Thermal Behaviour of Titania Based Materials: Mathematical modeling of emanation thermal analysis results

Emanation thermal analysis (ETA) was used in the characterization of microstructure changes during heating ofprecursors for the titania based materials: hydrous titania, TiO₂nH₂O (n=0.58) and hydrous titania containing 10% ruthenia,(TiO₂)_0.9(RuO₂)_0.1nH₂O (n=1.5). The precursors were heated at the constant rate 6 K min^–1 in argon flow in the range 20–1000°C. ETA results were compared with the theoretical curves simulating the temperature dependences of radon release rate, E(T). Two mathematical models were used in the simulation. The models considered either subsequent or simultaneous solid state processes (i.e. dehydration, crystallization orphase transition, resp.) during thermal treatment of titania based materials. A good agreement was found between experimental and the simulated ETA curves. The results of ETA were confirmed by XRD patterns of intermediate products of thermal treatment of the precursors.This revised version was published online in November 2005 with corrections to the Cover Date.     

RuO2修饰纳米多孔Ni-Mo复合电极及其电催化析氢性能

采用脱合金化结合胶体聚沉的方法制备了纳米多孔Ni/RuO_2、Ni-Mo/RuO_2复合电极材料。通过X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、透射电镜(TEM)对电极材料的物相、元素组态、形貌结构、孔径大小和结晶度进行表征,并通过线性扫描伏安、交流阻抗以及循环伏安等方法测试多孔电极的电催化析氢性能。分析结果显示:RuO_2由于聚沉作用包覆在Ni基合金的骨架表面。Mo的加入使Ni-Mo合金非晶化的同时,促使其骨架细化,形成双连续的纳米多孔结构。Mo与RuO_2的加入以及Mo含量的增加均提高了电催化析氢性能。纳米多孔Ni_(2.5)Mo_(2.5)/RuO_2复合电极在50 mA·cm~(-2)的电流密度下析氢过电位为182 mV。     

Electrocatalytic Phenol Oxidation on Mixed Pt‐RuO2 Nanoparticle Modified Electrode

Abstract

Nanoscale Pt/RuO₂ colloid with carbon paste support was synthesized and used to prepare a modified electrode for phenol detection. The results showed that the Pt/RuO₂ catalyst has high activity for electrooxidation of phenol with reduced intermediate polymerization due to its significantly low potential for phenol oxidation. The detection limit was as low as 10^?9 mol L^?1 for the polishable Pt/RuO₂/C paste electrode with good reproducibility.     

Reactivity of RuO species in RuO2/CeO2 catalysts prepared by a wet reduction method

The paper deals with the reactivity of RuO₂/CeO₂ prepared by a wet reduction method: ruthenium was supported on Ce(OH)₃, which was precipitated by alkali-hydrolysis of Ce(NO₃)₃, under a reduction condition with formaldehyde at pH 11 and transformed into RuO₂/CeO₂ catalysts by calcination in air at 773 K. The catalysts were investigated with an ESR technique and were tested for oxidation of propylene. They had no ESR signals by themselves at room temperature, but gave two sets of anisotropic signals upon contact with propylene. These signals were derived from the reaction products between RuO and propylene. The intensities of the signals were kept unchanged at room temperature for more than 1 h in the absence of excess propylene. The signals decayed in the presence of excess propylene and the upfield signal decayed more rapidly. A prior heating of the catalyst in air at 473 K or above caused the increase in the intensity of the upfield signal. The time course of the signal changes discriminated between ethylene and olefins with allylic hydrogen toward RuO species.     

