氧化石墨烯/聚苯胺复合材料的制备及电化学电容性能的研究

以对苯二胺为引发剂,用苯胺和氧化石墨烯(GO)为原料,采用化学原位聚合法制备了氧化石墨烯/聚苯胺(GP)复合材料,不添加任何表面活性剂和模板剂。采用傅里叶变换红外(FTIR)光谱、X射线粉末衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对复合材料进行了物性表征,并对其电化学性能进行了测试。结果显示,复合材料保持了氧化石墨烯的基本形貌,聚苯胺纤维分布在氧化石墨烯层间及所形成的褶皱上。二者形成的二元纳米复合材料,发挥良好的协同作用,电化学性能得到了改善。当电流密度为0.5A·g-1时,复合材料的比电容可以达到623F·g-1,远大于石墨烯和聚苯胺单体的比电容。     

Surfactant-assisted electrodeposition and improved electrochemical capacitance of silver-doped manganese oxide pseudocapacitor electrodes

Ag-doped MnO₂ pseudocapacitor electrodes with dendrite and foam-like structures were successfully produced for the first time using an electrodeposition method employing structure-directing agents, i.e., sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) acting through micelle formation at solid–liquid interfaces. Doping silver with MnO₂ enhanced their electronic conductance. Controlling pseudocapacitor electrode morphologies with surfactants accelerated ion transport. The specific capacitance values of the Ag-doped MnO₂ films produced with SDS and CTAB, measured in 0.5?M Na₂SO₄ at a scan rate of 5?mV?s^?1 were 551 and 557?F?g^?1, respectively. These values are about 2.7-fold higher than that of the pure MnO₂ film and about 1.4-fold higher than that of the Ag-doped MnO₂ film made without using surfactants.     

Evaluating the performance of organic coatings under mechanical stress using electrochemical impedance spectroscopy

Stress in coatings originating from a mechanical load imposed during exploitation is a relatively unexplored field of investigation. Paradoxically, a number of constructions and installations seem to operate under such conditions. The purpose of this work was to investigate the impact of a cyclic mechanical load exerted on coating/metal systems. It was the authors aim to verify whether repeated mechanical stress constitutes a significant factor contributing to coating degradation. Epoxy coated St3SAl steel samples were subjected to 21,000 uniaxial strain/release cycles. The maximum force applied assured maintenance within the elastic deformation region of the metal substrate. The state of the protective film was monitored using electrochemical impedance spectroscopy. The coating response to the mechanical load occurred in a three-stage process. The system subjected to the strain/release cycles revealed signs of degradation earlier compared to a non-strained, reference sample.Contribution to the 3rd Baltic Conference on Electrochemistry GDASK-SOBIESZEWO, 23–26 April 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

Magnetoelectrochemistry of gold nanoparticle quantized capacitance charging

Magnetoelectrochemical studies of gold nanoparticle quantized capacitance charging were carried out at ambient conditions. The single electron transfer responses were found to be sensitive to external magnetic fields, reflected in the enhancement of voltammetric peak currents and shifts of peak formal potentials with increasing magnetic field intensities. Additionally, splittings of voltammetric peaks were also observed upon the application of an external magnetic field. These phenomena might be partly attributed to the paramagnetic characters (electron parity) of nanosized gold particles which are contingent upon their charge states. These novel observations suggest that the nanoparticle electronic energy structures can be varied by magnetic fields, leading to molecular manipulations of the nanoscale charge-transfer chemistry.     

High-performance electrochemical sensor based on electrodeposited iron oxide nanoparticle: catecholamine as analytical probe

In this paper, we report the synthesis and electrocatalytic activity of electrodeposited Fe₂O₃ nanoparticles modified on a glassy carbon electrode as highly sensitive sensors for determination of catecholamines. Results showed that the Fe₂O₃ nanoparticles on a glassy carbon electrode exhibit excellent catalytic activity toward catecholamines oxidation, including levodopa, dopamine, and epinephrine, resulting in a marked lowering in the peak potential and considerable improvement of the peak current as compared to the electrochemical activity at the bare glassy carbon electrode. The electrochemical characterizations of catecholamines were performed using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry techniques. The electrocatalytic currents increase linearly with the levodopa, dopamine, and epinephrine concentrations in the ranges of 0.0625–1000, 0.25–1500, and 0.125–1000 µM, respectively, and the detection limits (3σ) were 24 ± 2, 14 ± 2, and 12 ± 2 nM, respectively.     

