Nanostructured Engineered Photoelectrode for Unassisted Photoelectrochemical Hydrogen Peroxide Production = 무보조 광전기화학적 과산화수소 생산을 위한 나노구조 설계 광전극

다국어 초록 (Multilingual Abstract)

Hydrogen peroxide (H2O2) is known as a "green oxidant" in green chemical fields such as pollution control, medical disinfection and semiconductor cleaning due to its strong oxidizing properties and non-polluting decomposition products. Current industrial production mainly relies on the anthraquinone (AQ) method. Although the process is mature, it has high energy consumption, strong centralization, and is accompanied by transportation and safety risks, making it difficult to meet the growing demand for decentralized and low-carbonization. Photoelectrochemical (PEC) technology can directly convert solar energy into chemical energy, produce H2O2 at the photoanode through the two-electron water oxidation reaction (2e⁻ WOR), and simultaneously precipitate H2 at the cathode, realizing a high value-added path of "one water, two products". Among the many visible light photoanode materials, bismuth divanadate (BiVO4) is regarded as the most promising 2e⁻ WOR electrode due to its band gap of about 2.4 eV, suitable valence band position, non-toxicity and abundant reserves. However, BiVO4 still faces bottlenecks such as short hole diffusion length, high surface trap density and easy photocorrosion, which leads to serious recombination at the semiconductor/electrolyte interface and makes it difficult to fully utilize photogenerated holes.
In this respect, this doctoral dissertation proposes the utilization of BiVO4 as efficient water oxidation photoanodes by introducing nanostructure, heterojunction, and H2O2 cocatalysts. For unassisted solar water splitting, PV-PEC tandem cells comprising nanostructured heterojunction photoanodes and perovskite/Si solar cells are fabricated, and solar-to-chemicals conversion efficiency is evaluated.
The first study reports the introduction of metal oxide passivation layers hinder the OER activity and enhance the H2O2 production of PEC performances of BiVO4. Although traditional oxygen evolution catalysts (NiOx, CoOₓ, FeOOH, IrOₓ, etc.) can accelerate interfacial charge transfer, they tend to favor the four-electron O₂ evolution reaction and even introduce new recombination centers, offsetting the improvement in H2O2 selectivity. The recently emerged "non-catalytic" oxide coatings (TiO2, In2O3, Al2O3) focus on surface passivation, but TiO2 has poor conductivity and band mismatch, while In2O3 and Al2O3 are prone to forming insulating barriers, resulting in increased interface resistance. The ideal coating should have high conductivity, appropriate band alignment and chemical inertness to fully release the potential of BiVO4. This work uses the single-layer precise control and high conformality of atomic layer deposition (ALD) to construct an ultra-thin SnO2 shell of ≤ 5 nm on the surface of nanoporous BiVO4, and systematically compares it with TiO2, In2O3, and Al2O3. The results show that the SnO2 coating exhibits triple synergistic advantages, the most critical of which are: interface band reregulate alleviating excessive band bending Excessive downward band bending will raise the hole injection barrier and enhance interface recombination. Relying on the above advantages, the SnO2/BiVO4 photoanode achieves leading photocurrent density and H2O2 Faraday efficiency, and shows excellent photostability, laying a material foundation for PEC-driven distributed H₂O₂∕H₂ synergistic production.
The second study focuses on a novel configuration of CaSnO3/SnO2/BiVO4 photoanode as an archetype to boost photoelectrochemical performance by exploiting the synergistic combination of heterojunction construction and morphology modification. It is discovered that the introduction of WO3 NRs as the ETL creates an optimized type II heterojunction with BiVO4, which enhances charge separation by enabling favorable electron transport and hole. Also a synergistic strategy is employed by introducing SnO2 as a passivation layer on the BiVO4 photoanode and utilizing CaSnO3 as a cocatalyst, which achieves highly selective and efficient solar-driven PEC H2O2 generation by effectively suppressing O2 formation. The SnO2 overlayer can modulate interfacial energetics of BiVO4 and alleviates surface charge recombination. Furthermore, the heterostructure SnO2/BiVO4 reduce band bending at the photoanode/electrolyte interface, which near-completely inhibits O2 evolution. After loading cocatalyst CaSnO3, further enhances the H2O2 generated efficiency toward the two-electron water oxidation pathway. The resulting CaSnO3/SnO2/BiVO4 photoanode achieves an average Faradaic efficiency (FE) of 90% over wide potential range of 0.6-2.1 VRHE, with a H2O2 generation rate of 0.838 μmol cm−2 min−1 and a photocurrent density of 5.3 mA·cm−2 at 1.23 VRHE under AM 1.5 illumination. Unassisted photoelectrochemical (PEC) water oxidation for solar-to-chemical conversion (SCC) of hydrogen peroxide (H2O2) on the anode is challenging, but it holds significant potential for advancing sustainable development. Unassisted photoelectrochemical (PEC) water oxidation for solar-to-chemical conversion (SCC) of hydrogen peroxide (H2O2) on the anode is challenging, but it holds significant potential for advancing sustainable development. When integrated with a perovskite/Si tandem solar cell under tandem illumination, the system demonstrates a SCC efficiency of 1.12% and a high H2O2 production rate of approximately 0.576 μmol cm−2 min−1, representing a new direction for maximizing solar energy utilization. This work offers a promising step toward the development of fully self-powered PEC devices for decentralized H2O2 production in environmental applications.
Hexagonal boron nitride (h-BN) is an excellent support material for nanocatalysts due to its two-dimensional (2D) architecture morphology and physiochemical stability. In this study, a chemically stable, recoverable, eco-friendly, and magnetic h-BN/Pd/Fe2O3 catalyst was prepared by a one-step calcining process, in which Pd and Fe2O3 nanoparticles (NPs) were uniformly decorated on the surface of h-BN via a typical adsorption−reduction procedure. In detail, nanosized magnetic (Pd/Fe2O3) NPs were derived from Prussian blue analogue prototype, a well-known porous metal–organic framework (MOF), and then further surface−engineered to produce magnetic BN nanoplate supported Pd nanocatalysts. The structural and morphological features of h-BN/Pd/Fe2O3 were investigated by spectroscopic and microscopic characterization techniques. Moreover, h-BN nanosheets characteristic endow its thermal stability and appropriate chemical anchoring sites that solve the inefficiency of reaction rate and high consumption caused by the inevitable agglomeration of precious metal NPs. Under mild reaction conditions, the developed nanostructured h-BN/Pd/Fe2O3 as catalyst shows high yield and efficient reusability in reducing nitroarenes into corresponding anilines using sodium borohydride (NaBH4) as a reductant.

