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Tahira, A., Ibupoto, Z., Mazzaro, R., You, S., Morandi, V., Natile, M. M., . . . Vomiero, A. (2019). Advanced Electrocatalysts for Hydrogen Evolution Reaction Based on Core–Shell MoS2/TiO2 Nanostructures in Acidic and Alkaline Media. ACS APPLIED ENERGY MATERIALS, 2(3), 2053-2062
Open this publication in new window or tab >>Advanced Electrocatalysts for Hydrogen Evolution Reaction Based on Core–Shell MoS2/TiO2 Nanostructures in Acidic and Alkaline Media
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2019 (English)In: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, no 3, p. 2053-2062Article in journal (Refereed) Published
Abstract [en]

Hydrogen production as alternative energy source is still a challenge due to the lack of efficient and inexpensive catalysts, alternative to platinum. Thus, stable, earth abundant, and inexpensive catalysts are of prime need for hydrogen production via hydrogen evolution reaction (HER). Herein, we present an efficient and stable electrocatalyst composed of earth abundant TiO2 nanorods decorated with molybdenum disulfide thin nanosheets, a few nanometers thick. We grew rutile TiO2 nanorods via the hydrothermal method on conducting glass substrate, and then we nucleated the molybdenum disulfide nanosheets as the top layer. This composite possesses excellent hydrogen evolution activity in both acidic and alkaline media at considerably low overpotentials (350 mV and 700 mV in acidic and alkaline media, respectively) and small Tafel slopes (48 and 60 mV/dec in acidic and alkaline conditions, respectively), which are better than several transition metal dichalcogenides, such as pure molybdenum disulfide and cobalt diselenide. A good stability in acidic and alkaline media is reported here for the new MoS2/TiO2 electrocatalyst. These results demonstrate the potential of composite electrocatalysts for HER based on earth abundant, cost-effective, and environmentally friendly materials, which can also be of interest for a broader range of scalable applications in renewable energies, such as lithium sulfur batteries, solar cells, and fuel cells.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
acidic, alkaline, catalyst, hydrogen evolution reaction, MoS2, TiO2
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-73610 (URN)10.1021/acsaem.8b02119 (DOI)000462944700053 ()
Note

Validerad;2019;Nivå 2;2019-04-12 (oliekm)

Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-12Bibliographically approved
Zur, L. Z., Armellini, C., Belmokhtar, S., Bouajaj, A., Cattaruzza, E., Chiappini, A., . . . Enrichi, F. (2019). Comparison between glass and glass-ceramic silica-hafnia matrices on the down-conversion efficiency of Tb3+/Yb3+ rare earth ions. Optical materials (Amsterdam), 87, 102-106
Open this publication in new window or tab >>Comparison between glass and glass-ceramic silica-hafnia matrices on the down-conversion efficiency of Tb3+/Yb3+ rare earth ions
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2019 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 87, p. 102-106Article in journal (Refereed) Published
Abstract [en]

In this paper, the investigation of energy transfer efficiency in Tb3+-Yb3+ co-doped SiO2-HfO2 glass and glass-ceramic waveguides is presented. Cooperative energy transfer between these two ions allows to cut one UV or 488 nm photon in two 980 nm photons and could have important applications in improving the performance of photovoltaic solar cells. Thin films with different molar concentrations of rare earths, up to a total concentration of 21%, were prepared by a sol-gel route, using dip-coating deposition technique on SiO2 substrates. The ratio between Yb3+ and Tb3+ ions in all the prepared thin films is constant and equal to 4. The energy transfer between Tb3+ and Yb3+ ions in glass and glass-ceramic waveguides shows the higher efficiency for glass-ceramic with a maximum quantum transfer efficiency of about 190% for the sample containing 19% of rare earths.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Rare earths, Down-conversion, Energy transfer, Waveguides, Sol-gel
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-68810 (URN)10.1016/j.optmat.2018.05.008 (DOI)000457505900020 ()2-s2.0-85047221245 (Scopus ID)
Note

Konferensartikel i tidskrift

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2019-03-08Bibliographically approved
Leduc, J., Goenuellue, Y., Ghamgosar, P., You, S., Mouzon, J., Choi, H., . . . Mathur, S. (2019). Electronically-Coupled Phase Boundaries in α‑Fe2O3/Fe3O4 Nanocomposite Photoanodes for Enhanced Water Oxidation. ACS APPLIED NANO MATERIALS, 2(1), 334-342
Open this publication in new window or tab >>Electronically-Coupled Phase Boundaries in α‑Fe2O3/Fe3O4 Nanocomposite Photoanodes for Enhanced Water Oxidation
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2019 (English)In: ACS APPLIED NANO MATERIALS, E-ISSN 2574-0970, Vol. 2, no 1, p. 334-342Article in journal (Refereed) Published
Abstract [en]