Analysis of diffusion-controlled stochastic events of iridium oxide single nanoparticle collisions by scanning electrochemical microscopy

We investigated the electrochemical detection of single iridium oxide nanoparticle (IrO(x) NP) collisions at the NaBH(4)-treated Pt ultramicroelectrode (UME) in a scanning electrochemical microscope (SECM) over an insulating surface. The NP collision events were monitored by observing the electrocatalytic water oxidation reaction at potentials where it does not take place on the Pt UME. These collisions occurred stochastically, resulting in a transient response ("blip") for each collision. The frequency of the collisions is proportional to the flux of NPs to the UME tip, and thus equivalent to the SECM current. A plot of collision frequency versus distance followed the theoretical approach curve behavior for negative feedback for a high concentration of mediator, demonstrating that the collisions were diffusion-controlled and that single-particle measurements of mass transport are equivalent to ensemble ones. When the SECM was operated with a Pt substrate at the same potential as the tip, the behavior followed that expected of the shielding mode. These studies and additional ones result in a model where the IrO(x) NP collision on the Pt UME is adsorptive, with oxygen produced by the catalyzed water oxidation causing a current decay. This results in a blip current response, with the current decay diminished in the presence of the oxygen scavenger, sulfite ion. Random walk and theoretical bulk simulations agreed with the proposed mechanism of IrO(x) NP collision, adsorption, and subsequent deactivation.     

Ceramic nanoparticle/monodisperse latex coatings

Ceramic nanoparticle/monodisperse latex coatings with a nanoparticle-rich surface and a latex-rich body were created by depositing aqueous dispersions of monodisperse latex, approximately 550 nm in diameter, and nanosized ceramic particles onto substrates and drying. On the top surface of the dried coating, the latex particles are closely packed with nanoparticles uniformly occupying the interstitial spaces, and along the cross section, nanoparticles fill the spaces between the latex particles in the near surface region; a compacted latex structure, nearly devoid of nanoparticles, lies beneath. Cryogenic scanning electron microscopy images of partially dried coatings at successive drying stages reveal two important steps in forming this structure: top-down consolidation of latex particles and accumulation of nanoparticles in interstitial spaces among latex particles near the surface. A systematic study of the effect of processing conditions, including nanoparticle concentration, nanoparticle size, latex glass transition temperature, and drying conditions, on the final microstructure was carried out. The unique microstructure described above forms when the monodisperse latex is large enough to create pore channels for the transport of nanosized particles and the drying conditions favor "top-down" as opposed to "edge-in" drying.     

The formation of submonolayer thorium coatings on a silicon oxide surface by electrochemical deposition

Data are reported on the mechanisms of the formation of submonolayer coatings based on thorium oxide on the surface of Si(111) single crystal with natural oxide as a result of electrochemical deposition. It is experimentally shown that the deposition of thorium atoms from an acetone solution of Th(NO₃)₄ onto the surface of natural silicon oxide leads to the formation of defects in the thin silicon oxide layer, which is accompanied by the deposition of thorium nanoclusters onto a pure silicon surface. The observed effects have been qualitatively explained assuming the breakdown of natural silicon oxide due to the presence of an electrical double layer in the near-surface region of the cathode.     

Liquid crystal-gold nanoparticle composite-modified indium tin oxide (ITO) substrates and their electrochemical characterisation

A simple efficient strategy for the simultaneous synthesis and anchoring of liquid crystal (LC)-stabilised gold nanoparticles (NPs) on indium tin oxide (ITO) substrate is described. A monolayer of 3-mercaptopropyltrimethoxy silane (MPS) compound was formed on ITO and quality of the monolayer was assessed using electrochemical techniques namely cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Gold NP preparation was carried out on this monolayer-modified substrate (and on bare ITO), in a single-step reaction, simply by drop-casting a solution containing an appropriate amount of chloroauric acid and a LC compound possessing a terminal amino group, on the MPS monolayer-modified substrate and heating (70degree) for 2-3 min.. The LC compound served as a reducing agent as well as a capping ligand. LC-capped NPs were chemically anchored onto the ITO substrate through bonding to thiol moiety of the MPS. The CV and EIS analysis of the MPS monolayer showed a complete blocking behaviour for the electron transfer across the electrode/electrolyte interface confirming the formation of a high-quality dense compact monolayer. On the other hand, upon immobilisation of LC-gold NP composite on self-assembled monolayer-modified ITO substrates, both CV and impedance studies showed a small current indicating the gold NP-mediated electron transfer, thus confirming the successful immobilisation of NPs.     

