Local Gas-Phase Current Contributions Influenced By Porous Media Properties and Geometric Features in PEM Electrolysis

Abstract

To expand the commercialization of polymer electrolyte membrane water electrolysis (PEMWE) devices, it is beneficial to understand how cell geometry and porous media properties can impact cell performance. Due to the use of precious materials in PEMWE, particularly with an acidic membrane, it is cost-effective to simulate cell performance using a number of proposed designs to limit the number of prototypes. The use of three-dimensional (3-D) computational fluid dynamics (CFD) to simulate PEMWE 1 and alkaline 2 electrolysis operation has been previously demonstrated. This analysis sheds additional light on evaporation and the important role that it plays in facilitating the anodic and cathodic reactions.Evaporation rates in porous media vary immensely with changes in water content, which has been demonstrated experimentally. Zenyuk et al. 3 used computed tomography to quantify the liquid saturation and gas/liquid interfacial area inside a carbon gas diffusion layer. They linked these variables to evaporation rate using the injection feed pressure to adjust the liquid saturation. The authors determined that evaporation rates in fuel cells increase dramatically with a decrease in water content. Evaporation rate depends on the specific interfacial area (SIA). Measurements in porous media, namely sands and soils, have shown an increase in SIA with a decrease in liquid saturation. One may notice from Ouni et al. 4 that the SIA is indirectly proportional to liquid saturation when the maximum SIA is small and somewhat inversely proportional when the SIA is large. The nature of these relationships is considered in the present CFD model for evaporation in the porous transport layer (PTL) and catalyst layer.This study explores the effects of manifold geometry, flow field geometry, and properties such as PTL porosity, permeability, interfacial area, and anisotropy on local current density. Special emphasis is given to the contribution of the gas phase to the overall current and the conditions under which the gas-phase reaction is favorable. Changes in operating conditions, such as the feed temperature, feed rate, and cell potential, and how they impact local void fraction, relative humidity, and temperature at the anode are also investigated. The sensitivity of overall performance to material properties was found to be dependent on these operating conditions, primarily the anode inlet feed rate.References J. Lopata, Z. Kang, J. Young, G. Bender, J. W. Weidner, H-S. Cho, and S. Shimpalee, J. Electrochem. Soc., 168, 054518 (2021).J. S. Lopata, S-G. Kang, H-S. Cho, C-H. Kim, J. W. Weidner, S. Shimpalee, Electrochim. Acta, 390, 138802 (2021).I. V. Zenyuk, A. Lamibrac, J. Eller, D. Y. Parkinson, F. Marone, F. N. Büchi, and A. Weber, J. Phys. Chem. C, 120, 28701-28711 (2016).A. E. Ouni, B. Guo, H. Zhong, M. L. Brusseau, Chemosphere, 263, 128193 (2021). Figure 1