Effects of oxygen bubble formation in the porous transport layer on the performance of polymer-electrolyte-membrane water electrolyzer

The influence of porous-transport-layer (PTL) microstructures on the performance of polymer-electrolyte-membrane-water-electrolyzers (PEMWEs) is investigated. Oxygen bubble dynamics in powder-type PTLs (P-PTLs) and fiber-type PTLs (F-PTLs) with varying porosities and pore diameters are simulated using a lattice Boltzmann method, where oxygen-water interactions and capillary effects are resolved at the pore scale. To quantify the impact of microscale dynamics on device-level performance, a separate PEMWE model is constructed based on the Navier–Stokes equations, where contact resistance at the PTL-catalyst interface is incorporated. The PEMWE model is validated against experimental polarization curves, while pore-scale bubble behavior is verified using droplet and bubble tests. In P-PTLs, oxygen saturation near the catalyst layer is reduced, and water transport is enhanced as porosity increases. Larger powder diameters promote the formation of consolidated oxygen pathways, which further facilitate water supply. However, these structural advantages are accompanied by increased contact resistance due to a decrease in interfacial contact area. In contrast, F-PTLs are characterized by secondary fingering and excessive oxygen accumulation, limiting water supply, and resulting in higher contact resistance at the same porosity. A clear trade-off between mass transport and interfacial resistance is identified, and P-PTLs are shown to provide superior overall PEMWE performance compared to F-PTLs.