Investigation of capacitance storage and cyclic voltammetry for the electrochemical oxidation of phenol on iridium and lead oxide electrodes

Journal of Solid State Electrochemistry - The capacitance storage and cyclic voltammetry (CV) of electrochemical oxidation of phenol were investigated using IrO2–Ta2O5/Ti and β-PbO2/Ti...     

Layer-by-layer nanoparticle coatings on lignocellulose wood microfibers

The layer-by-layer (LbL) self-assembly technique was applied to deposit organized multilayers of TiO₂ or SiO₂ nanoparticles of 30–80 nm diameter, and 50-nm diameter halloysite clay nanotubes on softwood fibers. Fluorescent and scanning electron microscopy images showed complete nanoparticle coating on these fibers. The thickness of the two-layer coating was estimated as 46, 58, and 115 nm for TiO₂, SiO₂, and halloysite tubules, respectively, which corresponds to ca. 1 wt% nanoparticle loading of the fibers. The brightness test of paper handsheets prepared from nanocoated fibers showed that TiO₂ nanoparticle coating gave handsheet reflectance of 84% at 450 nm, which is 4% higher than the brightness of the control sample from virgin fibers. The paper handsheets prepared with nanoparticle-coated fibers had 30–50% higher porosity with tensile strength index retained close to the control sample.     

Ion-induced rectification of nanoparticle quantized capacitance charging in aqueous solutions.

Ion-induced rectification of nanoparticle quantized capacitance charging was studied using nanoparticle self-assembled monolayers in aqueous solutions in the presence of some unique electrolyte ions. The rectified charging features were interpreted on the basis of a Randles equivalent circuit where the binding of hydrophobic electrolyte ions to surface-confined particle molecules led to the manipulation of the electrode interfacial capacitance. It was found that the rectification effects were directly related to the ion hydrophobicity, manifested by the cathodic (anodic) shift of the onset potential with anions (cations) of increasing hydrophobicity Additionally, the voltammetric responses evolved from those similar to conventional molecular diodes to those of quantized charging rectifiers with increasing anion hydrophobicity. Electron-transfer kinetics evaluated by using various electrochemical methods yielded a rate constant within the range of 10-100 s(-1) which decreased with increasing length of the alkyl spacers with a coupling coefficient (beta) within the range of 0.8-0.9. Comparisons with conventional electroactive functional moieties were also discussed.     

Effects of activation conditions on the electrochemical capacitance of activated carbon nanotubes

The effects of different activation conditions (including KOH/CNTs ratio, activation temperature, activation time and nitrogen flow rate) on the electrochemical capacitance of activated carbon nanotubes (CNTs) have been investigated. All the four factors can affect the activated CNTs’ electrochemical capacitance. And the effects on the activated CNTs’ electrochemical capacitance carried out by virtue of their effects on activated CNTs’ BET specific surface area and graphitized degree.     

Effect of pore characteristics on electrochemical capacitance of activated carbons

Activated carbons (ACs) for electric double layer capacitors (EDLCs) were fabricated from waste tea leaves, activated with the pore-forming substances ZnCl₂ then, carbonized at high-temperature in N₂ atmosphere. The surface texture and porosity of the ACs were determined using transmission electron micros-copy and N₂ adsorption/desorption studies. The surface area of the 20 wt % ZnCl₂ treated sample was found to be 1029 m²g^?1 and had a distribution of micropores and mesopores. The electrochemical properties of the ACs were evaluated by using cyclic voltammetry and galvanostatic charge-discharge studies. ACs from waste tea leaves exhibited excellent specific capacitance as high as 196 F g^?1 in the 0.1 M Na₂SO₄ neutral electrolyte, with rectangular-like cyclic voltammetry curves at a cell potential of 1.5 V and good cyclability with a capacitance retention of 95% at a high current density of 100 mA g^?1 for 2000 cycles. The results show that the pore texture properties and specific surface area of ACs are dominated by changing carbonization temperature and the amount of activating agent ZnCl₂. The electrochemical performance is influenced mainly by surface area, but the pore size distribution becomes a dominating factor for specific capacitance of a carbon electrode material when the pore structure is in range of micropores/mesopores.     

