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1
Arán-Ais, Rosa M. « Interfacial reactivity : model surfaces and tailored shape-controlled nanocatalysts ». Doctoral thesis, Universidad de Alicante, 2016. http://hdl.handle.net/10045/70091.
Texte intégralRésumé :
El trabajo realizado en esta tesis ha seguido dos líneas de investigación principales: por un lado, el uso de electrodos monocristalinos de Pt ha permitido realizar estudios fundamentales de la interfase electrodo│disolución, así como de la electrocatálisis de moléculas orgánicas simples (C2) bifuncionalizadas, y por otro lado, el efecto que la estructura superficial ejerce sobre la electrocatálisis de ciertas reacciones se ha aplicado a la síntesis y caracterización de nanopartículas de Pt con forma controlada. Este campo se ha ampliado al estudio de nanocatalizadores bimetálicos y trimetálicos para la ORR. El estudio que aquí se presenta ha profundizado en el conocimiento sobre las relaciones que hay entre estructura superficial – actividad – y estabilidad morfológica y composicional de electrocatalizadores basados en Pt destinados a PEMFCs.
2
Myedi, Noluthando. « Electrochemical kinetics and sensing of conjugated dienes in acetonitrile ». University of the Western Cape, 2011. http://hdl.handle.net/11394/5424.
Texte intégralRésumé :
>Magister Scientiae - MScThis thesis focuses on the electroanalysis of some dienes (2-methyl-1.3-butadiene (MBD), tran-1.3-pentadiene (PD), 1.3-cyclohexadiene (CHD) and 3-cyclooctadiene (COD)) found in gasoline and the development of simple electrochemical diene sensors. The detection of dienes in fuels is important as they readily polymerise and form gum in fuel tanks. The electroctivity of the dienes was studied with glassy carbon electrode (GCE) and Pt electrode in tetrabutylammonium perchlorate (TBAP)/acetonitrile solution. Polyaniline-polystyrene sulfonic acid (PANi-PSSA) composite films were electro-deposited or drop-coated on GCE, with and without gold nanoparticles (AuNPs) and characterized by cyclic voltammetry (CV), high resolution transmission electron microscopy (HRTEM) and ultraviolet-visible (UV-vis) spectroscopy. Both composite polymers were found to be of nanofibral structure, and the spherical gold nanoparticles were dispersed uniformly within the polymer. The dienes exhibited no redox peaks on GCE/PANi-PSSA and GCE/PANi-PSSA/AuNPs electrode systems from -1.0 V to +1.5 V, beyond which PANi would overoxidize and lose its electroactivity. Therefore, cyclic voltammetry and steady state amperometry of the four dienes (MBD, PD, CHD and COD) were studied with unmodified Pt and GCE electrodes. Subtractively normalised interfacial-fourier transform infra-red (SNIFTIR) spectroscopic studies of the dienes were performed with Pt electrode. SNIFTIR data showed that there was a definite electro-oxidation of 1.3-cyclohexadiene as electrode potential was changed from E = 770 mV to E = 1638 mV. Severe electrode fouling was observed when steady state amperometric detection of CHD, as a representative diene, was performed on Pt electrode. Randel-Sevčik analysis of the CVs of the dienes on Pt electrode gave diffusion coefficient (Dox) values of 10.65 cm²/s, 9.55 cm²/s, 3.20 cm²/s and 3.96 cm²/s for CHD, COD, PD, and MBD, respectively. The corresponding detection limits (3σn-1) were 0.0106 M, 0.0111 M, 0.0109 M, and 0.0107 M.
3
Briega-Martos, Valentín. « Unraveling the oxygen reduction reaction mechanism : occurrence of a bifurcation point before hydrogen peroxide formation ». Doctoral thesis, Universidad de Alicante, 2019. http://hdl.handle.net/10045/102311.
Texte intégralRésumé :
En la presente tesis doctoral se realiza un estudio detallado sobre el mecanismo de la reacción de reducción de oxígeno (ORR) en electrodos monocristalinos de platino. Para ello, se han realizado medidas electroquímicas usando la configuración de electrodo rotatorio de menisco colgante (HMRDE) con superficies con distinta estructura superficial y variando condiciones de la disolución de trabajo como el pH, fuerza iónica o la ausencia o presencia de bromuros. La conclusión principal que se extra de estos experimentos es la posibilidad de la existencia de un punto de bifurcación en el mecanismo, implicando el intermedio OOH, antes de la formación de peróxido de hidrógeno. Además, también se estudia la ORR y la reacción de oxidación de ácido fórmico en electrodos monocristalinos de Pt en presencia de acetonitrilo, como estudio previo al estudio de estas reacciones en disolventes orgánicos con pequeñas cantidades de agua. Por último, se estudia la ORR en un Aza-CMP, lo cual permite obtener información fundamental que se puede aplicar en estudios sobre el mecanismo de la ORR en los sitios activos de materiales de carbón funcionalizados con nitrógeno.
4
Khanfar, Mohammad F. « Molybdenum-modified platinum electrodes / ». Internet access available to MUN users only, 2003. http://collections.mun.ca/u?/theses,160874.
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5
Koda, Ryo. « Electrochemical deposition of metal on microporous silicon electrodes influenced by hydration structures of solutes and electrode surfaces ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199323.
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6
Morimoto, Yu. « Electrochemical oxidation of methanol on platinum and platinum based electrodes ». Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058206604.
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7
Rudge, Andrew John. « The photoelectrochemistry of platinum ». Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358597.
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8
Aixill, W. Joanne. « Electrode processes ». Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:9578fd22-42fe-41cc-9d92-96f8272956d8.
Texte intégralRésumé :
The work presented in this thesis first characterises a high speed channel flow cell and then applies the system to the electro-reduction of nitromethane in aqueous solution. Potential step transient measurements are carried out with the current-time transients simulated using a model based on the absence of axial diffusion. The excellent agreement between theory and experiment confirms the proposed mass transport model and further demonstrates that the combination of current-time transients recorded using the high speed channel flow cell and numerical simulations provide a powerful tool to access homogeneous rate constants of the order 1 x 106s̄¹. The high speed channel flow cell is then used in combination with a range of complementary electrochemical techniques, numerical modelling, in-situ ESR, single crystal experiments and kinetic isotope measurements to infer a mechanistic scheme for the complex electro-reduction pathway of nitromethane in aqueous solution. Platinum, gold, mercury/copper and mercury/gold electrodes are investigated enabling the most conclusive description of the reduction mechanism to date. The reaction pathway is shown to follow an ECEEE type process with the chemical step proceeding at the electrode surface. The heterogeneous rate constant, khet, describing the chemical step is calculated for each electrode surface. For platinum in the pH range 7.0 - 9.0 this value is 0.3 ± 0.06 cm s̄¹. For mercury/copper it is 0.18 cm s̄¹, for gold/mercury it is 0.06 cm s̄¹ and for Au it is 0.095 cm s̄¹. Consideration of these values shows a surprising independence of the heterogeneous rate constant on the chemical identity of the surface with all of the values being similar to within less than an order of magnitude. The reason for the apparent paradox of the observed surface indifference of the chemical reaction step is explained by a homogeneous H transfer from the carbon to the oxygen of the nitromethane radical anion, formed form the initial electron transfer step, occurring in the layer of solution immediately adjacent to the electrode solution as shown in the scheme below. The resulting species, •CH2 N(OH))ˉ then undergoes a rapid irreversible adsorption to the electrode surface and subsequent transformation to the final product the hydroxylamine, CH3NHOH. It is proposed that if the energy barrier to the adsorption of •CH2 N(OH))ˉ is less than that required for the H atom transfer then the reaction rate will be insensitive to the adsorption step and hence the chemical identity of the electrode. This introduces the concept of a whole new electrochemical process: the surface indifferent electrocatalytic reaction.