On the charge storage mechanism at RuO<Subscript>2</Subscript>/0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> interface

Comparative study of capacitative properties of RuO₂/0.5 M H₂SO₄ and Ru/0.5 M H₂SO₄ interfaces has been performed with a view to find out the nature of electrochemical processes involved in the charge storage mechanism of ruthenium (IV) oxide. The methods of cyclic voltammetry and scanning electron microscopy (SEM) were employed for the investigation of electrochemical behavior and surface morphology of RuO₂ electrodes. It has been suggested that supercapacitor behavior of RuO₂ phase in the potential E range between 0.4 and 1.4 V vs reference hydrogen electrode (RHE) should be attributed to double-layer-type capacitance, related to non-faradaic highly reversible process of ionic pair formation and annihilation at RuO₂/electrolyte interface as described by following summary equation:

Ni-Co/RuO2复合电极的制备及其电催化析氢性能

采用快速凝固结合去合金化的方法制备纳米多孔Ni-Co合金,利用RuO_2对Ni-Co合金进行表面修饰,通过X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)对多孔材料进行物相分析和形貌表征,并通过线性扫描伏安法、多电位阶跃法、交流阻抗法和恒电流电解法测试多孔电极的电催化析氢性能。结果表明,Ni-Co/RuO_2复合电极材料在50 mA·cm~(-2)电流密度下析氢过电位为180 mV,析氢过程由Volmer-Heyrovsky步骤控制,交换电流密度为4.42 mA·cm~(-2),经10 h恒电流电解后电位仅增加20 mV,表现出良好的析氢稳定性。     

Surface and electrocatalytic properties of well-defined and vicinal RuO2 single crystal faces

The kinetics of Cl₂ evolution from concentrated NaCl solutions on the (110) and (230) faces of RuO₂ single crystals has been investigated by determining the Tafel slope, the stoichiometric number and the reaction orders with respect to Cl^– and H⁺. The experimental parameters suggest that the mechanism is presumably similar to that put forward earlier by Krishtalik [51] for RuO₂ layers, but a step common to oxygen evolution, like the case of polycrystalline samples, is present only with the (230) face. Reasons for this difference and for the apparent lower activity of the (110) face with respect to the (230) are discussed. A detailed analysis of the surface behavior of the two faces in Cl^– free acid and alkaline solutions has also been carried out by cyclic voltammetry.Dedicated to Professor G. Horanyi on the occasion of his 70th birthday     

An EQCM investigation of charging RuO2 thin films prepared by the polymeric precursor method

An electrochemical quartz crystal microbalance (EQCM) study of RuO₂ thin films, prepared by the sol-gel precursor method, is presented. The X-ray diffraction (XRD) analysis demonstrates that RuO₂ films were crystallized in the rutile phase and scanning electron microscopy investigations indicated the formation of a smooth surface. Cyclic voltammetry and EQCM studies were performed simultaneously in order to investigate the charging processes of the RuO₂ films in 0.1 M HClO₄. The voltammetric and mass versus potential responses present three well-defined regions associated with the RuO₂ redox couples. Based on these results and on the mass-charge relationships, the corresponding charging mechanisms are proposed. In the potential region governed by the Ru³⁺/Ru⁴⁺ redox couple, the mass-charge relation can be associated with the double-injection of protons and electrons. The other regions correspond to water release and oxyhydroxide species formation during charging.     

Kinetics for the Oxygen Evolution Reaction and Application of the Ti/SnO<Subscript>2</Subscript> + RuO<Subscript>2</Subscript> + MnO<Subscript>2</Subscript> Electrode

A Ti/SnO₂ + RuO₂ + MnO₂ electrode was prepared by thermal decomposition of their salts. Results from SEM and XPS analyses, respectively, indicate that the coating layer exhibits a compact structure and the oxidation state of Mn in the coating layer is +IV. The experimental activation energy for the oxygen evolution reaction, which increased linearly with increasing overpotential, is about 8 kJ⋅mol⁻¹ at the equilibrium potential (η=0). The electrocatalytic characteristics of the anode are discussed in terms of ligand substitution reaction mechanisms (Sn1 and Sn2). It was found that the transition state for oxygen evolution at the anode in acidic solution follows a dissociative mechanism (Sn1 reaction). The Ti/SnO₂ + RuO₂ + MnO₂ anode in conjunction with UV illumination was used to degrade phenol solutions, where the concentration of phenol remaining was determined by high-performance liquid chromatography (HPLC). The results indicate that the degradation efficiency of phenol on the anode can reach 96.3% after photoelectrocatalytic oxidation for 3 h.     

