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.     

单纵模Nd:YAG激光泵浦H2气中的受激喇曼散射

Strong backward first Stokes (BS) in H2 is observed when a single longitudinal mode fundamental frequency Nd:YAG laser (1.06 μm, pulsed width about 9 ns, linewidth 0.003 cm-1) is used as the pump source. Using a pump energy of 120 mJ, photon conversion efficiency of FS and BS was determmed to be 66% and 15% respectively in 1.5 MPa H2, while in 4.0 MPa H2 the respective values are 46% and 39%. Due to their propagation in opposite directions, there is tension between FS and BS, which leads to a relaxation of the oscillation that splits both FS and BS pulses into two peaks, with the BS pulses being narrowed to about 1 ns. Surprisingly, the BS peak power reaches twice that of the pump, which can never happen in the FS case. Furthermore, the beam quality of BS is much better than that of both FS and pump. At 4 MPa of H2 pressure and a 10 Hz cycle rate, the thermal release of the Raman process deteriorates the FS beam quality, without noticeably affecting that of BS. According to this calculations, within the present experimental conditions, the stimulated Raman scattering process does not reach the steady state. Because of this, all of the experimental results can be explained explained by a related transient state, theory of stimulated Raman scattering.     

Trace gas detection of molecular hydrogen H(2) by photoacoustic stimulated Raman spectroscopy (PARS)

Photoacoustic stimulated Raman spectroscopy (PARS) has been used for sensitive and selective trace gas detection of molecular hydrogen under ambient conditions. In one experiment, 532 nm output of a seeded pulsed Nd:YAG laser is employed as Raman pump source and a Raman shifter filled with gaseous H(2) to obtain Stokes shifted radiation at 683 nm, suitable to stimulate H(2) Raman detection in a photoacoustic cell. A noise equivalent detection limit of 40 ppm by volume H(2) in 1 atm N(2) is obtained (14 mJ at 532 nm, 18 mJ at 683 nm, 10 Hz repetition rate, 58 s measurement time). Another experiment employs a dye laser for stimulating Raman radiation between 681-684 nm, allowing tuneable PARS. A Gaussian spectral fitting procedure has been applied giving a noise equivalent detection limit of 4.6 ppm by volume H(2) in 1 atm N(2) (35 mJ pulse energy at 532 nm, 45 mJ at 681-684 nm, 10 Hz repetition rate, 256 s measurement time). Spectroscopic detection offers the advantage of high selectivity along with the ability to obtain temperature and dynamic information from the rotational population and a line shape analysis, and also allows the discrimination between ortho- and para-H(2).     

异硫氰基孔雀石绿受激拉曼光谱研究

本文报道了具有时间分辨能力的全频宽带受激拉曼（BBSRS）系统和关于异硫氰基孔雀石绿（MGITC）受激拉曼光谱（sRs）的研究．BBSRS系统的探测光为450-800nm宽带连续白光,泵浦光为280～900nm范围内连续可调谐的ps窄带可见光（带宽≈7．5cm-1,脉宽≈2．5ps）．在合适的泵浦波长下,该系统可同时获取拉曼损失和拉曼增益光谱．MGITC的SRS研究结果表明,当拉曼损失谱峰出现在最大吸收波长（≈627nm）时,共振SRS谱峰强度最大;当泵浦或增益谱峰在最大吸收波长附近时,未观察到明显的共振拉曼信号;共振峰强度随浓度增大而增大,随泵浦功率增大而迅速增大,后趋于饱和;共振和非共振峰强在延时零点附近达到最大值,并随延时绝对值的增大而减小．     

Quantum theory of (femtosecond) time-resolved stimulated Raman scattering

We present a complete perturbation theory of stimulated Raman scattering (SRS), which includes the new experimental technique of femtosecond stimulated Raman scattering (FSRS), where a picosecond Raman pump pulse and a femtosecond probe pulse simultaneously act on a stationary or nonstationary vibrational state. It is shown that eight terms in perturbation theory are required to account for SRS, with observation along the probe pulse direction, and they can be grouped into four nonlinear processes which are labeled as stimulated Raman scattering or inverse Raman scattering (IRS): SRS(I), SRS(II), IRS(I), and IRS(II). Previous FSRS theories have used only the SRS(I) process or only the "resonance Raman scattering" term in SRS(I). Each process can be represented by an overlap between a wave packet in the initial electronic state and a wave packet in the excited Raman electronic state. Calculations were performed with Gaussian Raman pump and probe pulses on displaced harmonic potentials to illustrate various features of FSRS, such as high time and frequency resolution; Raman gain for the Stokes line, Raman loss for the anti-Stokes line, and absence of the Rayleigh line in off-resonance FSRS from a stationary or decaying v=0 state; dispersive line shapes in resonance FSRS; and the possibility of observing vibrational wave packet motion with off-resonance FSRS.     

