Au core-PtAu alloy shell nanowires for formic acid electrolysis

Inefficient electrocatalysts and high-power consumption are two thorny problems for electrochemical hydrogen(H2)production from acidic water electrolysis.Herein we report the one-pot precise synthesis of ultrafine Au core-Pt Au alloy shell nanowires(Au@PtxAu UFNWs).Among them,Au@Pt_0.077 Au UFNWs exhibit the best performance for formic acid oxidation reaction(FAOR)and hydrogen evolution reaction(HER),which only require applied potentials of 0.29 V and-22.6 m V to achieve a current density of 10 m A cm^-2,respectively.The corresponding formic acid electrolyzer realizes the electrochemical H2 production at a voltage of only 0.51 V with 10 m A cm^-2 current density.Density functional theory(DFT)calculations reveal that the Au-riched Pt Au alloy structure can facilitates the direct oxidation pathway of FAOR and consequently elevates the FAOR activity of Au@Pt_0.077 Au UFNWs.This work provides meaningful insights into the electrochemical H₂ production from both the construction of advanced bifunctional electrocatalysts and the replacement of OER.     

Layered Ag-graphene films synthesized by Gamma ray irradiation for stable lithium metal anodes in carbonate-based electrolytes

Lithium metal batteries are considered as high energy density battery systems with very promising prospects and have bee n widely studied.However,The uncon trollable plating/strippi ng behavior,infinite volume change and den drites formation of lithium metal anode restrict the applicati on.The unc on trolled n ucleati on of lithium caused by the non uniform multi-physical field distributions,can lead to the undesirable lithium deposition.Herein,a graphene composite uniformly loaded with Ag nano-particles(Ag NPs)is prepared through a facile Gamma ray irradiation method and assembled into self-supported film with layered structure(Ag-rGO film).Whe n such film is used as a lithium metal an ode host,the uncontrolled deposition is converted into a highly nucleation-induced process.On one hand,the Ag NPs distributed between the in terlayers of graphe ne can preferentially induce lithium nu cleati on and en able uniform deposition morphology of lithium between interlayers.On the other hand,the stable layered graphene structure can accommodate volume change,stabilize the interface between anode and electrolyte and inhibit dendrites formation.Therefore,the layered Ag-rGO film as anode host can reach a high Coulombic efficiency over 93.3% for 200 cycle(786 h)at a current density of 1 mA cm^-2 for 2 mAh cm^-2 in carbonate-based electrolyte.This work proposes a facile Gamma ray irradiation method to prepare metal/3D-skeleton structure as lithium anode host and demonstrates the potential to regulate the lithium metal deposition behaviors via manipulating the distribution of lithiophilic metal(e.g.Ag)in 3D frameworks.This may offer a practicable thinking for the subsequent design of the lithium metal anode.     

中国纤维素乙醇技术的研究进展

中国面临着严重的能源短缺和环境污染问题,中国政府正在局部几个省份内政策性鼓励燃料乙醇生产和使用.尽管当前主要是用玉米和谷物作为生产乙醇的原料,然而中国具有大量潜在的低成本的纤维素生物质原料,可以极大地扩大乙醇的产量,降低原料成本.近20年来,由于技术的革命性进步,已使得纤维素乙醇的生产成本从4美元/加仑以上,降低至约1.2-1.5美元/加仑.其中,每吨生物质约44美元.因此,目前乙醇掺汽油具有十分强的市场竞争力.已有几个公司正在建造首批商业纤维素乙醇工厂,虽然这些刚起步的小型设施在合理利用和管理上风险较小,但规模经济需要较大型工厂.尽管配送生物质原料的成本会随需求的增加而增加,但在乙醇生产基础上的生物精炼技术的发展,尤其是化工产品和动力的协同生产,将会使全过程的经济可行性大大提高.进一步深入的基础研究,将解决低成本下实现纤维素的完全利用,以确保在无政策性补贴的前提下,真正使纤维素乙醇成为具有市场竞争力的低成本纯液体燃料.     

