一锅法合成四芳基吡咯并[3,2-b]吡咯空穴传输材料及其在无掺杂倒置钙钛矿太阳电池的应用

本文采用一锅法合成了四芳基吡咯并[3,2-b]吡咯有机空穴输运材料(D41、D42、D43和D44),制备出无掺杂的倒置型平面钙钛矿太阳电池. 材料D41的芳环上含有甲基,具有供体-π-给体-π-供体结构;而D42、D43和D44具有受体-π-给体-π-受体结构,其中,芳环上分别含有氰基、氟和三氟甲基. 研究表明,芳环上取代基对其分子表面电荷分布和空穴输运层薄膜形貌有显著影响,钙钛矿晶体颗粒的大小与空穴输运材料分子结构有关,含有氰基的材料D42最有利于形成较大的钙钛矿晶粒,这主要是由于吡咯并[3,2-b]吡咯结构具有丰富的电子性质的缘故. D42制备的倒置型平面钙钛矿太阳电池光电转换效率为17.3%,在黑暗条件下22天后,仍保留了初始效率的55%. 吡咯并[3,2-b]吡咯结构具有良好的给电子特性,可作为高效钙钛矿薄膜的空穴传输材料.     

Sono-photo-Fenton oxidation of bisphenol-A over a LaFeO3 perovskite catalyst

In this study, oxidation of bisphenol-A (IUPAC name – 2,2-(4,4-dihydroxyphenyl, BPA), which is an endocrine disrupting phenolic compound used in the polycarbonate plastic and epoxy resin industry, was investigated using sono-photo-Fenton process under visible light irradiation in the presence of an iron containing perovskite catalyst, LaFeO₃. The catalyst prepared by sol–gel method, calcined at 500 °C showed a catalytic activity in BPA oxidation using sono-photo-Fenton process with a degradation degree and a chemical oxygen demand (COD) reduction of 21.8% and 11.2%, respectively. Degradation of BPA was studied by using individual and combined advanced oxidation techniques including sonication, heterogeneous Fenton reaction and photo oxidation over this catalyst to understand the effect of each process on degradation of BPA. It was seen, the role of sonication was very important in hybrid sono-photo-Fenton process due to the pyrolysis and sonoluminescence effects caused by ultrasonic irradiation. The prepared LaFeO₃ perovskite catalyst was a good sonocatalyst rather than a photocatalyst. Sonication was not only the effective process to degrade BPA but also it was the cost effective process in terms of energy consumption. The studies show that the energy consumption is lower in the sono-Fenton process than those in the photo-Fenton and sono-photo- Fenton processes.     

Magnetic properties and magnetocaloric effect of Sr-doped Pr0.7Ca0.3MnO3 compounds

In this work, we pointed out that Sr substitution for Ca leads to modify the magnetic and magnetocaloric properties of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds. Analyzing temperature dependence of magnetization, M(T), proves that the Curie temperature (T_C) increased with increasing Sr content (x); T_C value is found to be 130–260 K for x = 0.0–0.3, respectively. Using the phenomenological model and M(T,H) data measured at several applied magnetic field, the magnetocaloric effect of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds has been investigated through their temperature and magnetic field dependences of magnetic entropy change ΔS_m(T,H) and the change of the specific heat change ΔC_P(T,H). Under an applied magnetic field change of 10 kOe, the maximum value of -ΔS_m is found to be about 3 J/kg·K, and the maximum and minimum values of ΔC_P(T) calculated to be about ±60 J/kg·K for x = 0.3 sample. Additionally, the critical behaviors of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds around their T_C have been also analyzed. Results suggested a coexistence of the ferromagnetic short- and long-range interactions in samples. Moreover, Sr-doping favors establishing the short-range interactions.     

Perovskite-type Ba0.5Sr0.5Al0.1Fe0.9O3-δ as Intermediate-Temperature Solid Oxide Fuel Cell Cathode

A cobalt-free perovskite-type Ba_0.5Sr_0.5Al_0.1Fe_0.9O_3-δ (BSAF) is developed and electro-chemically studied as solid oxide fuel cell (SOFC) cathode. The structures, electrical con-ductivity, and electrode polarizations in symmetrical cell based on mixed ion conducting electrolyte were investigated, respectively. The temperature dependence of conductivity of BSAF in air shows a typical semiconductor behavior with positive temperature coefficient up to 450 oC where the conductivity reaches 14.0 S/cm while above this temperature the negative temperature coefficient dominates the total conductivity. Electrochemical charac-terizations show desirable polarization resistance of BSAF cathode in a symmetric cell based on mixed ion conducting electrolyte at 650-700 oC. A single SOFC with BSAF cathode shows OCV of 1.0 V and maximum output of 420 mW/cm₂ at 700 oC with humidified hydrogen fuel and static air oxidant.     

