Nucleation and growth mechanism for the electropolymerization of aniline on highly oriented pyrolytic graphite at higher potentials

In this work, the nucleation and growth mechanism for the electropolymerization of aniline was investigated at higher potentials on highly oriented pyrolytic graphite by potentiostatic current-time transient and atomic force microscopic (AFM) measurements. The electrochemical data fitted to the theoretical curves for the nucleation and growth suggest that electropolymerization of aniline follows the three-dimensional growth and progressive nucleation mechanism. These results were also compared with the results obtained at lower potentials. The results obtained from transient analysis, at higher potentials, were in good agreement with the results of AFM images. Electronic Publication     

Evaluation of Structure,Nucleation and Growth Mechanism of Electropolymerized Polypyrrole on Highly Oriented Pyrolytic Graphite Electrode

Chronoamperometry (i–t) and atomic force microscopy (AFM) were used to study the nucleation and growth mechanism of electropolymerized polypyrrole formed on highly oriented pyrolytic graphite (HOPG) substrate surface. From i–t measurements it was found that the nucleation and growth mechanism was a 3‐D progressive after nuclei overlapping. However, before nuclei overlapping, it was not clear whether the mechanism was 2‐D instantaneous or 3‐D progressive. This ambiguity in the nucleation and growth mechanism was confirmed as 3‐D progressive from the results of AFM measurements. In addition to nucleation and growth mechanism, possible models were proposed for different structures observed on the AFM image of polypyrrole, obtained from very early stages of polymerization.     

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.     

In situ AFM study of electrochemical synthesis of polypyrrole/Au nanocomposite

In this work, in situ AFM measurements with simultaneously electrochemical characterization were developed to study the mechanisms of both polypyrrole (PPy) and PPy/Au composite deposition. The nanoscale information derived from the in situ AFM images associated with theoretical simulation from the measured current–time transient (i–t) reveals that Au nanoparticles with negatively charged carboxylic groups can be the nuclei by both adsorption on the electrode surface and doping on PPy for the polymerization, and thus has faster nucleation and growth rate than Py alone at the early polymerization stage. The PPy/Au deposition shows parallel nucleation processes of Au nanoparticle and Py, and an instantaneous 3D nucleation mode. The work not only provides fundamental insights for PPy/Au nanocomposite deposition process, but also optimization approaches to fabricate a superior PPy/Au film with favorable features for greater potential applications.     

n-Alkanoic acid monolayers on 316L stainless steel promote the adhesion of electropolymerized polypyrrole films

The formation of a self-assembled monolayer significantly promotes the adhesion of electrodeposited polypyrrole on stainless steel. The monolayer affects the nucleation and growth mechanism of polypyrrole as a result of its hydrophobic nature. This was confirmed by analyzing current-time transients of the initial stages of electropolymerization and was in agreement with AFM images.     

表面活性剂对苯胺电聚合的影响

利用胶束在电极一有面的定向及增溶作用研究了表面活性剂对苯胺电聚合的影响，结果表明：在阴离子表面活性剂十二烷基硫酸钠（ＳＤＳ）胶束体系中，胶束介质能催化苯胺的电聚合反应，使其氧化电位负移，减少膜的降解，提高膜的稳定性，同时，也使得聚合速率增大，在０．１ｍｏｌ／Ｌ的ＳＤＳ的胶束溶液中，其聚合效率提高到不含ＳＤＳ的纯体系的２５倍，在含有１０＾－４ｍｏｌ／ＬＳＤＳ的硫酸溶液中，聚苯胺（ＰＡＮ）的成核生长为     

Electrocrystallization of palladium from Pd(NH3)4Cl2 bath on stainless steel 316L

Electrochemical deposition of palladium from 0.04 M Pd(NH₃)₄Cl₂, NH₄Cl, and NH₄OH bath (pH = 10) on stainless steel electrode was studied by voltammetry, chronopotentiometry, and chronoamperometry. Crossovers in cyclic voltammograms demonstrate that the deposition of palladium proceed via a nucleation/growth mechanism. Chronopotentiograms indicate that palladium reduction is not controlled by diffusion and Sand’s law is not obeyed. In the early stage of the deposition, two-dimensional (2D) nucleation and growth proceeding through instantaneous and a multitude of progressive steps followed the initial double layer charging. The processes are manifested as broad maxima in chronoamperogram and after which the current transient terminates to a plateau. Non-linear fitting methods were applied to obtain the kinetic parameters in the light of Bewick, Fleischmann, and Thirsk theory for 2D and Armstrong, Fleischmann, and Thirsk model for 3D nucleation and growth process.     

