Electrochemical Deposition of Gold Metal Particles into 3‐Dimensional Polypyrrole Film Deposited on a Highly Oriented Pyrolytic Graphite

Electrochemical techniques and lateral friction microscopy (LFM) are exploited to characterize the deposition of gold metal particles onto the 3‐dimensional (3‐D) polypyrrole (PPy) film deposited on 2‐dimensional (2‐D) highly oriented pyrolytic graphite (HOPG) substrate surface in an aqueous solution involving 0.01 M pyrrole and 0.1 M LiClO₄? 3H₂O. Cyclic voltammetry is utilized to find the gold deposition potential onto the PPy film from 0.001 M KAu(CN)₂/KOH solution. The gold deposition potential is found to be in the range of ?1.2 V to ?1.4 V. Chronoamperometry is used to find out the nucleation and growth mechanism of gold metal particles onto PPy film. When the PPy film is thin, the mechanism follows the 3‐D instantaneous and moved towards 3‐D progressive as the film thickness increases. Considering the high resistance of thick PPy film and insulating and compact nature of the film at more cathodic potentials, it is suggested that the gold nuclei are formed first on the HOPG substrate surface, move to the PPy film surface and then distributed inside the PPy matrix. Since the friction of gold and the PPy film is different, the LFM is found to be an effective tool to see the distribution of gold particles in the domain boundaries of the PPy film.     

高序石墨电极上单分散纳米铜粒子的电结

Mechanism of copper electrocrystallization on highly oriented pyrolytic graphite electrode from a solution of 1 mmol/L CuSO4 and 1.0 mol/L H2SO4 has been studied using cyclic voltammogram and chronoamperometry. The results show that in copper electrodeposition the charge-transfer step is fast and the rate of growth is controlled by the rate of mass transfer of copper ions to the growing centers. Reduction of Cu(Ⅱ) ions did not undergo underpotential deposition. The initial deposition kinetics of Cu electrocrystallization corresponds to a model including progressive nucleation and diffusion controlled growth. Copper nanocrystals with size of 75.6 nm and relative standard deviation of 9% can be obtained by modulation potential electrodeposition.     

吡嗪衍生物在石墨表面上的自组装单层膜结构

利用扫描隧道显微镜研究了荧光液晶分子2, 5-二-[2-(3, 4-二-十二烷氧基-苯基)-乙烯基]-3, 6-二甲基吡嗪(BPDP12)在石墨表面上自组装单层膜的结构. 实验结果表明, 该化合物在石墨表面形成两种自组装结构：一种是稳定的, 分子的共轭中心相互平行, 烷基链相互交错的密排结构；另一种是不稳定的, 分子的共轭中心彼此为烷基链所分隔的非密排结构. 分子之间较强的π-π作用和分子烷基链之间的范德华作用力对分子组装的取向形成竞争, 是产生两种不同组装结构的根本原因.     

Nucleation and growth mechanism for the electropolymerization of aniline in trifluoroacetic acid/lithium perchlorate/propylene carbonate medium

In the present work, the nucleation and growth mechanism for the electropolymerization of aniline in propylene carbonate medium containing 0.06 M trifluoroacetic acid and 0.05 M lithium perchlorate was investigated at different potentials on highly oriented pyrolytic graphite (HOPG) by potentiostatic current-time transients (i-t) and atomic force microscopic (AFM) measurements. The electrochemical data fitted with the theoretical curves for nucleation and growth suggest that the electropolymerization of aniline consists of progressive nucleation followed by 3D growth at an early stage and layer-by-layer growth in subsequent periods. The results obtained from transient analysis were in good agreement with the results of the AFM analysis. In our previous studies with aqueous solutions, we observed only progressive nucleation followed by a 3D growth mechanism for the electropolymerization of aniline in a higher potential range, 1.5–2.0 V vs. Ag/AgCl. Hence, the results obtained from the present work indicate that the nucleation and growth mechanism depends on the medium.     

