Bromide Ions Triggered Synthesis of Noble Metal-Based Intermetallic Nanocrystals

Ordered intermetallic nanomaterials with a well-defined crystal structure and fixed stoichiometry facilitate the predictable control of their electronic structure and catalytic performance. To obtain the thermodynamically stable intermetallic structures, the conventional approaches with high-temperature annealing are still far from satisfactory, because of annealing-induced aggregation and sintering of nanomaterials. Herein, a general wet-chemical method is developed to synthesize a series of noble metal-based intermetallic nanocrystals, including hexagonal close-packed (hcp) PtBi nanoplates, face-centered cubic (fcc) Pd₃ Pb nanocubes, and hcp Pd_2.5 Bi_1.5 nanoparticles. During the synthetic process, Br^- ions play two important roles for the formation of ordered intermetallic structures: i) Br^- ions can coordinate with the metal ions to decrease their reduction potentials thus slowing down the reduction kinetics. ii) Br^- ions can combine with molecular oxygen to generate an oxidative etching effect, hence reconstructing the atom arrangement, which is beneficial for the formation of the intermetallic structure. As a proof-of-concept application, Pd₃ Pb nanocubes are used as electrocatalysts for ethanol and methanol oxidation reactions, which exhibit significantly improved electrochemical performance compared with the commercial Pd black catalyst.