纳米NiCo_2O_4电极材料的结构表征及超级电容性能研究

本文通过电沉积法在泡沫镍上沉积了绿色(Co,Ni)氢氧化物前驱体,并通过退火处理制备了纳米NiCo2O4电极材料。利用扫描电子显微镜(SEM)和透射电子显微镜(TEM)表征了生长在泡沫镍上的纳米NiCo2O4电极材料的形貌特征,成分和显微结构。通过对这些样品进行恒流密度充放电以及循环伏安测试对纳米NiCo2O4电极材料进行了电化学性能评价。结果表明,电化学性能最佳的纳米Ni Co2O4生长厚度为2.80μm,纳米片长度在390~785 nm之间,该电极材料在1 m A/cm2的充放电电流密度下比容量达到了1.4 F/cm2,在30 m A/cm2电流密度下比容量依然保持了0.68 F/cm2。该样品在5 m A/cm2的充放电电流密度下循环充放电2 000次之后依然保持了94%的初始比容量,显示出了较高的循环稳定性。     

Mesoporous NiCo2O4 Nanowire Arrays Grown on Carbon Textiles as Binder‐Free Flexible Electrodes for Energy Storage

Binary metal oxides has been regarded as a promising class of electrode materials for high‐performance energy storage devices since it offers higher electrochemical activity and higher capacity than mono‐metal oxide. Besides, rational design of electrode architectures is an effective solution to further enhance electrochemical performance of energy storage devices. Here, the advanced electrode architectures consisting of carbon textiles uniformally covered by mesoporous NiCo₂O₄ nanowire arrays (NWAs) are successfully fabricated by a simple surfactant‐assisted hydrothermal method combined with a short post annealing treatment, which can be directly applied as self‐supported electrodes for energy storage devices, such as Li‐ion batteries, supercapacitors. The as‐prepared mesoporous NiCo₂O₄ nanowires consist of numerous highly crystalline nanoparticles, leaving a large number of mesopores to alleviate the volume change during the charge/discharge process. Electrode architectures presented here promise fast electron transport by direct connection to the growth substrate and facile ion diffusion path provided by both the abundant mesoporous structure in nanowires and large open spaces between neighboring nanowires, which ensures every nanowire participates in the ultrafast electrochemical reaction. Benefiting from the intrinsic materials and architectures features, the unique binder‐free NiCo₂O₄/carbon textiles exhibit high specific capacity/capacitance, excellent rate capability, and cycling stability.     

Identifying the Conversion Mechanism of NiCo2O4 during Sodiation–Desodiation Cycling by In Situ TEM

For alkali metal ion batteries, probing the ion storage mechanism (intercalation‐ or conversion‐type) and concomitant phase evolution during sodiation–desodiation cycling is critical to gain insights into understanding how the electrode functions and thus how it can be improved. Here, by using in situ transmission electron microscopy, the whole sodiation–desodiation process of spinel NiCo₂O₄ nanorods is tracked in real time. Upon the first sodiation, a two‐step conversion reaction mechanism has been revealed: NiCo₂O₄ is first converted into intermediate phases of CoO and NiO that are then further reduced to Co and Ni phases. Upon the first desodiation, Co and Ni cannot be recovered to original NiCo₂O₄ phase, and divalent metal oxides of CoO and NiO are identified as desodiated products for the first time. Such asymmetric conversion reactions account for the huge capacity loss during the first charging–discharging cycle of NiCo₂O₄‐based sodium‐ion batteries (SIBs). Impressively, a reversible and symmetric phase transformation between CoO/Co and NiO/Ni phases is established during subsequent sodiation–desodiation cycles. This work provides valuable insights into mechanistic understanding of phase evolution during sodiation–desodiation of NiCo₂O₄, with the hope of assistance in designing SIBs with improved performance.     

A Self‐Standing High‐Performance Hydrogen Evolution Electrode with Nanostructured NiCo2O4/CuS Heterostructures

An efficient self‐standing 3D hydrogen evolution cathode has been developed by coating nickel cobaltite (NiCo₂O₄)/CuS nanowire heterostructures on a carbon fiber paper (CFP). The obtained CFP/NiCo₂O₄/CuS electrode shows exceptional hydrogen evolution reaction (HER) performance and excellent durability in acidic conditions. Remarkably, as an integrated 3D hydrogen‐evolving cathode operating in acidic electrolytes, CFP/NiCo₂O₄/CuS maintains its activity more than 50 h and exhibits an onset overpotential of 31.1 mV, an exchange current density of 0.246 mA cm^?2, and a Tafel slope of 41 mV dec^?1. Compared to other non‐Pt electrocatalysts reported to date, CFP/NiCo₂O₄/CuS exhibits the highest HER activity and can be used in HER to produce H₂ with nearly quantitative faradaic yield in acidic aqueous media with stable activity. Furthermore, by using CFP/NiCo₂O₄/CuS as a self‐standing electrode in a water electrolyzer, a current density of 18 mA cm^?2 can be achieved at a voltage of 1.5 V which can be driven by a single‐cell battery. This strategy provides an effective, durable, and non‐Pt electrode for water splitting and hydrogen generation.     