Photoelectrochemical (PEC) water splittingreactions are promising for sustainable hydrogen productionfrom renewable sources. We report here, the preparation of α-Fe2O3/Fe3O4 composite films via a single-step chemical vapordeposition of [Fe(OtBu)3]2 and their use as efficient photoanode materials in PEC setups. Film thickness and phase segregation was controlled by varying the deposition time and corroborated through cross-section Raman spectroscopy and scanning electron microscopy. The highest water oxidationactivity (0.48 mA/cm2 at 1.23 V vs RHE) using intermittent AM 1.5 G (100 mW/cm2) standard illumination was found forhybrid films with a thickness of 11 μm. This phenomenon is attributed to an improved electron transport resulting from ahigher magnetite content toward the substrate interface and an increased light absorption due to the hematite layer mainly located at the top surface of the film. The observed high efficiency of α-Fe2O3/Fe3O4 nanocomposite photoanodes is attributed to the close proximity and establishment of 3D interfaces between the weakly ferro- (Fe2O3) and ferrimagnetic (Fe3O4) oxides, which in view of their differential chemical constitution andvalence states of Fe ions (Fe2+/Fe3+) can enhance the charge separation and thus the overall electrical conductivity of the layer.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
solar water splitting, valence dynamics, magnetite, Raman, single-source CVD, heterostructures
National Category
Composite Science and Engineering Chemical Process Engineering
Research subject
Experimental Physics; Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-73139 (URN)10.1021/acsanm.8b01936 (DOI)
Note

Validerad;2019;Nivå 1;2019-03-13 (oliekm)

Available from: 2019-03-08 Created: 2019-03-08 Last updated: 2019-04-19Bibliographically approved
Mazzaro, R., Bibi, S. B., Natali, M., Bergamini, G., Morandi, V., Ceroni, P. & Vomiero, A. (2019). Hematite nanostructures: An old material for a new story. Simultaneous photoelectrochemical oxidation of benzylamine and hydrogen production through Ti doping. Nano Energy
Open this publication in new window or tab >>Hematite nanostructures: An old material for a new story. Simultaneous photoelectrochemical oxidation of benzylamine and hydrogen production through Ti doping
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2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282Article in journal (Refereed) Accepted
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Hematite, Photoelectrochemistry, Photoanode, Benzylamine, Hydrogen
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-73692 (URN)10.1016/j.nanoen.2019.04.013 (DOI)
Available from: 2019-04-17 Created: 2019-04-17 Last updated: 2019-04-17
Liu, G., Mazzaro, R., Wang, Y., Zhao, H. & Vomiero, A. (2019). High efficiency sandwich structure luminescent solar concentrators based on colloidal quantum dots. Nano Energy, 60, 119-126
Open this publication in new window or tab >>High efficiency sandwich structure luminescent solar concentrators based on colloidal quantum dots
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2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 60, p. 119-126Article in journal (Refereed) Published
Abstract [en]

Luminescent solar concentrators (LSCs) have received significant attention because of their low cost, large-area and high efficiency sunlight energy harvesting. Colloidal core/shell quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs. However, due to the limitation of QDs properties and device architectures, LSCs fabricated using QDs still face the challenges of low optical efficiency and limited long-term stability for the large-area LSCs. In this work, we synthesized CdSe/CdS QDs, and found that higher CdS shell growth temperature results in improved uniformity in structure and morphology and more suitable optical properties. Based on the CdSe/CdS QDs, a large-area (∼100 cm 2 ) sandwich structure luminescent solar concentrator (LSC) was fabricated. By laminating the QDs layer between two sheets of optical clear glass, the reabsorption losses of the device can be reduced due to the decrease of photon escape. The as-fabricated sandwich structure device exhibits an external optical efficiency of ∼ 2.95% under natural sunlight illumination, which represents a 78% enhancement in efficiency over the single layer film LSCs based on CdSe/CdS QDs. More importantly, the sandwich structure can protect the QDs interlayer from the impact of the ambient environment (e.g. oxygen, moisture and alkalinity) and enhance the long-term stability of LSCs. Our work shows that the use of suitably tuned core-shell QDs and the sandwich structure in LSC architecture can dramatically enhance the external optical efficiency of LSC devices based on CdSe/CdS QDs.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
CdSe/CdS QDs, External optical efficiency, Luminescent solar concentrators, Microstructure, Sandwich structure
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-73372 (URN)10.1016/j.nanoen.2019.03.038 (DOI)2-s2.0-85063026102 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-04-01 (svasva)

