A Catalyst Layer Flooding Model for Polymer Electrolyte Fuel Cells

Abstract

It is widely recognized that the performance degradation and the limiting current behavior in polymer electrolyte fuel cells (PEFC) are mainly attributed to the excessive build up of liquid water in the cathode side and the resulting flooding phenomena. Liquid water blocks the open pore space in the catalyst layer (CL) and the gas diffusion layer (GDL) leading to hindered oxygen transport and covers the electrochemically active sites in the CL thereby rendering reduced catalytic activity. The CL flooding therefore plays a crucial role in the overall PEFC performance limitation. In order to elucidate the primary mechanisms of liquid water removal out of the CL, the factors affecting CL flooding and to discern the role and contribution of CL flooding on the overall PEFC voltage loss, a CL flooding model has been developed. The flooding model is based on a simplified structure-wettability representation of the PEFC CL and a physical description of water and heat balance along with electrochemical performance analysis. The model shows that the evaporation mechanism, depending upon the cell operating temperature and the GDL thermal conductivity, plays a crucial role in the CL flooding behavior and the cell performance.

Key findings

• ▸Liquid water build-up in the cathode side and resulting flooding phenomena are the main causes of performance degradation and limiting current behavior in PEFC.
• ▸The evaporation mechanism plays a crucial role in catalyst layer flooding, depending on cell operating temperature and GDL thermal conductivity.
• ▸The model shows that catalyst layer flooding covers electrochemically active sites, hindering oxygen transport and reducing catalytic activity.

Keywords

Identifiers

DOI

10.1115/fuelcell2008-65021

Journal

ASME 2008 6th International Conference on Fuel Cell Science, Engineering and Technology

Year

2007