Electrochemical characterisation of the Pt/YSZ interface exposed to a reactive gas phase

The Pt/yttria-stabilized cubic zirconia (YSZ) interface exposed to a reactive gas was characterised by solid electrolyte potentiometry and cyclic voltammetry. The catalytic reactions included total combustion of C₃H₈ and C₃H₆ to CO₂ and H₂O as well as NO reduction by C₃H₆ in the presence of O₂ under oxygen-rich and stoichiometric conditions. The solid electrolyte potentiometry as a function of the temperature in C₃H_x/O₂ (with x=6 or 8) reflected the catalytic properties of Pt for C₃H_x oxidation. In C₃H₆/NO/O₂, the reduction of NO was evidenced below 300 °C. The cyclic voltammetry evidenced the formation of an oxygen chemisorbed layer on the Pt surface under anodic potential. Propane had no effect on this chemisorbed layer, whereas propene weakened significantly the strength of this Pt–O bond. Addition of NO to C₃H₆/O₂ led to the disappearing of this chemisorbed layer. The use of solid electrolyte potentiometry in conjunction with cyclic voltammetry allowed us to determine the surface oxidation state of Pt during the catalytic reactions.     

H2/Pt/Ce0.9Gd0.1O1.95/Pt/O2 fuel cell operated in the intermediate temperature range 500 – 700°C

Ce_0.9Gd_0.1O_1.95 (GCO), is one of the potential candidate electrolytes for intermediate temperature Solid Oxide Fuel Cells (ITSOFC). GCO has high oxide ion conductivity in the intermediate temperature range (500 – 700 °C) compared to other Ce_1−yGd_yO_2-2/y compositions and the Gd³⁺ ion is the most appropriate dopant material compared to other rare earth materials such as Sm³⁺, Y³⁺, Zr³⁺, etc. Our results show that the fuel cell H₂/Pt/Ce_0.9Gd_0.1O_1.95/Pt/O₂ operated in the temperature range 500 – 700°C gives the maximum power densities 0.0049 W/cm² at 500 °C and 0.0126 W/cm² at 650 °C for cell voltages 0.6275 V and 0.6278 V, respectively, where the electrolyte was kept in 5% H₂ (+ Argon) for 12 hours before use in the fuel cell. Maximum power densities are 0.0038 W/cm² at 500 °C and 0.0270 W/cm² at 650 °C for cell voltages 0.5986 and 0.5913 V, respectively, where the electrolyte was kept in 2 % O₂ (+ Argon) for 12 hours before use in the fuel cell. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Electrochemical promotion of the NO reduction by C2H4 on Pt/YSZ and by CO on Pd/YSZ

The effect of electrochemical promotion was investigated for the catalytic reduction of nitric oxide with ethylene and carbon monoxide on polycrystalline Pt and Pd, respectively, deposited on yttria-stabilized zirconia (YSZ). It was found in both cases that applying negative potentials and thus lowering the catalyst work function results in a pronounced increase in the catalytic rate and in the selectivity to nitrogen. A 7-fold increase was observed for the NO+C₂H₄ reaction on Pt while a 2-fold increase was obtained for the NO+CO reaction on Pd. The induced changes in catalytic rates were found to be 7 to 50 times higher than the rates of ion transfer from the catalyst surface. In both reactions, the observed electrophilic behavior can be attributed to the strengthening of the chemisorptive NO bond and concomitant enhanced dissociation of NO as the catalyst potential and work function is decreased. Forced periodic oscillations of the applied current was investigated and resulted in a enhanced production of CO₂, but an intermediate selectivity towards N₂, as compared to constant current application. The effect of the cycling waveform, frequency and amplitude was studied and provided evidence that the synergy observed during the cycling experiment results from a favorable transient coverage of adsorbed species on the catalyst surface as the catalyst potential oscillates from negative to positive values. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

50-5000 eV电子被C4H8O, C5H10O2, C6H5CH3和C4H8O2散射的总截面

使用电子被C, H和O原子散射总截面的实验数据, 利用修正后的可加性规则计算了能量为50-5000 eV的电子被4个复杂大分子C4H8O, C5H10O2, C6H5CH3和C4H8O2散射的总截面, 并将计算结果与实验结果及其他理论计算结果进行了比较. 结果表明, 即使是在几十电子伏的入射能量下, 修正后的可加性规则计算出的总截面依然能与实验结果符合很好, 而使用未修正的可加性规则进行计算, 即使是在几百电子伏的入射能量下得到的总截面仍偏离实验值较远. 分析表明, 未修正的可加性规则计算得到的总截面在中低能区过大、随电子入射能量的增加而衰减太快的问题是由可加性规则本身引起的, 其实质是未考虑低能下分子内原子间的相互屏蔽对散射总截面的计算所带来的影响.     