Immobilization of phthalocyanines in conducting polymers. Polyaniline-copper tetrasulfophthalocyanine

Interaction between the anilinium cation and copper tetrasulfophthalocyanine anion (CuTSPc) was studied in an aqueous sulfuric acid solution using electronic absorption spectra. It was shown that up to 0.15 M aniline could be introduced into the solution at the dye concentration of 10⁻³ M, after which a solid deposit of a complex (salt) between the anilinium cation and copper tetrasulfophthalocyanine anion started precipitating rapidly. The effect of the dye on the kinetics of aniline polymerization on conducting glasses and on the properties of the polymer obtained was studied. It was found that phthalocyanine accelerates electropolymerization of aniline and is immobilized within the polymer matrix. It was shown that the self-catalytic synthesis mechanism characteristic of polyaniline is also preserved in the case of the composite of polyaniline-copper tetrasulfophthalocyanine.     

Early stages of mercury electrodeposition on HOPG

The electrodeposition of mercury on highly oriented pyrolytic graphite (HOPG) from nitrate solution was studied using cyclic voltammetry, potentiostatic current transients, and in situ scanning tunneling microscopy (STM), in order to correlate the results of the kinetic nucleation with the deposit morphology. At relatively low overpotentials, the mercury deposition can be described by a model involving progressive nucleation on active sites and diffusion-controlled 3D growth without overlapping of diffusion zones. The deposition was initiated on step edges and surface defects forming 3D islands following the Volmer–Weber mechanism. The small number of atoms in the critical nucleus (n_k=1), together with the linear log J vs. η dependence, indicated that the nucleation process can be described by the atomistic model.     

Electrochemical functionalization of single walled carbon nanotubes with polyaniline in ionic liquids

Single walled carbon nanotubes (SWNTs) are covalently functionalized during the electropolymerization of aniline in ionic liquids. In our experiment, 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIPF₆) containing 1 M trifluoroacetic acid (CF₃COOH) was selected as the ionic liquid media to separate SWNTs and to perform the electropolymerization of aniline within. The morphology of the resulting composite material of SWNT and polyaniline (PANI) was studied by scanning electron microscopy (SEM). Covalent bonding was evidenced by the increase of intensity ratio of the D band vs. G band in the Raman spectrum, whilst SWNTs may also be incorporated as big dopant anions to the PANI backbone. This paper provides a novel method by which large amount of SWNTs (15 mg/ml) can be modified by aniline electrochemically. p-type conducting polymer and n-type SWNTs can be thus copolymerized and applied to organic photovoltaics.     

Gelatin/poly(aniline) composite films: Synthesis and characterization

In this work, glyoxal (Glox) - crosslinked gelatin (Gel) films have been loaded with aniline molecules, followed by their in-situ oxidative polymerization to yield Gel/poly(Ani) composite films. The films, so prepared, have been characterized by FTIR, XRD, TGA and AFM analysis. The water absorption of these films has been studied in the physiological fluid of pH 7.4 at 37°C.The dynamic water uptake data has been interpreted by various kinetic models such as power function model and Schott kinetic model. The various diffusion coefficients have also been evaluated.     

Electrosynthesis of Cu-Se films on copper electrodes in alkaline media: a voltammetric, electrochemical quartz crystal microbalance and I/t transient study

