Relaxation studies of spray deposited Bi2Co0.1V0.9O5.35 solid electrolyte thin films on stainless steel substrate

The room temperature-stabilized γ-phase ion conducting Bi₂Co_0.1V_0.9O_5.35 thin film was deposited by spray pyrolysis on stainless steel substrate. The intra-grain and grain interior charge transfer was confirmed in these films with impedance spectroscopic measurements done from 1 Hz to 10 MHz in the temperature range 550 K to 741 K. Impedance data further revealed non-Debye kind of relaxation dispersion in the film. The relaxation frequency ranges from 10 to 100 Hz, which predicts long range jumping of the oxygen ions with chemical diffusivity. The Arrhenius plots for relaxation frequency and grain boundary conductivity were found to have same activation energy revealing grain boundary dominant conduction. The effect of polycrystallinity on relaxation dispersion is investigated for the first time on Bi₂Co_0.1V_0.9O_5.35 thin films using impedance formalism.     

热处理温度对钴卟啉负载碳黑电催化剂的结构及氧还原性能的影响

制备了钴卟啉负载碳黑催化剂(CoTMPP/BP2000)用于燃料电池阴极氧还原反应. 利用循环伏安法研究了200～900 ℃热处理温度对催化性能的影响. 研究结果表明, 热处理能够提高CoTMPP/BP2000的催化活性, 热处理温度为900 ℃时, 催化剂的氧还原能力最好. 利用紫外-可见光谱、透射电镜、红外光谱、热重分析及X射线光电子能谱等手段研究了热处理温度对催化剂结构的影响. 结果表明, 热处理改变了催化剂的活性中心结构, 400 ℃以上热处理使催化剂中钴卟啉环的结构坍塌, Co—N4键断裂; 900 ℃高温下形成了稳定的Co—Nx—C结构, 新的活性位使催化剂的氧还原能力得到提高.     

Structural features, nonstoichiometry and high-temperature transport in SrFe1−xMoxO3−δ

The oxide solid solutions SrFe_1−xMo_xO_3−δ, where x=0.05, 0.1 and 0.2, are studied in this work. It is shown that substitution of iron for molybdenum results in stabilization of a cubic quasi-perovskite locally inhomogeneous structure, which is evidenced by HREM and Mössbauer spectroscopy. The coulometric titration is used in order to determine changes of oxygen nonstoichiometry in the obtained solutions with temperature and ambient oxygen partial pressure. Partial molar thermodynamic functions of the labile oxygen are calculated from the measured data. The variations of partial molar entropy with oxygen content follow the ideal gas model reasonably well thus demonstrating approximately random distribution of oxygen vacancies in the doped ferrite at high temperatures. The partial molar enthalpy is found to increase with doping, which is indicative of a progressive decrease in average values of the bonding energy of labile oxygen ions. The measurements of total conductivity are used in order to determine partial contributions of charge carriers. The oxygen ion component is shown to increase at small level of doping, x=0.05 while further increase in molybdenum content is accompanied with the decline in the ion conductivity. The electron contribution in reducing conditions tends to increase with molybdenum content, which is interpreted as a manifestation of involvement of Mo⁵⁺ cations in electron transport. Concentration and mobility of electron carriers are calculated. Some increase in mobility of electron holes at small doping is explained as related to the filling of oxygen vacancies.     

Synthesis, crystal structure and magnetic properties of the Sr2Al0.78Mn1.22O5.2 anion-deficient layered perovskite

A new layered perovskite Sr₂Al_0.78Mn_1.22O_5.2 has been synthesized by solid state reaction in a sealed evacuated silica tube. The crystal structure has been determined using electron diffraction, high-resolution electron microscopy, and high-angle annular dark field imaging and refined from X-ray powder diffraction data (space group P4/mmm, a=3.89023(5) Å, c=7.8034(1) Å, R_I=0.023, R_P=0.015). The structure is characterized by an alternation of MnO₂ and (Al_0.78Mn_0.22)O_1.2 layers. Oxygen atoms and vacancies, as well as the Al and Mn atoms in the (Al_0.78Mn_0.22)O_1.2 layers are disordered. The local atomic arrangement in these layers is suggested to consist of short fragments of brownmillerite-type tetrahedral chains of corner-sharing AlO₄ tetrahedra interrupted by MnO₆ octahedra, at which the chain fragments rotate over 90°. This results in an averaged tetragonal symmetry. This is confirmed by the valence state of Mn measured by EELS. The relationship between the Sr₂Al_0.78Mn_1.22O_5.2 tetragonal perovskite and the parent Sr₂Al_1.07Mn_0.93O₅ brownmillerite is discussed. Magnetic susceptibility measurements indicate spin glass behavior of Sr₂Al_0.78Mn_1.22O_5.2. The lack of long-range magnetic ordering contrasts with Mn-containing brownmillerites and is likely caused by the frustration of interlayer interactions due to presence of the Mn atoms in the (Al_0.78Mn_0.22)O_1.2 layers.     

