石墨烯掺杂LiFePO4电极材料的合成及其电化学性能

采用水热辅助法合成石墨烯改性的LiFePO4多孔微球电极材料.并对材料进行了X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),傅里叶变换红外(FT-IR)光谱,充放电等表征.从结果可以看出在2 mol·L-1LiNO3电解液体系中单纯包碳的LiFePO4微球在1C、50C倍率时的比容量分别为137、64 mAh·g-1,而石墨烯改性的LiFePO4微球的比容量分别为141、105 mAh·g-1,表现出较好的倍率特性.恒流循环充放电测试60次后两种材料容量保持率分别为70.2％、83.7％.说明掺杂石墨烯构成的三维导电网络能明显改善LiFePO4的电化学性能.     

控制结晶-微波碳热还原法制备高密度LiFePO4/C

应用控制结晶法从溶液相制备球形FePO4.xH2O,再高温烧结得到FePO4前驱体,最后用微波碳热还原法合成高密度L iFePO4/C.由XRD和SEM表征该材料的结构、形貌,并测试其电化学性能.     

Facile low-temperature polyol process for LiFePO4 nanoplate and carbon nanotube composite

Crystalline LiFePO₄ nanoplates were incorporated with 5 wt.% multi-walled carbon nanotubes (CNTs) via a facile low temperature polyol process, in one single step without any post heat treatment. The CNTs were embedded into the LiFePO₄ particles to form a network to enhance the electrochemical performance of LiFePO₄ electrode for lithium-ion battery applications. The structural and morphological characters of the LiFePO₄–CNT composites were investigated by X-ray diffraction, Fourier Transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were analyzed by cyclic voltammetry, electrochemical impedance spectroscopy and charge/discharge tests. Primary results showed that well crystallized olivine-type structure without any impurity phases was developed, and the LiFePO₄–CNT composites exhibited good electrochemical performance, with a reversible specific capacity of 155 mAh g⁻¹ at the current rate of 10 mA g⁻¹, and a capacity retention ratio close to 100% after 100 cycles.     

Carbon encapsulated magnetic nanoparticles produced by hydrothermal reaction

Carbon encapsulated magnetic nanoparticles(CEMNs)were synthesized by heating an aqueous glucose solution containing Fe-Au(Au coated Fe nanoparticles)nanoparticles at 160-180℃ for 2 h.This novel hydrothermal approach is not only simple but alsoprovides the surface of CEMNs with functional groups like-OH.The formation of carbon encapsulated magnetic nanoparticles wasnot favored when using pure Fe nanoparticles as cores because of the oxidation of Fe nanoparticles by H2O during the reaction and,therefore,the surfaces of the naked Fe nanoparticles had to be coated by Au shell in advance.TEM,XRD,XPS and VSMmeasurments characterized that they were uniform carbon spheres containing some embedded Fe-Au nanoparticles,with asaturation of 14.6 emu/g and the size of the typical product is$350 nm.     

新型球状磷酸铁锂的合成及电化学性能

在水热条件下,制备了水合碱式磷酸铁微球,500 oC焙烧后生成直径为5μm的碱式磷酸铁,接着与碳酸锂一起焙烧后生成了球形磷酸铁锂．我们的方法可以有效地控制所获得产物的尺寸和形貌,同时在产物表面形成均匀碳包覆,改善了磷酸铁锂的电化学性能．     

Synthesis and Electrochemical Property of Flowerlike LiFePO4 by Poly(ethylene glycol)-assisted Hydrothermal Process

Flowerlike LiFePO4 particles self-assembled by plate-like crystals with about 200 nm thickness were prepared by the poly(ethylene glycol)-assisted hydrothermal synthesis. Poly(ethylene glycol) in the hydrothermal system played an important role in reducingthe thickness of the plate-like LiFePO₄ crystals as a co-solvent and forming the flower-like structure as a soft template. The flowerlike LiFePO₄ exhibits high discharge capacity of 140 mAh/g and shows quite good cycling performance in the lithium-ion batteries. Con-sidering that the conductive carbon in the obtained LiFePO₄ is negligible, the excellent cellperformance suggests that the flowerlike LiFePO₄ is a promising cathode material for the lithium-ion batteries.     

Excess capacity on compound phases of Li2FeTiO4 composite cathode materials synthesized by hydrothermal reaction using optional titanium sources to boost battery performance

Li₂ FeTiO₄ composites have been produced using commercial LiAC,FeCl₂ and different titanium sources by hydrothermal synthesis(HS) at 175℃ and subsequent annealing at 700℃.Impure phase TiO₂,Fe₂ O₃ and FeTi04 were detected out among the Li2 FeTiO₄ composites with different titanium sources.Micron and nano-sized particles of Li2 FeTiO₄ were prepared from various titanium raw materials,with nano-sized particles p...     

