Carmen Cavallo | University of Oslo (original) (raw)

Papers by Carmen Cavallo

Energies, May 22, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Scientific Reports, Jul 27, 2017

Journal of Physical Chemistry C, Nov 21, 2013

Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepar... more Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (≈650 nm) and rice-grain-shaped at the nanoscopic level (≈20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m 2 g −1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with Sc Ti substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0−1.0 at. % of Sc, the flat band energy changes from −4.15 to −4.07 eV, whereas the band gap height increases by 0.03 eV. The presence of Sc modifies heavily the cathodoluminescence spectrum of anatase at the lowest concentration too. Several DSSCs with photoanodes at different Sc doping were tested both under solar simulator and in the dark. The maximum efficiency of 9.6% was found at 0.2 at. % of Sc in anatase that is 6.7% higher with respect to the DSSCs with pure anatase.

Batteries & supercaps, Jun 2, 2021

Progress in the field of Na-based batteries strongly relies on the development of new advanced ma... more Progress in the field of Na-based batteries strongly relies on the development of new advanced materials. However, one of the main challenges of implementing new electrode materials is the understanding of their mechanisms (sodiation/desodiation) during electrochemical cycling. Operando studies provide extremely valuable insights into structural and chemical changes within different battery components during battery operation. The present review offers a critical summary of the operando X-ray based characterization techniques used to examine the structural and chemical transformations of the active materials in Na-ion, Na-air and Na-sulfur batteries during (de)sodiation. These methods provide structural and electronic information through diffraction, scattering, absorption and imaging or through a combination of these X-ray-based techniques. Challenges associated with cell design and data processing are also addressed herein. In addition, the present review provides a perspective on the future opportunities for these powerful techniques.

Batteries & supercaps, Mar 16, 2021

Progress in the field of Na-based batteries strongly relies on the development of new advanced ma... more Progress in the field of Na-based batteries strongly relies on the development of new advanced materials. However, one of the main challenges of implementing new electrode materials is the understanding of their mechanisms (sodiation/desodiation) during electrochemical cycling. Operando studies provide extremely valuable insights into structural and chemical changes within different battery components during battery operation. The present review offers a critical summary of the operando X-ray based characterization techniques used to examine the structural and chemical transformations of the active materials in Na-ion, Na-air and Na-sulfur batteries during (de)sodiation. These methods provide structural and electronic information through diffraction, scattering, absorption and imaging or through a combination of these Xray-based techniques. Challenges associated with cell design and data processing are also addressed herein. In addition, the present review provides a perspective on the future opportunities for these powerful techniques. List of Acronyms AI Artificial intelligence CT Computed tomography DEG-DME Diethylene glycol dimethyl ether DFT Density functional theory EDX Energy dispersive X-ray spectroscopy EXAFS Extended X-ray absorption fine structure FTIR Fourier transform infrared spectroscopy FWHM Full width at half maximum HAXPES Hard X-ray photoelectron spectroscopy LIB Li-ion battery, lithium-ion battery MCR-ALS Multivariate curve resolution alternating least square ML Machine learning NASICON Na superionic conductor NIB, SIB Na-ion battery, sodium-ion battery NMR Nuclear magnetic resonance PBA Prussian blue analogues

Journal of Power Sources, Dec 1, 2014

ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized so... more ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized solar cells. These compositions are based on benzonitrile and non volatile. These electrolytes show high stability over time under natural sunlight. Efficiencies >8% can be achieved with common N719 dye and without coadsorbents. a b s t r a c t The beneficial effect of benzonitrile as electrolyte solvent in Dye Sensitized Solar Cells (DSSCs) is demonstrated. The very low vapour pressure of benzonitrile (133 Pa @ 25 C) ensures long-term stability to the cells and efficiency values were found around 8% for more than 1300 hours. These results were obtained by using commercial P90 titania photoanodes sensitized by N719 dye, i.e., by making use of common and low priced materials. In this way, neither complex dyes nor passivating agents are required to maintain satisfactory efficiencies in a non-volatile electrolyte solvent as 3-methoxypropionitrile, as reported in literature. The results of this work have to be considered an important step towards an easy and economic fabrication of devices with stable performances for commercially convenient periods. Twelve electrolytes were examined: 9 of them had benzonitrile as solvent, different ratios I -/I 2 and different ionic liquid iodide salts whereas, for comparison, one electrolyte in acetonitrile and another in 3-methoxypropionitrile were studied. As reference, the redox couple I À 3 =I À in benzonitrile without ad-ditives was also examined. The electrolytes were characterized by specific conductivity vs. temperature, diffusion coefficient of I 3 À and redox potential of the I À 3 =I À couple measurements. Efficiency, dark current and IPCE of DSSCs were determined for each electrolyte.

