As depicted in Figure , the tin oxide-decorated platinum catalysts (denoted as SnOx-Pt/C) were prepared by a conventional impregnation of high surface area carbon (Kejten black 300J) support platinum (Pt/C) in Sn precursors, and followed by heat treatment under 4% H2/Ar at 200 ˚C for 2 h (see more experimental details in the Supporting information). The initial Pt weight content on Pt/C is ~20%. The Pt:Sn atomic ratios were adjusted to 1:5, 1:10 and 1:20, respectively. According to the X-ray powder diffraction (XRD) patterns (Figure ), a low Sn content (1:10) does not change the crystal structure of SnOx-Pt/C catalysts, as confirmed by the similar diffraction peaks to the standard Pt (PDF No. 04-0802). However, SnO2 peaks corresponding to standard SnO2 (PDF No. 41-1445) are observed in the XRD of sample SnOx-Pt/C (1:5). This implies that Sn is less likely to form alloys with Pt but tends to form tin oxides.