Application of Protonic Acid-Doped Silica Gels to Electric Double-Layer Capacitors

Silica gels doped with several protonic acids such as HClO₄, H₂SO₄ and H₃PO₄ have been prepared by the sol-gel method and totally solid electric double-layer capacitors have been successfully fabricated using the highly proton-conductive silica gels as an electrolyte and activated carbon powder (ACP) hybridized with the silica gels as a polarizable electrode. It was found that the addition of HClO₄, which had the highest value of acid dissociation constant among these three acids, most effectively increased the proton conductivity of the resultant acid-doped silica gels. Tablets of the HClO₄-doped silica gels exhibited conductivities as high as 10^–5–10^–2 S cm^–1 at room temperature in dry N₂ atmosphere. One of the capacitors fabricated using the protonic acid-doped silica gels had a capacitance of 44 F/(gram of total ACP in the capacitor), which was comparable to those of conventional capacitors using liquid electrolytes.     

Synthesis and Properties of the Mixed Hydrated Oxides V2?yWyO5 + δ < eqid2 > nH2O

Compounds of the general formula V_{2 − y}W_yO_{5 + δ} < eqid3 > nH₂O (0 < y ≤ 0.25) with the layered structure of polyvanadic acid V₂O₅ < eqid4 > nH₂O (H₂V₁₂O_{31 − δ} < eqid5 > nH₂O) have been prepared from peroxide solutions using the sol–gel process. The samples contain up to 5–8 wt% vanadium (IV). The water content changes within the range of 0.7 ≤ n ≤ 1.5 in depending on tungsten concentration. The V_{2 − y}W_yO_{5 + δ} < eqid6 > nH₂O (y ≤ 0.125) form the thin films described an interlayer distance of 11.60 ± 0.05 Å. The thermal properties, IR, and X-ray photoelectron spectra of the compounds synthesized have been studied. The thermal stability of the phases increases with the rising of tungsten content. The dehydration finishes with the forming solid solution V_2−yW_yO₅ and WO₃. The electrical conductivity of V_2−yW_yO_{5 + δ} < eqid7 > nH₂O (0 < y ≤ 0.25) powders was measured between 293 and 473 K at a relative humidity of 12%. The activation energy of conduction is independent upon the W content and equals 0.22–0.24 eV. Partial substitution of vanadium for tungsten was found to reduce the conductivity of the phases. The conductivity of the films increases with the increasing of relative air humidity and is governed by proton diffusion across the V-O-W layers.     

Sr2NiMoO6−δ as anode material for LaGaO3-based solid oxide fuel cell

The double-perovskite Sr₂NiMoO_6−δ (SNMO) was investigated as an anode material of a solid oxide fuel cell (SOFC). With a 300 μm thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−σ (LSGM) disk as electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ as the cathode, the SNMO anode showed power densities of 819 mW cm⁻² in hydrogen at 1123 K. Moreover, there was no buffer layer between anode and electrolyte, which would reduce design techniques and save design cost. After test no chemical reaction was discovered between anode and electrolyte. The anode exhibited good conductivity and the value was around 60 S cm⁻¹ in H₂. Also it had almost linear thermal expansion from room temperature to 1253 K and the average thermal expansion coefficient was about 12.14 × 10⁻⁶ K⁻¹, which was quite close to that of La_0.9Sr_0.lGa_0.8Mg_0.2O₃ (12.17 × 10⁻⁶ K⁻¹) electrolyte.     

An oxygen deficient fluorite with a tunnel structure: Bi8La10O27

A new lanthanum bismuth oxide, Bi₈La₁₀O₂₇, has been synthesized. It crystallizes in the Immm space group with the following parameters: a = 12.079 (2) Å, b = 16.348 (4) Å, c = 4.0988 (5) Å. Its structure was determined from powder X-ray and neutron diffraction data. It can be described as an oxygen deficient fluorite superstructure (a ≈ 3a_F/√2, b ≈ 3a_F, c ≈ a_F/√2) in which bismuth and lanthanum, as well as oxygen vacancies, are ordered. The structure consists of fully occupied (110) or lanthanum planes (La) which alternate with mixed planes and fully occupied oxygen planes (A) which alternate with two sorts of oxygen deficient (110) or planes (B and C) according to the sequence . The anionic distribution determines tunnels where the bismuth ions are located, forming diamond-shaped based tunnels. The coordination of bismuth and lanthanum is discussed. The high thermal factor of some oxygen atoms suggests that this oxide exhibits ionic conductivity.     