Materials Today Energy, 2020

Hybrid energy storage systems aim to achieve both high power and energy densities by combining su... more Hybrid energy storage systems aim to achieve both high power and energy densities by combining supercapacitor-type and battery-type electrodes in tandem. The challenge is to find sustainable materials as fast charging negative electrodes, which are characterized by high capacity retention. In this study, mesoporous anatase beads are synthetized with tailored morphology to exploit fast surface redox reactions. The TiO 2-based electrodes are properly paired with a commercial activated carbon cathode to form a Li-ion capacitor. The titania electrode exhibits high capacity and rate performance. The device shows extremely stable performance with an energy density of 27 mWh g-1 at a specific current of 2.5 A g À1 for 10,000 cycles. The remarkable stability is associated with a gradual shift of the potential during cycling as result of the formation of cubic LiTiO 2 on the surface of the beads. This phenomenon renews the interest in using TiO 2 as negative electrode for Li-ion capacitors.

Nanotechnology, Feb 10, 2022

Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are ... more Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are promising solutions for energy storage benefiting from low-cost materials comprised of abundant elements. However, despite the mechanistic similarities, Na-ion batteries require a different set of active materials than Li-ion batteries. Bismuth molybdate (Bi2MoO6) is a promising NIB anode material operating through a combined conversion/alloying mechanism. We report an operando x-ray diffraction (XRD) investigation of Bi2MoO6-based anodes over 34 (de)sodiation cycles revealing both basic operating mechanisms and potential pathways for capacity degradation. Irreversible conversion of Bi2MoO6 to Bi nanoparticles occurs through the first sodiation, allowing Bi to reversibly alloy with Na forming the cubic Na3Bi phase. Preliminary electrochemical evaluation in half-cells versus Na metal demonstrated specific capacities for Bi2MoO6 to be close to 300 mAh g−1 during the initial 10 cycles, followed by a rapid capacity decay. Operando XRD characterisation revealed that the increased irreversibility of the sodiation reactions and the formation of hexagonal Na3Bi are the main causes of the capacity loss. This is initiated by an increase in crystallite sizes of the Bi particles accompanied by structural changes in the electronically insulating Na–Mo–O matrix leading to poor conductivity in the electrode. The poor electronic conductivity of the matrix deactivates the Na x Bi particles and prevents the formation of the solid electrolyte interface layer as shown by post-mortem scanning electron microscopy studies.

Some results dealing with the synthesis, characterization and functional properties, as DSSC phot... more Some results dealing with the synthesis, characterization and functional properties, as DSSC photo-anode active material, of solid solutions of nanostructured oxide materials hierarchically organized will be presented. The host lattice is TiO2-anatase and solute is a metal cation aliovalent with respect to Ti (IV). The scope of this work is to modify usefully the band structure of anatase with respect to the electronic levels of the light harvesting dye and to improve its electronic conductivity due to the creation of donor or acceptor levels. The final objective is to increase the DSSC conversion yield through searching for the better electronic coupling TiO2-anatase/dye since this is one of the necks that influence the whole efficiency of a DSSC. Another cause of the lack of efficiency is the electron-hole recombination in the TiO2-anatase film and we obtained satisfactory results [1] by TiO2-anatase/MWCNT nanocomposites that behave as Schottky junctions being multi walled carbon ...

