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First-principles study of doped hematite surfaces for photoelectrochemical water splitting
Thesis (PhD (Physics))--Univesity of Pretoria, 2020.
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University of Pretoria
2020
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| _version_ | 1867613435540275200 |
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| access_status_str | Open Access |
| author2 | Diale, M. (Mmantsae Moche) |
| author_browse | Diale, M. (Mmantsae Moche) |
| author_facet | Diale, M. (Mmantsae Moche) |
| collection | Thesis |
| dc_rights_str_mv | © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD (Physics))--Univesity of Pretoria, 2020. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/77390 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:36:06.245Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/77390 First-principles study of doped hematite surfaces for photoelectrochemical water splitting Diale, M. (Mmantsae Moche) josephsimfukwe2013@gmail.com Mapasha, Refilwe Edwin Simfukwe, Joseph UCTD Photoelectrochemical water splitting Thesis (PhD (Physics))--Univesity of Pretoria, 2020. Photoelectrochemical (PEC) water splitting, using sunlight and appropriate semiconductors to produce hydrogen (H2) fuel, is a promising route to solve both the production of clean H2 fuel and storage for solar energy. Owing to its various advantages, hematite (α-Fe2O3) has emerged as a promising photoanode material for PEC water splitting. However, its poor electrical conductivity, low carrier mobility, short-hole diffusion length, and fast recombination rates of the electron-hole pairs have greatly limited its full potential for PEC performance. One way to improve the PEC activity of α-Fe2O3 is by doping with other elements. In particular, surface doping is proved to be more beneficial than bulk doping because it reduces the distance moved by the charge carriers from inside the bulk to the surface where they are required for interfacial transfer. In this study first-principles calculations based on density functional theory (DFT) were carried out to investigate the influence of Cu, Zn, Ti and Zr on the {0001} and {01 2} hematite surfaces for enhanced PEC water splitting. Various surfaces of hematite were constructed and their thermodynamic stabilities were determined by calculating surface and formation energies. The {0001} and {01 2} surfaces were found to be the most stable. Besides, all the doped systems were found thermodynamically stable. Furthermore, it was found that Cu doped surface systems does not only decrease the bandgap but also leads to the correct conduction band alignment for spontaneous water splitting. In all calculations, the charge density difference plots and the Bader charge analysis showed accumulation of charge at the top outmost surface, implying the photogenerated charge carriers can efficiently diffuse to the surface for enhanced interfacial charge transfer to the adsorbates. Morever, it was found that even with mono doping of Zn on the topmost layer of the {0001} α-Fe2O3 surface, the bandgap can be decreased without impurity states in the band structure which normally acts as recombination centres. Furthermore, the energetic stability and electronic properties of bimetallic doped {0001} α-Fe2O3 surface with (Zn, Ti) and (Zn, Zr) pairs for enhanced PEC water splitting was also studied. Bimetallic doping is viewed as an important and executable way of not only increasing the conductivity of a semiconductor material but also reducing the quick recombination of the electron-hole pairs. The doped systems showed negative formation energies under both O-rich and Fe-rich conditions implying that they are thermodynamically stable and could be prepared experimentally. Additionally, bimetallic doping of (Zn, Ti) and (Zn, Zr) on the {0001} surface is expected to enhance the PEC performance of α-Fe2O3 because Ti or Zr is capable of increasing the conductivity of α-Fe2O3 due to the substitution of Fe3+ with Ti4+ or Zr4+, while Zn can foster the surface reaction and reduce quick recombination of the electron-hole pairs. We hope that our results provided here will be of great interest to both experimental and theoretical researchers. Ministry of Higher Education, Copperbelt University, Zambia The University of Pretoria, Department of Physics Centre for High-Performance Computer (CHPC), Cape Town Physics PhD (Physics) Restricted 2020-12-17T12:37:30Z 2020-12-17T12:37:30Z 2021-04 2020-01 Thesis * A2021 http://hdl.handle.net/2263/77390 en © 2019 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Photoelectrochemical water splitting First-principles study of doped hematite surfaces for photoelectrochemical water splitting |
| title | First-principles study of doped hematite surfaces for
photoelectrochemical water splitting |
| title_full | First-principles study of doped hematite surfaces for
photoelectrochemical water splitting |
| title_fullStr | First-principles study of doped hematite surfaces for
photoelectrochemical water splitting |
| title_full_unstemmed | First-principles study of doped hematite surfaces for
photoelectrochemical water splitting |
| title_short | First-principles study of doped hematite surfaces for
photoelectrochemical water splitting |
| title_sort | first principles study of doped hematite surfaces for photoelectrochemical water splitting |
| topic | UCTD Photoelectrochemical water splitting |
| url | http://hdl.handle.net/2263/77390 |