Dissertations / Theses on the topic 'Molybdenum electrodeposition'

This work demonstrates the deposition of molybdenum in a deep eutectic solvent for the first time, and explores the processes needed for electrorefining of molybdenum. The electrochemical and transport behavior of chloride-coordinated molybdenum in ethaline was initially studied to determine if deposition was possible. Cyclic voltammetry was used to show that MoCl5 added to ethaline exhibits quasi-reversible behavior. Both the measured transfer coefficient and the precipitation of MoCl3 suggest that the reduction of MoCl5 in ethaline is a two-electron transfer reaction where the oxidation state of molybdenum in the product is Mo(III). No deposit was formed with the use of MoCl5 alone and the presence of a shuttling reaction may be partly responsible for the lack of a deposit. However, the deposition of molybdenum was accomplished in ethaline at 80 °C by altering the speciation of the metal complex with the introduction of fluoride ions. A change in coordinating ligands in the presence of fluoride was evidenced by a change in the electrochemical behavior of the Mo species, as determined with cyclic voltammetry. Chronoamperometry was then used to produce Mo deposits on nickel substrate in the presence of fluoride ion. The deposits were imaged with SEM and the presence of Mo was confirmed with EDX. In order to study the effect of the newly introduced fluoride ion on the anodic dissolution of molybdenum in ethaline, linear sweep voltammetry was used. In addition, a chloride-free electrolyte composed of 1M KF in ethylene glycol was used to anodically dissolve Mo at a faradaic efficiency of 63%. The ability of Mo to be anodically dissolved in the presence of fluoride showed the addition of fluoride enables Mo deposition without significantly hindering the anodic dissolution of Mo. Thus, both dissolution and deposition of molybdenum are possible in a deep eutectic solvent, opening the way for possible development of a Mo electrorefining process.

This dissertation presents studies electrodeposited MoS2 and metal-doped MoS2 thin films, and their performance for energy storage, catalysis, and biosensor applications. Ni-doped MoS2 thin films were fabricated by electrodeposition from electrolytes containing both MoS42- and varying concentrations of Ni2+, followed by annealing at 400 ºC for 2 h in an Ar atmosphere. The film resistivity increased from 11.3 µΩ-cm for un-doped MoS2 to 32.8 µΩ-cm for Ni-doped MoS2 containing 9 atom% Ni. For all Ni dopant levels studied, only the x-ray diffraction (XRD) pattern expected for MoS2 is observed, with the average grain size increases with increasing Ni content. Ni-doped MoS2 thin films were tested for their activity towards the hydrogen evolution reaction (HER) in 0.5M H2SO4. Tafel equation fits reveal that the catalytic activity for HER, as measured by the exchange current density, increases up to 6 atom% Ni, and then decreases slightly for 9 atom% Ni. Ni-doped MoS2 thin films were also tested in 1.0 M Na2SO4 for use within electrochemical supercapacitors, and the capacitance per unit area increases by 2-3x for 9 atom% Ni-doped MoS2 relative to un-doped MoS2. The highest specific capacitance obtained for Ni-doped MoS2 during galvanostatic charge-discharge measurements is ~300 F/g

The foremost aim for performing this study was to focus on the electrodeposition of mixed hydrogen molybdenum tungsten bronze films, which have the potential for e– transfer interactions carrying out the reduction of carbon dioxide. A yellow peroxymolybdic tungstate solution was prepared and used for the electrodeposition of hydrogen molybdenum tungsten bronze films on conductive carbon paper. Electrodeposition was carried out at -2.0 V from 20 - 120 minutes to determine the effect of deposition time on film thickness and CO2 reduction. These films were characterized by X-ray photoelectron spectroscopy. The deposited films served as a working electrode for CO2 electrochemical reduction utilizing 0.8 M NaHCO3 as the electrolyte. Carbon dioxide gas was bubbled into the cathode solution for an hour while bulk electrolysis was carried out at different applied potentials. Products were identified and evaluated using ion chromatography.