Eu（C8H7O3）3·C12N2·H2O配合物的合成与表征

合成了新的Eu(C8H7O3)3·C12H8N2·H2O配合物.并经元素分析、摩尔电导、IR、UV、1H NMR等表征,初步确定配体3-甲氧基苯甲酸以桥式双齿形式和Eu(Ⅲ)配位.     

Polarisation conductivity of the O2,Pt/Zr(Y)O2 and H2-H2O, Pt/Zr(Y)O2 electrodes

Pt electrodes with defined contact geometries were studied by using impedance spectroscopy. The specific polarisation conductivity per unit length of the three-phase boundary was determined. It is found to be 1 × 10⁻⁴ S·cm⁻¹ at 977 °C in an atmosphere of “pure” hydrogen with an oxygen partial pressure of 10⁻²⁰ atm at 1000 °C. Investigations carried out in an atmosphere of pure oxygen revealed a pronounced dependence of the polarisation conductivity on the electrode history. The polarisation conductivity was found to be in a range of 2 × 10⁻⁴ to 6.5 × 10⁻⁴ S·cm⁻¹ at a temperature of 977 °C. It was possible to estimate the area of the electrolyte surface which takes part in the electrode reaction. The real exchange current density was determined.     

A study on detonation-diffraction reflection point distances in H2/O2, C2H2/O2, and C2H4/O2 systems

Recently, Kawasaki and Kasahara (2019) reported that reflection point distance, which is a detonation characteristic length relevant to the diffraction process, is a useful measure; i.e., the critical condition for detonation diffraction can be universally expressed in terms of the diffraction point distance, independent of mixture stability. However, their findings were limited to their experimental conditions only. In this study, we performed high-speed visualization of processes of cylindrical (line-symmetric) detonation diffraction around a 90-degree corner for two series of experiments to obtained reflection point distances, l_r, as a novel characteristic length, and examined critical conditions of reinitiation expressed in terms of the reflection point distance. In the first experimental series, stoichiometric C₂H₂/O₂ mixtures with 50% Ar dilution were employed, and the channel width l_c was varied to 5, 10, 15, and 20 mm to investigate the influences of the boundary condition of the flow field. In the second experimental series, H₂/O₂, C₂H₂/O₂, or C₂H₄/O₂ mixtures with different equivalence ratios were employed to investigate influences of the reaction systems. Our results confirmed that the channel width does not affect the reflection point distance or the critical condition. The critical condition was also independent of fuel species and equivalence ratio, and can be uniquely expressed as l_r / l_c = 4.0 ± 0.6 in terms of the reflection point distance.     

配合物La（C5O3H3）3·C12H8N2·H2O的合成和表征

本以α－呋喃甲酸（Ｃ５Ｏ３Ｈ４）和邻菲罗啉（Ｃ１２Ｈ８Ｎ２）为配体,在乙醇８溶剂中与硝酸镧反应,合成了与稀土离子Ｌａ（Ⅲ）的三元混配配合物。经元素分析确定其配合物的组成为Ｌａ（Ｃ５Ｏ３Ｈ３）·Ｃ１２Ｈ８Ｎ２·Ｈ２Ｏ,同时还通过了ＩＲ、＾１ＨＮＭＲ、ＵＶ、ＴＧ－ＤＴＡ等谱光的测试与分析,表征了配合物的组成结构和性质。ＩＲ、＾１ＨＮＭＲ和ＵＶ谱的分析结果表明配体羧酸是以脱质子的酸根形式与中心稀土离子     

C_8H_8O_7H_2O单晶的振动光谱

Ｃ８Ｈ８Ｏ７Ｈ２Ｏ单晶的振动光谱李丽霞（山东大学环境工程系济南２５０１００）ＴｈｅＶｉｂｒａｔｉｏｎａｌＳｐｅｃｔｒｕｍｏｆＣ８Ｈ８Ｏ７Ｈ２ＯＣｒｙｓｔａｌＬｉＬｉＸｉａ（ＥｎｖｉｒｏｎｍｅｎｔａｌＥｎｇｉｎｅｒｉｎｇＤｅｐａｒｔｍｅｎｔ，Ｓｈａｎｄ...     

