Добірка наукової літератури з теми "Scanning Gel Electrochemical Microscopy (SGECM)"

The thermal decomposition behavior of gel precursor, the structure, morphology and electrochemical properties of NiO thin films prepared by sol-gel process were characterized by thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and constant current charge-discharge techniques. The results show that the gel precursor completely decomposes and gradually forms the nanocrystalline NiO at 450°C during the sintering. The NiO thin film is smooth, uniform and free of cracks drying at 200°C as pretreatment and sintering at a low temperature rise rate. The structure of NiO films sintered at 500°C for 2h becomes integrity, whose discharge capacity after 20 cycles remains at 714mAh/g. It is promising to be used in Li-ion battery for great initial specific capacity and well cycle performances.

We demonstrate two approaches to prepare mesoporous metal oxide nanowires by surfactant assembly and nanoconfinement via sol-gel or electrochemical deposition. For example, mesoporousTa2O5and zeolite nanowires are prepared by block copolymer Pluronic 123-templated sol-gel method, and mesoporous ZnO nanowires are prepared by electrodeposition in presence of anionic surfactant sodium dodecyl sulfate (SDS) surfactant, in porous membranes. The morphologies of porous nanowires are studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses.

A strong relationship between the surface structure and the redox activity of Li₂O₂ is visualized directly using scanning electrochemical cell microscopy, employing a dual-barrel nanopipette containing a unique gel polymer electrolyte.

The aim of this paper is to evaluate the efficiency of hybrid sol-gel coatings reinforced with electrospinning nanofibers doped with cerium nitrate and ceria particles to increase the corrosion properties of the coating. Poly(vinyl alcohol) solutions doped with cerium nitrate and ceria were electrospun onto clean commercial aluminum alloy AA2024-T3 plates and then coated with a hybrid sol-gel system using the dip-coating procedure. The hybrid materials synthesized via sol-gel chemistry were prepared from inorganic-organic precursors: zirconium (IV) propoxide and 3-glycidoxypropyltrimetoxysilane. The electrochemical impedance spectroscopy technique was applied to evaluate the electrochemical properties of the film whereas scanning electron microscopy and atomic force microscopy were employed to characterize the surface characteristics. The incorporation of nanofibers into the sol-gel system provides good barrier properties that increase the corrosion resistance of the aluminum at longer exposure times in saline media. This protection depends of the type of inhibitor loaded within the electrospun nanofibers.

LiMn2O4spinel cathode materials have been successfully synthesized by solid-state reaction. Surface of these particles was modified by nanostructured LiFePO4via sol gel dip coating method. Synthesized products were characterized by thermally analyzed thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The results of electrochemical tests showed that the charge/discharge capacities improved and charge retention of battery enhanced. This improved electrochemical performance is caused by LiFePO4phosphate layer on surfaces of LiMn2O4cathode particles.

