电极/离子液体界面电容

用电化学阻抗方法研究了铂片电极在BMIMPF6,BMIMBF4,BMIMClO4,BMIMTf2N,BMIMCl,BMIMBr,C3OHMIMBF4,C3OHMIMClO4和BMMIMPF6(BMIM:1-butyl-3-methylimidazolium;C3OHMIM:1-(3-hydroxypropyl)-3-methylimidazolium;BMMIM:1-butyl-2-methyl-3-methylimidazolium;Tf2N:bis(trifluoromethylsulfonyl)amide)等离子液体中的界面电容及结构.结果表明:当阴、阳离子半径相差不大且不存在特性吸附时,在零电荷电势附近,电极/离子液体界面的电容-电势曲线将出现电容单峰或者双峰.电极的零电荷电势对应于单峰的峰电势或者双峰之间的谷电势.当电极电势远离零电荷电势时,电极/离子液体界面成紧密层结构,可由紧密层理论来描述.如果存在离子的特性吸附,相应的电容峰可能不再出现,而表现为双层电容随电极电势对零电荷电势的偏离而单调增加.还研究了添加小的Li+离子对电极/离子液体界面电容的影响.通过向BMIMTf2N中加入LiTf2N,发现Li+离子可以改变电极/离子液体界面的双层结构,但无助于界面电容的提高,甚至可能引起电容的降低.最后探讨了不同条件下,尤其考虑阴阳离子特性吸附时,电极/离子液体的界面结构.     

聚腺嘌呤核苷酸在金电极上的吸附氧化

采用微电极循环伏安法和吸附转移溶出伏安法研究了单链多聚腺瞟吟核苷酸Poly(A)在金电极上的伏安行为.重点考察了Poly(A)的吸附和氧化过程.发现Poly(A)分子在金电极表面能够形成多种状态的特性吸附.影响吸附态和吸附强度的主要因素是吸附电势,吸附时间和溶液浓度.在负电位区,随着吸附时间(T_s)的变化,Poly(A)分子在金电极表面发生不同状态的以腺嘌呤碱基为吸附位点的强吸附,这种以腺嘌呤碱基吸附的Poly(A)分子能够在零伏附近给出很强的氧化电流峰和对应的还原峰.     

界面电场对血红蛋白在多孔金电极上的吸附和生物活性的影响(英文)

蛋白质的界面吸附及其生物活性因它在构建生物传感、生物电子器件和生物燃料电池等方面具有重要的作用而倍受关注.对此,界面电场是吸附的一个重要影响因素,它能明显地影响蛋白质分子在材料界面的吸附量、分子构象以及分子定向.本文应用电化学方法和红外光谱技术研究了血红蛋白在三维多孔金膜电极上的吸附动力学及其生物活性随界面电场的变化关系.结果表明,由界面电场产生的过量表面电荷可借助与蛋白质分子之间的静电作用加速蛋白质分子在电极表面的吸附,提高其吸附量;但是,过高的界面电场将破坏吸附蛋白质的构象以及降低它还原过氧化氢的催化活性;只有在零电荷电位下,吸附在电极表面的血红蛋白才能保持其天然的构象和生物催化活性.本研究将为生物传感器、生物电子器件和生物燃料电池的构建提供理论依据,加深对荷电生物界面上生物分子界面行为的认识.     

聚腺嘌呤核苷酸在金电极上的吸附氧化

采用微电极循环伏安法和吸附转移溶出伏安法研究了单链多聚腺嘌呤核苷酸Poly(A)在金电极上的伏安行为。重点了考察了Poly(A)的吸附和氧化过程。发现Poly(A)分子在金电极表面能够形成多种状态的特性吸附。影响吸附态和吸附强度的主要因素是吸附电势, 吸附时间和溶液浓度。在负电位区, 随着吸附时间(t~s)的变化, Poly(A)分子在金电极表面发生不同状态的以腺嘌呤碱基为吸附位点的强吸附, 这种以腺嘌呤碱基吸附的Poly(A)分子能够在零伏附近给出很强的氧化电流峰和对应的还原峰。     

