Nanoscale metal oxide and supported metal catalysts for Li-air battery

The dissertation work focuses on research and development of durable nanoscale catalysts and supports for rechargeable Li-air batteries that use aqueous catholytes. Transition metal oxides, TiO2 and Nb2O5 in particular, were prepared from a sol-gel process in the form of nanocoatings (5~50 nm) on carbon nanotubes (CNTs) and studied as catalyst supports. Carbon doping in the oxides and post annealing significantly increased their electronic conductivity. Pt catalyst on the support with TiO2 (Pt/c-TiO2/CNTs) showed a much better oxygen reduction reaction (ORR) activity than a commercial Pt on carbon black (Pt/C). Negligible loss (\u3c 3%) in ORR activity was found in Pt/c-TiO2/CNTs as compared to more than 50% loss in Pt/C, demonstrating a significantly improved durability in the developed catalysts. However, Pt/c-Nb2O5/CNTs was found to be worse in ORR activity and durability, suggesting that c-Nb2O5/CNTs may not be a good support. CNTs have fibrous shape and would provide a unique porous structure as electrode. Their buckypapers were made and used to support catalysts of Pt and IrO2 in the cathodes of Li-air batteries with sulfuric acid catholyte. At low Pt loading (5 wt.%) without IrO2 on the buckypaper cathode, the Li-air cell achieved a discharging capacity of 306 mAh/g and a specific energy of 1067 Wh/kg at 0.2 mA/cm2. A significant charge overpotential reduction (~ 0.3 V) was achieved when IrO2 was also used to form a bifunctional catalyst with Pt on the buckypapers. The round trip efficiency was increased from 72% to 81% with the bifunctional cathode, demonstrating a higher energy conversion efficiency --Abstract, page iv

Impact of the Short-Term Consumption of a Moderately High Fat Diet on Nitric Oxide Production and Bioavailibility

Nitric oxide (NO) plays an essential role in the regulation of numerous biological processes. Its bioavailability is assured by a well regulated balance between NO generation and NO removal. Disruptions in this balance contribute to the pathogenesis of various diseases, including hypertension, Alzheimer’s disease, diabetes mellitus and arthritis. Many factors contribute to the maintenance of NO bioavailability by controlling nitric oxide synthase (NOS) expression, NOS activity, the availability of substrates and cofactors involved in the generation of NO by NOS, levels of reactive oxygen species (ROS), and the formation and mobilization of NO reservoirs. Dietary factors have a significant impact on NO bioavailability. Of the major dietary constituents, fats have been the most extensively studied. The long-term consumption of high fat diets decreases NO bioavailability and induces some irreversible pathological changes in various organs of experimental animal models. The effect of the short-term consumption of excessive dietary fat is still unclear. The primary objective of the studies presented in this dissertation was to investigate the impact of the short-term consumption of a moderately high fat diet (MHFD) on NO generation and the mechanisms involved in the maintenance of NO bioavailability. The consumption of the MHFD markedly reduced urinary excretion of stable NO metabolites and levels of these metabolites in the plasma within a week of the onset of dietary treatment. eNOS expression was suppressed in a tissue-specific and time-dependent manner. The earliest decrease in expression occurred in the liver at week one. In addition, hepatic NOS activity was depressed and nitrotyrosine levels were elevated; increased nitrotyrosine formation is indicative of the increased production of ROS. Other tissues in which NOS expression was suppressed in rats on the MHFD included the heart and kidney medulla. In addition to affecting NO bioavailability, the ingestion of a MHFD also caused a decrease in drinking behavior. A portion of this reduction in drinking behavior may be attributable to the physical properties of the diet whereas the remainder is probably due to variations in the nutrient composition of the diet. The rats adapted to reduced drinking behavior by decreasing urine output and increasing urine osmolality. Nitric oxide synthase expression in the supraoptic and paraventricular nuclei did not change. In conclusion, the short-term consumption of a MHFD has profound effects on circulating NO levels by affecting mechanisms that regulate NO availability in specific tissues. In addition, the ingestion of a MHFD may affect other biological functions such as drinking behavior

Interlayer-spin-interaction-driven Sliding Ferroelectricity in a van der Waals Magnetic Heterobilayer

Sliding ferroelectricity is widely existed in van der Waals (vdW) two-dimensional (2D) multilayers, exhibiting great potential on low-dissipation non-volatile memories. However, in a vdW heterostructure, interlayer sliding usually fails to reverse or distinctly change the electric polarization, which makes the electrical control difficult in practice. Here we propose that in a vdW magnetic system, the interlayer spin interaction could provide an extra degree-of-freedom to remarkably tune the electric polarization. Combining tight-binding model analysis and first-principles calculations, we show that in the CrI3/MnSe2 and other vdW magnetic heterobilayers, the switching of the interlayer magnetic order can greatly change, even reverse the off-plane electronic polarization. Furthermore, interlayer sliding causes a non-volatile switching of the magnetic order and, thus, reverses the electric polarization, suggesting a non-volatile magnetoelectric coupling effect. These findings will significantly advances the development of 2D ferroelectrics and multiferroics for spintronic applications