9
Jayaratna, Husantha G. « Stripping/plating analysis at carbon and metallic interdigitated electrodes / ». The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487848078449337.
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10
Pegg, David John. « Structural and chemical promotion of platinum electrodes ». Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242320.
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11
Sandoval, Andrea P. « Reacciones electroquímicas modelo en la interfaz líquido iónico-electrodo monocristalino de platino ». Doctoral thesis, Universidad de Alicante, 2015. http://hdl.handle.net/10045/53433.
Texte intégralRésumé :
Las reacciones de oxidación de hidrógeno, reducción de oxígeno y la síntesis de PEDOT fueron evaluadas en líquidos iónicos y sobre electrodos monocristalinos de platino mediante técnicas electroquímicas clásicas, impedancia electroquímica, microscopía de fuerza atómica y espectroscopia infrarroja de reflexión externa. Se desarrolló un protocolo de purificación del líquido iónico y de la limpieza de los electrodos monocristalinos para garantizar condiciones reproducibles, y se observó que las reacciones de oxidación de hidrógeno y de polimerización son sensibles a la estructura superficial del electrodo, no así la reducción de oxígeno, cuyos productos no son estables en esta interfaz. Además, el comportamiento del PEDOT muestra una dependencia sistemática de las propiedades y del tamaño de los iones de los líquidos iónicos, junto con alta velocidad de intercambio iónico y altos niveles de dopado tipo-n. El PEDOT mostró ser catalítico también, en este medio, frente a la reacción del DMcT, aunque no en la misma proporción que se observa en los disolventes moleculares. Finalmente, este estudio permitió profundizar en los factores que afectan la transferencia de carga en la interfaz electrodo-electrolito.
12
Sheppard, Sally-Ann. « Characterisation of dispersed, platinum-coated fuel cell electrodes ». Thesis, University of Portsmouth, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264837.
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13
Sanchez, Pablo Lozano. « Fabrication and electroanalytical properties of mesoporous platinum electrodes ». Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413929.
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14
Clark, Stacey L. « Sonovoltammetric detection of cadmium (II) at mercury thin film electrodes ». Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1422.
Texte intégralRésumé :
Thesis (M.S.)--West Virginia University, 2000.Title from document title page. Document formatted into pages; contains vii, 57 p. : ill. Includes abstract. Includes bibliographical references (p. 55-57).
15
Ahmed, Mujib. « An electrochemical study of well-defined nafion coated platinum and platinum-bimetallic electrodes ». Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/42261/.
Texte intégralRésumé :
In this investigation, cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and rotating disc electrode (RDE) measurements of the oxygen reduction reaction (ORR) have been used to explore the complex three-phase Nafion-platinum-electrolyte interface. This interface is at the heart of the functioning membrane electrode assembly (MEA) of a fuel cell. CV was primarily used to analyse ultra-thin Nafion films, deposited (without contamination) onto various flat and stepped platinum and platinum bimetallic single crystal electrodes. For Pt{111}, XPS measurements were also used to determine Nafion surface layer thickness and to obtain surface chemical composition. CV results have shown that Nafion is a probe of adsorbed OH on platinum electrodes and for stepped surfaces, unusual structural sensitivity of Nafion-induced voltammetric peaks, ascribable to Nafion interactions with step sites, is observed as a function of average terrace width. Voltammetric results for palladium adlayers (up to two monolayers) adsorbed on Nafion coated Pt{111} and {100} in aqueous 0.1M HClO4, show the first layer palladium hydrogen underpotential deposition (HUPD) peak being much sharper and intense as compared to Nafion free surfaces. A similar phenomenon was found for platinum-palladium surface alloys in that Nafion adsorption would produce sharper, palladium HUPD peaks. This behaviour is ascribed to stronger specific adsorption of the Nafion sulphonate groups with palladium compared to platinum. It was interesting to note that for bismuth adlayers adsorbed onto Nafion coated Pt{111} and {100}, attenuation of HUPD features was identical whether or not Nafion was adsorbed but the Bi-OH redox features for Nafion coated surfaces exhibited marked differences, again ascribable to competitive adsorption of sulphonate and OH. Using RDE, it was found that the ORR for various Nafion coated Pt{hkl} electrodes was inhibited compared to Nafion free electrodes. The electrooxidation of formic acid on palladium modified, Nafion coated Pt{111}, in aqueous 0.1M HClO4, was found not to be affected by the presence of Nafion. However methanol electrooxidation was inhibited on palladium modified, Nafion coated Pt{111}. Finally a number of actual fuel cell electrocatalysts, provided by Johnson Matthey were characterised using CV. The {111} and {100} surface site densities were quantified using bismuth and germanium as surface probes. Comparisons between Nafion coated electrocatalysts and Nafion free electrocatalysts are also reported. It was found that only very marginal differences between the CV responses of both types of catalyst are recorded (in contrast to the single crystal data).
16
Brew, Ashley. « Electrochemical studies of the oxygen reduction reaction : platinum and platinum bimetallic single crystal electrodes ». Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/88050/.
