恒电位下铜电极电流振荡的延时控制

采用铜电极的阳极溶解作为研究对象,开展电流振荡的延迟控制方法的研究.调节控制信号中延迟时间及控制系数的大小,延迟时间对电流影响作用明显,观察到周期变长和变短的结果,小延时下振荡周期变大,大延时下周期变小.延时控制也使振荡的波形产生明显的变化,并使原有的周期振荡呈现出混沌振荡.控制系数对振荡产生不同的影响,呈现出波形分裂、混合振荡等现象.控制系数加大时,这种峰的分裂变得更加强烈,阳极溶解电流产生了混沌振荡.控制后的振荡频率与原有频率有简单的比例关系.文中对延迟控制产生特定波形的机制进行了分析和讨论.     

葡萄糖、半乳糖和乙醇恒电流氧化过程电位振荡的EQCM研究

采用电化学石英晶体微天平(EQCM)研究了0.5 mol•L^-1 NaOH水溶液中铂电极上葡萄糖、半乳糖和乙醇恒电流氧化过程中伴随的电位振荡行为. 两个糖体系的电位振荡过程伴随EQCM频率的同步振荡响应, 而乙醇体系中相应的频率响应却非常小；三个体系振荡过程的同步动态电阻响应均很小, 表明振荡过程频率响应主要为质量效应. 虽然葡萄糖和半乳糖结构相似, 电位和频率振荡的幅度相当, 但频率波数和周期明显不同, 表明电位振荡行为对两者呈现良好的分子识别能力. 本文也讨论了相关振荡机理和NaOH浓度效应及碱性介质中铂电极电化学过程, 提出了所形成的铂氧化物主要是PtO₂-3H₂O_ad以及两糖体系振荡过程中糖酸根阴离子伴随着高/低电位在铂电极上吸/脱附的新观点.     

单向耦合Hindmarsh-Rose系统的同步

采用数值模拟方法, 研究了由两个具有不同初始条件单向耦合的Hindmarsh-Rose神经元所组成系统的动力学行为. 研究结果表明, 耦合强度对两个神经元的同步具有重要的影响. 当两个神经元的控制参数取值不同时, 即在驱动系统和响应系统均处于混沌态及驱动系统处于周期振荡态, 响应系统处于混沌态两种情况下, 随耦合强度的增加其放电活动都能从不同步达到相位同步, 最后实现近似完全同步.     

化学自催化混沌反应模型中的耦合作用与混沌同步

选用混沌自催化反应作为子系统,构造了耦合自催化反应系统,研究了耦合变量、耦合系数对混沌动力学行为的影响,给出了不同耦合系数下系统的动力学特征,探讨了耦合作用机制.结果表明,耦合作用能明显地改变子系统的动力学行为,强化系统间的相关性.耦合后的混沌运动受到调整与抑制,耦合强度加大时,呈现出混沌运动轨线的周期化,耦合系数大于临界值,两子系统实现了完全的同步.不同变量的耦合时,影响最大的是第二种变量.对于三种物质均有耦合时,更容易出现混沌的抑制、运动状态的锁相与周期化和混沌的完全同步.     

CSTR中Ferroin催化BZ反应中的倍周期振荡和混沌

Ferroin催化的BZ反应是化学时空斑图研究中最常用的反应体系, 研究该体系时发现了简单倍周期、混合模式倍周期振荡、混沌以及低流速下溴离子选择电极的混合模式振荡, 并用Györgyi和Field两环偶合的BZ反应模型进行数值模拟解释. 该研究为用于光学测定的时空斑图研究提供了从简单振荡到各种复杂振荡的反应介质, 也表明BZ反应复杂振荡与混沌研究可扩展到不同催化剂催化的溴酸盐驱动的非线性反应体系.     

铜电极阳极溶解过程恒电位电流振荡的动力学模型

研究了铜电极在酸性氯化钠溶液中的恒电位电流振荡行为,分析了电极过程中的非线性步骤及电化学耦合因素,提出了一个可能的电极过程动力学模型,并借助线性稳定性分析及分支分析得到了参数坐标空间中的动力学行为区域图。在此基础上,将极化曲线视为稳定非平衡定态区态函（电流）与外控参数（电位）的关系,同时将恒电位电流振荡模拟为稳定极限环振荡,分别计算出了极化曲线与时间－电流振荡曲线,其结果与实验数据相符,表明该类电     

甲醇在Pt表面电化学氧化过程中的化学振荡

基于甲醇电化学氧化的双途径机理,建立了能够表征甲醇电化学氧化过程电位振荡的非线性动力学模型.所建甲醇氧化系统动力学演化模型涉及三个主要的变量:电极电位(e),毒性中间体CO的表面覆盖度(x),含氧物种H2Oa的表面覆盖度(y).通过反应速率常数ki=exp(ai(e-ei))实现了化学反应与电极电位的耦合.研究发现,在不同的电流密度范围内甲醇电化学氧化呈现不同的动力学特征.甲醇电化学氧化时出现的电位振荡现象可以归因为:一是氧化过程中生成了毒性中间体CO,这是产生电化学振荡的诱因;二是强烈依赖于电极电位的非电化学反应,即,含氧物种H2Oa在Pt表面的生成与消失,则是维系振荡的直接原因.而甲醇电化学氧化体系复杂的动力学行为根源在于电极电位e对CO和含氧物种H2Oa所参与反应的耦合反馈作用.对所建模型的数值分析成功地解释了为什么甲醇电化学氧化时出现的电位振荡现象只发生在一定的电流密度范围.     

