燃料电池低Pt核壳结构催化剂的最新研究进展

传统的Pt/C催化剂,由于仅仅是处于纳米粒子表层的Pt原子参与电催化反应,而大多数位于粒子内层的Pt却未能得到有效利用,由此造成燃料电池成本高昂,阻碍了它的大规模商业化进程。核壳结构催化剂是近年来出现的一类极其重要的低Pt催化剂,这类催化剂是使用廉价贵金属、过渡金属、合金及导电化合物的纳米粒子作为核,在其表面覆盖一个原子层厚度或者几个原子层厚度的Pt为壳层而制得的新型高性能催化剂。核壳结构低Pt催化剂可大幅度降低燃料电池的贵金属Pt的使用量,进而降低燃料电池的成本,是实现质子交换膜燃料电池大规模商业化的希望所在。有关核壳结构低Pt催化剂的研究已成为燃料电池领域最热门的研究课题之一。综述了近年来低Pt核壳结构催化剂的研究进展,包括低Pt核壳结构催化剂制备技术的研究进展,以廉价贵金属、合金及导电化合物纳米粒子作为核的低Pt核壳结构催化剂的设计、制备及其相关研究情况。介绍了不同类型的核与Pt壳层之间的相互作用,讨论和总结了影响低Pt核壳结构催化剂电催化活性的相关因素,并对低Pt核壳结构催化剂的研究及其应用进行了展望。     

(Pt/Sn)-碳纳米管复合物的电催化性能

以碳纳米管(Carbon nanotubes,CNTs)为载体、乙二醇和甲酸钠为还原剂,采用浸渍法制备了不同Pt/Sn原子比的(Pt/Sn)-CNT复合物.通过X-射线衍射(XRD)和透射电子显微镜(TEM)对碳纳米管负载金属颗粒过程中的显微结构变化进行了研究.结果表明:Pt、Sn粒子在碳纳米管上高度分散,粒径分布在3.5nm～6.5nm之间,Sn元素以Pt-Sn合金和SnO2结构存在.循环伏安(CV)测试表明:Pt/Sn原子比为2.5:1～3.5:1时,(Pt/Sn)-CNT复合物的催化活性和抗毒化能力最佳.(Pt/Sn)-CNT复合物中CNTs保持了完整结构,对Pt、Sn粒子起到了稳定性作用,有利于提升(Pt/Sn)-CNT复合物对甲醇的氧化活性.     

薄壳层核壳型Ni/Pt纳米粒子的制备及电催化性能

通过胶体-化学镀法制备不同厚度薄壳层核壳型Ni/Pt纳米粒子, 采用HRTEM、EDS、XPS和XRD手段对粒子的形貌、晶型和组成进行物理表征. 采用动电位、循环伏安法对其氧电还原和甲醇电氧化活性进行测试. 实验结果表明, 核壳结构Ni/Pt纳米颗粒基本为球形, 其中Ni₁-Pt_0.067平均直径为7 nm左右, 壳层厚度约1 nm. 与Pt/C相比, 核壳型Ni/Pt纳米粒子对氧电还原和甲醇电氧化的催化活性显著提高. 在所制备的不同壳层厚度催化剂中, Ni₁-Pt_0.067/C在0.5 mol/L H₂SO₄中氧电还原的最大峰电流密度可达到143.06 mA/mg, 是相同反应条件Pt/C峰电流密度的1.4倍; 而Ni₁-Pt_0.067/C在0.5 mol/L H₂SO₄+1.0 mol/L CH₃OH溶液中甲醇电氧化峰电流密度可达538.3 mA/mg, 是Pt/C峰电流密度的5.2倍. 若以1 mg贵金属Pt为基准, Ni₁-Pt_0.067/C的比质量活性相对Pt/C的提高了30倍.     

电化学共沉积法制备Au-Pt纳米枝晶催化剂及其对醇氧化反应的催化性能

本文采用电化学共沉积法,在无任何表面活性剂的条件下,在Au纳米颗粒表面制备了不同Pt覆盖度的Au@Pt纳米枝晶催化剂。电化学测试表明,在中等Pt覆盖度时,其对甲醇氧化反应具有最好的催化性能,作为直接甲醇燃料电池阳极催化剂具有较好的应用前景。     

C/Co核壳亚微米复合物的吸波性能

采用液相合成和后续的热处理工艺制备钴包碳的C/Co核壳亚微米复合物,研究了复合物的吸波性能。结果表明:热处理使C/Co核壳亚微米复合物的结晶性增强,使形貌由C/Co-雪花片壳层的核壳结构转变为C/Co-壳层闭合的核壳结构,饱和磁化强度提高而矫顽力降低。C/Co壳层闭合的核壳亚微米复合物(50%,质量分数)-石蜡的吸波样品具有优异的吸波性能,在11 GHz处最小反射损耗为-23 d B,厚度为2.5 mm,单层厚度的吸波频带(RL-10 d B)达到3 GHz。随着吸波样品厚度的增大吸收峰向低频移动,并出现多重吸收峰。C/Co核壳亚微米复合物优异的吸波性能,可归因于较好的阻抗匹配、介电损耗和1/4波长干涉相消原理。     