酞菁氧钒分子及纳米簇在高定向石墨表面的自组装

报导了酞菁氧钒(VOPc)分子及其纳米簇在高定向石墨(HOPG)表面的自组装. 在室温下, 将HOPG浸入含有VOPc纳米簇(2-20 nm)和VOPc分子(约为10-3 g·L-1)的1,2-二氯乙烷胶体溶液中, VOPc分子在HOPG表面自组装形成单分子层(SAM), VOPc纳米簇在上述SAM表面进行尺寸选择性自组装. 组装于VOPc单分子层表面的纳米簇的粒径为(4.60±0.47) nm. 扫描隧道显微镜研究表明, 随着酞菁氧钒胶体溶液浓度由2.5×10^-2 g·L^-1增至2.5×10^-1 g·L^-1, 组装于SAM表面的VOPc纳米粒子的数量逐渐增多, 最终形成稠密的单层粒子组装体. 本文提供的自组装结构及方法在发展光电功能体系等方面具有潜在应用价值.     

聚合电流对锂/聚吡咯电池正极电化学行为的影响

在Pt微盘电极上用恒电流技术在电流密度为0.05-10 mA·cm-2范围合成了1 滋m厚度的聚吡咯(PPy)膜. 采用循环伏安(CV)、计时电势、交流阻抗(EIS)技术考察了不同聚合电流下得到的聚吡咯的电化学行为. 结果表明, 最佳聚合电流区间为1-5 mA·cm-2, 对应的电势一般在3.9-4.1V (vs Li/Li+)之间, PPy的掺杂度为30%左右. 在这一聚合电流密度范围得到的PPy具有较大的电化学容量, 较佳的电化学反应可逆性能、较高的氧化还原电势数值和稳定性能. 处于氧化态的聚吡咯具有优良的导电性. 上述条件下得到的PPy适合于作为锂离子二次电池的正极材料. 适当选择电流, 可以得到有相对完整的共轭仔键的长链结构的PPy 膜.     

Pt在多晶Au微盘电极上电沉积成核与晶体生长

于不同H2PtCl6浓度和超电势下,应用Fleischmann的电结晶成核及晶体生长模型和Barradas Bosco的电化学成相吸附成核模型,拟合多晶Au微盘电极( =30μm)上电沉积Pt的恒电势阶跃电流暂态曲线.得出:在稀H2PtCl6溶液中,上述沉积过程初期,发生H2PtCl6吸附并遵循二维瞬时成核与圆柱形生长模型.二维生长速率常数随超电势线性增加.跟随其后的是核的层状生长,其速率常数随超电势呈非线性变化.而在高浓H2PtCl溶液中,沉积机理转变为H2PtCl6的吸附、瞬时成核及三维正圆锥形的生长模式.其晶核的垂直生长速率常数kPERP比水平生长速率常数kPARA大两个数量级以上.况且,logkPERP随超电势线性增加,而logkPARA则随超电势呈反S形变化的关系.相同超电势下,无论kPERP还是kPARA,均比稀H2PtCl6溶液中的二维层状生长速率常数大几个数量级.     

电聚吡咯固定化酷氨酸酶电极的制备及性能

在应用恒电位法电化学聚合吡咯的同时 ,将酪氨酸酶固定在导电聚吡咯膜内 ,制成一种灵敏、稳定的酪氨酸电极 .讨论了溶液 pH值和聚合电位对酶固定化的影响 ,对酶分子嵌入吡咯膜前后的SEM图和CV曲线进行了分析、比较 .该电极对甲苯酚响应的线性范围为 5 .0× 10 -8～ 1.0× 10 -6mol/L ,最适 pH值为 6 .6 ,酶反应表观上遵循Michaelis_Menten动力学 ,表观米氏常数为 2 .2× 10 -5mol/L .     

