Numerical Modeling of Water Transport in a Microporous Layer-Coated Porous Transport Layer for a Polymer Electrolyte Membrane Water Electrolyzer with an Interdigitated Flow Field for Internal Gas-Liquid Separation
Authors: Nakajima Hironori , Bolay Linda , Ekström Henrik , Shima Asuka , Lindbergh Göran , Sone Yoshitsugu 
Published: December 2024

We have developed a novel interdigitated flow field for polymer electrolyte membrane electrolyzers (proton exchange membrane water electrolysis cells) for ground and space applications1),2), which are supposed to work in a hybrid system with a low temperature Sabatier reactor for effective use of heat3),4). This design separates the oxygen and liquid water inside the anode of the cell. It dispenses with water circulators and external separators that use natural or centrifugal buoyancy. To date, we have developed a numerical model for optimizing cell structures. Finite element modeling (COMSOL Multiphysics) of water transport is three-dimensionally conducted for the anode porous transport layer coated with a hydrophobic microporous layer (MPL) (SIGRACET 29BC, SGL Carbon Inc.) assembled with the interdigitated flow field. The MPL can separate the evolved oxygen gas and pressurized liquid water owing to capillary pressure5). The electrochemical kinetic parameters for the model are determined using electrochemical impedance spectra. We model the current densities and the current ratio between the reactant liquid water and water vapor at the interface between the MPL and catalyst layer (CL)6). The model involves the fractional bubble coverage of the produced oxygen gas at the CL, as well as liquid water saturation and liquid water permeability in the MPL7). The vapor evaporating from the liquid water in the MPL is assumed to be mixed with the evolved oxygen for diffusive water transport. The volumetric evaporation rate was estimated from experimental data8).

Acknowledgement

This study is based on results obtained from a project, JPNP21014, commissioned by the New Energy and Industrial Technology Development (NEDO).
References
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