电化学原位表面增强拉曼光谱研究Au@Pd纳米粒子薄膜电极上吸附 CO的斯塔克效应

电化学 Stark效应是指电极溶液界面的吸附物或金属-吸附物之间的化学键的振动频率随电极电势而发生变化的现象.研究该效应,可以更好地理解吸附物与基底的相互作用(如吸附构型、吸附取向和覆盖度等随电位的变化),也可反过来推断电极基底的电子构型及其随电势的变化规律,对理解电化学双电层的结构以及电催化反应的构效关系都很有帮助.多年以来,电极表面吸附 CO的电化学 Stark效应广受关注,是由于 CO为很多小分子氧化的中间产物,研究 CO的谱学行为,可加深对 CO以及其它能产生 CO中间物有机小分子的电催化氧化机理和动力学的理解;另一方面, CO与过渡金属之间普遍存在s给电子以及p反馈电子作用,因此 CO也可作为探针分子,通过考察 COad以及 M–COad的振动频率的变化,可推断相应条件下基底的电子与几何结构等信息.
　　本文使用电化学原位表面增强拉曼技术,在一个大的电势范围内考察了 Au@Pd纳米粒子薄膜电极上饱和吸附 CO的振动光谱行为,以期更好地理解 COad与基底的成键作用与电极电势之间的关系.由于纯 Pd电极表面的拉曼信号太弱,实验使用具有核壳结构的 Au@Pd纳米粒子薄膜作为模型电极,并利用 Au核的拉曼增强特性.宽广的电势范围约–1.5到0.55V vs. NHE,通过使用酸性、中性以及碱性电解质得以实现.实验考察的电势上限由 COad氧化起始电位决定,而下限由强烈氢析干扰测量所限制.结果表明,在检测的电势范围内, C–OM(M指在电极表面的桥式吸附CO和穴位吸附 CO所形成的谱带重叠)和 Pd–COM键的振动频率可以分为三段： dνC–OM/dE在–1.5~–1.2 V范围内是185~207 cm–1/V,在–1.2~–0.15 V是83~84 cm–1/V,在–0.2~0.55 V是43 cm–1/V;而 dνPd–COM/dE在–1.5~–1.2 V范围内是–10~–8 cm–1/V,在–1.2~–0.15 V是–31~–30 cm–1/V,在–0.2~0.55 V是–15 cm–1/V.与同时记录的极化曲线对比,认为在中性和碱性介质中所观察到 dνC–OM/dE在–1.2 V附近的急剧变化与电极表面发生了强烈的析氢反应有关.另外,结合密度泛函理论模型计算,认为共吸附的 H减少了 COad从桥式构型到穴位构型的转变,在酸性介质中这种变化不明显,可能是由于对应的电势较高,桥式吸附的 CO比例越大,桥式向穴位的转变本身相对较少.     

电化学原位表面增强拉曼光谱研究Au@Pd纳米粒子薄膜电极上吸附CO的斯塔克效应（英文）

电化学Stark效应是指电极溶液界面的吸附物或金属-吸附物之间的化学键的振动频率随电极电势而发生变化的现象.研究该效应,可以更好地理解吸附物与基底的相互作用(如吸附构型、吸附取向和覆盖度等随电位的变化),也可反过来推断电极基底的电子构型及其随电势的变化规律,对理解电化学双电层的结构以及电催化反应的构效关系都很有帮助.多年以来,电极表面吸附CO的电化学Stark效应广受关注,是由于CO为很多小分子氧化的中间产物,研究CO的谱学行为,可加深对CO以及其它能产生CO中间物有机小分子的电催化氧化机理和动力学的理解;另一方面,CO与过渡金属之间普遍存在σ给电子以及π反馈电子作用,因此CO也可作为探针分子,通过考察CO_(ad)以及M–CO_(ad)的振动频率的变化,可推断相应条件下基底的电子与几何结构等信息.本文使用电化学原位表面增强拉曼技术,在一个大的电势范围内考察了Au@Pd纳米粒子薄膜电极上饱和吸附CO的振动光谱行为,以期更好地理解CO_(ad)与基底的成键作用与电极电势之间的关系.由于纯Pd电极表面的拉曼信号太弱,实验使用具有核壳结构的Au@Pd纳米粒子薄膜作为模型电极,并利用Au核的拉曼增强特性.宽广的电势范围约–1.5到0.55V vs.NHE,通过使用酸性、中性以及碱性电解质得以实现.实验考察的电势上限由COad氧化起始电位决定,而下限由强烈氢析干扰测量所限制.结果表明,在检测的电势范围内,C–OM(M指在电极表面的桥式吸附CO和穴位吸附CO所形成的谱带重叠)和Pd–COM键的振动频率可以分为三段:dνC–O_M/d E在–1.5~–1.2 V范围内是185～207 cm~(–1)/V,在–1.2~–0.15 V是83～84 cm~(–1)/V,在–0.2～0.55 V是43 cm~(–1)/V;而dν_(Pd–COM)/d E在–1.5~1.2 V范围内是–10～–8 cm~(–1)/V,在–1.2~–0.15 V是–31~–30 cm~(–1)/V,在–0.2～0.55 V是–15 cm~(–1)/V.与同时记录的极化曲线对比,认为在中性和碱性介质中所观察到dν_(C–OM)/d E在–1.2 V附近的急剧变化与电极表面发生了强烈的析氢反应有关.另外,结合密度泛函理论模型计算,认为共吸附的H减少了CO_(ad)从桥式构型到穴位构型的转变,在酸性介质中这种变化不明显,可能是由于对应的电势较高,桥式吸附的CO比例越大,桥式向穴位的转变本身相对较少.     