亚氯酸盐-硫代硫酸盐非缓冲体系的动力学

研究了亚氯酸盐-硫代硫酸盐反应体系在非缓冲条件下的复杂动力学行为.结果发现,在开放体系中反应的pH值和Pt电位存在准周期振荡分叉和混合模式振荡分叉通向混沌的过程，且pH峰与Pt电位峰反相位.当与起始浓度比相对较小时，随着流速的逐渐升高，体系的pH值和Pt电位从简单的小振幅振荡(S)经过准周期振荡分叉到混沌，最后回到简单大振幅振荡(L)；而当与起始浓度比相对较高时，随着流速的降低，体系的pH值和Pt电位出现LS1、LS2、LS3…LSn的混合模式振荡,并在每对(LSn、LSn＋1)振荡区间发现了LSn、LSn＋1随机出现的非周期振荡行为.运用硫价态变化的一般动力学模型，模拟出了反应体系的混合模式振荡及非周期振荡.     

亚氯酸盐氧化硫脲非缓冲体系的复杂动力学行为

研究了ClO2--SC(NH2)2的非缓冲体系中的动力学行为,发现在开放体系中,体系的铂电极电位和pH呈现反相位连续的大幅度振荡,随着流速的降低,体系行为更加丰富,在高流速的混合模式之后出现了低流速的混合模式;在外部条件变化时,观察到了准周期振荡和倍周期振荡现象;考察了温度、流速、酸度以及反应物的初始浓度比等主要的影响因素,发现分叉参数的变化与体系的行为紧密相关。     

含钼碱性电解液中小分子醇在铂黑电极上氧化时的周期性及非周期性振荡

乙醇和甲醇在含钼碱性溶液中的铂黑电极上氧化时,在一定条件下可得到循环伏安曲线的周期性及非周期性振荡．通过微调下限电位可控制振荡的周期,其中非周期性振荡具有混沌的特性．讨论了钼的存在及碱浓度的变化对振荡的影响．结果表明,钼的氧化还原振子在电极表面与小分子醇的氧化过程中发生耦合作用是导致振荡的关键     

Alternating current-bipolar electrochemistry

Rotation of a bipolar electrode in a constant electric field between feeder electrodes causes an alternating bipolar current at an AC frequency that depends on the rotation rate. The corresponding oscillation of the feeder current is evaluated by means of a lock-in amplifier. This innovative approach allows the current flowing through the non-wired bipolar electrode in an open bipolar system to be extracted without relying on electrochemical reporter reactions.     

Dynamics of electrochemical oscillators with electrode size disparity: asymmetrical coupling and anomalous phase synchronization

Experiments are carried out in dual electrode oscillatory Ni electrodissolution in which the two electrodes have different surface areas. The transition to phase synchronization is analyzed as asymmetrical coupling strength, induced by placing a cross resistance between the electrodes, is varied. It is shown that because of nonisochronicity (phase shear, i.e., strong dependence of period on amplitude) of the oscillators, anomalous phase synchronization effects can be observed: advanced/delayed synchronization and, to a lesser extent, frequency difference enhancement. The type of synchronization is strongly affected by the underlying heterogeneities of the oscillators; in the experiments with a slow driver (large surface area) electrode the synchronization is advanced, with a fast driver electrode the synchronization is delayed with respect to symmetrical coupling. The findings thus reveal that the interplay of asymmetrical coupling with the types of inherent heterogeneities plays an important role for the interpretation of size effects in the dynamical behavior of a nonlinear chemical reaction.     

等离子体甲烷偶联体系中纯氢气放电消除积炭

发现了等离子条件下甲烷偶联反应中形成的积炭可以通过该体系中纯氢气放电而消除.将消除积炭使用直流电场的正高压和负高压与使用交流电场作了比较，发现直流电场中无论使用正高压还是负高压，只有阴极上的积炭可以被消除，而交流电场中两极积炭均可被消除，反应器壁上的积炭在以上任何情况下均可被消除.基于实验事实提出了机理假设.消除积炭的量与输入功率、反应器对电极的直径比以及电极材料有关.     