High quality Sb-doped SnO2 electrodes with high oxygen evolution potential prepared by in situ hydrothermal synthesis method

High quality Sb-doped SnO_2 electrode,with high oxygen evolution potential of 3.0 V,was successfully synthesized on the Ti substrates by in situ hydrothermal synthesis method.     

前驱体配料温度对水热法制备LiFePO4的影响

研究了配料温度对水热法制备磷酸铁锂的影响.通过X射线衍射（XRD）、扫描电镜（SEM）、循环伏安（CV）以及元素分析等手段分析了不同温度下制备的前驱体和最终的LiFePO₄样品,其结果表明配料温度对磷酸铁锂前驱体颜色和特性有明显影响.通过仔细控制该温度可以制得高纯Li₃PO₄中间体并抑制前驱体中Fe（OH）₃的形成.有利于进一步获得结晶良好不含Fe³⁺的LiFePO₄样品,显著提高了LiFePO₄材料的放电比容量.当配料温度为30℃时获得的样品,0.1C倍率下放电比容量达到156 mAh·g^-1,0.5C倍率下放电比容量为151 mAh·g^-1,10C倍率下放电比容量为127 mAh·g^-1,循环20次容量保持率达99%.     

Excess capacity on compound phases of Li2FeTiO4 composite cathode materials synthesized by hydrothermal reaction using optional titanium sources to boost battery performance

Li₂FeTiO₄ composites have been produced using commercial LiAC, FeCl₂ and different titanium sources by hydrothermal synthesis (HS) at 175 ℃ and subsequent annealing at 700 ℃. Impure phase TiO₂, Fe₂O₃ and FeTiO₄ were detected out among the Li₂FeTiO₄ composites with different titanium sources. Micron and nano-sized particles of Li₂FeTiO₄ were prepared from various titanium raw materials, with nano-sized particles predominating when titanium raw materials were layered hydrogen titanate nanowire (H₂Ti₃O₇NW, HTO-NW) and titanium oxide nanotubes (TiO₂NB). The Li₂FeTiO₄ composites synthesized by HTO-NW shows a primary particle size of 50-200 nm of high crystallinity staggered with undissolved nanowire with a diameter size of about 100 nm. The samples using one-dimensional nanometer titanium oxide (TiO₂ NB) as the raw material can get a super high initial discharge capacity of 367.8 mAh/g at the rate of C/10 and excellent cycling stability. The selection of raw materials and adopting multi-phase modification can be considered as an effective strategy to improve the electro-chemical properties of Li₂FeTiO₄ composite cathode materials for the lithium secondary battery.     

Preparation and Electrochemical Performance of V2O3-C Dual-Layer Coated LiFePO4 by Carbothermic Reduction of V2O5

The V₂O₃-C dual-layer coated LiFePO₄ cathode materials with excellent rate capability and cycling stability were prepared by carbothermic reduction of V₂O₅. X-ray powder diffraction, elemental analyzer, high resolution transmission electron microscopy and Raman spectra revealed that the V₂O₃ phase co-existed with carbon in the coating layer of LiFePO₄ particles and the carbon content reduced without graphitization degree changing after the carbothermic reduction of V₂O₅. The electrochemical measurement results indicated that small amounts of V₂O₃ improved rate capability and cycling stability at elevated temperature of LiFePO₄/C cathode materials. The V₂O₃-C dual-layer coated LiFePO₄ composite with 1wt% vanadium oxide delivered an initial specific capacity of 167 mAh/g at 0.2 C and 129 mAh/g at 5 C as well as excellent cycling stability. Even at elevated temperature of 55 oC, the specific capacity of 151 mAh/g was achieved at 1 C without capacity fading after 100 cycles.     