Binary ligand strategy toward interweaved encapsulation-nanotubes structured electrocatalyst for proton exchange membrane fuel cell

Hierarchically porous architecture of ir on-nitroge n-carb on(Fe-N-C)for oxyge n reducti on reaction(ORR)is highly desired towards efficient mass transfer in the fuel cell device manner.Herein,we reported a binary ligand strategy to prepare zeolitic imidazolate frameworks(ZIFs)-derived precursors,wherein the addition of secondary ligand endows precursors with the capabilities to transform into porously interweaved encapsulation-nanotubes structured composites after calcination.The optimal catalyst,i.e.,termed as Fe₆-M/C-3,exhibits excellent durability with 88.8%current retention after 50,000 seconds in 0.1 M HClO₄solution by virtue of nanoparticles-encapsulation features,which is more positive than the benchmark commercial 20 wt%Pt/C catalyst.Moreover,a promising maximum power density of Fe₆-M/C-3 as cathode catalyst was also dem on strated in proton exchange membrane fuel cells(PEMFCs)measurements.Therefore,this binary ligand approach to the fabrication of hierarchically porous structures would also have significant implications for various other electrochemical reactions.     

Molten salt as ultrastrong polar solvent enables the most straightforward pyrolysis towards highly efficient and stable single-atom electrocatalyst

Currently,pyrolysis as the most widely used method still has some key issues not well resolved for synthesis of carbon-supported single-atom catalysts(C-SACs),e.g.,the sintering of metal atoms at high temperature as well as the high cost and complicated preparations of precursors.In this report,molten salts are demonstrated to be marvellous medium for preparation of C-SACs by pyrolysis of small molecular precursors(ionic liquid).The ultrastrong polarity on one hand establishes robust interaction with precursor and enables better carbonization,resulting in largely enhanced yield.On the other hand,the aggregation of metal atoms is effectively refrained while no nanoparticle or cluster is formed.By this strategy,a C-SAC with atomically dispersed Fe-N₄ sites and a high specific area over 2000 m² g^-1 is obtained,which illustrates high ORR activity in both acid and alkaline media.Moreover,this SAC exhibits superior methanol tolerance and stability after acid soaking at 85℃ for 48 h.It is believed that the molten-salts-assisted pyrolysis can be developed into a routine strategy as it not only can largely simply the synthesis of C-SACs,but also can be extended to prepare other types of SACs.     

镧对Mg-Si合金中Mg2Si相变质的影响

研究了Mg-5Si合金中La的添加对初生Mg2Si相变质的影响。结果表明,适量的La能够有效地变质初生Mg2Si相。基于本文的研究,在添加约0.5%La时,获得了最佳的变质效果,此时,初生Mg2Si相的尺寸减小到25μm以下,其形态从粗大的树枝形状变为多面体形状。然而,当La增加到0.8%或者更高时,初生Mg2Si相又生长为粗大的树枝形态。而且,在凝固过程中发现形成了一些LaSi2化合物,这些化合物的数量随着La的增加而呈现逐渐增加的趋势。     

电感耦合等离子体质谱法测定天然水体中19种元素

建立STD/KED模式-电感耦合等离子体质谱（ICP-MS）法同时测定天然水体中铍、硼、钛、钒、铬、锰、钴、镍、铜、锌、钼、镉、锑、钡、铊、铅、铁、砷和硒19种元素的分析方法。仪器调谐校准后,样品在线加入锂、钪、铑、铋校准溶液校正,以标准曲线内标法定量分析。标准曲线相关系数均大于0.999,样品加标回收率为92.6%～103.6%,质控样品测定值相对标准偏差为0.20%～2.6%(n=6),方法检出限为0.01～0.70μg/L。该方法灵敏度高,操作简便,节省人力,能满足天然水体中19种元素的同时检测需要。     

电解质-非电解质混合溶液活度系数的关联及溶解的推算 II:NH3-NaCl-Na2SO4-H2O体系的液固平衡热力学

由于在研究的体系中, Na2SO4是非对称电解质, 且能生成水合盐, 故推导了由非对称型电解质与非电解质所构成的混合溶液的各组分的活度系数关联通式, 并在此基础上讨论了水合盐液固平衡的计算方法.     

黄花棘豆化学成分的研究II:两种三萜皂苷的结构

从黄花棘豆的总皂苷中分离出两个新皂苷1和2.经光谱分析及化学方法确证,1为3-O-[α-L-鼠李吡喃糖基(1→2)-β-D-葡萄吡喃糖基(1→4)-β-D-葡萄吡喃糖醛酸基]-黄豆醇B;2为3-O-[α-L-鼠李吡喃糖基(1→2)-α-L-阿拉伯吡喃糖基(1→4)-β-D-葡萄吡喃糖醛酸基]-黄豆醇B.     

二氧化钛纳米管的研究进展

二氧化钛纳米管由于其新奇的光电、催化、气敏等性能引起了广泛的关注,在太阳能电池、光催化、环境净化、气体传感器等领域有潜在的应用价值.本文概述了近年来在制备方法、反应机理和组成、晶型和形貌及掺杂和应用方面的进展,并讨论了今后可能的研究发展方向.     