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved
Botella, P., Errandonea, D., Garg, A., Rodriguez-Hernandez, P. & Vomiero, A. (2019). High-pressure characterization of the optical and electronic properties of InVO4, InNbO4, and InTaO4. SN Applied Sciences
Open this publication in new window or tab >>High-pressure characterization of the optical and electronic properties of InVO4, InNbO4, and InTaO4
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2019 (English)In: SN Applied Sciences, ISSN 2523-3963Article in journal (Refereed) Epub ahead of print
Abstract [en]

We have studied the electronic properties at ambient pressure and under high pressure of InVO4, InNbO4, and InTaO4 powders, three candidate materials for hydrogen production by means of photocatalytic water splitting using solar energy. A combination of optical absorption and resistivity measurements and band structure calculations have allowed us to determine that these materials are wide band-gap semiconductors with a band-gap energy of 3.62(5), 3.63(5), and 3.79(5) eV for InVO4, InNbO4, and InTaO4, respectively. The last two compounds are indirect band-gap materials, and InVO4 is a direct band-gap material. The pressure dependence of the band-gap energy and the electrical resistivity have been determined too. In the three compounds, the band gap opens under compression until reaching a critical pressure, where a phase transition occurs. The structural transition triggers a band-gap collapse larger than 1.2 eV in the three materials, being the abrupt decrease in the band-gap energy related to an increase in the pentavalent cation coordination number. The phase transitions also cause changes in the electrical resistivity, which can be correlated with changes induced by pressure in the band structure. An explanation to the reported results is provided based upon ab initio calculations. The conclusions attained are of significance for technological applications of the studied oxides.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Wolframite, Band gap, optical properties, High pressure, Phase transition, Electronic properties
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-73617 (URN)10.1007/s42452-019-0406-7 (DOI)
Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-12
Bortoluzzi, M., Castro, J., Girotto, M., Enrichi, F. & Vomiero, A. (2019). Luminescent copper(I) coordination polymer with 1-methyl-1H-benzotriazole, iodide and acetonitrile as ligands. Inorganic Chemistry Communications, 102, 141-146
Open this publication in new window or tab >>Luminescent copper(I) coordination polymer with 1-methyl-1H-benzotriazole, iodide and acetonitrile as ligands
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2019 (English)In: Inorganic Chemistry Communications, ISSN 1387-7003, E-ISSN 1879-0259, Vol. 102, p. 141-146Article in journal (Refereed) Published
Abstract [en]

The Cu(I) coordination polymer [Cu33-I)3(μ-btzMe)(NCCH3)]n (btzMe = 1-methyl-1H-benzotriazole) was prepared and characterized by X-Ray diffraction. The compound showed strong green emission upon excitation with wavelengths below 475 nm, with lifetime of 47 μs. The emission was attributed to 3(X,M)LCT transition on the basis of experimental data and DFT calculations.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Copper iodide, Coordination polymer, N-donor ligands, Luminescence
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-73034 (URN)10.1016/j.inoche.2019.02.016 (DOI)000462803900027 ()2-s2.0-85061636648 (Scopus ID)
Available from: 2019-02-27 Created: 2019-02-27 Last updated: 2019-04-17
Ibupoto, Z., Tahira, A., Tang, P., Liu, X., Morante, J. R., Fahlman, M., . . . Vomiero, A. (2019). MoSx@NiO Composite Nanostructures: An Advanced Nonprecious Catalyst for Hydrogen Evolution Reaction in Alkaline Media. Advanced Functional Materials, 29(7), Article ID 1807562.
Open this publication in new window or tab >>MoSx@NiO Composite Nanostructures: An Advanced Nonprecious Catalyst for Hydrogen Evolution Reaction in Alkaline Media
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2019 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 7, article id 1807562Article in journal (Refereed) Published
Abstract [en]

The design of the earth‐abundant, nonprecious, efficient, and stable electrocatalysts for efficient hydrogen evolution reaction (HER) in alkaline media is a hot research topic in the field of renewable energies. A heterostructured system composed of MoSx deposited on NiO nanostructures (MoSx@NiO) as a robust catalyst for water splitting is proposed here. NiO nanosponges are applied as cocatalyst for MoS2 in alkaline media. Both NiO and MoS2@NiO composites are prepared by a hydrothermal method. The NiO nanostructures exhibit sponge‐like morphology and are completely covered by the sheet‐like MoS2. The NiO and MoS2 exhibit cubic and hexagonal phases, respectively. In the MoSx@NiO composite, the HER experiment in 1 m KOH electrolyte results in a low overpotential (406 mV) to produce 10 mA cm−2 current density. The Tafel slope for that case is 43 mV per decade, which is the lowest ever achieved for MoS2‐based electrocatalyst in alkaline media. The catalyst is highly stable for at least 13 h, with no decrease in the current density. This simple, cost‐effective, and environmentally friendly methodology can pave the way for exploitation of MoSx@NiO composite catalysts not only for water splitting, but also for other applications such as lithium ion batteries, and fuel cells.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-72878 (URN)10.1002/adfm.201807562 (DOI)000459719800018 ()2-s2.0-85059344786 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-13 (johcin)

