Bubble management via catalyst layer characteristics and morphology of proton exchange membrane water electrolyzers

Efficient oxygen removal from the anode side of proton exchange membrane water electrolyzers (PEMWEs) is critical for reducing transport resistance and sustaining high current density operation. In this work, a three-dimensional free-surface lattice Boltzmann model incorporating reaction boundary driven bubble generation is developed to investigate oxygen evolution, bubble growth, and transport across the catalyst layer (CL), porous transport layer (PTL), and flow channel. The effects of reaction rate, wettability, catalyst morphology, and PTL architecture on bubble dynamics are systematically examined. Results show a critical reaction-rate threshold for initiating observable bubble formation, while surface wettability strongly modulates nucleation activation and bubble expansion. Catalyst geometry exerts a decisive impact on bubble coalescence and spatial dispersion, with spherical domains promoting large cohesive bubbles and ordered structures enabling controlled nucleation and enhanced gas distribution. Comparative analysis of fiber- and sphere-based PTLs further reveals two distinct transport layer types: periodic breakthrough controlled by capillary barriers in fibrous media, and smooth multidirectional percolation in isotropic sphere networks. These insights demonstrate that coordinated design of catalyst-layer morphology and PTL microstructure can markedly enhance oxygen-removal pathways, providing a mechanistic foundation for optimizing mass-transport processes in high-performance PEM water electrolyzers. • 3D free-surface LBM with reaction boundary captures spontaneous oxygen nucleation. • Wettability governs bubble nucleation thresholds and early-stage bubble growth. • Catalyst morphology regulates bubble nucleation, coalescence and dispersion. • Ordered 3D catalyst layers lower nucleation barriers and enhance spatial dispersion. • PTL architecture controls breakthrough behavior and gas transport into flow channels.