Transition Metal Dichalcogenides for Use in Hydrogen Evolution Reaction, CO2 Reduction and Their Photoluminescence Spectroelectrochemistry
Transition metal dichalcogenides (TMDs) are semiconductors of the form MX2, where M is a transition metal (Mo, W, etc.) and X is a chalcogen atom. They are structured in layers of M atoms sandwiched between two layers of X atoms. Two-dimensional TMDs (2D-TMDs) consist of a single layer of atoms that have the structure X-M-X and have electronic properties that differ from the bulk material. In the search for efficient and low-cost catalysts for renewable energy harvesting and conversion and storage, TMDs have emerged as promising catalysts for alternative energy such as photovoltaic water splitting anodes, hydrogen evolution reaction, CO2 reduction, photovoltaic absorber layers, and protective layers for photovoltaic devices. The structure of the TMDs can also be tuned at the monolayer level to increase catalytic activity by doping and introducing defects to enhance electrocatalytic hydrogen reduction. The highly tunable structure also leads to tunable optical properties that are useful in next-generation optoelectronics such as light-emitting diodes (LEDs), field-effect transistors (FETs), and ultra-sensitive molecular sensing due to their unique surface-sensitive optical properties. Learning how the structure affects the catalytic and optical properties serves as an important area of research to tune TMDs to produce more efficient catalysts and serve in various optical applications. This dissertation will focus on developing and understanding TMD catalysts for proton reduction, CO2 reduction, and also their spectroelectrochemical properties. Chapter 1 of this dissertation provides an overview of recent progress made in the field of TMDs and the goals of this doctoral research work. Chapter 2 summarizes the operation principles of the critical instrumental and experimental methods of this research work. Chapter 3 describes proton reduction characteristics of electrodeposited TMD thin-film electrodes and structural confirmation with advanced characterization techniques such as XPS depth profiling to understand the synthesized structure. Chapter 4 is devoted to the investigation of the photophysical properties and spectroelectrochemistry performance of 2D TMDs using SECM, SECCM, and spectroelectrochemical techniques. Chapter 5 describes the electrocatalytic CO2 reduction characterization of liquid exfoliated MoS2 film and an extensive literature overview of the field of photocatalytic CO2 reduction with TMD heterostructures. Finally, Chapter 6 summarizes the entire research work and challenges and proposed plans to address these challenges.