crucial guidance for controlling ionomer morphology on IrO₂/TiO₂ catalyst surfaces and can effectively increase the utilization efficiency.