电聚吡咯固定化酪氨酸酶电极的制备及性能

在应用恒电位法电化学聚合吡咯的同时 ,将酪氨酸酶固定在导电聚吡咯膜内 ,制成一种灵敏、稳定的酪氨酸电极 .讨论了溶液 pH值和聚合电位对酶固定化的影响 ,对酶分子嵌入吡咯膜前后的SEM图和CV曲线进行了分析、比较 .该电极对甲苯酚响应的线性范围为 5 .0× 10 -8～ 1.0× 10 -6mol/L ,最适 pH值为 6 .6 ,酶反应表观上遵循Michaelis_Menten动力学 ,表观米氏常数为 2 .2× 10 -5mol/L .     

Nucleation and Growth Mechanism of Electropolymerization of Methylene Blue: The Effect of Preparation Potential on Poly(methylene blue) Structure

Nucleation and growth mechanism of electropolymerization of methylene blue (MB) in a basic medium and the effect of preparation potential on poly(MB) film structure were investigated by using cyclic voltammetry, potentiostatic current‐time transient, scanning tunneling microscopy (STM), atomic force microscopy (AFM), and UV‐vis. absorption spectroscopy techniques. Electropolymerization of MB has been achieved by potentiodynamic (cyclic voltammetry) and potentiostatic (constant potential) techniques. The potentiostatic current‐time transients fitted with a theoretical model and morphological studies indicate that nucleation and growth mechanism of poly(MB) starts with a progressive layer‐by‐layer nucleation and growth besides random adsorption. Nucleation and growth of poly(MB) follows a process between progressive layer‐by‐layer and 3‐D instantaneous mechanism resulting in highly‐oriented poly(MB) nanofibers with increasing poly(MB) film thickness. Cyclic voltammetry and morphological studies exhibit that poly(MB) film structure changes depending on the preparation potential. Poly(MB) films prepared at the potential values of 900 and 950 mV show a well‐ordered, smooth surface but at the potential values higher than 1000 mV, rough polymer surface arises as overoxidation takes place. UV‐vis. absorption spectra of poly(MB) film and MB monomer show three peaks. The peak at 410 nm for poly(MB) shows 100 nm blue shift when compared to the MB monomer and is attributed to poly(MB) formation on the electrode.     

Development of a Controlled Release System for Risperidone Using Polypyrrole: Mechanistic Studies

Polypyrrole (PPY) film has been selected as a platform material for drug delivery due to its inherent conductivity, ease of preparation and apparent biocompatibility. PPY films were prepared containing the antipsychotic drug risperidone as a model compound. Drug release profiles could be altered by applying different electrical stimulation to these films. Atomic force microscopy was used to investigate changes in PPY film thickness when different stimuli were applied. The highest levels of drug release were observed when PPY was reduced; this was accompanied by expansion of the film. Technology such as this could be utilized for implantable drug delivery devices, where the dose could be adjusted by external signaling.     

On-Surface Photochemistry of Pre-Ordered 1-Methyl-2-phenyl-acetylenes: C-H Bond Activation and Intermolecular Coupling on Highly Oriented Pyrolytic Graphite

In this contribution we report on light-induced metal-free coupling of propynylbenzene molecular units on highly oriented pyrolytic graphite. The reaction occurs within the self-assembled monolayer and leads to the generation of covalently coupled 1,5-hexadiyne and para-terphenyl derivatives under topological control. Such photochemical uncatalysed pathway represents an original approach in the field of topological C−C coupling at the solid/liquid interface and provides new insight into the low temperature formation of aromatic compounds at the surface of carbonaceous supports.     

