Effect of cation-exchange layer thickness on electrochemical and transport characteristics of bipolar membranes

To study the effect of cation-exchange layer thickness on the electrochemical and transport characteristics of bipolar membranes (BPM), asymmetric BPM with varied cation-exchange layer thickness (of 10, 30, 50 and 70 μm) were investigated. High influence of BPM monopolar layers thickness on its selectivity had been shown. This fact is non-trivial in relation to monopolar ion-exchange membranes as their selectivity does not depend on their thickness. At the same time, increase or decrease in the thickness of BPM monopolar layers can increase products purity or, on the contrary, combine ion transport and pH shift functions.     

Electrochemical characterization and assessment of performance of zirconium phosphate and zinc modified zirconium phosphate membranes in aqueous sodium chloride solutions

Prepared membranes, zinc-zirconium phosphate (M-1 and M-2) and zirconium phosphate (M-3) were electrochemically characterized by membrane potential and membrane conductance measurements using aqueous sodium chloride solution of varying compositions. The data have been used for the estimation of transport number of ions and solvent in the membrane phase in addition to permselectivity and membrane fixed charge density. Membrane conductance data were used to estimate the ionic permeability and verify diffusion controlled criteria endowed with the membrane phase. Solute and co-ion permeabilities were compared and found that their values were comparable. Solute rejection of membranes was examined for limiting and intermediate cases of solute–solvent interaction in the membrane phase along with positional solute rejection. Zirconium phosphate membrane showed considerable polarization index deviation from unity indicates its minor perspective than zinc-zirconium phosphate membrane. Results show that zinc modified zirconium phosphate membranes reflected modified elastic properties than zirconium phosphate membrane. The well-known Teorell–Meyer–Sievers (TMS) theory, which describes the membrane potential for charged membranes, was considered as a frame work.     

Vacuum sintering of a ceramic based on zirconium dioxide

The results of a study of the phase composition and mechanical properties of a ceramic based on ZrO₂-Y2O₃ after vacuum sintering of powders with complex morphology in a wide range of temperatures and sintering holding times are reported. Dense ceramic materials with high mechanical properties were obtained.Translated from Steklo i Keramika, Nos. 5–6, pp. 27–29, May–June, 1994.     

High-strength ceramic based on zirconium dioxide: preparation and properties

Strength properties are considered for ZrO₂ hot-pressed ceramic materials stabilized with 4 – 6 wt.% Y₂O₃ in relation to original powder preparation method: solid phase synthesis, high-temperature salt thermolysis, combined hydroxide precipitation followed by freezing, drying and calcining, and the sol-gel method. Ceramic material with the highest strength in bending (up to 1350 MPa) are prepared from ZrO₂ – 5 wt.% Y₂O₃ powders, synthesized by coprecipitation of hydroxides followed by freezing.     

A strong ceramic based on aluminum oxide and zirconium dioxide

The theoretical premises and experimental results on fabrication of ceramics based on aluminum oxide with a regulatable structure which ensures high strength properties and the possibility of wide use in different areas of technology were reported. The effect of adding zirconium oxide to aluminum oxide on the structure and strength properties of the ceramics was demonstrated. New ceramic materials having a high strength were developed with highly disperse powders. The technological parameters of corundum ceramics of the “Koral” type and materials from mixtures of zirconium dioxide and aluminum oxide containing tetragonal and cubic solid solutions based on zirconium dioxide were developed. Stable results were obtained for the strength properties of ceramics made of special-purity tetragonal zirconium dioxide.     

Corrosion electrochemical behavior of epoxy anticorrosive paints based on zinc molybdenum phosphate and zinc oxide

Electrochemical impedance spectroscopy (EIS) was applied as a principal tool to describe the efficiency of anticorrosive epoxy paints (primers) based on zinc molybdenum phosphate (ZMP) pigment. Steel-coated samples were exposed to a 0.5 M NaCl solution. During the study the corrosion potential (E_oc) and R_p values also were monitored every 24 h. It is discussed the incorporation of micronized ZnO (1 μm) pigment to the base mixture and its positive, reinforcement effect on the protective properties of ZMP primer. The explanation is related to the izoelectric point (IEP) of ZnO particles (pH < 9), which determines their positive surface charge and electrostatic attraction with the molybdate anion. In this case the charge of the formed double layer capacitor is very high. Moreover, the mentioned attraction inhibits and saves ZnO particles from their rapid dissolution to hydroxide.     

