Electrochemical CO2 Reduction to Multicarbon Products on MoS2 Catalysts

Abstract

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.