Early Stages of CeO2 Thin-film Nucleation and Growth with Photo Irradiation

In this paper, the early stages of nucleation and photoirradiation growth of CeO₂ thin films have been studied. Cyclic voltammetry, chronoamperometry and scanning electron microscopy were used to analyze the nucleation process of CeO₂ thin films deposited on the anode with photo irradiation. Experimental results show that the anodic deposition process with photo illumination is controlled by diffusion. Compared with the dark state, photo illumination mainly contributed to increase the current density of the three-dimensional nucleation process, because photo illumination is helpful to create active sites and accelerate the nucleation progress on the surface that a thin ceria film has been formed. Two-dimensional nucleation process mainly exists within the initial 2 s, and then only three-dimensional instantaneous nucleation process continues, which may be the main reason why the thickness of the CeO₂ film can continue to grow with photo illumination but not in the dark state. Increasing the deposition overpotential can promote two-dimensional nucleation and growth rate, whilst when the potential exceeds 0.65 V, three-dimensional current density decreases. The li-miting factor at that time may be the diffusion rate of cerium ions in the solution towards the electrode substrate.     

Characterization of the Reduction of Oxygen at Anthraquinone-Modified Glassy Carbon and Highly Oriented Pyrolytic Graphite Electrodes

1-(N-Boc-aminomethyl)-4-(aminomethyl)benzene, bearing a protected amine group, was electrochemically grafted to glassy carbon and edge plane and basal plane highly oriented pyrolytic graphite electrodes by the oxidation of the corresponding linker. Following the removal of tert-butyloxycarbonyl protecting group, anthraquinone-2-carboxylic acid was coupled to the amine-terminated linker using solid-phase synthesis. The surface coverage of the immobilized anthraquinone redox centers was investigated by cyclic voltammetry and found to be the highest at edge plane and the lowest at the basal plane electrodes. The electrocatalytic activity of the anthraquinone-modified electrodes toward oxygen reduction was explored by cyclic voltammetry, chronoamperometry, and chronocoulometry at the unmodified and modified graphite electrodes. The immobilized anthraquinone was shown to catalyze the reduction of oxygen to hydrogen peroxide and the number of electrons transferred was two for all modified electrodes.     

Anodic Stripping Voltammetry: An AFM Study of Some Problems and Limitations

The use of anodic stripping voltammetry for quantitative analytical measurements using solid electrodes is addressed in the light of generic limitations arising from i) electrode heterogeneity, ii) electrode morphology, iii) inhibited electrodeposition, and iv) incomplete stripping of deposited metal in the anodic sweep. It is shown, using direct imaging of electrode surfaces via AFM and optical microscopy, that each of the preceding factors may produce significant deviations from ideal electrode behavior. The use of atomic force microscopy to fully characterize any developed ASV procedures is strongly recommended. To ensure reproducible and accurate stripping voltammetry, steps should be taken to minimize the effects discussed.     

Patterned Monolayers of Neutral and Charged Functionalized Manganese Arene Complexes on a Highly Ordered Pyrolytic Graphite Surface

Complex patterns : The arene manganese tricarbonyl complexes [Mn(η⁵‐2,5‐didodecoxy‐1,4‐semiquinone)(CO)₃] and [Mn(η⁶‐1,4‐dioctyloxybenzene)(CO)₃] BF₄ form patterned monolayers on the surface of highly ordered pyrolytic graphite (HOPG), as a result of hydrogen‐bonding, hydrophobic, and electrostatic interactions, leading to an ordered 2D array of manganese atoms or ions.

     

Nanoscale degradation of polypyrrole films under oxidative stress: An atomic force microscopy study and review

Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) films grown on vitreous carbon substrates during the catalytic reduction of Cr(VI) to Cr(III). The morphology of freshly-prepared films depends on substrate characteristics. Upon reaction, uniform nodules of aggregated PPy clusters appear. No significant differences in surface morphology are found between its oxidized and reduced forms. Loss of catalytic activity after 8-9 oxidation/reduction cycles of exposure to the chromate solution (oxidation) and electrochemical recharging of the film at negative potentials (reduction) correlates well with the observed polymer film dissolution/detachment from the carbon substrate. Formation of well-defined circular features (PPy rings) at different stages leads to a model for the film degradation process that includes formation of Cl₂ gas inside the polymer matrix. In the final stages, the bulk of the film typically fractures and detaches from the electrode. A catalytically inactive, ultrathin PPy layer remains on the substrate even after prolonged exposure to the target solution. A review of techniques for the study of PPy aging/degradation is given.     

