Shape-controlled Synthesis Of Rh And Rh-based Alloy Nanoparticles

Platinum group metallic nanomaterials have demonstrated widely potential applications in many fields owing to their special physical and chemical properties.Their properties are strongly dependent on their sizes,shapes and surface structures.In order to improve the performance efficiency of platinum group metals and lower their cost,the shape-controlled synthesis of their nanomaterials has been paid much attention.Up to now,the controlled syntheses of Pd or Pt nanoparticles with different morphologies have been extensively studied,while few reports about the shape-controlled synthesis of Rh nanoparticles have been made.Rh has been widely used as catalysts for oxidation of CO as well as some organic reactions.So,the study on the shape-controlled synthesis of Rh nanoparticles is of great significance to improve their catalytic performances.Rh nanocubes with a mean size of about 7.5nm were successfully synthesized by means of oil-bath heating method with Na₃RhCl₆ as a precursor,tetraethylene glycol?TEG?as both a solvent and a reducing agent,polyvinylpyrrolidone?PVP?as a stabilizer in the presence of an appropriate amount of cetyltrimethylammonium bromide?CTAB?.The as-prepared Rh nanocubes were characterized by transmission electron microscopy?TEM?,X-ray diffraction?XRD?and X-ray photoelectron spectrometry?XPS?.The results demonstrated that the use of the CTAB was crucial to the formation of Rh nanocubes.The coordination of Br^-1 ions with Rh precursor reduced the reduction of Rh?III?ions.On the other hand,the selective adsorption of Br^-1 ions on Rh?100?facets was favorable for the formation of Rh nanocubes.Uniform size and well-defined tetrahedral Rh nanoparticles with a mean size of about 18.4nm were synthesized with Na₃RhCl₆ as a precursor,TEG as both a reducing agent and a solvent,PVP as a stabilizer in the presence of an appropriate amount of glucose by oil-bath heating at 160 °C for 2 h.The as-prepared Rh tetrahedral nanoparticles were characterized by TEM,scanning electron microscopy?SEM?,XRD and XPS.The results show that glucose played an essential role in controlling the formation of tetrahedral Rh nanoparticles.The optimum molar ratio of Na₃RhCl₆?PVP?C₆H₁₂O₆ was 1?10?40.The as-prepared tetrahedral Rh nanoparticles showed good electrochemical stability.Pt-Rh alloy concave nanocubes with a mean size of about 30.4nm were successfully synthesized under microwave irradiation with H₃RhCl₆ and H₂PtCl₆ as precursors,TEG as both a solvent and a reducing agent,PVP as a stabilizer in the presence of an appropriate amount of KI.The as-prepared Pt-Rh alloy concave nanocubes were characterized by TEM,SEM,high angle annular dark field-scanning transmission electron microscopy?HAADF-STEM?,XRD and XPS.The electrochemical experiments were conducted and the results showed that Pt-Rh alloy concave nanocubes exhibited higher electrocatalytic activities than that of commerial Pt black for the electro-oxidations of formic acid and methanol.