PbO2-MnO2共沉积电化学行为研究

采用旋转圆盘电极(Rotating disk electrode,RDE),通过循环伏安法(Cyclic voltammetry,CV)分析了硝酸锰浓度、硝酸浓度、硝酸铅浓度和溶液温度对PbO_2和MnO_2共沉积的影响规律,获得了PbO_2和MnO_2共沉积的最优条件。探究了旋转圆盘电极转速对PbO_2和MnO_2共沉积的影响,发现最优条件下其共沉积行为主要受电化学控制。使用扫描电镜(Scanning electron microscope,SEM)观察PbO_2-MnO_2沉积层表面形貌,发现PbO_2-MnO_2沉积层表面以圆球状结构为主。通过X射线衍射仪(X-ray diffraction,XRD)检测到PbO_2-MnO_2沉积层表面出现了一种α-MnO_2、α-PbO_2、β-PbO_2三相同时存在的混合结晶状态。     

Synthesis of flake-like MnO2/CNT composite nanotubes and their applications in electrochemical capacitors

MnO2/CNT composite nanotubes with nanometer-sized flake-like MnO2 on carbon nanotubes' surfaces have been synthesized through an easy and efficient solution-based method. Similarly, Mn3O4/CNT composite nanotubes have also been synthesized by using the same method but different heat treatment process. The structures and compositions of the two types of composite nanotubes are characterized by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption isotherms. Electrochemical measurements indicate that the MnO2/CNT composites nanotubes exhibit significantly enhanced supercapacitance performance compared with the Mn3O4/CNT composite nanotubes, the as-synthesized MnO2 nanoparticles and commercial MnO2. The possibilities of the enhanced properties are illustrated on the basis of analysis of XRD and X-ray photoelectron spectroscopy measurements. Our results presented here can give clear evidence of the superiority of nanocrystalline MnO2 to nanocrystalline Mn3O4 toward the applications as electrode materials in electrochemical capacitors.     

Hydrothermal Synthesis and Electrochemical Behavior of Nanosized Orthorhombic LiMnO2

Nanosized orthorhombic LiMnO2 was successfully synthesized using Mn2O3 and LiOH-H2O as starting materials. Not only the reaction temperature was lower, but the reaction time for synthesizing was notably shortened to 1h. In this hydrothermal process, the cations of the starting materials were capable of mixing and interacting in ionic scale, which resulted in the rapid formation of o-LiMnO2 powders at relatively low temperature. The particle size conformed by transmission electron microscopy is around 50-150 nm. Benefiting from its small particle size and good uniformity, the obtained o-LiMnO2 can reach the maximum discharge capacity of 163 mA·h·g-1 at 0.1 C rate after several cycles. X-ray diffraction data and electrochemical properties suggested the phase transformation from orthorhombic LiMnO2 to defect-type spinel LiMn2O4 with minor Li2MnO3, which resulted in the capacity fading during cycling.     

Structure,Morphology, and Electromagnetic Properties of Manganese Dioxide with Ni Doping

Hydrothermal synthesis between (NH ₄)₂S ₂O ₈ and MnSO ₄ was carried out to investigate the structure, morphology, and electromagnetic properties of Ni-doped MnO ₂ with different doping amounts. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and vector network analysis. The analysis results revealed that all the final products were α-MnO ₂ and few amounts of γ-MnO ₂, and the morphology changed obviously with the increase of the Ni doping amount. The doping of Ni had a certain effect on the electromagnetic properties, and some other properties derived from electromagnetic performances were also investigated, such as dielectric and magnetic loss tangent and microwave-absorbing properties. All the reflection loss (RL) peaks of the final products were moving toward lower frequency with increasing thickness, and with the thickness of 2 mm, the final products all had the maximum effective absorption bandwidth (RL < ?10 dB), and the Ni-doped MnO ₂ had better reflection loss performance than the undoped MnO ₂ in the range of high frequency.     

