Multiscale Modeling of a Proton Exchange Membrane Fuel Cell: Effect of Electric Double Layer Structure

Proton Exchange Membrane Fuel Cells (PEMFCs) are very promising to generate electric energy for transport and electronic devices because they produce minimal pollutant emissions and can operate at low temperature [1]⁠. Despite of enormous progresses made to date, this technology has to reach all technical requirements in order to be competitive.

The presence of solvated cations as charge-transporting species has a direct influence on the potential profile at interfaces involved in PEMFCs. This leads to a shift in the electric potential acting on the reactants and modifies their activation energies. In this way, the rate of mass and charge transfer processes are determined by the electric double layer (EDL) morphology and structure. For instance, a simple modification in the medium permittivity close to the surface results in appreciable increase of the apparent reaction rate constant [2].

The importance of EDL structure on transfer mechanisms has led to several researches based on mean field theories and molecular simulations [3-4]. However, an integration of EDL structure simulations with PEMFC reaction model is still lacking. This will contribute to understand and cuantify the effect of electrolyte and solvent compositions on the reaction kinetics.

In order to simulate the EDL structure and its modifications with respect to applied potential and solution composition, it is required a proper molecular model that resembles the size, polar and chemical characteristics of reactants, electrolyte and solvent species involved in PEMFCs, which is proposed to carry out in this work by means of molecular dynamics (MD) simulations.

The results achieved by molecular simulations would enable to evaluate the modification of reaction rates by the EDL structure, under an applied potential in PEMFC. In order to accomplish this, it is employed the Stillinger-Weber interaction potential of water and platinum [7], coupled with electrostatic interactions for the molecular simulations of EDL.

References:

[1] Y. Wang, K.S. Chen, J. Mishler, S.C. Cho, X.C. Adroher, Appl. Energy 88 (2011) 981.

[2] Zhdanov, V. P. and Kasemo, B., Role of the field fluctuations in electrochemical reactions, Surf. Sci. 521 (2002) L655.

[3] Guidelli, R. and Schmickler, W., Recent developments in models for the interface between a metal and an aqueous solution, Electrochim. Acta.45 (2000) 2317.

[4] Fawcet, W. R. and Smagala, T. G., New developments in the theory of the diffuse double layer, Langmuir 22 (2006) 10635.

[5] Siepmann, J. I. and Sprik, M., Influence of surface topology and electrostatic potential on water/electrode systems, J. Chem. Phys. 102 (1995) 511.