Pt-, PtNi- and PtCo-supported catalysts for oxygen reduction in PEM fuel cells

The most widely used supporting material for ORR catalysts is high-surface-area carbon (such as Vulcan XC-72). However, at elevated temperatures, burning of the carbon-to-catalyst contact takes place and drying out of the cathode may destroy the three-phase zones. In order to avoid these problems, Pt catalysts supported on silica were synthesized and characterized parallel to those supported on carbon. In a search for more active and stable catalysts, in addition to supported Pt powders, we have synthesized and characterized carbon- and silica-supported PtNi and PtCo catalysts via the same electroless-deposition route. In order to avoid agglomeration of the platinum particles, a classic three-step electroless deposition (sensitization and activation, nucleation and growth) on silica and XC-72 was used for the first time. The PtNi- and the PtCo-supported catalysts have smaller crystal size (as low as 2.2 nm) and larger electrochemical surface area (up to 57 m² g^-1) than do pure Pt-supported catalysts. The stability of the alloy catalysts in acidic medium was tested. Catalysts post-treated in acid were found to be stable and had a platinum-rich (or pure) "skin" structure. Some conclusions were drawn regarding catalyst structure and corrosion mechanism.