Membrane Modulus as the Governing Factor in the Mechanism of Catalyst Layer Transfer for Membrane Electrode Assemblies

Hydrocarbon-based proton-conducting membranes are promising alternatives to perfluorinated sulfonic acid (PFSA) membranes for hydrogen-related electrochemical devices. However, inefficient catalyst layer (CL) transfer onto the hydrocarbon membranes through decal transfer remains a critical barrier to membrane electrode assemblies (MEAs) integration. In general, the poor CL transfer efficiency is typically attributed to chemical incompatibility between the hydrocarbon membranes and PFSA-based catalyst binder. Here, we demonstrate, experimentally and theoretically, that the mechanical modulus of the membrane is the primary determinant of transfer efficiency, outweighing chemical affinity. By systematically varying the ion exchange capacity (IEC, 1.6-2.6 mequiv/g) of sulfonated poly(p-phenylene)-based membranes and controlling humidity (0-100% relative humidity), we show that transfer efficiency scales with modulus, but not clearly with interfacial tension, representing chemical affinity. Humidity-induced softening drives >200% variation in transfer efficiency (η) when the modulus decreases from ∼5.0 to ∼1.0 GPa with a strong power-law decay, η ∼ E-3.3. Fracture-mechanics modeling, combining Griffith energy release rates with Kendall's peeling framework, shows that efficiency transitions are governed by the ratio of strain energy release rates at the polyimide film (PI)-CL and membrane (M)-CL interfaces (GPI-CL/GM-CL), relative to their interfacial toughness. These findings establish a mechanics-driven framework for CL transfer and provide guidance for MEA integration with stiff hydrocarbon membranes in water electrolyzers and fuel cells.