Oxidation studies of anodes layer microstructures in metal supported solid oxide fuel cells

The effect of oxidation on the microstructural and mechanical stability of ceramic layers in metal supported solid oxide fuel cells is reported. Half-cells that are produced with a reduced nickel based anode are oxidized for different times and temperatures in order to assess stability limits. Samples are analyzed in terms of the effective cell curvature and microstructure, where further insight is obtained via the observation of microstructures before and after oxidization. The interpretation is aided by a comparison to the behavior of structures without electrolyte layer. Electrolyte cracking and anode delamination are observed after oxidation, where the latter is absent in case of oxidation experiments without electrolyte layer, highlighting the failure relevance of strain induced by electrolyte deposition.     

The electrochemical oxidation of organics using tungsten oxide based electrodes

High surface area tungsten oxide (WO_x) based electrodes containing centers of Pt, Sn or Ru were synthesized. The WO_x electrodes were found to display good capacitive behavior and relatively high specific capacitance values of up to 180 F g⁻¹. The oxidation behavior of particularly HCOOH and (COOH)₂, using the WO_x electrodes containing Pt and Sn centers (Pt/WO_x and Sn/WO_x, respectively), was studied in detail in aqueous solutions at high potentials, i.e. at which O₂ is evolved. Both HCOOH and (COOH)₂ appear to be oxidized following 1st order kinetics. The (COOH)₂ oxidation reaction is faster than the HCOOH reaction using otherwise the same experimental conditions. The reaction mechanism of both the HCOOH and (COOH)₂ oxidation was found to most likely involve the adsorptive interaction of the two organics with the anode surface. The WO_x based anodes appear to be promising catalysts for the anodic oxidation of both (COOH)₂ and HCOOH.     

Anodically deposited manganese–molybdenum–tungsten oxide anodes for oxygen evolution in seawater electrolysis

Ternary manganese–molybdenum–tungsten oxides were anodically deposited on to IrO₂-coated titanium substrates at current densities of 60–600 A m^–2 in 0.4 M MnSO₄ solutions containing 0.003 M Na₂MoO₄ and 0.003 M Na₂WO₄ at pH 0–1.5 and at 30–90 °C. The effect of anodic deposition conditions on the activity, selectivity and durability of the anodes for oxygen evolution in 0.5 M NaCl solution was investigated. Most of the oxide anodes prepared initially gave an oxygen evolution efficiency of almost 100%. When the anodic deposition was performed at temperatures lower than 90 °C, gradual oxidative dissolution occurred during the electrolysis in the NaCl solution, due to formation of poorly crystalline oxides. In contrast, the oxide deposited at 90 °C revealed no obvious dissolution during electrolysis for more than 1500 h. The oxygen evolution efficiency, however, decreased gradually with time of electrolysis because of partial detachment of the deposited oxide. The anodic deposition in electrolytes at lower pH and at higher current density resulted in the formation of oxides with better adhesion to the substrate, resulting in improved anode durability. The durability was further improved by repeated anodic deposition with the oxide surface washed during intervals.     

Catalytic oxidation of methanol over molybdenum oxide–tungsten oxide

The vapour phase oxidation of methanol to formaldehyde over molybdenum oxide, tungsten oxide and their mixtures has been investigated in an integral flow reactor at atmospheric pressure. The effect of several process variables on the conversion and yield were determined. A high conversion of 95.6% methanol with nearly 95% selectivity was obtained at 430°C. A rate expression has been derived from the kinetics of the reaction.     

Electrosynthesis at oxide coated electrodes Part 2. The oxidation of alcohols and amines at spinel anodes in aqueous base

The oxidation of alcohols and primary amines at a NiCo₂O₄ anode in aqueous base has been investigated. It is shown that a range of compounds undergo oxidation at the same potential, that for the conversion of the oxide surface to a higher oxidation state, and that the limiting current densities approach those expected for mass transfer control. Using a flow cell, it is confirmed that the conversation of primary alcohols to carboxylic acids, secondary alcohols to ketones and primary amines to nitriles can all be achieved with high selectivity and reasonable current efficiency at high current densities. The oxide coating appears to be quite stable during repeated electrolyses.     

正丁烷选择性氧化制顺酐技术发展

本文介绍了正丁烷氧化制顺酐固定床,循环流化床工艺技术进展;并对上述三种技术进行了比较。     

Chemical and electrochemical oxidation of heterogeneous carbon anodes

At the electrode electrolyte interface, three reactions have been found to occur during the electrochemical oxidation of carbon while electrowinning aluminium. The three reactions are: electrochemical evolution of carbon monoxide, which is dependent on the structure of the carbon; electrochemical evolution of carbon dioxide; and thirdly a chemical reàction between carbon dioxide and carbon which occurs in the pore structure immediately behind the electrode interface. The first and last mentioned of these are very strongly dependent on the carbon structure real surface area and porosity of constituent carbons leading to differential reactivity in the normal heterogeneous anodes.     