Texte intégralRésumé :
The general objective of this investigation was to elucidate the effect that surface species such as OHads, Oads and the interfacial water layer have on the oxygen reduction reaction activity of active platinum and platinum alloy catalysts in perchloric acid electrolyte. To that end, these are the investigations that were carried out: [Pt n{111}x{100}] and [Pt n{100}x111}] series of surfaces. These surfaces exhibit OHads/Oads formation at terrace and step sites in the potential range relevant to loss in ORR activity. The increase in activity observed at low step density was assigned to the disruption by steps of a long range ordered OHads terrace over-layer. Hydrogen peroxide oxidation/reduction reaction activity of [Pt n{111}x{100}] and [Pt n{100}x{111}] series of surfaces. The results imply that if oxygen reduction proceeds via the series pathway the rate determining step lies in the later stages of the reaction, i.e after H2O2 formation. CV and ORR of kinked surfaces based upon Pt{332}. These results indicate that low-coordinate {100} kink sites do not have unique ORR activity, i.e. their activity is identical to {100} linear step sites. CV, XPS, STM and ORR of single crystal Pt{111}-M (where M=Ni, Co or Fe) alloy surfaces showed that the onset of electrochemical oxide formation shifts positive in the order Ni, Co, Fe. This shift correlated with increased activity towards the ORR which we ascribe to the greater availability of highly active metallic sites for oxygen reduction at ORR potentials. (1x1) and disordered (1x2) surface atomic arrangements of Pt{110} were created and compared. For the first time, the voltammetry of the Pt{110}-(1x1) surface has been reported in aqueous perchloric acid and sodium hydroxide. The activity of the Pt{110}-(1x1) surface for oxygen reduction was found to be approximately 30 - 40 mV less active than the disordered (1x2) surface.
17
Hudak, Eric Michael. « Electrochemical Evaluation of Platinum and Diamond Electrodes for Neural Stimulation ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1301967862.
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18
Lin, Zhan. « Platinum and Platinum Alloy-Carbon Nanofiber Composites for Use as Electrodes in Direct Methanol Fuel Cells ». NCSU, 2010. http://www.lib.ncsu.edu/theses/available/etd-03312010-171722/.
Texte intégralRésumé :
In response to the energy needs of modern society and emerging ecological concerns, the pursuit of novel, low-cost, and environmentally friendly energy conversion and storage systems has raised significant interest. Among various energy conversion and storage systems, fuel cells have become a primary research focus since they convert chemical energy directly into electrical energy with high efficiency and low pollutant emissions. For example, direct methanol fuel cells (DMFCs), which supply the electrical energy by converting methanol to energy, are an ideal fuel cell system for applications in electric vehicles and electronic portable devices due to their relatively quick start-up, rapid response to catalyst loading, and low operating temperature. However, the wide commercial use of DMFCs in advanced hybrid electric vehicles and electronic portable devices is hampered by their high cost, poor durability, and relatively low energy and power densities. In order to address these problems, their research focuses on the development of highly active electrode catalysts coupled with a suitable electrode structure for the oxidation of methanol at the anode and the reduction of oxygen at the cathode to attain high efficiency of DMFCs, and subsequently lowering the cost. In this dissertation, the fabrication of novel platinum and platinum alloy nanoparticle-loaded carbon nanofibers (CNFs) for use as electrodes in DMFCs is demonstrated through electrospinning, carbonization, and deposition. The resulting CNF-based electrodes possess the properties of high electroactive surface area, good catalytic abilities towards the oxidation of methanol and the reduction of oxygen, and great long-time stability. As a result, DMFCs using these CNFs-supported platinum and platinum alloy nanoparticles as electrodes offer many advantages, such as improved electrocatalytic abilities, long-term stability, easy fabrication, low cost, and environmental benignity. Therefore, this new technology opens up new opportunities to develop high-performance electrode materials in the future for high-performance DMFCs, which are one of the promising power sources for consumer devices and electric vehicles, and play a critical role in solving the worldwide critical energy issue.
19
Noh, Tae-Geun. « Spatiotemporal pattern formation in the electro-oxidation of formic acid on Pt effect of electrode geometry and lowered symmetry / ». [S.l. : s.n.], 2005. http://www.diss.fu-berlin.de/2005/108/index.html.
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20
Mougenot, Mathieu. « Elaboration et optimisation d'électrodes de piles PEMFC à très faible taux de platine par pulvérisation plasma ». Phd thesis, Université d'Orléans, 2011. http://tel.archives-ouvertes.fr/tel-00667739.
Texte intégralRésumé :
Cette thèse réalisée dans le cadre des projets PIE CNRS AMELI-0Pt et AMEPlas et ANR AMADEUS a regroupé plusieurs entités autour de la thématique des piles à combustible : Dreux Agglomération puis l'Agence Innovation Made In Dreux (MID), le GREMI, le LACCO et initialement l'industriel MHS Equipment. L'objectif de ce travail est l'élaboration par voie plasma et l'optimisation d'électrodes de piles à combustible de type PEMFC et SAMFC dans le but d'obtenir de bonnes performances avec des charges de platine ultra faibles ou sans platine. Le projet a été organisé en quatre étapes : l'étude de la croissance simultanée de platine et de carbone co-pulvérisés par plasma, la dispersion optimale de quantités ultra faibles de catalyseur, le remplacement du platine par un alliage bimétallique à base de palladium, et le dépôt direct du catalyseur sur la membrane par plasma. En utilisant un faisceau synchrotron de rayons X (Synchrotron SOLEIL), en collaboration avec le CRMD, l'étude GISAXS des couches minces Pt-C co-pulvérisés a révélé l'organisation particulière du platine dans ce type de nanostructure. Ces couches minces Pt-C offrent d'excellentes performances (20 kW.gPt-1) avec des charges de platine ultra faibles. Des électrodes PdPt (5 %at Pt) faiblement chargées permettent d'atteindre de bonnes performances en PEMFC quasiment sans platine (12,5 kW.gPd-1 et 250 kW.gPt-1). L'étude de l'activité de catalyseurs PdAu vis-à-vis de l'oxydation du glycérol a révélé l'origine des effets synergiques du palladium et de l'or en milieu alcalin. Le dépôt plasma direct de platine associé ou non au dépôt de carbone sur membrane a été optimisé. Les performances obtenues avec des CCM (Catalyst Coated Membrane) plasma démontrent l'intérêt de ce type d'architecture.
21
Singer, Simcha Lev. « Low platinum loading electrospun electrodes for proton exchange membrane fuel cells ». Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38280.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 104-106).
An experimental study was performed to evaluate the utility of electrospun carbon nanofiber supports for sputtered platinum catalyst in proton exchange membrane fuel cells. The performance of the sputtered nanofiber supports was similar to that of sputtered commercial gas diffusion layers in single cell fuel cell tests. However, sputtered platinum electrodes performed significantly worse than commercial thin film electrodes due to high activation and concentration voltage losses. Cyclic voltammetry and rotating disc electrode experiments were performed in order to evaluate the influence of platinum loading and particle size on the electrochemical active area and oxygen reduction performance of the sputtered platinum. Active area per weight catalyst decreased with sputtering time, and the oxygen reduction activity slightly increases with increasing sputtering time. Both of these effects are thought to be due to increasing platinum particle size as sputtering time is increased.
by Simcha Lev Singer.
S.M.
22
Hunter, Katherine. « Fundamental studies of electrochemical oxide formation on platinum single crystal electrodes ». Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/100871/.