Electrochemical hydrogen evolution in hydroxide hydrate down to 110 K

Electrochemical hydrogen evolution was studied at an Au electrode in liquid and solid tetramethylammonium hydroxide hydrate (CH₃)₄NOH·10H₂O (m.p. 253 K) down to almost 110 K. The current–potential relationships were obtained by slow scan voltammetry. The lowering of temperature causes substantial decrease of the slope of linear Tafel plots. This was interpreted as a decrease of charge transfer coefficient from 0.37 at room temperature to 0.01 at 113 K. The activation energy of the electrochemical hydrogen evolution at temperatures below 200 K is equal to 0.25±0.03 eV and is larger than the activation energy of the electrolyte conductivity.     

The defect solid solution Na7/8(Fe7/8+xTi9/8−2xSbx)O4 (0 ≤ x ≤ 1/3): Evidence of Na mobility in the tunnels of a quadruple rutile-chain structure

A new defect solid solution, the series Na_7/8(Fe^III_7/8+xTi^IV_9/8−2xSb^V_x)O₄, was synthesized. Its homogeneity range is rather wide: 0 <- x ≤ 0.33. The incorporation of Sb^V gives rise to a progressive increase of the parameters of the orthorhombic unit cell. X-ray powder structure calculations point to a partial occupancy of the large double tunnels in a quadruple rutile-chain structure. A significant ordering of cations over the octahedral framework is observed, owing to a Ti^IV---Sb^V segregation. Electrical measurements emphasize a cationic conductivity, mainly related to a 1D motion of Na^I cations. A transition from a low activation energy process—E_A ≤ 0.20 eV—to a high activation energy one—E_A ≈ 0.75 eV—systematically occurs at T ≈ 440°C, independent of the Sb^V concentration. A possible skew motion from a half tunnel to another one is proposed as a tentative explanation of the high-temperature conductivity mechanism.     

XPS spectroscopic study of potentiostatic and galvanostatic oxidation of Pt electrodes in H2SO4 and HClO4

The surface oxides produced from potentiostatic and galvanostatic oxidation of Pt electrodes in HClO₄ and H₂SO₄ are examined using X-ray photoelectron spectroscopy. The oxide I species produced as the initial oxidation product by successively more anodic potentiostatic oxidation in 0.2 M HClO₄ is found to have a Pt²⁺ oxidation state, a binding energy characteristic of neither PtO, Pt(OH)₂ or PtO₂, and a limiting thickness of 8 Å. Galvanostatic oxidation in HClO₄ and H₂SO₄ is found to produce PtO₂·H₂O as an unlimiting growth oxide or a limiting growth oxide layer depending on the concentration of the acid electrolyte. The incorporation of the acid electrolyte anion in the surface layer is shown to have an effect on which type of oxide layer is produced. X-ray decomposition and chemical modification by Ar⁺ stripping are shown to produce chemical artifacts complicating any interpretation of a Pt oxide surface layer.     

A novel anode supported BaCe0.4Zr0.3Sn0.1Y0.2O3−δ electrolyte membrane for proton conducting solid oxide fuel cells

A novel BaCe_0.4Zr_0.3 Sn_0.1Y_0.2O_3−δ (BSY) electrolyte membrane with thickness of 20 μm was fabricated on NiO-based anode substrate via a one-step all-solid-state method followed by a co-sintering at 1450 °C for 5 h. Chemical stability test demonstrated that BSY electrolyte showed adequate chemical stability against CO₂ and H₂O at intermediate temperature. Besides, the doping of Sn also enhanced the conductivity in humidified hydrogen. With Nd_0.7Sr_0.3MnO_3−σ cathode and hydrogen fuel, the fuel cell generated maximum output of 320, 185 and 105 mW cm⁻² at 700, 650 and 600 °C, respectively. The interfacial resistance of the fuel cell was studied under open circuit conditions and the short-term cell performance also confirmed the stability of BSY electrolyte membrane.     