A Low‐Cost,Self‐Standing NiCo2O4@CNT/CNT Multilayer Electrode for Flexible Asymmetric Solid‐State Supercapacitors

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo₂O₄@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g^?1 at 0.5 A g^?1 while maintaining excellent stability. The NiCo₂O₄@CNT/CNT film electrodes are fabricated via stacking NiCo₂O₄@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm^?3 (with an areal mass of 2.5 mg cm^?2) at 0.5 A g^?1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg^?1) at 0.55 kW kg^?1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.     

Seed‐Induced Vertical Growth of 2D Bi2O2Se Nanoplates by Chemical Vapor Transport

As two‐dimensional (2D) layered materials attract more attention owing to their unique optical, electrical, and thermal properties, there are persistent efforts to grow high‐quality 2D layered materials for fundamental research and device applications. While large‐area 2D layered materials with high crystal quality can be obtained through chemical vapor transport, the strong binding between 2D layered materials and substrates poses a significant challenge for attempts to reveal their intrinsic properties and to use these 2D building blocks for constructing advanced heterostructured devices. Therefore, it would be ideal to grow high‐quality 2D materials with minimized contact and binding with substrate. Through both calculation and experiment, it is demonstrated that by introducing a seed layer at the nucleation stage, the crystallographic disregistry and the corresponding adhesion energy between 2D materials and substrate can be altered, resulting in a change of crystal surface in contact with the substrate, and therefore vertical growth of 2D materials on substrates. As an example, it is demonstrated that with Bi₂O₃ serving as a seed layer, vertical growth of 2D plates of Bi₂O₂Se on mica substrates can be realized. These vertically grown 2D nanoplates of Bi₂O₂Se can be conveniently transferred with their thermal properties investigated for the first time.     

Direct Conversion of Single‐Layer SnO Nanoplates to Multi‐Layer SnO2 Nanoplates with Enhanced Ethanol Sensing Properties

Direct conversion of single‐layer SnO nanoplates to multi‐layer SnO₂ nanoplates is achieved by annealing in an O₂ ambient at 700 °C. For 50 ppm ethanol, the sensitivities of the multi‐layer SnO₂ nanoplates are more than double that of single‐layer SnO₂ nanoplates, which are also formed from the single‐layer SnO. The higher sensitivity of the multi‐layer nanoplates is attributed to their larger surface/volume ratio. The facile fabrication of interconnected multi‐layer SnO₂ nanoplates at low temperature directly on a Si substrate and sensing chip without the aid of catalysts offers vast advantages over competing methods for the fabrication of high‐sensitivity SnO₂ sensors.     

BaCu(B_2O_5)掺杂2.5ZnO-2.5Nb_2O_5-5TiO_2陶瓷的低温烧结及其与Ag的相容性(英文)

研究了不同BaCu(B2O5)(BCB)掺杂量对2.5ZnO-2.5Nb2O5-5TiO2(ZNT)陶瓷烧结行为、介电性能及与Ag相容性的影响规律。添加BCB可有效地将ZNT陶瓷的烧结温度从1 100℃降低至900℃。BCB添加量为3.0wt%,900℃烧结3h所制得的ZNT陶瓷的微波性能良好:εr=48,Qf=15 258GHz,τf=41×10-6/℃。且在BCB掺杂ZNT陶瓷与Ag共烧样品中未检测到新生相和Ag的扩散,表明3.0wt%BCB掺杂的ZNT陶瓷与Ag的相容性良好,是一种很有潜力的LTCC材料。     