Zn-Mo coatings are very promising environment friendly anticorrosive coatings as replacement materials for cadmium and chromium (VI) based conversion layers. Electrodeposition has become a favorable technique in fabricating coatings due to its low cost, ease of use, and overall experimental control of coating quality. Very little research so far has been done for the electrodeposition of Zn-Mo coatings under alkaline conditions. In this work, Zn and Zn-Mo coatings were electrochemically deposited on stainless steel from an aqueous alkaline citrate solution. An organic compound, vanillin, was added to the electrolyte as a leveling agent for improving interlayer adherence and corrosion resistance of Zn-Mo coatings. Ni-Mo alloys have been known to possess high tensile strength and excellent corrosion protection of steels, and MoTe2 layers have a potential for the application in anticorrosive coatings due to their hydrophobic properties. In this study, MoTe2-Ni-Mo coatings were deposited on stainless steel using both sputtering and electrodeposition methods. These coatings with high corrosion resistance and other desirable properties are in demand in the oil and gas industry since they can protect and thus extend the lifetime of the underlying materials when exposed to aggressive environments. The Zn-Mo and MoTe2-Ni-Mo coatings were evaluated for chemical composition and corrosion behavior using different types of instrumental and electrochemical techniques. The addition of vanillin to the electrolyte did not change the crystalline structure or composition of the Zn-Mo coating, however, the corrosion resistance of the coating was significantly improved by the leveling effect of vanillin during the electrodeposition. The corrosion resistance of the Ni-Mo coating was also enhanced by applying the hydrophobic MoTe2 monolayer on the top surface.

Electrodeposition of metallic molybdenum from aqueous electrolyte has in most cases previously yielded poor results due to the extremely high rate of the secondary hydrogen evolution reaction occurring at the cathode. This results in low current efficiencies and thin brittle films. The use of a highly concentrated aqueous-acetate based electrolyte containing molybdate ions has been used to deposit thick (~50 μm) adhered, mirror like metallic molybdenum coatings. Plating variables were investigated to determine the optimum deposition conditions; it was seen that current density was the most influential factor for the successful deposition of the refractory metal. The coating surface was analysed using SEM and EDX. XRD analysis confirmed the deposits were amorphous in nature with broad peaks in the (110) orientation. The deposition mechanisms were studied through electrochemical techniques such as PDP and CV. It was concluded that metallic molybdenum is deposited in a two-step reduction process, with the formation of an intermediate coating of molybdenum oxide, requiring hydrogen gas to fully reduce. Corrosion studies have shown the coatings stability in a chlorinated environment however active uniform corrosion in alkaline conditions resulted in film failure. Exposure to strong acidic conditions result in oxidation and delamination of the coating. Up-scaling of the process was seen to be successful and large deposits of well adhered and uniform metallic molybdenum were formed under high applied currents.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

