Effects of carboxylate stabilizers on the structure and activity of carbon-supported Pt-Cu nanoparticles towards methanol oxidation

Carbon-supported Pt-Cu nanoparticles were prepared by alcohol reduction method in the presence of carboxylate stabilizers with different molecular structure (malonate, succinate, adipate, and citrate). The longer was the carbon chain of stabilizer, the smaller dispersed Pt-Cu alloy crystallites and fewer aggregates were obtained, which was attributed to steric effect of the molecular backbone to protect fine dispersed crystallites. Dispersed nanoparticles were Pt-rich and aggregates were high-Cu crystallites due to competitive chemisorption of carboxylate and Cu2+ on metal surface in the course of nanoparticle formation. Citrate gave aggregates of several low-Cu alloy crystallites dispersed on carbon support, which was attributed to strong chemisorption of citrate on metal surface via tridentate coordination. The length of molecular backbone of stabilizer mainly affected size and dispersivity of Pt-Cu nanoparticles while the chemisorption strength of stabilizer on metal surface affected the degree of alloying. The Pt-Cu prepared with succinate showed the highest methanol oxidation activity, which was attributed to moderate size and moderate alloying degree leading to a moderate chemisorption strength of reactants and intermediates.