Novel Synthetic Routes to Metal Oxide Nanomaterials for Energy Storage and Environmental Remediation Applications

Date of Completion

January 2012

Keywords

Chemistry, General|Chemistry, Inorganic|Engineering, Materials Science

Degree

Ph.D.

Abstract

Clean energy sources and sustainable environments have been very important research areas in the 21st century. The objective of this dissertation work is to develop novel synthetic routes to fabricate metal oxide nanomaterials. The synthetic methodologies are expected to be more energy saving, chemical saving, and facile. The structures of as-prepared metal oxide materials are controlled on a nanometer scale. ^ A variety of bottom-up synthetic techniques based on wet-chemistry methods, such as hydrothermal, reflux, solvothermal, and microwave-assisted techniques, are employed to fabricate one dimensional (1D), two dimensional(2D), and three dimensional (3D) nanostructured metal oxide materials and nanocomposites. Porous manganese oxide octahedral molecular sieves (OMS) and octahedral layers (OL) are promising for electrode applications in lithium batteries and oxidation catalysts in environmental chemistry because of their unique mixed-valence character, tunable pore size and versatile nano-structures. ^ Lithium-ion secondary batteries have been commercialized in laptops, cellphones, and part of electrified vehicles. However, the current specific capacities of developed electrode materials are still low and far from theoretical values. Recent research has clearly shown that the size and morphology effect the performance of metal oxides used as electrode materials. Designing nanostructured semiconducting metal oxide materials has been the key to success in developing large specific capacities in lithium-ion batteries. A single-step procedure has been developed to synthesize well-ordered 3D lithium manganese oxide nanomaterials and has been demonstrated to be a good Li intercalative material in half coin-cell test. These materials possessing 3D nanostructures can facilitate Li ion transportation when used as electrode materials. ^ In addition, manganese oxides are also bifunctional electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), which are critical in the discharge and charge processes in Li-air batteries. Li-air batteries are known to bring up new hopes for even larger capacities (∼ 10 times of Li-ion batteries) due to their favorable energy storage nature by releasing about 11.7 kWh's energy per kilogram in a discharge process, which is comparable to gasoline. A single-step reaction process has been developed to prepare a 1D Ag-containing 2×2 tunnel type OMS (Ag-OMS-2) and a 1D 2×4 tunnel type OMS (OMS-5) material. These two nanomaterials have shown excellent performance as electrocatalysts in primary Li-O2 batteries and achieved an average specific capacity of 2741 mAh/g and 2708 mAh/g of carbon, respectively. ^ Cu-containing layered manganese oxide (Cu-K-OL-1) nanomaterials have been hydrothermally synthesized in one-step and used as catalysts in low temperature CO oxidation and used for heavy metal removal in aqueous media. Pure K-OL-1 materials showed the best adsorptive capacity. ^

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