Doctoral Dissertations

Date of Award

12-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Stephen J. Paddison

Committee Members

Bamin Khomami, Sharani Roy, Joshua R. Sangoro

Abstract

Fuel cells, redox flow batteries, and secondary ion batteries are under active investigation to fulfill the requirements of efficient and sustainable energy storage and conversion technologies. The discovery of high-performance stable electrolytes that are relatively cheap and versatile is crucial to the commercialization of these electrochemical devices and necessitates a comprehensive understanding of the materials (i.e., from the atomistic to continuum levels). This dissertation is on multiscale modeling and simulations of several electrolytes under consideration in vanadium redox flow batteries (VRFBs), alkaline fuel cells (AFCs), or secondary magnesium batteries.

The hydrated structure and associated solvation Gibbs energies were determined for vanadium cations at four oxidation states using first principles based electronic structure calculations and quasi-chemical theory. The effect of sulfuric and trifluoromethanesulfonic (triflic) acids on the local structures of the hydrated vanadium cations was explored by employing hybrid density functional theory (DFT) in conjunction with a continuum solvation model. The results indicate that the hydration structure of vanadium at the oxidation state of three was the most perturbed in acidic media and that the oxo-group of vanadate may be protonated by either acid.

Dissipative particle dynamics (DPD) simulations were undertaken and a novel parametrization method developed to study the meso-scale behavior and hydrated morphology of proton and anion exchange membranes (PEMs and AEMs). The results for hydrated Nafion with the absorbed vanadium species indicate that the hydrated cations increase the aggregation of the sulfonate groups and that this effect is a function of both the cation charge and the degree of hydration. It was also observed that the simulated morphology and the size of the water domains in AEMs based on triblock copolymers depend on the hydration level and the anion type.

Vibrational frequencies of model clusters were calculated using DFT for two ionic liquid-based electrolytes and their experimental IR and Raman spectra were assigned. Moreover, the hydration of ten acids commonly used in electrolytes was investigated using DFT in order to provide a fundamental understanding of their hydrated acidity and proton transfer.

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