Co-precipitation synthesis and characterization of NiO-Ce0.8Sm0.2O1.9 nanocomposite powders: effect of precipitation agents

NiO-Ce0.8Sm0.2O1.9 (NiO-SDC) nanocomposite powders applied as promising anode material for low-temperature solid oxide fuel cells (SOFCs) were synthesized by hydroxide co-precipitation method using NH3 x H2O, NaOH and NH3 x H2O + NaOH as precipitation agents. The crystal phases, morphologies and sintering behavior of the synthesized NiO-SDC nanocomposite powders were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and sintering experiments. The effect of precipitation agents on the synthesis of the NiO-SDC nanocomposite powders was discussed. Results show that different precipitation agents influence greatly the synthesis and characteristics of the NiO-SDC nanocomposite powders. The NiO-SDC nanocomposite powders synthesized with NH3 x H2O deviate from the original composition due to the loss of Ni. The loss of Ni is avoided and nano-sized NiO-SDC composite powders are synthesized, when NaOH and NH3 x H2O + NaOH are used as precipitation agents. The NiO-SDC nanocomposite powders can be synthesized at relatively low temperature using NH3 x H2O + NaOH as precipitation agent, and the synthesized NiO-SDC nanocomposite powders show good sintering characteristics.     

Hydrothermal-reduction synthesis of manganese oxide nanomaterials for electrochemical supercapacitors

In the present work, amorphous manganese oxide nanomaterials have been synthesized by a common hydrothermal method based on the redox reaction between MnO4(-) and Fe(2+) under an acidic condition. The synthesized MnO2 samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and electrochemical studies. XRD results showed that amorphous manganese oxide phase was obtained. XPS quantitative analysis revealed that the atomic ratio of Mn to Fe was 3.5 in the MnO2 samples. TEM images showed the porous structure of the samples. Electrochemical properties of the MnO2 electrodes were studied using cyclic voltammetry and galvanostatic charge-discharge cycling in 1 M Na2SO4 aqueous electrolyte, which showed excellent pseudocapacitance properties. A specific capacitance of 192 Fg(-1) at a current density of 0.5 Ag(-1) was obtained at the potential window from -0.1 to 0.9 V (vs. SCE).     

干电池阴极活性材料化学MnO2的研究

在一定条件下,用碱金属和碱土金属金属的氯酸盐浆Mn2+氧化制得的化学MnO2,通过对其进行晶型和放电性能的测试,结果表明：所得产品均为γ-MnO2,且γ-MnO2的放电性能与相应的掺杂同族金属阳离子的半径大小变化呈现一定关系。     

Thermal Growth and Nanomagnetism of the Quasi-one Dimensional Iron Oxide

Quasi-one dimensional iron oxide nanowires with flat needle shape were synthesized on the iron powders by a rather simple catalyst-free thermal oxidation process in ambient atmosphere. The characterization by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman and high-resolution transmission electron microscopy (HRTEM) revealed that these nanostructures are single crystalline α-Fe2O3. The various dimensions with 40-170 nm in width and 1-8 μm in length were obtained by tuning the growth temperature from 280 to 480℃. A surface diffusion mechanism was proposed to account for the growth of quasi-one dimensional nanostructure. The typical α-Fe2O3 nanowires synthesized at 430℃ had a reduced Morin temperature TM of 131 K in comparison with their bulk counterpart. The coercivitis Hc of these nanowires are 321 and 65 Oe at 5 and 300 K, respectively. The temperature of synthesis also has important effects on the magnetic properties of these nanowires.     

