Date of Award

Spring 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering & Materials Science (ENAS)

First Advisor

Cha, Judy

Abstract

Meeting the growing energy demands of the 21st century is one of the greatest problems facing humanity, which has led to intense research into improving energy generation, storage, and transportation. To meet this challenge, many researchers have focused on nanomaterials, which offer unique opportunities for property modulation, attractive kinetics, and increased surface area. Two-dimensional (2D) materials are a class of nanomaterial consisting of atomically thin sheets with a wide range of attractive properties and the weak interlayer van der Waals interactions in these compounds can be exploited to stack layers of different materials with an atomically smooth interface to form a hybrid material called a heterostructure. Despite recent advances in identifying promising 2D materials and heterostructures for potential applications for energy technology, there is a significant need for the development of mechanistic understandings of these materials. In this dissertation, 2D materials are integrated into a nanodevice architecture to systematically probe the mechanisms of 2D electrochemical energy materials. We investigate the synthesis of high-quality monolayer crystals of MoS2, and highlight the role of elevated sulfur concentration in suppressing the formation of unwanted suboxide and oxysulfide intermediate products during the stepwise sulfurization of MoO3 to MoS2. Using these high-quality crystals of MoS2, we investigate the electrocatalytic production of hydrogen with MoS2/WTe2 heterostructures, and demonstrate that enhanced charge injection through the heterointerface optimizes the catalytic performance of MoS2. Our investigation of the electrochemical intercalation of lithium into heterostructures of hexagonal boron nitride, graphene, and MoS2 demonstrates the key role that heterointerfaces play in controlling both the kinetics and thermodynamics of the lithium-induced structural phase transition in MoS2. We further probe the staging of intercalated lithium within graphene, and the effect of mechanical strain on this ordering. Finally, we investigate the influence of the thickness of MoS2 flakes on the kinetics of its lithium-induced structural phase transition. The nanodevice approach in this dissertation seeks to systematically probe the factors that can affect the electrochemistry of 2D energy materials. We demonstrate the importance of charge injection upon the performance of 2D electrocatalysts and how heterointerfaces, support substrates, and mechanical strain can modify the phase stability and intercalation dynamics of 2D materials. These findings have implications for the production of renewable fuels, nanostructuring metal-ion battery and supercapacitor electrodes, and for many other device applications utilizing 2D nanomaterials. Our aim is to inform future materials engineering and energy device architecture for the next generation of nanostructured energy technology.

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