Shape regulation of high-index facet nanoparticles by dealloying

Stabilizing rougher nanoparticles For many reactions catalyzed by metal nanoparticles, the more exposed metal atoms on high-index faces can be more active than metal atoms on smooth, low-index faces. Surface ligands can be used to stabilize high-index surfaces, but they can also be hard to remove. Huang et al. report the solid-state synthesis of metal nanoparticles such as platinum and chromium that can form tetrahexahedral nanoparticles with high-index faces. Metals such as bismuth and lead were alloyed with the transition metals at high temperatures and then evaporatively dealloyed during a quench to room temperature. Science, this issue p. 1159 An alloying-dealloying reaction with metals such as bismuth produced tetrahexahedral transition-metal nanoparticles. Tetrahexahedral particles (~10 to ~500 nanometers) composed of platinum (Pt), palladium, rhodium, nickel, and cobalt, as well as a library of bimetallic compositions, were synthesized on silicon wafers and on catalytic supports by a ligand-free, solid-state reaction that used trace elements [antimony (Sb), bismuth (Bi), lead, or tellurium] to stabilize high-index facets. Both simulation and experiment confirmed that this method stabilized the {210} planes. A study of the PtSb system showed that the tetrahexahedron shape resulted from the evaporative removal of Sb from the initial alloy—a shape-regulating process fundamentally different from solution-phase, ligand-dependent processes. The current density at a fixed potential for the electro-oxidation of formic acid with a commercial Pt/carbon catalyst increased by a factor of 20 after transformation with Bi into tetrahexahedral particles.