Au cours des 30 dernières années, les techniques de microscopie à sonde électrochimique à balayage (SEPM) ont été développée comme outils puissants pour des études électrochimiques à l’échelle micro/nano. Les techniques les plus développées et commercialisées sont la microscopie électrochimique à balayage (SECM) et la microscopie de conductance ionique à balayage (SICM). Cependant, les mesures impliquent l’immersion totale de l’échantillon au sein de la solution d’électrolyte, qui peut produire des modifications incontrôlées de la surface en raison du long temps de balayage. A défaut de localiser l’électrode elle-même, l’électrolyte peut également être localisé, ce qui est connu sous le nom de microscopie de cellules à balayage de gouttelettes (SDC) ou de microscopie à balayage de cellule électrochimique (SECCM). Ceci permet de réaliser les expériences dans des conditions ambiantes. Toutefois, l’étalement des gouttelettes sur la surface de l’échantillon peut être affecté par l’hydrophilie et la rugosité de l’échantillon, ce qui pose des problèmes pour l’analyse quantitative. Récemment, la microscopie électrochimique à balayage à sonde à gel (SGECM) a été proposée comme nouvelle technique de SEPM. Elle est principalement basée sur une sonde à gel qui immobilise l’électrolyte sur une électrode de type micro-disque. Par conséquent, l'analyse peut être réalisée dans un environnement ambiant avec un étalement d'électrolyte contrôlable. Cette thèse est consacrée aux développements ultérieurs de la SGECM. Avant tout, le contexte des développements de SGECM est présenté dans le chapitre I. Différentes techniques SEPM, électrolytes polymères gel, réalisations de SGECM sont systématiquement présentées, respectivement. Au chapitre II, la résolution physique latérale de la SGECM est étudiée de manière approfondie et quantitativement en marquant des pixels uniques et en balayant périodiquement les échantillons. Dans le chapitre III, le mode potentiométrique de la SGECM est développé à partir d’une nouvelle électrode de micro-référence Ag/AgCl-gel. Comme la sonde à gel subit des milliers de cycles d’étirement et de compression au cours d’une mesure de cartographie, il est très important d’améliorer sa résistance mécanique. Le chapitre IV décrit une approche préliminaire basée sur la réticulation chimique du gel de chitosane par le glutaraldéhyde. Le chapitre V pousse plus loin le développement des sondes à gel ainsi que l’intégration des électrodes de travail et de référence
In the past 30 years, scanning electrochemical probe microscopy (SEPM) techniques have been developed as powerful tools for studying electrochemistry at micro/nano scale. The most developed and commercialized techniques are Scanning Electrochemical Microscopy (SECM) and Scanning Ion Conductance Microscopy (SICM). However, the entire sample is immersed in the electrolyte solution during the measurements, which may yield uncontrolled change of the surface due to the long scanning time. Instead of localizing electrode, the electrolyte can also be localized, which is known as Scanning Droplet Cell (SDC) or Scanning Electrochemical Cell Microscopy (SECCM). The experiments are carried out under ambient conditions. However, the spreading of droplet over sample surface may be affected by the hydrophilicity and roughness of sample, which brings challenges in quantitative analysis. Recently, Scanning Gel Electrochemical Microscopy (SGECM) was reported by our group as a novel SEPM technique. It is mainly based on a gel probe that immobilizes the electrolyte on a micro-disk electrode. Thus, the analysis can be achieved in ambient environment with controllable electrolyte spreading. This thesis is devoted to the further developments of SGECM. Foremost, the background of developments of SGECM is introduced in Chapter I. Different SEPM techniques, gel polymer electrolytes, achievements of SGECM are systematically presented, respectively. In Chapter II, the lateral physical resolution of SGECM is thoroughly and quantitatively studied by both marking single pixels and scanning over periodic samples. In chapter III, the potentiometric mode of SGECM is developed based on a novel Ag/AgCl-gel micro-reference electrode. As the gel probe undergoes thousands of pressing-stretching cycles in a mapping measurement, it is highly important to improve its mechanical strength. Chapter IV describes the preliminary effort of chemically cross-linking chitosan gel by glutaraldehyde. Chapter V further pushes forward the development of integrated gel probes with both working and reference electrode

Philosophiae Doctor - PhD
To meet a fast-growing market demand for next generation portable electronic devices with higher performance and increased device functionalities, efficient electrical energy devices with substantially higher energy, power densities and faster recharge times such as supercapacitors are needed. The overall aim of this thesis was to synthesize nanostructured sulphonated polyaniline and transition metal single, binary and ternary mixed oxide doped nanocomposites with electro-conductive properties. These nanocomposites were anchored on activated graphitic carbon and used in design of asymmetric supercapacitors. Tantalum(IV)oxide, tantalum(IV)oxide-nickel(II)oxide, tantalum(II)oxide-manganese(III)oxide, tantalum(II)oxide-nickel(II)oxide-manganese(II,III)oxide nanoparticles were synthesised using modified sol-gel methods. These were then dispersed, individually, in acidic media through sonication and incorporated in-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped with poly(4-styrene sulphonic acid). These novel polymeric nanocomposites were characterised with FTIR, UV-visible, TEM, SEM, EDS, XRD to ascertain successful polymerization, doping, morphology and entrapment of the metal oxide nanoparticles. SECM approach curves and interrogation of CV revealed that these nanocomposites are conductive and electro-active. The cells showed good supercapacitor characteristics with high specific capacitances of 170.5 Fg⁻¹ in TaO₂- PANi-PSSA, 166.1 Fg⁻¹ in TaO₂-NiO-PANi-PSSA, 248.4 Fg-1 in TaO-Mn₂O₃-PANi- PSSA and 119.6 Fg⁻¹ in TaO-NiO-Mn₃O₄-PANi-PSSA. Their corresponding energy densities were calculated as 245.5 Whg⁻¹, 179.4 Whg⁻¹, 357.7 Whg⁻¹ and 172.3 Whg⁻¹ respectively. They also gave respective power densities of 0.50 Whg⁻¹, 0.61 Whg⁻¹, 0.57 Whg⁻¹ and 0.65 Whg⁻¹ and showed good coulombic efficiencies ranging between 77.97% and 83.19%. These materials are found to have a long cycle life and therefore good electrode materials for constructing supercapacitor cells.
National Research Foundation (NRF)

