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- Boscolo Bibi, Sara, 1993-
(författare)
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Going for gold : A spectroelectrochemical and catalytic study of gold materials
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the increase in demand for renewable energy, understanding chemical processes is essential for improving the design of catalysts in order to achieve better performance. This thesis summarises the experimental investigation of three types of catalytic gold materials: gold oxide formed from gold films, oxide-derived gold (OD-Au) produced from gold films, and gold nanoparticles supported on metal oxides. Different spectroscopic techniques were employed, such as operando sum frequency generation (SFG) and in situ and ex situ X-ray spectroscopies. These methods allowed the probing of the electronic and chemical states of gold after oxidising electrochemical treatments. The results indicate the presence of subsurface gold oxide remnants after formation of OD-Au, which may help explain its improved catalytic properties with respect to pure gold. In addition, a mathematical model to couple the early stages of gold oxide formation with the nonlinear optical response of gold during this process is presented. This model suggests that the growth proceeds from small oxide islands to 3D oxide growth, while SFG oxidation variation is due to the suppression of the free electron density by negatively-charged adsorbing oxygen atoms. Gold oxide was also studied with both in situ and operando X-ray spectroscopies, showing the importance of a continuous electrochemical treatment during measurements to avoid beam induced effects. Furthermore, gold nanoparticles supported on metal oxides (TiO2 and γ-Fe2O3) were investigated mainly with mass spectrometry. The results indicate two different reaction pathways for oxidation of CO to CO2 depending on the type of metal oxide support. These findings could be used to help design future gold-based catalysts.
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| 3. |
- Boscolo Bibi, Sara, 1993-, et al.
(författare)
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Multi-spectroscopic study of electrochemically-formed oxide-derived gold electrodes
- 2024
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 26:3, s. 2332-2340
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Tidskriftsartikel (refereegranskat)abstract
- Oxide-derived metals are produced by reducing an oxide precursor. These materials, including gold, have shown improved catalytic performance over many native metals. The origin of this improvement for gold is not yet understood. In this study, operando non-resonant sum frequency generation (SFG) and ex situ high-pressure X-ray photoelectron spectroscopy (HP-XPS) have been employed to investigate electrochemically-formed oxide-derived gold (OD-Au) from polycrystalline gold surfaces. A range of different oxidizing conditions were used to form OD-Au in acidic aqueous medium (H3PO4, pH = 1). Our electrochemical data after OD-Au is generated suggest that the surface is metallic gold, however SFG signal variations indicate the presence of subsurface gold oxide remnants between the metallic gold surface layer and bulk gold. The HP-XPS results suggest that this subsurface gold oxide could be in the form of Au2O3 or Au(OH)3. Furthermore, the SFG measurements show that with reducing electrochemical treatments the original gold metallic state can be restored, meaning the subsurface gold oxide is released. This work demonstrates that remnants of gold oxide persist beneath the topmost gold layer when the OD-Au is created, potentially facilitating the understanding of the improved catalytic properties of OD-Au.
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| 5. |
- Boscolo Bibi, Sara
(författare)
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Study of polycrystalline gold surfaces by potential-dependent optical sum frequency generation
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the increase in demand for renewable energy, the comprehension of chemical processes is essential to improve the design of catalysts in order to achieve better performance. This thesis summarizes the experimental investigation of redox reactions on polycrystalline gold surfaces by combining electrochemistry with operando surface-specific sum frequency generation (SFG) for a wider anodic potential interval than previously studied in acidic aqueous medium (H3PO4, pH 1). This configuration provides new insight about the chemical processes involved in the formation and reduction of gold oxides. More precisely, the migration of oxygen below the gold surface leading to a stratified structure has been suggested for the first time. This information is relevant to bring more clarity about redox reactions on gold surface during catalytic reactions.
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| 8. |
- Holm, Alexander, 1983-, et al.
(författare)
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A Water-Promoted Mars-van Krevelen Reaction Dominates Low-Temperature CO Oxidation over Au-Fe2O3 but Not over Au-TiO2
- 2024
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Ingår i: ACS Catalysis. - 2155-5435. ; 14:5, s. 3191-3197
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Tidskriftsartikel (refereegranskat)abstract
- We provide experimental evidence that is inconsistent with often proposed Langmuir−Hinshelwood (LH) mechanistic hypotheses for water-promoted CO oxidation over Au–Fe2O3. Passing CO and H2O, but no O2, over Au-γ-Fe2O3 at 25 °C, we observe significant CO2 production, inconsistent with LH mechanistic hypotheses. Experiments with H218O further show that previous LH mechanistic proposals cannot account for water-promoted CO oxidation over Au-γ-Fe2O3. Guided by density functional theory, we instead postulate a water-promoted Mars–van Krevelen (w-MvK) reaction. Our proposed w-MvK mechanism is consistent both with observed CO2 production in the absence of O2 and with CO oxidation in the presence of H218O and 16O2. In contrast, for Au-TiO2, our data is consistent with previous LH mechanistic hypotheses.
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| 9. |
- Mazzaro, Raffaello, et al.
(författare)
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Hematite nanostructures : An old material for a new story. Simultaneous photoelectrochemical oxidation of benzylamine and hydrogen production through Ti doping
- 2019
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 61, s. 36-46
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Tidskriftsartikel (refereegranskat)abstract
- Overall water splitting represents one of the most promising approaches toward solar energy conversion and storage, which is, however, severely challenged by the four-electron/four-proton nature of the oxygen evolution reaction (OER). One option to overcome this issue is to replace OER with a more useful reaction, for simultaneous production of both hydrogen and chemicals of interest. For the purpose, in this paper a cheap, hydrothermally prepared Ti-doped nanostructured hematite photoanode was employed for the first time as highly stable, heterogeneous catalyst for the low bias, efficient and highly selective photoinduced oxidation of benzylamine to N-benzylidenebenzylamine, and for the simultaneous production of hydrogen in a double solvent/environment cell. A preliminary estimate indicates the possibility to obtain a ∼150 μmol h−1 H2 production, with the contemporary production of stoichiometric benzylidene N-benzylamine in a 5 × 5 cm2 area electrode. This study contributes to overcome the 40-year lasting issues limiting the use of hematite in industrial photoelectrochemical sunlight conversion and storage, due to poor performance of hematite and lack of economic value of oxygen production, providing solid evidence for the simultaneous use of hematite in hydrogen production and alternative oxidation reactions of industrial importance.
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