Tunability of Gas Adsorption Enthalpies in Carbonaceous Materials for Energy-Related Applications

Citation

Quine, Cullen Mackenzie (2023) Tunability of Gas Adsorption Enthalpies in Carbonaceous Materials for Energy-Related Applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/r5ad-1j85. https://resolver.caltech.edu/CaltechTHESIS:05292023-054311609

Abstract

Carbonaceous materials provide a porous, high surface area framework for the adsorption of gases through physisorption. Physisorption operates through van der Waals forces, resulting in highly reversible, densified gas storage. The density of adsorbed gas species approaches the bulk liquid density, providing a method to increase the volumetric energy density of hydrogen and natural gas at conditions where the adsorbate is a non-liquid in the bulk phase. This dissertation explores the tunability of the strength of gas adsorption to surfaces of carbon adsorbents, known as the enthalpy of adsorption. Two methods are studied: modification of the surface atomic composition and microstructural changes to the carbon porosity. Applications are considered for both energy storage and carbon capture applications.

The first chapter presents a brief overview of the energy storage field, with emphasis on non-conventional methods to store gases efficiently. Chapter 2 provides the thermodynamic and statistical mechanical derivations used throughout this work, and the assumptions that go into the models used to analyze adsorption data. Chapter 3 reports work on a copper-modified commercial carbon MSC-30 for hydrogen storage, which exhibits an activated dissociative chemisorption desorption feature around ambient temperature. Chapter 4 presents the densification of a novel architected carbon structure, zeolite-templated carbon, for adsorbed natural gas storage. Through the pelletization process, the pore morphology of the underlying adsorbent framework is compressed, resulting in increased adsorption enthalpies with applied pelletization pressure. Chapter 5 focuses on the tunability of pore structure through potassium hydroxide activation, and the resulting adsorption properties pertinent to carbon dioxide capture from a simulated flue-gas stream. The last chapter provides insight into the work as a whole and identifies areas of future work that would improve the fundamental understanding and broader impact of adsorbent materials.

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