Fundamental Study of the Synthesis, Structural and Electrochemical Characterization of Nanoparticulate Transition Metal Oxide and Nitride Based Supercapacitor Systems

摘要

Supercapacitors are electrochemical charge storage devices capable of delivering large bursts of charge over a very short period of time. There is a need for identification and development of alternative low-cost, high energy, high-power materials for widespread implementation of supercapacitor technologies. Nanostructured vanadium nitride (VN) coated with a thin vanadium oxide (VOx) surface layer has previously been identified to be a very promising electrode material for supercapacitor application.udIn this work, attempt was made to develop a fundamental understanding of the supercapacitor response of both the nitride and oxide nanomaterials. In order to understand the charge storage behavior of the nitride nanomaterials, both the materials and electrode properties were altered to understand the exact role of each aspect on the charge storage characteristics. Using a combination of solid state and wet-chemical methods a number of nitride materials were synthesized and via a thorough materials and electrochemical characterization, a fundamental understanding of the structure-property relationships in the nitride materials was obtained. The roles of particle size, electronic conductivity, and electrode thickness and most importantly, the surface oxide nature are also explored in this work.ududThe investigations conducted in the nitride systems made it clear that the prodigious amount of charge storage in nitride nanomaterials was primarily due to a surface oxide layer and that the stabilization and improvement in electronic conductivity of the surface oxide was pivotal in attaining a reversible and stable charge storage. Nanostructured oxides of vanadium (VOx) as standalone supercapacitor materials were therefore explored. Thin films of vanadium oxide were deposited on an array of vertically aligned carbon nanotubes (VACNTs) derived using chemical vapor deposition (CVD). This study also made it very clear that the presence of a conductive support structure is imperative to achieve good charge storage response in oxides. Using dopants identified by ab-initio computational studies of doped vanadium oxide materials (VOx: M), very high areal and gravimetric capacitances in doped materials coated on VACNTs was demonstrated.ududIdentical doping strategies were used to derive doped vanadium nitride (MyV1-yN) with a doped surface oxide layer (MyV1-yOx). Dopants were selected on the basis of improvement in electronic conductivity without compromising the chemical stability. Improvement in charge storage properties of nanoparticulate nitride particles by systematic tailoring of the architecture was demonstrated.