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Platinum single crystal electrodes were used to investigate electrochemical oxides and related surface species and their impact upon important catalytic reactions such as the oxygen reduction reaction (ORR). Notions of perchlorate anions being “non-specifically adsorbed” were re-evaluated and challenged. For example, the voltammetry of Pt single crystal electrodes as a function of perchloric acid concentration (0.05–2.00 M) was studied in order to test the assertion by Watanabe et al. that perchlorate anions specifically adsorb on polycrystalline platinum. Specific adsorption of perchlorate anions was found in varying degrees for Pt(hkl) surfaces. By flame-annealing and cooling a series of Pt n(110)x(111) and Pt n(110)x(100) single crystal electrodes in a CO ambient, new insights into the nature of the electrosorption processes associated with Pt{110} voltammetry in aqueous acidic media were elucidated. For Pt n(110)x(111) electrodes, a systematic change in the intensities of voltammetric peaks indicated a lack of surface reconstruction (in contrast to hydrogen cooled analogues). Pt n(110)x(100) stepped electrodes displayed a marked tendency towards surface reconstruction irrespective of cooling environment. Pt(110) terrace sites were found to afford a specific affinity for sulphonate groups contained within a Nafion adlayer. Pt n(100)x(110) surfaces showed rapid quenching of the Nafion ‘spike’ as a function of increasing step density. Reactivity measurements involving oxygen reduction and hydrogen peroxide oxidation/reduction largely revealed the importance of adsorbed oxide/OH in regulating activity. Kinetic studies suggested that for Pt(100) terraces, oxide formation was also accompanied by rapid surface reconstruction. Fast potential cycling of all electrode surfaces confirmed the likelihood of structural changes occurring in real fuel cells. It is deduced that roughened catalyst particles should actually exhibit an enhanced ORR activity, even in the presence of Nafion.
23
Williams, Mario. « Characterization of platinum-group metal nanophase electrocatalysts employed in the direct methanol fuel cell and solid-polymer electrolyte electrolyser ». Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&.
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Bauer, Alexander Günter. « Direct methanol fuel cell with extended reaction zone anode : PtRu and PtRuMo supported on fibrous carbon ». Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/913.
Texte intégralRésumé :
The direct methanol fuel cell (DMFC) is considered to be a promising power source for portable electronic applications and transportation.
At present there are several challenges that need to be addressed before the widespread commercialization of the DMFC technology can be implemented. The methanol electro oxidation reaction is sluggish, mainly due to the strong adsorption of the reaction intermediate carbon monoxide on platinum. Further, methanol crosses over to the cathode, which decreases the fuel utilization and causes cathode catalyst poisoning. Another issue is the accumulation of the reaction product CO₂ (g) in the anode, which increases the Ohmic resistance and blocks reactant mass transfer pathways.
A novel anode configuration is proposed to address the aforementioned challenges. An extended reaction zone (thickness = ∼100-300 µm) is designed to facilitate the oxidation of methanol on sites that are not close to the membrane-electrode interface. Thus, the fuel concentration near the membrane may decrease significantly, which may mitigate adverse effects caused by methanol cross-over. The structure of the fibrous electrode, with its high void space, is believed to aid the disengagement of CO₂ gas.
In this thesis the first objective was to deposit dispersed nanoparticle PtRu(Mo) catalysts onto graphite felt substrates by surfactant mediated electrodeposition. Experiments, in which the surfactant concentration, current density, time and temperature were varied, were conducted with the objective of increasing the active surface area and thus improving the reactivity of the electrodes with respect to methanol electro-oxidation. The three-dimensional electrodes were characterized with respect to their deposit morphology, surface area, composition and catalytic activity.
The second objective of this work was to utilize the catalyzed electrodes as anodes for direct methanol fuel cell operation. The fuel cell performance was studied as a function of methanol concentration, flow rate and temperature by using a single cell with a geometric area of 5 cm².
Increased power densities were obtained with an in-house prepared 3D PtRu anode compared to a conventional PtRu catalyst coated membrane.
Coating graphite felt substrates with catalytically active nanoparticles and the utilization of these materials, is a new approach to improve the performance of direct fuel cells.
25
Hogarth, Martin P. « The development of the direct methanol fuel cell ». Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295055.
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Abaoud, Hassan Abdulaziz. « Studies on proton exchange membrane fuel cells with low platinum loading electrodes ». Thesis, Cranfield University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422711.
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Maxakato, Nobanathi Wendy. « Electrocatalysis of fuel cell molecules on carbon nanotube platinum-ruthenium based electrodes ». Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/30786.
Texte intégralRésumé :
The investigation of the kinetics of fuel cell (FC) molecules such as methanol (MeOH), ethylene glycol (EG) and formic acid (FA) on platinum (Pt), platinum/ruthenium (PtRu) and platinum based metal complexes (ruthenium tetrakis(diaquaplatinum)octacarboxy-phthalocyanine (RuOcPcPt) modified basal plane pyrolytic graphite electrode (BPPGE) was carried out. One of the major limitations of FC molecules is that Pt undergoes surface poisoning by strongly adsorbed reaction intermediates, carbon monoxide (CO) that eventually decreases the fuel cell efficiency. Thus, the integration of Pt and or Pt/Ru with functionalized multi-walled carbon nanotubes (fMWCNTs) and some N4-macrocycles such as ruthenium phthalocyanine complexes on the BPPGE towards these FC molecules have been studied in this work. However, this study focused mainly on Pt, Pt/Ru, ruthenium octacarboxy-phthalocyanine (RuOcPc) and RuOcPcPt nanoparticles. The MWCNTs, metal and N4-macrocycles provided the needed platform for the efficient electrooxidation of FC molecules with minimum or no poisoning. The first part of the thesis deals with electrocatalytic oxidation of the FC molecules using electrodes prepared by electrodeposition techniques. The section describes the comparative electrocatalytic behaviour of MeOH, EG and FA at MWCNT-Pt/Ru immobilized on BPPGE. The Pt/Ru nanoparticles were deposited on the substrate using the electrodeposition technique. The second part of this work deals with electrocatalysis of the FC molecules using BPPG electrode modified with chemically synthesized Pt nanoparticles integrated with RuOcPc. In both cases, successful modification of the electrodes with the metal nanoparticle/carbon nanotube or metal nanocomplex nanocomposite was established using the field emission /high resolution scanning electron microscopy (FESEM/HRSEM), high resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) spectroscopy and electron dispersive x-ray spectroscopy (EDS). The average particle size for the synthesised Pt nanoparticles is 1.4 nm. The electrocatalytic behaviour of the modified electrodes was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results of the electrodeposition study showed that the presence of Pt nanoparticles, together with Ru nanoparticles, gave better performance with the FA showing the least tolerance to electrode poisoning. The impedance spectra of the MWCNT-Pt/Ru hybrids in all the FC materials studied showed some dependence on the oxidation potential. These spectra were somewhat complicated but generally followed electrical equivalent circuit models characteristic of adsorption-controlled charge transfer kinetics. EG and MeOH showed conventional positive Faradaic impedance spectra, irrespective of the applied oxidation potential. FA impedance spectra exhibited an inductive loop only at the extreme forward anodic peak potential, characteristic of Faradaic current being governed by the occupation of an intermediate state. On the other hand, the presence of phthalocyanine with the synthesized Pt-Ru nanocatalysts showed an improvement on the tolerance to CO poisoning during MeOH oxidation and therefore its application in the direct fuel cell oxidation is encouraged. The synthesized Pt-based nanoparticles gave better performance compared to the electrodeposited Pt-based nanoparticles. The comparative electrocatalytic behaviour of the chemically synthesized nanocatalysts indicated that the BPPGE-fMWCNT/RuOcPcPt electrode gives the best performance towards MeOH oxidation compared to other electrodes studied, while FA oxidation was favoured on the BPPGE-RuOcPcPt electrode without CNTs support. However, EG oxidation was not successful at the electrodes at all. The oxidation of these FC molecules are characterized by both diffusion (forward) and adsorption-controlled (reverse) processes. The two electrodes (BPPGE-fMWCNT/RuOcPcPt and BPPGE-RuOcPcPt) gave better tolerance to oxidation poison with the ratio of the current density of the forward anodic peak to the reverse anodic peak (Jfa/Jra) and (Jfa1/Jfa2) of 4.0 and 1.0 respectively. The electrodeposited and chemical synthesized nanocatalysts results shown in this work have for the first time provided some useful insights into the electrocatalytic response of FC molecules (MeOH, FA, EG) for potential application in fuel cell technology.
