Operational Performance Recovery of SO2-Contaminated Proton Exchange Membrane Fuel Cells

Airborne sulfur contaminants (SO₂, H₂ S, and COS) cause the performance of proton exchange membrane fuel cells (PEMFCs) to degrade because they adsorb to the Pt catalysts and modify reaction sites for oxygen reduction. Electrochemical methods can be used for PEMFC performance recovery by oxidizing adsorbed sulfur species (SO_x) on the Pt catalysts to sulfate (SO₄^2-) at high potentials and then removing them as water-soluble anions at low potentials. We examine the effectiveness of five distinct methods for PEMFC performance recovery after 3 h of exposure to 1 ppm SO₂ in air at 60°C and 48.3 _kPag (7 psi) and relative humidity of 100∫50% (anode∫cathode). The methods are tested when the Pt surface is partially covered but not completely saturated with sulfur species. The methods include variations in the cathode potential and gas environment (N₂ or air). In the optimum method, the cells are switched from normal H₂ ∫air operation to H₂ ∫ N₂ by electrochemically consuming O₂ in the air. The potential is then cycled between 0.09 and 1.1 V vs the potential at the anode to restore 97% of the platinum catalyst electrochemical surface area. This in situ N₂ cycling method returns the polarization curves of contaminated PEMFCs to their original performance in less than 3 min.