De nos jours, la modification de surface fait l'objet d'attentions particulières en raison de sa variété d'applications dans divers domaines. Dans ce contexte, l'objectif de cette thèse a été de traiter de la modification localisée de surfaces dans des conditions douces en utilisant le microscope électrochimique à balayage (SECM). En tant que preuve de concept pour l'écriture directe, différentes stratégies ont été menées pour la modification de surface par gravure de matériaux, greffage de couche organique et modification de la structure chimique surfacique. Des surfaces de verre et d'or ont été les principaux substrats qui ont été modifiés du fait de leur large utilisation notamment dans les nanotechnologies. Cette thèse est présentée sous forme de quatre chapitres et le premier est consacré à la technique SECM ainsi qu'à la modification de surface en général. Les trois autres parties concernent le travail effectué pour valider le concept d'écriture directe. Dans la première partie, une matrice de silice synthétisée par voie sol-gel et dopée avec un ion métallique (cuivre ou or) est utilisée comme matériau d'écriture à l'aide d'une sonde locale (ultramicroéléctrode). Le SECM est utilisé en mode de rétroaction avec des médiateurs tels que viologène de méthyle et le p-benzoquinone. Le diamètre de l'ultramicroélectrode (UME) et la durée d'hydrolyse ont été des facteurs pris en compte pour étudier l'effet sur la taille des plots métalliques électrogénérés. Dans la deuxième partie, la gravure par voie humide localisée de la surface de l'or a été réalisée en utilisant le SECM opérant dans un électrolyte à base de diméthylsulfoxide chargé avec de l'iode. Dans cette méthode, une UME est positionnée (à une distance connue) à proximité de la surface d'or pour générer électrochimiquement l'ion triiodure à la pointe de l'UME de platine, agissant comme oxydant à la surface d'or. La troisième partie comprend deux travaux expérimentaux différents mais complémentaires. Le premier porte sur la réduction électrochimique sur électrode d'or d'un sel de diazonium préparé à partir de l'éthylènediamine, une molécule aliphatique. Pour la première fois, la fonctionnalisation covalente sur or d'un sel de diazonium est démontrée via la diazotation d'un groupe amino de l'éthylènediamine. Dans la seconde partie, un substrat de verre a été greffé par un film à base de 3-aminopropyle silane qui a été réalisée par un procédé sol-gel. Ensuite, la lame de verre modifiée a été fonctionnalisée avec du glutaraldéhyde pour greffer la tyrosinase. Enfin, le mode de réaction du SECM a également été utilisé pour vérifier l’activité catalytique de cette enzyme. La pointe de l’UME est positionnée à proximité de la surface modifiée par l’enzyme afin de réaliser une mesure de courant de l’activité enzymatique à partir d’un balayage horizontal dans le plan x-y
Nowadays, the modification of surfaces has drawn more attention due to its variety of applications in various domains. Therefore, the purpose of this thesis deals with the localized modification of surfaces in mild condition by using the scanning electrochemical microscope (SECM) instrument. As a proof of concept for direct writing, different strategies have been used for surface modifications through removing surface materials, grafted organic layer and changing the chemical structure of the surface. Gold wafer and glass surfaces were the main substrates which have been modified since these materials are very used especially in nanotechnologies. This dissertation is conducted in four chapters and the first one focuses on SECM technique and surface modifications in general. The three other parts concern the work performed to validate the concept of direct writing. In the first part, metal ion (copper and gold)-doped silica matrices have been prepared by the well-known sol-gel method. Copper and gold metallic particles are produced locally by using the SECM in feedback mode with mediators such as methyl viologen and p-benzoquinone. The diameter of ultramicroelectrode (UME) tip and hydrolysis period were factors taken into account to study the effect on the size of electrogenerated metallic spots. In the second part, the localized wet etching of gold surface has been achieved by using SECM where a dimethylsulfoxide-based electrolyte charged with iodine is used. In this method an UME probe is positioned (at a known distance) close to the gold surface. Friendly environment method was used as etching process to generate electrochemically triiodide ion at the platinum UME tip, acting as an oxidant for gold surface. he third part includes two different experimental works. The first one covers the electrochemical reduction on gold electrode of diazonium salt prepared from ethylenediamine, an aliphatic diamine molecule. For the first time, the covalent functionalization on gold of a diazonium salt is demonstrated, and required diazotization of one amine group from ethylenediamine. In the second work, glass substrate was grafted by 3-aminopropyl silane film which was performed by sol-gel method. Then the modified-glass slide was functionalized by glutaraldehyde solution in order to immobilize tyrosinase molecules. Finally, the feedback mode of SECM has also been used to monitor the catalytic activity of tyrosinase. The tip of ultramicroelectrode was positioned close to the enzyme-modified surface and was scanned horizontally in x-y plane while measuring current from re-generated mediator molecules was carried out