The third part of the thesis describes the electrocatalytic reduction of molecular oxygen in alkaline solution using a novel ruthenium tetrakis (diaquaplatinum)octacarboxyphthalocyanine (RuOcPcPt) electrocatalyst supported on MWCNTs. The results revealed that the MWCNT-RuOcPcPt electrode is electro-catalytically active than MWCNT, MWCNT-RuOcPc, RuOcPc and RuOcPcPt electrodes towards oxygen reduction reaction. The study shows that the oxygen reduction activity follows a direct 4-electron transfer process with high kinetic rate constant, 3.57 x 10-2 cm s-1. The results obtained imply that more energy has been achieved and therefore the electrode is a promising candidate as a catalyst in the cathodic reaction of fuel cell.Thesis (PhD)--University of Pretoria, 2012.
Chemistry
Unrestricted
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Olivera, Bernat. « Electronic transport in metals at the atomic scale : capacitance emergent magnetism and f-electrons influence ». Doctoral thesis, Universidad de Alicante, 2017. http://hdl.handle.net/10045/73051.
Texte intégralRésumé :
Hemos desarrollado una técnica de medida a 4 puntas en corriente alterna con amplificadores “Lock-in” sincronizados para obtener la variación local de la capacidad entre los electrodos de un STM simultáneamente con su conductancia. La resolución a la que llegamos es de fF. En la evolución de la capacidad frente a la distancia entre electrodos distinguimos tres regiones: capacidad clásica (cuando los electrodos están más alejados), capacidad cuántica (en un régimen intermedio) y fuga de capacidad (cuando se entra en corriente túnel). En el régimen de emisión de campo, en los puntos en los que la energía incidente del electrón coincide con la de los niveles discretos por encima de la barrera túnel, se produce fuga de capacidad. Por otro lado, hemos encontrado evidencias de una emergencia del momento magnético en cadenas atómicas de platino que conectan dos electrodos hechos del mismo metal. El ajuste de las anomalías a voltaje de polarización cero a la función Kondo-Fano muestra un apantallamiento del momento magnético por parte de los electrones de conducción. Por último, hemos estudiado el papel que juegan los electrones f en el transporte electrónico en nanocontactos. Para ello, hemos realizado medidas de corriente eléctrica en nanocontactos hechos de gadolinio y europio, respectivamente. Hemos visto que para ambos metales la conductancia del contacto de un átomo está por debajo del cuanto de conductancia. Asimismo, los histogramas de conductancia en Gd son reproducibles lo cual contrasta con el caso de Eu en el que dichos histogramas no muestran tal reproducibilidad. Atribuimos este último hecho al desorden magnético que los electrones f causan en el metal. Con el ajuste de las anomalías a voltaje cero a la función Kondo-Fano hemos visto que los electrones f son apantallados por los de conducción. Además, en el caso de Gd vemos que presenta dos temperaturas Kondo, debidas al apantallamiento de los electrones d y f, respectivamente.
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Foster, Simon Edward. « Routes to interfacial deposition of platinum microparticles in solid polymer fuel cells ». Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/28053.
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Mayedwa, Noluthando. « Development of platino-iridium/ruthenium telluride nanoalloy electrode systems for possible application in ammonia fuel cell ». University of the Western Cape, 2015. http://hdl.handle.net/11394/5018.
