Oxygen evolution on Ru and RuO2 electrodes studied using isotope labelling and on-line mass spectrometry

Oxide layer formation and O₂ evolution on Ru and RuO₂ films have been studied in sulphuric acid using ¹⁸O labelling together with differential electrochemical mass spectrometry (DEMS). It was shown that ¹⁶O¹⁸O is evolved from a H₂¹⁶O solution on a Ru oxide layer previously formed in H₂¹⁸O. ¹⁶O¹⁸O was also observed when oxygen is evolved on Ru¹⁶O₂ in H₂¹⁸O solution. Consequently, the oxide layer takes part in the oxygen evolution process on both types of electrode. In the case of Ru, formation of RuO₄ was observed when oxygen evolution takes place.     

Oxygen diffusion in SrCe<Subscript>0.95</Subscript>Yb<Subscript>0.05</Subscript>O<Subscript>3−δ</Subscript>

¹⁸O/¹⁶O isotope exchange depth profiling (IEDP) combined with secondary ion mass spectrometry (SIMS) has been used to measure the oxygen tracer diffusivity of SrCe_0.95Yb_0.05O_3– between 800 °C and 500 °C at a nominal pressure of 200 mbar. The values of D* (oxygen tracer diffusion coefficient) and k (surface exchange coefficient) increase steadily with increasing temperature, and the activation energies are 1.13 eV and 0.96 eV, respectively. Oxygen ion conductivities have been calculated using the Nernst–Einstein equation. The transport number for oxide ions at 769 °C, the highest temperature studied, is only ~0.05. Moreover, SrCe_0.95Yb_0.05O_3– has been studied using impedance spectroscopy under dry O₂, wet O₂ and wet H₂ (N₂/10% H₂) atmospheres, over the range 850–300 °C. Above ~550 °C, SrCe_0.95Yb_0.05O_3– shows higher conductivity in dry O₂ than in wet O₂ or wet H₂; below that temperature the results obtained for the three atmospheres are comparable. Dry O₂ shows the highest activation energy (0.77 eV); the activation energies for wet O₂ and wet H₂ are identical (0.62 eV).Abbreviations HTPC high-temperature proton conductor - IEDP isotope exchange depth profiling - SIMS secondary ion mass spectrometryPresented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Does the oxide layer take part in the oxygen evolution reaction on platinum?: A DEMS study

Using ¹⁸O labelling together with differential electrochemical mass spectroscopy (DEMS) it was found that (i) an ¹⁸O containing Pt-oxide layer does not exchange oxygen with H₂¹⁶O; (ii) only ¹⁶O¹⁶O is evolved from H₂¹⁶O on an ¹⁸O containing oxide layer, both in acid and in alkaline solutions. Consequently, the oxide layer does not take part in the oxygen evolution reaction on Pt electrodes.     

Dinuclear vanadium and tetranuclear iron complexes obtained with the open Wells–Dawson [Si2W18O66] tungstosilicate

Reaction of two transition metal cations M (M = V^V, Fe^III) on the open Wells–Dawson anion α-[{K(H₂O)₂}Si₂W₁₈O₆₆]^15– leads to dinuclear and tetranuclear complexes, respectively. The molecular anions [{KV₂O₃(H₂O)₂}(Si₂W₁₈O₆₆)]^11– and [{Fe₄(OH)₆}(Si₂W₁₈O₆₆)]^10– have been structurally characterized by single crystal X-ray diffraction. The oxo/hydroxometallic clusters [KV₂O₃(H₂O)₂]⁵⁺ and [Fe₄(OH)₆]⁶⁺ are included in the pocket between the two subunits of [Si₂W₁₈O₆₆]^16–. The Fe^III atoms of the iron complex can be reduced to Fe^II by a single four-electron step. To cite this article: N. Leclerc-Laronze et al., C. R. Chimie 9 (2006).     

Guest-guest interaction and phase transitions in the natural zeolite laumontite

The zeolite water arrangement in laumontite Ca_3.85Na_0.23K_0.06Al_7.96Si_16.03O₄₈·nH₂O (n=16–18) and leonhardite (n=12–14.4) has been studied from¹H and²⁷Al-NMR data at temperatures of 200–390 K. Close agreement is found between NMR data obtained for samplesn=12 andn=18 and previous X-ray and neutron diffraction data. The H₂O arrangement in the powder sample withn=14.4 and in a laumontite single crystal is represented by a combination of the H₂O arrangements in samples withn=12 andn=18 with increased orientational H₂O disordering. Concentration-type phase transitions are found in the single crystal and then=16 andn=18 samples at 226 and 230 K, and orientational-type phase transitions are found in the sample withn=14.4 at 230 K, and in the sample withn=18 at 293 K. The smooth transformations into an orientationally disordered glassy state arrangement of H₂O in the zeolite channels is found in smaples withn=14.4, 16, and 18 at 300–330 and 305–315 K.     

