Balancing Reactant Transport and PTL-CL Contact in PEM Electrolyzers by Optimizing PTL Design Parameters via Stochastic Pore Network Modeling

Abstract

Optimizing the porous transport layer (PTL) structure is crucial for high current density operation of polymer electrolyte membrane (PEM) electrolyzers. Previous studies from the literature demonstrated that PTL structures, mainly porosity and titanium powder diameter, can be strategically chosen to improve the performance (1-3). However, transport mechanisms in the PTL can be further explained from the perspective of mass transport. In this work, we employed modelling approaches to investigate the effect of porosity and titanium particle size of the sintered titanium powder based PTL on mass transport. PTLs were numerically generated using a stochastic model (Figure 1) with three titanium powder diameters, 25 µm, 50 µm, and 75 µm, and three porosities, 26.5%, 40.5%, and 63.5%. Pore network modelling was used to calculate the gas saturation and the permeability of liquid water in the presence of oxygen gas. We observed that all simulated PTLs exhibited similar gas saturation profiles and relative permeabilities, yet the PTLs with higher porosities had significantly higher liquid water permeabilities. For a constant powder diameter of 25 μm, increasing the porosity from 26.5% to 63.5% led to an increase in the average surface roughness from 8.9 μm to 38.6 μm. For a constant porosity of 26.5%, increasing the powder size from 25 μm to 75 μm resulted in an increase in the average surface roughness from 8.9 μm to 18.3 μm. Larger open pore spaces were acquired for PTLs with higher surface roughness, resulting in higher liquid water permeabilities (two-phase permeability). Therefore, PTLs with higher porosities and larger particle sizes provide superior liquid water permeation and gas removal. Figure 1. The 3D reconstruction of the PTL generated with titanium powder diameter of (a) 25 µm, (b) 50 µm, and (c) 75 µm at overall porosity of 40.5%. References S. A. Grigoriev, P. Millet, S. A. Volobuev and V. N. Fateev, Int J Hydrogen Energy, 34, 11, p. 4968-4973 (2009). J. O. Majasan, F. Iacoviello, P. R. Shearing and D. J. Brett, Energy Procedia, 151 (2018). L. Zielke, A. Fallisch, N. Paust, R. Zengerle and S. Thiele, Royal Society of Chemistry Advances, 4, p. 58888-58894 (2014). Figure 1