Texte intégralRésumé :
Philosophiae Doctor - PhDSouth Africa is undergoing a serious consideration of hydrogen economy in an effort to develop safe clean and reliable alternative energy sources for fossil fuels. Ammonia is one of the promising candidates due to its low production cost, ease in liquefaction at ambient temperatures, and high energy density as compared to methanol. Ammonia has a high content of hydrogen atoms per unit volume and can easily be cracked down into hydrogen and nitrogen. In the last four years carbon intensive coal dependent South Africa has become one of the leading global destinations for renewable energy investment. Another driving force behind the technology is the prevalence of platinum reserves found in South Africa. Platinum group metals are the key catalytic materials used in most fuel cells, and with more than 75 % of the world’s known platinum reserves found within South Africa. In this thesis, I have developed novel electrocatalysts that are highly specific and selective for production of hydrogen using ammonia as a fuel source. The electro-oxidation of ammonia on platinum electrode drop coated platinum nanoparticles (PtNP), platinum iridium nanoparticles (PtIrNP), platinum ruthenium nanoparticles (PtRuNP), platinum telluride nanoparticles (PtTeNP) and ternary nanoparticles (PtIrTeNP) finally (PtRuTeNP) was systematically studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrocatalysts were synthesised using sodium borohydride as a reducing agent and polyvinylpyrrolidone (PVP) as a stabilising agent from aqueous solutions of H2PtCl6/IrCl3/RuCl3/NaHTe mixtures. XRD confirmed that the binary and ternary electro-catalyst displayed characteristic patterns which indicated that all catalysts have shown the Pt face-centred-cubic (fcc) crystal structure and that the nanoparticles were poly-orientated. The structural characterization was further confirmed with FTIR and UV-vis, FTIR showed the most striking evidence that the PVP stabilized Pt presented a broad peak between 1288 cm-1 and 1638 cm‐1 which corresponded to C‐N stretching motion and C=O stretching motion of monomer for PVP, respectively. The narrow absorption peak centered at 1420 cm‐1 and 2880 cm‐1 occurred in which was ascribed to the C–H bonding due to the presence of PVP. This was due to the formation of coordinate bond between the nitrogen atom of the PVP and the Pt2+, Ir3+, Ru3+ and Te2+ ions. UV-vis was able to show the oxidation state of the nanoparticles and obtained an exponential graph shape which indicated complete reduction because there was no peak observed. Morphological characterization in the form of high resolution scanning electron microscope (HRSEM) revealed the formation of poly-orientated nanoparticles with average particle size of 23- 46 nm with slightly aggregated crystalline materials. The elemental composition of the alloy nanoparticles measured using energy dispersive spectroscopy (EDS) showed the presence of the four elements; Pt, Ir, Ru and Te. High resolution transmission electron microscopy (HRTEM) revealed the formation of crystalline non-aggregated 0.6-5 nm sized nanoparticles. The elemental composition of the alloy nanoparticles measured using energy dispersive X-ray (EDX) showed the presence of the four elements; Pt, Ir, Ru and Te. Selected area electron diffraction pattern (SAED) nanoparticles showed characteristic electron diffraction rings of Pt, PtIr, PtRu, PtTe, PtIrTe and PtRuTe, confirmed the phase and crystallinity of the materials. The electrocatalytic behaviour of the PtIrTe and PtRuTe nanoparticles for ammonia oxidation in KOH solution showed reduced overpotential properties and an increased current density compared to the bare Pt nanoparticles electrode thus providing a promising alternative for development of low-cost and high-performance electrocatalyst for electro-oxidation of ammonia. In terms of minimising the ammonia oxidation overpotential, catalyst selection were ranked as follows PtTe > PtRuTe > PtIr > PtRu > PtIrTe > Pt, with regards to maximising the exchange current density, the ranking was PtTe > PtIrTe > Pt > PtRu > PtIr > PtRuTe. The results were further interrogated with EIS which revealed in terms of minimising charge transfer resistance (Rct) the nano catalysts selection were ranked as follows PtRuTe ˃ PtIrTe ˃ PtRu ˃ PtIr ˃ Pt ˃ Bare Pt electrode ˃ PtTe. That meant that the conductivity of the catalysts facilitated the flow of charge through the nanoalloys onto the surface of the electrode. The difference in charge transfer resistance revealed that PtRuTe and PtIrTe nanoalloys had an obvious advantage in reaction activity. The application of ternary metal nanoparticles had significantly enhanced the catalytic activity toward ammonia oxidation. The role of the third component (Te) had improved the catalysts in reducing Nads adsorption on Pt. The enhanced catalytic activity has been attributed by a number of factors including the change in Pt–Pt inter atomic distance, number of Pt nearest neighbours, Pt 5d band vacancy, and Pt metal content on particle surface.
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Gcilitshana, Oko Unathi. « Electrochemical Characterization of Platinum based anode catalysts for Polymer Exchange Membrane Fuel Cell ». Thesis, University of the Western Cape, 2008. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5972_1266961431.
Texte intégralRésumé :
In this study, the main objective was to investigate the tolerance of platinum based binary anode catalysts for CO poisoning from 10ppm up to1000ppm and to identify the
best anode catalysts for PEMFCs that tolerates the CO fed with reformed hydrogen.
32
Zeszut, Ronald Anthony Jr. « Effects of Transport and Additives on Electroless Copper Plating ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1497271315649528.
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Morin, Sylvie. « Electrochemical studies of two-dimensional processes at well-defined platinum single crystal electrodes ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq21011.pdf.
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Zhang, Tianhou. « Theoretical studies of fuel cell reaction mechanisms H₂ and O₂ on platinum electrodes / ». online version, 2008. http://rave.ohiolink.edu/etdc/view.cgi?acc%5Fnum=case1215456813.
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Ogbu, Chidiebere. « Peroxide Sensing Using Nitrogen-Doped and Platinum Nanoparticle-modified Screen-Printed Carbon Electrodes ». Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/etd/3622.
Texte intégralRésumé :
Nitrogen-doped carbon materials have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (oxygen reduction) and biosensing (hydrogen peroxide reduction). Here, we demonstrate fabrication methods and determine electrocatalytic properties of nitrogen-doped screen-printed carbon (N-SPCE) electrodes. Nitrogen doping of graphite was achieved through a simple soft-nitriding technique which was then used in lab-formulated screen-printing inks to prepare N-SPCEs. N-SPCEs displayed good electrocatalytic activity, reproducibility and long term stability towards the electrochemical reduction of hydrogen peroxide. N-SPCEs exhibited a wide linear range (20 µM to 5.3 mM), reasonable limit of detection of 2.5 µM, with an applied potential of -0.4 V (vs. Ag/AgCl). We also demonstrate that nitrided-graphite can similarly be used as a platform for the deposition of electrocatalytic platinum nanoparticles, resulting in Pt-N-SPCEs with a lower limit of detection (0.4 µM) and better sensitivity (0.52 µA cm-2 µM-1) towards H2O2 reduction.
36
Zhang, Tianhou. « Theoretical Studies of Fuel Cell Reaction Mechanisms : Water and Oxygen on Platinum Electrodes ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1215456813.
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Maunier-Morin, Marie-Christine. « Oxydation électrocatalytique de l'éthanol sur le platine et l'or : effets de structure, étude des mécanismes sur le platine par voltammétrie à potentiel programme et par spectroscopie infrarouge de réflexion ». Poitiers, 1988. http://www.theses.fr/1988POIT2308.
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Mandadi, Deepika. « A Characterization of Caffeine Imprinted Polypyrrole Electrode ». TopSCHOLAR®, 2009. http://digitalcommons.wku.edu/theses/130.
Texte intégralRésumé :
Nanotechnology holds great potential for improving our lives by creating many new materials and devices in medical sciences, electronics and also in energy production. Molecularly imprinted polymers (MIPs) are highly stable synthetic polymers that possess molecular recognition properties due to cavities created in the polymer matrix that are complementary to an analyte both in shape and in positioning of functional groups. These MIPs have been widely employed for diverse applications (e.g., in chromatographic separation, drug screening, chemosensors, catalysis, immunoassays etc) due to their specificity towards the target molecules and high stability against physicochemical perturbations. Conductive polymers, (CPs) such as polypyrrole, can be likened to semiconductors because of small band gaps and low electronic mobility. CPs are exploited as an excellent tool for the preparation of nanocomposites with nano scaled biomolecules. Polypyrrole (Ppy) was the first of this key family of compounds to show high conductivity. So, electrically conducting polypyrrole (Ppy) has numerous applications.
