Facile Synthesis of Pd−Cu Bimetallic Twin Nanocubes and a Mechanistic Understanding of the Shape Evolution

This paper presents a facile synthesis of Cu twin cubes, with a yield of ca. 70%, from seeds based on Pd hexagonal nanoplates. The lattice mismatch, capping agent, and number of planar defects in the seeds all play important roles in directing the shape evolution of Cu on the Pd seeds. Initially, the Cu atoms are only deposited on one of the two basal planes of a Pd nanoplate in the form of small islands. As the growth continues, Cu {100} facets developed in the presence of hexadecylamine and Cl⁻, two capping agents with selectivity towards the Cu(100) surface. When switched to Pd triangular nanoplates, Cu right bipyramids instead of cubes are obtained and only three {100} facets are created from each side of the seed. Atomic-resolution transmission electron microscopy analysis indicates that the correspondence between the type of the seed and the shape of the final product can be attributed to the number of planar defects along the vertical direction of the plate-like seed, with two and one twin planes corresponding to cube and right bipyramid, respectively. By adjusting the experimental condition, this synthetic method can also be extended to Pd−Ag and other bimetallic systems.