Time-Resolved Spectroscopy and High-Efficiency Light-Driven Hydrogen Evolution of a {Mo3 S4 }-Containing Polyoxometalate-Based System.

Polyoxothiometalate ions (ThioPOM) are active hydrogen-evolution reaction (HER) catalysts based on modular assembly built from electrophilic clusters {MoSx } and vacant polyoxotungstates. Herein, the dumbbell-like anion [{(PW11 O39 )Mo3 S4 (H2 O)3 (OH)}2 ]8- exhibits very high light-driven HER activity, while the active cores {Mo3 S4 } do not contain any exposed disulfido ligands, which were suspected to be the origin of the HER activity. Moreover, in the catalyst architecture, the two central {Mo3 S4 } cores are sandwiched by two {PW11 O39 }7- subunits that act as oxidant-resistant protecting groups and behave as electron-collecting units. A detailed photophysical study was carried out confirming the reductive quenching mechanism of the photosensitizer [Ir(ppy)2 (dtbbpy)]+ by the sacrificial donor triethanolamine (TEOA) and highlighting the very high rate constant of the electron transfer from the reduced photosensitizer to the ThioPOM catalyst. Such results provide new insights into the field of molecular catalytic systems able to promote high HER activity.

Supramolecular Association between γ-Cyclodextrin and Preyssler-Type Polyoxotungstate.

The development of hybrid materials based on polyoxometalates constitutes a strategy for the design of multifunctional materials. The slow evaporation of an aqueous solution of [NaP5W30O110]14- in the presence of γ-Cyclodextrin (γ-CD) led to the crystallization of a K6Na8{[NaP5W30O110]•(C48H80O40)}•23H2O (NaP5W30•1CD) supramolecular compound, which was characterized by single-crystal X-ray diffraction, IR-spectroscopy, thermogravimetric and elemental analyses. Structural analysis revealed the formation of 1:1 {[NaP5W30O110]•[γ-CD]}14- adduct in the solid state. Studies in solution by cyclic voltammetry, electrochemical impedance spectroscopy, 1H NMR spectroscopy, and 31P DOSY, have demonstrated weak interactions between the inorganic anion and the macrocyclic organic molecule.

Nanostructured conducting polymers for stiffness controlled cell adhesion.

We propose a facile and reproducible method, based on ultra thin porous alumina membranes, to produce cm(2) ordered arrays of nano-pores and nano-pillars on any kind of substrates. In particular our method enables the fabrication of conducting polymers nano-structures, such as poly[3,4-ethylenedioxythiophene]:poly[styrene sulfonate] ( PEDOT: PSS). Here, we demonstrate the potential interest of those templates with controlled cell adhesion studies. The triggering of the eventual fate of the cell (proliferation, death, differentiation or migration) is mediated through chemical cues from the adsorbed proteins and physical cues such as surface energy, stiffness and topography. Interestingly, as well as through material properties, stiffness modifications can be induced by nano-topography, the ability of nano-pillars to bend defining an effective stiffness. By controlling the diameter, length, depth and material of the nano-structures, one can possibly tune the effective stiffness of a (nano) structured substrate. First results indicate a possible change in the fate of living cells on such nano-patterned devices, whether they are made of conducting polymer (soft material) or silicon (hard material).

Atomic Layer Deposition of Pd Nanoparticles on TiO2 Nanotubes for Ethanol Electrooxidation: Synthesis and Electrochemical Properties.

Palladium nanoparticles are grown on TiO2 nanotubes by atomic layer deposition (ALD), and the resulting three-dimensional nanostructured catalysts are studied for ethanol electrooxidation in alkaline media. The morphology, the crystal structure, and the chemical composition of the Pd particles are fully characterized using scanning and transmission electron microscopies, X-ray diffraction, and X-ray photoelectron spectroscopy. The characterization revealed that the deposition proceeds onto the entire surface of the TiO2 nanotubes leading to the formation of well-defined and highly dispersed Pd nanoparticles. The electrooxidation of ethanol on Pd clusters deposited on TiO2 nanotubes shows not only a direct correlation between the catalytic activity and the particle size but also a steep increase of the response due to the enhancement of the metal-support interaction when the crystal structure of the TiO2 nanotubes is modified by annealing at 450 °C in air.

A large electrochemical setup for the anodization of aluminum towards highly ordered arrays of cylindrical nanopores.

A new electrochemical setup and the associated procedures for growing ordered anodic aluminum oxide pore arrays on large surfaces are presented. The typical size of the samples is 14 × 14 cm(2). The most crucial experimental parameters that allow for the stabilization of the high-field procedures are a very efficient cooling of sample and electrolyte, as well as the initial ramping up of the voltage at an accurately defined rate. The morphology of the cylindrical, parallel alumina pores is similar to those obtained on smaller scales with standard setups. Our setup facilitates the availability of porous anodic alumina as a template system for a number of applications.

3D-nanoarchitectured Pd/Ni catalysts prepared by atomic layer deposition for the electrooxidation of formic acid.

Three-dimensionally (3D) nanoarchitectured palladium/nickel (Pd/Ni) catalysts, which were prepared by atomic layer deposition (ALD) on high-aspect-ratio nanoporous alumina templates are investigated with regard to the electrooxidation of formic acid in an acidic medium (0.5 M H2SO4). Both deposition processes, Ni and Pd, with various mass content ratios have been continuously monitored by using a quartz crystal microbalance. The morphology of the Pd/Ni systems has been studied by electron microscopy and shows a homogeneous deposition of granularly structured Pd onto the Ni substrate. X-ray diffraction analysis performed on Ni and NiO substrates revealed an amorphous structure, while the Pd coating crystallized into a fcc lattice with a preferential orientation along the [220]-direction. Surface chemistry analysis by X-ray photoelectron spectroscopy showed both metallic and oxide contributions for the Ni and Pd deposits. Cyclic voltammetry of the Pd/Ni nanocatalysts revealed that the electrooxidation of HCOOH proceeds through the direct dehydrogenation mechanism with the formation of active intermediates. High catalytic activities are measured for low masses of Pd coatings that were generated by a low number of ALD cycles, probably because of the cluster size effect, electronic interactions between Pd and Ni, or diffusion effects.