Synthesis and Characterization of Transition Metal Oxide/Hydroxide-Based Functional Materials for Environmental and Energy Applications

In this thesis, transition metal oxide/hydroxide-based functional nanomaterials with specific structures and properties are developed and characterized for targeting applications in environmental pollution abatement and energy conversion and storage. In the first part, graphene supported Co3O4 composite is synthesized in one-step using a facile microwave-assisted method. Graphene serves as the substrate, providing high surface area, good conductivity, and good mechanical and chemical durability. The wide pore size distribution, synergistic effect, and high surface area of the composite are found to contribute to the high performance of lithium-ion batteries. In the second part, we focused on the synthesis of a series of heterogeneous electrocatalysts based on graphene coupled mixed-metal (oxy)hydroxides containing specific concentrations of nickel, cobalt, and iron to investigate the influence of metal composition on the structure, properties, and activities for the oxygen evolution reaction (OER). Characterization results indicate iron incorporation induced structural disorder, ultra-small nanosheets, and high surface area of metal (oxy)hydroxides. In addition, the trend in Tafel slopes is related to the abundance of surface adsorbed hydroxyl groups. Density functional theory (DFT) calculations demonstrate electronic structure and free energy change of ternary metal oxyhydroxide enhance the energetics for OER electrocatalysis. The optimized ternary metal oxyhydroxide exhibits superior OER electrocatalytic activity than the state-of-the-art IrO2 catalyst. In the third part, we further developed unique mesoporous NiO/MnO2 in one step using modified UCT (University of Connecticut) methods. Both the OER and the oxygen reduction reaction (ORR) electrocatalytic activities and stabilities in alkaline media are promoted after further coating with polyaniline (PANI). Many factors are found to contribute to the improved catalytic activity, for example, accessible mesoporous structure, high surface area, core-shell structure, and good electrical conductivity. Beside the development of nanomaterials for renewable energy, we also created novel catalysts for environmental pollution abatement. Last but not least, a series of manganese oxide-based core-shell nanoarrays are integrated on the cordierite monolithic substrates. Different manganese-cobalt oxide core-shell nanoarrays are further evaluated due to the high activity for CO oxidation. This fast, cost-effective, and scalable method will provide a new route for synthesizing efficient core-shell nanoarray monolithic catalysts for low temperature catalysis