Molybdenum disulfide (MoS) has emerged as a promising electrocatalyst for the electrochemical reduction of CO, primarily yielding carbon monoxide. However, product selectivity is known to be highly sensitive to structural features such as edge termination and defect density. In this work, we report the formation of higher hydrocarbons (C+ products) enabled by the presence of inherent sulfur vacancies in MoS when combined with various ionic liquids as co-catalysts. While MoS has traditionally shown limited hydrocarbon output, our findings demonstrate for the first time that native defect sites, interacting synergistically with the electrolyte environment, can facilitate the production of significant amounts of C+ species. These results provide new insights into defect-mediated catalytic pathways and highlight the importance of electrolyte design in tuning product distribution during CO electroreduction.

Electrochemical carbon dioxide reduction represents a promising pathway toward a circular carbon economy and the achievement of net zero emissions. Realising this potential requires catalysts that balance activity, selectivity, stability, earth-abundance, and economic feasibility. Molybdenum disulfide is an attractive candidate for this purpose due to its layered structure, tunable properties, and scalable synthesis, yet its performance in the electrochemical reduction of carbon dioxide remains limited by fundamental factors that affect conductivity, active site formation, and product selectivity. This thesis investigates strategies to enhance the catalytic behaviour of molybdenum disulfide by engineering its structural and electronic environment through alkali ion intercalation, vacancy induction, and the use of co-catalysts.

The thesis begins with an introduction to the electrochemical reduction of carbon dioxide and the challenges associated with achieving efficient and selective conversion. A detailed literature review follows, covering the properties of molybdenum disulfide, its reported behaviour in carbon dioxide reduction, and known structural limitations. Background on alkali ion intercalation, associated phase transitions, and force field considerations for molecular dynamics simulations is also provided to support the modelling work presented later.

The first research component examines the tunability of the electronic properties of molybdenum disulfide through controlled intercalation of alkali metal ions. Molecular dynamics simulations reveal the atomic scale mechanism of intercalation, demonstrating that the hydration shell of incoming ions forms an energy barrier that must be reorganised for successful insertion. Complementary experimental characterisation confirms that intercalation introduces additional defects and increases electronic conductivity. Potassium produces a more pronounced effect than sodium, consistent with its weaker hydration and greater structural impact. However, increased conductivity does not improve performance in carbon dioxide reduction. Instead, it correlates with a decline in catalytic efficiency, indicating that electronic enhancement alone is not sufficient to promote the desired reaction pathways.

Subsequent chapters, not detailed here, expand this investigation toward vacancy engineering and co-catalyst selection to influence product distribution and promote formation of higher carbon products. Combined molecular simulations and experimental studies provide insight into how local structure and interfacial environment govern the selectivity of the reaction.

Overall, this thesis demonstrates that the catalytic behaviour of molybdenum disulfide can be systematically tuned through structural modification and environmental control. The findings highlight key mechanistic factors that influence conductivity, defect formation, and selectivity, offering guidance for the rational design of improved catalysts for electrochemical carbon dioxide reduction.

2D materials, characterized by their extensive surface area and customizable chemical and electronic properties, offer compelling advantages as advanced materials. These unique attributes pave the way for the development of next-generation electronics and optoelectronics, photo- and electro-catalysis, energy storage and conversion devices, and sensors. The most prominent and commonly available 2D transition metal dichalcogenide, molybdenum disulfide (MoS₂), has already shown its potential for advanced applications. However, its relatively unfavorable electronic structure and limited intrinsic conductivity lower its suitability for applications that require high conductivity, such as electrocatalysts. One way to enhance its conductivity is by electrochemically intercalating alkali metal ions, e.g., Na⁺ and K⁺, into its layered structure, potentially adjusting its electronic structure. Here, we present a comprehensive investigation into the atomic-scale intercalation mechanism using molecular dynamics simulations, complemented by experimental analysis of structural and electronic properties at the macro scale through various characterization techniques. It is demonstrated that the hydration shell of ions serves as an energy barrier to intercalation as it undergoes a structural change during the intercalation. When alkali metal ions are intercalated into MoS₂, they introduce more defects and enhance conductivity. Notably, these effects are more pronounced for potassium than for sodium.

There is no denying that the world is heading towards an era powered by green energy resources. The need for highly efficient devices for sustainable energy storage and utilization is vital in transitioning towards the full-time realization of renewable energy for our society. In the last four decades, there have been groundbreaking developments in the large-scale commercialization of Li-ion batteries, electric vehicles, and solar power, all made possible by an in-depth understanding of the science of materials. Theoretically, there exists no problem in the production of green hydrogen, as oxides of Ir, Rh, and Pt, and the elements themselves, are excellent catalysts for the electrochemical hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with fast kinetics. Thus, more work remains to be done in the area of green energy material technology. The problem lies with the critical availability and cost of these materials, which is the underlying motivation for finding alternative energy materials and technologies. This energy transition era presents us with an opportunity to expand our horizons and knowledge in chemical engineering, materials science, and allied fields through two-dimensional (2D) nanomaterials. These materials exhibit intriguing characteristics in contrast to their bulk counterparts, coupled with interchangeable electronic properties depending on the synthesis methodologies employed. The chapter begins by introducing the family of graphene nanosheets and expands into a discussion of advanced 2D families, such as transition metal dichalcogenides (TMDs), MXenes, transition metal oxides (TMOs), and hexagonal boron nitride (h-BN).