Frontiers in Energy Research

Over the past decade, Na-ion batteries (NIBs) have gained a substantial interest within the resea... more Over the past decade, Na-ion batteries (NIBs) have gained a substantial interest within the research community and relevant industry. NIBs are now emerging as a cost-effective and sustainable alternative to modern Li-ion batteries (LIBs). Similar to the parent LIB technology, NIB requires a new set of materials, which can boost battery capacity without sacrificing cycling stability, rate capabilities, and other performance targets. In NIB chemistry, anodes have received less attention compared to cathode chemistry, leaving hard carbon as a primary anode material, although its intercalation/adsorption mechanism limits the allowed number of Na-ions. Promising alternative groups of anodes are materials that undergo the combined conversion and alloying reactions (i.e., conversion-alloying anodes), due to the beneficial high theoretical capacity and good cycling stability. The conversion reaction in conversion-alloying anodes can be either reversible or irreversible, each possessing its ...

Nanotechnology, 2022

Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are ... more Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are promising solutions for energy storage benefiting from low-cost materials comprised of abundant elements. However, despite the mechanistic similarities, Na-ion batteries require a different set of active materials than Li-ion batteries. Bismuth molybdate (Bi2MoO6) is a promising NIB anode material operating through a combined conversion/alloying mechanism. We report an operando x-ray diffraction (XRD) investigation of Bi2MoO6-based anodes over 34 (de)sodiation cycles revealing both basic operating mechanisms and potential pathways for capacity degradation. Irreversible conversion of Bi2MoO6 to Bi nanoparticles occurs through the first sodiation, allowing Bi to reversibly alloy with Na forming the cubic Na3Bi phase. Preliminary electrochemical evaluation in half-cells versus Na metal demonstrated specific capacities for Bi2MoO6 to be close to 300 mAh g−1 during the initial 10 cycles, foll...

Scientific reports, Jul 27, 2017

Applied Physics A, 2017

This paper investigates the effect of Zr, Hf, and Ta doping on the performances of Dye-sensitized... more This paper investigates the effect of Zr, Hf, and Ta doping on the performances of Dye-sensitized solar cells (DSSCs) with photoanodes comprising mesoporous hierarchical anatase spheres. Morphology, structure, and optical properties of doped and undoped materials were examined by Field Emission Scanning Electron Microscopy, X-ray diffraction, and Diffuse Reflectance Spectroscopy, and materials’ characteristics were related to DSSC fundamental photovoltaic parameters by polarization curves (under illumination and dark conditions) and external quantum efficiency measurements. Photoanodes’ charge transport and recombination properties were investigated by Electrochemical Impedance Spectroscopy. Although doping were carried out by inserting a small amount (from 0.1 to 0.3 at %) of homo and aliovalent and electron-rich (with respect to Ti4+) cation, energy conversion efficiency turned out to be lower than pure anatase photoanodes. Electron-impurity scattering phenomena in conjunction with reduced specific surface area caused by the increased bulk free energy are believed to account for the efficiency drop. However, a small beneficial effect introduced by doping on the trap-mediated recombination mechanisms has been identified.

Scientific Reports, 2015

Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase T... more Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase TiO2 have been synthesized as mesoporous beads in the concentration range 0.1–0.3% of metal atoms. The solid solutions were have been characterized by XRD, SEM, diffuse reflectance UV-Vis spectroscopy, BET and BJH surface analysis. All the solid solutions possess high specific surface areas, up to more than 100 m2/g. The amount of adsorbed dye in each photoanode has been determined spectrophotometrically. All the samples were tested as photoanodes in dye-sensitized solar cells (DSSCs) using N719 as dye and a nonvolatile, benzonitrile based electrolyte. All the cells were have been tested by conversion efficiency (J–V), quantum efficiency (IPCE), electrochemical impedance spectroscopy (EIS) and dark current measurements. While lighter RE cations (Pr3+, Nd3+) limit the performance of DSSCs compared to pure anatase mesoporous beads, cations from Sm3+ onwards enhance the performance of the de...