Solid-liquid phase equilibria in the system water + methanol + MgSO4·7H2O + MnSO4·4H2O

The solubilities and complex phase equilibria for the system of MnSO₄·4H₂O + MgSO₄·7H₂O + H₂O + CH₃OH were determined at the temperatures 291.2 and 301.2 K over the methanol mole fraction range of 0.00–0.12.The solubility data were used for modelling with the modified extended electrolyte non-random two-liquid equation. The salting-out effect of MgSO₄ and methanol on the solubilities of two manganese salts (MnSO₄·H₂O and MnSO₄·4H₂O) are represented in the several thermodynamic figures as a function of temperature. The solventing-out effect was stronger than the salting-out effect, which results in a decrease of the solubilities of manganese, salts even though the solubility of MnSO₄·H₂O decreased and solubility of MgSO₄·4H₂O increased as temperature increased.     

Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

Système ternaire : H2O–Fe(NO3)3–Co(NO3)2 isotherme : 30 °C

Ternary system: H₂O–Fe(NO₃)₃–Co(NO₃)₂ isotherm: 30 °C. The H₂O–Co(NO₃)₂ binary system has been investigated in the –28 to 50 °C temperature range. The solid–liquid equilibria of the ternary system H₂O–Fe(NO₃)₃–Co(NO₃)₂ were studied by using a synthetic method based on conductivity measurements. One isotherm is established at 30 °C, and the stable solid phases that appear are iron nitrate nonahydrate: Fe(NO₃)₃·9 H₂O, iron nitrate hexahydrate: Fe(NO₃)₃·6 H₂O, cobalt nitrate hexahydrate: Co(NO₃)₂·6 H₂O, and cobalt nitrate trihydrate: Co(NO₃)₂·3 H₂O. To cite this article: B. El Goundali et M. Kaddami, C. R. Chimie 9 (2006).     

Kinetics and mechanism of “reduced CO2” electrooxidation on electrodispersed platinum in different acid solutions

The electrooxidation of “reduced CO₂” electroadsorbates on electrodispersed platinum electrodes has been investigated in 0.05 M HClO₄, 1 M HClO₄, 0.5 M H₂SO₄ and 1 M H₃PO₄ at 25° C through voltammetry and potential step techniques. The overall reaction comprises three distinguishable processes, namely a first order triggering process, and two second order surface processes. The latter are influenced remarkably by the solution composition (anions). The second order reaction mechanism involves two distinguishable “ reduced CO₂” electroadsorbates which react independently with the OH species formed from H₂O electrooxidation on the bare platinum sites as the reaction proceeds. An interaction term has to be included in the rate equations to account for the experimental results. The mechanistic interpretation accounts for the values of the number of electrons per site ranging from 1 to 2.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

Thermodynamic representation of the NaCl + Na2SO4 + H2O system with electrolyte NRTL model

A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H₂O binary, the Na₂SO₄ + H₂O binary and the NaCl + Na₂SO₄ + H₂O ternary. The NRTL binary parameters for pairs H₂O-(Na⁺, Cl⁻) and H₂O-(Na⁺, SO₄²⁻), and the aqueous phase infinite dilution heat capacity parameters for ions Cl⁻ and SO₄²⁻ are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H₂O binary and the Na₂SO₄ + H₂O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl_(s), NaCl·2H₂O_(s), Na₂SO_4(s) and Na₂SO₄·10H₂O_(s) are obtained by fitting experimental data on solubilities of NaCl and Na₂SO₄ in water. The NRTL binary parameters for the (Na⁺, Cl⁻)-(Na⁺, SO₄²⁻) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na₂SO₄ + H₂O ternary.     

Oxygen evolution on nanocrystalline RuO2 and Ru0.9Ni0.1O2−δ electrodes – DEMS approach to reaction mechanism determination

The mechanism of the oxygen evolution on RuO₂ and Ru_0.9Ni_0.1O_2−δ anodes was studied in 0.1 M HClO₄ using ¹⁸labeling combined with differential electrochemical mass spectrometry (DEMS). It was shown that the mechanism of the oxygen evolution is potential sensitive. At potentials negative to 1.12 V vs. SCE all the evolved oxygen originates from the electrolyte solution. At higher potentials an additional mechanism involving an exchange of the oxygen between electrolyte and electrocatalyst starts to apply. The extent of this oxygen exchange mechanism reflects the chemical composition of the electrocatalyst and is significantly higher at Ru_0.9Ni_0.1O_2−δ electrodes.     

