A Relative Hydrophobicity-Driven Framework for Liquid Water Transport in Overlapping Porous Transport Layers of Polymer Electrolyte Fuel Cells

Abstract

Conventional physics-based fuel cell models have faced limitation in explaining the through-plane liquid water distributions observed by state-of-the-art imaging techniques. To elucidate these experimental findings, we advance a temperature-dependent phase separation model (TDPSM) framework by introducing separate liquid transport equations for each porous constituent. The proposed theoretical framework incorporates relative hydrophobicity at overlapping interfaces and employs a volume-averaging scheme to reveal the physics underlying optical liquid visualization. A novel validation approach is proposed, enabling simultaneous prediction of through-plane liquid profiles and conventional polarization curves with strong agreement to experimental data. Extensive numerical simulations comparing water transport scenarios with and without a microporous layer (MPL) integrate previously fragmented experimental findings on the MPL's dual role. The study also presents water management strategies for two operating regimes: (i) low-temperature high-humidity (LTHH), where liquid flooding dominates, and (ii) high-temperature low-humidity (HTLH), where membrane dehydration presents an emerging industrial challenge. Under LTHH conditions, a hydrophobicity order of catalyst layer (CL) > MPL > gas diffusion layer (GDL) establishes an interfacial liquid pump that enables effective liquid removal. In contrast, under HTLH operation, a more hydrophobic MPL relative to the CL (MPL > CL) forms an interfacial barrier that sustains reliable membrane water retention. Overall, this theoretical framework redefines water management as a synergistic outcome of relative hydrophobic characteristics between adjacent porous layers, rather than as properties of isolated components.