Journal of Nanomaterials, 2015

The present work aims at optimizing titanium dioxide morphology for dye-sensitized solar cells ap... more The present work aims at optimizing titanium dioxide morphology for dye-sensitized solar cells applications. Five different anatase phase mesoporous titanias were prepared and tested as photoanodes in dye-sensitized solar cells. The materials were prepared by using a template approach. Two materials were synthesized by using monodisperse silica nanospheres and the other three using two different organic templating agents (Pluronic P123 and Brij 58). A complete characterization of the obtained materials was performed by powder XRD, FEG-SEM, UV-Vis reflectance spectroscopy, BET surface area measurements, and TG-DTA. Several cells were assembled using N719 as dye and a nonvolatile electrolyte based on benzonitrile. The cells were tested by means ofJ-Vcurves under simulated solar radiation, IPCE, and dark current measurements. The highest efficiencies were achieved with titania prepared by using Pluronic P123 as template (ηmax=6.8%), while the lowest efficiencies were recorded with usin...

The Journal of Physical Chemistry C

ABSTRACT: Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes w... more ABSTRACT: Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (≈650 nm) and rice-grain-shaped at the nanoscopic level (≈20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m2 g−1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with ScTi substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0−1.0 at. % of Sc, the...

Journal of Power Sources, 2014

ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized so... more ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized solar cells. These compositions are based on benzonitrile and non volatile. These electrolytes show high stability over time under natural sunlight. Efficiencies >8% can be achieved with common N719 dye and without coadsorbents. a b s t r a c t The beneficial effect of benzonitrile as electrolyte solvent in Dye Sensitized Solar Cells (DSSCs) is demonstrated. The very low vapour pressure of benzonitrile (133 Pa @ 25 C) ensures long-term stability to the cells and efficiency values were found around 8% for more than 1300 hours. These results were obtained by using commercial P90 titania photoanodes sensitized by N719 dye, i.e., by making use of common and low priced materials. In this way, neither complex dyes nor passivating agents are required to maintain satisfactory efficiencies in a non-volatile electrolyte solvent as 3-methoxypropionitrile, as reported in literature. The results of this work have to be considered an important step towards an easy and economic fabrication of devices with stable performances for commercially convenient periods. Twelve electrolytes were examined: 9 of them had benzonitrile as solvent, different ratios I -/I 2 and different ionic liquid iodide salts whereas, for comparison, one electrolyte in acetonitrile and another in 3-methoxypropionitrile were studied. As reference, the redox couple I À 3 =I À in benzonitrile without ad-ditives was also examined. The electrolytes were characterized by specific conductivity vs. temperature, diffusion coefficient of I 3 À and redox potential of the I À 3 =I À couple measurements. Efficiency, dark current and IPCE of DSSCs were determined for each electrolyte.

The Journal of Physical Chemistry C, 2013

Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepar... more Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (≈650 nm) and rice-grain-shaped at the nanoscopic level (≈20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m 2 g −1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with Sc Ti substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0−1.0 at. % of Sc, the flat band energy changes from −4.15 to −4.07 eV, whereas the band gap height increases by 0.03 eV. The presence of Sc modifies heavily the cathodoluminescence spectrum of anatase at the lowest concentration too. Several DSSCs with photoanodes at different Sc doping were tested both under solar simulator and in the dark. The maximum efficiency of 9.6% was found at 0.2 at. % of Sc in anatase that is 6.7% higher with respect to the DSSCs with pure anatase.

Scientific Reports, 2016

The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = C... more The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid organic-inorganic solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodynamic stability of the materials towards decomposition, which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that ...

Energies, May 22, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Scientific Reports, Jul 27, 2017

Journal of Physical Chemistry C, Nov 21, 2013

Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepar... more Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (≈650 nm) and rice-grain-shaped at the nanoscopic level (≈20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m 2 g −1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with Sc Ti substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0−1.0 at. % of Sc, the flat band energy changes from −4.15 to −4.07 eV, whereas the band gap height increases by 0.03 eV. The presence of Sc modifies heavily the cathodoluminescence spectrum of anatase at the lowest concentration too. Several DSSCs with photoanodes at different Sc doping were tested both under solar simulator and in the dark. The maximum efficiency of 9.6% was found at 0.2 at. % of Sc in anatase that is 6.7% higher with respect to the DSSCs with pure anatase.

