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Rettenmaier K, Zickler GA, Berger T. Conformal Coverage of ZnO Nanowire Arrays by ZnMnO 3 : Room-temperature Photodeposition from Aqueous Solution. Chemphyschem 2023; 24:e202300250. [PMID: 37534548 PMCID: PMC10962551 DOI: 10.1002/cphc.202300250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 08/02/2023] [Accepted: 08/02/2023] [Indexed: 08/04/2023]
Abstract
Compositionally and structurally complex semiconductor oxide nanostructures gain importance in many energy-related applications. Simple and robust synthesis routes ideally complying with the principles of modern green chemistry are therefore urgently needed. Here we report on the one-step, room-temperature synthesis of a crystalline-amorphous biphasic ternary metal oxide at the ZnO surface using aqueous precursor solutions. More specifically, conformal and porous ZnMnO3 shells are photodeposited from KMnO4 solution onto immobilized ZnO nanowires acting not only as the substrate but also as the Zn precursor. This water-based, low temperature process yields ZnMnO3 /ZnO composite electrodes featuring in 1 M Na2 SO4 aqueous solution capacitance values of 80-160 F g-1 (as referred to the total mass of the porous film i. e. the electroactive ZnMnO3 phase and the ZnO nanowire array). Our results highlight the suitability of photodeposition as a simple and green route towards complex functional materials.
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Affiliation(s)
- Karin Rettenmaier
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Straße 2a5020SalzburgAustria
| | - Gregor A. Zickler
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Straße 2a5020SalzburgAustria
| | - Thomas Berger
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Straße 2a5020SalzburgAustria
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Debgupta J, Lari L, Isaacs M, Carey J, McKenna KP, Lazarov VK, Chechik V, Douthwaite RE. Predictive Removal of Interfacial Defect-Induced Trap States between Titanium Dioxide Nanoparticles via Sub-Monolayer Zirconium Coating. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:660-671. [PMID: 36660098 PMCID: PMC9841567 DOI: 10.1021/acs.jpcc.2c06927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 12/13/2022] [Indexed: 06/17/2023]
Abstract
First principles modeling of anatase TiO2 surfaces and their interfacial contacts shows that defect-induced trap states within the band gap arise from intrinsic structural distortions, and these can be corrected by modification with Zr(IV) ions. Experimental testing of these predictions has been undertaken using anatase nanocrystals modified with a range of Zr precursors and characterized using structural and spectroscopic methods. Continuous-wave electron paramagnetic resonance (EPR) spectroscopy revealed that under illumination, nanoparticle-nanoparticle interfacial hole trap states dominate, which are significantly reduced after optimizing the Zr doping. Fabrication of nanoporous films of these materials and charge injection using electrochemical methods shows that Zr doping also leads to improved electron conductivity and mobility in these nanocrystalline systems. The simple methodology described here to reduce the concentration of interfacial defects may have wider application to improving the efficiency of systems incorporating metal oxide powders and films including photocatalysts, photovoltaics, fuel cells, and related energy applications.
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Affiliation(s)
| | - Leonardo Lari
- Department
of Physics, University of York, Heslington, York YO10 5DD, UK
| | - Mark Isaacs
- HarwellXPS, R92 Research Complex at Harwell, Rutherford Appleton Laboratories,
Harwell, Didcot OX11 0QS, UK
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - John Carey
- Department
of Physics, University of York, Heslington, York YO10 5DD, UK
| | - Keith P. McKenna
- Department
of Physics, University of York, Heslington, York YO10 5DD, UK
| | - Vlado K. Lazarov
- Department
of Physics, University of York, Heslington, York YO10 5DD, UK
| | - Victor Chechik
- Department
of Chemistry, University of York, York YO10 5DD, UK
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Rettenmaier K, Zickler GA, Redhammer GJ, Berger T. Substrate-Enabled Room-Temperature Electrochemical Deposition of Crystalline ZnMnO 3. Chemphyschem 2023; 24:e202200586. [PMID: 36070988 PMCID: PMC10092203 DOI: 10.1002/cphc.202200586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 09/07/2022] [Indexed: 01/04/2023]
Abstract
Mixed transition metal oxides have emerged as promising electrode materials for electrochemical energy storage and conversion. To optimize the functional electrode properties, synthesis approaches allowing for a systematic tailoring of the materials' composition, crystal structure and morphology are urgently needed. Here we report on the room-temperature electrodeposition of a ternary oxide based on earth-abundant metals, specifically, the defective cubic spinel ZnMnO3 . In this unprecedented approach, ZnO surfaces act as (i) electron source for the interfacial reduction of MnO4 - in aqueous solution, (ii) as substrate for epitaxial growth of the deposit and (iii) as Zn precursor for the formation of ZnMnO3 . Epitaxial growth of ZnMnO3 on the lateral facets of ZnO nanowires assures effective electronic communication between the electroactive material and the conducting scaffold and gives rise to a pronounced 2-dimensional morphology of the electrodeposit forming - after partial delamination from the substrate - twisted nanosheets. The synthesis strategy shows promise for the direct growth of different mixed transition metal oxides as electroactive phase onto conductive substrates and thus for the fabrication of binder-free nanocomposite electrodes.