含水离子液体/金属界面结构的SERS研究

利用表面增强拉曼光谱(SERS)研究了不同含水量下离子液体及水分子在银电极上随电位变化吸附方式的改变,通过水的O-H伸缩振动谱峰频率变化特征,详细探究了水在离子液体/电极界面上的存在形式及作用方式以及体系零电荷电位与水含量的关系.水含量较低时O-H伸缩振动的Stark系数值较低,随水含量的增加O-H伸缩振动的谱峰位置逐渐向高波数方向移动,同时O-H伸缩振动的Stark系数也逐渐增大,1molL-1[BMIM]Br水溶液中达到76cm-1V-1,且体系的零电荷电位正移,这些差异与水在离子液体中所形成氢键的程度及水分子的存在形式密切相关,在水的含量较低时水与离子液体阳离子通过氢键作用而存在于界面层中,当水的含量增加时,水分子间氢键的作用增强,水与电极表面直接作用的可能性增大.     

乙腈溶液中银电极的表面增强拉曼光谱研究

利用共焦显微拉曼系统研究了非水体系0.1mol·L^-1LiClO4/CH3CN溶液中,乙腈分子在粗糙银和金电极表面的吸附和解离行为。结果表明非水体系中乙腈可在银、金表面发生还原反应,产物CN^-离子与电极表面作用形成的表面配合物可以较宽的电位区间吸附于电极表面。溶液中的微量水、激光照射以及电极电位均对该反应有较大的影响。通过拉曼谱图的比较,得出乙腈分子解离出的CN^-在金电极表面比在银电极表面有更强的吸附作用。     

胞嘧啶吸附在粗糙金电极上的表面增强拉曼光谱

应用电化学伏安法和表面增强拉曼光谱(SERS)研究在-1.0 V~0 V电位区间内胞嘧啶于粗糙金电极表面的吸附行为.结果表明,在本实验的电位区间,胞嘧啶是以其N3位垂直吸附在粗糙金电极表面的.在负电位区间环呼吸振动模的强度出现极大值,与其它振动模强度相比,作者认为电磁场的增强和电荷转移均使该谱峰的拉曼信号增强.胞嘧啶的环呼吸振动频率随着电位负移而红移,这意味着它与金电极的成键作用减弱.同时也表明SERS谱可用于研究生物分子在金属电极表面的吸附行为.     

氧在CuCl(111)表面吸附的密度泛函理论研究

运用广义梯度密度泛函理论的PW91方法结合周期平板模型,在DNP基组下研究了氧分子和氧原子在CuCl(111)表面上的吸附.对氧分子在CuCl(111)表面吸附的相关计算和比较发现,覆盖度为0.25单层时的吸附构型为稳定的吸附构型,氧分子倾斜地吸附在CuCl(111)表面的顶位时比较稳定,吸附后O2分子的伸缩振动频率与自由O2分子相比发生了红移.态密度和Mulliken电荷布居分析结果表明,整个吸附体系发生了由Cu原子向O2分子的电荷转移.氧原子在CuCl(111)表面吸附的计算结果表明,氧原子倾向于以穴位(hollow)吸附在CuCl(111)表面,通过Mulliken电荷布居和态密度分析对氧原子在CuCl表面的吸附行为作了进一步探讨.     

Potential-dependent vibrational spectroscopy of solvent molecules at the Pt(111) electrode in a water/acetonitrile mixture studied by sum frequency generation

Sum frequency generation (SFG) vibrational spectra of D(2)O and/or acetonitrile (CH(3)CN) on a Pt(111) single-crystal electrode were obtained as a function of applied potential in a 5 mol % water/acetonitrile mixed solvent with different 0.1 molar MSO(3)CF(3) salts (M = H(+), Li(+), Na(+), K(+), and Cs(+)). The results provide a very specific model for the composition of the inner Helmholtz layer as a function of potential and surface charge. Acetonitrile dominates the inner layer with the CN group directed toward the metal at potentials where the metal has a positive charge. As the surface becomes negatively charged, the acetonitrile orientation flips 180 degrees, with the CH(3) group pointing toward the surface. At even more negative surface charge, D(2)O displaces acetonitrile from the inner layer and is the predominant molecule on the surface. Here water is present as an oriented molecule with the oxygen end pointing toward the metal. The potential (and surface charge) where water is the dominant molecule in the inner Helmholtz layer is determined by the solvation energy of the cation.     