Batteries & supercaps, Jun 2, 2021

Progress in the field of Na-based batteries strongly relies on the development of new advanced ma... more Progress in the field of Na-based batteries strongly relies on the development of new advanced materials. However, one of the main challenges of implementing new electrode materials is the understanding of their mechanisms (sodiation/desodiation) during electrochemical cycling. Operando studies provide extremely valuable insights into structural and chemical changes within different battery components during battery operation. The present review offers a critical summary of the operando X-ray based characterization techniques used to examine the structural and chemical transformations of the active materials in Na-ion, Na-air and Na-sulfur batteries during (de)sodiation. These methods provide structural and electronic information through diffraction, scattering, absorption and imaging or through a combination of these X-ray-based techniques. Challenges associated with cell design and data processing are also addressed herein. In addition, the present review provides a perspective on the future opportunities for these powerful techniques.

Batteries & supercaps, Mar 16, 2021

Progress in the field of Na-based batteries strongly relies on the development of new advanced ma... more Progress in the field of Na-based batteries strongly relies on the development of new advanced materials. However, one of the main challenges of implementing new electrode materials is the understanding of their mechanisms (sodiation/desodiation) during electrochemical cycling. Operando studies provide extremely valuable insights into structural and chemical changes within different battery components during battery operation. The present review offers a critical summary of the operando X-ray based characterization techniques used to examine the structural and chemical transformations of the active materials in Na-ion, Na-air and Na-sulfur batteries during (de)sodiation. These methods provide structural and electronic information through diffraction, scattering, absorption and imaging or through a combination of these Xray-based techniques. Challenges associated with cell design and data processing are also addressed herein. In addition, the present review provides a perspective on the future opportunities for these powerful techniques. List of Acronyms AI Artificial intelligence CT Computed tomography DEG-DME Diethylene glycol dimethyl ether DFT Density functional theory EDX Energy dispersive X-ray spectroscopy EXAFS Extended X-ray absorption fine structure FTIR Fourier transform infrared spectroscopy FWHM Full width at half maximum HAXPES Hard X-ray photoelectron spectroscopy LIB Li-ion battery, lithium-ion battery MCR-ALS Multivariate curve resolution alternating least square ML Machine learning NASICON Na superionic conductor NIB, SIB Na-ion battery, sodium-ion battery NMR Nuclear magnetic resonance PBA Prussian blue analogues

Journal of Power Sources, Dec 1, 2014

ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized so... more ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized solar cells. These compositions are based on benzonitrile and non volatile. These electrolytes show high stability over time under natural sunlight. Efficiencies >8% can be achieved with common N719 dye and without coadsorbents. a b s t r a c t The beneficial effect of benzonitrile as electrolyte solvent in Dye Sensitized Solar Cells (DSSCs) is demonstrated. The very low vapour pressure of benzonitrile (133 Pa @ 25 C) ensures long-term stability to the cells and efficiency values were found around 8% for more than 1300 hours. These results were obtained by using commercial P90 titania photoanodes sensitized by N719 dye, i.e., by making use of common and low priced materials. In this way, neither complex dyes nor passivating agents are required to maintain satisfactory efficiencies in a non-volatile electrolyte solvent as 3-methoxypropionitrile, as reported in literature. The results of this work have to be considered an important step towards an easy and economic fabrication of devices with stable performances for commercially convenient periods. Twelve electrolytes were examined: 9 of them had benzonitrile as solvent, different ratios I -/I 2 and different ionic liquid iodide salts whereas, for comparison, one electrolyte in acetonitrile and another in 3-methoxypropionitrile were studied. As reference, the redox couple I À 3 =I À in benzonitrile without ad-ditives was also examined. The electrolytes were characterized by specific conductivity vs. temperature, diffusion coefficient of I 3 À and redox potential of the I À 3 =I À couple measurements. Efficiency, dark current and IPCE of DSSCs were determined for each electrolyte.