The electroformation of Cu-Se phases, obtained by selenizing a thin film of copper deposited on the quartz/gold electrode system, was studied with an electrochemical quartz crystal microbalance (EQCM) and by cyclic voltammetry (CV) in an alkaline solution (0.05 M Na(2)B(4)O(7)) containing selenide ion. Potentiodynamic parameters showed that the formation of the initial Cu-Se phases (Cu(2-x)Se/Cu(3)Se(2)) is ruled by an irreversible diffusion controlled mechanism, where a first electron transfer is the rate-determining step. A CV study was also performed with a bulk copper electrode in 1 M NaOH solution containing selenide ion. The deconvolution of the anodic and cathodic I/E profiles corresponding to the electroformation and electroreduction of the Cu-Se film formed allowed us to establish that, depending on the anodic potential limit of the potentiodynamic scan, the Cu-Se phases formed were either a mixture of Cu(2)(-x)Se/Cu(3)Se(2) or Cu(2-x)Se/Cu(3)Se(2)/CuSe. An EQCM study showed that, during the initial stage of Cu-Se phase electroformation, water molecules were released from the electrode. In advanced stages of the process, when the electrode was completely covered by Cu-Se compounds, selenide anions were adsorbed on the formed phase. When the anodic potential limit was extended to -0.2 V, copper oxide compounds were formed. The analysis of the cathodic charge related to Cu-Se phase electroreduction and Energy Dispersive X-ray Spectroscopy (EDXS) analysis confirmed that when the anodic limit was -0.8 V, a mixture of different Cu-Se phases was formed. A I/t transient study performed with a bulk copper electrode in alkaline solution containing selenide established that the nucleation and growth mechanism (NGM) of the Cu-Se phases takes place through an initial bidimensional-instantaneous nucleation (IN2D), followed by four bidimensional-progressive nucleations (PN2D). These results and atomic force microscopy (AFM) experiences supported that the growth of the Cu-Se films occurs through a layer-by-layer mechanism.     

Modeling the Characteristics of a Polyaniline–DNA Film from the Voltammetric Response of the Product of Electropolymerization

Russian Journal of Electrochemistry - The article studies the anodic voltammetric response of polyaniline obtained by electropolymerization of aniline from a 3.7 M sulfuric acid solution in the...     

Electrodeposition of Lead at Boron‐Doped Diamond Film Electrodes: Effect of Temperature

The electrodeposition of lead on boron‐doped diamond has been studied with a view to identifying the fundamental parameters controlling the sensitivity and lower detection limit in anodic stripping voltammetry. Chronoamperometric transients are used to explore the deposition, indicating a progressive growth mechanism confirmed by ex situ AFM images. Linear sweep ASV experiments show a threshold concentration of ca 10^?6 M below which no lead is detected; this is attributed to the need for nucleation of the solid phase on the electrode. Experiments with variable temperature show that this threshold can be usefully lowered at elevated temperatures.     

Polyaniline micro-/nanostructures: morphology control and formation mechanism exploration

This article provides a brief overview of recent work by the authors’ group as well as related researches reported by others on controlling the morphology and exploring the formation mechanism of typical micro-/nanostructures of polyaniline (PANI) and aniline oligomers through template-free aniline chemical oxidation process. The contents are organised as follows: (i) tuning the morphology of aniline polymerisation products by employing ultrasonic irradiation, mass transfer, and pH profiles; (ii) exploring the formation mechanism of micro-/nanostructures during aniline chemical oxidation through examining the precipitation behaviours of aniline oligomers and polymers in a post-synthetic system; (iii) tailoring PANI micro-/nanostuctures into pre-designed morphology by introducing certain heterogeneous nucleation centres; (iv) application potential of PANI nanofibres in the areas of transparent conductive film, electromagnetic interference-shielding coating and graphene-based electrode materials. This short review concludes with our perspectives on the challenges faced in gaining the exact formation mechanism of PANI micro-/nanostructures and the future research possibility for morphologically precisely controlled PANI micro-/nanostructures.     

聚苯胺/二氧化钛纳米管固相微萃取纤维的组装及应用

以钛丝表面原位阳极氧化生成的二氧化钛纳米管为基体,通过电聚合苯胺组装得到新型聚苯胺包覆二氧化钛复合纳米管阵列固相微萃取纤维。实验讨论了无机酸介质、苯胺浓度和氧化电压对电聚合苯胺的影响,经过对纤维表面形貌和元素成分的分析,得到最佳的纤维涂层条件：电解液组成为1 mol/L的H₂SO₄-0.5 mol/L的苯胺,聚合电压10 V,氧化时间60 min。采用所制备的纤维与高效液相色谱联用萃取水样中的紫外线吸收剂并优化萃取条件,固相微萃取条件如下：萃取时间40 min,解吸时间4 min,萃取温度40℃,搅拌速率600 r/min,样品溶液中不加NaCl。同时对环境水样中的目标物分析测定,并做加标试验,目标分析物的平均回收率为78.2%~118%,相对标准偏差为4.4%~8.9%。该方法简便、灵敏、准确,适用于环境水样中紫外线吸收剂的快速测定。     