氮掺杂的碳材料中石墨化氮和吡啶氮对氧还原反应的催化特性

目前,开发高效的阴极氧还原反应(ORR)电催化剂是实现燃料电池和金属-空气电池商业化发展急需完成的目标。在过去的几十年中,人们在探索廉价高效的 ORR电催化剂(如 N掺杂的非金属及非铂电催化剂)领域做了广泛的研究。在 N掺杂的碳基 ORR催化剂中,已知的 N基活性位点主要分为四类,即吡啶类氮(P-N)、吡咯类氮(Py-N)、石墨化氮(G-N)和氧化类氮(O-N)。尽管人们对这四种类型氮的活性位点做了大量的研究,但是它们在催化反应中起到的 ORR催化作用以及催化机理和活性位点本身结构的关系仍不够明确。早期的研究中有人认为 P-N或者 Py-N是 ORR催化活性位点,也有人认为是 G-N起作用。最近也有研究表明, P-N和 G-N都是 ORR催化活性位点,只是在 ORR中所起的催化能力不同。因此,很有必要认清这些问题。
　　本文通过 Hummer法酸性氧化一次和两次碳黑 Vulcan XC-72(VXC-72)以及随后高温热处理,制备了一系列 ORR催化剂 VXCO-1, VXCO-2, VXCO-1(900)和 VXCO-2(900),采用场发射扫描电子显微镜(SEM), N2吸附脱附法,元素分析仪(EA), X射线光电子能谱(XPS),拉曼光谱仪(Raman), X射线衍射能谱(XRD),电化学循环伏安法和线性伏安法测试等手段研究 Hummers法酸氧化和高温热处理对 VXC-72形貌组成的影响,以及这些碳基中成分和其催化 ORR能力的关系。
　　 SEM结果表明, Hummer法酸性氧化处理 VXC-72一次和两次后可以逐层剥落其最外边的碳层结构,最终得到表面光滑的类片层状结构的碳材料(VXCO-1和 VXCO-2)。这种表面光滑的类片层状结构的碳材料比表面积大于处理前的 VXC-72,而高温热处理之后的碳材料(VXCO-1(900)和 VXCO-2(900))由于类石墨层碎片结构蒸发损失暴露出更多内部的微孔和介孔结构使比表面积增加。 Raman和 XRD结果表明,氧化处理使碳材料的石墨化程度增加,而高温热处理则降低了其石墨化程度。
　　 EA和 XPS结果表明, Hummer法酸性氧化处理可以使在碳材料中掺入的 N以石墨化的为主,高温热处理却使得石墨化氮转变为吡啶类的氮。 ORR结果发现,活性的石墨化氮倾向于使 ORR反应经历两电子过程,从而生成 H2O2为主要产物;而吡啶类氮的活性位点更倾向于使 ORR反应经过四电子过程,主产物是水。该结果有助于新型碳基氧还原催化剂的设计和分析。     

Preparation and properties of nickel site doped material Ni1-yXyCo2O4 as supercapacitor materials by in-situ growth method

Although NiCo₂O₄ has been widely applied in supercapacitors, its actual capacity has been limited by the low conductivity and reactivity. Due to the relationship between the performance of the spinel-structured NiCo₂O₄ electrode material and its microstructure, in this paper, in order to modify the nanostructure of NiCo₂O₄ to improve its electrochemical performance, hydrothermal method is adopted to synthesize Ni_0.98X_0.02Co₂O₄(X = Fe, Cu, Mg, V, Ag, Mn, Mo, Ti) grown on nickel foam. After the synthesis, the physical morphology of the selected Ni_0.98Mg_0.02Co₂O₄ and Ni_0.98Mn_0.02Co₂O₄ are tested and analyzed by XRD, SEM, XPS and FT-IR. According to the characterization results, it can be found that different kinds of metals are doped in the nickel site of NiCo₂O₄, and the microscopic morphology of materials is different. It can be seen from the SEM figure that Ni_0.98Mg_0.02Co₂O₄ is a small nano-scale particle, while Ni_0.98Mn_0.02Co₂O₄ presents rod-like braided structure, and doping at the nickel site does not affect the main structure of the material. It can be seen from EDS data that the atomic ratio and weight ratio of nickel and cobalt elements are consistent with the molecular formula. The XPS spectra of the corresponding elements showed that Ni, Co and O elements were corresponding to NiCo₂O₄ materials. In conclusion, the result of physical morphology characterization analysis shows that the material is still in standard NiCo₂O₄ spinel structure.     

Ultrafine molybdenum carbide nanoparticles supported on nitrogen doped carbon nanosheets for hydrogen evolution reaction

Nitrogen doped carbon nanosheets supported molybdenum carbides nanoparticles (Mo_xC/NCS) have been synthesized by tuning the mass ratio of melamine and ammonia molybdate. The Mo₂C/NCS-10 exhibits superior electrocatalytic performance and stability for HER, which was attributed to N-doped carbon nanosheets, small particle size, mesoporous structure, and large electrochemical active surface area.     