Electroreduction of various Ni(II) and Co(II) complexes in chloride, sulfate, citrate, pyrophosphate and pyrophosphate –ammonia solutions, electrodeposition of Ni and Co and their alloys with W and Mo and composition of obtained coatings and surface morphology, structure and corrosion properties have been studied. W and Mo alloys were electrodeposited from citrate – borate and pyrophosphate –ammonia solutions, and the corrosion behavior of obtained alloys was investigated in sulfate solutions. The shapes of voltammetric curves obtained for Co(II) and Ni(II) electroreduction are similar to the typical shapes of curves for processes occurring under mixed kinetics, and clear plateau presences in voltammogram. However, based on the data obtained by the electrochemical impedance spectroscopy was confirmed that the obtained plateau does not attribute to the diffusion limitations. A slow adsorption stage of electrochemicaly active complex of Co and Ni on the electrode was assumed. It was determined that Ni electrodeposition rate from pyrophosphate baths without ammonia is relatively small. Adding of (NH4)2SO4 and further forming of Ni(II) complexes with ammonia in the solution accelerates sufficiently the rate of Ni electrodeposition. The effect well correlates with increasing the calculated molar fraction of various ammonia complexes with Ni(II). Based on the received data we conclude that electrochemicaly active Ni and Co complexes are different, i.e. CoOH+ and Ni(NH3)162+... [to full text]
Buvo tiriama Co(II) ir Ni(II) įvairių kompleksų elektroredukcija chloridiniuose, sulfatiniuose, citratiniuose, pirofosfatiniuose bei pirofosfatiniouose-amoniakiniuose tirpaluose, Ni ir Co lydinių su W ir Mo elektronusodinimas, gautų dangų sudėtis ir paviršiaus morfologija, struktūra bei korozinės savybės. W ir Mo lydiniai buvo nusodinami iš citratinių - boratinių ir pirofosfatinių – amoniakinių elektrolitų, o koroziniai tyrimai atlikti sulfatiniuose tirpaluose. Tiriant Co(II) ir Ni(II) elektroredukciją nustatyta, kad voltamperinių kreivių forma primena būdingas mišriai kinetikai voltamperines kreives, jose yra ryškus persilenkimas. Tačiau tyrimai EIS metodu parodė, kad šio persilenkimo negalima sieti su difuziniais apribojimais. Padaryta prielaida apie elektrochemiškai aktyvaus Co arba Ni komplekso lėtą adsorbciją ant elektrodo. Nustatyta, kad Ni elektonusodinimo greitis iš pirofosfatinių tirpalų be amonio jonų yra labai mažas. Pridėjus (NH4)2SO4 ir taip formuojant amoniakinius nikelio kompleksus tirpale, labai pagreitėja Ni elektronusodinimas. Šis efektas labai gerai koreliuoja su didėjančia apskaičiuotų įvairių Ni (II) kompleksų su amonio jonais frakcija. Tačiau amonio jonų buvimas praktiškai neturi įtakos Co elektronusodinimo greičiui. Iš gautų duomenų daroma išvada, kad elektrochemiškai aktyvus Ni ir Co kompleksai yra skirtingi, t.y. CoOH+ ir Ni(NH3)162+ yra krūvį pernešančios dalelės pirofosfatiniuose – amoniakiniuose tirpaluose. Tiriant Co-Mo ir Co-Mo-P lydinius... [toliau žr. visą tekstą]

Hydrogen molybdenum oxide, known has molybdenum bronze, is a material of interest due to catalyzing electron transfer reactions. Specifically, molybdenum bronze is an electrocatalyst toward carbon dioxide reduction. Electrochemical deposition from a peroxymolybdic acid solution is a method for preparing molybdenum bronze films. This work demonstrates reproducible electrodeposition on indium tin oxide substrates and conductive carbon paper. Film thickness depends on concentration, time and pH. After characterization by film thickness, resistance, XRD and XPS, the as deposited films served as the working electrode for electrochemical reduction of carbon dioxide in 0.1 M NaHCO3. Ion chromatography determined formate resulting in 8% faradaic efficiency at an applied potential of -0.4 V. Interestingly, this potential is similar to use of formate dehydrogenase as an electrocatalyst. Carbon monoxide levels were attempted to be determined by GC in the headspace of an H type electrochemical cell. Results show that these films are applicable towards electrochemical CO2 reduction to formate when supported on carbon.

