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Functional alkali & transition metal-based ternary chalcogenides: design, properties and energy applications
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Date
2025-12
Abstract
This thesis reports the synthesis of novel, environmentally benign colloidal nanocrystals (NCs) from the ABZ class (A = alkali metals or +1 cations, B = metals with variable valency, Z = chalcogen) and evaluates their potential for sustainable energy applications. Particular emphasis is placed on the influence of reaction parameters, such as ligands, precursors, temperature, and time, on reaction kinetics and mechanisms. These processes are elucidated through advanced structural, spectroscopic, and compositional analysis. A central theme of this work is the mechanistic understanding of ternary metal chalcogenide NC formation, advancing colloidal synthesis toward rational and retrosynthetic design strategies.
Chapter 3 presents the synthesis of sustainable and tunable Na3Cu4S4 and Na2Cu4S3 NCs. A single source precursor decomposes in oleylamine to form a Cu-S template into which Na incorporates. By tuning the reactivity of sulfur precursors, phase selection between the two ternaries is achieved. Mechanistic insights reveal a previously unobserved predictive formation pathway in alkali-metal-based ternary chalcogenides. Density Functional Theory (DFT) calculations predict semiconducting behaviour for Na2Cu4S3 and metallic behaviour for Na3Cu4S4, highlighting their potential in thermoelectric and photovoltaic applications.
Chapter 4 introduces a template-based colloidal synthesis strategy for NaInS2 and its selenium analogue, NaIn3Se5, representing the first report of the latter. This two-step mechanism, supported by advanced characterisation, demonstrates how binary metal chalcogenide templates direct Na intercalation to yield phase-pure ternary NCs. Mechanistic studies reveal a predictive crystallographic pathway, while optical characterisation establishes a foundation for exploring their functional properties in energy applications.
Chapter 5 explores an alternative design strategy in which Cu occupies the “A” site, demonstrating the first colloidal synthesis of nanoscale Cu4Bi4Se9. This complex ternary chalcogenide requires precise tuning of reaction conditions for the formation of a phase-pure product. Mapping the reaction space identified key parameters governing synthesis. When applied as an anode material for potassium-ion batteries, Cu4Bi4Se9 NCs exhibited strong tolerance to volume expansion, excellent cycling stability, and a progressively dominant surface-controlled charge storage behaviour at high scan rates. This class of materials is showcased as promising candidates for sustainable energy storage.
Overall, this thesis establishes design principles and mechanistic insights for the colloidal synthesis of ABZ nanomaterials, expanding access to novel ternary phases and highlighting their structure-property relationships for targeted energy applications.
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University of Limerick
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Sustainable Development Goals
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Attribution-NonCommercial-ShareAlike 4.0 International