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.

abstract: Waste heat energy conversion remains an inviting subject for research, given the renewed emphasis on energy efficiency and carbon emissions reduction. Solid-state thermoelectric devices have been widely investigated, but their practical application remains challenging because of cost and the inability to fabricate them in geometries that are easily compatible with heat sources. An intriguing alternative to solid-state thermoelectric devices is thermogalvanic cells, which include a generally liquid electrolyte that permits the transport of ions. Thermogalvanic cells have long been known in the electrochemistry community, but have not received much attention from the thermal transport community. This is surprising given that their performance is highly dependent on controlling both thermal and mass (ionic) transport. This research will focus on a research project, which is an interdisciplinary collaboration between mechanical engineering (i.e. thermal transport) and chemistry, and is a largely experimental effort aimed at improving fundamental understanding of thermogalvanic systems. The first part will discuss how a simple utilization of natural convection within the cell doubles the maximum power output of the cell. In the second part of the research, some of the results from the previous part will be applied in a feasibility study of incorporating thermogalvanic waste heat recovery systems into automobiles. Finally, a new approach to enhance Seebeck coefficient by tuning the configurational entropy of a mixed-ligand complex formation of copper sulfate aqueous electrolytes will be presented. Ultimately, a summary of these results as well as possible future work that can be formed from these efforts is discussed. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2015