Synthesis of SnO2-based hetero-nanostructure and their applications for environmental monitoring and energy storage

Abstract

Nanoporous materials have been attracted many attention due to its high-surface-to-volume ratio and structural features resulting their peculiar and fascinating properties. Various synthesis techniques have been suggested and the enhanced physical and chemical properties of nanoporous materials are confirmed in various fields such as optic device, sensors, and energy application. In this research, the two main topics will be discussed: 1) synthesis of Sn-based porous structure using electrochemical methods and their gas sensing properties, 2) electrochemical performance of SnO2/TiO2 heterostructured nanotube synthesized by atomic layer deposition and PAN template In the first chapter, nanoporous Sn based nanostructures for semiconductor gas sensor is synthesized via electrochemical methods, anodic oxidation and electrodeposition. Tin oxide is a well-known semiconductor-type gas sensor material detecting inflammable and toxic gases and the gas adsorption/desorption on the surface of sensor material changes its electric resistivity. Therefore, the surface area is one of the key factors to determine the gas sensing performance such as sensitivity, selectivity, and response-recovery time. In order to synthesize a porous structure, electrochemical methods of anodizing (top-down) and electrodeposition (bottom-up) are chosen. The synthesized porous structures exhibited enhanced gas sensing properties in terms of gas response, reaction time and recovery time and it is confirmed that the structural effect of porous structure lead to improved sensing performance. In addition, heterostructuring with CuO forming PN junction is applied to give functionality on selective sensing toward H2S and the mechanism on enhanced selectivity toward H2S is investigated. In the second chapter, synthesis of SnO2/TiO2 hetero-structured nanotube for anode material of Li ion battery is studied. The technical needs for high performance lithium ion batteries (LIBs) have increased in a wide range, from hybrid electric vehicles (HEVs) to light-weight and portable electronic devices. In this manner, SnO2 is one of the promising materials for anode electrode in LIBs due to its high theoretical capacity (782 mAh g-1) to replace commercially used graphite-based materials (372 mAh g-1). However, a large volume expansion about 300% during lithium insertion/extraction causes a pulverization and electrical connectivity loss. Hollow nanotube is the most promising structure due to the interior free space accommodating the volume change during lithiation/ delithiation. In addition, titanium dioxide (TiO2) as anode materials of LIBs is considered another promising anode material in term of achieving higher safety and stability even though it shows low reversible capacity (170 mAh g-1). The volume change of TiO2 is less than 4% during the formation of typical Li-ion intercalation compound in the reaction, which thus greatly improves the overall safety of battery and this structural stability enable outstanding faster charge/discharge properties at high C-rate. So, to obtain solution for practical implementation, heterostructure of SnO2 and TiO2 nanotubes resulting synergetic effect is suggested for the anode of LIBs. The electrochemical performances of the products are investigated and highly enhanced properties of SnO2/TiO2 hetero-nanotube are confirmed especially in term of reversible capacity and high rate cyclability.