Catalytic reactors based on porous ceramic membranes

This overview discusses some of the developments and outstanding opportunities in the field of catalytic reactors based on porous ceramic membranes, both inert and catalytic. This is an emerging area, where inputs from heterogeneous catalysis, material science and reactor engineering are playing the key roles. Rather than attempting a thorough review of the relevant literature, this work deals with some general concepts and then concentrates on a few selected examples that illustrate the application of membrane reactors.     

二茂铁表面活性剂的合成及其电化学行为研究

合成了具有可逆特性的二茂铁表面活性剂N,N-二甲基二茂铁甲基正辛烷基溴化铵(Fc8),并以玻碳电极为工作电极,采用循环伏安法研究了Fc8在0.1 mol/L NaCl溶液中的电化学行为,讨论了pH、扫描速度及底物浓度对Fc8电化学行为的影响。结果表明,Fc8在pH<8的条件下具有良好的可逆性,可在氧化态(I2+)与还原态(I+)之间实现变换;Fc8在玻碳电极上的氧化峰电流(Ipc)与扫描速度呈现线性关系(R2>0.998),说明Fc8的电化学行为是受扩散控制的可逆过程;Ipc和扩散系数(D)在Fc8的临界胶束浓度(CMC)附近出现突变,在CMC以上,Ipc与D随表面活性剂浓度缓慢变化,该规律与Fc8表面张力变化趋势吻合,表明峰电流和扩散系数随Fc8浓度变化较快。     

Pore model parameters of cation-exchange membranes

Parameters of the equivalent pore model of different membranes (NAFION-125, MRF-26, and the polyethylene-polystyrenesulphonic acid membranes (PE/PSSA)) were estimated from measurements of water hydraulic permeabilities. The pore radius calculations were performed according to the modified Ferry-Elford equation r_θ = r_FEθ, where r_FE is the radius calculated from the Ferry-Elford relation and Å the tortuosity factor. The PE/PSSA membranes, expanded in hot water, were similar to the MRF-26 membranes in their equivalent pore model parameters (radius 20 – 24 Å, and specific permeation rate 5.09 and 4.30.10^?16 cm², respectively). The NAFION-125 membrane exhibits the smallest pore radius (14 Å) and specific permeation rate (0.841·10^?16 cm²).     

Modification of refractory ceramic composites with coatings based on compounds of titanium and zirconium

This article describes the properties and features of formation of modifying coatings developed for refractory materials on the basis of compounds of titanium and zirconium. It also explains the principles behind the interaction of the resulting composites with melts of metallurgical slag and borosilicate glass.     

Microwave-sintering preparation and densification behavior of sodium zirconium phosphate ceramics with ZnO additive

The dense NaZr₂(PO₄)₃ (NZP) ceramics were successfully prepared by a microwave sintering process with x wt.% ZnO as a sintering aid (where x = 0, 0.5, 1.0, 2.0 and 3.0). The effects of ZnO additive on the crystal structure, microstructure and sintering behavior of as-prepared NZP ceramics were systematically investigated. The single NZP phase can be achieved in the wide temperature range of 900–1200 °C holding for 2 h by microwave-sintering technology. The addition of ZnO sintering aid would not noticeably change the crystal structure of NZP. Importantly, ZnO additive significantly promoted the densification and 1.0 wt% ZnO-added sample possessed the maximum relative density of 96.5% after sintering at 1100 °C, considerably higher than that of pure NZP sample. Besides, the Vickers hardness of the above sample could attain near 800 MPa, which is about four times as hard as the pure NZP ceramics without ZnO additive. It was suggested that the combination of microwave sintering with appropriate addition of ZnO sintering aid would provide a convenient and efficient method for rapid fabrication of dense NZP ceramics.     