Redox kinetics of benzene oxidation to maleic anhydride

Steady state kinetics of the oxidation reaction have been determined with the help of a gradientless semi-differential, fixed-bed reactor. The Mars and van Krevelen phenomenological model satisfactorily correlates the experimental data but a modification of the Langmuir-Hinshelwood model taking into account partial coverage of the catalyst surface with reaction intermediates is preferred. Transient kinetics have been studied with a new automated periodic-pulse reactor, directly connected to a gas chromatograph. The response of a catalyst (essentially V₂O₅–MoO₃) to reduction and oxidation has been investigated. The rate of bulk (lattice) oxygen utilization as well as the degree of carbon coverage are estimated by this technique. Selectivity is dependent on the oxidation state of the catalyst: high partial pressure of either benzene or oxyen and high temperatures are detrimental to selectivity.     

Oxidation of Sintered Cobalt Oxide

The kinetics and mechanism of the oxidation of sintered pellets of CoO and Co_0.5Mg_0.5O in air at high temperatures were investigated to find stable heat sources containing ⁶⁰Co. The initial stages of oxidation of both materials were nuclei-growth-controlled, i.e. In [1/(1-X)] =kt^m. The reaction rate constant for CoO decreased at 800° to 960°C, the temperature where the cobalt oxide spinel decomposed. The reaction-rate constant for decomposition of the mixed oxide was maximum at 700°C and decreased at higher temperatures. This decrease confirmed the validity of the nuclei-growth solid-state reaction-rate equations.     

正丁烷氧化制取顺酐的Huntsman工艺技术进展

正丁烷制顺酐Huntsman工艺于1975年首次由Monsanto公司(前Huntsman公司)实现工业化,该工艺采用了固定床列管式反应器、新型催化剂MarsV及有机溶剂吸收与精制新技术.2010年全球Huntsman工艺装置有10套左右,利用Huntsman工艺制顺酐的生产能力高达249 kt/a,其生产总能力约占整...     

贱金属氧化物不溶性阳极的研究进展

介绍了 PbOZ.SnO2.MnO2.CO3O4等贱金属氧化物不溶性阳极的研究和应用状况以及存在的问题,认为有效改善贱金属氧化物阳极的使用性能特别是表面催化性能以及如何搭配各种贱金属氧化物将是其替代贵重金属氧化物阳极的关键.     

Electrolytic recovery of iron from pickling solutions by tungsten carbide gas-diffusion anodes

The performance of gas-diffusion electrodes catalysed with tungsten carbide as anodes for the electrolytic recovery of iron from pickling solutions was investigated. The conditions under which the cathodic current efficiency of electrolytic cells utilizing such anodes increases significantly were determined. It was found that the energy consumption is two times lower than for a conventional electrolysis using lead anodes.     

Electrogenerative oxidation of model alcohols at packed bed anodes

The electrogenerative oxidation of dissolved ethanol and 2-propanol in aqueous 1 to 3 M sulphuric acid electrolyte was investigated at several types of packed bed anodes in ion exchange membrane separated cells. The operation of these electrogenerative cells which incorporated a platinum-catalysed commercial oxygen gas-diffusion-type cathode is described. It appears that for dissolved normal primary alcohols composite Teflon-platinum fuel-cell-type electrodes favour aldehyde formation while platinum on graphite electrodes favour carboxylic acid formation. Oxidation of dissolved 2-propanol could be controlled to give acetone exclusively.Nomenclature A current accountability (see Equation 4) (%) - d thickness of the packed bed (cm) - F Faraday constant (C mol^–1) - i current density (A cm^–2) - I cell current (A) - conductivity of the electrolyte (^–1 cm^–1) - N molar production rate (g mol s^–1) - charge transfer coefficient - void fraction - potential in the electroyte phase (V) - n number of electrons passed in the electrode reaction     

The topotactic transformation of tungsten oxide to a cubic tungsten carbide

The solid transformation of tungsten trioxide to a cubic tungsten carbide via nitride has been studied. Product carbide particles possessed specific surface area ofca. 90 m²g^*-1 and average diameter ofca. 4 nm. Transmission electron microscope (TEM) exhibited that these particles formed porous aggregates with a spotty electron diffraction pattern. This provides an evidence that the topotactic solid transformation has been involved.     

