Steady-State Water Drainage by Oxygen in Anodic Porous Transport Layer of Electrolyzers: A 2D Pore Network Study

Abstract

Recently, pore network modelling has been attracting attention in the investigation of electrolysis. This study focuses on a 2D pore network model with the purpose to study the drainage of water by oxygen in anodic porous transport layers (PTL). The oxygen gas produced at the anode catalyst layer by the oxidation of water flows counter currently to the educt through the PTL. When it invades the water-filled pores of the PTL, the liquid is drained from the porous medium. For the pore network model presented here, we assume that this process occurs in distinct steps and applies classical rules of invasion percolation with quasi-static drainage. As the invasion occurs in the capillary-dominated regime, it is dictated by the pore structure and the pore size distribution. Viscous and liquid film flows are neglected and gravity forces are disregarded. The curvature of the two-phase interface within the pores, which essentially dictates the invasion process, is computed from the Young Laplace equation. We show and discuss results from Monte Carlo pore network simulations and compare them qualitatively to microfluidic experiments from literature. The invasion patterns of different types of PTLs, i.e., felt, foam, sintered, are compared with pore network simulations. In addition to this, we study the impact of pore size distribution on the phase patterns of oxygen and water inside the pore network. Based on these results, it can be recommended that pore network modeling is a valuable tool to study the correlation between kinetic losses of water electrolysis processes and current density.

Computational Optimization of Porous Structures for Electrochemical Processes

“…The pore network model used in this study was developed in [45] and validated by comparison with reference experiments from the literature in [38]. The model is comprised of two tools: (i) the structure computation tool and (ii) the invasion simulation tool.…”

“…At first, the structure is described extensively to give a detailed overview of the studied gradients. The invasion part is shortly summarized below-more details are given in [38,45].…”

“…The pore network simulation is based on the drainage invasion algorithm with liquid clustering presented in [38,45]. The pores and throats are initially completely filled with liquid water.…”

“…As a first step, we use idealized 2D and 3D regular lattices, firstly to draw an overall picture of the impact of the pore structure on the distribution of wetting and non-wetting phases during a drainage invasion process, and secondly to develop a generic upscaling strategy using the transport coefficients and morphological data from the pore network model in a macroscopic continuum model. While we have demonstrated the relevance of pore size distribution in a recent paper related to water electrolysis [38], here the focus is on the defined gradients of the pore structure. The background for this investigation involves two factors.…”

Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer

“…These porosities are needed to allow efficient mass transport of reactants and products without diffusion limitations. 59 Therefore, the highly porous structure of the NiMPL-PTL with a wide range of microsizes can facilitate the mass-transfer rate, which increases the overall AEMWE cell performance.…”