|
| Titre : |
Fabrication of Nanostructured Heterojunction Electrode for Photo-Electrocatalytic Hydrogen Evolution Reaction |
| Type de document : |
document électronique |
| Auteurs : |
Ikam Zizi, Auteur ; Rettab, Maroua Nihed, Auteur ; Hamza Belhadj, Directeur de thèse |
| Editeur : |
Sétif:UFA1 |
| Année de publication : |
2025 |
| Importance : |
1 vol (62 f .) |
| Format : |
29cm |
| Langues : |
Français (fre) |
| Catégories : |
Thèses & Mémoires:Chimie
|
| Mots-clés : |
Electrocatalytic activity
Photo-electrocatalysis
Hydrogen Evolution Reaction (HER)
Heterojunction |
| Index. décimale : |
540 - Chimie et sciences connexes |
| Résumé : |
Abstract
Heterojunction nanostructures based on transition metal oxide electrodes have attracted significant attention as electrocatalysts for the hydrogen evolution reaction (HER). In this work, a CoWO₄/ZnO nanostructure heterojunction was developed as an HER electrocatalyst. The individual components were synthesized via the co-precipitation method and subsequently integrated into a heterostructure using the ball milling technique. Compared to pristine CoWO₄ and ZnO, the CoWO₄/ZnO heterojunction demonstrated superior HER activity, requiring a low overpotential of 525.31 mV to achieve a current density of 20 mA cm⁻² in alkaline medium. This enhanced performance is attributed to the synergistic interaction between CoWO₄ and ZnO, resulting in a large number of exposed heterointerfaces that serve as highly abundant active sites. The heterojunction also exhibited rapid charge transfer and a high electrochemical active surface area (ECSA: 9.5 cm²), along with a roughness factor of 38. These characteristics reflect a strong correlation between interfacial engineering and electrocatalytic performance. Furthermore, the CoWO₄/ZnO heterojunction exhibited a significantly higher photocurrent density compared to the individual ZnO and CoWO₄ components, indicating that heterojunction formation enhances the separation efficiency of photogenerated electron–hole pairs in HER. In addition, the band gap energy of the heterojunction was reduced, thereby improving the material’s ability to absorb visible light. These outstanding features, achieved through heterojunction engineering, position the CoWO₄/ZnO electrocatalyst as a highly effective and promising candidate for future applications in photo-electrocatalytic hydrogen production. |
| Note de contenu : |
Table of contents
Abbreviations……………………………………………………………………………….....i
List of figures……………………………………………………………………………….....ii
List of tables……………………………………………………………………...………….. 5
General introduction………………………………………………………………………….1
References……………………………………………………………………………………..3
Chapter I: Literature review
I.1. Nanomaterials…………………………………………………………………………….4
I.1.1. General Properties of Nanomaterials…………………………………………………..…4
I.1.2. Classification of Nanomaterials by Dimensions………………………………………….5
I.2. Approaches for the Synthesis of Nanomaterials…………………………...……………6
I.2.1. Bottom-up Approaches………………………………………………………...……..….7
I.2.2. Top-down Approaches………………………………………………………...………....8
I.3. Characterization of Nanomaterials…………………………………………………..….8
I.4. Metal Oxide Semiconductors……………………………………………………….…....9
I.4.1. Fundamental Properties of Semiconductors………………………………..…………….9
I.4.2. The Fermi Level…………………………………………………………………….…..10
I.4.3. Intrinsic Semiconductor………………………………………………………………...10
I.4.4. Extrinsic Semiconductors……………………………………………………………….10
I.4.5. Flat-band Potential ……………………………………………………………………...11
I.4.6. Band Gap Energie …………………………………………………………………..…..11
I.4.7. Applications of Metal Oxides…………………………………………………………...11
I.5. Hydrogen Production…………………………...……………………………….….......11
I.5.1. Electrocatalysis…………………………………………………………………………12
I.5.1.1. Reaction Mechanism in Different Media……………………………………………..12
I.5.2. Photo-electrocatalysis…………………………………………………………………..13
I.5.3. Electronic Band Alignment in an Electrocatalyst……………………………….………14
I.5.4. The Hydrogen Evolution Reaction (HER)………………………………………………15
I.6. Challenges and Strategies in Photo-electrocatalytic Hydrogen Production………….16
I.7. Heterojunction of Semiconductor………………………………………………….…...17
I.7.1. Straddling Band Alignment (type I heterojunction)…………………………………….18