Buvo tiriama Co(II) ir Ni(II) įvairių kompleksų elektroredukcija chloridiniuose, sulfatiniuose, citratiniuose, pirofosfatiniuose bei pirofosfatiniouose-amoniakiniuose tirpaluose, Ni ir Co lydinių su W ir Mo elektronusodinimas, gautų dangų sudėtis ir paviršiaus morfologija, struktūra bei korozinės savybės. W ir Mo lydiniai buvo nusodinami iš citratinių - boratinių ir pirofosfatinių – amoniakinių elektrolitų, o koroziniai tyrimai atlikti sulfatiniuose tirpaluose. Tiriant Co(II) ir Ni(II) elektroredukciją nustatyta, kad voltamperinių kreivių forma primena būdingas mišriai kinetikai voltamperines kreives, jose yra ryškus persilenkimas. Tačiau tyrimai EIS metodu parodė, kad šio persilenkimo negalima sieti su difuziniais apribojimais. Padaryta prielaida apie elektrochemiškai aktyvaus Co arba Ni komplekso lėtą adsorbciją ant elektrodo. Nustatyta, kad Ni elektonusodinimo greitis iš pirofosfatinių tirpalų be amonio jonų yra labai mažas. Pridėjus (NH4)2SO4 ir taip formuojant amoniakinius nikelio kompleksus tirpale, labai pagreitėja Ni elektronusodinimas. Šis efektas labai gerai koreliuoja su didėjančia apskaičiuotų įvairių Ni (II) kompleksų su amonio jonais frakcija. Tačiau amonio jonų buvimas praktiškai neturi įtakos Co elektronusodinimo greičiui. Iš gautų duomenų daroma išvada, kad elektrochemiškai aktyvus Ni ir Co kompleksai yra skirtingi, t.y. CoOH+ ir Ni(NH3)162+ yra krūvį pernešančios dalelės pirofosfatiniuose – amoniakiniuose tirpaluose. Tiriant Co-Mo ir Co-Mo-P lydinius... [toliau žr. visą tekstą]
Electroreduction of various Ni(II) and Co(II) complexes in chloride, sulfate, citrate, pyrophosphate and pyrophosphate –ammonia solutions, electrodeposition of Ni and Co and their alloys with W and Mo and composition of obtained coatings and surface morphology, structure and corrosion properties have been studied. W and Mo alloys were electrodeposited from citrate – borate and pyrophosphate –ammonia solutions, and the corrosion behavior of obtained alloys was investigated in sulfate solutions. The shapes of voltammetric curves obtained for Co(II) and Ni(II) electroreduction are similar to the typical shapes of curves for processes occurring under mixed kinetics, and clear plateau presences in voltammogram. However, based on the data obtained by the electrochemical impedance spectroscopy was confirmed that the obtained plateau does not attribute to the diffusion limitations. A slow adsorption stage of electrochemicaly active complex of Co and Ni on the electrode was assumed. It was determined that Ni electrodeposition rate from pyrophosphate baths without ammonia is relatively small. Adding of (NH4)2SO4 and further forming of Ni(II) complexes with ammonia in the solution accelerates sufficiently the rate of Ni electrodeposition. The effect well correlates with increasing the calculated molar fraction of various ammonia complexes with Ni(II). Based on the received data we conclude that electrochemicaly active Ni and Co complexes are different, i.e. CoOH+ and Ni(NH3)162+... [to full text]

Energy storage provides sustainability when coupled with renewable but intermittent energy sources such as solar, wave and wind power, and electrochemical supercapacitors represent a new storage technology with high power and energy density. For inclusion in supercapacitors, transition metal oxide and sulfide electrodes such as RuO2, IrO2, TiS2, and MoS2 exhibit rapid faradaic electron–transfer reactions combined with low resistance. The pseudocapacitance of RuO2 is about 720 F/g, and is 100 times greater than double-layer capacitance of activated carbon electrodes. Due to the two-dimensional layered structure of MoS2, it has proven to be an excellent electrode material for electrochemical supercapacitors. Cathodic electrodeposition of MoS2 onto glassy carbon electrodes is obtained from electrolytes containing (NH4)2MoS4 and KCl. Annealing the as-deposited Mo sulfide deposit improves the capacitance by a factor of 40x, with a maximum value of 360 F/g for 50 nm thick MoS2 films. The effects of different annealing conditions were investigated by XRD, AFM and charge storage measurements. The specific capacitance measured by cyclic voltammetry is highest for MoS2 thin films annealed at 500°C for 3h and much lower for films annealed at 700°C for 1 h. Inclusion of copper as a dopant element into electrodeposited MoS2 thin films for reducing iR drop during film charge/discharge is also studied. Thin films of Cu-doped MoS2 are deposited from aqueous electrolytes