Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Thesis (Ph. D.)--Open University. BLDSC no. DXN049333.

>Magister Scientiae - MSc / Transition metals are a group of metals which are light in weight and have high hydrogen solubility. Their interaction with hydrogen is exorthermic and this phenomenon makes them “ideal” candidates for various applications of hydrogen storage systems. This explains why the phenomenon of hydrogen storage in Pd is used as a model for hydrogen storage systems because of the nature of absorption associated with it (like a sponge even at low temperatures). The hydrogenation process can be conducted at either room or high temperatures in a furnace under low pressure-low hydrogen gas concentration-short hydrogenation time (LP-LC-ST) and in intelligent gravimetric analyser under high pressurehigh hydrogen gas concentration-long hydrogenation time conditions. Most of the research on hydrogen storage sytems is based on gravimetric analysis of absorbed and desorbed hydrogen concentration. In this work, a comparison study of the hydrogen content in pure Pd, Pd-Pt coated systems, Pd-Pt alloys, commercially pure Ti and Ti-6Al-4V alloy determined by gravimetric methods and elastic recoil detection analysis (which is based on the detection of recoiled hydrogen after interaction with He+ ions) technique was investigated. The changes in the structural properties and the hydrogen content of the materials when exposed to a hydrogen gas environment for different durations at various system temperatures and pressures will be reported. These changes have an effect on the microstructure of CP-Ti and Ti-6Al-4V alloy and structural properties of all the hydrogenated materials. The results obtained from optical microscopy, scanning electron microscopy, x-ray diffraction, intelligent gravimetric analyser, digital balance, elastic recoil detection analysis and Vickers hardness test, show the following: it is found that hydrogenation of Pd at elevated temperatures (550 ˚C and 650 ˚C) does not yield hydrides under LP-LC-ST conditions. However, at room temperature the absorption of hydrogen occurred faster at the beginning of the process. Furthermore, the absorption of hydrogen increased with pressure where optimum absorption (0.67 wt. % hydrogen concentration) occurred under a system pressure of 2000 mbar. After pressure release, the remaining hydrogen content in the Pd sample was 0.6 wt. %. The Pd-Pt coated system provide hydrogen mobility at 550 and 650 ˚C where hydrides were formed under LP-LC-ST conditions. In addition to the decrease of hydrogen solubility in Pd-Pt alloys with an increase in Pt content, the probability of the alloys to achieve full saturation also decreases with an increase in Pt content under HP-HC-LT conditions. CP-Ti and Ti-6Al-4V alloy absorb substantial amount of hydrogen in the first hour of room temperature hydrogenation under LP-LC-ST conditions but hydrides were not formed. Therefore, under LP-LC-ST conditions at room temperature, Pd is able to store hydrogen in the form of hydrides whereas Ti and Ti-6Al-4V alloy could not. The 550 ˚C is the optimum temperature for hydrogenation of CP-Ti under LP-LC-ST conditions. The Ti- 6Al-4V alloy absorb optimum hydrogen at 650 ˚C under LP-LC-ST conditions. Consequently, the change of microhardness of CP-Ti and Ti-6Al-4V alloy was found to depend on hydrogenation temperature.

Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2021 / Recently, the use of electrochemical supercapacitors as energy storage devices has drawn great attention due to their high charge/discharge rate, long life span, high power and energy densities. However, the choice of electrode materials used is vital for the performance of supercapacitors. This study focused on the development of a low cost hybrid electrode based on reduced graphene oxide/metal organic framework composite (rGO/MOF) and a novel palladium (Pd) nanoparticles loaded on rGO/MOF termed Pd-rGO/MOF nanocomposite. The prepared nanocomposites were used for high performance electrochemical double layer capacitor-(EDLC) and battery-type supercapacitors known as supercabattery. The rGO material reported in this work was chemically derived through the oxidation reduction method using a hydrazine as a reducing agent. Furthermore, palladium nanoparticles were loaded on the rGO using the electroless plating method. The rGO/MOF and novel Pd-rGO/MOF nanocomposites were prepared using an impregnation method in dimethylformamide. The physical and morphological properties of the synthesised materials were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The XRD and FTIR analyses showed crystalline phases and vibrational bands for both parent materials, respectively. The TGA/DSC results showed enhancement of the thermal stability of the composite as compared to MOF material. The SEM/EDS and TEM/EDX confirmed the presence of octahedral structure of MOF in the rGO sheet like structure and elemental composition of the synthesised composite. The resultant of Pd-rGO/MOF nanocomposite showed a morphology in which a thin layer of rGO coating existed over MOF with unique bright spots indicating the presence of Pd nanoparticles. This observation agreed well with the structural properties revealed by both XRD and FTIR with the reduction of MOF intensities upon Pd-rGO loading as well as enhancement of thermal stability of the nanocomposites. The electrochemical properties of the prepared electrodes were determined using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). To evaluate the electrochemical performance of the prepared electrode materials, both two and three electrode cells were assembled. From the CV and GCD results, the nanocomposites demonstrated a battery-type behaviour and therefore asymmetric supercabattery cells were assembled using the composites as positive electrodes, and activated carbon as a negative electrode. The specific capacity of rGO/MOF in three electrode cell was found to be 459.0 C/g at a current density of 1.5 A/g in 3M potassium hydroxide. Furthermore, the asymmetric supercapacitor based on the rGO/MOF nanocomposite and activated carbon (AC) as a negative electrode exhibited a maximum energy density of 11.0 Wh/kg and the maximum power density of 640.45 W/kg. The loading of palladium nanoparticles on the nanocomposite was to improve the electrochemical active sites and the performance of the supercapacitor electrode. After incorporation of Pd nanoparticles, the specific capacitance in three electrode cell improved to 712 C/g at a higher current density of 2 A/g with the same electrolyte. The assembled supercabattery has shown improved maximum energy and energy density of 26.44 Wh/kg and 1599.99 W/kg, respectively. Based on these findings, the synthesised rGO/MOF and Pd-rGO/MOF nanocomposites are promising electrode materials for future supercabattery applications. / NRF (National Research Foundation) and SASOL foundation

Les nanoparticules (NPs) métalliques ont de nombreuses applications en catalyse. Certaines d’entre elles (or, argent, cuivre) présentent une absorption dans le visible résultant de l’excitation du plasmon de surface par un champ électromagnétique extérieur. Nous proposons dans ce projet de coupler les propriétés catalytiques de nanoparticules à base d’or avec leurs propriétés de résonance de plasmon de façon à assister la réaction catalytique notamment par l’effet thermique qui en découle. Cette approche de catalyse assistée par plasmon, est générale et peut être utilisée pour une variété de procédés catalytiques exothermiques et endothermiques impliquant des nanoparticules. Cette catalyse assistée par plasmon permettra de réaliser des réactions catalytiques à moindre coût énergétique sous lumière solaire. / Metallic nanoparticles (NPs) have many applications in catalysis. Some of them (gold, silver, copper) have a visible absorption resulting from the excitation of the surface plasmon by an external electromagnetic field. In this project, we propose to couple the catalytic properties of gold-based nanoparticles with their plasmon resonance properties in order to assist the catalytic reaction, in particular by the resulting thermal effect. This plasmon-assisted catalysis approach is general and can be used for a variety of exothermic and endothermic catalytic processes involving nanoparticles. This plasmon-assisted catalysis will make it possible to carry out catalytic reactions at lower energy cost under solar light.

The main objective of this investigation was to study palladium-catalyzed coupling of 2-aryl-4-chloro-3-iodoquinolines with phenyl boronic acid in order to assess the regioselectivity of carbon-carbon bond formation at either C3 or C4. The 2-aryl-4- chloro-3-iodoquinolines were subjected to Pd(PPh3)4-catalyzed coupling reaction with phenyl boronic acid in DMF in the presence of 2M sodium carbonate (aq) to afford 2,3-diaryl-4-chloroquinolines. Reaction of 2,3-diaryl-4-chloroquinolines with sodium methoxide in MeOH-DMF mixture under reflux afforded the corresponding 2,3-diaryl-4-methoxyquinoline. An alternative route to the latter involving palladiumcatalyzed cross-coupling reaction of 2-aryl-3-iodo-4-methoxyquinolines derived from the reaction of 2-aryl-4-chloro-3-iodoquinolines with sodium methoxide in refluxing methanol-THF mixture was also investigated. The 2,3-diaryl-4-methoxyquinolines were subjected to further studies of chemical transformation with boron tribromide to afford the corresponding 2,3-diarylquinolin-4(1H)-ones. All new compounds were characterized using a combination of NMR (1H and 13C), IR and mass spectroscopic techniques as well as elemental analysis. / Chemistry / M. Sc. (Chemistry)

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.