Fuel-Cell Membrane Degradation

Degradation of Nafion, a common fluoropolymer membrane used to separate electrodes and reactants in fuel cells, involves the reaction of H₂, O₂, and platinum to produce radical species that then attack the intact polymer rather than defect sites, reports a group led by Caltech’s William A. Goddard III (J. Am. Chem. Soc., DOI: 10.1021/ja2074642). Understanding how Nafion degrades is key to finding ways to make fuel cells work longer. Researchers have long believed that radical species play a role in Nafion damage, but how the radicals arise and react with the polymer has been uncertain. Using a theoretical analysis, Goddard and colleagues found that HO∂ forms from H₂O₂ produced at the surface of Pt, which is used as a catalyst in fuel cells. The researchers then observed that HO∂ can degrade the polymer in two ways: either by attacking C–S bonds or by reacting with H₂ to form H∂, which attacks C–F bonds. The results point to ways to prevent membrane damage, such as by modifying catalysts to prevent H₂O₂ formation or creating polymers that are more resistant to radical attack, the authors say.