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Affiliation(s)
- Karin Rettenmaier
- Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Straße 2a, A-5020, Salzburg, Austria
| | - Gregor A Zickler
- Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Straße 2a, A-5020, Salzburg, Austria
| | - Günther J Redhammer
- Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Straße 2a, A-5020, Salzburg, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Straße 2a, A-5020, Salzburg, Austria
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Rettenmaier K, Berger T. Impact of Nanoparticle Consolidation on Charge Separation Efficiency in Anatase TiO 2 Films. Front Chem 2021; 9:772116. [PMID: 34858947 PMCID: PMC8631187 DOI: 10.3389/fchem.2021.772116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/06/2021] [Indexed: 12/03/2022] Open
Abstract
Mesoporous films and electrodes were prepared from aqueous slurries of isolated anatase TiO2 nanoparticles. The resulting layers were annealed in air at temperatures 100°C ≤ T ≤ 450°C upon preservation of internal surface area, crystallite size and particle size. The impact of processing temperature on charge separation efficiency in nanoparticle electrodes was tracked via photocurrent measurements in the presence of methanol as a hole acceptor. Thermal annealing leads to an increase of the saturated photocurrent and thus of the charge separation efficiency at positive potentials. Furthermore, a shift of capacitive peaks in the cyclic voltammograms of the nanoparticle electrodes points to the modification of the energy of deep traps. Population of these traps triggers recombination possibly due to the action of local electrostatic fields attracting photogenerated holes. Consequently, photocurrents saturate at potentials, at which deep traps are mostly depopulated. Charge separation efficiency was furthermore investigated for nanoparticle films and was tracked via the decomposition of hydrogen peroxide. Our observations evidence an increase of charge separation efficiency upon thermal annealing. The effect of particle consolidation, which we associate with minute atomic rearrangements at particle/particle contacts, is attributed to the energetic modification of deep traps and corresponding modifications of charge transport and recombination, respectively.
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Affiliation(s)
- Karin Rettenmaier
- Department of Chemistry and Physics of Materials, University of Salzburg, Salzburg, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, University of Salzburg, Salzburg, Austria
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Jiménez JM, Perdolt D, Berger T. Reactivity of Hydrogen-Related Electron Centers in Powders, Layers, and Electrodes Consisting of Anatase TiO 2 Nanocrystal Aggregates. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:13809-13818. [PMID: 34239660 PMCID: PMC8256420 DOI: 10.1021/acs.jpcc.1c01580] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 05/06/2021] [Indexed: 05/04/2023]
Abstract
Anatase TiO2 nanoparticle aggregates were used as model systems for studying at different water activities the reactivity of electron centers at semiconductor surfaces. The investigated surface conditions evolve from a solid/vacuum interface to a solid/bulk electrolyte interface. Hydrogen-related electron centers were generated either chemically-upon sample exposure to atomic hydrogen at the semiconductor/gas interface-or electrochemically-upon bias-induced charge accumulation at the semiconductor/electrolyte interface. Based on their corresponding spectroscopic and electrochemical fingerprints, we investigated the reactivity of hydrogen-related electron centers as a function of the interfacial condition and at different levels of complexity, that is, (i) for dehydrated and (partially) dehydroxylated oxide surfaces, (ii) for oxide surfaces covered by a thin film of interfacial water, and (iii) for oxide surfaces in contact with a 0.1 M HClO4 aqueous solution. Visible (Vis) and infrared (IR) spectroscopy evidence a chemical equilibrium between hydrogen atoms in the gas phase and-following their dissociation-electron/proton centers in the oxide. The excess electrons are either localized forming (Vis-active) Ti3+ centers or delocalized as (IR-active) free conduction band electrons. The addition of molecular oxygen to chemically reduced anatase TiO2 nanoparticle aggregates leads to a quantitative quenching of Ti3+ centers, while a fraction of ∼10% of hydrogen-derived conduction band electrons remains in the oxide pointing to a persistent hydrogen doping of the semiconductor. Neither trapped electrons (i.e., Ti3+ centers) nor conduction band electrons react with water or its adsorption products at the oxide surface. However, the presence of an interfacial water layer does not impede the electron transfer to molecular oxygen. At the semiconductor/electrolyte interface, inactivity of trapped electrons with regard to water reduction and electron transfer to oxygen were evidenced by cyclic voltammetry.