Lithium ion batteries (LIBs) are attractive for energy storage application. In this regard, lithium rich layered oxides (LLOs), are considered viable cathodes due to their tempting properties such as lower production cost, faster manufacturing process, excellent reversible capacity, and better electrochemical performance at high voltages. Despite these properties, LLOs lack in cyclic stability and inferior capacity retention. This study proposes a surface modification technique to overcome the above-mentioned limitations in which a layer of silica (SiO2) has been coated on the particles of Li1.2Ni0.13Mn0.54Co0.13O2. The Li1.2Ni0.13Mn0.54Co0.13O2 was synthesized by a sol-gel process and then coated with SiO2 (SiO2=1.0 wt. %, 1.5 wt. %, and 2.0 wt. %). The coatings were undertaken through a dry ball milling technique. Different characterization test such as X-Ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), elemental mapping, and X-ray photoelectron spectroscopy (XPS), were utilized to prove phase pure material formation and identify the SiO2 layer on the surface of Li1.2Ni0.13Mn0.54Co0.13O2. The electrochemical measurements, confirm the improvement in capacity retention and cyclability of SiO2 coated Li1.2Ni0.13Mn0.54Co0.13O2 samples with reference to the uncoated samples. This improvement can be ascribed to the protective and barrier effect of the coated layer on the LLOs particles avoiding any unwanted side reactions when the cathode is exposed to the electrolyte. A small trade-off between electrochemical performances and the coating thickness confirms the best efficiency of 1 wt.% SiO2 coated Li1.2Ni0.13Mn0.54Co0.13O2 when compared to other coated samples.

Electroosmotic pumping has been extensively used in biomedical lab-on-a-chip devices and micropumps for critical applications such as microelectronic cooling. In many applications, a high flow rate is a key requirement in desired performance so constant efforts have been made to increase the pumping flow rate through unit area to achieve the compact design. We report here an attempt of using SiO2-coated anodic porous alumina membrane as the material to achieve high electroosmotic pumping flow rate. High quality porous alumina membranes of controllable pore diameter in the range of 20-300 nm and pore length of 60 - 100 μm have been fabricated with electrochemical anodization. The pores are uniform and hexagonally packed with a high porosity of up to 50% and a tortuosity of a bare minimum of unity. In addition, the inner surface of the pores could be conformally coated with a thin layer (~ 5 nm) of SiO2 with sol-gel chemistry to achieve a high zeta potential. Scanning electron microscopy of the cross section of the membrane verified these facts. Electroosmotic pumping performance of these membranes has been investigated using standard relevant aqueous electrolyte buffer solutions and results showed that SiO2-coated porous alumina could achieve a higher flow rate compared with other microporous materials such as glass frit and porous silicon reported in the literature.