LAUSR

Abstract Alloy-type Sn-Pt/C electrocatalysts with desired Pt/Sn = 3.0 ratio have been prepared using commercial 20 wt.% Pt/C (20Pt/C (Q: Quintech)) and home-made 20Pt/C (H) catalysts by means of Controlled Surface Reactions. According to in situ XPS and in situ XRD studies the exclusive incorporation of Sn onto the Pt sites was achieved resulting in exclusive formation of Pt-Sn alloy phase. No evidence of the presence of SnO 2 phase was found by means of the XRD and EDS analysis. According to in situ XPS studies pre-treatment of the air exposed catalyst in H 2 even at 170 °C resulted in complete reduction of the ionic tin to Sn 0 , suggesting alloy formation. After contact of Sn-Pt/C catalysts with air Sn tends to segregate to the surface, where it oxidizes to a certain extent. Reversible interconversion of PtSn ↔ Sn 4+  + Pt in the presence of O 2 and H 2 was convincingly demonstrated by in situ XPS and in situ XRD studies. The electrocatalytic performance of the alloy catalysts was tested in CO oxidation and oxygen reduction reaction (ORR). Only minor changes of the surface composition of the Sn-20Pt/C electrocatalysts were observed after 20 polarization cycles. Better performance in the CO electrooxidation for our Sn-Pt/C catalysts compared to the state-of-art CO tolerant PtRu/C benchmark was demonstrated. Optimal surface composition of the Sn-20Pt/C (H) catalysts results in increased activity in the ORR compared to the Sn-20Pt/C (Q) and both parent 20Pt/C catalysts.