Shape-Controlled Synthesis of Palladium Single-Crystalline Nanoparticles: The Effect of HCl Oxidative Etching and Facet-Dependent Catalytic Properties

This paper reports a convenient and facile preparation of single-crystalline palladium with controllable shape based on the reduction of kinetic control via hydrochloric acid oxidative etching. The concentration of HCl added to the reaction solution was found to be crucial for the shape evolution of palladium nanocrystals from nanocubes bounded by {100} facets to octahedrons by {1 1 1} facets. Palladium nanocubes can be readily obtained at a fast reduction rate without the involvement of additional HCl. With the introduction of a certain amount of HCl to the precursor solution, truncated nanocubes with {111} facets were formed, and the increase of HCl led to the slower reduction rate and the formation of palladium cuboctahedrons enclosed by six {100} facets and eight {111} facets at the expense of gradual shrinkage of {100} facets. The probable mechanism of morphological transformation was proposed upon a batch of experiments. The shape-dependent catalytic performances of as-obtained palladium nanocrystals were investigated by the structure-sensitive reaction of formic acid oxidation. It was found that catalytic activities of palladium nanocrystals displayed a strong dependence on the facets exposed on the surface, and cubic palladium exhibited the best catalytic performance compared with cubooctahedral and octahedral palladium nanocrystals.