An in situ XAS study of high surface-area IrO2 produced by the polymeric precursor synthesis.

Iridium oxide powders with a surface area of more than 1 m2 g-1 (4 m2 g-2 from the H-UPD charge) and iridium-oxide crystallites less than 10 nm across were synthesized by heat treating gels formed from citric acid, ethylene glycol and dihydrogen hexachloroiridate(iv) in air. The characteristics of the resulting material was found to be strongly dependent on the heat-treatment step in the synthesis. A single heat-treatment of the gel resulted in a material with a substantial fraction of elemental iridium metal, i.e. iridium in oxidation state zero (Ir0). Post-synthesis modification of the powder by potential cycling resulted in oxidation peaks consistent with the conversion of the metal phase to iridium oxide. Linear combination of the near-edge part of the X-ray absorption data (X-ray absorption near-edge spectroscopy, XANES) collected in situ during potential cycling and an analysis of the extended X-ray fine-structure (EXAFS) part of the spectrum showed that the overall metal fraction was not significantly affected by the cycling. The oxidation of the metal phase is therefore limited to a thin layer of oxide at the metal surface, and a significant part of the iridium is left inactive. A modification of the heat treatment procedure of the sample resulted in iridium oxide containing only insignificant amounts of elemental iridium metal.

Strategies for the analysis of the elemental metal fraction of Ir and Ru oxides via XRD, XANES, and EXAFS.

Iridium and ruthenium oxide are active electrocatalysts for oxygen evolution. The relation between preparation method, structure, and behavior of mixed oxides of iridium and ruthenium are of interest in order to obtain active and stable catalysts. In this work the structure of mixed Ru-Ir oxides synthesized by the polymeric precursor method, which involves the formation of a gel containing the metal precursors and subsequent heat-treatment in air, was studied for the IrxRu1-xO2 system. An in-depth analysis of X-ray diffraction (XRD) and X-ray absorption (XAS) data, including EXAFS and linear combination of XANES, shows that the polymeric precursor synthesis method is capable of providing an intimate mixing of Ir and Ru in the catalyst. In addition to the oxide phase, metal phases, i.e. with Ru or Ir or both in oxidation state zero (Ir(fcc) and Ru(hcp)), were also found in the product materials. Facing complex structures such as some of those synthesized here, we have shown that a representation of shells with more than one atom type are efficiently represented using mixed sites, i.e. including scattering contributions from several elements in a site corresponding to a partial occupancy of the site by these elements, this method forming a very efficient basis for analyzing EXAFS data.

Exploration of the Smallest Diameter Tin Nanowires Achievable with Electrodeposition: Sub 7 nm Sn Nanowires Produced by Electrodeposition from a Supercritical Fluid.

Electrodeposition of Sn from supercritical difluoromethane has been performed into anodic alumina templates with pores down to 3 nm in diameter and into mesoporous silica templates with pores of diameter 1.5 nm. Optimized deposits have been characterized using X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy (bright field, high-angle annular dark field, and energy-dispersive X-ray elemental mapping). Crystalline 13 nm diameter Sn nanowires have been electrodeposited in symmetric pore anodic alumina. Direct transmission electron microscopy evidence of sub 7 nm Sn nanowires in asymmetric anodic alumina has been obtained. These same measurements present indirect evidence for electrodeposition through 3 nm constrictions in the same templates. A detailed transmission electron microscopy study of mesoporous silica films after Sn deposition is presented. These indicate that it is possible to deposit Sn through the 1.5 nm pores in the mesoporous films, but that the nanowires formed are not stable. Suggestions of why this is the case and how such extreme nanowires could be stabilized are presented.

A Versatile Precursor System for Supercritical Fluid Electrodeposition of Main-Group Materials.

For the first time, a versatile electrolyte bath is described that can be used to electrodeposit a wide range of p-block elements from supercritical difluoromethane (scCH2 F2 ). The bath comprises the tetrabutylammonium chlorometallate complex of the element in an electrolyte of 50×10(-3)  mol dm(-3) tetrabutylammonium chloride at 17.2 MPa and 358 K. Through the use of anionic ([GaCl4 ](-) , [InCl4 ](-) , [GeCl3 ](-) , [SnCl3 ](-) , [SbCl4 ](-) , and [BiCl4 ](-) ) and dianionic ([SeCl6 ](2-) and [TeCl6 ](2-) ) chlorometallate salts, the deposition of elemental Ga, In, Ge, Sn, Sb, Bi, Se, and Te is demonstrated. In all cases, with the exception of gallium, which is a liquid under the deposition conditions, the resulting deposits are characterised by SEM, energy-dispersive X-ray analysis, XRD and Raman spectroscopy. An advantage of this electrolyte system is that the reagents are all crystalline solids, reasonably easy to handle and not highly water or oxygen sensitive. The results presented herein significantly broaden the range of materials accessible by electrodeposition from supercritical fluid and open up the future possibility of utilising the full scope of these unique fluids to electrodeposit functional binary or ternary alloys and compounds of these elements.

Tin, Bismuth, and Tin-Bismuth Alloy Electrodeposition from Chlorometalate Salts in Deep Eutectic Solvents.

The electrodeposition of tin, bismuth, and tin-bismuth alloys from SnII and BiIII chlorometalate salts in the choline chloride/ethylene glycol (1:2 molar ratio) deep eutectic solvent was studied on glassy carbon and gold by cyclic voltammetry, rotating disc voltammetry, and chronoamperometry. The SnII-containing electrolyte showed one voltammetric redox process corresponding to SnII/Sn0. The diffusion coefficient of [SnCl3]-, detected as the dominating species by Raman spectroscopy, was determined from Levich and Cottrell analyses. The BiIII-containing electrolyte showed two voltammetric reduction processes, both attributed to BiIII/Bi0. Dimensionless current/time transients revealed that the electrodeposition of both Sn and Bi on glassy carbon proceeded by 3D-progressive nucleation at a low overpotential and changed to instantaneous at higher overpotentials. The nucleation rate of Bi on glassy carbon was considerably smaller than that of Sn. Elemental Sn and Bi were electrodeposited on Au-coated glass slides from their respective salt solutions, as were Sn-Bi alloys from a 2:1 SnII/BiIII solution. The biphasic Sn-Bi alloys changed from a Bi-rich composition to a Sn-rich composition by making the deposition potential more negative.

Divalent ytterbium complexes with crown and heterocrown ethers.

Several unusual complexes of ytterbium(ii) stabilised by coordination to mixed O4X2-donor macrocyclic ligands (X = O, NH, S or Se) are described. Distorted 8-coordination is evident from the crystal structure of the neutral [YbI2([18]aneO4Se2)], forming the first reported example of Yb(ii)-selenoether coordination.