Current pulse measurement of capacitance during molten salt electrochemical experiments

In earlier work in our laboratories, a current pulse method was developed that allows in situ (dynamic) measurements of electrode capacitance. The present work describes the successful application of the technique to the study of electrode properties in molten salt electrolytes. As expected, the electrode capacitance increases as the electrode surface area exposed to a molten salt bath increases. Furthermore, creep of the bath along the surface of a conductive ceramic anode and subsequent ingress into the anode pores is observed as an increase in capacitance. The pulse technique also gives an indication of phase changes that occur during the reduction of a solid titanium dioxide cathode and a highly sensitive measure of the temperature at which initial freezing of the calcium chloride electrolyte begins. These observations provide useful in situ information about changes in electrode properties in molten salt electrolytes that are difficult to obtain from other techniques. For consideration in the Special Edition: Oldham Festchrift Dedicated to our dear friend Keith B. Oldham on the occasion of his 80th birthday.     

Sulfide-enhanced electrochemical capacitance of cobalt hydroxide on nanofibered parent substrate

Two approaches—substrate nanostructuring and incorporation of sulfide—were studied with the aim to increase electrochemical capacitance of cobalt (hydro)oxide. A fiber structure of cobalt was deposited electrochemically with the fibers in the order of tens of nanometers in thickness and hundreds of nanometers in length. Cobalt hydroxide film was formed on the nanostructured substrate by anodic polarization in an alkaline solution. The hydroxide formation and its electrochemical capacitance have been studied by cyclic voltammetry in conjunction with the electrochemical quartz crystal microbalance (EQCM). An irreversible behavior was typical of the first anodic polarization cycle; it turned gradually to a reversible one during subsequent cycling. EQCM measurements indicated exponential electrode mass growth during the first cycle, with subsequent transition to a quasipassive state. The redox transitions Co(II) → Co(III) → Co(IV), which determine pseudocapacitance, did not cause remarkable electrode mass change. The electrochemical capacitance of the nanofiber sample was found up to five times higher when compared to that formed on conventional cobalt (abraded surface). Specifics of “per 1 g” evaluation of capacitance performance is discussed. Measurements showed that about 10% of the entire hydroxide structure took part in the capacitive process. The capacitance value determined per 1 g of active Co(OH)₂ was in agreement with the limiting value predicted by the Faraday’s law (2,421 F g⁻¹) sulfide-enhanced system with 18% CoS exhibited up to three times higher capacitance when compared to that of the sulfide-free counterpart. The system shows promise for practical applications due to its low cost and technical simplicity.     

Gold nanoparticle based optical and electrochemical sensing of dopamine

This review (with 110 refs.) gives an overview on the progress that has been made in the past few years on the use of gold nanoparticles (AuNPs) for use in sensors and analytical tools for the determination of dopamine (DA). Both AuNPs and their composites with other organic and inorganic materials including noble metals are treated. Following an overview on the clinical significance of DA, we discuss the various analytical methods that are (a) electrochemiluminescence (ECL); (b) surface enhanced Raman scattering (SERS); (c) colorimetric probing and visual detection; and (d) the large class of electrochemical sensors. Subsections cover sensors based on plain AuNPs, bimetallic NPs, AuNP-metal@metal oxide nanocomposites, AuNP nanocomposites with organic polymers, AuNP nanocomposites with carbon nanotubes or with graphene, and finally sensors based on ternary materials containing AuNPs. The review ends with a conclusion on current challenges of sensors for DA and an outlook on future trends.

We review the recent progress in sensing dopamine based on AuNPs and its nanocomposites including bimetallic nanoparticles, AuNPs-/metal oxide, AuNPs-polymer, AuNPs-carbon nanotubes, AuNPs-graphene and ternary materials using different types of sensing techniques such as electrochemiluminescence (ECL), colorimetric, surface enhanced Raman scattering (SERS) and electrochemical techniques.

     

Electrochemical capacitance of nickel oxide nanotubes synthesized in anodic aluminum oxide templates

Nickel oxide (NiO) nanotubes for supercapacitors were synthesized by chemically depositing nickel hydroxide in anodic aluminum oxide templates and thermally annealing at 360 °C. The synthesized nanotubes have been characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The capacitive behavior of the NiO nanotubes was investigated by cyclic voltammetry, galvanostatic charge–discharge experiment, and electrochemical impedance spectroscopy in 6 M KOH. The electrochemical data demonstrate that the NiO nanotubes display good capacitive behavior with a specific capacitance of 266 F g⁻¹ at a current density of 0.1 A g⁻¹ and excellent specific capacitance retention of ca. 93% after 1,000 continuous charge–discharge cycles, indicating that the NiO nanotubes can become promising electroactive materials for supercapacitor.