Valeri Petkov

Oxide-Supported IrNiO x Core-Shell Particles as Efficient, Cost- Effective, and Stable Catalysts for Electrochemical Water Splitting**

Active and highly stable oxide-supported IrNiO(x) core-shell catalysts for electrochemical water splitting are presented. IrNi(x)@IrO(x) nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiO(x)/Meso-ATO) were synthesized from bimetallic IrNi(x) precursor alloys (PA-IrNi(x) /Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNi(x)/Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core-shell particles. The core-shell IrNiO(x)/Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.

Nanostructure by high- energy X-ray diffraction

Detailed knowledge of the atomic-scale structure is needed to understand and predict properties of materials. For ordinary crystals, this information is obtained by traditional (Bragg) X-ray diffraction. It is difficult to use this approach on materials structured at the nanoscale because their diffraction patterns show few, if any, Bragg peaks, and have a pronounced diffuse component. A non traditional approach based on high-energy X-ray diffraction and atomic pair distribution function data analysis may be used instead. This article describes the essentials of this approach and its great potential. The purpose is to encourage the nanoscience community go beyond traditional X-ray diffraction.

ISAACS – interactive structure analysis of amorphous and crystalline systems

ISAACS (interactive structure analysis of amorphous and crystalline systems) is a cross-platform program developed to analyze the structural characteristics of three-dimensional structure models built by computer simulations. The models may have any degree of periodicity (i.e. crystallinity) and local symmetry. The following structural information is computed from the models: total and partial radial distribution functions and structure factors for X-ray or neutron scattering, coordination numbers, bond-angle and near atomic neighbor distributions, bond-valence sums, ring statistics, and spherical harmonics invariants. The information may be visualized conveniently and stored for further use.

FTIR and XPS Study of Pt Nanoparticle Functionalization and Interaction with Alumina

Platinum nanoparticles with a mean size of 1.7 nm were synthesized by reduction in sodium acetate solution in 1,2-ethanediol. The particles were then functionalized with dodecylamine, dodecanethiol, and omega-mercapto-undecanoic acid (MUDA). Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed important variations of the particle surface state with functionalization whereas their structure differs only slightly. Platinum-to-sulfur charge transfer inferred from XPS of thiol-coated particles enabled the identification of the formation of Pt (delta+)-S (delta-) bonds. The native carbon monoxide (CO) at the surface of the particles was a very efficient probe for following the functionalization of the particles by FTIR. The red shift of nu(CO) accounts for the nature of the ligands at the surface of the particles and also for their degree of functionalization. Immobilization on alumina substrates of particles functionalized with MUDA was realized by immersion in colloidal solutions. Free molecules, isolated particles, and aggregates of particles interconnected by hydrogen bonds at the surface of alumina were evidenced by FTIR. With successive washings, the energy variation of the CO stretch of carbon monoxide and of carboxylic acid groups and the relative intensity nu(CH2)/nu(CO) showed that the free molecules are eliminated first, followed by aggregates and less-functionalized particles. Particles presenting a high degree of functionalization by MUDA remain and interact strongly with alumina.

STRUCTURE OF NANOCRYSTALLINE MATERIALS USING ATOMIC PAIR DISTRIBUTION FUNCTION ANALYSIS: STUDY OF LIMOS2

The structure of

Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy x-ray diffraction.

{\mathrm{LiMoS}}_{2}

High Real-Space Resolution Measurement of the Local Structure of Ga{sub 1-x}In{sub x}As Using X-Ray Diffraction

has been experimentally determined. The approach of atomic pair distribution function analysis was used because of the lack of well-defined Bragg peaks due to the short structural coherence (\ensuremath{\sim}50 \AA{}) in this intercalation compound. The reduction of Mo by Li results in Mo-Mo bonding with the formation of chains of distorted

Local structure of nanoporous carbons

\mathrm{Mo}\ensuremath{-}{\mathrm{S}}_{6}

Pt-Au alloying at the nanoscale.

octahedra. Using refined structural parameters the electronic band structure for this material has been calculated and is in good agreement with observed material properties.

Simulation of nanoporous carbons: a chemically constrained structure

Structure factors for Ca (x/2)Al xSi 1-xO (2) glasses (x = 0,0.25,0. 5,0.67) extended to a wave vector of magnitude Q = 40 A (-1) have been obtained by high-energy x-ray diffraction. For the first time, it is possible to resolve the contributions of Si-O, Al-O, and Ca-O coordination polyhedra to the experimental atomic pair distribution functions. It has been found that the connectivity of Si/Al-O tetrahedral network decreases with increasing x due to the emerging of nonbridging oxygens located on Si-O tetrahedra. Calcium maintains a rather uniform coordination sphere for all values of x and so it plays a certain role in determining the glass structure.