Electrochemical deposition and properties of PbO2 + Co3O4 composites

Electrolysis of suspensions of Co₃O₄ particles in Pb²⁺-containing electrolytes has been used for depositing PbO₂ + Co₃O₄ composite layers on Ni rotating dise anodes. A sufficiently high angular speed of the electrode is necessary to obtain layers of homogeneous thickness and Co₃O₄ concentration. The volume fraction of Co₃O₄ particles in the deposit α reaches a limiting value of ca. 0.1 when the volume fraction of particles in suspension C exceeds 0.008. The current density j has little effect on α as long as it is in the range 1 to 20 mA cm⁻²; if j increases further, α decreases.PbO₂ + Co₃O₄ composite layers have been studied as electrode materials for the oxygen evolution reaction (mainly in NaOH solution). The overpotential and Tafel slope decrease upon increasing α. At a fixed potential, j is roughly proportional to OH⁻ concentration. The PbO₂ + Co₃O₄ electrode performance is fairly stable at 25°C but declines with time at higher temperature.     

Structure and electron density analysis of electrochemically and chemically delithiated LiCoO2 single crystals

Single crystals of Li_0.68CoO₂, Li_0.48CoO₂, and Li_0.35CoO₂ were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO₂ single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3¯m space group and the hexagonal lattice parameters a=2.8107(5) Å, c=14.2235(6) Å, and c/a=5.060 for Li_0.68CoO₂; a=2.8090(15) Å, c=14.3890(17) Å, and c/a=5.122 for Li_0.48CoO₂; and a=2.8070(12) Å, c=14.4359(14) Å, and c/a=5.143 for Li_0.35CoO₂. The crystal structures were refined to the conventional values R=1.99% and wR=1.88% for Li_0.68CoO₂; R=2.40% and wR=2.58% for Li_0.48CoO₂; and R=2.63% and wR=2.56% for Li_0.35CoO₂. The oxygen-oxygen contact distance in the CoO₆ octahedron was determined to be shortened by the delithiation from 2.6180(9) Å in LiCoO₂ to 2.5385(15) Å in Li_0.35CoO₂. The electron density distributions of these Li_xCoO₂ crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found around the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed.     

硫酸溶液中苯酚在Ti/PbO2电极上的循环伏安研究

用循环伏安法研究了Ti/PbO₂电极在苯酚硫酸溶液中的电催化作用. 结果表明, 在硫酸溶液中, Ti/PbO₂阳极对苯酚具有电催化氧化作用. 如果苯酚浓度较低, 产生的吸附态羟基自由基可以将苯酚氧化, 直至完全矿化. 当苯酚浓度较高或产生的羟基自由基量相对较小时, 苯酚或中间产物可吸附在电极表面, 降低电极的真实表面积, 减少电极的活性点, 阻止反应物接近电极表面, 抑制苯酚的进一步氧化. 随着电解时间的延长, 这些吸附物由于逐渐被氧化, 电极活性恢复.     

Preparation of LiVO2 crystals

The synthesis of LiVO₂ crystals exhibiting two different morphologies is reported. Black hexagonal platelet-type and octahedral-like dendritic crystals were obtained using a fused-salt electrolytic method. DSC, TGA, magnetic susceptibility, and X-ray diffraction data are presented. Weak reflections observed in X-ray precession photographs of the platelets indicate a hexagonal superstructure with a unit cell a = 9.838(4) Å = 2√3a′, where a′ = 2.84Å, and c = 14.755(6) Å. Observed systematic absences are consistent with the space groups P6₂22 and P6₄22. The dendrites appear to be a pseudocubic phase with a face-centered unit cell, a = 8.31(1) Å.     