Simple correction to the classical theory of homogeneous nucleation

Formation of the new disperse phase via homogeneous nucleation plays a fundamental role wherever the first-order phase transitions occur. Inconsistent temperature dependence of the nucleation rates and poor agreement of theoretical critical supersaturations with experimental data for a number of substances are fundamental problems of the classical nucleation theory (CNT). Here we show that these problems can be solved with a simple empirical correction to CNT. Despite its simplicity, the corrected CNT (CCNT) accurately predicts temperature dependences and absolute values of the critical supersaturations for both organic and inorganic substances with widely varying properties at different ambient conditions and it works surprisingly well in a wide size range down to few molecules. The difference in predictions of CCNT and other versions of the classical nucleation theory commonly used in analyzing experimental data is discussed. It has been found that CCNT consistently gives better agreement with experimental data than other versions of classical nucleation theory.     

Homogeneous nucleation rates of higher n-alcohols measured in a laminar flow diffusion chamber

Nucleation rate isotherms of n-butanol, n-pentanol, n-hexanol, n-heptanol, and n-octanol were measured in a laminar flow diffusion chamber using helium as carrier gas. The measurements were made at 250-310 K, corresponding to reduced temperatures of 0.43-0.50, and at atmospheric pressure. Experimental nucleation rate range was from 10(3) to 10(7) cm(-3) s(-1). The expression and accuracy of thermodynamic parameters, in particular equilibrium vapor pressure, were found to have a significant effect on calculated nucleation rates. The results were compared to the classical nucleation theory (CNT), the self-consistency corrected classical theory (SCC) and the Hale's scaled model of the CNT. The average ratio between the experimental and theoretical nucleation rates for all alcohols used was 1.5x10(3) when the CNT was used, and 0.2x10(-1) when the SCC was used and 0.7x10(-1) when the Hale's scaled theory was used. The average values represent all the alcohols used at the same reduced temperatures. The average ratio was about the same throughout the temperature range, although J(exp)/J(the) calculated with the Hale's scaled theory increased slightly with increasing temperature. The saturation ratio dependency was predicted closest to experiment with the classical nucleation theory. The nucleation rates were compared to those found in the literature. The measurements were in reasonable agreement with each other. The molecular content of critical alcohol clusters was between 35 and 80 molecules. At a fixed reduced temperature, the number of molecules in a critical cluster decreased as a function of alcohol carbon chain length. The number of molecules in critical clusters was compared to those predicted by the Kelvin equation. The theory predicted the critical cluster sizes well.     

Nitrous oxide: Saturation properties and the phase diagram

The experimental values of the coordinates of the triple point and of the critical point of nitrous oxide registered in the literature were assessed and those judged as most reliable have been selected. Empirical equations have been found for the vapour pressure, sublimation and fusion curves. The virial coefficients and saturation properties as functions of temperature along the equilibrium curves are described by reduced equations. They were used in arriving at the molar enthalpies at the triple point and the normal boiling temperature. Equations for the sublimation and fusion curves resulting from the exactly integrated Clapeyron equation compare favourably with the results from the empirical treatment and the experimental data.     

Properties of 1,8-cineole: a thermophysical and theoretical study

This paper reports on an experimental and theoretical study of 1,8-cineole, one of the main components of essential oils in different plants. The pressure-volume-temperature behavior of this fluid was evaluated accurately over wide temperature and pressure ranges and correlated successfully with the empirical TRIDEN equation. From the measured data, the relevant derived coefficients isothermal compressibility, isobaric expansibility, and internal pressure were calculated. The isobaric heat capacities at high pressure were extrapolated from the data measured at atmospheric pressure. The cubic equations of state by Soave, Peng-Robinson, Stryjek-Vera modification of Peng-Robinson, Patel-Teja, Sako-Wu-Prausnitz, and the SAFT and PC-SAFT molecularly based equations of state were used to predict the PVT behavior. The SAFT and PC-SAFT parameters for 1,8-cineole were obtained from correlation of available saturation literature data; the best results were provided by Sako-Wu-Prausnitz and PC-SAFT equations of state, whereas the classical ones were shown to be inadequate. The molecular structure was studied by quantum computations at the B3LYP/6-311++g(d) level and classical molecular dynamics simulations in the NPT ensemble with the OPLS-AA forcefield. On the basis of both macroscopic and microscopic studies, a complex fluid structure was inferred.     