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Affiliation(s)
- Juan Miguel Jiménez
- Department
of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
| | - Daniel Perdolt
- Department
of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
| | - Thomas Berger
- Department
of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
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Neige E, Diwald O. Paramagnetic electron centers in BaTiO 3 nanoparticle powders. Phys Chem Chem Phys 2021; 23:12881-12888. [PMID: 34075975 DOI: 10.1039/d1cp01128f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Knowledge about the emergence and depletion of point defects in BaTiO3 (BTO) nano-structures during materials processing is key to our understanding of their later activity as components in functional dielectric devices or as photocatalysts. In this electron paramagnetic resonance (EPR) study we investigated BaTiO3 nanoparticle powders produced by flame spray pyrolysis (FSP) with powders of TiO2 anatase nanocrystals of comparable size as reference system. Paramagnetic Ti3+ ions located at regular lattice sites and with well-defined EPR signatures were measured in vacuum annealed BaTiO3 nanoparticles, which convert upon further annealing in the temperature range between 873 K and 1173 K from monocrystalline grains with an average size of d = 12 nm, BTO (873 K), to polycrystalline particles with d = 70 nm, BTO (1173 K). Whereas the starting material hosts predominantly polaron-type Ti3+ ions being surrounded by compressed O2- ion octahedra, barium-oxygen divacancy complexes, , become susceptible to electron trapping in polycrystalline and tetragonal BTO (1173 K) particles after pre-annealing at temperatures T > 873 K. The insights obtained provide a base for the detection of local distortion effects, for the identification of charge trapping sites and for the elucidation of their impact on spontaneous polarization in BaTiO3 nanoparticles as photocatalysts or dielectric components.
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Affiliation(s)
- Ellie Neige
- Department of Chemistry and Physics of Materials, Paris Lodron Universität Salzburg, Jakob-Haringer Strasse 2a, A-5020 Salzburg, Austria.
| | - Oliver Diwald
- Department of Chemistry and Physics of Materials, Paris Lodron Universität Salzburg, Jakob-Haringer Strasse 2a, A-5020 Salzburg, Austria.
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Benazzi E, Rettenmaier K, Berger T, Caramori S, Berardi S, Argazzi R, Prato M, Syrgiannis Z. Photoelectrochemical Properties of SnO 2 Photoanodes Sensitized by Cationic Perylene-Di-Imide Aggregates for Aqueous HBr Splitting. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2020; 124:1317-1329. [PMID: 32903288 PMCID: PMC7116044 DOI: 10.1021/acs.jpcc.9b11039] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Perylene-sensitized mesoporous SnO2 films were used as electrodes for photoelectrochemical HBr splitting in aqueous solution. Upon AM 1.5 G illumination a 3-4 fold increase of the saturated photocurrent was observed when decreasing the pH of the aqueous solution from pH 3 to pH 0 (j max = 0.05 ± 0.01 mAcm-2 at pH 3 and 0.17 ± 0.02 mAcm-2 at pH 0, respectively). A detailed spectroscopic and electrochemical analysis of the hybrid material was carried out in order to address the impact of interfacial energetics on charge separation dynamics. UV/Vis spectroelectrochemical measurements showed that the energy of semiconductor states in such systems can be adjusted independently from the molecular levels by varying proton concentration. Photoelectrochemical measurements and ns-μs transient absorption spectroscopy reveal that pH-related changes of the interfacial energetics have only a minor impact on the charge injection rate. An increase of the proton concentration improves charge collection mainly by retarding recombination, which in the case of Br- oxidation is in critical competition with perylene regeneration. Control of the back recombination appears to be a key feature in heterogeneous molecular systems tasked to drive energetically demanding redox reactions.
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Affiliation(s)
- Elisabetta Benazzi
- Department of Chemical and Pharmaceutical Sciences of the University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara
| | - Karin Rettenmaier
- Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Straße 2a, A-5020 Salzburg, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Straße 2a, A-5020 Salzburg, Austria
- Thomas Berger: ; Stefano Caramori:
| | - Stefano Caramori
- Department of Chemical and Pharmaceutical Sciences of the University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara
- Thomas Berger: ; Stefano Caramori:
| | - Serena Berardi
- Department of Chemical and Pharmaceutical Sciences of the University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara
| | - Roberto Argazzi
- Department of Chemical and Pharmaceutical Sciences of the University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara
- ISOF-CNR, c/o Department of Chemical and Pharmaceutical Sciences of the University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara
| | - Maurizio Prato
- Center of Excellence for Nanostructured Materials (CENMAT), INSTM UdR di Trieste, Department of Chemical and Pharmaceutical Sciences, University of Trieste, Piazzale Europa 1, 34127 Trieste, Italy
- Carbon Bionanotechnology Laboratory, CIC biomaGUNE, Paseo de Miramón 182, San Sebastian, Spain
- Basque Fdn Sci, Ikerbasque, Bilbao 48013, Spain
| | - Zois Syrgiannis
- Center of Excellence for Nanostructured Materials (CENMAT), INSTM UdR di Trieste, Department of Chemical and Pharmaceutical Sciences, University of Trieste, Piazzale Europa 1, 34127 Trieste, Italy
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