Kinetics of the transformation process of PbSO4 to PbO2 in a lead anodic film

The kinetics of the nucleation and growth of PbO₂ during the potentiostatic oxidation of PbSO₄ in a lead anodic film was studied using linear sweep voltammetry, potential-step and ac impedance tracing methods. The film investigated is the partially reduced anodic PbO₂ film formed by polarizing a lead electrode in 4.5 M H₂SO₄ solution first at 1.3 V vs. Hg|HgSO₄ for 20 min and then at 0.9 V for 5 min. The nucleation and growth process begins some time after the potential step and is completed within 60 s. The pre- and post-nucleation and growth processes correspond to the growth of the anodic film formed by the oxidation of the lead substrate. The mathematical equations representing the current-time and capacitance-time transients are derived taking the background oxidation current into account. The experimental results are well fitted by these equations. The process obeys the laws of two-dimensional instantaneous nucleation and growth.     

Performance of PbO2/activated carbon hybrid supercapacitor with carbon foam substrate

PbO₂/activated carbon（AC） hybrid supercapacitor in H₂SO₄ with a carbon foam current collector is studied.The PbO₂/AC hybrid is designed with electrodeposited PbO₂ thin film as positive electrode to match with AC negative electrode.The discharge curve shows capacitive characteristics between 1.88 V and 0.65 V.The hybrid system exhibits excellent energy and power performance,with specific energy of 43.6 Wh/kg at a power density of 654.2 W/kg.The use of carbon foam current collector ensures stability of the PbO₂ electrode in H₂SO₄ environment.After 2600 deep cycles at 15 C high rate of charge/discharge,the capacity remains nearly unchanged from its initial value.     

Growth and characterization of n-WS2 and niobium-doped p-WS2 single crystals

Single crystals of n- and p-WS₂ were obtained by chemical vapor transport using chlorine and bromine as transporting agents. The best niobium-doped WS₂ crystals were obtained when the concentration of the charge (formulated (1 ? x)WS₂ · (x)NbS₂) was ? 37 mg charge/ml of tube, and x = 0.01 to 0.03. A thermodynamic analysis of the crystal growth process is consistent with the observed doping concentration and other properties of the crystals obtained by this process. The crystals grown are characterized by electrical transport and surface photovoltage measured capacitance techniques.     

Magnetic properties of Mn2V2O7 single crystals

Magnetic properties of Mn₂V₂O₇ single crystals are investigated by means of magnetic susceptibility, magnetization, and heat capacity measurements. A structural phase transition of the α-β forms is clearly observed at the temperature range of 200-250 K and an antiferromagnetic ordering with magnetic anisotropy is observed below 20 K. A spin-flop transition is observed with magnetic field applied along the [110] axis of β-Mn₂V₂O₇, of which corresponds to the [001] axis of α-Mn₂V₂O₇, suggesting that the spins of Mn²⁺ ions locate within honeycomb layers which point likely in the [110] direction of β-Mn₂V₂O₇ or the [001] axis of α-Mn₂V₂O₇. However, a rather small jump of magnetization at spin-flop transition suggests a possible partition of crystal to some domains through β-to-α transition on cooling or much complex spin structure in honeycomb lattice with some frustration.     

Ti/PbO2和Ti/Ru-Ti-Sn氧化物涂层电极上苯酚的电化学氧化和降解

用紫外-可见光谱(UV-Vis)研究了Ti/PbO2和Ti/Ru-Ti-Sn三元氧化物涂层电极对苯酚的电化学氧化及其中间产物的影响, 通过高效液相色谱(HPLC)方法检测了苯二酚的生成. 结果表明, 苯酚的电化学氧化和降解是羟基化产物对苯二酚和邻苯二酚进一步氧化的结果.     

Study on a new single flow acid Cu–PbO2 battery

The present paper reports a new single flow acid battery, Cu–H₂SO₄–PbO₂ battery, in which smooth graphite is employed as negative electrode, lead dioxide as positive electrode and the intermixture of H₂SO₄–CuSO₄ as electrolyte. The reaction CuCu²⁺ takes place on the negative electrode. The working process of the battery is only the circulation of H₂SO₄–CuSO₄ intermixture by means of a single pump. No cationic membrane is needed. A miniature acidic copper single flow battery with a rated capacity of 2000 mAh can offer a discharge voltage of 1.29 V, an average coulombic efficiency of 97% and an energy efficiency of 83% during 450 cycles at a charge/discharge current of 1000 mA.     

