Two-dimensional multi-physics modeling of porous transport layer in polymer electrolyte membrane electrolyzer for water splitting

Polymer electrolyte membrane (PEM) electrolyzers have received increasing attention for renewable hydrogen production through water splitting. In present work, a two-dimensional (2-D) multi-physics model is established for PEM electrolyzer to describe the two-phase flow, electron/proton transfer, mass transport, and water electrolysis kinetics with focus on the porous transport layer (PTL) and the channel-land structure. After comparing four sets of experimental data, the model is employed to investigate PTL thickness impact on liquid water saturation and local current density. It is found that the PTL under the land may have much lower liquid saturation than that under the channel due to land blockage. The PTL thickness may significantly impact liquid water access to the catalyst layer (CL) under the land. Specifically, the 100 mu m thick PTL shows less than 1% liquid saturation at the CL-PTL interface under 4-5 A/cm(2), leading to water starvation and electrolyzer voltage increase. As the operating current density decreases under 2-3.5 A/cm(2), the liquid saturation recovers and increases to about 10-20%. In thicker PTLs, the liquid saturation is higher under the land reaching 30-40% at the CL-PTL interface under 5 A/cm(2) for 200 and 500 mu m thick PTLs. For the 100 mu m thick PTL, the local current density drops to below 0.5 A/cm(2) under the land with 5 A/cm(2) average current density. For the 200 and 500 mu m thick PTLs, the local current is almost uniform in the in-plane direction. The numerical model is extremely valuable to investigate PTL properties and dimensions to optimize channel-land design and configuration for high performing electrolyzers. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.