Search

Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co3Sb4O6F6 and the new compound CoSbO4. The compounds express large differences in their morphology: CoSbO4 grows as thin needles whereas Co3Sb4O6F6 grows as larger facetted crystals. Despite the smaller surface area the latter compound shows a better catalytic performance. When the compound Co3Sb4O6F6 was used it gave a low increase of +0.028 mV h−1 at an overpotential of η=472 mV after 10 h and a stability of +0.48 mV h−1 at an overpotential of η=488 mV after 60 h. The leakages of Co and Sb were negligible and only <0.001 at % Co and approximately 0.02 at % Sb were detected in the electrolyte. [ABSTRACT FROM AUTHOR]

In this work, the kinetics of barium sulfate recrystallization has been studied in acidic 0.01 mol dm sodium sulfate solution using Ra and Ba tracers at very low total radium concentration, i.e. less than 10 mol dm. It was found that the system follows the homogeneous recrystallization model and that recrystallization rates, inferred by the decrease of Ra and Ba in the aqueous solution, are fast. Therefore, even at very low concentrations, below the solubility limit, radium will be retained by barium sulfate-a mineral present in the deep underground repository. [ABSTRACT FROM AUTHOR]

The two dimethyl sulfoxide solvated rhodium(iii) compounds, [Rh(dmso-κO)5(dmso-κS)](CF3SO3)3(1& 1*at 298 K and 100 K, respectively) and [Rh(dmso-κO)3(dmso-κS)2Cl](CF3SO3)2(2), crystallize with orthorhombic unit cells in the space group Pna21(No. 33), Z= 4. In the [Rh(dmso)6]3+complex with slightly distorted octahedral coordination geometry, the Rh–O bond distance is significantly longer with O transto S, 2.143(6) Å (1) and 2.100(6) Å (1*), than the mean Rh–O bond distance with O transto O, 2.019 Å (1) and 2.043 Å (1*). In the [RhCl(dmso)5]3+complex, the mean Rh–O bond distance with O transto S, 2.083 Å, is slightly longer than that for O transto Cl, 2.067(4) Å, which is consistent with the transinfluence DMSO-κS> Cl > DMSO-κOof the opposite ligands. Raman and IR absorption spectra were recorded and analyzed and a complete assignment of the vibrational bands was achieved with support by force field calculations. An increase in the Rh–O stretching vibrational frequency corresponded to a decreasing trans-influence from the opposite ligand. The Rh–O force constants obtained were correlated with the Rh–O bond lengths, also including previously obtained values for other M(dmso)63+complexes with trivalent metal ions. An almost linear correlation was obtained for the MO stretching force constants vs.the reciprocal square of the MO bond lengths. The results show that the metal ion-oxygen bonding of dimethyl sulfoxide ligands is electrostatically dominated in those complexes and that the stretching force constants provide a useful measure of the relative trans-influence of the opposite ligands in hexa-coordinated Rh(iii)-complexes. [ABSTRACT FROM AUTHOR]

Water Splitting Catalytic water splitting is a very active research field, and many organic and inorganic catalysts have been tested for the oxidation reaction that is more challenging to catalyse at a low overpotential than the reduction reaction. Metalorganic catalysts most often survive only for short time period, so inorganic compounds are in general more promising. Several promizing oxide compounds containing cobalt have previously been identified and studied. To investigate direct synthesis of catalytically active compounds and their long time behavior, H. Svengren et al. have synthesized crystals of Co3Sb4O6F6 and the new compound CoSbO4 directly onto carbon electrodes. In their Full Paper on page 568 ff., they show the importance of making long‐term stability tests when ranking the performance of different catalysts. [ABSTRACT FROM AUTHOR]

Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co 3 Sb 4 O 6 F 6 and the new compound CoSbO 4 . The compounds express large differences in their morphology: CoSbO 4 grows as thin needles whereas Co 3 Sb 4 O 6 F 6 grows as larger facetted crystals. Despite the smaller surface area the latter compound shows a better catalytic performance. When the compound Co 3 Sb 4 O 6 F 6 was used it gave a low increase of +0.028 mV h -1 at an overpotential of η=472 mV after 10 h and a stability of +0.48 mV h -1 at an overpotential of η=488 mV after 60 h. The leakages of Co and Sb were negligible and only <0.001 at % Co and approximately 0.02 at % Sb were detected in the electrolyte., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The aqua ions of palladium(II) and platinum(II) undergo extremely slow hydrolysis in strongly acidic aqueous solution, resulting in polynuclear complexes. The size and structures of these species have been determined by EXAFS and small angle X-ray scattering, SAXS. For palladium(II), the EXAFS data show that the Pd-O and Pd···Pd distances are identical to those of crystalline palladium(II) oxide, but the intensities of the Pd···Pd distances in the Fourier transform at 3.04 and 3.42 Å are significantly lower compared to those of crystalline PdO. Furthermore, no Pd···Pd distances beyond 4 Å are observed. These observations strongly indicate that the polynuclear palladium(II) complexes are oxido- and hydroxido-bridged species with the same core structure as solid palladium(II) oxide. Based on the number of Pd···Pd distances, as derived from the EXAFS data, their size can be estimated to be approximately two unit cells, or ca. 1.0 nm(3). For platinum(II), EXAFS data of the polynuclear species formed in the slow hydrolysis process show Pt-O and Pt···Pt distances identical to those of amorphous platinum(II) oxide, precipitating from the solution studied. The Pt···Pt distances are somewhat different from those reported for crystalline platinum(II) oxide. The polynuclear platinum(II) complexes have a similar structure to the palladium ones, but they are somewhat larger, with an estimated diameter of 1.5-3.0 nm. It has not been possible to precipitate any of these species by ultracentrifugation. They are detectable by SAXS, indicating diameters between 0.7 and 2 nm, in excellent agreement with the EXAFS observations. The number of oxido- relative to hydroxido bridges will increase with increasing size of the complex. The charge of the complexes will remain about the same, +4, at growth, with approximate formulas [Pd10O4(OH)8(H2O)12](4+) and [Pt14O8(OH)8(H2O)12](4+) for complexes with a size of 2 and 3 unit cells of the corresponding solid metal oxide, respectively. Their high ionic charge in acidic aqueous solution will result in a stabilizing hydration shell.

The speciation in the mixed Th(IV)-Fe(III) system has been studied in aqueous solution in the pH range of 2.0-4.8. In the individual systems iron(III) and thorium(IV) hydrolyze easily and hydrolysis products precipitate at approximately pH ≥ 2.0 and 4.0, respectively, at the metal concentrations used in this study, 0.02-0.05 mol dm(-3). In the mixed Th(IV)-Fe(III) system precipitation of ferrihydrite takes place after months of storage at low pH values, 2.0 (six-line ferrihydrite) and 2.3 (two-line ferrihydrite), as identified by X-ray powder diffraction. In the pH range 2.9-4.5 no precipitation was observed after 24 months. Two thorium(IV)-iron(III) solutions with pH = 2.9, C(Th) = 0.02 and 0.05 mol dm(-3) and C(Fe) = 0.02 mol dm(-3), were studied by extended X-ray absorption fine structure, EXAFS, using the Fe K and Th L(3) edges, and a third solution with pH = 2.9 and C(Th) = C(Fe) = 0.40 mol dm(-3) by large angle X-ray scattering, LAXS, to determine the structure of the predominating species. A heteronuclear hydrolysis complex with the composition [Th(2)Fe(2)(μ(2)-OH)(8)(H(2)O)(12)](6+) is proposed to form in solution, with Th···Th, Th···Fe and Fe···Fe distances of 3.94(2) and 3.96(2), 3.41(3) and 3.43(2), 3.04(2) and 3.02(4) Å, as determined by EXAFS and LAXS, respectively.

The two dimethyl sulfoxide solvated rhodium(III) compounds, [Rh(dmso-κO)(5)(dmso-κS)](CF(3)SO(3))(3) (1 & 1* at 298 K and 100 K, respectively) and [Rh(dmso-κO)(3)(dmso-κS)(2)Cl](CF(3)SO(3))(2) (2), crystallize with orthorhombic unit cells in the space group Pna2(1) (No. 33), Z = 4. In the [Rh(dmso)(6)](3+) complex with slightly distorted octahedral coordination geometry, the Rh-O bond distance is significantly longer with O trans to S, 2.143(6) Å (1) and 2.100(6) Å (1*), than the mean Rh-O bond distance with O trans to O, 2.019 Å (1) and 2.043 Å (1*). In the [RhCl(dmso)(5)](3+) complex, the mean Rh-O bond distance with O trans to S, 2.083 Å, is slightly longer than that for O trans to Cl, 2.067(4) Å, which is consistent with the trans influence DMSO-κS > Cl > DMSO-κO of the opposite ligands. Raman and IR absorption spectra were recorded and analyzed and a complete assignment of the vibrational bands was achieved with support by force field calculations. An increase in the Rh-O stretching vibrational frequency corresponded to a decreasing trans-influence from the opposite ligand. The Rh-O force constants obtained were correlated with the Rh-O bond lengths, also including previously obtained values for other M(dmso)(6)(3+) complexes with trivalent metal ions. An almost linear correlation was obtained for the MO stretching force constants vs. the reciprocal square of the MO bond lengths. The results show that the metal ion-oxygen bonding of dimethyl sulfoxide ligands is electrostatically dominated in those complexes and that the stretching force constants provide a useful measure of the relative trans-influence of the opposite ligands in hexa-coordinated Rh(III)-complexes.