Harmonic Imaging of Nano-confined Aqueous Phase Transitions and the Electrochemical Reduction of Carbon Dioxide Using a Nano-structured Electrolyte

Schunk, Francisco M.

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Year:: 2016
Contributor:: Schunk, Francisco M (creator); Rose-Petruck, Christoph (Director); Diebold, Gerald (Reader); Doll, Jimmie (Reader); Brown University. Chemistry (sponsor)
Genre:: theses
Subject:: X-ray imaging; confined aqueous phase transitions; Carbon nanotubes
Extent:: 20, 99 p.
DOI: https://doi.org/10.7301/Z0C53J8J

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Abstract:: Aqueous phase transitions within multi-walled carbon nanotubes (MWCNTs) were studied as a function of temperature, time and chemical functionalization via X-ray Spatial Frequency Heterodyne Imaging (SFHI). SFHI is an imaging modality that produces an absorption and several scatter images from a single exposure. The absorbance and scatter from the samples revealed information about the carbon nanotube (CNT) geometric cross-section and the configuration of contained water during evaporation and condensation. Water confined to the inner pore of a CNT is a favored system in the study of nanofluidics. Experimental observation of nano-confined water typically makes use of CNTs with inner diameters greater than 70 nm and less than 3 nm. Water restricted to CNTs belonging to the larger diameter class is seen to have behavior predictable by equilibrium thermodynamics. Water confined within a CNT of the smaller diameter class has markedly different behavior from that of bulk water and the molecular identity takes precedence in determining the liquid dynamics. Therefore the equilibrium thermodynamic description of water breaks down between confinements of 70 nm and 3 nm. The MWCNTs used in the present study possessed an inner diameter of 7 nm, and the water confined within them was determined to behave as bulk water. The change in evaporation time scale with temperature also coincided with the boiling point for water predicted by the Kelvin equation, further confirming an equilibrium thermodynamic description. These results effectively narrowed the range of confinement sizes over which the behavior of water changes dramatically, having implications for condensed matter physics at large and the ability to execute chemical reactions with elevated kinetics using CNTs as reaction vessels. Novel electrochemical experiments with a clathrate hydrate electrolyte were conducted with the goal of reducing carbon dioxide (CO2) to more chemically versatile species. The clathrates increased CO2 concentration within the electrolyte, which suppressed the hydrogen evolution reaction and increasing the Faraday efficiency of carbonaceous products at low overpotentials compared to similar experiments absent of clathrates. This work possess the potential for guiding significant reform in the current capture and utilization of CO2 on an industrial scale.
Notes:: Thesis (Ph.D. -- Brown University (2016)

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Schunk, Francisco M., "Harmonic Imaging of Nano-confined Aqueous Phase Transitions and the Electrochemical Reduction of Carbon Dioxide Using a Nano-structured Electrolyte" (2016). Chemistry Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0C53J8J

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Chemistry Theses and Dissertations

Theses and Dissertations for the Chemistry department.
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