聚合溶液pH值对染料敏化太阳电池中聚吡咯对电极结构和性能的影响

电化学合成聚吡咯（PPy）时,聚合电解液的pH 值对PPy 薄膜的形貌和性质有较大的影响,进而影响PPy薄膜对I^-/I₃^-的电催化活性以及基于PPy对电极（CE）的染料敏化太阳电池（DSSCs）的光电转换性能. 本文采用电化学恒电位方法,在掺杂氟的SnO₂（FTO）导电玻璃上合成出了对甲苯磺酸根离子掺杂的聚吡咯（PPy-TsO）电极,并将其作为DSSCs 的对电极. 通过改变吡咯聚合时聚合电解液的pH值,借助扫描电镜（SEM）、紫外-可见（UV-Vis）吸收光谱、X-射线光电子能谱（XPS）和循环伏安（CV）等表征技术,详细探讨了聚合溶液pH值对PPy CE形貌、结构及其对I^-/I₃^-的电催化性能的影响. 研究发现在pH 2.0下合成的聚吡咯对阴离子掺杂率最高且链共轭性最佳,具有对I^-/I₃^-氧化还原介质最强的催化能力,基于此PPy CE的电池光电转化效率也最高.pH 值太大或太小都不利于生成具有高掺杂率和高催化活性的PPy电极,组装成DSSCs后的光电转换效率也较低.     

聚合溶液pH值对染料敏化太阳电池中聚吡咯对电极结构和性能的影响

电化学合成聚吡咯(PPy)时,聚合电解液的pH值对PPy薄膜的形貌和性质有较大的影响,进而影响PPy薄膜对I-/I3-的电催化活性以及基于PPy对电极(CE)的染料敏化太阳电池(DSSCs)的光电转换性能.本文采用电化学恒电位方法,在掺杂氟的SnO2(FTO)导电玻璃上合成出了对甲苯磺酸根离子掺杂的聚吡咯(PPyTsO)电极,并将其作为DSSCs的对电极.通过改变吡咯聚合时聚合电解液的pH值,借助扫描电镜(SEM)、紫外-可见(UV-Vis)吸收光谱、X-射线光电子能谱(XPS)和循环伏安(CV)等表征技术,详细探讨了聚合溶液pH值对PPy CE形貌、结构及其对I-/I3-的电催化性能的影响.研究发现在pH 2.0下合成的聚吡咯对阴离子掺杂率最高且链共轭性最佳,具有对I-/I3-氧化还原介质最强的催化能力,基于此PPy CE的电池光电转化效率也最高.pH值太大或太小都不利于生成具有高掺杂率和高催化活性的PPy电极,组装成DSSCs后的光电转换效率也较低.     

温度对PbO2电沉积形核生长过程的影响研究

为了探讨温度对PbO₂电沉积形核生长过程的影响,在25℃、35℃、45℃、55℃、65℃使用电化学工作站测试了PbO₂在玻碳电极上沉积过程的循环伏安曲线、计时电位曲线及计时电流曲线,并对不同温度下电沉积的PbO₂镀层进行了SEM和XRD分析. 结果表明,在不同温度下PbO₂都经历了成核和核生长过程. 温度的升高没有改变PbO₂电沉积三维连续成核的模式,降低了沉积过程溶液阻力,对成核和晶体生长速率均有促进作用,在晶核密度达到饱和晶核密度以前,是以促进成核速率为主,减小PbO₂颗粒尺寸. 达到饱和晶核密度后,电沉积后期以促进晶体生长速率为主,不利于形成细小PbO₂颗粒.高温使得析氧速率提高,能耗增大.由实验结果得出,在55℃时得到的PbO₂镀层粒径最小.