Pt/ZrP-Th-CNTs复合催化剂的制备及其对甲醇的电催化氧化

利用硫堇(Th)和碳纳米管(CNTs)对磷酸锆(ZrP)改性,并以改性的ZrP复合材料作为催化剂载体,采用化学还原法制备得到Pt/ZrP-Th-CNTs复合催化剂.SEM研究结果表明,金属铂(Pt)微粒在载体表面具有很高的分散度,且颗粒大小均匀,电极的比表面积也得到较大提高.考察了复合电极在酸性介质中对甲醇的电催化氧化...     

聚苯乙烯-金纳米复合材料的可控组装及表面增强拉曼散射性能

无皂乳液聚合制备单分散聚苯乙烯(PS)微球,经过阳离子化后,在其表面通过界面可控自组装方法修饰金纳米粒子(Au NPs)制备PS-Au复合物SERS基底,通过调制组装体系中Au NPs数量控制PS微球表面金纳米粒子密度。采用紫外-可见吸收光谱、扫描电子显微镜、热重分析和拉曼光谱对PS微球及PS-Au复合物的表面形貌、组成及性能进行了表征。结果显示,金纳米粒子尺寸为40 nm、体积为3 mL时,组装得到的PS-Au复合材料具有较好的分散性和稳定性,并展现出较好的表面增强拉曼散射(SERS)活性,其增强因子达到10~5。该复合物材料作为增强基底进一步被应用于农药福美双的SERS检测,其灵敏度达到0.1×10~(-6)。     

核壳型量子点-纳米金颗粒组装体高效检测神经性毒剂模拟剂

实验设计制备了一种由12层硫化锌包覆硒化镉的核壳型量子点(CdSe/12ZnS QDs)和纳米金颗粒(Au NPs)自组装形成的CdSe/12ZnS QDs/Au NPs复合结构, 并将其应用于神经性毒剂模拟剂氰基磷酸二乙酯(Diethyl Cyanophosphonate, DCNP)的高效检测。QDs由于与Au NPs存在荧光共振能量转移作用(Fluorescence Resonance Energy Transfer, FRET)而发生荧光猝灭, 乙酰胆碱酯酶(AChE)水解氯化硫代乙酰胆碱(ATC)生成的硫胆碱能够将量子点取代而使量子点荧光恢复。当QDs与Au NPs的摩尔浓度比为20 : 1时, QDs荧光猝灭效果最佳, AChE浓度为1.0×10 ^-3 U/L时, QDs荧光恢复效果最好。DCNP的存在会抑制AChE的活性, 减少硫胆碱的生成并降低QDs的荧光恢复效率, 通过对QDs荧光恢复效率测定能够检测DCNP。在最优条件下对DCNP的检测结果表明, 量子点的荧光恢复效率与DCNP浓度的对数在5.0×10 ^-9~5.0×10 ^-4mol/L的范围内存在良好的线性关系, 检出限达5.0×10 ^-9mol/L。     

氧化锌晶须／聚苯胺核壳结构复合物的制备与性能研究

对氧化锌晶须(ZnOw)进行正硅酸乙酯(TEOS)和γ-氨丙基三乙氧基硅烷(APTES)改性后得到共改性氧化锌晶须(TA-ZnOw),在其表面进行聚苯胺(PANi)接枝聚合,制备了TA-ZnOw/PANi复合物.将其与只经APTES改性的氧化锌晶须(A-ZnOw)和聚苯胺复合而成的A-ZnOw/PANi复合物,及未经任何改性的氧化锌晶须(N-ZnOw)和聚苯胺合成的N-ZnOw/PANi复合物进行形貌、结构及性能比较.结果表明,TA-ZnOw/PANi复合物中的聚苯胺接枝效果最好,而且接枝在TA-ZnOw表面的聚苯胺结构与纯聚苯胺结构相同.且TA-ZnOw/PANi核壳结构复合物表现出最好的介电性能和热稳定性能,介电常数虚部最大值为6.86,壳层聚苯胺热分解温度为350℃.TEOS作为保护层,APTES作为自组装层,在制备TA-ZnOw/PANi核壳结构复合物过程中起了重要作用.     