Efficient Preparation of D2 Molecules in v=2 by Stimulated Raman Pumping

We report the preparation of D₂ molecules in v=2 level in molecular beam condition. A single longitudinal mode laser system was used for excitation of D₂ from (v=0, j=0) to (v=2, j=0) with the scheme of stimulated Raman pumping. An excitation efficiency of 25.2% has been achieved, which was determined by the scheme of resonance-enhanced multiphoton ionization. Dependence of relative excitation efficiency on laser energy has been measured. We found that the increasing rate of excitation efficiency became slower as pulse energy of Stokes laser increase, while the excitation efficiency still increases approximately linearly with pump pulse energies up to 60 mJ. The spectral line shapes of Raman transition was also measured at different laser energies and considerable dynamical Stark effect was observed. A single peak was found on the three dimension surface of relative excitation efficiency, indicating the process occurred in the present study is a process of stimulated Raman pumping instead of stimulated adiabatic Raman passage.     

激光促进乙醇氧化偶联表面反应机理

利用红外光谱（IR）和激光促进表面反应（LSSR）等技术，研究了沉淀法制得Cu2（PO4）（OH）表面上的乙醇氧化偶联合成1，4-丁二醇激光表面反应机理，结果表明：固体表面键激发是激光表面反应的有效激发模式; 乙醇在固体表面材料上的特定化学吸附态形式（－P＝O…H－CH2CH2OH）决定了反应产物的高选择性；固体材料表面晶格氧参与反应是使标题反应能够实现的一个重要因素．     

Stimulated Raman laser excitation of spontaneous resonance Raman scattering

The efficient conversion of the second and third harmonics of a Nd YAG laser to near UV radiation in the 395–500 nm range by stimulated Stokes (and anti-Stokes) Raman scattering (SRS) in a 1 m Raman oscillator containing compressed H₂ or D₂ is used as an excitation source for spontaneous resonance Raman spectroscopy (RRS). SRS excited RR spectra are shown for the anion radical of tetracyanoquinodimethane (TCNQ).     

Probe Beam Dichroism and Birefringence in Stimulated Raman Scattering in Polyatomic Molecules

Dichroism and birefringence in Stimulated Raman Scattering (SRS) in polyatomic molecules were studied theoretically. General expressions describing the change of the polarization matrix of the probe laser beam transmitted through initially isotropic molecular sample excited by the pump laser beam have been derived. Arbitrary polarization states and propagation directions of the incoming pump and probe beams were considered. The expressions were written in terms of spherical tensor operators that allowed for separation of the field polarization tensor and the molecular part containing three scalar values of nonlinear optical susceptibility with =0,1,2. The geometry of almost collinear propagation of the pump and probe beams through the molecular sample was considered in greater details. It was shown that the dichroism and birefringence refer to the nonlinear optical susceptibility element and that their contributions to the SRS signal can be separated experimentally by using an appropriate probe beam polarization analyzer installed in front of the photodetector. Particular cases of the off-resonant SRS and resonant SRS have been considered. The results obtained were expressed in terms of the Stokes polarization parameters of the pump and probe beams.     

Multiphoton ionization of molecules: A comparison between femtosecond and nanosecond laser pulse ionization efficiency

Multiphoton ionization mass spectra of nonvolatile molecules laser desorbed into a supersonic beam are recorded. It is shown by indirect measurements that the laser desorption of neutrals is not mass limited, but lead to the formation of neutrals with intesities large enough for intense signals. To investigate the efficiency of the multiphoton ionization process with varying laser pulse durations, simultaneous laser pulses of 500 fs and 5 ns or 100 fs and 5 ns have been applied to the neutral beam. The energies of both femtosecond and nanosecond laser pulses are held in a comparable magnitude, and thus produce, in the resulting ion intensity, very large differences up to 4 orders of magnitude. For larger evaporated molecules (> 500 u) the ionization efficiency from nanosecond laser pulses drops significantly in comparison to femtosecond laser pulse excitation. A variety of possible reasons for the different ionization and dissociation behavior in femtosecond and nanosecond laser pulse excitations are discussed in this paper. It is rationalized that even with very short laser pulses and large molecules the “ladder switching model” for ionization and fragmentation is valid.     

用超短脉冲激光研究1,3-二氯苯激发态动力学

利用啁啾脉冲放大技术建立了一套掺钛蓝宝石飞秒激光放大系统,该系统输出中心波长808nm,单脉冲能量8mJ,脉冲宽度60fs,脉冲重复频率20Hz.利用飞秒激光泵浦-探测及分子束技术,结合飞行时间质谱,对1,3-二氯苯分子的激发态动力学过程进行了研究,实验中观察到该分子能级间的量子拍频现象,并获得了第一单重激发态寿命及其拍频频率,阐述了飞秒激光场下间位二氯苯分子的电离解离机理.