Role of the Secondary Metal in Ordered and Disordered Pt–M Intermetallic Nanoparticles: An Example of Pt₃Sn Nanocubes for the Electrocatalytic Methanol Oxidation

When comparing alloy catalysts with different degrees of ordering, it is important to maintain surface facets to understand the effect of different arrangements of surface atoms. This is even more important when both metals are involved in the reaction steps, which is the case of Pt 3 Sn for the methanol oxidation reaction (MOR). We have prepared 95 and 60% ordered Pt 3 Sn nanocubes with {100} facets for the MOR. We show that the Sn atoms in the 60% ordered Pt 3 Sn nanocubes can be electrochemically oxidized to Sn 4+, whereas the Sn atoms in the 95% ordered Pt 3 Sn nanocubes are more resistant to oxidation. The Sn 4+ in the disordered catalysts makes them more active than the ordered catalysts. At low overpotentials, the electrochemically formed Sn 4+ in the 60% ordered Pt 3 Sn nanocubes bind OH, oxidizing the CO intermediate adsorbed on Pt more efficiently. At high overpotentials, Sn 4+ prevents the passivation of the Pt sites due to adsorption of OH. These effects lead to a 5.6 times higher activity of the 60% ordered nanocubes compared to the 95% ordered nanocubes. These results illustrate the importance in catalyst design of controlling the environment and especially the atoms neighboring Pt for intermetallic Pt–M electrocatalysts.