掺杂Y2O3氧化锌压敏陶瓷的显微组织及电性能

采用掺杂Y2O3、高能球磨和低温烧结技术,制备了电位梯度(ES)达1 934~2 197 V/mm、非线性系数(α)为20.8~21.8、漏电流(IL)为0.59~1.04μA、密度(ρ)为5.46~5.57 g/cm3的氧化锌压敏陶瓷。利用电子探针观察了压敏陶瓷的分布和形貌。X-射线衍射仪(XRD)证实了Y4样品(x(Y2O3)=0.1%)中Y2O3相的存在。随着Y2O3含量的增加,ES、α提高,IL、ρ和晶粒尺寸(D)降低;施主浓度(Nd)及界面态密度(Ns)降低,而势垒高度(φB)和势垒宽度(ω)增大。     

表面包覆的ZnFe204纳米粒子的光吸收边红移

采用表面包覆的方法对共沉淀法制备的ZnFe2O4纳米粒子进行表面改性,使其能分散在有机溶剂中形成ZnFe2O4纳米微粒有机溶胶,并以该有机溶胶为前驱体通过提拉成膜技术制备了ZnFe2O4纳米粒子薄膜.光吸收测量显示,表面包覆改性可导致ZnFe2O4纳米粒子的光吸收边出现较大幅度的红移,且红移的幅度随着ZnFe2O4纳米粒子的尺寸减小而增大;光吸收带边特性分析表明,ZnFe2O4纳米材料是间接带隙半导体.根据吸收带边与光吸收系数间的关系,计算了ZnFe2O4纳米粒子的间接和直接光学带隙能.     

蓝色长余辉材料SrAl4O7:Eu2 ,Dy3 的合成及其发光特性

为了进一步探索铝酸盐系列长余辉材料的显色范围,改善其粉体特性,采用铝酸盐阳离子草酸盐共沉淀及湿法混合原材料方法,在传统绿色长余辉荧光粉SrAl2O4Eu2+,Dy3+合成的基础上,增加基质Al的比例,并由通常α-Al2O3改成AlCl3·6H2O,选用硼酸氨与氟化铝为助溶剂,成功合成了高效、低硬度和细粒径良好粉体特性的浅蓝色长余辉发光材料SrAl4O7Eu2+,Dy3+.测量了样品的X射线衍射(XRD)图谱、激发与发射光谱、余辉衰减曲线及热释光谱图等,并对其进行了分析.结果表明,Eu2+在这两种基质中均存在2个发光中心,其衰减速度不一样,蓝发光中心寿命要远大于绿发光中心寿命.相对SrAl2O4Eu2+,Dy3+而言,SrAl4O7Eu2+,Dy3+发射光谱峰值从520 nm蓝移至480 nm,衰减到可辨认发光强度0.32 mcd/m2的余辉时间从30 h延长到60 h以上,且合成样品表现出更好的结晶状态、分散性及较小的中心粒径.     

ZnO对BaSm_2Ti_4O_(12)陶瓷性能的影响

讨论了Zn O对Ba Sm2Ti4O12介质陶瓷烧结机制和微波介电性能的影响。结果表明:Zn O添加能推动Ba Sm2Ti4O12微波介质陶瓷的烧结,可至少将其烧结温度降低至1 280℃。当添加过多的Zn O时,Zn2+会进入晶格,可能导致晶格畸变,由此造成颗粒间产生微小孔隙及晶格内形成许多缺陷,降低了材料的εr和Q×f值。含0.5 wt%Zn O的Ba Sm2Ti4O12试样在1 280℃烧结时,综合介电性能最好:εr=76.46,Q×f=6 334 GHz。     

sol-gel法制备ZnFe2O4及其NO2气敏性能的研究

采用sol-gel法制备了尖晶石结构的ZnFe2O4粉体,以其为电极材料在钇稳氧化锆陶瓷片(YSZ)上利用丝网印刷技术制备了片式NO2传感器,并对传感器在不同NO2浓度和不同温度下的输出电动势E和响应时间进行了研究。结果显示:在φ(NO2)为(68～494)×10–6范围内,E随着NO2浓度的增大而增大,并与NO2浓度的对数呈现良好的线性关系。在600℃高温时,传感器上升和下降响应时间分别为60和120s,且重复性较好。但随着工作温度的升高,传感器的灵敏度下降。     

SHS法制备NiZnFe_2O_4预烧料的工艺研究

利用自蔓延高温合成的方法制备出纯度较高的NiZnFe2O4预烧料,并且利用XRD图谱,通过外推法及Vegard定律等分析了SHS法中保温时间及压坯相对密度对产物结构的影响。结果表明:NiZnFe2O4的标准图谱中应当去掉原有的第三条特征峰,同时添加(622)晶面上的一条特征峰;SHS合成的NiZnFe2O4预烧料中还有少量残余的Fe2O3,其在产物中的质量分数不超过4%,且随着保温时间的延长而减少;随着粉料压坯相对密度(ρr)的提高,预烧料的主相,即固溶体NiZnFe2O4中所固溶的ZnFe2O4的含量增多,且在相对密度为57%~63%时,其摩尔分数接近配方比例。     