{H3[PMo12O40]/Pt/PAMAM}复合膜的制备及对甲醇的电催化氧化

采用循环伏安法在玻碳电极上制备了{H3[PMo12O40]/Pt/PAMAM}复合膜,用X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、电子能谱技术(EDS)、原子力显微镜(AFM)和循环伏安法(CV)研究了膜的组成、形貌及其对甲醇的电催化氧化活性。结果表明,Pt纳米粒子在PAMAM基底上分散均匀;最外层沉积H3[PMo12O40]后,与相同条件下制备的Pt/PAMAM膜相比,{H3[PMo12O40]/Pt/PAMAM}复合膜修饰电极对甲醇的氧化有更强的电催化活性。     

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.     

Measurement of the thermal expansion of metal and FRPs

Thermal expansion is an important parameter for characterization of different binding forces, lattice dynamics, band and crystal structure of any solids. Many investigators have focused their attention to study this property theoretically and experimentally at different temperatures. It is one of the important properties of metals and its alloys, which helps to calculate the thermal stress. This parameter is also used to determine the compatibility of an insulator as load bearing materials. Different experimental setups have been developed to study thermal expansions of the materials using different techniques namely capacitance method, interferometric principle, LASER, optical, quartz tube etc. This paper reviews most of the experimental setups available to measure thermal expansion of metals, alloys, polymers and fibre-reinforced plastics at temperature ranging from 1 to 1100 K.     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

Development of No-Vent™ liquid hydrogen storage system for space applications

A number of technological advances required to store and maintain normal-boiling-point and densified cryogenic liquids, including liquid hydrogen, under zero boil-off conditions in-space, for long periods of time, have been developed. These technologies include (1) thermally optimized compact cryogen storage systems that reduce environmental heat leak to the lowest-temperature cryogen, which minimizes cryocooler size and input power, and (2) actively-cooled shields that surround the storage systems and intercept heat leak. The processes and tools used to develop these technologies are discussed. A zero boil-off liquid hydrogen storage system technology demonstrator for validating the actively-cooled shield technology is presented.     

Analysis of optimum configuration of two-stage thermoelectric modules

In this paper, the theoretical analysis and stimulating calculation were conducted for a basic two-stage thermoelectric module, which contains one thermocouple in the second stage and several thermocouples in the first stage. The study focused on the configuration of the two-stage thermoelectric module, especially investigating the influences of some parameters, such as the allocation of the junction temperature difference in the module, the length of thermocouples and the number of thermocouples, on the cooling performance of the module. The obtained analysis results indicate that changing the junction temperature difference in the second stage, the length of thermocouples and the number of thermocouples in the first stage can improve the cooling performance of the module. These results can be used to optimize the configuration of the two-stage thermoelectric module, and provide guides for the design and application of thermoelectric cooler.     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

Effect of cryogenic treatment on microstructure, mechanical and wear behaviors of AISI H13 hot work tool steel

This paper focuses on the effects of low temperature (subzero) treatments on microstructure and mechanical properties of H13 hot work tool steel. Cryogenic treatment at −72 °C and deep cryogenic treatment at −196 °C were applied and it was found that by applying the subzero treatments, the retained austenite was transformed to martensite. As the temperature was decreased more retained austenite was transformed to martensite and it also led to smaller and more uniform martensite laths distributed in the microstructure. The deep cryogenic treatment also resulted in precipitation of more uniform and very fine carbide particles. The microstructural modification resulted in a significant improvement on the mechanical properties of the H13 tool steel.     

Effect of different treatments of copper surface on its total hemispherical absorptivity bellow 77 K

Total hemispherical absorptivity of copper surfaces treated with standard industrial methods was measured in dependence on the temperature of thermal radiation, varying from 25 K to 300 K. The sample temperature was typically from 5 K to 40 K and did not exceed 70 K. Usability of chemical and mechanical Cu surface finishing as well as Cu plating with Ni and Au for cryogenic design is discussed. As an example of practical application of our results, the cryogenic design of a LN₂ trap is presented.     

Percolation and the resistive transition of the critical temperature Tc of Nb3Sn

The relationship between the distribution of the critical temperature, the percolation function, and the resistive transition of the critical temperature is explored for polycrystalline Nb₃Sn. In the neighborhood of the critical temperature, Nb₃Sn is assumed to be a random mixture of superconducting and normal grains. Percolation concepts are applied to a study of the resistivity. A general analysis is made showing that the onset and shape of the resistive transition for composite conductors are determined by the percolation function and the distribution of the critical temperature. An approximate form of the percolation function is determined based on a linear FEM analysis. Example resistive transitions are calculated for an assumed normal distribution of the critical temperature. An argument is presented that relates grain orientation and strain dependence in Nb₃Sn. It is noted that a dependence of the distribution of T_c with strain, in addition to the usual shift in T_c with strain, would be the result of a strain dependence that is a function of grain orientation. The analysis shows the extent to which the slope of the resistive transition is a measure of the distribution of the critical temperature, and therefore a measure of the grain orientation strain sensitivity. Finally, a method is described to determine the percolation function experimentally.