Modeling the impact of cation contamination in a polymer electrolyte membrane fuel cell

Abstract

Abstract Starting from fundamental principles, we have developed an isothermal, one‐dimensional model for cation contamination of a proton exchange membrane (PEM) fuel cell. When current is drawn, the foreign cations migrate toward the cathode under the influence of the potential gradient while diffusion acts to balance this migration. The model provides the electrolyte potential along with the concentration of water, cation, and proton across the membrane electrode assembly (MEA) at steady‐state condition. The voltage loss associated with cation contamination is largely thermodynamic in nature owing to the proton concentration (pH) difference that develops between the anode and cathode. This potential loss is proportional to current density and inversely proportional to water content. If the cation fraction in the cathode approaches unity, the cell current becomes limited because of proton starvation. The model is validated with experimental hydrogen pump performance data using lithium‐doped MEAs. Hydrogen/oxygen operation is presented experimentally and discussed, but not explicitly modeled because of the added complications introduced by the sluggish oxygen reduction reaction kinetics. Experimental data for cobalt‐doped MEAs, which can react in the cathode when the local pH increases above five, is presented and explained with the aid of cobalt's Pourbaix diagram. Finally, the effect of cobalt ion contamination (e.g., from PtCo cathode catalysts degradation) on H 2 /air PEMFC performance under automotive conditions is shown.

Key findings

• ▸Cation contamination leads to proton starvation and limits cell current when cation fraction approaches unity.
• ▸Voltage loss is inversely proportional to water content.
• ▸Model is validated with experimental data using lithium-doped MEAs.

Keywords

Identifiers

DOI

10.1002/9780470974001.f500049

Journal

Handbook of Fuel Cells

Year

2010