Energy band genesis from sublattice states in MgSiN2 and MgGeN2 crystals

The electronic structure of MgSiN₂ and MgGeN₂ orthorhombic crystals and their sublattices was analyzed at the density functional theory level using the sublattice method. The energy-band structure of the orthorhombic crystals is compared to the structure of their hypothetic analogues with the chalcopyrite lattice. The origin of the specific features of the valence band structure from the sublattice states is determined in the studied crystals, which is mainly due to the interaction of atoms in SiN₄ and GeN₄ cation tetrahedra.     

The standard enthalpies of formation of (ClOF2)2[MnF6] and ClOF2[BF4] crystals

The enthalpies of interaction of (ClOF₂)₂[MnF₆](cr) and ClOF₂[BF₄](cr) with water and an aqueous solution of alkali and the enthalpies of several auxiliary processes were measured at 298.15 K on an isothermic-shell calorimeter. Based on these and literature data, the standard enthalpies of formation of (ClOF₂)₂[MnF₆](cr) and ClOF₂[BF₄](cr) at 298.15 K were calculated by two independent methods (−1643 ± 11 and −1368 ± 5 kJ/mol, respectively). Original Russian Text ? A.A. Firer, S.N. Solov’ev, A.Ya. Dupal, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7, pp. 1391–1393.     

掺杂F-对PbO2阳极性能和电催化活性的影响

采用热分解-电镀法制备了Ti基PbO₂阳极(PbO₂阳极)和F^-掺杂PbO₂阳极(F-PbO₂阳极)。应用XRD和SEM技术对这两种电极进行了表征，采用加速电解寿命测试研究了其在硫酸溶液中的电解稳定性。结果表明，F-PbO₂阳极的寿命远大于PbO₂阳极的寿命，在4-氯苯酚(4-CP)的电催化降解过程中，F-PbO₂阳极表现出比PbO₂阳极较强的催化活性。本文对F^-掺杂提高PbO₂阳极性能和电催化活性的机理进行了探讨。并应用高效液相色谱确定了4-CP在F-PbO₂阳极上的降解历程。     

EPR study of the NO2+3 radical in irradiated K(UO2)(NO3)3 and K2(UO2)(NO3)4 single crystals

A new radical observed at low temperature in γ-irradiated K₂(UO₂)(NO₃)₄ single crystals has been tentatively assigned to a hitherto unknown oxyanion radical, NO²⁺₃. The assignment and the lack of ¹⁴N hyperfine structure, together with the g factors which are lower than the free-spin value, are discussed in terms of an orbital level scheme.     

Ti/TiO_2纳米管阵列/PbO_2-Pr电极制备及在电氧化有机废水中应用

以二氧化钛纳米管阵列(TiO_2NTs)为基体,利用脉冲电沉积的方法将Pr掺杂的PbO_2修饰到TiO_2NTs管中,制备出新型电极材料Ti/TiO_2NTs/nanoPbO_2-Pr用来降解有机废水。通过循环伏安测试(CV)和线性伏安法(LSV)等手段对电极性能进行评估,研究表明,新型电极材料Ti/TiO_2NTs/nanoPbO_2-Pr具有高的电催化活性。利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)等对其进行表面形貌、晶形结构和元素组成进行研究。结果表明,通过脉冲电沉积成功将Pr-PbO_2沉积到TiO_2纳米管中,其中元素Pr是以Pr_2O_3形式存在。亚甲基蓝降解实验证明,Ti/TiO_2NTs/nanoPbO_2-Pr电极降解120min后亚甲基蓝的去除率高达99.8%。     

