A Numerical Approach to Optimize Catalyst Layer Structure of Polymer Electrolyte Fuel Cells Using Non-Isothermal Three-Dimensional Simulation
Authors: Alizadeh Mehrzad , Suzuki Takahiro , Tsushima Shohji 
Published: November 2022

The world is struggling with a rapid increase in energy demand and the exacerbating problems of greenhouse gases (GHG) caused by the widespread exploitation of fossil fuels. These issues, however, have brought the attention of academics, investors, and governments throughout the world to hydrogen as a viable alternative during the transition from fossil resources to renewable energies. Hydrogen could be used to generate electricity using an electrochemical energy conversion device called polymer electrolyte membrane fuel cell (PEMFC), which converts the chemical energy stored in bonds of the fuel (hydrogen) directly to electric power. Although PEMFC technology has advanced significantly over the last decade, complete commercialization of this technology will still need more cost-cutting and performance enhancement [1]. From electrochemical and economic standpoints, the porous electrode is the most crucial of PEMFC components. Electrodes are porous media made up of different constituents that serve as the heart of PEMFC, facilitating different coupled transport phenomena such as heat, mass, and electric charge transfer. As a result, an optimized design of this component might significantly elevate performance and efficiency.
In recent years, designing architectured electrodes with the goal of improving overall energy conversion efficiency has started [2, 3]. However, full leverage of such state-of-the-art procedures for designing engineered electrodes strongly depends on the employment of novel design tools. Among various advanced design alternatives, the attention of researchers in different disciplines of engineering has recently been drawn to topology optimization methods [4]. While topology optimization was originally applied to structural mechanics, it has since been expanded to more complicated systems with multiple physics, including heat and fluid. However, with only a few exceptions [5, 6], most topology optimization applications to electrochemical devices are limited to enhancing flow fields to boost reaction dispersion and diminish pressure drop. Moreover, previous research studies like [5] mainly used simplified two-dimensional isothermal models, which are far from reality. Therefore, these studies are incapable of providing a comprehensive insight into optimal spatial distribution of catalyst, electrolyte, and voids in a porous electrocatalyst layer.
In the present study, a three-dimensional, non-isothermal, multi-phase model is developed to simulate the performance of PEMFC. The presented model is then used to determine the optimal spatial distribution of the porous electrocatalyst layer constituents, including catalyst, electrolyte, and voids. While increasing the catalyst content in the PEMFC electrode could improve cell performance, its excessive use leads to a substantial increment of cost and oxygen transport resistance. This mass transport resistance problem is especially critical at high current density regions with a higher risk of flooding. Hence, in the present study, the optimization process is formulated as a constrained problem so as to obtain maximum output voltage under a constant total catalyst loading. The results show that in an optimal design, the volume fraction of catalyst and electrolyte should be higher in the region under the channel where there is a higher potential for current density production. At the same time, it is desired to increase the porosity in the region under the rib where oxygen delivery involves more resistance.

Acknowledgment

This work was supported by JSPS KAKENHI Grant Number 21H04540.

References

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