Materials Today Energy, 2020

Hybrid energy storage systems aim to achieve both high power and energy densities by combining su... more Hybrid energy storage systems aim to achieve both high power and energy densities by combining supercapacitor-type and battery-type electrodes in tandem. The challenge is to find sustainable materials as fast charging negative electrodes, which are characterized by high capacity retention. In this study, mesoporous anatase beads are synthetized with tailored morphology to exploit fast surface redox reactions. The TiO 2-based electrodes are properly paired with a commercial activated carbon cathode to form a Li-ion capacitor. The titania electrode exhibits high capacity and rate performance. The device shows extremely stable performance with an energy density of 27 mWh g-1 at a specific current of 2.5 A g À1 for 10,000 cycles. The remarkable stability is associated with a gradual shift of the potential during cycling as result of the formation of cubic LiTiO 2 on the surface of the beads. This phenomenon renews the interest in using TiO 2 as negative electrode for Li-ion capacitors.

Nanotechnology, Feb 10, 2022

Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are ... more Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are promising solutions for energy storage benefiting from low-cost materials comprised of abundant elements. However, despite the mechanistic similarities, Na-ion batteries require a different set of active materials than Li-ion batteries. Bismuth molybdate (Bi2MoO6) is a promising NIB anode material operating through a combined conversion/alloying mechanism. We report an operando x-ray diffraction (XRD) investigation of Bi2MoO6-based anodes over 34 (de)sodiation cycles revealing both basic operating mechanisms and potential pathways for capacity degradation. Irreversible conversion of Bi2MoO6 to Bi nanoparticles occurs through the first sodiation, allowing Bi to reversibly alloy with Na forming the cubic Na3Bi phase. Preliminary electrochemical evaluation in half-cells versus Na metal demonstrated specific capacities for Bi2MoO6 to be close to 300 mAh g−1 during the initial 10 cycles, followed by a rapid capacity decay. Operando XRD characterisation revealed that the increased irreversibility of the sodiation reactions and the formation of hexagonal Na3Bi are the main causes of the capacity loss. This is initiated by an increase in crystallite sizes of the Bi particles accompanied by structural changes in the electronically insulating Na–Mo–O matrix leading to poor conductivity in the electrode. The poor electronic conductivity of the matrix deactivates the Na x Bi particles and prevents the formation of the solid electrolyte interface layer as shown by post-mortem scanning electron microscopy studies.

Some results dealing with the synthesis, characterization and functional properties, as DSSC phot... more Some results dealing with the synthesis, characterization and functional properties, as DSSC photo-anode active material, of solid solutions of nanostructured oxide materials hierarchically organized will be presented. The host lattice is TiO2-anatase and solute is a metal cation aliovalent with respect to Ti (IV). The scope of this work is to modify usefully the band structure of anatase with respect to the electronic levels of the light harvesting dye and to improve its electronic conductivity due to the creation of donor or acceptor levels. The final objective is to increase the DSSC conversion yield through searching for the better electronic coupling TiO2-anatase/dye since this is one of the necks that influence the whole efficiency of a DSSC. Another cause of the lack of efficiency is the electron-hole recombination in the TiO2-anatase film and we obtained satisfactory results [1] by TiO2-anatase/MWCNT nanocomposites that behave as Schottky junctions being multi walled carbon ...

Frontiers in Energy Research

Over the past decade, Na-ion batteries (NIBs) have gained a substantial interest within the resea... more Over the past decade, Na-ion batteries (NIBs) have gained a substantial interest within the research community and relevant industry. NIBs are now emerging as a cost-effective and sustainable alternative to modern Li-ion batteries (LIBs). Similar to the parent LIB technology, NIB requires a new set of materials, which can boost battery capacity without sacrificing cycling stability, rate capabilities, and other performance targets. In NIB chemistry, anodes have received less attention compared to cathode chemistry, leaving hard carbon as a primary anode material, although its intercalation/adsorption mechanism limits the allowed number of Na-ions. Promising alternative groups of anodes are materials that undergo the combined conversion and alloying reactions (i.e., conversion-alloying anodes), due to the beneficial high theoretical capacity and good cycling stability. The conversion reaction in conversion-alloying anodes can be either reversible or irreversible, each possessing its ...