Transport coefficients of titanium-doped Sb2Te3 single crystals

Titanium-doped single crystals (c_Ti=0-2×10²⁰ atoms cm⁻³) were prepared from the elements Sb, Ti, and Te of 5 N purity by a modified Bridgman method. The obtained crystals were characterized by measurements of the temperature dependence of the electrical resistivity, Hall coefficient, Seebeck coefficient and thermal conductivity in the temperature range of 3-300 K. It was observed that with an increasing Ti content in the samples the electrical resistivity, the Hall coefficient and the Seebeck coefficient increase. This means that the incorporation of Ti atoms into the Sb₂Te₃ crystal structure results in a decrease in the concentration of holes in the doped crystals. For the explanation of the observed effect a model of defects in the crystals is proposed. The data of the lattice thermal conductivity were fitted well assuming that phonons scatter on boundaries, point defects, charge carriers, and other phonons.     

Preferential growth orientation of laser-patterned LiNbO3 crystals in lithium niobium silicate glass

Dots and lines consisting of LiNbO₃ crystals are patterned on the surface of 1CuO-40Li₂O-32Nb₂O₅-28SiO₂ (mole ratio) glass by irradiations of continuous-wave Nd:YAG laser (wavelength: λ=1064 nm), diode laser (λ=795 nm), and Yb:YVO₄ fiber laser (λ=1080 nm), and the feature of laser-patterned LiNbO₃ crystal growth is examined from linearly polarized micro-Raman scattering spectrum measurements. LiNbO₃ crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. The growth direction of an LiNbO₃ along the laser scanning direction is the c-axis. It is proposed that the profile of the temperature distribution in the laser-irradiated region and its change along laser scanning would be one of the most important conditions for the patterning of crystals with a preferential growth orientation. Laser irradiation giving a narrow width is also proposed to be one of the important factors for the patterning of LiNbO₃ crystal lines with homogeneous surface morphologies.     

Overhauser shift in single crystals of FA2PF6

The shift ΔB_ov of the ESR line due to the saturation of the NMR of hyperfine-coupled nuclei (Overhauser shift) was measured for single crystals of the organic conductor (FA₂)^±PF₆^?. ΔB_ov is proportional to AP, where A is the average hyperfine interaction between the conduction electrons and the nuclei in resonance and P is the dynamic nuclear polarization. The proton spin relaxation times were measured from the time dependence of the Overhauser shift, ΔB_ov(t), after rf pulses.     

Superstructure and stacking faults in hydrothermal-grown KBe2BO3F2 crystals

The structure of the hydrothermal-grown nonlinear optical crystal KBe₂BO₃F₂ was investigated. A new structure of the R3?c space group with cell parameters of a=4.422(1) Å and c=37.524(3) Å was obtained by powder X-ray diffraction and Rietveld refinement. The new structure is a 1×1×2 superstructure of the previously reported R32 structure with a different stacking sequence of (Be₂BO₃F₂)_∞ layers along the c axis. The relationship between the refined structure and the experimental results is discussed. A stacking fault mechanism is proposed for the formation of the superstructure as well as the nonuniformity of the hydrothermal-grown KBBF crystals.     

Electric field gradients in the ionic crystals NaNO2, NaBF4, NaNO3, and Ba(NO3)2

The electric field gradients (EFG) at the sites of the cations and the “central” atoms of the anions in the ionic crystals NaNO₂, NaBF₄, NaNO₃ and Ba(NO₃)₂ are calculated by a method based on a combination of the semi-empirical INDO method for the charge distribution and the intramolecular EFG with a lattice summation in the framework of the extended multipole model. At some lattice sites the contribution of the induced dipole and quadrupole moments to the EFG is comparable with the contribution of the point charges. The charge distribution within the molecular ions is found by adjusting either the calculated asymmetry parameter η or the z-component of the EFG to the experimental value deduced from nuclear quadrupole coupling constants. These charge distributions are in good agreement with those gained from INDO calculations. The calculated and experimental quadrupole coupling constants of nuclei in anions and cations are compared.