The Synthesis Of Different Morphologies Of Palladium Nanoparticles And Its Electrocatalytic Performance

Shape-controlled synthesis of the nanoclusters of platinum family metals is the base tostudy the dependence of their catalytic performances upon morphologies. Platinum familymetals are widely used as the primary catalyst. To improve its catalytical activity, size-andshape-controlled synthesis of monodispersive nanostructures of platinum family metals havebeen investigated in recent years. A lot of platinum family metallic nanoparticles with variousmorphologies have been obtained by using surfactant or polymer as stabilizers, such asnanocubes, icosahedra, hexagonal nanosheets, nanocorolla, nanowires, concave tetrahedra,tetrapod/Mitsubishi-like Pd nanocrystals, and so on. These would provide a foundation forfurther study on the structure-activity relationship between morphologies of platinum groupmetal nanoclusters and their catalytic properties. In this paper, the shape-controlled synthesesof Pd nanocrystals with various morphologies, as well as their electrocatalytic activities, wereinvestigated.Monomorphologic and uniform square palladium nanoplates were synthesized withpalladium chloride as a precursor, tetraethylene glycol （TEG） as both a solvent and a reducingagent, polyvinylpyrrolidone （PVP） as a stabilizer in the presence of an appropriate amount ofKI under oil-bath heating at160°C for6h. The as-prepared square palladium nanoplates werecharacterized by transmission electron microscopy, X-ray powder diffraction and X-rayphotoelectron spectroscopy. The existence of I was crucial to the formation of squarepalladium nanoplates. The molar ratio of PVP/PdCl₂/KI was1/1/35.By oil-bath heating, uniform, dispersive and well-defined tetrapod-thorn Pd nanocrystalswere readily synthesized with Pd（acac）2as a precursor, PVP as a stabilizer, DMF and water asa mixed solvent and CO as a reducing agent in the presence of appropriate amount ofEDTA·2Na at100oC for3h. The as-prepared Pd nanocrystals were characterized by UV-visabsorption spectroscopy, TEM, XRD and XPS. The results show that the existence ofEDTA·2Na and the CO flow rate are the key to the growth of tetrapod-thorn Pd nanocrystals.The adsorption of EDTA·2Na on Pd seeds resulted in a change of the coverage of CO on thefaces of palladium. Due to the co-adsorption of CO and EDTA·2Na on Pd surfaces, theconfined-growth contributes to the formation of tetrapod-thorn Pd nanocrystal.The catalysis activities of the as-prepared Pd nanocrystals with various morphologies werestudied by electrocatalytic oxidation of formic acid. The results show that the maximumcurrent densities of the tetrapod-thorn Pd nanocrystals, tetrahedral Pd nanocrystals andhexagonal Pd nanosheets were measured to be10.58mA·cm^-2at0.35V,8.77mA·cm^-2at0.177 V, and7.66mA·cm^-2at0.171V, respectively, while that of square palladium nanoplates wasmeasured to be4.41mA·cm^-2at0.42V. The order of electrocatalytic activities is as follows:tetrapod-thorn Pd> tetrahedral Pd> hexagonal Pd nanosheets> square Pd nanoplates,indicating that the catalytic activity is dependent on the morphology.