In the search for effective high-tech materials for energy conversion and storage devices, spinel-structured nickel ferrite (NiFe₂O₄) has been identified as a promising anode material for lithium-ion batteries (LIBs). However, the influence of different morphologies and surface properties of NiFe₂O₄ nanoparticles on battery performance is hardly addressed. To understand the effect of different morphologies and surface properties on the lithium-ion storage performance, NiFe₂O₄ nanoparticles were synthesized through four different synthesis conditions: NFO-S, NFO-U, NFO-G, and NFO-C. The formation of polycrystalline inverse spinel NiFe₂O₄ was confirmed through XRD, FTIR, and Raman spectroscopy. The morphologies of the obtained samples were studied using FESEM, and it was found that the four different synthesis conditions employed here enabled us to obtain NiFe₂O₄ with four different morphologies. The surface chemistry, surface area and porosity of the NiFe₂O₄ samples were respectively characterized using XPS and BET. The electrochemical performance of the four NiFe₂O₄ samples as anode material was studied by fabricating lithium-ion half-cells. NiFe₂O₄ sample obtained from surfactant-free synthesis condition (NFO-S) displayed a high initial discharge and charge capacity of 2258 mAh/g and 1815 mAh/g, respectively at the current density of 100 mA/g. Even after 100 cycles, NFO-S showed a better discharge capacity of 116 mAh/g at the current density of 100 mA/g, compared to the other samples studied here. The observed higher capacity of the NFO-S sample is attributed to the higher surface area (40.8 m²/g) and pore volume (0.190 cm³/g). The NiFe₂O₄ sample prepared with cationic CTAB surfactant (NFO-C) showed better cyclic stability with a stable coulombic efficiency of 98.5% at the 100th cycle, mainly attributed to its nanocube morphology with lower surface area (16.1 m²/g) and pore volume (0.087 cm³/g).

Titanium surfaces featuring high-aspect ratio (HAR) nanopillars can have antimicrobial and osteogenic properties. Nevertheless, the impact of these surfaces on immune cells and their potential for immunomodulation remain unclear. In this study, the effects of HAR titanium nanopillars produced by dry-etching (DETi) on the response of unstimulated (M0) and pro-inflammatory (M1) murine macrophages (J774A.1) have been explored. The findings revealed changes in the morphology and crystallinity of the DETi nanopillars along their height. After 48 h of culture, both M0 and M1 stimulated macrophages displayed a more elongated morphology, a smoother cell surface, and shorter cellular protrusions on the more hydrophilic and rough DETi surfaces. Furthermore, DETi surfaces induced polarization of M0 cells towards M2 phenotypes, whereas M1 stimulated cells showed M2-like elongated morphologies while maintaining a stronger pro-inflammatory response to DETi surfaces relative to the glass control. The findings indicate that the DETi surfaces can induce morphological changes in macrophages and specific immunomodulatory effects depending on their initial phenotype, highlighting the potential of such biomaterials to incorporate an immunomodulatory biofunctionality next to the osteogenic and bactericidal ones.

The development of an effective and reliable sensor with the capability to detect ammonia (NH₃) gas at room temperature exerts a significant influence on the sensor industry. The gas sensing performance is notably improved by the formation of a heterostructure between metal oxide with metal sulfides. In this study, pure ZnIn₂S₄ (ZIS), Cu₂O and heterostructures of ZIS with 5, 10 and 20 wt% of Cu₂O were successfully prepared using hydrothermal, co-precipitation and heat treatment methods, respectively. A thorough investigation has been carried out to examine the sensing capabilities of all the materials upon exposure to NH₃ with different concentrations (1, 5, 10, 15, 20, 25 and 50 ppm) at room temperature (RT). Impressively, the composite material 0.9ZnIn₂S₄/0.1Cu₂O (ZIS-10) has exhibited remarkable gas sensitivity compared to pristine ZIS and Cu₂O towards 25 ppm NH₃, low limit of detection (1 ppm) with fast response/recovery times (37/25 sec). The improved performance of the ZIS-10 composite sensor may be ascribed to the synergistic effect between ZIS and Cu₂O, which facilitates the electron transfer from ZIS to the Cu₂O at the interface. The plausible gas-sensing mechanism and the pathways responsible for enhanced sensing are also discussed in detail.