Characterization of La(0.8)Sr(0.2)MnO(3 +/-delta) nanopowders synthesized by aerosol flame synthesis for SOFC cathode

Lanthanum strontium manganite (La(0.8)Sr(0.2)MnO(3 +/- delta), LSM) powders with a high specific surface area (55.26 m2/g) were successfully synthesized by aerosol flame synthesis (AFS) technique. The crystallinity and morphology of the synthesized powders sintered at various temperatures were studied by XRD, TEM and BET. The synthesized powders exhibited spherical shape mostly in a few nanometer ranges with a relatively high crystallinity due to thermal plasma reactions in a high temperature of oxy-hydrogen flame. To analyze electrochemical performances of synthesized LSM powders, impedance spectroscopy (IS) was carried out with the symmetric cells prepared by slurry based electrostatic spray deposition (ESD) onto the YSZ electrolyte pellet. The interfacial polarization resistances were 3.04 ohms cm2 at 750 degrees C which is relatively lower than that of micro-porous film (7.24 ohms cm2) applying micro-sized powders deposited on same condition.     

Preparation and Properties of Some Chemical and Electrochemical γ-MnO_2

Chemically prepared electrolytic γ-MnO2 and an electrodeposited MnO2 doped with Ce(III)were subjected to physicochemical studies. X-ray diffractometry, density measurements, chemical analysis and thermal analysis were used to determine the structure and chemical disorder present.The samples prepared chemically(CMD) or electrochemically (EMD) showed a variable amount of de Wolff disorder(Pr) and microtwinning (Tw). Manganese dioxide prepared in the presence of Ce(III) showed appreciable decrease in de Wolff defect and a large amount of microtwinning. Thermal analysis showed a loss of weight due to the physically adsorbed and the structural(OH)water, from which the activation energy was calculated. Chemical composition and formulae calculated on the bases of cation vacancy model, cleared that Ce(III)-doped sample has a remarkable increase in the vacancies population associated with higher structural water content. This leads to lower activation energy of water release, and consequently it is supposed to acquire higher electrochemical activity.     

基于阴离子还原剂制备的超级电容器用中孔MnO_2研究

以Na2S2O3为还原剂,KMnO4为氧化剂制备了超级电容器用MnO2,采用SEM、N2吸附-脱附和XRD对样品进行了分析.用循环伏安和恒流充放电测试对样品的电化学性能进行了表征.结果表明,实验制备的MnO2为无定型结构,呈类球状,直径为20～40nm,比表面积和平均孔径分别为182.6m2/g和6.2nm.在1mol/L (NH4)2SO4水溶液中,在-0.4～0.5V(vs.SCE)的电位范围内,MnO2具有典型的赝电容特性和高功率特性.在10mA/cm2的电流密度下,MnO2比容达到397F/g,且具有高循环效率.     

Synthesis of nitrogen-doped MnO/graphene nanosheets hybrid material for lithium ion batteries

Nitrogen-doped MnO/graphene nanosheets (N-MnO/GNS) hybrid material was synthesized by a simple hydrothermal method followed by ammonia annealing. The samples were systematically investigated by X-ray diffraction analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy. N-doped MnO (N-MnO) nanoparticles were homogenously anchored on the thin layers of N-doped GNS (N-GNS) to form an efficient electronic/ionic mixed conducting network. This nanostructured hybrid exhibited a reversible electrochemical lithium storage capacity as high as 772 mAh g(-1) at 100 mA g(-1) after 90 cycles, and an excellent rate capability of 202 mA h g(-1) at a high current density of 5 A g(-1). It is expected that N-MnO/GNS hybrid could be a promising candidate material as a high capacity anode for lithium ion batteries.     

SiO2-Fe2O3-Cr2O3-MnO2高温红外辐射节能涂料的制备及应用

以SiO2、Fe2O3、Cr2O3、MnO2为原料按比例混合,经固相高温烧结制备成基体粉料,再与粘结剂混合球磨制备出高温红外辐射节能涂料。通过XRD、半球点测试仪、红外辐射测量仪、纳米粒度测试仪对材料的微观结构和理化性能进行了表征,采用热震法对涂层的抗热震性能进行了研究。研究结果表明,随着平均粒径的减小,合成的SiO2-Fe2O3-Cr2O3-MnO2体系全波段红外辐射率有明显增大的趋势。当平均粒径达到2μm左右时,涂料全波段红外辐射率最高达到0.93。涂料的最高使用温度达1400℃以上,涂层的抗热震性能良好。此外,在燃气梭式干燥窑上使用该高温红外辐射节能涂料后,降低能耗15%左右,抗老化性能优良,使用一年后辐射率仍在0.90以上。     

