Contamination and Recovery of PEMFC Cathodes with Organohalides: Chlorobenzene and Bromomethane

Proton exchange membrane fuel cells (PEMFCs) are susceptive to airborne contaminants, which can deleteriously adsorb on the platinum electrocatalysts at the cathode and inhibit the oxygen reduction reaction. Numerous inorganic (e.g., S_x, HCl, NaCl) and organic contaminants (alcohols and hydrocarbons) have been studied with the finding that some contaminants adsorb irreversibly, and some can be eliminated by oxidation and/or electrostatic desorption leading to full or partial recovery of the PEMFC performance.  This paper describes the impact of the organohalide airborne contaminants, chlorobenzene and bromomethane, on PEMFC performance and recovery.

PEMFCs exposed to 20 ppm chlorobenzene lose significant activity, but the losses can be recovered after exposure to neat air. Under both wet and dry air streams, the cell voltage loss is rapid with a time scale <0.4 h and exceeds 500 mV. The performance recovery is slower than the contamination phase (time scale >3 h) and is incomplete with air (>40 mV loss remains). The effect of contamination with bromomethane is quite different. Bromomethane contamination causes relatively slow degradation (>19 h time scale) and recovery (>11 h time scale) of cell performance, but the losses appear to be largely irreversible (>250 mV).

The electrochemistry of the organohalide contamination processes is studied in combination with cyclic voltammetry, chronoamperometry and impedance spectroscopy. Gas chromatography/mass spectroscopy is used to determine the reaction intermediates and products of the organohalides. X-ray absorption spectroscopy at the Pt L₃ edge on catalyst coated membranes that have been exposed to the chlorobenzene and bromomethane have also been carried out over a range of potentials. Analysis of the XAS results suggests that the molecular orientation of the organohalides changes with potential.   

ACKNOWLEDGMENTS

This work is supported by the Department of Energy (DE-EE0000467) and the Office of Naval Research. Authors are also grateful to the Hawaiian Electric Company for their ongoing support of the operations of the Hawaii Sustainable Energy Research Facility.