containing SCN-, which acts as a complexing agent to shift the cathodic Cu deposition potential, which is much more anodic than that of MoS2. Annealed, Cu-doped MoS2 films exhibit enhanced charge storage capability about 5x higher than undoped MoS2 films. Coal combustion is currently the largest single anthropogenic source of CO2 emissions, and due to the growing concerns about climate change, several new technologies have been developed to mitigate the problem, including oxyfuel coal combustion, which makes CO2 sequestration easier. One complication of oxyfuel coal combustion is that corrosion problems can be exacerbated due to flue gas recycling, which is employed to dilute the pure O2 feed and reduce the flame temperature. Refractory metal diffusion coatings of Ti and Zr atop P91 steel were created and tested for their ability to prevent corrosion in an oxidizing atmosphere at elevated temperature. Using pack cementation, diffusion coatings of thickness approximately 12 and 20 µm are obtained for Ti and Zr, respectively. The effects of heating to 950°C for 24 hr in 5% O2 in He are studied in situ by thermogravimetric analyses (TGA), and ex situ by SEM analyses and depth profiling by EDX. For Ti-coated, Zr-coated and uncoated P91 samples, extended heating in an oxidizing environment causes relatively thick oxide growth, but extensive oxygen penetration greater than 2.7 mm below the sample surface, and eventual oxide exfoliation, are observed only for the uncoated P91 sample. For the Ti- and Zr-coated samples, oxygen penetrates approximately 16 and 56 µm, respectively, below the surface. In situ TGA verifies that Ti-and Zr-coated P91 samples undergo far smaller mass changes during corrosion than uncoated samples, reaching close to steady state mass after approximately four hours.

De nombreux secteurs industriels ont besoin de matériaux métalliques avec des propriétés de résistance à l'usure et de résistance à la corrosion dans des environnements agressifs ou à des températures élevées très élevées. Ces propriétés spécifiques, notamment mécaniques, électriques, magnétiques et optiques, peuvent être obtenues par la production de couches métalliques. Les revêtements d’alliage ou de métal nanocristallin offrent les caractéristiques de performance souhaitées.L'électrodéposition est un procédé largement utilisé pour fabriquer des revêtements sur des substrats métalliques. La structure et les propriétés des revêtements nanocristallins Co-Mo en font des matériaux prometteurs pour diverses applications. De nos jours, les alliages à base de cobalt sont utilisés dans les avions, l’automobile et l’électronique en raison de leur facilité d’utilisation. En outre, les alliages de cobalt sont largement étudiés en raison de leur utilisation prometteuse pour remplacer les alliages nocifs pour l'environnement dans le corps humain. Les alliages nanocristallins sont utilisés dans de nombreux secteurs industriels, tels que la biologie, l'énergie, la nanotechnologie, l'aviation et bien d'autres.Le but de ce travail est de produire des revêtements nanocristallins de Co-Mo électrodéposés et d'étudier l'effet de la microstructure sur leur résistance à la corrosion dans des solutions physiologiques simulées.Le travail est divisé en cinq chapitres:• Chapitre I. Bibliographie. Aspects métallurgiques de l’ingénierie des surfaces métalliques pour les revêtements nanocristallins de Co-Mo.Dans ce chapitre, les aspects métallurgiques de l’ingénierie de surface des revêtements nanocristallins de Co-Mo sont présentés sur la base des données de la littérature. Différentes méthodes utilisées pour le dépôt de revêtements métalliques sont discutées.• Chapitre II. Echantillons et méthodes et techniques expérimentales.Ce chapitre présente les conditions expérimentales d'électrodéposition pour les revêtements nanocristallins de Co-Mo et les techniques utilisées pour les caractériser.• Chapitre III. Structure, propriétés mécaniques et comportement électrochimique des revêtements nanocristallins Co-Mo.Ce chapitre présente la structure, les propriétés mécaniques et le comportement électrochimique des revêtements nanocristallins Co-Mo déposés sur du cobalt pur.• Chapitre IV. Co-Mo / TiO2 revêtements nano-composites.Ce chapitre présente la structure, les propriétés mécaniques et le comportement à la corrosion des revêtements nano-composites Co-Mo / TiO2 galvanisés sur du cobalt pur.