Numerical Study of the Impact of Two-Phase Flow in the Anode Catalyst Layer on the Performance of Proton Exchange Membrane Water Electrolysers

Mass transport losses in proton exchange membrane water electrolysis (PEMWE) cells have gained increased focus in recent years, however two-phase flow within the anode catalyst layer (ACL) has not been extensively studied. This work uses 2-D, finite element simulations with a capillary pressure based model to study two-phase flow in the ACL. The porous media are characterised using a pore size distribution (PSD), allowing for the impact of structural changes to be analysed. The results show the reaction distribution heavily influences gas accumulation within the ACL: bubbles produced close to the membrane induce high gas pressures in the ACL, while bubbles produced close to the porous transport layer (PTL) allow for an easy escape to the PTL. Very high gas saturations are required in the ACL to have an appreciable impact on performance, which is difficult to achieve given the hydrophilic nature of the anode electrode. Therefore, it is likely that sections of the ACL need to be screened by large bubbles to induce significant losses. The PTL saturation had a minimal effect on ACL saturation, as each layer has a very different intrusion curve. As such, characterization of the ACL microstructure is crucial to understanding PEMWE mass transport limitations.