In this study, caffeine imprinted electrodes (CIE) were prepared and characterized. This research project mainly focused on three important aspects: &#;To determine the thickness of the polymeric film. &#;To determine the Limit of detection (LOD) of the polymeric film at different conditions. &#;To determine the Analytical Sensitivity (γ) of the polymeric film at varied conditions.
In summary these are conclusions stated: •The thickness of the electrode increased with an increase in the number of pulses. The film thickness increased linearly up to an application of 30 pulses and after 30 pulses, an increase in slope occurred with again a linear correlation up to the maximum applied number of pulses, 42. This change in slope may indicate a different mechanism taking place.
•LOD is improved as the caffeine load is reduced from 10.0 to 3.0 mM and as the number of pulses is reduced from 36 to 24.
•γ increases the number of pulses increase from 24 to 36 and also increases as the caffeine load increases.
39
Coudray, Mathias. « Procédé de recyclage des Assemblages Membrane Electrode (AME) de piles à combustible utilisant des liquides ioniques ». Thesis, Lyon, 2019. https://n2t.net/ark:/47881/m6h70f5d.
Texte intégralRésumé :
Le recyclage des assemblages membrane électrode (AMEs) des piles à combustible à membrane échangeuse de protons (PEMFC) est en enjeu important pour le développement du marché de ces piles fonctionnant à l’hydrogène. Dans ces AMEs se trouvent le platine (Pt), un métal précieux et rare qui conditionne majoritairement le coût total de la pile. Le recyclage du Pt est encore largement effectué par hydro ou pyrométallurgie ce qui entraîne le rejet de gaz toxiques et polluants dans l’environnement. Plusieurs études ont porté sur la mise en place d’une voie plus soutenable écologiquement que le traditionnel usage d’acides forts pour lixivier le platine. Le procédé proposé ici s’inscrit dans ce domaine de recherche en proposant une nouvelle voie de séparation des constituants de l’électrode de PEMFC en vu de leur recyclage par l’utilisation de liquides ioniques. Ceux-ci par leur stabilité thermique et chimique et leur non-volatilité peuvent permettre la mise en place d’un procédé de récupération du platine sûr. Après l’étude d’une sélection de liquides ioniques plusieurs d’entre eux, dont le P66614Cl (trihexyltetradécylphosphonium chlorure), ont permis la récupération du platine sous forme de nanoparticules détachées et stabilisées dans le liquide ionique. Une étude des interactions du liquide ionique avec chacun des composants de l’AME a permis de mieux comprendre les mécanismes d’extraction. Le liquide ionique interagit ainsi fortement avec l’ionomère présent dans la couche catalytique. Cette forte interaction ouvre la voie à un retraitement simultané du Nafion et du platine des AMEsRecovery of the protons-exchange membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs) is an important issue for the growing of the fuel cells market. These MEAs contain platinum (Pt), which as a precious metal mainly influences the total cost of fuel cells. The recycling of Pt is still based to a great extent on hydro or pyrometallurgical techniques which produce toxic and pollutant gas emissions. Some studies aimed to set up processes to recycle platinum in a more sustainable way than traditional metal lixiviation using strong acids. The study here is part of this research field and is about a new way to separate the different components of the PEMFC electrode using ionic liquids for the recycling of these valuable materials. These liquids possess excellent thermal and chemical stability and their non-volatility can be useful to set up a safer way to recover platinum. A selection of ionic liquids was studied and some of them, including the P66614Cl (trihexyltetradecylphosphonium chloride), could be use to recover Pt nanoparticles detached from their carbon support and stabilized in the ionic liquid. A study on the interactions of ionic liquids and the components of the MEA allowed the extraction mecanisms to be better understood. Thus the ionics liquids interact strongly with Nafion in the catalyst layer which allows Pt nanoparticles to be recovered. These strong interactions set the stage for the simultaneous recycling of Nafion and Pt from MEAs
40
Russell, Jason Bradley. « Investigation of the Effect of Catalyst Layer Composition on the Performance of PEM Fuel Cells ». Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/34526.
Texte intégralRésumé :
The catalyst layer of a proton exchange membrane (PEM) fuel cell is a porous mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. In this research, sample membrane electrode assemblies (MEAs) are prepared using various combinations of polymer and carbon loadings while the platinum catalyst surface area is held constant. For each MEA, polarization curves are determined at common operating conditions. The polarization curves are compared to assess the effects of the catalyst layer composition. The results show that both Nafion and carbon content significantly affect MEA performance. The physical characteristics of the catalyst layer including porosity, thickness, active platinum surface area, ohmic resistance, and apparent Nafion film thickness are investigated to explain the variation in performance. The results show that for the range of compositions considered in this work, the most important factors are the platinum surface area and the apparent Nafion film thickness.Master of Science
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Roller, Justin. « Low platinum electrodes for proton exchange fuel cells manufactures by reactive spray deposition technology ». Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/4458.
Texte intégralRésumé :
Reactive spray deposition technology (RSDT) is a method of depositing
films or producing nanopowders through combustion of metal-organic
compounds dissolved in a solvent. This technology produces powders of
controllable size and quality by changing process parameters to control the
stoichiometry of the final product. This results in a low-cost, continuous
production method suitable for producing a wide range of fuel cell related catalyst
films or powders. In this work, the system is modified for direct deposition of both
unsupported and carbon supported layers on proton exchange membrane (PEM)
fuel cells. The cell performance is investigated for platinum loadings of less than
0.15 mg/cm² using a heterogeneous bi-layer consisting of a layer of unsupported
platinum followed by a composite layer of Nafion®, carbon and platinum.
Comparison to more traditional composite cathode architectures is made at
loadings of 0.12 and 0.05 mg platinum/cm². The composition and phase of the
platinum catalyst is confirmed by XPS and XRD analysis while the particle size is
analyzed by TEM microscopy. Cell voltages of 0.60 V at 1 A/cm² using H₂/O₂ at a
loading of 0.053 mg platinum/cm² have been achieved.
42
De, Cliff Steve V. « Electrochemical Quartz Crystal Microbalance and Impedance Analysis investigations of surface processes at platinum electrodes ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq20996.pdf.
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Feltovich, Susanne D. « Influence of solvent on the infared spectrum of carbon monoxide adsorbed on platinum electrodes ». Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09292009-020247/.
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Boulenouar-Mohamedi, Fatma Zohra. « Étude de l'oxydation anodique de l'hydrogène à l'interface métal/zircone stabilisée à haute température (métal=platine, nickel, cuivre) ». Grenoble INPG, 1995. http://www.theses.fr/1995INPG0055.
