Porous electrodes form a critical part of electrochemical energy systems such as polymer electrolyte fuel cells (PEFCs). In order to improve their performance and reduce cost, novel designs for porous electrodes are being envisioned, e.g., non-PGM catalyst layers, ultra-thin Pt/Pt-Ni based catalyst layers, or NSTF catalyst layers.¹ These electrodes have features spanning multiple length scales: from nano-scale catalyst particles to micrometer thick catalyst layers; with meso-scale porous structure in between. In order to understand the impact of these new designs on cell performance, a detailed understanding of the multi-scale structure is required. Furthermore, the physical processes at each length scale must be understood and up-scaled in order to evaluate the macro-scale cell performance.

The aim of this work is to develop multi-scale models which can account for the effect of micro and meso scale structure on macro-scale performance. Figure 1 shows a schematic of the multi-scale approach for modeling PEM fuel cells. This approach can be used for conventional Pt based electrodes, or for non-PGM based electrodes where large catalyst particles induce significant local flooding and reactant losses. The microstructure is generated using stochastic techniques.^2,3 The crucial micro-structural properties such as pore sizes, ECSA, phase distributions are obtained using physical characterization methods such as imaging, Cyclic voltammetry, and BET. The generated microstructures will be used to simulate pore-level physics, where local transport, and reactions will be modeled. The pore scale performance will then be upscaled and used with macro-scale models to simulate system level performance.

To analyze critical parameters for fuel cell performance, sensitivity studies will be performed using the macro-scale model. The aim is to identify parameters which affect the cell performance significantly and therefore must be measured accurately and provide a way to optimize cell performance. Apart from macro-scale parameters, the multi-scale sensitivity study can also be used to optimize ionomer and catalyst distribution.

Acknowledgements

The work is funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231.

References

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3. L. M. Pant, S. K. Mitra and M. Secanell, Phys. Rev. E, 92, 063303 (2015).