Publication Date

Fall 2018

Advisor(s) - Committee Chair

Sanju Gupta (Director), Michael Carini, and Ivan Novikov

Degree Program

Department of Physics and Astronomy

Degree Type

Master of Science

Abstract

Graphene-family nanomaterials (GFNs) have attracted a great deal of attention both in academia and in industry for a range of applications relevant for homeland security. In this thesis, an array of graphene-based hybrid materials and aerogels are synthesized for use as novel thermo-electrochemical energy harvesters and for ascorbic acid biosensing devices. The graphene-family nanomaterials include graphene oxide-GO, thermally reduced GO-rGOth, nitrogenated functionalized graphene-NFG, graphene aerogel-GA, nitrogen-doped graphene aerogel-NGA, multi-walled carbon nanotube aerogel-MWCNT, single-walled carbon nanotube aerogel-SWCNT, graphene and nanotube combined ‘hybrid’ aerogels-Gr:(SW/MW)CNT of various ratios, along with multilayered nanostructured architectures such as gold (AuNP) and silver nanoparticles (AgNP) decorated NFG coated with a thin layer of polyaniline (PANi). Precursor aerogel materials were also analyzed to demonstrate the effect of mesoporous architectures and the interplay of various components in augmenting physical-chemical properties.

These precursors were combined through multiple deposition schemes including electrodeposition, hydrothermal synthesis, and freeze drying techniques. This project was developed in an effort to enhance electrochemical properties through modification of the morphology, surface and structural properties, making them more suitable for thermal energy harvesting and bio-sensing applications. Hydrothermal synthesis created chemical bridged interfaces, interconnectedness, and improved electrical conductivity besides increasing the surface area of mesoporous aerogels created by freeze-drying. This causes an increase in the number density of electrochemically active sites. The surface morphology, lattice vibrations, and electrochemical activity of the materials were investigated using electron microscopy, micro-Raman Spectroscopy, and electrochemical microscopy techniques [namely cyclic voltammetry (CV), alternating current electrochemical impedance spectroscopy (acEIS), amperometric techniques, and scanning electrochemical microscopy (SECM)]. For thermoelectric and thermoelectrochemical power measurements, a custom-designed set up was made for creating a temperature gradient across two legs of a thermocell and experiments were performed in various device configurations (a) symmetric and asymmetric, (b) single thermocells, and (c) multiple (“in-tandem”) thermocells. Interestingly, we observed changes in conducting behavior from Ohmic to semiconducting and polarity shifts from positive to negative or vice versa on introduction of the redox electrolyte solution. The parametric correlations (thermopower and resistivity or conductivity) are established and the results are discussed in terms of the polarity switching behavior observed for some of the aerogels combinations.

Disciplines

Chemistry | Defense and Security Studies | Physics

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