Anodic composite deposition of RuO2·xH2O–TiO2 for electrochemical supercapacitors

This communication demonstrates the first work on anodic composite deposition of oxide nanocomposites. Rutile TiO₂ nanoflowers with an average petal size of ca. 10 nm in diameter and 100 nm in length were synthesized from a TiCl₃ solution purged with air at 25 °C for 12 days prior to the composite deposition. Hydrous ruthenium oxide (RuO₂·xH₂O) and TiO₂ nanoflowers were composite-deposited onto Ti substrates for supercapacitors. In comparing with RuO₂·xH₂O deposits, RuO₂·xH₂O–TiO₂ nanocomposites with a highly porous nature exhibit the weakly mass-dependent specific capacitance and high-power capacitive characteristics.     

Synthesis and Characterization of Hyperbranched RuO2 Nanostructures

RuO₂ nanostructures were synthesized by heating Ru nanoparticles in air at 280°C using Cu as catalyst. The Ru nanoparticles were prepared by the pyrolysis of ruthenium precursors in a vacuum using multi-walled carbon nanotubes as templates. The RuO₂ nanostructures grew radically with diameters of 50–150 nm, and lengths of 0.5–2.0 μm. The growth of nanostructure mainly depends on the dispersivity of Ru nanoparticles on MWNTs. The electrochemical property of these nanostructures was studied by cyclic voltammetry. Electronic Supplementary Material Supplementary material for this article is available at and is accessible for authorized users.     

Anomalies in Heat Capacity Measurements of RuO2-TiO2 System

DSC was used for heat capacity measurements of pure RuO₂ in the temperature range from 300 to 1170 K of solid solutions corresponding to the compositions of (Ti_1−x Ru_x )O₂ (x ≤0.15 and x ≥0.85) and in the temperature range from 300 to 1550 K of pure TiO2. The analysis of experimental data obtained within ±2% of accuracy has shown that the characteristic temperatures representing the harmonic lattice vibrations do not strongly depend on the chemical composition x . It was demonstrated that non-harmonic heat capacity is strongly correlated to x. The existence of additional excess heat capacity was observed with the mixed oxide solid solution samples of low Ru content and explained by the defect formation model. This revised version was published online in August 2006 with corrections to the Cover Date.     

X-ray photoelectron spectroscopic and electrochemical impedance spectroscopic analysis of RuO2-Ta2O5 thick film pH sensors

The paper reports on investigation of the pH sensing mechanism of thick film RuO₂-Ta₂O₅ sensors by using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Interdigitated conductimetric pH sensors were screen printed on alumina substrates. The microstructure and elemental composition of the films were examined by scanning electron microscopy and energy dispersive spectroscopy. The XPS studies revealed the presence of Ru ions at different oxidation states and the surface hydroxylation of the sensing layer increasing with increasing pH. The EIS analysis carried out in the frequency range 10 Hz–2 MHz showed that the electrical parameters of the sensitive electrodes in the low frequency range were distinctly dependent on pH. The charge transfer and ionic exchange occurring at metal oxide-solution interface were indicated as processes responsible for the sensing mechanism of thick film RuO₂-Ta₂O₅ pH sensors.     

氧化钌/石墨纳米片复合阵列电极的制备及其电容性能

通过电化学剥离法在石墨棒表面构筑了层数不等、彼此平行且垂直于基底的二维石墨纳米片(GNS)阵列, 而后采用阴极还原电沉积法在GNSs 表面均匀地包覆了一层氧化钌(RuO₂·xH₂O)薄膜, 形成了RuO₂·xH₂O/GNS 复合阵列电极. 电化学测试表明, RuO₂·xH₂O/GNS 复合阵列电极具有优良的超电容性能, 在0.5mol·L^-1 H₂SO₄电解质溶液中, 扫描速率为5 mV·s^-1, 电位窗口为0.9 V时, 其比电容高达4226 F·m^-2, 并且具有优异的循环性能, 经过20000圈充放电循环后, 电容保持率高达94.18%.     

