Universität zu Köln

Ji, Seulgi (2025). Thermodynamics-based Design of Wide Band Gap Semiconductor Catalysts. PhD thesis, Universität zu Köln.

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Abstract

Thermodynamics is capable of giving accurate predictions of phase stabilities of materials and rate-determining steps in chemical reactions. Numerous studies based on thermodynamic principles, especially when combined with computational methods, have made significant contributions to materials development. In particular, the currently adopted thermodynamics-based theoretical models have successfully elucidated surface chemical reactions and catalytic phenomena on metallic materials. However, as modern energy conversion technologies involve electrochemical and photochemical reactions of complicated nanostructured materials, conventional ab initio thermodynamics approach showed unreliable predictions and low feasibilities originating from the limitations of conventional atomic scale modeling and first principles calculation methods. In this regard, my PhD research has focused on advancing a theoretical model for enhanced understanding of surface reaction mechanisms in semiconductors and complex materials by combining quantum mechanics ab initio calculations and Fermi-Dirac statistics and by considering vibrational entropy terms for certain catalytic reactions having a narrow temperature window. With the consideration of the electron chemical potential (Fermi level) in the computation of adsorption energies for catalytic reaction intermediates on wide band gap semiconductor surfaces, catalytic phenomena in (complex) nanomaterials could be well explained with much improved accuracy and precision. This work presents how the new theoretical model can advance the understanding of catalytic and photoelectrochemical reactions in wide band gap semiconductors with complex nanostructures using two model systems: cerium dioxide (CeO2) for the complex reaction of methane oxidation, and titanium dioxide (TiO2) for the widely studied reaction of photocatalytic water splitting. To verify the reliability of the theoretical model, experimental studies were performed for water oxidation on TiO2 photoanodes. TiO2 thin films with varied grain sizes were prepared by the chemical vapor deposition (CVD) of [Ti(OiPr)4] precursors under kinetic control, leading to distinct photoelectrochemical catalytic activities. By considering both surface reaction kinetics and the hole transport efficiency in adsorption energy calculations, this study demonstrates the applicability of theoretical model in bridging theoretical predictions with experimental PEC results. Overall, this work expands the new theoretical framework from electrochemical catalysis to photoelectrochemical catalysis, providing new insights and theoretical strategies for rationally designing the semiconductor catalysts.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Ji, Seulgi 157ch157@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-795961
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Inorganic Chemistry
Subjects:	Physics Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language Thermodynamics English Semiconductor Catalysts English Multi-scale Theoretical Modeling English Experimental Validation English
Date of oral exam:	27 November 2025
Referee:	Name Academic Title Mathur, Sanjay Prof. Dr. Dr. (h.c.) Lindfors, Klas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79596