• Chapitre V. Mécanismes de croissance des revêtements nano-composites Co-Mo / TiO2.Ce chapitre étudie la structure des revêtements nanocomposites Co-Mo / TiO2 électrodéposés pour des temps d'électrodéposition courts et longs dans des conditions potentiostatiques sur des électrodes ayant la forme d’un film ou d’un disque.En résumé, des revêtements nanocristallins Co-Mo et des revêtements nanocomposites Co-Mo / TiO2 ont été obtenus par dépôt électrochimique. Leur structure et l'influence de différentes conditions d'électrodéposition sur leur structure ont été étudiées. Leur résistance à la corrosion a été testée dans des solutions physiologiques simulées. De plus, le mécanisme de croissance des couches a été déterminé sur les deux types d'électrodes.Cette thèse a été réalisée sous la forme d'une coopération en Cotutelle entre l'Université des sciences et technologies AGH Stanisław Staszic à Cracovie et l'Université de Bourgogne à Dijon pour promouvoir les relations scientifiques franco-polonaises. Ce travail a été soutenu financièrement par le gouvernement français et l'ambassade de France en Pologne
Currently, various methods are used in surface engineering for the production of surface layers and coatings on many metal substrates to improve their performance. Different industry sectors are oriented to increase the wear resistance and corrosion resistance of materials that are used in aggressive environments or work at high temperatures. Specific properties, including mechanical, electrical, magnetic and optical, can be achieved by the production of metallic layers. Nanocrystalline and amorphous metal or alloy coatings are unique and offer the desired performance characteristics. They are often characterized by very high strength, associated with the effect of strengthening the edge grain.Electrodeposition is a widely used method of producing coatings on metallic substrates. The structure and properties of Co-Mo nanocrystalline coatings make them promising materials for various applications. Nowadays, cobalt based alloys are used in aircraft, automotive and electronics due to their good usability. In addition, cobalt alloys are widely studied due to their promising use in replacing alloys harmful to the environment or the human body. Nanocrystalline alloys are used in many industrial sectors, such as biology, energy, nanotechnology, aviation and many others.The aim of this work is to obtain electrodeposited Co-Mo nanocrystalline coatings and to investigate the effect of microstructure on their corrosion resistance in simulated physiological solutions.The work is divided into five chapters:• Chapter I. Bibliography. Metallurgical aspects of metal surface engineering for Co-Mo nanocrystalline coatings.In this chapter, metallurgical aspects of surface engineering of Co-Mo nanocrystalline coatings are presented on the basis of literature data. Various methods used for deposition of metallic coatings are discussed.• Chapter II. Samples and experimental methods and techniques.This chapter presents experimental electrodeposition conditions for Co-Mo nanocrystalline coatings and techniques used to characterize them.• Chapter III. Structure, mechanical properties and electrochemical behavior of Co-Mo nanocrystalline coatings.This chapter presents the structure, mechanical properties and electrochemical behavior of nanocrystalline Co-Mo coatings deposited on pure cobalt.• Chapter IV. Co-Mo / TiO2 nano-composite coatings.This chapter presents the structure, mechanical properties and corrosion behavior of Co-Mo / TiO2 nano-composite coatings electroplated on pure cobalt.• Chapter V. Growth Mechanisms of Co-Mo / TiO2 nano-composite coatings.This chapter investigates the structure of Co-Mo / TiO2 nanocomposite coatings electrodeposited for short and long electrodeposition times under potentiostatic conditions on the electrode from pure cobalt-shaped cobalt and pure cobalt electrode in the form of a wire.In summary, nanocrystalline Co-Mo coatings were obtained by electrochemical deposition as well as Co-Mo / TiO2 nano-composite coatings. Their structure and the influence of different electrodeposition conditions on the structure were investigated and their corrosion resistance was tested in simulated physiological solutions. In addition, the mechanism of layer growth was determined on two types of electrodes: a disk-shaped electrode and a wire-shaped electrode.This thesis was carried out in the form of Cotutelle cooperation between the AGH University of Science and Technology Stanisław Staszic in Krakow and the University of Burgundy in Dijon to promote Polish-French scientific relations. This work was financially supported by the French government and the French Embassy in Poland