DFT and experimental examination of the oxidation/reduction of a thiol-substituted carotenoid with gold versus glassy carbon electrodes

The oxidation/reduction properties of the thiol-substituted carotenoid, 7'-apo-7'-(4-mercaptomethylphenyl)-beta-carotene (AMC), on gold and glassy carbon electrodes were investigated. Similarities of the first and second oxidation potentials of AMC when the glassy carbon electrode is used are attributed to stabilization of the dication in the presence of CH(2)Cl(2). This does not occur for AMC tethered to gold, where the second oxidation potential is higher than the first by 145 mV. Self-assembled monolayers between AMC and the gold electrode causes the first oxidation potential to be lower by 90 mV than that on glassy carbon electrode. These phenomena are examined with density functional theory (DFT) calculations, which show that the ionization potential for the AMC-transition metal complex is lower than that of AMC. DFT calculations also show that the LUMO of the carotenoid-transition metal complex is independent of the chain length of the carotenoid but is related to the transition metal. Upon reduction at -1.185 V versus SCE the C-S bond of self-assembled AMC is cleaved.     

Probing electric fields at the ionic liquid-electrode interface using sum frequency generation spectroscopy and electrochemistry

The arrangement of ions at the platinum electrode in the room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate has been determined using sum frequency generation vibrational spectroscopy (SFG), electrochemical impedance spectroscopy (EIS), and the vibrational Stark effect. The results indicate that CO adsorbed on the Pt electrode has a Stark shift of 30-35 cm(-1)/V in the ionic liquid. The potential of zero charge (PZC) of the ionic liquid-Pt system is approximately -500 mV (vs Ag wire), with a capacitance of 0.12 F/m2. Further, polarization-dependent SFG experiments suggest the ions reorganize at the surface depending on the electrode charge. In combination, all these results indicate that the ions of a neat ionic liquid are organized in a Helmholtz layer at the electrified metal electrode interface.     

Preparation and electrochemistry of azobenzene self-assembled monolayers on gold--long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.     

Electrochemical behavior of dopamine and ascorbic acid at osmium(II) complex cationic monolayer modified gold electrodes.

The electrooxidation of dopamine (DA) and ascorbic acid (AA) was studied using gold electrodes modified by a cationic self-assembled monolayer of [Os(bpy)2(bpy-(CH2),3SH)]2+ by cyclic voltammetry. At an [Os(bpy)2(bpy-(CH2)13SH)]2+/Au electrode, the oxidation peak of DA shifted to a much more positive potential as compared with that of a bare gold electrode, while the oxidation peak potential of AA showed a slightly negative shift due to their different electrostatic interactions with the cationic monolayer. Thus, a sufficient potential difference was achieved for distinguishing the electrochemical responses of DA and AA. However, when CH3(CH2)11SH was mixed into the cationic monolayer, the enhanced packing of the mixed monolayer blocked the access of DA or AA to the electrode, resulting in further positive shifts for both oxidation-peak potentials.     

Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer of a triruthenium cluster studied by in situ infrared spectroscopy

Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer (SAM) of an oxo-centered triruthenium cluster [Ru(3)(mu3-O)(mu-CH3COO)6(CO)(L1)(L2)] (L1 = [(NC5H4)CH2NHC(O)(CH2)10S-]2, L2 = 4-methylpyridine) have been extensively investigated on the surface of a gold electrode in aqueous and nonaqueous solutions. The SAM exhibits three consecutive one-electron transfers and four oxidation states, which have been characterized by electrochemistry, in situ infrared spectroscopy, and in situ sum frequency generation (SFG) vibrational spectroscopy measurements. The original electron-localized state of the Ru cluster center was changed to electron delocalization states by oxidation or reduction of the central Ru ions. These changes are revealed by the IR absorptions of the CO ligand and the bridging acetate ligands of the triruthenium cluster in the SAM. The IR absorptions of the two kinds of ligands are strongly dependent on the oxidation state of the Ru cluster center. One-electron oxidation of the central Ru ion in the SAM triggers a CO ligand liberation process. Solvent molecules may then occupy the CO site to result in a CO-free SAM. One-electron reduction of this CO-free SAM in a CO-saturated solution leads to re-coordination of the CO ligand into the SAM. Both processes can be precisely controlled by tuning the electrode potential. The kinetics of the CO exchange cycle in the SAM, including liberation and coordination, has been investigated by in situ IR and SFG measurements for the first time. The CO exchange cycle is significantly dependent on the temperature. The reaction rate greatly decreases with decreasing solution temperature, which is an important factor in the CO ligand exchange process. The activation energies of both CO liberation and coordination have been evaluated from the reaction rate constants obtained at various temperatures.     