Properties and structure of aromatic ester solvents

This paper reports on an experimental and theoretical study of the aromatic ester solvents family. Several compounds were selected to analyze the different factors that influence their liquid-state properties and structures. The pressure-volume-temperature behavior of these fluids was measured accurately over wide temperature and pressure ranges and correlated successfully with the empirical TRIDEN equation. From the measured data the relevant derived coefficients of isothermal compressibility, isobaric expansibility, and internal pressure were calculated. The statistical associating fluid theory (SAFT) and perturbed chain statistical associating fluid theory (PC-SAFT) molecularly based equations of state were used to predict the PVT behavior with model parameters obtained from the correlation of available saturation literature data; the results provided by PC-SAFT equations of state were clearly superior for all of the studied solvents. The fluid's molecular level structure was studied by quantum computations at the B3LYP/6-311++g** level and classical molecular dynamics simulations in the NPT ensemble with the OPLS-AA forcefield. Molecular parameters, such as torsional barriers or cluster energetics, were analyzed as a function of ester structures. The molecular dynamics study provides, on one hand, theoretical values of thermophysical properties, which are compared with the experimental ones, and, on the other hand, valuable molecular level structural information. On the basis of both macroscopic and microscopic studies complex fluid structures were inferred with important effects arising from the geometries of the studied molecules and from the existence of remarkable intermolecular forces of dominating dipolar nature.     

Nucleation of ethanol, propanol, butanol, and pentanol: A systematic experimental study along the homologous series

We present homogeneous vapor-liquid nucleation rates of the 1-alcohols (C(n)H(2n+1)OH, n = 2-4) measured in the well-established two-valve nucleation pulse chamber as well as in a novel one-piston nucleation pulse chamber at temperatures between 235 and 265 K. The nucleation rates and critical cluster sizes show a very systematic behavior with respect to the hydrocarbon chain length of the alcohol, just as their thermo-physical parameters such as surface tension, vapor pressure, and density would suggest. For all alcohols, except ethanol, predictions of classical nucleation theory lie several orders of magnitude below the experimental results and show a strong temperature-dependence typically found in nucleation experiments. The more recent Reguera-Reiss theory [J. Phys. Chem. B 108(51), 19831 (2004)] achieves reasonably good predictions for 1-propanol, 1-butanol, and 1-pentanol, and independent of the temperature. Ethanol, however, clearly shows the influence of strong association between molecules even in the vapor phase. We also scaled all experimental results with classic nucleation theory to compare our data with other data from the literature. We find the same overall temperature trend for all measurement series together but inverted and inconsistent temperature trends for individual 1-propanol and 1-butanol measurements in other devices. Overall, our data establishe a comprehensive and reliable data set that forms an ideal basis for comparison with nucleation theory.     

Argon nucleation in a cryogenic nucleation pulse chamber

Homogeneous nucleation of argon droplets has been measured with a newly designed cryogenic nucleation pulse chamber presented already in a previous paper [Fladerer and Strey, J. Chem. Phys. 124, 16 (2006)]. Here we present the first systematic nucleation onset data for argon measured in a temperature range from 42 to 58 K and for vapor pressures from 0.3 to 10 kPa. For these data we provide an analytical fit function. From the geometry of the optical detection system and the time of nucleation the experimental nucleation-rate range can be estimated. This allows a comparison of the data with the predictions of classical nucleation theory. We found 16-26 orders of magnitude difference between theory and experiment, and a too strong theoretical dependence of the nucleation rate on temperature. A comparison with the self-consistent theory of Girshick and Chiu [J. Chem. Phys. 93, 1273 (1990)] showed improved temperature dependence but still discrepancies of 11-17 orders of magnitude compared to experimental data. The thermodynamically consistent theory of Kashchiev [J. Chem. Phys. 118, 1837 (2003)] was found to agree rather well with experiment in respect to the temperature dependence and to predict rates about 5-7 orders of magnitude below the experimental ones. With the help of the Gibbs-Thomson equation we were able to evaluate the size of the critical nucleus to be 40-80 argon atoms.     

Nucleation rates in a new phenomenological model

In this paper we develop a new theory to evaluate the nucleation rate in the framework of the EMLD-DNT model. Beyond the model, our theory deals with cluster translation and exclusion, effects that have been virtually ignored in classical nucleation theory. We apply the model to the case of 1-pentanol, and compare the predictions with experimental results. We find an excellent agreement between the nucleation rate predicted by our theory and experimental data. The distinguishing feature of the model is its ability to predict successfully the rate of formation of the critical nucleus without the use of an intermolecular potential, employing only macroscopic thermodynamic properties.