Hydrothermal Synthesis and Crystal Structure of Barium Hewettite: BaV6O16·nH2O

Ba analogues of hewettite (CaV₆O₁₆·9H₂O) were synthesized by the hydrothermal methods. The compounds exhibit two phases formulated by BaV₆O₁₆·nH₂O and Ba_1+xV₆O₁₆·nH₂O (x≈0.2,n≈3), and the structure of BaV₆O₁₆·nH₂O has been determined from a single crystal study. It crystallizes in the orthorhombic systemPnmmwitha=12.162(3) Å,b=10.841(4) Å,c=17.035(4) Å, andZ=6 and the structure refinements led toR=0.066 andR_w=0.076 for 1480 reflections withI>3σ(I). The structure is basically analogous to that ofγ-Li_1+xV₃O₈or CaV₆O₁₆·9H₂O, consisting of V₆O₁₆layers and interstitial hydrated Ba atoms. The V₆O₁₆layers stack along thecaxis with 8.518-Å spacing which is half of thecaxis; adjacent layers are mirror images of each other. Ba atoms reside in three kinds of sites with totally different oxygen coordinations. Their interlayer distributions result in another long period along thebaxis which is triple the ordinary 3.6-Å period of the hewettite compounds. This is the first single-crystal structural study of the synthetic hewettite compounds.     

Schwingungsspektren und normalkoordinatenanalyse von CF3,-verbindungen : XXVI. Molekülstrukturen und schwingungsspektren von α-CF3HgN3 und CF3HgNCO

The crystal structures of the isostructural compounds α-CF₃HgN₃ (I) and CF₃HgNCO (II) were determined by X-ray methods. Centrosymmetric dimers are formed with weak Hg---n′ bonds of 2.74(2) Å in I and 2.88(2) Å in II. The Hg---N distance and Hg---N---N angle are 2.02(2) Å and 127(2)° in the monomeric fragment of I, the corresponding values in II are 2.03(2) Å and 137(2)°. Raman and, in part, IR spectra of both compounds in the solid state were recorded and assigned for Cs and C_2h symmetry of the monomers and dimers, respectively. A normal coordinate analysis proved that the stretching vibrations of the (HgN)₂ four-membered ring appeared at ≈400 and ≈75 cm^-1; the force constants amounted to ≈2.0 for the short and to ≈0.25 X 10² N/m for the long HgN bonds.     

Structure Determination of Sr1.25Bi0.75O3 and Sr0.4K0.6BiO3 as a Function of Temperature from Synchrotron X-Ray Powder Diffraction Data

The structures of Sr_1.25Bi_0.75O₃ and superconducting Sr_0.4K_0.6BiO₃ have been determined from synchrotron X-ray powder diffraction data between 4 K and the decomposition temperature, at 973 and 573 K, respectively. The symmetry remains monoclinic (a≈ a_p, b≈ a_p, c≈2a_p, β≈90°, P2₁/n space group with two Bi sites allowing charge localization) for the undoped compound, and tetragonal (a≈ a_p, c≈2a_p, I4/mcm space group with a unique Bi site implying a charge delocalization) for the K-doped phase, over the whole temperature range. In both cases the distortion from cubic symmetry decreases as temperature increases. Above 400 K, Sr_0.4K_0.6BiO₃ progressively loses oxygen until it reaches the Sr_0.4K_0.6BiO_2.5 stoichiometry, after which it decomposes.     

RbAuUSe3, CsAuUSe3, RbAuUTe3, and CsAuUTe3: Syntheses and structure; magnetic properties of RbAuUSe3

The compounds RbAuUSe₃, CsAuUSe₃, and RbAuUTe₃ were synthesized at 1073 K from the reactions of U, Au, Q, and A₂Q₃ (A=Rb or Cs; Q=Se or Te). The compound CsAuUTe₃ was synthesized at 1173 K from the reaction of U, Au, Te, and CsCl as a flux. These isostructural compounds crystallize in the KCuZrS₃ structure type in space group Cmcm of the orthorhombic system. The structure consists of layers that contain nearly regular UQ₆ octahedra and distorted AuQ₄ tetrahedra. The infinite layers are separated by bicapped trigonal prismatic A cations. The magnetic behavior of RbAuUSe₃ deviates significantly from Curie–Weiss behavior at low temperatures. For T>200 K, the values of the Curie constant C and the Weiss constant θ_p are 1.82(9) emu K mol⁻¹ and −3.5(2)×10² K, respectively. The effective magnetic moment μ_eff is 3.81(9) μ_B. Formal oxidation states of A/Au/U/Q may be assigned as +1/+1/+4/−2, respectively.