K-004

Michael Eikerling

m.eikerling@fz-juelich.de

Forschungszentrum Jülich, Germany

Ionomer in Catalyst Layers of PEM Fuel Cells: Insights from Theory and Computation

The integration of ionomer into cathode catalyst layers (CCLs) [1,2] elicited a breakthrough in the performance of polymer electrolyte fuel cells (PEFCs). However, the multifarious impacts of the ionomer phase on physical properties and processes in the CCL continue to challenge the scientific community. At the microscopic scale, a skin-type layer of ionomer controls the local reaction environment at the catalyst surface. Percolation through ionomer and water phases determines the proton conductivity of the layer [3,4]. Furthermore, dispersed interfacial ionomer films tune the wettability distribution in pores and the water sorption behavior of the pore network in the layer [5,6]. Lastly, the distribution and structure of ionomer and water in the operating CCL impact oxygen diffusivity at various scales, which in turn determines the distribution of reaction rates and the effectiveness factor of catalyst utilization [2]. In this context, the presentation will explore the following interrelated questions: How does ionomer interact with catalyst and support surfaces? How do these interactions and correlation effects determine the structure of the ionomer skin-layer and the formation of a thin water film at microscopic interfaces with catalyst and support? How do electrolyte structure and reaction conditions in this water film depend on charging properties of metal and ionomer walls? What is the impact of the ionomer’s dispersion behavior on the wettability distribution and the water sorption characteristics of the catalyst layer? We harness a well devised hierarchy of approaches in theory and computation, encompassing DFT-based computation, classical molecular dynamics simulations, and pseudo-kinetic statistical modeling, to tackle these questions. The current state of understanding of these intertwined aspects will be discussed and put into perspective in view of the design of novel ionomer materials for integration into catalyst layers. 

References:

[1] I.D. Raistrick, US Patent No. 4876115, 1989.

[2] M. Eikerling and A.A. Kulikovsky, Polymer Electrolyte Fuel Cells – Physical Principles of Materials and Operation, CRC Press Taylor & Francis Group, 2014.

[3] M. Eikerling, J. Electrochem. Soc. 153 (2006) E58-E70.

[4] W. Olbrich, T. Kadyk, U. Sauter, M. Eikerling, and J. Gostick, Scientific Reports 13 (2023) 14127. 

[5] W. Olbrich, T. Kadyk, U. Sauter, and M. Eikerling, J. Electrochem. Soc. 169 (2022) 054521. 

[6] W. Olbrich, T. Kadyk, U. Sauter, and M. Eikerling, Electrochim. Acta 431 (2022) 140850.