SO<inf>2</inf>adsorption on carbon-supported Pt electrocatalysts

Abstract

Adsorption of SO2on a Pt/C catalyst typically used in proton exchange- membrane fuel cells (PEMFCs) has been investigated by temperature programmed desorption (TPD). SO2concentrations in N2were varied from 5 ppm to 1% (vol) and adsorption isotherms were determined at 25, 50, and 80 °C. Oxygen assisted (O-assisted) desorption experiments (i.e., successive TPD experiments following exposure to room temperature O2after the first TPD event) produced an additional SO2peak at a temperature higher than the initial SO2peak. These two types of SO2adsorption were identified as weakly adsorbed SO2species desorbed between 140 and 200 °C, depending on concentration, and a strongly adsorbed, dissociated species. For the strongly adsorbed, dissociative species,18O2isotope introduction during O-assisted desorption yielded ratios of 50%, 36%, and 14% for SO2masses of 64, 66, and 68, respectively. The activation energy and kinetic constant of desorption are reported for weakly adsorbed SO2at 1% and 20 ppm SO2using the Polanyi-Wigner equation. © 2011 American Chemical Society.