New ESRElectrochemical Cell Designs for Coaxial Microwave Cavity

本文报道了一种适用于同轴微波腔的新型ＥＳＲ—电化学池的设计。工作电极的长度可调节，部分屏蔽微波辐射的功能由上下两个屏蔽套承担。除了传统的螺线管，工作电极还可由打孔的金属筒、金属网、甚至复合材料制成。对电极可根据需要置于共振腔的外面或里面。总之，新设计灵活实用，适合更多的研究场合。本文列举了一些应用实例。New cell designs for simultaneous electrochemical(EC) and electron spin resonance (ESR) measurements are reported for coaxial microwave cavity. Adjustable shieldings are introduced so that the working electrode can be much shorter than the full height of the cavity. Besides the traditional helical electrode, the working electrode can be cylinders made from metal plates, metallic meshes or even composite materials. The counter electrode can be placed either inside or outside the cavity. These features make the new designs more flexible than that previously reported. With a nonperforated cylindrical electrode, this cell can be used to determine the standard potential and the number of electrons of electrode reactions involving radicals. Other possible applications are also briefed.作者联系地址：武汉大学化学系Author's Address: Dept. of Chem., Wuhan Univ., Wuhan 43007

Raman Scattering near Metal Nanostructures

We study Raman scattering in active media placed in proximity of different types of metal nanostructures, at wavelengths that display either Fabry-Perot or plasmonic resonances, or a combination of both. We use a semi-classical approach to derive equations of motion for Stokes and anti-Stokes fields that arise from quantum fluctuations. Our calculations suggest that local field enhancement yields Stokes and anti-Stokes conversion efficiencies between five and seven orders of magnitudes larger compared to cases without the metal nanostructure. We also show that to first order in the linear susceptibility the local field correction induces a dynamic, intensity-dependent frequency detuning that at high intensities tends to quench Raman gain

Time-Resolved Electron Spin Resonance Spectroscopy for in-situ Studies of Electrochemical Systems

在电子自旋共振（ＥＳＲ）对电化学暂态过程的研究中，人们通常将磁场固定在对被研究信号敏感的位置，记录ＥＳＰ强度随时间（或电极电势）的变化。这种作法常导致大量的信息遗失，不但得不到完整ＥＳＲ谱线的变化，也很难分析多种顺磁物种共存的情况。最近，我们致力于发展用于现场电化学研究的时间分辨ＥＳＲ波谱技术，它提供了整个ＥＳＲ谱线随时间变化的三维信息，以微机为控制中心的系统可每１０ｍｓ记录一个包含１０００个数据点的ＥＳＲ谱图，基于Ｗｉｎｄｏｗｓ的软件提供了平滑、Ｆｏｕｒｉｅｒ变换、积分、谱线的叠加和差减等多种辅助功能。本文还以苯酚的电氧化为例演示了这个技术的实际应用。作者联系地址：武汉大学化学系Author's Address: Dept.of Chem. Wuhan Univ.,Wuhan,43007

Designing Advanced Alkaline Polymer Electrolytes for Fuel Cell Applications

Although the polymer electrolyte fuel cell (PEFC) is a superior power source for electric vehicles, the high cost of this technology has served as the primary barrier to the large-scale commercialization. Over the last decade, researchers have pursued lower-cost next-generation materials for fuel cells, and alkaline polymer electrolytes (APEs) have emerged as an enabling material for platinum-free fuel cells.To fulfill the requirements of fuel cell applications, the APE must be as conductive and stable as its acidic counterpart, such as Nafion. This benchmark has proved challenging for APEs because the conductivity of OH^– is intrinsically lower than that of H⁺, and the stability of the cationic functional group in APEs, typically quaternary ammonia (−NR₃⁺), is usually lower than that of the sulfonic functional group (−SO₃^–) in acidic polymer electrolytes.To improve the ionic conductivity, APEs are often designed to be of high ion-exchange capacity (IEC). This modification has caused unfavorable changes in the materials: these high IEC APEs absorb excessive amounts of water, leading to significant swelling and a decline in mechanical strength of the membrane. Cross-linking the polymer chains does not completely solve the problem because stable ionomer solutions would not be available for PEFC assembly.In this Account, we report our recent progress in the development of advanced APEs, which are highly resistant to swelling and show conductivities comparable with Nafion at typical temperatures for fuel-cell operation. We have proposed two strategies for improving the performance of APEs: self-cross-linking and self-aggregating designs. The self-cross-linking design builds on conventional cross-linking methods and works for APEs with high IEC. The self-aggregating design improves the effective mobility of OH^– and boosts the ionic conductivity of APEs with low IEC.For APEs with high IEC, cross-linking is necessary to restrict the swelling of the membrane. In our self-cross-linking design, a short-range cross-linker, tertiary amino groups, is grafted onto the quaternary ammonia polysulfone (QAPS) so that the cross-linking process can only occur during membrane casting. Thus, we obtain both the stable ionomer solution and the cross-linked membrane. The self-cross-linked QAPS (<i>x</i>QAPS) possesses a tight-binding structure and is highly resistant to swelling: even at 80 °C, the membrane swells by less than 3%.For APEs with low IEC, the key is to design efficient OH^– conducting channels. In our self-aggregating design, long alkyl side-chains are attached to the QAPS. Based on both the transmission electron microscopy (TEM) observations and the molecular dynamics (MD) simulations, these added hydrophobic groups effectively drive the microscopic phase separation of the hydrophilic and hydrophobic domains and produce enlarged and aggregated ionic channels. The ionic conductivity of the self-aggregated QAPS (<i>a</i>QAPS) is three-fold higher than that of the conventional QAPS and is comparable to that of Nafion at elevated temperatures (e.g., greater than 0.1 S/cm at 80 °C)