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Structure-property modeling and testing of transport layers for PEM fuel cells and water electrolysis cells Nouri Khorasani, Amin

Abstract

Widespread application of polymer electrolyte membrane fuel cells (PEMFC) and water electrolyzers (PEMWE) in renewable energy systems depend on their performance in high current density conditions. For both applications, transport of species to/from the oxygen electrode is crucial to the system operation. Recent in-situ imaging of both PEMFC and PEMWE systems have shown that the product material accumulates at the interface of the oxygen electrode with the adjacent porous transport layer (PTL), and negatively affects the performance. This interface is therefore worth scrutinizing in terms of mass transport and electrostatics. In this thesis, I investigated how the structural and electrostatic properties of the catalyst layer and the PTL in each system leads to the electrochemical performance of the system. For a PEMWE cell, I modeled the bubble nucleation, growth and stability inside a PTL pore. Then, I analyzed the performance stability of the PEMWE in a diagnostic cell. The results show the distribution of electrolytic bubbles lifetime and directly address their performance impact for the first time. For a PEMFC, I investigated two interfaces at the fuel cell catalyst layer and PTL to find out how the properties of the interface affect the distribution of species at the interface. For a promising PTL candidate material, I investigated how engineering the pore and particle sizes could maximize the cathode catalyst layer (CCL) utilization. I modeled how liquid water pressure build-up should be balanced with the distance from the PTL interstitial pores to allow for the liquid water to diffuse out of the CCL. The developed models can be used as applied material development tools with respect to the transport. In the catalyst layer, I investigated how the oxidation state of Pt affects the local distribution of H⁺ at the Pt-O-H₂O-H⁺ interface using classical molecular dynamics. The results showed for the first time that classical double layer theories do not properly address the effect of surface oxide dipoles on the ion interactions at the charged interface. The results from my thesis can guide the material design for the transport layers in PEMFC and PEMWE applications that improve the two-phase transport and efficiency.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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