Two-phase flow modeling and understanding of transport limitations in the porous transport layer of a polymer electrolyte membrane electrolyzer

The current investigation examines the flow characteristics within an idealized single-pore anodic porous transport layer (PTL) of a proton exchange membrane (PEM) type electrolyzer. At the onset, the article focuses on a thorough validation study against an experimental dataset available in the literature to establish the numerical simulation method of choice for conducting the required PTL simulations. This initiative identified the coupled level set volume of fluid as the optimal numerical technique for the study. The subsequent PTL simulations explore the fluid flow characteristics within a single pore under different operating conditions like the current density, the electrode channel water flow rate, and the pore dimensions. The analysis investigates the effects of different physics on the size of the bubble that gets detached from the pore. The overarching objective is to identify the main bottleneck behind the concentration overpotential existing in PEM electrolyzers and to make effective design improvements. The detailed simulations (albeit two-dimensional) reveal an annular flow regime existing within the pore that indicates the possibility of the lack of water as the primary reason for the electrochemical inefficiency of a PEM electrolyzer. A parametric study was able to collapse all the simulation results to follow a single curve like form through an appropriate grouping of non-dimensional parameters, thereby enabling an empirical strategy to predict the detached bubble size for a host of operating conditions.