水热法制备具有高光催化活性的镧掺杂二氧化钛纳米晶

采用水热法合成钛酸钾(K₂Ti₈O₁₇)纳米棒,并将它作为前驱体水热转晶合成TiO₂纳米晶,同时通过在水热体系中引入稀土元素La³⁺实现对TiO₂的La掺杂.考察了不同条件下钛酸盐向TiO₂的转晶过程,发现水热溶液的pH值、温度以及预处理步骤对转晶过程有很大的影响.利用X射线衍射以及透射电子显微镜对样品的晶相和形貌进行了表征.利用电感耦合等离子体原子发射光谱测量了所合成的La掺杂TiO₂样品中的La含量.通过在紫外光下降解甲基橙(MO,10mg/L)测试了La掺杂TiO₂样品的光催化性能.结果表明La掺杂后TiO₂的光催化活性大大提高.在0.15mol/LLa³⁺浓度下180oC水热合成的La掺杂TiO₂样品显示了最佳的光催化活性.其对MO的光催化降解反应常数高达0.11min^-1,大约是空白TiO₂样品的9.20倍,P25TiO₂的3.69倍.     

Acceleration of the corrosion reaction of magnesium by Fenton reagents

Abstract

Magnesium alloys have attracted increased attention for a variety of applications, chief among which are alternative energy and medical implants. The use of biodegradable implants in the complex system of the human body, in which myriad reactions occur, must consider the potential effects of the body’s natural chemical reactions on implant corrosion rates. The aim of this study was to elucidate the synergistic effects of pure Mg and Mg alloys on the Mg corrosion reaction with reagents that participate in the Fenton reaction. We corroborated our results with six different measurement methods (hydrogen evolution rate [HER], gas chromatography [GC], potentiodynamic polarization, inductively coupled plasma [ICP] spectrometry, Auger electron spectroscopy [AES], and scanning electron microscope [SEM]). The results point out that the corrosion and hydrogen evaluation rates of Mg were elevated by the addition of Fenton reagents, divalent iron and hydrogen peroxide, to a saline solution. In the context of Mg-based alloy medical implant development and use, this observation is significant.     

Synthesis and photocatalytic activity for water-splitting reaction of nanocrystalline mesoporous titania prepared by hydrothermal method

Nanocrystalline mesoporous TiO₂ was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO₂ had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m²/g. The photocatalytic activity of synthesized TiO₂ was evaluated with photocatalytic H₂ production from water-splitting reaction. The photocatalytic activity of synthesized TiO₂ treated with appropriate calcination temperature was considerably higher than that of commercial TiO₂ (Ishihara ST-01). The utilization of mesoporous TiO₂ photocatalyst with high crystallinity of anatase phase promoted great H₂ production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.     

A novel synthetic route for LiFePO_4/C cathode materials by addition of starch for lithium-ion batteries

LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.     

微米橄榄石型LiFePO4的水热合成优化

为深入研究大颗粒磷酸铁锂(LiFePO₄)锂离子电池正极材料的性能衰退机理并据此改善其体积能量密度和功率密度, 进而切实推进该材料在电动汽车、混合动力汽车和电站储能等领域的高效广泛应用, 本文通过优化水热合成条件制备了粒径为2 μm的均匀微米LiFePO₄颗粒粉末. 在未经任何改性(包覆或掺杂)的情况下,该材料表现出本征大颗粒LiFePO₄典型的充放电和循环性能, 可作为后续研究的代表样品进一步考察大颗粒材料相对纳米材料性能衰退的机制和根本原因, 最终通过有的放矢地改性手段获得高密度、高能量和高功率的LiFePO₄ 正极材料. 实验结果表明, 增加反应物浓度、水热温度和保温时间以及降低溶液pH 值均有利于LiFePO₄颗粒的长大. 通过比较不同粒径的LiFePO₄的电化学性能确证了其随颗粒尺寸的增大而衰退. 当颗粒大小由0.7 μm增加到16.5 μm时, LiFePO₄在0.1C倍率下的放电比容量由152 mAh·g^-1下降至80 mAh·g^-1.同时, 1C倍率下的循环测试结果表明, 颗粒尺寸越大, LiFePO₄的容量衰减愈严重.     

铬离子掺杂对LiFePO4电化学性能的影响

采用机械球磨和共沉淀的方法合成了两种Cr3＋掺杂的LiFePO4. 通过对合成样品的XRD、SEM及其电化学性能（循环性能、大电流放电性能）的研究表明，少量Cr3＋的掺杂未影响到LiFePO4的晶体结构，但显著改善了它的电化学性能，在低放电倍率（0.1 C）时，机械球磨掺杂和共沉淀掺杂Cr3＋的LiFePO4的放电容量分别为144和158 mAh•g－1，而当放电倍率提高到2 C时，两种掺杂的LiFePO4仍分别具有110和130 mAh•g－1的放电容量，且循环性能良好.同时表明通过铁源共沉淀掺杂是一条改善离子掺杂效果的有效途径.