超级电容器用CeO_2-MnO/3D石墨烯复合材料的制备

以西瓜瓜瓤为碳源,采用两步碳化法制备三维石墨烯(3D-Fiberbased Graphene,3D G)材料,并使用水热法制备了CeO_2-MnO/3DG复合材料,以期获得比电容高,循环寿命好的石墨烯超级电容器电极材料。结果表明:3DG材料具有较高比表面积,最高可达到332m~2·g~(-1)。CeO_2-MnO/3DG复合材料具有三维导电网络结构,金属氧化物颗粒在石墨烯片层间生长均匀,粒径在10nm左右。电化学测试结果显示:在0.5 mol·L~(-1)的Na_2SO_4溶液中,电流密度1A·g~(-1),当摩尔比MnO∶CeO_2=4∶1,复合负载量在80%时得到的CeO_2-MnO/3D G复合材料拥有最高比电容,达308.5F·g~(-1),经过1 000次循环充放电测试比电容保持率为95.5%。CeO_2-MnO/3DG复合材料电化学性能的提高主要是因为两种金属氧化物复合负载与石墨烯的协同作用。     

Spinel-layered integrate structured nanorods with both high capacity and superior high-rate capability as cathode material for lithium-ion batteries

Spinel phase LiMn2O4 was successfully embedded into monoclinic phase layeredstructured Li2MrnO3 nanorods,and these spinel-layered integrate structured nanorods showed both high capacities and superior high-rate capabilities as cathode material for lithium-ion batteries (LIBs).Pristine Li2MnO3 nanorods were synthesized by a simple rheological phase method using α-MnO2 nanowires as precursors.The spinel-layered integrate structured nanorods were fabricated by a facile partial reduction reaction using stearic acid as the reductant.Both structural characterizations and electrochemical properties of the integrate structured nanorods verified that LiMn2O4 nanodomains were embedded inside the pristine Li2MnO3 nanorods.When used as cathode materials for LIBs,the spinel-layered integrate structured Li2MnO3 nanorods (SL-Li2MnO3) showed much better performances than the pristine layered-structured Li2MnO3 nanorods (L-Li2MnO3).When charge-discharged at 20 mA·g-1 in a voltage window of 2.0-4.8 V,the SL-Li2MnO3 showed discharge capadties of 272.3 and 228.4 mAh.g-1 in the first and the 60th cycles,respectively,with capacity retention of 83.8％.The SL-Li2MnO3 also showed superior high-rate performances.When cycled at rates of 1 C,2 C,5 C,and 10 C (1 C =200 mA·g-1) for hundreds of cycles,the discharge capacities of the SL-Li2MnO3 reached 218.9,200.5,147.1,and 123.9 mAh·g-1,respectively.The superior performances of the SL-Li2MnO3 are ascribed to the spineMayered integrated structures.With large capacities and superior high-rate performances,these spinel-layered integrate structured materials are good candidates for cathodes of next-generation high-power LIBs.     

Controllable synthesis of α- and β-MnO(2): cationic effect on hydrothermal crystallization

α-?and β-MnO(2) were controllably synthesized by hydrothermally treating amorphous MnO(2) obtained via a reaction between Mn(2+) and MnO(4)(-), and cationic effects on the hydrothermal crystallization of MnO(2) were investigated systematically. The crystallization is believed to proceed by a dissolution-recrystallization mechanism; i.e.?amorphous MnO(2) dissolves first under hydrothermal conditions, then condenses to recrystallize, and the polymorphs formed are significantly affected by added cations such as K(+), NH(4)(+) and H(+) in the hydrothermal systems. The experimental results showed that K(+)/NH(4)(+) were in competition with H(+) to form polymorphs of α-?and β-MnO(2), i.e., higher relative K(+)/NH(4)(+) concentration favoured α-MnO(2), while higher relative H(+) concentration favoured β-MnO(2).     