Structures of Concentrated Sulfuric Acid Determined from Density, Conductivity, Viscosity, and Raman Spectroscopic Data

Addition of water to stoichiometric 100% sulfuric acid increases the density untila maximum results near 87 mole% H₂SO₄. The density and conductivity maximaand viscosity minimum, the latter two near 75 mole%, are direct macroscopicresponses to microscopic quantum mechanical properties of H₃O⁺ and of nearlysymmetric H-bond double-well potentials, as follows: (1) lack of H bonding tothe O atom of H₃O⁺; (2) short, 2.4–2.6 A, O—O distances of nearly symmetricH bonds; and, (3) increased mobility of protons in such short H bonds, give riseto the density maximum via (1) and (2); (1) produces the viscosity minimum;and the conductivity maximum results from (2) and (3). A pronounced minimumnear 1030 cm^–1 in the symmetric SO₃ stretching Raman frequency of HSO₄ ^–,observed near 45 mole% also results from double-well effects involving the shortH bonds of direct hydronium ion—bisulfate ion pair interactions. Estimates of theconcentrations of the (H₃O⁺)(HSO₄ ^–) and (H₂SO₄)(HSO₄ ^–) pair interactions weredetermined from Raman intensity data and are given for compositions between42–100 mole%     

State of the hydroxide ion in water and aqueous solutions

Conclusion Analysis of these experimental facts leads to the conclusion that in water and aqueous solutions of alkali metal hydroxides it is extremely probable that the hydroxide ion exists in the form H₃O₂ ^–. The marked displacement of the extrapolated chemical shift of the proton of the H₃O₂ ^– ion towards weak fields and the displacement of the frequency of the bending vibrations of the OH bond towards higher frequencies for hydroxide solutions indicate strong hydrogen bonding between the OH^– ion and the H₂O molecule. The comparatively low heat of hydration of the OH^– ion (111 cal/mole) compared with the heat of hydration of the H₊ ion (276 cal/mole) cannot, as has been shown, serve as proof that there is no strong electrostatic bond between the OH^– ion and a water molecule. All the heat of hydration is used up in the formation of this bond; this can be regarded as additional confirmation of the hydrophobic nature of the ion produced. The experimental data on the absolute value of the chemical shift of the proton of the H₃O₂ ^– ion indicate the important role played by the excited state of the proton in this complex. This conclusion agrees with the spectroscopic data.M. V. Lomonosov Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 12, No. 6, pp. 969–974, November–December, 1971.     

Zinc(II) oxide solubility and phase behavior in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility is used to investigate the solubility/phase behavior of zinc(II) oxide in aqueous sodium phosphate solutions at temperatures between 17 and 287°C. ZnO solubilities are observed to increase continuously with temperature and phosphate concentration. At higher phosphate concentrations, a solid phase transformation to NaZnPO₄ is observed. NaZnPO₄ solubilities are retrograde with temperature. The measured solubility behavior is examined via a Zn(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria are obtained from a least-squares analysis of the data. The existence of two new zinc(II) ion complexes, Zn(OH)₂(HPO₄)^2– and Zn(OH)₃(H₂PO₄)^2–, is reported for the first time. A summary of thermochemical properties for species in the systems ZnO–H₂O and ZnO–Na₂O–P₂O₅–H₂O is also provided.     

Isotopic oxygen exchange rates between [V18O42]12− and water

Summary From kinetic studies of¹⁸O-exchange between aqueous solutions of K₁₂V₁₈O₄₂ · 16H₂O and water it is concluded that [V₁₈O₄₂]^12– exists as a discrete ion in this medium. The rate of exchange is relatively slow (t_1/2 ca. 6×10⁴s at 0°C) and obeys the McKay equation within the precision obtainable. The sensitivity of the ion to its environment in the solid state, leading to induced exchange, prevented a decision as to whether all oxygens are kinetically equivalent. It is clear, however, that the ions remains intact for long periods in solution in the absence of air.     