Silicate and zirconium phosphate modified Nafion/PTFE composite membranes for high temperature PEMFC

The PEMFC performance of MEAs prepared from Nafion-212 (thickness 50 μm, Du Pont Co), porous poly(tetrafluoro ethylene) (PTFE, thickness 15 ~ 18 μm) film reinforced Nafion (NF, thickness 20 ± 2 μm), silicate hybridized NF (NF-Si, thickness 21 ± 2 μm), and zirconium phosphate hybridized NF (NF-Zr, thickness 21 ± 2 μm) membranes were investigated at 110 °C/ 51.7% RH, 120 °C/ 38.2% RH, and 130 °C/ 28.6% RH. We show PEMFC performances of these MEAs decrease in the sequence of: NF-Zr> NF-Si> NF> Nafion-212. The NF, NF-Si, and NF-Zr membranes have lower membrane thickness and lower Nafion content and require less water for proton transport than Nafion-212 at temperatures above 110 °C, and thus have higher conductivity and better PEMFC performance than Nafion-212. Incorporating silicate and zirconium phosphate into NF membranes enhances water retention of membranes at temperatures above 110 °C and improves PEMFC performances. Besides enhancing water retention, incorporating zirconium phosphate into membranes also provides more routes for proton transport via H⁺ exchange between H₃ ⁺O and HPO₄-Zr- and between H₂ ⁺PO₄-Zr- and HPO₄-Zr-. Thus NF-Zr has a higher conductivity and better PEMFC performance than NF and NF-Si.     

Battery-like behavior of Ni-ceria based systems: Synthesis,surface defects and electrochemical assessment

NiO, CeO₂ and respective composites are extensively used in energy storage devices due to mostly their high electrochemical activity. However, the assessment of battery-like behavior of Ni-ceria based systems comprising (Ni or Gd)-doped ceria combined with NiO seems to be neglected in the literature. In this work, NiO and ceria-based solid solutions composite powders were obtained by a co-precipitation synthesis method. The structure and particle size of the calcined powders were investigated by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM), respectively. Oxidative states of composites were inspected by X-ray photoelectron spectroscopy (XPS). The electrochemical performance of powders was evaluated by cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy. Refinement of the XRD patterns showed that powders have nanosized crystallites and mean size of particles within 20 – 70?nm were revealed by FESEM. The improved specific capacity of the NiO-CeO₂ electrode material (about 2.5 times higher than that of NiO-CGO at 5?mV?s^?1) is due to an increase in Faradic reactions taken place on its surface with a higher fraction of defects (namely Ni³⁺, Ce³⁺ and oxygen vacancies), as determined by XPS. The superior electrochemical performance of the NiO-CeO₂ electrode is also confirmed by electrochemical impedance spectroscopy.     

Selective oxidation on chromia-pillared zirconium phosphate and phenylphosphonate

Chromia-pillared zirconium phosphate and zirconium phenylphosphonate were prepared by an indirect intercalation method. The pillared materials have surface area in the range of 316–462 m²/g and narrow pore size distributions with mesoporosity. They are efficient catalysts for selective oxidation of aromatics, alkanes, cycloalkanes, cycloalkenes and alcohols using 30% H₂O₂ as the oxidant with catalytic activities much higher than CrAPOs and CrMCM-41. This revised version was published online in July 2006 with corrections to the Cover Date.     

镁离子掺杂磷酸铁锂的制备及其电化学性能

通过简单水热反应制备磷酸铁锂前驱体,并结合后期热处理过程制备了镁离子掺杂碳包覆的磷酸铁锂正极材料。利用X射线衍射（XRD）、扫描电镜（SEM）和透射电镜（TEM）等表征了镁离子掺杂磷酸铁锂的成分、形貌和结构。元素分布结果证明镁离子均匀掺杂在磷酸铁锂材料中。通过恒流充放电和循环伏安、交流阻抗等方法对材料的电化学性能进行测试。结果表明,镁离子掺杂后的磷酸铁锂材料具有较高的放电比容量（0.1C放电比容量为 160.1 mA·h/g）和优越的倍率性能（20C放电比容量为77.2 mA·h/g）,同时减小了极化和电荷迁移电阻。这条合成路线是提高水热法制备磷酸铁锂正极材料电化学性能的有效方法。     

有序介孔磷酸锆的研究进展

简要阐述了磷酸锆材料的特点和应用发展现状,重点探索了有序介孔磷酸锆的制备方法及表征技术,对于磷酸锆材料研究及制备中存在的问题进行了归纳。