L'électrochimie bipolaire est un phénomène basé sur la polarisation d'un objet conducteur soumis à un champ électrique. Contrairement à l'électrochimie conventionnelle, c’est la chute de potentiel en solution imposée par les deux électrodes sources qui permet de réaliser les réactions électrochimiques. Lorsqu'un objet conducteur est immergé dans une solution électrolytique et soumis à un champ électrique, il est polarisé et se comporte comme une électrode bipolaire. La différence de potentiel entre l'électrolyte et l'électrode bipolaire est la force motrice pour les réactions de réduction et d’oxydation promus aux deux extrémités de l'électrode bipolaire. L'oxydation se produira à l’une des extrémités, combinée simultanément avec la réduction à l'autre extrémité.L'électrochimie bipolaire est une technique d’adressage sans fil qui permet de générer une réactivité électrochimique asymétrique à la surface d'un objet conducteur. Au cours de la dernière décennie, l'électrochimie bipolaire a trouvé de nombreuses applications telles que la synthèse de micro- et nanoparticules asymétriques, l'électrodéposition, la détection, la propulsion de micro-objets, etc. L'avantage de cette technique repose sur le mode d’adressage sans fil qui peut être utilisé pour modifier des matériaux fragiles sans contact ou encore pour modifier simultanément un ensemble de particules en même temps.Dans la présente thèse, l'électrochimie bipolaire a été appliquée à différents matériaux semi-conducteurs et systèmes biologiques. De plus, les nouvelles propriétés générées sur ces nouveaux substrats ont été étudiées en utilisant diverses techniques de caractérisation.L'électrodéposition bipolaire est un outil de choix pour la génération d'objets asymétriques. En utilisant cette approche, un dépôt de métal a été réalisé sur substrats organiques de type complexes de transfert de charge. Ces nouveaux matériaux hybrides métal/organique se sont révélés de bons candidats pour la génération asymétrique de photo-voltage sous illumination.Un matériau semi-conducteur inorganique, tel que les dichalcogénures de métaux de transition a également été utilisé comme substrat pour l'électrochimie bipolaire. Différents dépôts de métaux ont été réalisés sur les macro-particules de MoSe2. Les dichalcogénures de métaux de transition sont également connus pour leur activité électrocatalytique, notamment pour la réaction d'évolution de l'hydrogène. La production d'hydrogène sans fil sur des cristaux de MoSe2 a également été réalisée par électrochimie bipolaire. De plus, l'électrochimie bipolaire peut être utilisée avec une suspension de microparticules de MoSe2 pour réaliser une électrolyse quantitative d’une solution contenant une espèce chimique oxydable.Enfin, l'électrochimie bipolaire pourrait également être utilisée pour étudier indirectement la conductivité de molécules biologiques telles que l’ADN. L'objectif principal était de développer une méthode en électrochimie bipolaire pour la modification asymétrique de l'ADN par des nanoparticules métalliques. Tout d'abord, des expériences ont été réalisées en utilisant l'électrodéposition bipolaire à l’aide d’une électrophorèse capillaire (CABED) suivie d'une imagerie par TEM. Des résultats positifs ont été obtenus mais avec une faible reproductibilité.La seconde approche consiste à étirer des molécules d'ADN sur une surface isolante par peignage et à visualiser cette fois-ci les dépôts par microcopie AFM
Bipolar electrochemistry is a phenomenon based on the polarization of conductive objects in an electric field. In contrast to conventional electrochemistry, the drop of potential in the electrolyte solution triggers the involved redox reactions. When a conductive object is positioned in an electric field present in a solution between two feeder electrodes, it is polarized and becomes a bipolar electrode. The potential difference between the electrolyte and the bipolar electrode is the driving force for reduction/oxidation reactions at the two extremities of the bipolar electrode; oxidation will occur at one end, combined simultaneously with reduction at the other end.Bipolar electrochemistry is a concept that allows generating an asymmetric reactivity at the surface of a conductive object. During the last decade, bipolar electrochemistry found many applications such as the synthesis of asymmetric micro- and