I.7.2. Staggered Band Alignment (type II heterojunction)…………………………………….18
I.7.3. Broken Band Alignment (type III)………………………………………………………19
References……………………………………………………………………………………20
Chapter Ⅱ: Experimental procedure
Ⅱ.1. Properties of ZnO and CoWO4………………………………………….……………..25
Ⅱ.1.1. Zinc Oxide (ZnO)……………………………………………………………………... 25
Ⅱ.1.2. Cobalt Tungstate (CoWO₄)……………………………………...……………………. 26
Ⅱ.2. Synthesis of CoWO4 and ZnO……………………………………….……………….. 28
II.2.1. Co-precipitation Method…………………………………………….………………....28
II.2.2. Preparation of CoWO4 and ZnO by Co-precipitation…………………………………..28
II.3. Fabrication of CoWO4/ZnO Heterojunction …………………………………..…......32
II.3.1. Vibration Ball Mill ………………………………………….……………………… ...32
II.3.2. CoWO4/ZnO Heterojunction…………………………………………………………..33
Ⅱ.4. Electrode Fabrication………………………………………………………………….34
Ⅱ.4.1. Doctor Blading Method………………………………………………………………...35
Ⅱ.4.2. Electrode Coating Procedure…………………………………………………………..35
Ⅱ.5. Experimental Setup…………………………………………………………………… 36
II.5.1. Setup Assembly…………………………………………………………………...…...36
Ⅱ.5.2. Electrochemical Cell…………………………………………………………………...37
Ⅱ.5.3. Description of Electrodes……………………………………………………………... 37
Ⅱ.6. Electrochemical and Photoelectrochemical Characterization……………………….38
References……………………………………………………………………………………40
Chapter Ⅲ: Results and discussion
III.1. Characterization Techniques…………………………………………………………43
III.1.1. X-Ray Diffraction (XRD)……………………………………………………………..43
III.1.2. UV-Visible Spectroscopy……………………………………………………………..45
III.2. Electrochemical Characterization……………………………………………………46
III.2.1. Linear Sweep Voltammetry…………………………………………………………...46
III.2.2. Tafel Measurement……………………………………………………………………47
III.2.3. Electrochemical Impedance Spectroscopy (EIS)……………………………………...48
III.2.4. Cyclic Voltammetry (CV)…………………………………………………………….49
III.2.5. Electrocatalytic Stability………………………………………………………………51
III.2.6. Photocurrent Analysis………………………………………………………………...52
Ⅲ.2.7. Mott–Schottky Analysis……………………………………………………………...53
Ⅲ.2.8. Mechanism of p-n Heterojunction Formation…………………………………………55
References……………………………………………………………………………………57
Conclusion……………………………………………………………………………………61
Abstract |
| Côte titre : |
MACH/0371 |
Fabrication of Nanostructured Heterojunction Electrode for Photo-Electrocatalytic Hydrogen Evolution Reaction [document électronique] / Ikam Zizi, Auteur ; Rettab, Maroua Nihed, Auteur ; Hamza Belhadj, Directeur de thèse . - [S.l.] : Sétif:UFA1, 2025 . - 1 vol (62 f .) ; 29cm. Langues : Français ( fre)
| Catégories : |
Thèses & Mémoires:Chimie
|
| Mots-clés : |
Electrocatalytic activity
Photo-electrocatalysis
Hydrogen Evolution Reaction (HER)
Heterojunction |
| Index. décimale : |
540 - Chimie et sciences connexes |
| Résumé : |
Abstract
Heterojunction nanostructures based on transition metal oxide electrodes have attracted significant attention as electrocatalysts for the hydrogen evolution reaction (HER). In this work, a CoWO₄/ZnO nanostructure heterojunction was developed as an HER electrocatalyst. The individual components were synthesized via the co-precipitation method and subsequently integrated into a heterostructure using the ball milling technique. Compared to pristine CoWO₄ and ZnO, the CoWO₄/ZnO heterojunction demonstrated superior HER activity, requiring a low overpotential of 525.31 mV to achieve a current density of 20 mA cm⁻² in alkaline medium. This enhanced performance is attributed to the synergistic interaction between CoWO₄ and ZnO, resulting in a large number of exposed heterointerfaces that serve as highly abundant active sites. The heterojunction also exhibited rapid charge transfer and a high electrochemical active surface area (ECSA: 9.5 cm²), along with a roughness factor of 38. These characteristics reflect a strong correlation between interfacial engineering and electrocatalytic performance. Furthermore, the CoWO₄/ZnO heterojunction exhibited a significantly higher photocurrent density compared to the individual ZnO and CoWO₄ components, indicating that heterojunction formation enhances the separation efficiency of photogenerated electron–hole pairs in HER. In addition, the band gap energy of the heterojunction was reduced, thereby improving the material’s ability to absorb visible light. These outstanding features, achieved through heterojunction engineering, position the CoWO₄/ZnO electrocatalyst as a highly effective and promising candidate for future applications in photo-electrocatalytic hydrogen production. |
