(111g) Multi-Scale Modeling of Polymer Electrolyte Membrane Fuel Cells

            The polymer electrolyte membrane fuel cell (PEMFC) is a mult-physics, mult-scale system with phenomena that occur on various time/length scales.  The system is composed of anode and cathode gas channels (GC) through which fuel enters, gas diffusion layers (GDL) that create uniform gas distribution, catalyst layers where the electrochemical reactions take place, and the polymer electrolyte membrane (PEM) at the center of the device. Within each of these layers critical issues of momentum, mass, and heat transfer that must be addressed to make PEMFC viable for widespread commercialization.  These issues include preventing CO poisoning of the catalyst particles, utilizing the optimal size and shape of the catalyst particles, developing accurate models of fluid flow in the GC and GDL, and water management in the PEM. Due to the lack of novel methodology to integrate phenomena on each sub-system, demand on the new paradigm of multi-scale modeling becomes critical to resolve the issues. Here, we provide the multi-scale approach to the PEMFC from atomic to system design scales.

The PEM is the heart of the PEMFC system, through which protons are conducted from the anode side to the cathode side.  The complex structure of PEM composed of hydrated perfluorosulfonic acid (PFSA) ionomer enables proton diffusion while it controls fuel transfer through a membrane.  Microstructure of PEM has been investigated via classical molecular dynamics (MD), which exhibits hydrophilic phase agglomeration by sulfonate anion groups [1,2].

To profoundly understand the proton conduction mechanism and the complex microstructure in the PEM, accurate intra- and intermolecular force field parameters for the PFSA, water, and proton species are required. The atomistic scale study includes ab-initio methods to determine accurate force field parameters for the PFSA ionomer's intramolecular degrees of freedom and its interaction with water and proton. The approach of Seminaro [3] is used for the intramolecular parameterization of force field parameters. 

            As a bottom level of our multi-scale modeling approach [4], this force field development will be implemented to the molecular / mesoscale, which will be linked to middle (i.e., continuum scale) through a systematic coarse graining procedure. By utilizing the lattice Boltzmann method (LBM) we have developed [5], continuum level will be hybridized to the coarse-grained molecular scale simulation. The coarse graining procedure will allow for the establishment of a multi-scale integration framework suitable for our optimization model of the PEMFC [6], which addresses objectives such as lowering cost and raising power density and sustainability.   

1. Weber, A.Z.; Newman, J.,?Modeling Transport in Polymer-electrolyte fuel cells,? Chem. Rev., 104, 4679-4726 (2004).

2. Jinnouch, R.; Okazakiz K., ?Molecular Dynamics Study of Transport Phenomena in Perfluorosulfonate Ionomer Membranes for Polymer Electrolyte Fuel Cells,? J. Elec. Soc., 150, E66-E73 (2003).

3. Seminario, J. "Calculation of Intramolecular Force Fields from Second-Derivative Tensors" International Journal of Quantum Chemistry: Quantum Chemistry Symposium 30, 1271-1277 (1996).

4. Kim, D; Chung P.S.; Jain, P.; Vemuri, S.H.; Jhon, M.S., ?Multiscale Modeling of Head Disk Interface,? IEEE Trans. Magn., 46 (published on June 2010).

5. Kim, W.T.; Jhon, M.S.; Zhou, Y.; Staroselsky, I.; Chen, H., ?Nanoscale Air Bearing Modeling via Lattic Boltzmann Method,? J. Appl. Phys., 97, 10P304 (2005).

6. Jain, P.; Biegler, L.T.; Jhon M.S., ?Parametric Study and estimation in CFD-based PEM fuel cell models,? AIChE Journal, 54, 2089-2100 (2008).