Doctoral Dissertations

Date of Award

5-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Thomas A. Zawodzinski

Committee Members

Robert M. Counce, Jack S. Watson, Matthew M. Mench

Abstract

This dissertation considers the development of porous carbon materials as the substrates for Al deposition/dissolution in an Al based ionic liquid flow battery (ILFB) and demonstration of an Al based hybrid supercapacitor. The Aluminum chloride/ 1-ethyl-3-methylimidazolium chloride chloroaluminate ionic liquid is utilized as the electrolyte for these Al based energy storage devices. The ILFB has less capital cost than the all-vanadium redox flow battery because of the inexpensive AlCl3. The feasibility to equip a tank of solid aluminum chloride in an ILFB system aiming to improve energy density is investigated. A critical range of temperature data (50-130 celsius degree) for aluminum chloride dissolution and precipitation from saturated chloroaluminate ionic liquids is measured by differential scanning calorimetry. The process of Al deposition on porous carbon materials is investigated in the static electrolyte and a flow-through cell aiming to improve the current density, the amount of Al deposits stored in substrates and limit the dendrite growth. Fourier transform infrared spectroscopy and scanning electron microscope are applied to characterize the Al deposits on the porous carbon materials. By the flow-through method providing enhanced diffusion to porous carbon materials, the current density of Al deposition on carbon paper is remarkably higher than that on Al disk. However, dendrites prefer to grow on the Al disk substrate. The electrolyte flow rate and the flow direction also play important roles in determining current densities and dendrite formation for Al deposition on porous carbon materials. We successfully demonstrate an Al based hybrid supercapacitor using high surface area carbon materials such as graphene and activated carbon. The activated carbon is preferred because of less catalytic ability to evolve chlorine. The mismatch between the small pore size of activated carbon and the large ion size of complex ions results in the high charge-transfer resistance measured by the electrochemical impedance measurements. The wettability of electrodes determined by different polymer binders, Polytetrafluoroethylene and the aqueous base modified styrene butadiene rubber, has a significant effect on specific capacitance of activated carbon. The hydrophilic property of SBR may promote the entrance of ions to the micropores of activated carbon.

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