Nanotechnology, 2022

Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are ... more Based on the same rocking-chair principle as rechargeable Li-ion batteries, Na-ion batteries are promising solutions for energy storage benefiting from low-cost materials comprised of abundant elements. However, despite the mechanistic similarities, Na-ion batteries require a different set of active materials than Li-ion batteries. Bismuth molybdate (Bi2MoO6) is a promising NIB anode material operating through a combined conversion/alloying mechanism. We report an operando x-ray diffraction (XRD) investigation of Bi2MoO6-based anodes over 34 (de)sodiation cycles revealing both basic operating mechanisms and potential pathways for capacity degradation. Irreversible conversion of Bi2MoO6 to Bi nanoparticles occurs through the first sodiation, allowing Bi to reversibly alloy with Na forming the cubic Na3Bi phase. Preliminary electrochemical evaluation in half-cells versus Na metal demonstrated specific capacities for Bi2MoO6 to be close to 300 mAh g−1 during the initial 10 cycles, foll...

Scientific reports, Jul 27, 2017

Applied Physics A, 2017

This paper investigates the effect of Zr, Hf, and Ta doping on the performances of Dye-sensitized... more This paper investigates the effect of Zr, Hf, and Ta doping on the performances of Dye-sensitized solar cells (DSSCs) with photoanodes comprising mesoporous hierarchical anatase spheres. Morphology, structure, and optical properties of doped and undoped materials were examined by Field Emission Scanning Electron Microscopy, X-ray diffraction, and Diffuse Reflectance Spectroscopy, and materials’ characteristics were related to DSSC fundamental photovoltaic parameters by polarization curves (under illumination and dark conditions) and external quantum efficiency measurements. Photoanodes’ charge transport and recombination properties were investigated by Electrochemical Impedance Spectroscopy. Although doping were carried out by inserting a small amount (from 0.1 to 0.3 at %) of homo and aliovalent and electron-rich (with respect to Ti4+) cation, energy conversion efficiency turned out to be lower than pure anatase photoanodes. Electron-impurity scattering phenomena in conjunction with reduced specific surface area caused by the increased bulk free energy are believed to account for the efficiency drop. However, a small beneficial effect introduced by doping on the trap-mediated recombination mechanisms has been identified.

Scientific Reports, 2015

Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase T... more Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase TiO2 have been synthesized as mesoporous beads in the concentration range 0.1–0.3% of metal atoms. The solid solutions were have been characterized by XRD, SEM, diffuse reflectance UV-Vis spectroscopy, BET and BJH surface analysis. All the solid solutions possess high specific surface areas, up to more than 100 m2/g. The amount of adsorbed dye in each photoanode has been determined spectrophotometrically. All the samples were tested as photoanodes in dye-sensitized solar cells (DSSCs) using N719 as dye and a nonvolatile, benzonitrile based electrolyte. All the cells were have been tested by conversion efficiency (J–V), quantum efficiency (IPCE), electrochemical impedance spectroscopy (EIS) and dark current measurements. While lighter RE cations (Pr3+, Nd3+) limit the performance of DSSCs compared to pure anatase mesoporous beads, cations from Sm3+ onwards enhance the performance of the de...