锰掺杂的钙钛矿型钛铌酸盐基复合阴极高温电解水蒸气

通过在氧化还原稳定的钙钛矿材料钛铌酸盐的B位晶格中掺杂具有氧化还原活性的锰元素提高固体氧化物电解池复合电极电催化性能．研究发现,锰元素成功取代钛铌酸盐B位的Ti／Nb．掺杂后的样品的离子电导率在800℃下的氧化气氛和还原气氛下的离子电导率分别提高了约1和0．5个数量级．基于掺杂后的钛铌酸盐基复合阴极,氧离子传导型固体氧化物电解池电解水蒸汽的电流效率在有和无还原气体保护下分别提高了25％和30％．     

Preparation and characterization of KTa0.9Fe0.1O3– δ perovskite electrodes

The effect of the partial substitution of tantalum by iron on the structural and electrical properties of the KTaO₃ perovskite-type oxide powders has been studied. The powders were prepared by the standard ceramic method, and the respective structural characterization performed by X-ray powder diffraction. From the synthesized oxide samples, iron-coated electrodes were fabricated and tested as the anode for the oxygen evolution reaction in alkaline medium. An estimation of the electrode's capacity has been calculated from the charging currents and the corresponding roughness factor evaluated. The electrocatalytic activity/stability of the oxide electrodes in alkaline solutions has been analysed through the kinetic parameters. Electronic Publication     

Soft mode dynamics of perovskite type crystals

The soft mode dynamics and related properties of perovskite, ABO₃-type crystals have been studied using the operator form of the model Hamiltonian proposed by Pytte. The correlations have been evaluated using the double time thermal Green’s function technique and Dyson’s equation. Without any decoupling, the higher order correlations, appearing in the dynamical equation, have been evaluated using the renormalized Hamiltonian. The dielectric properties are directly related to the optical soft mode. The phonon width and shift have been calculated for different structural phases. The analysis of the temperature dependence of microwave loss tangent and dielectric constant explains the experimental results.     

Effect of the rare earth in the perovskite-type mixed oxides AMnO3 (A=Y, La, Pr, Sm, Dy) as catalysts in methanol oxidation

The effect of the rare earth in the perovskite-type mixed oxides AMnO₃ (A=Y, La, Pr, Sm, Dy) on catalytic properties in methanol oxidation was investigated in this work. The perovskites were prepared by reactive grinding in order to enhance the specific surface area in comparison with other classical synthesis procedures. These catalysts were characterized by N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction (TPR-H₂), O₂-, CH₃OH- and CO₂-temperature-programmed desorption (TPD). The activity of the five catalysts under study in the methanol oxidation reaction was evaluated. The behaviour of the α-O₂ from the surface of the perovskite was strongly related to the nature of the A-site cation and particularly to its electronegativity but also to its density. Concerning the β-O₂ from the bulk, the rare earth only induces an indirect effect notably due to structural modifications. As suggested in a previous study, the activity in methanol oxidation was directly linked with the surface oxygen density. Under an excess of α-oxygen, the reaction intermediate was found to be a monodentate carbonate that decomposes into CO₂. The stability of monodentate carbonates was also found to be related to the electronegativity of the rare earth during both CH₃OH- and CO₂-temperature-programmed desorption. However, as soon as a lack of α-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate that induces a consumption of anion vacancies in spite of the production of CO₂. Nevertheless, the accumulation of these carbonates leads to a decrease in the oxidation rate since their desorption requires high temperatures.     

The enhancement of oxygen flux on Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) hollow fibers using silver surface modification

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) hollow fibers were fabricated using a phase inversion/sintering method. As oxygen permeation of BSCF hollow fibers is controlled by the rate surface exchange kinetics, catalytic Ag particles were coated on both inner and outer surfaces using chemical deposition method, as verified by SEM and EDX. The Ag coated BSCF membranes showed up to 100% increase in oxygen permeation at 700 °C, and improvements lower than 10% were measured at 950 °C as compared with unmodified membranes. It was found that Ag catalyst surface loading was non-homogenous and concentrated on the perovskite grain boundaries. As a result, lighter Ag surface loading delivered improved oxygen flux while oxygen flux reached a maximum even though in the presence of excess catalyst loading. The catalytic activity of Ag was beneficial in enhancing surface reaction kinetics up to 850 °C attributed to the spillover effect. Above this temperature, the increase in oxygen permeation rate was marginally diminished due to the reduction of the spillover effect.