Electrodeposition of Crystalline MoS2-Based Heterostructures and Amorphous MoSx-based Alloys and Matrix as Catalysts for the Hydrogen Evolution Reaction

With increasing global energy consumption, increased ammonia demands, ever decreasing fuel reserve, and severe climate change, there has been a large drive to explore various clean, renewable, and affordable energy sources. However, several prolific renewable energy sources, such as wind and solar, suffer from intermittent availability. To overcome this, several strategies have been explored to enable the storage of excess energy in chemical bonds to be utilized later during high demand. H2 has the highest energy density among all chemical fuels and can be combusted to release “clean” energy, with water being the only product. Currently, the primary methods of generating H2 is through steam reforming, coal/oil coke/biomass gasification, and H2O splitting. As all but the latter generate enormous amounts of CO2, there is a drive to develop H2O splitting, a pollution-free, low-cost, and efficient H2 and O2 production technology.
The hydrogen evolution reaction (HER) is a pivotal process in the field of energy conversion and storage, particularly in the context of sustainable hydrogen production. Current electrocatalysts for HER, while effective, are often reliant on precious metals such as platinum, which are expensive and scarce. This highlights the urgent need for the development of new, cost-effective, and abundant electrocatalysts. In this context, molybdenum disulfide (MoS2) based materials have emerged as promising candidates for HER. MoS2, a transition metal dichalcogenide, offers several advantages including natural abundance, cost-effectiveness, and tunable electronic properties. However, the catalytic performance of bulk MoS2 is limited due to a low density of active sites, however, recent research has shown that the catalytic activity of MoS2 can be significantly enhanced by engineering its morphological and structural properties.
This thesis will first explore the challenges and advancements of existing MoS2-based electrocatalysts. Through the rest of the thesis, we use electrodeposition to form various MoS2-based heterostructures, such as CoSx/MoS2, ZnO/MoS2, and ZnO/ZnS/MoS2, as well as the amorphous MoSx phases and several MoSx-based alloys, such as MoSxSey, MoSxOy, and MoTey/MoSx. We utilize a combination of substrate modifications and post-synthesis treatments to modify the overall morphology, crystallinity, and chemistry of the studied material. Using a variety of characterization techniques, this thesis studies the processing-structure-properties of the various electrocatalysts towards the hydrogen evolution reaction with the goal of enabling viable HER electrocatalysts.