Heterogeneous Ordered Mesoporous Carbon/Metal Oxide Composites for the Electrochemical Energy Storage
Lee, Sang Bok
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The combination of high electronic conductivity, enhanced ionic mobility, and large pore volume make ordered mesoporous carbons (OMCs) promising scaffolds for active energy storage materials. However, mesoporous structures and material morphology need to be more thoroughly addressed. This dissertation discusses the effects of mesoporous structures and material morphologies on the electrochemical performance of OMC/Fe2O3 composites. In the first approach, Fe2O3 was embedded into 1D cylindrical (FDU-15), 2D hexagonal (CMK-3), and 3D bicontinuous (CMK-8) symmetries of mesoporous carbons. These materials were used as supercapacitors for a systematic study of the effects of mesoporous architecture on the structure stability, ion mobility, and performance of mesoporous composite electrodes. The results show that the CMK-3 and CMK-8 synthesized by hard template method can provide high pore volume, but the instability of their mesostructures hinders the total electrode performances upon oxide impregnation. In contrast, the FDU-15 from the soft template method can provide a stable mesostructure. However, it contains much smaller pore volume and surface area, leading to limited metal oxide loading and electrode capacitance. Based on these results, anodized aluminum oxide (AAO) and triblock copolymer F127 are used together as hard and soft templates to fabricate ordered mesoporous carbon nanowires (OMCNW) as a host material for Fe2O3 nanoparticles. The synergistic effects in the dual template strategy provide a high pore volume and surface area, and the structure remains stable even with high metal oxide loading amounts. Additionally, the unique nanowire morphology and mesoporous structure of the OMCNW/Fe2O3 facilitate high ionic mobility in the composite, leading to a large capacitance with good rate capability and cycling stability. I further evaluated this OMCNW/Fe2O3 as a lithium-ion battery (LIB) anode, which showed that the porous symmetry, material morphology, and structure stability are even more important in the rate and cycling performances of LIBs. This work helps further the understanding and optimization of porous structures and morphologies of heterogeneous composites for next generation electrochemical energy storage materials.