Epitaxial Growth of 2D Bi2O2Se Nanoplates/1D CsPbBr3 Nanowires Mixed-Dimensional Heterostructures with Enhanced Optoelectronic Properties

The 2D/1D mixed-dimensional van der Waals heterostructures have great potential for electronics and optoelectronics with high performance and multifunctionality. The epitaxy of 1D micro/nanowires on 2D layered materials may efficiently realize the large-scale preparation of 2D/1D heterostructures, which is critically important for their practical applications. So far, however, only the wires of Bi₂S₃, Te, and Sb₂Se₃ have been epitaxially grown on MoS₂ or WS₂. Here, it is reported that the epitaxial growth of 1D CsPbBr₃ nanowires on 2D Bi₂O₂Se nanoplates through a facile vertical vapor deposition method. The CsPbBr₃ wires are well aligned on the Bi₂O₂Se plates in fourfold symmetry with the epitaxial relationships of [001]_CsPbBr3||[200]_Bi2O2Se and [1-10]_CsPbBr3||[020]_Bi2O2Se. The photoluminescence results reveal that the emission from CsPbBr₃ is significantly quenched in the heterostructure, which implies the charge carriers transfer from CsPbBr₃ to Bi₂O₂Se. The waveguide characterization shows that the epitaxial CsPbBr₃ wires may efficiently confine and guide their emission, which favors the light absorption of Bi₂O₂Se. Importantly, the photocurrent mapping and spectra of the devices based on these 2D/1D heterostructures prove that the epitaxial CsPbBr₃ wires remarkably enhances the photoresponse of Bi₂O₂Se, which indicates these heterostructures can be applied in high-performance optoelectronic devices or on-chip integrated photonic circuits.     

钙铝硼硅玻璃/氧化铝复合材料性能研究

通过高温熔融法制备的CaO-Al2O3-B2O3-SiO2玻璃粉末与α-Al2O3粉末按照质量分数50:50混合,烧结制备了钙铝硼硅玻璃/氧化铝系低温共烧陶瓷材料,研究了烧结温度对复合材料的物相组成、微观结构、力学性能及介电性能的影响.结果表明,875℃烧结制备的复合材料性能最佳,抗弯强度为164 MPa,介电常数为7.8,介电损耗为0.001 3,热膨胀系数为5.7×10-6/℃,具有良好的综合性能,可用作低温共烧陶瓷基板材料.     

ZnCr2O4湿敏陶瓷工艺研究

研究了ZnO不同含量对ZnCr2O4湿敏陶瓷线性度及LiCl,Al2O3,CaCO3掺杂对湿阻特性的影响,实验表明,过量的ZnO可含理可改善陶瓷的线性度,Ca^2 的加入可提高湿敏陶瓷的机械强度,降低烧结温度。     

Cu掺杂对ZnO氧化物电子结构与电输运性能的影响

采用平面波超软赝势密度泛函理论计算的方法研究了p型Cu掺杂的纤锌矿结构氧化物ZnO的电子结构,在此基础上分析了其电输运性能。计算结果表明,Cu掺杂ZnO氧化物具有0.6eV的直接带隙,且为p型半导体,在导带和价带中都出现了由Cu电子能级形成的能带,体系费米能级附近的能带主要由Cup态、Cud态和Op态电子构成,且他们之间存在着强相互作用。电输运性能分析结果表明,Cu掺杂的ZnO氧化物价带中的载流子有效质量较大,导带中的载流子有效质量较小;其载流子输运主要由Cup态、Cud态、Op态电子完成,且需要载流子（空穴和电子）跃迁的能隙宽度较未掺杂的ZnO氧化物减小。     

超声波化学法合成纳米铁酸钴粉末

用超声波化学法合成了纳米铁酸钴(CoFe2O4)粉末,并用XRD、TEM、红外光谱对产品的纯度、结晶度,粒径以及内部形态及结构进行了分析表征。结果表明:当r(Co:Fe)为1:2时,超声频率为24.45kHz,超声辐射45min时,得到了粒径为10~20nm的铁酸钴纳米粉末。其δs、Hc分别为32.18Am2/kg和1.48×104A/m。