nano-particles, electrodeposition, sensing, propulsion of microobjects, electroanalysis etc. The advantage of this technique is its wireless character, which allows the modification of delicate materials and also to electrochemically address many objects simultaneously.In the present thesis, the approach was applied to different semiconducting materials and biological systems. In addition, properties of substrates of different nature have been studied using bipolar electrochemistry.In this way, it was possible to create metal deposits on organic charge transfer salts in a site-specific way. The resulting hybrid metal/organic particles were tested for the asymmetric generation of photovoltage under illumination.Inorganic transition metal dichalcogenides were also used as a substrate for bipolar electrochemistry. Deposition of different metals on MoSe2 macroparticles was performed. Transition metal dichalcogenides are known for their catalytic activity with respect to hydrogen evolution reaction. Therefore, wireless hydrogen production on MoSe2 crystals and microparticles could be demonstrated by using bipolar electrochemistry. In the latter case it is possible to envision their use for electrochemical decontamination of solutions in the bulk.Finally, bipolar electrochemistry has also been used for studying the conductivity of biological molecules (DNA). The primary goal was to develop a new approach for the asymmetric modification of DNA by metal nanoparticles. Experiments were performed by using either Capillary Assisted Bipolar Electrodeposition (CABED) with the DNA molecules present in the bulk, or by immobilizing DNA as stretched entities on model surfaces for subsequent modification. Encouraging first results could be evidenced by TEM or AFM measurements

碩士
大同大學
化學工程學系(所)
104
In this study, molybdenum disulfide (MoS2) thin films were directly deposited on fluorine-doped tin oxide (FTO) glass substrates via potentiostatic (PS) and pulse-reversal (PR) methods in deposition bath containing [NH4]2MoS4 and KCl at 60℃. The effects of the composition and pH value of the deposition bath on the electrocatalytic activity of the as-prepared MoS2 were systemically investigated. According to the results of Raman spectra, X-ray photoelectron spectroscopy, and scanning electron microscope analyses confirmed that the amorphous structured MoS2 CEs were successfully deposited homogeneous on FTO glass substrates while using PS and PR methods. Firstly, we using the PS mode to find that the addition of KCl into the deposition bath can efficiently enhance the deposition rate of MoS2. However, MoS2-PS9 at -1.0V, MoS2-PS5 at -0.9V have great electrocatalytic activity. Secondly, we proposed a PR mode to further improve the electrocatalytic activity of the electrodeposited MoS2 CEs. It demonstrated an impressive lower charge-transfer resistance (Rct ~18.4Ω). Also, the DSSC using MoS2-PR5 offered outstanding power conversion efficiency of 8.77%, which is as similar as Pt (9.01%) CE. However, MoS2-PR5 have great transmittance, so that the CE offered the power conversion efficiency of 4.82% on the rear, which is as similar as Pt (5.41%) CE. Moreover, it can be a bifacial CE for DSSC. Finally, we employed the optimal deposition condition to deposite MoS2 thin film on ITO-PEN substrate. The as-prepared flexible MoS2-PR5 still demonstrated excellent electrocatalytic activity. The DSSC based on the flexible MoS2-PR5 can achieve the power conversion efficiency of 5.40%.

碩士
國立中山大學
材料與光電科學學系研究所
107
In this study, an electrodeposition method is used to synthesize a nickel molybdenum sulfide (NiMoS) electrocatalyst for hydrogen evolution. The electrodeposition method has many advantages, including scalability and can be carried out at ambient temperature. Nickel-based metal sulfides are widely used as hydrogen evolution electrocatalyst since nickel is Earth-abundant and synergistic effects can be aroused from nickel and other transition metals. The results of X-Ray diffractometer analysis, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy suggest that NiMoS is a mixed phase composed of metallic nickel, part of Mo doped Ni3S2, nickel hydroxide, nickel oxide, and molybdenum oxide. Electrochemical study suggests NiMoS can be operated in near-neutral electrolyte for at least 2 hours. The NiMoS also shows high electrocatalytic activity with an overpotential of 220 mV at a current density of -1 mA/cm2 , and its Faraday efficiency for hydrogen evolution is close to 90%.