Multiscale Modeling of a Proton Exchange Membrane Fuel Cell: Atomistic Oxygen Reduction Reaction Model

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.

In this sense, the research of the physicochemical processes in PEMFCs is primordial to characterize and to understand the operation of these devices, aiming to suggest strategies to enhance their performance. Numerical simulations are able to provide detail of quantities that are difficult to measure experimentally, thus they can complement the experimental approaches allowing a comprehensive understanding of the PEMFCs operation [2]⁠.

Several processes on different scales occur in the PEMFC components. The most important processes include the electrochemical reactions in the catalytic layers, ion transport in the electrolyte membrane, and mass transport in all regions of the PEMFC. Different simulation approaches study these processes [3–6]⁠, but these models describe the electrochemical reactions using Butler-Volmer equations with empirical parameters, which rely on operation conditions.

Furthermore, the oxygen reduction reaction (ORR) is fundamental in the development of fuel cells, and it is required a deeper understanding of these macroscopic parameters relating to chemical and structural properties of the catalyst, in order to enhance catalysts and catalytic layers used in this technology. Thus, in this work, it is shown an atomistic approximation using density functional theory (DFT) to describe the reaction processes in the kinetic section of a PEMFC model, which includes transport phenomena at the electrolyte membrane.

It is considered a dissociative mechanism to describe ORR in the cathode of the cell. DFT calculations of a Pt model surface with adsorbed species are carried out to determine activation energies of each elemental step and hence the kinetic parameters are estimated applying the transition state theory.

The kinetic modeling based on DFT calculations enables further insight into reaction mechanisms and deeper understanding of the ORR .

References:

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

[2] A. A. Shah, K.H. Luo, T.R. Ralph, F.C. Walsh, Electrochim. Acta 56 (2011) 3731.

[3] A.Z. Weber, J. Newman, J. Electrochem. Soc. 151 (2004) A311.

[4] A.Z. Weber, R.L. Borup, R.M. Darling, P.K. Das, T.J. Dursch, W. Gu, D. Harvey, A. Kusoglu, S. Litster, M.M. Mench, R. Mukundan, J.P. Owejan, J.G. Pharoah, M. Secanell, I. V. Zenyuk, J. Electrochem. Soc. 161 (2014) F1254.

[5] P.K. Das, X. Li, Z.-S. Liu, J. Electroanal. Chem. 604 (2007) 72.

[6] W. Sun, B. A. Peppley, K. Karan, Electrochim. Acta 50 (2005) 3359.