Texte intégralRésumé :
Ce travail s'inscrit dans le cadre de recherches conduites sur les piles a combustible fonctionnant a haute temperature et mettant en jeu un electrolyte solide conducteur par ions oxydes (zircone stabilisee a l'oxyde d'yttrium: ysz). L'objet de cette recherche est de preciser les influences respectives des pressions partielles d'hydrogene et d'eau dans la polarisation anodique de l'interface metal/ysz, le metal etant: le platine, le nickel ou le cuivre. A l'equilibre, l'etude a montre l'interet de differencier les roles respectifs de l'hydrogene et de la vapeur d'eau et de ne pas traiter les resultats uniquement en terme de pression partielle d'oxygene. Des circuits equivalents rendant compte des reponses de l'electrode sont proposes. Par ailleurs, les resultats obtenus sous polarisation ont montre l'effet electrocatalytique de la vapeur d'eau sur la reaction d'oxydation anodique de l'hydrogene
45
Silwana, Bongiwe. « Graphene supported antimony nanoparticles on carbon electrodes for stripping analysis of environmental samples ». University of the Western Cape, 2015. http://hdl.handle.net/11394/5141.
Texte intégralRésumé :
>Magister Scientiae - MScPlatinum Group Metals (PGMs), particularly palladium (Pd), platinum (Pt) and rhodium (Rh) have been identified as pollutants in the environment due to their increased use in catalytic converters and mining in South Africa (as well as worldwide). Joining the continuous efforts to alleviate this dilemma, a new electrochemical sensor based on a nanoparticle film transducer has been developed to assess the level of these metals in the environment. The main goal of this study was to exploit the capabilities of nanostructured material for the development and application of an adsorptive stripping voltammetric method for reliable quantification of PGMs in environmental samples. In the study reported in this thesis, glassy carbon electrode (GCE) and screen-printed carbon electrode (SPCE) surfaces were modified with conducting films of nanostructured reduced graphene oxide-antimony nanoparticles (rGO-SbNPs) for application as electrochemical sensors. The rGO-SbNPs nanocomposite was prepared by Hummer`s synthesis of antimony nanoparticles in reaction medium containing reduced graphene oxide. Sensors were constructed by drop coating of the surfaces of the carbon electrodes with rGO-SbNPs films followed by air-drying. The nanocomposite material was characterised by: scanning and transmission electron miscroscopies; FTIR, UV-Vis and Ramanspectrosocopies; dc voltammetry; and electrochemical impedance spectroscopy. The real surface area of both electrodes were studied and estimated to be 1.66 × 10⁶ mol cm⁻² and 4.09 × 10³ mol cm⁻² for SPCE/rGO-SbNPs and GCE/rGO-SbNPs, respectively. The film thickness was also evaluated and estimated to be 0.36 cm and 1.69 × 10⁻⁶ cm for SPCE/rGO-SbNPs and GCE/rGO-SbNPs, respectively. Referring to these results, the SPCE/rGO-SbNPs sensor had a better sensitivity than the GCE/rGO-SbNPs sensor. The electroanalytical properties of the PGMs were first studied by cyclic voltammetry followed by indepth stripping voltammetric analysis. The development of the stripping voltammetry methodology involved the optimisation of experimental conditions such as selection of adequate supporting electrolyte, choice of pH and /or concentration of supporting electrolytes, deposition potential, deposition time, stirring conditions. The detection of Pd(II), Pt(II) and Rh(III) in environmental samples were performed SPCE/rGO-SbNPs and GCE/rGO-SbNPs at the optimised experimental conditions For the GCE/rGO-SbNPs sensor, the detection limit was found to be 0.45, 0.49 and 0.49 pg L⁻¹ (S/N = 3) for Pd(II), Pt(II) and Rh(III), respectively. For the SPCE/rGO-SbNPs sensor, the detection limit was found to be 0.42, 0.26 and 0.34 pg L⁻¹ (S/N = 3) for Pd(II), Pt(II) and Rh(III), respectively. The proposed adsorptive differential pulse cathodic stripping voltammetric (AdDPCSV) method was found to be sensitive, accurate, precise, fast and robust for the determination of PGMs in soil and dust samples. The simultaneous determination of PGMs was also investigated with promising results obtained. The AdDPCSV sensor performance was compared with that of inductive coupled plasma mass spectroscopy (ICP-MS) for the determination of PGM ions in soil and dust samples. It was found that though the metals could be determined by ICP-MS technique, it was limited from the standpoints of sensitivity, ease of operation and versatility compared to the AdDPCSV sensor. This study has show cased the successful construction and application of novel SPCE/rGO-SbNPs and GCE/rGO-SbNPs AdDPCSV sensors forthe determination of PGMs in environmental samples (specifically roadside dust and soil samples). The study provides a promising analytical tool for monitoring PGMs pollutants that are produced by automobiles and transported in the environment.
46
Essis-Yei, L. Hortense. « Oxydation electrocatalytique du glucose sur le platine et l'or en milieu aqueux ». Poitiers, 1987. http://www.theses.fr/1987POIT2277.
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Martínez-Hincapié, Ricardo. « Efecto del pH en la estructura de la doble capa eléctrica y su influencia en la reactividad electroquímica ». Doctoral thesis, Universidad de Alicante, 2019. http://hdl.handle.net/10045/94050.
Texte intégralRésumé :
El trabajo realizado en esta tesis busca entender el efecto de la doble capa eléctrica en la reactividad electroquímica. El uso de electrodos de monocristalinos de platino ha permitido realizar estudios fundamentales de la estructura interfacial electrodo/disolución poniendo de manifiesto la sensibilidad estructural que tienen la mayoría de los procesos electroquímicos. Así mismo, el uso de diferentes condiciones de pH ha permitido la obtención de información molecular. La primera parte de la tesis lidia sobre aspectos más fundamentales, como lo es la obtención del potencial de carga cero, parámetro fundamental para entender la interfase electroquímica. Para obtener los valores del potencial de carga cero, se han usado principalmente dos técnicas: desplazamiento de carga por CO y sondas locales. La sonda local usada ha sido la reducción del anión peroxodisulfate. La segunda parte de la tesis presenta dos casos de estudio: La adsorción de iones bicarbonato y carbonato y la adsorción/oxidación del ácido glioxílico como ejemplos del efecto que tienen algunas propiedades interfaciales en la reactividad electroquímica.
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García, García Vicente. « Reducción electroquímica de β-cloropropiofenona sobre electrodos de mercurio y platino en DMF ». Doctoral thesis, 1991. http://hdl.handle.net/10045/3533.
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Rodes, García Antonio. « Una aproximación molecular al estudio de procesos electródicos : caracterización electroquímica de superficies escalonadas de platino y su aplicación al estudio de diferentes procesos de reconstrucción superficial ». Doctoral thesis, 1991. http://hdl.handle.net/10045/3920.
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Herrero, Enrique. « Adsorción y oxidación de metanol, ácido fórmico y CO sobre electrodos monocristalinos de platino modificados con adátomos ». Doctoral thesis, 1995. http://hdl.handle.net/10045/3609.
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