Anodic oxidation of copper cyanide on graphite anodes in alkaline solution

The anodic oxidation of copper cyanide has been studied using a graphite rotating disc with reference to cyanide concentration (0.05–4.00 M), CN:Cu mole ratio (3–12), temperature (25–60 °C) and hydroxide concentration (0.01–0.25 M). Copper had a significant catalytic effect on cyanide oxidation. In the low polarization region (about 0.4 V vs SCE or less), cuprous cyanide is oxidized to cupric cyanide complexes which further react to form cyanate. At a CN:Cu ratio of 3 and [OH^–] = 0.25 M, the Tafel slope was about 0.12 V decade^–1. Cu(CN)₃ ^2– was discharged on the electrode and the reaction order with respect to the predicted concentration of Cu(CN)₃ ^2– is one. With increasing CN:Cu mole ratio and decreasing pH, the dominant discharged species shifted to Cu(CN)₄ ^3–. Under these conditions, two Tafel slopes were observed with the first one being 0.060 V decade^–1 and the second one 0.17–0.20 V decade^–1. In the high polarization region (about 0.4 V vs SCE or more), cuprous cyanide complexes were oxidized to copper oxide and cyanate. Possible reaction mechanism was discussed.     

Anodic oxidation of sulphite ions on graphite anodes in alkaline solution

The anodic oxidation of sulphite ions in alkaline 1 M Na₂SO₄ solution on graphite rotating disc electrodes has been studied over the range from 25 to 60 °C. The reaction order with respect to sulphite ions is below 1 at low potentials and 1 at high potentials. The reaction order with respect to hydroxide ions is close to zero. Two Tafel slopes were observed, 0.060V decade^–1 at low potentials and 0.190.20V decade^–1 at high potentials. The reaction activation energy was calculated at different potentials. The results obtained, using the potential sweep method, are consistent with those realized using the rotating disc. A possible reaction mechanism has been proposed and the diffusion coefficients of sulphite ions and the diffusion activation energy have been calculated.     

糠醛气相法催化氧化制顺丁烯二酸酐

利用浸渍法制备负载型V2O5-MoO3-P2O5 /γ-Al2O3催化剂。采用ICP、N2吸附-脱附等温线及XRD表征催化剂的物化性质、结构特征,通过TPR考察催化剂晶格氧的供氧能力。在固定床连续微反应装置上,以来源于可再生生物资源的糠醛为原料,进行催化剂的性能评价。实验结果表明：当催化剂中MoO3和V2O5质量比为0.4、反应混合气体（糠醛体积分数2%的空气混合气体）空速为3000 h-1、反应温度为305 ℃的工艺条件下,测得糠醛转化率为82%,顺酐的收率为50%,说明适当地引入MoO3能够调节催化剂活性中心与载体间的强相互作用,达到促进催化剂晶格氧快速交换的目的,从而进一步提高催化剂的活性和选择性。     

Development of novel anodes for solid oxide fuel cells

Ni cermet anodes pose considerable problems for SOFC operation in natural gas fuels, particularly with regard to carbon deposition due to hydrocarbon cracking. Oxide anodes offer a good alternative, particularly if a material combining good electronic and ionic transport properties can be utilised. In our search for alternative anode materials, we have investigated fluorite-based systems containing reducible early transition metal dopants. The extent of phase stability has been investigated by solid-state chemical techniques and electrical properties have been investigated by ac impedance techniques as a function of both temperature and oxygen partial pressure. The Nb---Zr---Y---O system has been found to provide a good model system exhibiting reasonable electrical properties. Niobium pentoxide exhibits a wide range of solid solubility in the yttria-zirconia cubic fluorite system and the fluorite structure is retained under reducing conditions. Electronic conductivity increases as niobium concentration increases; however oxide-ionic conductivity decreases with extent of niobium substitution. The defect chemistry of this system, which determines the electrical properties, is dominated by the high concentration of oxide vacancies necessary to stabilise the cubic structure, hence electronic conductivity exhibits a P(O₂)^-1/4 dependence on oxygen partial pressure.     

Utilization of gas-diffusion electrodes catalysed with tungsten carbide as anodes for zinc electrowinning

Gas-diffusion electrodes with varying amounts of tungsten carbide catalyst are studied, and their feasibility as suitable anodes for zinc electrowinning is demonstrated. The energy savings achievable with the use of such anodes are evaluated.     

Oxidation of coal in industrial conditions. 1. Kinetics of natural oxidation

In the light of research on the artificial oxidation of coal in the laboratory, earlier results on the natural oxidation of coal in open storage at different coke Ukrainian plants are analyzed. On the basis of the kinetics of coal oxidation in natural conditions, the need to correct existing standards for open storage is evaluated. Since the dependence of the degree of oxidation d _o on the storage time is sigmoid, the results are analyzed on the basis of the Avrami-Erofeev equation for the kinetics of heterogeneous reactions. The constants of that equation and the rate constants of oxidation are calculated for enriched coal of different ranks (G, Zh, K, and OS) in summer and winter. The influence of the degree of metamorphism on the rate constant of natural oxidation in summer and winter is mathematically described. On the basis of the Avrami-Erofeev equation, limiting open-storage times for the coal are established. The earlier limiting storage times must be corrected.