PEMFCs Multiscale Modeling Including Effect of Overpotential in Cathodic Edl Among Water, O2, H+ Ions and Ionomer
Authors: Nuñez Toledo Laura Elisa , Castañeda Ramírez Sergio , Ribadeneira Paz Rafael 
Published: May 2020

This work is the continuation of our previous works 1,2 in which PEMFC cathodic EDL is simulated with only water and and then integrated in a multiscale model. In this work the PEMFC cathodic EDL is simulated with charges in the electrode surface, water, O2, H+ ions and ionomer using molecular dynamics (MD) 3,4 to obtain the electric overpotential associated with the organization of charges in the interface, this aims to get a more realistic representation of EDL, also considering operational concentrations of in the interface and a proportion of low index facets of platinum and according common composition of catalyst layer.

The combined effect of O2, H+ ions, ionomer chains and electrode charge in the overall performance of the cell is validated with a multiscale model and then compared with our past results considering the uncharged electrode and water, also we compare the results with experimental data 5,6. In this way we analyze three study cases, all of these related with other published works and experimental findings: i) A base case with uncharged electrode and water that gets a good representation for relative humidities in the cathode >60% and low current densities, ii) a second case related with recent founds of Litster et al 7 and Eikerling et al 8 when there are pores of catalyst layer filled with water and inaccessible for ionomer chains and iii) the complete system adding also the effect of ionomer, related with Balbuena et al findings9.

These cases let us to compare the effect of every species in the system. Besides, in the development of this work, we have seen the need of study the effect of overpotential located at different distance at the interface, where an important conclusion have emerged about the selection of outer, inner Helmholtz planes, the plane at 10Å of the surface or the limit between diffuse layer and bulk; finally other structural and theoretical aspects of EDL are presented for every case.

In general with this study we hope to improve the description of EDL and also achieve a better fitting of our multiscale model, specifically, at high current densities and low water contents in the cathode, where the presence of charge in the metal surface and intermediate species could have a crucial role.

References

1. L. E. Núñez Toledo, S. Castañeda Ramírez, A. E. Pérez Mendoza, and R. Ribadeneira Paz, in (2016) http://ma.ecsdl.org/content/MA2016-02/53/4091.abstract.

2. L. E. Núñez Toledo, S. Castañeda Ramírez, and R. Ribadeneira Paz, in ECS Meeting Abstracts, (2018) http://ma.ecsdl.org/content/MA2018-02/41/1360.abstract.

3. D. Frenkel and B. Smit, Understanding molecular simulations: from algorithms to applications, Academic Press, (2002).

4. S. Plimpton, 1–19 (1995) http://lammps.sandia.gov.

5. S. Castañeda Ramírez, A. E. Pérez Mendoza, and R. Ribadeneira Paz, ECS Trans., 66, 7–18 (2015).

6. S. Castañeda Ramírez, A. E. Pérez Mendoza, and R. E. Ribadeneira Paz, ECS Trans., 66, 19–39 (2015).

7. L. Hu, M. Zhang, S. Komini Babu, A. Kongkanand, and S. Litster, ChemElectroChem, 6, 2659–2666 (2019).

8. A. Nouri-Khorasani et al., Catal. Today, 262, 133–140 (2016).

9. R. Callejas-tovar, W. Liao, J. M. Martinez, D. Hoz, and P. B. Balbuena, Simulation, 4104–4113 (2011).