| Note de contenu : |
Table of contents
Abbreviations……………………………………………………………………………….....i
List of figures……………………………………………………………………………….....ii
List of tables……………………………………………………………………...………….. 5
General introduction………………………………………………………………………….1
References……………………………………………………………………………………..3
Chapter I: Literature review
I.1. Nanomaterials…………………………………………………………………………….4
I.1.1. General Properties of Nanomaterials…………………………………………………..…4
I.1.2. Classification of Nanomaterials by Dimensions………………………………………….5
I.2. Approaches for the Synthesis of Nanomaterials…………………………...……………6
I.2.1. Bottom-up Approaches………………………………………………………...……..….7
I.2.2. Top-down Approaches………………………………………………………...………....8
I.3. Characterization of Nanomaterials…………………………………………………..….8
I.4. Metal Oxide Semiconductors……………………………………………………….…....9
I.4.1. Fundamental Properties of Semiconductors………………………………..…………….9
I.4.2. The Fermi Level…………………………………………………………………….…..10
I.4.3. Intrinsic Semiconductor………………………………………………………………...10
I.4.4. Extrinsic Semiconductors……………………………………………………………….10
I.4.5. Flat-band Potential ……………………………………………………………………...11
I.4.6. Band Gap Energie …………………………………………………………………..…..11
I.4.7. Applications of Metal Oxides…………………………………………………………...11
I.5. Hydrogen Production…………………………...……………………………….….......11
I.5.1. Electrocatalysis…………………………………………………………………………12
I.5.1.1. Reaction Mechanism in Different Media……………………………………………..12
I.5.2. Photo-electrocatalysis…………………………………………………………………..13
I.5.3. Electronic Band Alignment in an Electrocatalyst……………………………….………14
I.5.4. The Hydrogen Evolution Reaction (HER)………………………………………………15
I.6. Challenges and Strategies in Photo-electrocatalytic Hydrogen Production………….16
I.7. Heterojunction of Semiconductor………………………………………………….…...17
I.7.1. Straddling Band Alignment (type I heterojunction)…………………………………….18
I.7.2. Staggered Band Alignment (type II heterojunction)…………………………………….18
I.7.3. Broken Band Alignment (type III)………………………………………………………19
References……………………………………………………………………………………20
Chapter Ⅱ: Experimental procedure
Ⅱ.1. Properties of ZnO and CoWO4………………………………………….……………..25
Ⅱ.1.1. Zinc Oxide (ZnO)……………………………………………………………………... 25
Ⅱ.1.2. Cobalt Tungstate (CoWO₄)……………………………………...……………………. 26
Ⅱ.2. Synthesis of CoWO4 and ZnO……………………………………….……………….. 28
II.2.1. Co-precipitation Method…………………………………………….………………....28
II.2.2. Preparation of CoWO4 and ZnO by Co-precipitation…………………………………..28
II.3. Fabrication of CoWO4/ZnO Heterojunction …………………………………..…......32
II.3.1. Vibration Ball Mill ………………………………………….……………………… ...32
II.3.2. CoWO4/ZnO Heterojunction…………………………………………………………..33
Ⅱ.4. Electrode Fabrication………………………………………………………………….34
Ⅱ.4.1. Doctor Blading Method………………………………………………………………...35
Ⅱ.4.2. Electrode Coating Procedure…………………………………………………………..35
Ⅱ.5. Experimental Setup…………………………………………………………………… 36
II.5.1. Setup Assembly…………………………………………………………………...…...36
Ⅱ.5.2. Electrochemical Cell…………………………………………………………………...37
Ⅱ.5.3. Description of Electrodes……………………………………………………………... 37
Ⅱ.6. Electrochemical and Photoelectrochemical Characterization……………………….38
References……………………………………………………………………………………40
Chapter Ⅲ: Results and discussion
III.1. Characterization Techniques…………………………………………………………43
III.1.1. X-Ray Diffraction (XRD)……………………………………………………………..43
III.1.2. UV-Visible Spectroscopy……………………………………………………………..45
III.2. Electrochemical Characterization……………………………………………………46
III.2.1. Linear Sweep Voltammetry…………………………………………………………...46
III.2.2. Tafel Measurement……………………………………………………………………47
III.2.3. Electrochemical Impedance Spectroscopy (EIS)……………………………………...48
III.2.4. Cyclic Voltammetry (CV)…………………………………………………………….49
III.2.5. Electrocatalytic Stability………………………………………………………………51
III.2.6. Photocurrent Analysis………………………………………………………………...52
Ⅲ.2.7. Mott–Schottky Analysis……………………………………………………………...53
Ⅲ.2.8. Mechanism of p-n Heterojunction Formation…………………………………………55
References……………………………………………………………………………………57
Conclusion……………………………………………………………………………………61
Abstract |
| Côte titre : |
MACH/0371 |
|
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