Pt₃Sn Nanoparticles with Controlled Size: High-Temperature Synthesis and Room-Temperature Catalytic Activation for Electrochemical Methanol Oxidation

We report a new method of preparing carbon-supported Pt 3 Sn nanoparticle catalysts for methanol and CO oxidation. Alloyed Pt 3 Sn nanoparticles with a cubic phase were synthesized by coreduction of platinum acetylacetonate and tin acetylacetonate in a high-boiling solvent, trioctylamine. Particle sizes in the range of 3.0 to 6.5 nm were controlled by varying the amount of introduced capping agents (oleylamine and oleic acid). The as-prepared particles displayed a narrow size distribution and were catalytically inactive. The ligands were removed to activate the nanoparticles for catalysis by treatment with tetramethylammonium hydroxide (TMAOH) solution. The treated Pt 3 Sn particles can be stabilized in TMAOH solution and finally loaded on XC-72 carbon support by physical deposition. Cyclic voltammetry and CO-stripping showed that all the Pt 3 Sn particles exhibited high electrocatalytic activity for methanol and CO oxidation. The size-dependent CO-stripping study indicated CO ads oxidation started at low potentials (∼50 mV) on all the particles with the 3.5 nm Pt 3 Sn catalyst having the lowest peak potential. Also, the alloyed catalysts displayed a good stability in acidic environment at low potential (<500 mV).