목차 (Table of Contents)

• Nanostructured Engineered Photoelectrode for Unassisted Photoelectrochemical Hydrogen Peroxide Production i
• List of Tables 10
• List of Figures 11
• Chapter 1 Photoelectrochemical two-electron water oxidation for hydrogen peroxide generation 19
• 1.1 Introduction 20
• 1.2 Overview of photoelectrochemical water splitting for hydrogen evolution 24
• 1.2.1 Principle of photocatalysis 24
• 1.2.2 Principle of Photoelectrochemical Water Splitting 28
• 1.3 State-of-the-Art Developments in PEC Catalysts 33
• 1.4 Overview of high-value photoelectrochemical water splitting for hydrogen peroxide production 35
• 1.4.1 Properties and Applications of H2O2 37
• 1.5 Photoelectrochemical synthesis of hydrogen peroxide 39
• 1.5.1 Oxygen reduction reaction 39
• 1.5.2 Water oxidation reaction 41
• 1.6 Development of anodic H2O2 generation via EC/PEC 43
• 1.7 Strategies for highly efficient photoelectrochemical H2O2 production 46
• 1.7.1 Bismuth vanadate as a photoanode material 46
• 1.7.2. Unassisted PEC water splitting 48
• 1.8 References 50
• Chapter 2 Tailoring Surface Passivation Layers to Boost PEC H2O2 Generation on BiVO4 Photoanodes 53
• 2.1 Introduction 54
• 2.2 Experimental procedure 57
• 2.2.1 Materials 57
• 2.2.2 Preparation of nanoporous BiVO4 photoanode 58
• 2.2.3 Surface passivation with SnO2, In2O3, TiO2, and Al2O3 59
• 2.2.4 Characterizations 60
• 2.2.5 Products quantitation 61
• 2.2.6 Photoelectrochemical measurements 62
• 2.3 Results and discussion 64
• 2.4 Reference 79
• Chapter 3 82
• 3.1 Introduction 83
• 3.2 Experimental procedure 87
• 3.2.1 Materials 87
• 3.2.2 Preparation of photoanode 88
• 3.2.3 Surface passivation with SnO2 89
• 3.2.4 Synthesis of CaSnO3 co-catalysts 90
• 3.2.5 Fabrication method for perovskite/silicon tandem solar cells 91
• 3.2.6 Characterizations 92
• 3.2.7 Products quantitation 93
• 3.2.8 Photoelectrochemical measurements 94
• 3.2.9 PEC-PV tandem cell measurements 96
• 3.3 Results and discussion 97
• 3.3.1 Materials synthesis and characterization 97
• 3.3.2 PEC water oxidation performance 112
• 3.3.3 Carrier dynamic analysis 129
• 3.4 Unassisted H2O2 production 141
• 3.5 Conclusion 149
• 3.6 Reference 150
• Chapter 4 154
• 4.1 Introduction 155
• 4.2 Experimental 160
• 4.2.1 Materials and characterization 160
• 4.2.2 Preparation of h-BN/Pd/Fe2O3 catalyst 161
• 4.2.3 Catalytic reduction 162
• 4.3 Result and discussion 163
• 4.4 Conclusion 191
• 4.5 References 195