Available from: 2019-02-13 Created: 2019-02-13 Last updated: 2019-03-12Bibliographically approved
Enrichi, F., Belmokhtar, S., Benedetti, A., Bouajaj, A., Cattaruzza, E., Coccetti, F., . . . Zur, L. Z. (2018). Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics. Optical materials (Amsterdam), 84, 668-674
Open this publication in new window or tab >>Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics
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2018 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 84, p. 668-674Article in journal (Refereed) Published
Abstract [en]

In this paper we report the study of down-shifting silica-zirconia glass and glass-ceramic films doped by Tb3+ ions and Ag nanoaggregates, which combine the typical spectral properties of the rare-earth-ions with the broadband sensitizing effect of the metal nanostructures. Na-Tb co-doped silica-zirconia samples were obtained by a modified sol-gel route. Dip-coating deposition followed by annealing for solvent evaporation and matrix densification were repeated several times, obtaining a homogeneous crack-free film. A final treatment at 700 °C or 1000 °C was performed to control the nanoscale structural properties of the samples, resulting respectively in a glass (G) or a glass-ceramic (GC), where tetragonal zirconia nanocrystals are surrounded by an amorphous silica matrix. Ag introduction was then achieved by ion-exchange in a molten salt bath, followed by annealing in air to control the migration and aggregation of the metal ions. The comparison of the structural, compositional and optical properties are presented for G and GC samples, providing evidence of highly efficient photoluminescence enhancement in both systems, slightly better in G than in GC samples, with a remarkable increase of the green Tb3+ PL emission at 330 nm excitation: 12 times for G and 8 times for GC samples. Furthermore, after Ag-exchange, the shape of Tb3+ excitation resembles the one of Ag ions/nanoaggregates, with a broad significant absorption in the whole UV-blue spectral region. This broadband enhanced downshifting could find potential applications in lighting devices and in PV solar cells.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-70344 (URN)10.1016/j.optmat.2018.07.074 (DOI)000446145200099 ()2-s2.0-85050857389 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-13 (andbra)

Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2018-10-22Bibliographically approved
Enrichi, F., Cattaruzza, E., Ferrari, M., Gonella, F., Ottini, R., Riello, P., . . . Zur, L. (2018). Ag-Sensitized Yb3+ Emission in Glass-Ceramics. Micromachines, 9(8), Article ID 380.
Open this publication in new window or tab >>Ag-Sensitized Yb3+ Emission in Glass-Ceramics
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2018 (English)In: Micromachines, ISSN 2072-666X, E-ISSN 2072-666X, Vol. 9, no 8, article id 380Article in journal (Refereed) Published
Abstract [en]

Rare earth doped materials play a very important role in the development of many photonic devices, such as optical amplifiers and lasers, frequency converters, solar concentrators, up to quantum information storage devices. Among the rare earth ions, ytterbium is certainly one of the most frequently investigated and employed. The absorption and emission properties of Yb3+ ions are related to transitions between the two energy levels 2F7/2 (ground state) and 2F5/2 (excited state), involving photon energies around 1.26 eV (980 nm). Therefore, Yb3+ cannot directly absorb UV or visible light, and it is often used in combination with other rare earth ions like Pr3+, Tm3+, and Tb3+, which act as energy transfer centres. Nevertheless, even in those co-doped materials, the absorption bandwidth can be limited, and the cross section is small. In this paper, we report a broadband and efficient energy transfer process between Ag dimers/multimers and Yb3+ ions, which results in a strong PL emission around 980 nm under UV light excitation. Silica-zirconia (70% SiO2-30% ZrO2) glass-ceramic films doped by 4 mol.% Yb3+ ions and an additional 5 mol.% of Na2O were prepared by sol-gel synthesis followed by a thermal annealing at 1000 °C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 430 °C to induce the migration and aggregation of the metal. The structural, compositional, and optical properties were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag dimers/multimers, which could have important applications in different fields, such as PV solar cells and light-emitting near-infrared (NIR) devices.

Place, publisher, year, edition, pages
MDPI, 2018
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-71115 (URN)10.3390/mi9080380 (DOI)000443256300014 ()2-s2.0-85054930887 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-05 (johcin)

Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2019-03-27Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2935-1165

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