Submillimeter spectrum of NH3−H2O dimer in its equilibrium gas phase

The first observation of the microwave spectrum of the NH₃–H₂O molecular complex in its equilibrium gas phase is reported. Earlier, the spectrum of NH₃–H₂O was observed only in nonequilibrium cold supersonic molecular beams. As in the previous paper [1] dealing with the observation of the equilibrium spectrum of HF-HF dimer, we use a submillimeter spectrometer with a BWT and acoustic detector and a cooled absoprtion cell. The submillimeter line frequencies continuing the series known from the beam investigations have been measured. New series, which obviously correspond to the higher states of the dimer, have been detected. The primary results of the analysis of the dimer spectrum together with the earlier data are presented.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia; Molecular Physics Department, National Institute for Standards and Technologies, USA. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 7, pp. 738–742, July, 1995.     

A conversion electron Mössbauer spectroscopy study of pulsed laser treatment at α-Fe2O3/H2O interface

Magnetite (Fe₃O₄) has been synthesized for the first time by using pulsed ruby laser induced reactive quenching process at α-Fe₂O₃/H₂O interface. Iron foils (99.99% pure) were oxidised at 450° C for four hours to form a thick layer of α-Fe₂O₃ on it. These oxidised samples were immersed in water and then treated with ruby laser pulses (λ=0.694 μm, pulse width = 30 ns, energy density = 10 J/cm²). The conversion electron Mössbauer spectroscopy (CEMS) has been used to characterize the laser induced surface modifications. It is shown that laser treated samples show the formation of Fe₃O₄ phase along with FeO. The stability of magnetite phase in laser treated sample against thermal treatment is also studied by investigating the changes in hyperfine interaction parameters upon vacuum annealing at 300° C.     

PVP在水/丙酮混合溶剂中分子运动行为的研究

通过对粘度、自旋-自旋弛豫时间以及1H NMR谱的测定,研究了PVP在不同体积配比的水/丙酮溶液中的特性粘数变化和分子运动规律,并讨论了引起这些变化的原因.结果表明:随着丙酮的不断加入,PVP的特性粘数[η]先增加后减小,而T2H先减小后增大.[η]出现最大值也是T2H出现最小值的时候,丙酮的体积百分数为40%.丙酮的加入破坏了水分子间自身氢键相互作用形成的网状结构,解离出来的水分子被PVP优先吸附到大分子链上,部分与羰基形成氢键,另一部分以自由水的形式被包裹在大分子线团内.水分子的不断进入以及与水形成新的氢键使PVP链逐渐伸展,引起特性粘数的增大,分子运动受阻.当丙酮含量增加到一定程度时,水的含量不足以使大分子链继续膨胀,故链呈卷缩状态,使大分子运动逐渐恢复自由.1H NMR谱中各质子的化学位移变化也证实了此过程中的氢键变化规律.     

Physical properties of LiMn2O4 spinel prepared at moderate temperature

A moderate-temperature method of preparation of the spinel LiMn₂O₄ was developed around 500 °C. Physical features of the products were identified by X-ray photoelectron spectroscopy, X-ray diffractometry, Raman scattering and FTIR spectroscopy. The electronic conductivity of LiMn₂O₄ has been studied as a function of annealing temperature. The product LiMn₂O₄ is identified as a micron-sized powder and analysis of the local environment is in good accordance with the classical structural model of Fd3m space group. LiMn₂O₄ exhibits an electrical conductivity of 1.9×10⁻⁵ S/cm at room temperature with an activation energy of 0.16 eV which corresponds to an electron hopping mechanism between the two charge states of Mn³⁺ and Mn⁴⁺ ions. A first-order phase transition is observed at 292 K.     

Origin of cathodic degradation and new phase formation at the La0.9Sr0.1MnO3/YSZ interface

New phase formation at the La_0.9Sr_0.1MnO₃/YSZ interface and its effects on the cathodic performances were studied at 900 °C in air. The resistance caused by the interfacial product layer kept increasing with time to reach up to 40% of the total resistance after 500 h. The interfacial product was identified as La₂Zr₂O₇ by XRD measurement. The electrical conductivity of La₂Zr₂O₇ (2.4 × 10⁻⁵ S cm⁻¹ at 1000 °C), measured by AC impedance and current interruption methods, was 4 to 7 orders of magnitude smaller than those of La_0.9Sr_0.1MnO₃ electrode or YSZ electrolyte. Either the electronic conductivity or the electrochemical O₂ reduction activity of La₂Zr₂O₇ was negligible. Combining these results, a conclusion was made that the cathodic degradation comes mainly from the growth of interfacial product layer and its contribution to the cell resistance increment is ohmic in nature.     