Low Temperature Synthesis of Single-crystal Alpha Alumina Platelets by Calcining Bayerite and Potassium Sulfate

Single-crystal alpha alumina (α-Al2O3) platelets were synthesized by calcining a powder mixture of bayerite (α-Al(OH)3) and potassium sulfate (K2SO4) at 900℃. The crystalline phase evolutions and morphologies of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The synthesized samples mainly consisted of single-crystal α-Al2O3 platelets with a diameter of 0.5-1.5 μm and a thickness of 50-150 nm. Moreover, with 3, 5, and 8 wt% (referred to the obtained alumina) α-Al2O3 seeds adding into the powder mixture of bayerite and potassium sulfate, the average diameter of α-Al2O3 platelets can be reduced to 450, 240, and 220 nm, respectively. It is found that the sequence of the phase transformation is the bayerite (α-Al(OH)3) → boehmite (γ-AlOOH) →γ-Al2O3 →α-Al2O3. Further analysis indicated that K2SO4 can promote the phase transformation from γ-Al2O3 to α-Al2O3 and the formation of single-crystal α-Al2O3 platelets might be attributed to the liquid phase K3Al(SO4)3.     

Electrochemical synthesis and characterization of hydroxyapatite powders

Electrochemical synthesis of hydroxyapatite powders was performed galvanostatically from homogeneous solution of Na₂H₂EDTA·2H₂O, NaH₂PO₄ and CaCl₂ at a concentration relationship Ca/EDTA/PO₄³⁻ of 0.25/0.25/0.15 M at current densities of 137 and 207 mA cm⁻² and pH values of 9.0 and 12.0. The hydroxyapatite powders were characterized by X-ray diffraction, size distribution measurements, transmission electron microscopy, scanning electron microscopy and thermogravimetric and differential thermal analysis. The influence of the electrochemical synthesis parameters, e.g. applied current density and pH value, on the phase composition, crystallite size, morphology and thermal characteristics of hydroxyapatite powders were investigated.     

Characterization of nanoparticles of LiMn2O4 synthesized by a one-step intermediate-temperature solid-state reaction

Nanoparticles of lithium manganese oxide (LiMn2O4) with a spinel structure have been synthesized by a one-step intermediate temperature solid-state reaction. The influence of the molar ratio of citric acid to the metal ions on the physicochemical properties of LiMn2O4 powders in air has been analyzed by means of X-ray diffraction and electron microscope techniques. The electrochemical behavior of the material has been examined by charge/discharge tests and cyclic voltammetry. Test results reveal that LiMn2O4 particles with lower molar ratios of citric acid to metal ions (1:2) are highly crystalline and highly electrochemically reversible, with better cycle capabilities when compared with a sample with a higher molar ratio (2:1). The LiMn2O4 powders obtained by this method have a uniform morphology with a narrow size distribution.     

Preparation of nano-sized flower-like ZnO bunches by a direct precipitation method

In this work, nano-sized ZnO particles were prepared by a direct precipitation method with Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials, and the impact of the synthesis process was studied. The optimal thermal calcined temperature of precursor precipitates of ZnO was obtained from the differential thermal analysis (DTA) and the thermal gravimetric analysis (TGA) curves. The purity, microstructure, morphology of the calcined ZnO powders were studied by X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The synthesized ZnO powders had a wurtzite structure with high purity. The final products were of flower-like shape and the nanorods which consisted of the flower-like ZnO bunches were 20–100 nm in diameter and 0.5–1 μm in length. The effect of process conditions on the morphology of ZnO was discussed.