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.

Halometallate complexes of germanium(II) and (IV): probing the role of cation, oxidation state and halide on the structural and electrochemical properties

The Ge(IV) chlorometallate complexes, [EMIM]2 [GeCl6 ], [EDMIM]2 [GeCl6 ] and [PYRR]2 [GeCl6 ] (EMIM=1-ethyl-3-methylimidazolium; EDMIM=2,3-dimethyl-1-ethylimidazolium; PYRR=N-butyl-N-methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single-crystal X-ray diffraction. The imidazolium chlorometallates exhibited significant CH⋅⋅⋅Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution (1) H NMR data also showed cation-anion association. The synthesis and characterisation of Ge(II) halometallate salts [EMIM][GeX3 ] (X=Cl, Br, I) and [PYRR][GeCl3 ], including single-crystal X-ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic-voltammetry experiments on the Ge(IV) species in CH2 Cl2 solution showed two distinct, irreversible reduction waves attributed to Ge(IV) -Ge(II) and Ge(II) -Ge(0) , whereas the Ge(II) species exhibited one irreversible reduction wave. The potential for the Ge(II) -Ge(0) reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from Ge(IV) to Ge(II) does have an effect; for a given cation, reduction from the [GeCl3 ](-) salts occurred at a less cathodic potential. The nature of the halide co-ligand also has a marked influence on the reduction potential for the Ge(II) -Ge(0) couple, such that the reduction potentials for the [GeX3 ](-) salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.

Surface State Trapping and Mobility Revealed by Junction Electrochemistry of Nano-Cr2O3

Hydrous chromium oxide nanoparticles (~15 nm diameter) are assembled from a colloidal solution onto tin-doped indium oxide (ITO) substrates by layer-by-layer electrostatic deposition with aqueous carboxymethyl-cellulose sodium salt binder. Calcination produces purely inorganic mesoporous films (average thickness increase per layer of 1 nm) of chromia Cr2O3. When immersed in aqueous carbonate buffer at pH 10 and investigated by cyclic voltammetry, a chemically reversible oxidation is observed because of a conductive layer at the chromia surface (formed during initial potential cycling). This is attributed to a surface CrIII/IV process. At more positive potentials higher oxidation states are accessible before film dissolution. The effects of film thickness and pH on voltammetric responses are studied. X-Ray photoelectron spectroscopy (XPS) evidence for higher chromium oxidation states is obtained. ITO junction experiments are employed to reveal surface conduction by CrIII/IV and CrIV/V ‘mobile surface states’ and an estimate is obtained for the apparent CrIII/IV charge surface diffusion coefficient Dapp = 10–13 m2 s–1. The junction experiment distinguishes mobile surface redox sites from energetically distinct deeper-sitting ‘trapped states’.