An Ab initio study of reactions in the H3BO3/B2O3/H2O system

The H₃BO₃ ? HBO₂ + H₂O, HBO₂ + HBO₂ ? (HBO₂ · HBO₂) complex, and (HBO₂ · HBO₂) ? B₂O₃ + H₂O reactions of forward and reverse conversion of H₃BO₃ into B₂O₃ and the (HBO₂ · HBO₂) ? (HBO₂)₂ reactions of forward and reverse transformation of the complex into a fairly stable dimer (HBO₂)₂ were studied ab initio at the MP2/6-31+G*//6-31+G* level. The transition state method and calculated equilibrium constants were used to determine forward and reverse reaction constants.     

Thermochemistry of the reactions between CN+ and H2O in the gas phase

The [H₂, C, N, 0]⁺ potential energy surface (PES) has been explored by means of high-level ab initio calculations, carried out in the framework of the G2 theory. From this survey we concluded that the predominant products of the CN⁺ + H₂O reaction are the result of the dissociation of HNCOH⁺ species and to a much lesser extent of the CNHOH⁺ cation to yield CNH⁺ + OH. According to our results HCN⁺ should not be a product of this reaction because all pathways leading to its formation are unfavourable with regards to other competitive processes. Other reactive channels lead to the formation of the H₂ONC⁺ structure which dissociates into CN + H₂O⁺. The loss of NH(3σ) and O(³P) seems to take place following spin-forbidden reaction paths through an intersystem crossing between the singlet and the triplet PESs. The global minimum of the PES, H₂NCO⁺ is easily accessible and should lead to the loss of carbon monoxide which has not been experimentally observed in CN⁺ + H₂O reactions. We cannot offer a clear explanation for this disagreement between theory and experiment.     

Kinematics of the reaction H2O+(H2,H)H3O+

The kinematics of the reaction H₂O⁺(H₂,H)H₃O⁺ were studied in crossed-beam experiments in the low collision-energy range 0.1–2 eV (c.m.). The scattering diagrams, center-of-mass angular distributions, and product relative translational energy distributions obtained show that the reaction proceeds predominantly by the impulsive, stripping mechanism. The translational exoergicity vs. collision energy plot obeys the spectator-stripping prediction.     

三维超分子化合物[Zn(H_2O)_6]·(C_(16)H_8O_8)的合成、晶体结构及荧光光谱

以醋酸锌和3,3’,4,4’-联苯四羧酸(H4BPTC)为原料,采用水热法合成了一个三维超分子化合物[Zn(H2O6)].(C16H8O8)(1)。通过红外光谱、元素分析和X射线单晶衍射对其结构进行了表征,X射线单晶衍射分析结果表明,该超分子化合物属于三斜晶系,PT空间群,晶胞参数a=0.654 8(1)nm,b=0.793 9(2)nm,c=0.968 1(2)nm,α=76.29(3)°,β=87.75(3)°,γ=86.43(3)°,Z=1,R1=0.066 5,wR2=0.183 3,GOF=1.021.并通过荧光光谱研究了1在溶液和固态时的发光性能,在室温DMSO溶液中,当激发波长为316nm时,化合物1在399nm处有一强发射峰,呈现蓝紫色荧光,在室温固态时,该化合物的发射峰发生明显红移,在525nm处有一宽谱带发射峰,呈现绿色荧光,这可以归因于在固态化合物1的分子中存在氢键和π—π堆积的相互作用,可以明显降低分子中基态与激发态之间的能量差距,从而使发射峰红移。     

Electrical conductivity in magnesium-doped Al2O3 crystals at moderate temperatures

Abstract

AC and DC electrical measurements between 273 and 800 K were used to characterize the electrical conductivity of Al₂O₃: Mg single crystals containing [Mg]⁰ centers. At low fields contacts are blocking. At high fields, electrical current flows steadily through the sample and the I–V characteristic corresponds to a directly biased barrier with a series resistance (bulk resistance). AC measurements yield values for the junction capacitance as well as for the sample resistance, and provide reproducible conductivity values. The conductivity varies linearly with the [Mg]⁰ concentration and a thermal activation energy of 0.67 eV was obtained, which agrees very well with the activation energy previously reported for the motion of free holes.     

The self-diffusion coefficient in the gas phase at moderate densities,obtained by computer simulations

The self-diffusion coefficient for Lennard-Jones molecules has been determined by molecular dynamics for densities up to the critical one and for temperatures ranging from T = 1.3∈/k to T = 5.56∈/k. At low density, the results are in a good agreement with the theoretical predictions; at elevated densities agreement with the available experimental results is found, although the scarcity of experimental data prevents a general comparison between real systems and the molecular dynamical calculations.Additional computations with different pair-potentials lead to results which throw some doubts on the reliability of the so-called Modified Enskog Theory.