Lihua Bi

Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at −200 mV from a solution of 1 M H2SO4+0.01 mM K2PdCl4. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45–60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O2 by a 4-electron process at −200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O2 gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at −390 and −600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O2 in this neutral medium. The former peak is ascribable to the 2-electron reduction of O2 to H2O2, while the latter is assigned to the reduction of H2O2 to H2O. The observed electrocatalysis for the reduction of O2 is attributable to the extraordinary catalytic activity of the Pd nanoparticles over the bulk gold electrode.

Synthesis, characterization and fabrication on a glassy carbon electrode of a tetra-iron substituted sandwich-type pentadecatungstodiarsenate heteropolyanion

A novel sandwich-type compound, Na12[Fe4(H2O)2(As2W15O56)2]·41H2O, has been synthesized. The compound was well-characterized by means of IR, UV-vis, 183W NMR and elemental analyses. The compound crystallizes in the triclinic, Pī symmetry group. The structure of the compound is similar to that of Na16[M4(H2O)2(As2W15O56)2]·nH2O (M = Cu, Zn, Co, Ni, Mn, Cd), and consists of an oxo-aqua tetranuclear iron core, [FeIII4O14(H2O)2], sandwiched by two trivacant α-Wells-Dawson structural moieties, α-[As2W15O56]. Redox electrochemistry of the compound has been studied in buffer solutions at pH = 4.7 using polarography and cyclic voltammetry (CV). The compound exhibited four one-electron couples associated with the Fe(III) center followed by three four-electron redox processes attributed to the tungsten-oxo framework. The compound-containing monolayer and multilayer films have been fabricated on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternating deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)2Cl]2+/−. CV, X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and atomic force microscopy (AFM) have been used to characterize the multilayer films. It is proved that the multilayer films are uniform and stable. The electrocatalytic activities of the multilayer films have been investigated on the reduction of two substrates of important analytical interest, NO2− and H2O2.

SINGLE-CRYSTAL X-RAY STRUCTURE AND PROPERTIES OF K10[Ni4 (H2O)2(AsW9O34)·4H2O

ABSTRACT The rational synthesis and the structural and magnetic characterization of a nickel cluster are presented. The compound comprises a rhomblike Ni4O16 group encapsulated between two-heptadentate tungstoarsenate ligands [AsW9O34]9−. The crystal structure of K10[Ni4(H2O)2(AsW9O34)2]·4H2O was solved in monoclinic, P21/n symmetry, with a=12.258(3) Å, b=21.232(4) Å, c=15.837(3) Å, β=92.05(3)°, V=4119.1(14) Å3, Z=2, and R=0.0862. The crystal structure of the Ni(II) derivative was compared with that of the Cu(II), Zn(II), Co(II) and Mn(II) derivatives. The Ni4O14-(H2O)2 unit in the compound shows no Jahn-Teller distortion. On the other hand, the Ni(II) derivative shows ferromagnetic exchange interactions within the Ni4O16 group (J=7.8 cm−1, J′=13.7 cm−1) and an S=4 ground state, the highest spin state reported in a heteropoly complex. Its redox electrochemistry has been studied in acid buffer solutions using cyclic voltammetry. It exhibited two steps of one-electron redox waves attributed to redox processes of the tungsten-oxo framework. The new catalyst showed an electrocatalytic effect on the reduction of NO2 −.