2-D assembly of colloidal particles on a planar electrode

Electrical voltage externally applied between parallel-plate electrodes can cause colloidal particles located near one of the electrodes to aggregate; thus monodisperse particles can be driven to form hexagonally close-packed arrays which can be useful in the fabrication of photonic materials. The mechanism for lateral motion of particles on the electrode surface is electroosmotic flow driven by the action of the applied electric field acting either on the equilibrium charges in the diffuse layer of the particles (ECEO) or on charge induced by the electric field on the surface of the electrode (ICEO). For steady currents, ECEO dominates whereas ICEO dominates for high-frequency alternating current. For intermediate frequencies (10 Hz to 1 kHz) both mechanisms are active. This critical review attempts to integrate concepts from electrochemistry and colloid chemistry to understand this electrokinetic phenomenon.     

Simulation of Duty Cycle-Based Trapping and Ejection of Massive Ions Using Linear Digital Quadrupoles: the Enabling Technology for High Resolution Time-of-Flight Mass Spectrometry in the Ultra High Mass Range

Duty cycle-based trapping and extraction processes have been investigated for linear digitally-driven multipoles by simulating ion trajectories. The duty cycles of the applied waveforms were adjusted so that an effective trapping or ejection electric field was created between the rods and the grounded end cap electrodes. By manipulating the duty cycles of the waveforms, the potentials of the multipole rods can be set equal for part of the waveform cycle. When all rods are negative for this period, the device traps positive ions and when all are positive, it ejects them in focused trajectories. Four Linac II electrodes[1] have been added between the quadrupole rods along the asymptotes to create an electric field along the symmetry axis for collecting the ions near the exit end cap electrode and prompt ejection. This method permits the ions to be collected and then ejected in a concentrated and collimated plug into the acceleration region of a time-of-flight mass spectrometer (TOFMS). Our method has been shown to be independent of mass. Because the resolution of orthogonal acceleration TOFMS depends primarily on the dispersion of the ions injected into the acceleration region and not on the ion mass, this technology will enable high resolution in the ultrahigh mass range (m/z > 20,000).     

氧化铁电极的半导体性能和光电化学 Ⅴ.烧结掺锌氧化铁电极的光电响应

Somorjai等曾报道在不同电势下,测得掺MgO氧化铁光电极具有n,p两种类型的光响应^[1]。最近本实验室首次报道了在同一电势下,热形成的掺MgO-Fe₂O₃光电极具有n,p型双重光响应共存现象^[2],由于其在电催化等中可能的应用价值引起了较广泛的兴趣。     

A novel electric ion resonance cell design with high signal-to-noise ratio and low distortion for Fourier transform mass spectrometry

Performing wideband ion image current detection mass spectrometry experiments with an electric ion trap—e. g., the Paul trap—is a difficult task, as there is a strong crosstalk current induced by the high voltages of the radio frequency (rf) storage field. In a classic Paul trap the metallic hyperbolic electrodes (a ring electrode and two end cap electrodes) are shaped following the isopotential lines of the quadrupole potential distribution. In our new design the ring electrode is replaced by a cylindrical series of ring electrodes with a parabolic potential distribution, whereas the end cap electrodes are used without modification. Thus the quadrupole field within the trap remains unchanged but the capacitances between the electrodes and therefore the crosstalk currents are significantly reduced. The remaining crosstalk is balanced out by an electronic compensation technique. As a consequence the weak signals of the ion-induced charge can be detected with a wideband low-noise amplifier to perform Fourier transform mass spectrometry experiments with improved signal-to-noise ratio.     

Transition of oscillatory mechanism for methanol electro-oxidation on nano-structured nickel hydroxide film (NNHF) electrode

Instead of CO(ad) formation and removal as on Pt electrodes, coupling of charge transfer with diffusion and convection mass transfer accounts for the oscillation found in the methanol electro-oxidation on the NNHF electrode.     

Control of particle alignment in water by an alternating electric field

We attempted to align a large number of silica particles dispersed in aqueous solution by controlling the alternating electric field between the two electrodes (400 microm apart). Relatively large particles (9.9 microm) were found to align forming strings in the direction parallel to the electric field while relatively small particles (2.0 and 4.9 microm) were observed to align making stripes in the direction perpendicular to the field. The number of stripes formed by particles between the electrodes increased with increasing frequency of the alternating field. This peculiar perpendicular particle alignment appeared when the contribution to particle alignment of electroosmotic flow exceeded that of dielectric polarization and the osmotic flow was found to be stronger around the particles than in the vicinity of the electrode surface.     

Response of Bi-disperse Polyelectrolyte Brushes to External Electric Fields——A Numerical Self-consistent Field Theory Study

The self-consistent field theory has been employed to numerically study the response of bi-disperse flexible polyelectrolyte (PE) brushes grafted on an electrode to electric fields generated by opposite surface charges on the PE-grafted electrode and a second parallel electrode. The numerical study reveals that, under a positive external electric field, the shorter and negatively charged PE chains are more responsive than the longer PE chains in terms of the relative changes in their respective brush heights. Whereas under a negative external electric field, the opposite was observed. The total electric force on the grafted PE chains was calculated and it was found that, under a positive external electric field, the magnitude of the total electric force acting on one shorter PE chain is larger than that on one longer PE chain, or vice versa. The underlying mechanism was unraveled through analyzing the total electric field across the two oppositely charged electrodes.