Mössbauer investigation of Fe doped La4Ni3O10±y phases

⁵⁷Fe doped La₄Ni_2.97Fe_0.03O_9.95 was synthesized by a citrate method and, afterwards, successfully oxidized and reduced by electrochemical methods. The compounds obtained were investigated by X-ray diffraction, electrical measurements and Mössbauer spectroscopy. The study allowed to follow the variation of the two nickel sites environment with the oxygen stoichiometry and a deeper understanding of the electrical behavior versus oxygen non-stoichiometry was achieved. The Mössbauer study revealed that after both oxidation and reduction treatments, the major modifications were observed on the octahedra adjacent to the La₂O₂ layers, while the middle octahedra of the triple perovskite block remained almost unchanged. The oxygen intercalation (oxidized treatment) takes place essentially in the La₂O₂ layers and the oxygen desintercalation (reduction treatment) occurs in the octahedral sites adjacent to those layers.     

Cyclic Voltammetrically Prepared MnO2‐Polyaniline Composite and Its Electrocatalysis for Oxygen Reduction Reaction (ORR)

The composite of manganese dioxide‐polyaniline (MnO₂‐PANI) was successfully prepared by cyclic voltammetry (CV) from a 0.5 M H₂SO₄ solution containing 0.2 M aniline and 0.5 M MnSO₄. Scanning electron microscopy (SEM) images revealed that cauliflower like manganese dioxides entangled with PANI were generated. The spectra obtained from UV‐vis spectrophotometry (UV‐vis) and Fourier transform infrared spectrometry (FTIR) strongly demonstrated that this novel composite was composed by MnO₂ and PANI, and also there was an interaction between MnO₂ and PANI. Then, for the first time, this resultant composite was modified on a graphite electrode and employed in the oxygen reduction reaction (ORR), subsequently, the obtained cyclic voltammograms (CVs) verified that ORR could proceed on this resultant composite of MnO₂‐PANI. Lastly, the possible catalysis mechanism of MnO₂‐PANI towards ORR was proposed based on the results we acquired. Developing a novel substrate on which ORR could proceed is the main contribution of this work.     

EPR study of radiation damage to DNA irradiated with synchrotron soft X-rays around nitrogen and oxygen K-edge

In order to obtain detailed insights into the physicochemical mechanism of DNA damage induction, “in situ” measurement of electron paramagnetic resonance (EPR) signal from DNA constituent nucleobases, guanine and adenine, has been performed in a vacuum using monochromatic synchrotron soft X-rays. We found that short-lived unpaired electron species arise only during irradiation to the evaporated thin film on a surface. The EPR spectrum of the short-lived species significantly depends on the photon energy irradiated, and the spin concentration obtained from the EPR spectra shows a similar fine structure to the X-ray photoabsorption spectra (X-ray absorption near edge structure; XANES). For the adenine sample, the spin concentration alters strikingly by water absorption on the sample surface. Trapping of photo- or Auger electrons into a newly generated potential in the nucleobases as the consequence of photoelectric effect is suggested as mechanisms of the induction of the short-lived species.     

氧原子在具有Pt皮肤的Pt3Ni(111)表面的吸附和扩散

用基于密度泛函理论的第一性原理方法研究了氧原子在具有Pt皮肤的Pt3Ni(111)[记为Pt-skin-Pt3Ni(111)]表面的吸附和扩散特性. 重点研究了氧原子在Pt-skin-Pt3Ni(111)表面的扩散问题, 这对理解Pt-skin-Pt3Ni(111)催化剂的高催化活性有重要意义. 结果表明: 氧原子容易吸附在fcc位; 催化剂Pt3Ni中的Ni原子对催化剂的电子结构有很大影响, 从而改变了其对氧原子的吸附. 用推拉弹性带(NEB)方法搜索氧原子的扩散势垒, 并解释了Pt-skin-Pt3Ni(111)催化剂的高催化活性.     

Modeling of vibration–electronic–chemistry coupling in the atomic–molecular oxygen system

The comprehensive analysis of the kinetic processes in the atomic–molecular oxygen system is conducted on the base of the novel state-to-state model involving both electronically and vibrationally excited O₂ molecules: and O(³P), O(¹D) atoms as well as vibrationally excited O₃(¹A₁) molecules. The model describes properly experimental data on the total removal rate of vibrationally excited molecules, the temporal evolution of the population of , and on the variation of vibrational temperature of behind strong shock wave. It is demonstrated that to describe with reasonable accuracy the variation of macroscopic flow parameters (pressure, temperature, density, and velocity) in the post shock region it is sufficient to use the widely applied model of mode approximation but in order to predict properly the species concentrations and populations of vibronic states of molecules just downstream the shock front it is needed to use state-to-state consideration.     

Ordered hierarchical mesoporous anatase TiO2 from yeast biotemplates

A novel approach is proposed to prepare ordered hierarchical mesoporous TiO₂ by using yeast cells as the template via biomimetic mineralization. The structure and the mophology were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), Raman spectra, high-resolution transmission electron microscopy (HRTEM), and N₂ adsorption–desorption isotherms (NADI). The bio-templated TiO₂ has a hierarchical pore structure mainly distributed at 4.7 nm and 11.3 nm. An air electrode fabricated using this hierarchical mesoporous TiO₂ exhibited remarkable electrocatalytic activity for oxygen reduction reaction (ORR). Compared to the electrolytic manganese dioxide (EMD) air electrode employed commercially, a 90% higher catalytic reduction current was achieved for this mesoporous TiO₂ electrode. It is supposed that the hierarchically mesoporous structure and ordered pore distribution play important roles in significantly reducing electrochemical polarization and improving mass transport of the air diffusion electrode. This simple and efficient approach could spread as a general way to prepare advanced mesoporous materials in mild condition.