An open-shell INDO study of models for the stabilized O− ion in γ-irradiated alkaline ices

Structural models for stabilized O^– in -irradiated alkaline ices are evaluated. INDO calculations on hydrated O^– indicate octahedral coordination and hydrogen bond orientations for the water molecules are preferred. INDO results for hydrated OH^– are compared with crystallographic data for NaOH hydrates: a scaling factor for calculated hydrogen bond lengths is developed and applied to hydrogen bonded O^– models. The hydrated O^– model is closely similar to the hydrated anions in KF · 4H₂O, NaOH · 4H₂O, and NaOH · 7H₂O. A second model is developed, involving H₃O⁺ along with H₂O, in the O^– stabilization shell. Both models are discussed in terms of alkaline ice radiation chemistry.     

Properties of Adsorbed Oxygen Forms on a Defective Ag(111) Surface. DFT Analysis

A cluster model of an Ag12–3O (AS_V) adsorption center using layered silver oxide as a prototype is proposed. The model includes a cation vacancy V on the Ag(111) surface and oxide type subsurface oxygen atoms O_ox. Density functional theory (DFT) (B3LYP/LANL1MB approximation) is used to analyze the electronic structure of AS_V and oxygen adsorption on this center, AS_V+O AS–O. As shown by the calculations, the adsorbed oxygen is associated with the subsurface oxygen atoms O_ss to form structures similar to metal ozonides — Ag–O_ss–O_ep–O_ss–Ag–O_ox–Ag, containing electrophilic oxygen O_ep along with the oxide oxygen O_ox. The optical spectra of the AS_V and AS–O centers were calculated by the configuration interaction method with single excitations (CIS). For AS_V, the most intense absorption bands were obtained in the region 500-700 nm. Oxygen association is accompanied by a sharp decrease in spectrum intensity in the range 600-700 nm and an increase in the intensity of the peak at 500 nm. Vibration frequencies and (IR) intensities were determined for the AS_V and AS–O centers. The AS_V center exhibits a characteristic spectrum in the region 350-500 cm^–1, which corresponds to the frequency spectrum of the surface oxide Ag₂O. For associated oxygen forms (AS–O center), the calculations predict additional peaks around 980, 640 and 230 cm^–1. These peaks are due to the vibrations of the O_ss–O_ep–O_ss structural unit, stabilized at the cation vacancy.     

Investigation of the oxygen evolution reaction on Ti/IrO2 electrodes using isotope labelling and on-line mass spectrometry

Oxygen evolution on Ti/IrO₂ anodes has been studied in 1M HClO₄ electrolyte using ¹⁸O labelling together with differential electrochemical mass spectrometry (DEMS) measurements.It has been shown that during successive cyclic voltammetric measurements in H₂ ¹⁸O containing electrolyte the amount of ¹⁶O₂ (m/z = 32) decreases, with a concomitant increase of ¹⁸O¹⁶O (m/z = 34) after each cycle before reaching a steady state after four cycles. The obtained higher ¹⁶O₂ concentration in the evolved oxygen during the first scans is because ¹⁶O from the IrO₂ film contribute in the oxygen evolution reaction.Analysis of the experimental data has shown that the amount of lattice oxygen, which is involved in the oxygen exchange reaction, is in the order of 1% of the total IrO₂ loading. This is an indication that only the outer surface of the oxide electrode participates in the oxygen evolution reaction.In a second series of experiments it has been demonstrated that oxygen evolution on Ir¹⁶O₂ in H₂¹⁸O containing electrolyte result in the formation of Ir¹⁸O₂.Consequently, we can conclude that the IrO₂ layers participate in the oxygen evolution reaction in acid media at least to a several monolayer extend.     

Determination of oxygen in fluoride glass by proton activation analysis

Oxygen was determined in three kinds of ZrF₄-based fluoride glass [ZrF₄–BaF₂–GdF₃–AlF₃ (ZBGA), ZrF₄–BaF₂–LaF₃–YF₃–AlF₃–LiF–NaF (ZBLYALN) and ZrF₄–BaF₂–LaF₃–YF₃–AlF₃–LiF (ZBLYAL)] used for fabricating optical fiberby¹⁸O(p, n)¹⁸F reaction without significant nuclear interference. The main long life⁹⁶Nb nuclide was produced by the⁹⁶Zr(p,n) reaction in a non-destructive analysis of ZBGA-fluoride glass and reduced by using a coincidence system with Ge(Li) and NaI(T1) detectors. Substoichiometric separation of¹⁸F was also used to determine oxygen in fluoride glass, especially in glass containing yttrium as a component element because the⁸⁹Zr produced by the⁸⁹Y(p,n) reaction is a positron emitter, the same as¹⁸F. It was confirmed that the oxygen concentration in fluoride glass was 13–2460 ppm related to the loss by scattering.     

