Hydrogen Sulfide Kinetics on PEM Fuel Cell Electrodes

A concise mechanism for the poisoning kinetics of hydrogen sulfide (H2S) on composite solid polymer electrolyte Pt (SPE- Pt) electrode is presented. The simplified version of the mechanism is validated experimentally by charge balances and theoretically by a model, which predicts the oxidation current as a function of the applied potential. H2S dissociatively adsorbs onto SPE-Pt electrode as linear and bridge bonded sulfur (S) species and, under favorable potentials, undergoes electro-oxidation to sulfur and then to sulfur dioxide (SO2). A fraction of the adsorbed S species remains as 'hard-to-oxidize' adsorbents and causes irreversible loss of catalytic activity. Deactivation of bridge sites due to sulfur poisoning occurs first followed by the loss of linear sites.