锌在玻璃碳上的电化学成核机理

线性扫描伏安法和电位阶跃法被用来研究氯化钾镀锌溶液中锌在玻璃碳上电结晶的初期阶段。发现锌在该基体上的沉积没有经历UPD过程。在本实验条件下, 成熟晶核的生长受溶液中锌离子的扩散所控制, 而晶核形成的机理依有无添加剂存在而异。通过分析恒电位暂态, 求出锌离子的扩散系数D, 以及不同过电位η下的成核速度常数A和晶核数密度N_0。A和η的关系表明“原子模型”比经典的成核模型更适合于本研究体系。N_0与η的经验关系式由曲线拟合而得。本文着重讨论了过电位和添加剂对成核作用的影响。     

Chemical trapping experiments support a cation-radical mechanism for the oxidative polymerization of aniline

The oxidative polymerization of aniline in aqueous acidic solution was carried out in the presence of a variety of organic compounds as potential traps for postulated intermediates. The polymerization was inhibited by hindered phenols and electron-rich alkenes, traps for cation-radicals. However, polyaniline was still obtained in the presence of electron-rich arenes, such as 1,3-dimethoxybenzene and 1,4-dimethoxybenzene, known as excellent receptors of nitrenium ions. Polymerization of N-phenyl-1,4-phenylenediamine was similarly carried out in the presence of potential traps. Polyaniline containing an N-phenyl group was obtained in the presence of 1,3-dimethoxybenzene and 1,4-dimethoxybenzene. Hindered phenols and 4-methoxystyrene only slightly inhibited polymerization of N-phenyl-1,4-phenylenediamine which most probably proceeded by way of the stable diarylamino radical. Copolymerization of aniline with 10 wt % of N-phenyl-1,4-phenylenediamine in the presence of these traps gave similar results to the polymerization of pure aniline. These results have led to the proposed cation-radical polymerization mechanism of aniline, in which the polymerization is a chain growth reaction through the combination of a polymeric cation-radical and an anilinium cation-radical. Step growth character is also present when a polymeric aminium cation-radical end combines with a diarylaminoended polymer. The copolymerization of N-phenyl-p-phenylenediamine can also occur by reaction of aniline cation-radical with a polyarylamine radical. The nitrenium mechanism was further rejected by the fact that attempted polymerization of N-phenylhydroxylamine, which forms authentic nitrenium ions in acid, failed to give polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2569–2579, 1999     

Electrochemical synthesis and nucleation and growth mechanism of Prussian blue films on p-Si(100) electrodes

In this study, we examined the synthesis of Prussian blue onto p-Si(100). The Prussian blue formation was carried out by means of the deposition of a Fe film and then its dissolution in presence of potassium hexacyanoferrate(II). In the first stage, a study by cyclic voltammetry was carried out, and then, using the potential step method, the corresponding nucleation and growth mechanism were determined. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy was carried out. The results are consistent with a 3D progressive nucleation with diffusion-controlled growth. Finally, this research is oriented to construct electrochemical storage devices which can be in situ loaded by the photovoltaic action of the semiconductor base material doped silicon.     

Electrochemical kinetic study about cobalt electrodeposition onto GCE and HOPG substrates from sulfate sodium solutions

In the present work, we analyze the electrodeposition of cobalt by electrochemical techniques onto GCE (system I) and HOPG (system II) electrodes from sulfate solutions. Cyclic voltammetry and current transient measurements were used to obtain the nucleation and growth mechanism. The results clearly showed that electrodeposition of cobalt is a diffusion-controlled process with a typical 3D nucleation mechanism in both substrates. The average ΔG calculated for the stable nucleus formation was 1.97 × 10⁻²⁰ J nuclei⁻¹ and 3.58 × 10⁻²⁰ J nuclei⁻¹ for system I and system II, respectively. The scanning electron microscope (SEM) images indicated similar nucleation and growth processes on GCE and HOPG substrates at same overpotential with a homogeneous disperse cobalt clusters. X-ray energy-dispersive spectroscopy (EDS) was performed in order to ensure that the clusters formed are cobalt. The nuclei’s size obtained was dependent of the overpotential applied; at lower overpotentials, the growth rate of the cobalt clusters diminishes when their number increases due to the strongly reduced concentration of cobalt ions because of their consumption by a larger number of growing particles. A theoretical quantum study employing PM6 method suggests that Na⁺ adsorbed deactivate the local surface occasionating the formation of disperse cobalt clusters on carbon electrodes.