Preparation of alkanethiol monolayers on mild steel surfaces studied with sum frequency generation and electrochemistry

An n-alkanethiol, octadecanethiol (ODT), monolayer was successfully prepared onto an oxide-free mild steel (MS) surface under cathodic polarization in a 0.1 M LiCl/CH(3)OH solution containing 1 mM ODT. Cyclic voltammetry (CV) and electrochemical impedance (EIS) and sum frequency generation (SFG) spectroscopy were applied to study and characterize the adsorption of ODT at a MS surface. In 0.1 M LiCl/CH(3)OH solution containing 1 mM ODT, CV of the MS electrode shows a dramatic decrease in charging current and a positive shift in oxidation potential when compared to a solution without ODT. The interfacial capacitance was obtained as 2.52 microF/cm(2) from the impedance data. An average chain tilt angle of 48 degrees for the ODT molecules was deduced from the comparison of the interfacial capacitances of the ODT/MS and ODT/Au monolayers. X-ray photoelectron spectroscopy confirmed the formation of the ODT monolayer on mild steel. The ppp SFG spectrum of the ODT-modified MS features three strong methyl vibrational modes at 2877, 2943, and 2967 cm(-1), indicating the formation of the oriented and densely packed ODT monolayer. However, the appearance of the two weak CH(2) groups' vibrational modes at 2850 and 2914 cm(-1) implies the presence of defects in the ODT monolayer. ODT/Au films were prepared to compare with the ODT/MS films. Orientation analysis of the air/solid interface suggests that the methyl group of ODT/Au films has a tilt angle of 30 degrees , while the methyl group of ODT/MS films has a tilt angle of 23 degrees . Water was found to have an impact on the shape of the SFG spectra of ODT/MS. This suggests that the solution penetrated through the defects to reach the MS surface.     

团聚铂纳米粒子电极在甲醇氧化中的电催化特性

用H2还原法并以Nafion作为稳定剂合成团聚的Pt纳米粒子，附载于玻碳表面制备电催化剂.透射电子显微镜（TEM）和扫描电子显微镜（SEM）表征结果指出,团聚Pt纳米粒子的平均尺寸约为400 nm.运用电化学循环伏安法(CV)和原位傅立叶变换红外反射光谱（in situ FTIRS）研究甲醇的氧化过程，发现团聚Pt纳米粒子电极具有较高的电催化活性.原位FTIRS研究结果检测到甲醇在所制备的电催化剂上氧化的中间体为线型吸附态CO物种，其红外吸收给出异常红外效应的光谱特征.     

Study of the effects of ion pairing and activity coefficients on the separation in standard potentials for two-step reduction of dinitroaromatics

The electrochemical reduction of 9,10-dinitroanthracene, 1, and 3,6-dinitrodurene, 2, occurs with potential inversion. That is, the standard potential for formation of the anion radical is shifted in the negative direction from the standard potential for the anion radical/dianion couple. This behavior has been attributed to significant structural changes accompanying the reduction steps. In this work, an assessment was made of the magnitude of the effects of activity coefficients and ion pairing, two effects which contribute to potential inversion. 1,4-Dinitrobenzene, 3, and 2,5-dimethyl-1,4-dinitrobenzene, 4, were studied in acetonitrile and N,N-dimethylformamide with R(4)N(+) salts as electrolytes (R = CH(3)-, CH(3)CH(2)-, CH(3)(CH(2))(3)-, and CH(3)(CH(2))(7)-) at concentrations from 0.010 to 0.100 M. Significant ion pairing between the dianion, A(2-), and R(4)N(+) was found for (CH(3))(4)N(+) with both 3 and 4 while the effects of the other electrolytes were smaller. The data were successfully interpreted without recourse to other ion pairs, e.g., ion pairing between the anion radical and the electrolyte cation. Ion pair formation constants are reported along with the infinite-dilution values of the difference in the two standard potentials. The effects of activity coefficients and ion pairing at 0.10 M electrolyte do not exceed 100 mV for (CH(3)N(+)) and are only 20 to 60 mV for (CH(3))(4)N(+), a cation commonly used in studies of potential inversion. It is concluded that structural changes accompanying the reduction, rather than activity and ion pairing effects, are the dominant factors underlying potential inversion.