Study of the equilibrium of formation of arsenic(iii) lacunar heteropolytungstates by Raman spectroscopy

The formation of lacunar heteropolyanions (HPA): [AsW₉O₃₃]^9–, [As₂W₁₉O₆₇(H₂O)]^14–, and [As₂W₂₀O₆₈(H₂O)]^10– in aqueous solutions was investigated by Raman spectroscopy at [Na₂HAsO₃]₀ = 0.1, [Na₂WO₄]₀ = 0.9 mol L^–1 and pH 9.4–1.6. The [AsW₉O₃₃]^9– HPA is characterized by the most intense band ns (W=O) at 948 cm^–1 retaining its position in the pH range from 8.9 to 7.5. Under these conditions, the equilibrium constant of [AsW₉O₃₃]^9– formation from H₂AsO₃ ^– and WO₄ ^2– ions was estimated (logK = 87.0±1.0). The asymmetrical band at 952 cm^–1 corresponding to H_x[As₂W₁₉O₆₇(H₂O)]^(14–x)– shifts to 960 cm^–1 as the pH decreases from 6.5 to 5.5, which is due to the change in HPA protonation. The [As₂W₂₀O₆₈(H₂O)]^10– HPA is formed at pH 3.1—1.6; it is characterized by a band at 972 cm^–1.     

XPS- and AES-investigations of electron and ion beam induced effects on SK16 glass surfaces

Summary Electron beam induced effects in the near surface region of SK16 glass samples (44% SiO₂, 25% B₂O₃, 28% BaO, 3% other) have been studied using Auger electron spectroscopy (AES) with 3 keV primary electrons at different current densities (4.7 mAcm^–2–75 mAcm^–2). It was found that the SiO₂ and B₂O₃ constituents dissociate during electron bombardment to form binding structures which are characteristic for elemental Si and B, respectively. To investigate the influence of the ion beam irradiation on the binding structure, the glass samples were bombarded with Ar⁺ ions of different kinetic energies (0.5 keV–5 keV), followed by XPS analysis. In comparison to the XPS signal of a virgin SK16 surface from a sample fractured in situ under UHV conditions, the FWHM of the photoelectron peaks were found to increase with the bombarding ion energy. Subsequent Auger spectra revealed that the ion bombardment also caused a dissociation of the SiO₂ and B₂O₃ components. Depending on the ion energy, a constant ratio between elemental and oxidized binding form is obtained.     

Laboratory investigations of negative ion molecule reactions of formic and acetic acids: implications for atmospheric measurements by ion-molecule reaction mass spectrometry

Laboratory measurements of gas-phase ion-molecule reactions of several negative ion species with formic and acetic acid have been carried out. A flow reactor operating at a temperature of 293 ± 3 K and total gas pressures of either 3 or 9 hPa was used. The negative reagent ion species investigated included OH⁻, O₂⁻, O₃⁻, CO₄⁻, CO₃⁻, CO₃⁻H₂O, HCO₃⁻H₂O, NO₃⁻, NO₃⁻H₂O, NO₂⁻, and NO₂⁻H₂O. The reactions were found to proceed either via proton transfer or clustering. Our measurements of ion-molecule reactions of negative ions with gaseous formic and acetic acids provide a firm base for quantitative detection of these acidic trace gases in the atmosphere by negative ion ion-molecule reaction mass spectrometry.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

UR-spektroskopische Untersuchungen an zeolithischen Heptagermanaten

Zusammenfassung Der direkte Nachweis von H₃O⁺-Ionen bzw. OH^–-Ionen in zeolithischen Germanaten wird durch UR-spektroskopische Untersuchungen erbracht. Hydronium-Ionen liegen vor beiM(I)₃HGe₇O₁₆·nH₂O sowie bei Ba- und Pb-Zeolithen der FormM(II)_2–x H_2x Ge₇O₁₆·nH₂O, während man in Ba- und Pb-Zeolithen der ZusammensetzungM(II)_2+x Ge₇O₁₆(OH)_2x ·nH₂O Hydroxyl-Ionen beobachtet.

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By IR-spectroscopic investigations of zeolitic germanates of formulaM(I)₃HGe₇O₁₆·nH₂O as well as of Ba- and Pb-zeolites of formulaM(II)_2–x H_2x Ge₇O₁₆·nH₂O the presence of H₃O⁺-ions can be detected. On the other hand inM(II)_2+x Ge₇O₁₆(OH)_2x ·nH₂O (M=Ba, Pb) hydroxyl ions are observed.

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