Partial Oxidation of Alcohols to Aldehydes and Ketones Under Mild Conditions

Abstract

A number of aldehydes and ketones were prepared by partial oxidation of alcohols in air catalyzed by RuO₂/ZSM‐5 which can be easily prepared with the industrial grade ZSM‐5 and RuCl₃ · xH₂O.     

RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO₂-PVC film electrodes, fabricated using RuO₂ powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700°C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO₂-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range −1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti’s formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO₂ (700°C)-PVC electrode shows two oxidation peaks in contrast to RuO₂ (300°C)-PVC electrode. Also, RuO₂ (700°C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300°C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis–Menten (MM) enzyme catalysis has shown that RuO₂ (700°C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K _M , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO₂ powder samples.     

Interaction Between Two Similar Plane Parallel Double Layers for (NH4)2Fe(SO4)2 or (NH4)2Cu(SO4)2 Type Complex Salt Electrolytes at Positive Surface Potential

Interaction energies between two similar plane parallel double layers for (NH₄)₂Fe(SO₄)₂ or (NH₄)₂Cu(SO₄)₂ type complex salt electrolytes at positive surface potential were expanded in a power series and accurate numeral results were given for 0.1 ≤ y _e  < y ₀ ≤ 20. The general expressions were given for the interaction energies of A _ν +B _ν′ +C_ν? type complex salt electrolytes at y > 0. The interaction energies for simple salts NaCl, CaCl₂, Na₂SO₄, FeCl₃, Na₃PO₄, Mg₃(PO₄)₂, Al₂(SO₄)₃, and complex salts (NH₄)₂Fe(SO₄)₂ or (NH₄)₂Cu(SO₄)₂ at y ₀ = 1 were compared. There was hardly difference between these simple salts and this complex salt for the interaction energies. The interaction energy for complex salt (NH₄)₂Fe(SO₄)₂ was close to that for simple salt Na₃PO₄.

Supplemental files are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.     

Investigation on The Thermal Properties of Fe2O(SO4)2. Part II

Fe₂O(SO₄)₂ is a secondary product of the decomposition of FeSO₄⋅H₂O. Part I of this study presents results on the synthesis of Fe₂O(SO₄)₂ in gaseous environment containing either low or high concentration of oxygen. In this paper the existence of differences between the structures of Fe₂O(SO₄)₂ and Fe₂(SO₄)₃ is proved on the basis of a detailed thermal study of Fe₂O(SO₄)₂ upon dynamic heating (differential thermal analysis) and upon isothermal heating (thermal-analytic balance) in various gaseous environments as well as by presenting kinetic data on the processes of decomposition of both compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isolated spin 3/2 plaquettes in Na3RuO4

The crystal structure of Na₃RuO₄ determined by powder neutron diffraction is reported. The structure consists of isolated tetramers of edge sharing RuO₆ octahedra in the ab plane, creating isolated four-member plaquettes of Ru atoms comprised of two equilateral triangles sharing an edge. Magnetic susceptibility measurements reveal an antiferromagnetic transition at ∼29 K, with . Neutron diffraction data indicate the onset of three-dimensional magnetic ordering at 29 K.     

Phenoxide-assisted P-C bond cleavage in PdCl2(PPh3)2 under very mild conditions

PdCl₂(PPh₃)₂ reacted with NaOAr (Ar = Ph, p-tolyl) at 0 °C to afford PdCl(Ph)(PPh₃)₂, instead of PdCl(OAr)(PPh₃)₂, in 12-16% isolated yields based on Pd. The structure was confirmed by NMR and X-ray crystallography. GC-MS analysis of the reaction solution revealed that OPPh₂(OAr), OPPh(OAr)₂, and OP(OAr)₃ are formed, while NMR studies indicated that PdCl(Ph)(PPh₃)₂ is produced when PdCl(OAr)(PPh₃)₂ decomposes. The reaction of PdCl₂(PPh₃)₂ with Bu₃Sn(OC₆H₄-p-OMe) also gave PdCl(Ph)(PPh₃)₂ in 8% isolated yield. These results suggest that PdCl(OAr)(PPh₃)₂ is highly labile and the aryloxy ligand exchanges with the phenyl groups in triphenylphosphine even under very mild conditions.