Abstract

Hydrogen is a promising carbon-free fuel source that can be produced sustainably and has broad applications like in aviation, maritime and road-based vehicles. However, the current commercial means of hydrogen production rely on fossil fuels. Water electrolysis is a green method of hydrogen production, but it is too expensive relative to current methods due to factors like the cost of electricity and catalysts to run the reaction. Creating more efficient water oxidation catalysts from first-row transition metals would provide a cheaper alternative to the expensive catalysts that are used currently. In addition to the production of hydrogen, improved hydrogen storage practices are needed to progress its commercialization. Current physical hydrogen storage methods are limited in volumetric energy density and can be unsafe to transport in mass. Solid-state hydrogen storage offers safer, energy-dense storage for broad commercial use. Ensuring the reversibility of solid-state storage methods expands the ability to further implement the use of hydrogen fuel. The body of work described in this thesis expands on key strategies to make sustainable hydrogen production more efficient and create reversible hydrogen storage materials. In the first project, we chose nanoconfinement as a strategy to improve the activity and stability of water oxidation catalysts. We used antimony-doped tin oxide (ATO) films as a host template to nanoconfine nickel oxyhydroxide. Here a method was developed to study the effects of nanoconfinement in the host material. Nickel oxyhydroxide in the ATO host showed higher activity and better stability for electrochemical water oxidation than the bare ATO host. Further study is needed to understand structure-property relationships of nanoconfinement for water oxidation electrocatalysts. Metal hydrides are a solid-state hydrogen storage solution that have high energy density. Metal hydrides need to reversibly release and absorb hydrogen at moderate temperature and pressure to be viable materials for commercial hydrogen storage. Metastable metal hydrides release hydrogen easily but fail to reabsorb hydrogen at reasonable conditions. Previously, somewhat reversible metal hydrides were made in which the combination of nanoconfinement and Lewis acid-base coordination was hypothesized to be the reason for success. This chapter on hydrogen storage studied nanoconfinement and Lewis acid-base coordination separately to understand their individual roles in creating reversible metastable AlH3 (alane). Three amines (1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecane, G2_PPI-dendrimer, and G2_PPI-dendrimer (NMe2)) were used to study Lewis-acid-base coordination. Antimony-doped tin oxide (ATO) was used to study nanoconfinement. NCMK-3, a mesoporous carbon, was used to expand on a previous study which successfully created reversible lithium aluminum hydride. Infrared spectroscopy (IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) confirmed successful infiltration and stabilization of alane in each of these materials. Re-hydrogenation was unsuccessful for all five materials. Based on these results, it was concluded that = Lewis acid-base coordination without nanoconfinement is not sufficient to make reversible hydrogen storage, and they must be combined in such a way that single-electron transfer stabilizes the metal hydride in order to develop a reversible metal hydride. The final project approaches a different aspect of water oxidation catalysts. Continued implementation of electrolysis will require a change in conditions in electrolysis reactors like using solutions without extreme pH to extend the lifetime of reactor components. Electrolysis in near-neutral pH needs high-performing catalysts, but the best catalysts for OER have mostly been studied in highly alkaline conditions. Understanding the change in activity and stability as the solution pH lowers to near neutral will help with catalyst design. We chose three material systems incorporating 1st-row transition metal oxides with both the layered double hydroxide and spinel structures for a total of six catalysts. Electrochemical techniques (cyclic voltammetry and chronopotentiometry) revealed the intrinsic activity and stability of each electrocatalyst at four pH values (14, 12.5, 11, and 9). The materials studied exhibited significantly differing pH dependencies, with the nickel-iron layered double hydroxide showing the most substantial pH dependence. The best catalyst at pH 14 (Ni-Fe LDH) was not the best in the lower pHs tested. At pH 9, Co-Mn LDH and Co-Fe spinel were the best performers. Therefore, near-neutral catalysts need to be studied in near-neutral conditions. This body of work engages with fundamental aspects of sustainable hydrogen implementation. The hydrogen storage work sought to reveal the individual structure-property relationships for nanoconfinement and Lewis acid-base coordination for metastable metal hydrides in hosts. We found that separately, the two methods do not promote reversibility. Together, using aromatic, chelating amine MOF hosts, single-electron transfer allows for proper alane stabilization to promote reversibility. The pH-dependence study found varying degrees of pH-dependent activity and stability in all electrocatalysts. It was noted that the phase transition in nickel-iron layered double hydroxide for active OER catalysis could be the cause for reduced activity in near-neutral conditions. Since the cobalt-based electrocatalysts did not have as drastic of an activity drop, further study must be done to determine the extent of structural changes in cobalt-based electrocatalysts to reach their active state for water oxidation. By applying systematic variances within water oxidation catalysts and hydrogen storage materials, we gained more detailed insight to structure-property relationships for a multitude of materials.

Committee Chair

Richard Loomis

Committee Members

Bryce Sadtler, Mark Allendorf; Robert Wexler; Rohan Mishra

Degree

Doctor of Philosophy (PhD)

Author's Department

Chemistry

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

4-27-2026

Language

English (en)

Author's ORCID

https://orcid.org/0000-0002-0257-4732

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Available for download on Saturday, April 24, 2027

Included in

Chemistry Commons

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