E. Mádai
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1
Electrochemical CO2 Reduction to Multicarbon Products on MoS2 Catalysts
Engineering sulfur-vacant MoS2 and Co-Catalyst Interfaces for Selective Electrochemical CO2 Reduction to Multicarbon Products
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. ...
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.
Molybdenum disulfide (MoS 2) has emerged as a promising electrocatalyst for the electrochemical reduction of CO 2, 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 2+ products) enabled by the presence of inherent sulfur vacancies in MoS 2 when combined with various ionic liquids as co-catalysts. While MoS 2 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 2+ species. These results provide new insights into defect-mediated catalytic pathways and highlight the importance of electrolyte design in tuning product distribution during CO 2 electroreduction.
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.
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).
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.
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.