Modeling Impact of Ce on Fuel-Cell Performance and Durability

Abstract

Throughout the lifetime of a polymer-electrolyte fuel cell, the membrane undergoes chemical degradation that causes defects to form and grow, contributes to a loss of performance, and can lead to cell failure. A combination of accelerated stress tests (ASTs) 1-2 and modeling studies 3-4 have been performed on this topic to better understand membrane degradation mechanisms and how to mitigate them 5-6 . During fuel-cell operation, formed peroxide radicals due to reactant gas crossover attack the polymer backbone and end chains, leading to membrane thinning and formation and growth of defects such as cracks and pinholes. This study builds upon our previous modeling study on membrane degradation to analyze the addition of chemical scavengers into the fuel-cell membrane to mitigate the effects of chemical degradation via radical attack. The developed model is transient and 1D across the fuel-cell sandwich. The transport and concentration of cerium is modeled using an ion-transport model based on concentration solution theory, thereby allowing the evaluation of how water gradients also move cerium ions throughout the ionomer, resulting in nonintuitive distributions. The model results also show how drive-cycle testing impacts the performance of the cell and the location of cerium, where relaxation of the applied gradients help redistribute the cerium in the ionomer. The purpose of the study is to optimize the cerium amount in both the membrane and catalyst layers by balancing effects of mitigation of chemical degradation and performance due to the impact of cerium on the ionomer material properties. For the latter, a key feature is accounting for the nonlinearities induced by the impacts of cerium on membrane and catalyst-layer ionomer properties. Acknowledgements The authors would like to thank Hans Johansen for helpful discussions and Los Alamos National Laboratory for providing material property data. Funding support was supplied by 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 R. Borup, et al., Chem. Rev. , 107 , 3904 (2007) F. A. de Bruijn, et al., Fuel Cells , 8 , 3 (2008). R. Singh, et al., J. Electrochem. Soc. , 165 , F3328 (2018) K. H. Wong and E. Kjeang, J. Electrochem. Soc. , 166 , F128 (2019). M. Zatón, et al., Sustainable Energy & Fuels , 1 , 409 (2017). F. D. Coms, et al., in The Chemistry of Membranes Used in Fuel Cells: Degradation and Stabilization , 1st ed., S. Schlick Editor, John Wiley & Sons, Inc. (2018).

Key findings

• ▸The addition of chemical scavengers to the fuel-cell membrane can mitigate the effects of chemical degradation via radical attack.
• ▸Cerium ions are transported throughout the fuel-cell sandwich via water gradients, affecting membrane performance and durability.
• ▸The developed model is transient and 1D, allowing for the evaluation of cerium ion transport and concentration.

Keywords

Identifiers

DOI

10.1149/ma2019-02/34/1524

Journal

ECS Meeting Abstracts

Year

2019