Multi-Scale Computational Fluid Dynamics Simulation of Alkaline Water Electrolyzers: A Numerical Investigation

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The utilization of water electrolyzers for hydrogen production represents one of the promising technologies in the global transition away from fossil fuels towards sustainable energy sources. Among the various types of electrolyzers, alkaline electrolyzers in the zero-gap configuration with different separator types, like diaphragms and anion conducting membranes, have garnered significant attention, among others, due to their potential to utilize non-precious metal catalysts such as iron and nickel for the electrodes. This characteristic holds promise for reducing costs and increasing accessibility to hydrogen production technologies, including the establishment of largescale stationary systems and hydrogen production powered by renewable energy.In order to accelerate the development process and to understand the important mechanisms in more detail within these cell types, numerical Computational Fluid Dynamics (CFD) simulations are conducted and combined with experimental cell testing at the Juelich Research Center. The studies focus on investigating the influence of variations in the porous transport anode-electrode, particularly nickel fiber fleece and nickel foam, along with their characteristic properties on the performance of the anion exchange membrane water electrolysis cells. This includes investigating porosity gradients, optional additional catalyst layers and their loadings, and the effects of changing types and thicknesses of porous transport electrodes. These studies are conducted at varying electrolyte concentrations and operating conditions.Using the open-source platform OpenFOAM® and the developed libraries of OpenFuelCell21, CFD simulations are performed at both the micro and meso scales to examine the aforementioned questions (see Fig. 1).The model incorporates all key transport phenomena, such as two-phase fluid flow, described via an Eulerian-Eulerian approach, heat and mass transfer, electrochemical reactions, species transfer, and charge transfer across the various functional layers of the cell. It allows for the analysis of electrochemical reactions by employing the Butler-Volmer equation to describe electrokinetics across various types of electrochemically active porous electrodes.For the multi-physical simulation of the detailed flow within the porous electrodes at micro scale, microtomography images are used as geometrical input. In addition, the microscopic data are subsequently utilized for characterizing the porous electrodes in the macro-homogeneous simulations performed at the meso-scale.Literature: Zhang, S. Hess, H. Marschall, U. Reimer, S. Beale, W. Lehnert, openFuelCell2: A new computational tool for fuel cells electrolyzers, and other electrochemical devices and processes, Comput. Phys. Commun. 298 (2024) 109092. Figures:Figure 1: Numerical simulation of the flow through different micro-porous electrodes (left) which results are used for the macro-homogeneous simulations of alkaline electrolysis cell in 2-D and 3-D (right). Figure 1