Journal of Nanomaterials, 2015

The present work aims at optimizing titanium dioxide morphology for dye-sensitized solar cells ap... more The present work aims at optimizing titanium dioxide morphology for dye-sensitized solar cells applications. Five different anatase phase mesoporous titanias were prepared and tested as photoanodes in dye-sensitized solar cells. The materials were prepared by using a template approach. Two materials were synthesized by using monodisperse silica nanospheres and the other three using two different organic templating agents (Pluronic P123 and Brij 58). A complete characterization of the obtained materials was performed by powder XRD, FEG-SEM, UV-Vis reflectance spectroscopy, BET surface area measurements, and TG-DTA. Several cells were assembled using N719 as dye and a nonvolatile electrolyte based on benzonitrile. The cells were tested by means ofJ-Vcurves under simulated solar radiation, IPCE, and dark current measurements. The highest efficiencies were achieved with titania prepared by using Pluronic P123 as template (ηmax=6.8%), while the lowest efficiencies were recorded with usin...

The Journal of Physical Chemistry C

ABSTRACT: Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes w... more ABSTRACT: Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (≈650 nm) and rice-grain-shaped at the nanoscopic level (≈20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m2 g−1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with ScTi substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0−1.0 at. % of Sc, the...

Journal of Power Sources, 2014

ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized so... more ABSTRACT h i g h l i g h t s We developed new high performance electrolytes for dye sensitized solar cells. These compositions are based on benzonitrile and non volatile. These electrolytes show high stability over time under natural sunlight. Efficiencies >8% can be achieved with common N719 dye and without coadsorbents. a b s t r a c t The beneficial effect of benzonitrile as electrolyte solvent in Dye Sensitized Solar Cells (DSSCs) is demonstrated. The very low vapour pressure of benzonitrile (133 Pa @ 25 C) ensures long-term stability to the cells and efficiency values were found around 8% for more than 1300 hours. These results were obtained by using commercial P90 titania photoanodes sensitized by N719 dye, i.e., by making use of common and low priced materials. In this way, neither complex dyes nor passivating agents are required to maintain satisfactory efficiencies in a non-volatile electrolyte solvent as 3-methoxypropionitrile, as reported in literature. The results of this work have to be considered an important step towards an easy and economic fabrication of devices with stable performances for commercially convenient periods. Twelve electrolytes were examined: 9 of them had benzonitrile as solvent, different ratios I -/I 2 and different ionic liquid iodide salts whereas, for comparison, one electrolyte in acetonitrile and another in 3-methoxypropionitrile were studied. As reference, the redox couple I À 3 =I À in benzonitrile without ad-ditives was also examined. The electrolytes were characterized by specific conductivity vs. temperature, diffusion coefficient of I 3 À and redox potential of the I À 3 =I À couple measurements. Efficiency, dark current and IPCE of DSSCs were determined for each electrolyte.

The Journal of Physical Chemistry C, 2013

Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepar... more Solid solutions of scandium in anatase as semiconductor material for DSSC photoanodes were prepared by the controlled hydrolysis of titanium(IV) isopropoxide and scandium(III) isopropoxide in hydroalcoholic medium. The final powder was constituted by mesoporous anatase beads doped with Sc. A superstructure characterizes the beads, which are spherical at the microscopic level (≈650 nm) and rice-grain-shaped at the nanoscopic level (≈20 nm). The BJH pore size distribution and BET surface area of the powder beads were found depending from the Sc content ranging the peak of the former between 7 and 25 nm and between 65 and 128 m 2 g −1 the latter. Data obtained by XRD and EXAFS confirm that we are dealing with real solid solutions with Sc Ti substitution defects. The electronic properties of the synthesized semiconductor material as a function of Sc doping were investigated by the measure of the flat band potential, band gap, and deep levels. In the range 0.0−1.0 at. % of Sc, the flat band energy changes from −4.15 to −4.07 eV, whereas the band gap height increases by 0.03 eV. The presence of Sc modifies heavily the cathodoluminescence spectrum of anatase at the lowest concentration too. Several DSSCs with photoanodes at different Sc doping were tested both under solar simulator and in the dark. The maximum efficiency of 9.6% was found at 0.2 at. % of Sc in anatase that is 6.7% higher with respect to the DSSCs with pure anatase.

Scientific Reports, 2016

The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = C... more The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid organic-inorganic solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodynamic stability of the materials towards decomposition, which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that ...