(Invited) Multiscale Modeling of Uptake and Transport in Redox-Flow-Battery Separators

Abstract

Understanding transport phenomena is a critical component of electrochemical engineering in terms of optimizing energy-conversion and -storage devices including fuel cells and flow batteries. In these systems, transport through the ion-conducting electrolytes including both polymer (e.g., perflurosulfonic-acid (PFSA) membranes) and liquid electrolyte control the overall device performance. In this talk, recent work on the multiscale modeling of ionomers will be discussed including thermodynamic and multiscale continuum treatments of multi-ion transport through the ionomer nanodomains and the relevant changes to the chemical potential resulting in selective ion and water uptake. This treatment involves a simple accounting for polymer backbone deformation, donnan equilibrium, solvation, and interactions with external electrolyte. The continuum modeling at the nanodomain uses a mean-field local-density theory that accounts for ion/ion, ion/water, and ion/polymer effects. In addition, upscaling methodologies using resistor-network approaches informed by experiment that explore phenomenon-dependent transport pathways for ions and electrolyte will be introduced and demonstrated to yield nonlinear and nonintuitive results. The overall modeling results will be compared to experimental property and uptake data and used to explain the nature of observed phenomena including electro-osmosis, ion conduction, and ion transference. Acknowledgements This work was funded under the Fuel Cell Performance and Durability Consortium (FC PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U.S. Department of Energy as well as by the ARPA-E IONICS program under contract DE-AC02-05CH11231.