Investigation of the effects of the catalyst structure parameter of an agglomerate model on the performance of a PEM water electrolyzer

In this work, a three-dimensional multiphase steady-state model coupled with a catalyst layer agglomerate model is developed. The numerical model was validated with experimental data. Based on the validated model, five key catalyst layer microstructural parameters: catalyst loading, agglomerate radius, Ir/C ratio, ionomer-to-carrier (I/C) ratio, porosity, and structural parameters of porous transport layers, are systematically evaluated. The results reveal that catalyst loading significantly influences performance, particularly at high current densities. Catalyst loading improves performance but exhibits clear diminishing returns. Beyond 1.5 mg cm−2, diminishing returns are observed due to competing effects: while higher loadings enhance electrochemically active surface area, they simultaneously increase mass transport resistance. Lower loadings result in non-uniform potential distribution, elevate ohmic resistance, and present challenges for thermal management. Agglomerate radius emerges as a critical microstructural parameter, with a smaller radius (0.25 μm versus 0.85 μm) achieving approximately 0.2 V overpotential reduction at high current densities by promoting uniform triple-phase boundary distribution and shortening proton transport pathways. The Ir/C ratio (0.5–0.7) and I/C ratio (0.5–0.7) demonstrate synergistic effects on balancing catalytic activity, electronic conductivity, and proton conduction. PTL analysis shows that a small contact angle, high porosity, and high permeability provide the best gas-liquid transport, with permeability emerging as the dominant determinant of two-phase mass-transfer efficiency.