Development of noble metal-based high entropy alloy thin film by atomic layer deposition

High entropy alloys (HEAs) have been proven to exhibit outstanding catalytic properties, as their electronic structures can be tuned by adjusting the compositions. Owing to the unique high entropy effect, HEAs are thermodynamically stable, which enable them to work in harsh environment without being...

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Main Author: Zou, Yiming
Other Authors: Alfred Tok Iing Yoong
Format: Thesis-Doctor of Philosophy
Language:English
Published: Nanyang Technological University 2024
Subjects:
Online Access:https://hdl.handle.net/10356/178757
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author Zou, Yiming
author2 Alfred Tok Iing Yoong
author_facet Alfred Tok Iing Yoong
Zou, Yiming
author_sort Zou, Yiming
collection NTU
description High entropy alloys (HEAs) have been proven to exhibit outstanding catalytic properties, as their electronic structures can be tuned by adjusting the compositions. Owing to the unique high entropy effect, HEAs are thermodynamically stable, which enable them to work in harsh environment without being corroded. Moreover, the highly disordered atomic arrangement of HEA leads to various active sites on the catalyst surface, enhancing the interaction between the surface and absorbents. However, challenges still remain, including the aggregation of HEA nanoparticles, the difficulty in synthesizing homogeneous multi-element alloys, and unknown relationship between the composition and catalytic properties of HEA, etc. In this thesis, a novel method combining atomic layer deposition and electrical Joule heating (ALD-EJH) is developed to synthesize noble metal high entropy alloy (HEA) thin film as a highly efficient catalyst towards hydrogen evolution reaction (HER). To achieve this goal, several major challenges are to be overcome, including the development of reliable noble metal ALD processes, verifying the feasibility of EJH process to multi-layer coatings, and modifying the catalytic performance of HEA thin films. Therefore, the scope of this thesis includes both the development of synthesis techniques and the investigation into the materials. For ALD process development, safe and reproducible ALD processes for Pt, Pd, Ir, Rh, and Ru coatings have been created and modified. The deposition of the selected noble metals is examined to obtained uniform surface and precisely controlled thickness. The mechanism behind the reaction is revealed and discussed based on experimental and simulation results. The concerned properties of the deposited thin films, such as growth rate, microstructure, and surface evolution are characterized. For the first time, EJH process has been applied to the multiple layers deposited by ALD method to accomplish the alloying. The ultrafast ramping and cooling rate provided by EJH treatment facilitate the interdiffusion within the multi-element system and prevent the phase separation, resulting in homogeneous HEA thin film, regardless of the large immiscible gaps between selected noble metals. Finally, RhRuPtPdIr HEA nanofilm is fabricated on glassy carbon electrode, and exhibits extraordinary catalytic activity and stability for HER in harsh environment. The mechanism of the performance was analyzed by simulation works, in which the adjustment of electronic structure of d-band of HEA accounts for the outstanding catalytic properties. By combining the experimental and simulation data, the relationship between the surface microstructure of HEA and its electronic structure is established. In terms of practical advances, this thesis validating the great potential of noble metal HEA nanofilm as an exceptional catalyst. Plus, ALD-EJH is introduced as a universal method to synthesize various nanomaterials, significantly expanding the range of materials that can be prepared using ALD.
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spelling ntu-10356/1787572024-08-01T08:11:46Z Development of noble metal-based high entropy alloy thin film by atomic layer deposition Zou, Yiming Alfred Tok Iing Yoong School of Materials Science and Engineering MIYTok@ntu.edu.sg Engineering Noble metals High entropy alloy Thin films Atomic layer deposition Electrical Joule heating Catalysis High entropy alloys (HEAs) have been proven to exhibit outstanding catalytic properties, as their electronic structures can be tuned by adjusting the compositions. Owing to the unique high entropy effect, HEAs are thermodynamically stable, which enable them to work in harsh environment without being corroded. Moreover, the highly disordered atomic arrangement of HEA leads to various active sites on the catalyst surface, enhancing the interaction between the surface and absorbents. However, challenges still remain, including the aggregation of HEA nanoparticles, the difficulty in synthesizing homogeneous multi-element alloys, and unknown relationship between the composition and catalytic properties of HEA, etc. In this thesis, a novel method combining atomic layer deposition and electrical Joule heating (ALD-EJH) is developed to synthesize noble metal high entropy alloy (HEA) thin film as a highly efficient catalyst towards hydrogen evolution reaction (HER). To achieve this goal, several major challenges are to be overcome, including the development of reliable noble metal ALD processes, verifying the feasibility of EJH process to multi-layer coatings, and modifying the catalytic performance of HEA thin films. Therefore, the scope of this thesis includes both the development of synthesis techniques and the investigation into the materials. For ALD process development, safe and reproducible ALD processes for Pt, Pd, Ir, Rh, and Ru coatings have been created and modified. The deposition of the selected noble metals is examined to obtained uniform surface and precisely controlled thickness. The mechanism behind the reaction is revealed and discussed based on experimental and simulation results. The concerned properties of the deposited thin films, such as growth rate, microstructure, and surface evolution are characterized. For the first time, EJH process has been applied to the multiple layers deposited by ALD method to accomplish the alloying. The ultrafast ramping and cooling rate provided by EJH treatment facilitate the interdiffusion within the multi-element system and prevent the phase separation, resulting in homogeneous HEA thin film, regardless of the large immiscible gaps between selected noble metals. Finally, RhRuPtPdIr HEA nanofilm is fabricated on glassy carbon electrode, and exhibits extraordinary catalytic activity and stability for HER in harsh environment. The mechanism of the performance was analyzed by simulation works, in which the adjustment of electronic structure of d-band of HEA accounts for the outstanding catalytic properties. By combining the experimental and simulation data, the relationship between the surface microstructure of HEA and its electronic structure is established. In terms of practical advances, this thesis validating the great potential of noble metal HEA nanofilm as an exceptional catalyst. Plus, ALD-EJH is introduced as a universal method to synthesize various nanomaterials, significantly expanding the range of materials that can be prepared using ALD. Doctor of Philosophy 2024-07-04T06:58:43Z 2024-07-04T06:58:43Z 2024 Thesis-Doctor of Philosophy Zou, Y. (2024). Development of noble metal-based high entropy alloy thin film by atomic layer deposition. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/178757 https://hdl.handle.net/10356/178757 10.32657/10356/178757 en A1983c0032 This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). application/pdf Nanyang Technological University
spellingShingle Engineering
Noble metals
High entropy alloy
Thin films
Atomic layer deposition
Electrical Joule heating
Catalysis
Zou, Yiming
Development of noble metal-based high entropy alloy thin film by atomic layer deposition
title Development of noble metal-based high entropy alloy thin film by atomic layer deposition
title_full Development of noble metal-based high entropy alloy thin film by atomic layer deposition
title_fullStr Development of noble metal-based high entropy alloy thin film by atomic layer deposition
title_full_unstemmed Development of noble metal-based high entropy alloy thin film by atomic layer deposition
title_short Development of noble metal-based high entropy alloy thin film by atomic layer deposition
title_sort development of noble metal based high entropy alloy thin film by atomic layer deposition
topic Engineering
Noble metals
High entropy alloy
Thin films
Atomic layer deposition
Electrical Joule heating
Catalysis
url https://hdl.handle.net/10356/178757
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