Dörthe Haase - Academia.edu (original) (raw)
Papers by Dörthe Haase
We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge ... more We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O 2 , with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O 2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co 3 O 4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.
Left – A schematic view of the XAS microfluidic set up at the beamline; fluorescence detector at ... more Left – A schematic view of the XAS microfluidic set up at the beamline; fluorescence detector at 90° angle to the X-ray beam (green line); right – microfluidic device setup on Balder beamline mounted perpendicular to beam path.
Journal of Polymer Science Part B: Polymer Physics, 2019
We report on X-ray scattering measurements of helical poly[9,9-bis(2ethylhexyl)-fluorene-2,7-diyl... more We report on X-ray scattering measurements of helical poly[9,9-bis(2ethylhexyl)-fluorene-2,7-diyl] by mapping the sample with 10 µm spatial resolution from 0.3 GPa to 36 GPa. We follow the strongest 00l reflection, which moves towards higher scattering angles with pressure indicating planarization of helical polyfluorene. Lateral inhomogeneity is increased for > 10 GPa concomitant with the solidification of the pressure transmitting medium (a 4:1 mixture of methanol and ethanol). We also follow the 00l reflection with increasing temperature at the constant pressure of 4.3 GPa in neon. We observe a sharp shift towards higher scattering angles indicative of a phase transition at 167-176 °C.
Physical Review E, 2016
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Phys. Chem. Chem. Phys., 2016
In situSR-PXD experiments revealed a new reaction mechanism of amide–hydride anionic exchange for... more In situSR-PXD experiments revealed a new reaction mechanism of amide–hydride anionic exchange for the K–Mg–N–H system.
Physical Chemistry Chemical Physics, 2016
Supporting information: 1. Synthesis methods and characterization: Synthesis of precursors: methy... more Supporting information: 1. Synthesis methods and characterization: Synthesis of precursors: methylammonium (MA) bromide (CH3NH3Br) and octylammonium (OTA) bromide (CH3(CH2)7NH3Br) were synthesized by reaction of the corresponding amine in water/HBr accordingly to the previously reports. In brief, for (CH3NH3Br) 36.9 ml of HBr and 83.4 ml of CH3NH2 were stirred for two hours in ice bath. The resulting solution was evaporated untill the formation of white crystals. The white crystals then were recrystallized from ethanol solution and then used as a precursor for CH 3 NH 3 PbBr 3 colloidal nanoparticles. The same procedures were repeated in order to prepare (CH3(CH2)7NH3Br) where 33.5 ml of CH3(CH2)7NH2 and 22.6 ml of HBr were stirred for two hours in ice bath. Synthesis of CH 3 NH 3 PbBr 3 bulk-like crystals: MAPbBr3 microcrystals were prepared by spin coating MAPbBr3 precursors in DMF onto glass substrates with 2000 rpm for 30 sec. Substrates were then annealed in air at 85 o C for half an hour to form orange colored crystals. In order to verify the crystal size, different dilution of precursors (original, ×2, ×4, ×8, ×16, ×25) were used which produced crystals with mean size of 14.7, 6.2, 4.2, 2.0 and 0.4 μm, respectively. Synthesis of CH 3 NH 3 PbBr 3 colloidal nanoparticles: CH 3 NH 3 PbBr 3 colloidal nanoparticles were synthesized via hot injection of MABr/OTABr and PbBr 2 precursors in coordinator solvent analogous to previous reports. In brief, 0.5 mmol oleic acid in 10 ml of octadecene was stirred and heated at 80 °C followed by addition of 0.3 mmol OTABr in 1 ml DMF. Then 0.2 mmol of MABr in 1 ml DMF and 0.5 mmol PbBr2 in 1 ml DMF were injected subsequently. The yellow dispersion containing nanoparticles was directly precipitated by acetone. Finally, the nanoparticles were redispersed in toluene for use. Here the ratio between OTABr and MABr is 6:4. UV/Vis spectroscopy. The ground state optical absorption spectra of the nanoparticles and bulk samples have been measured using a UV/Vis absorption spectrophotometer (PerkinElmer, Lambda 1050) equipped with integrated sphere to exclude signal from light scattering. Steady-state photoluminescence was measured using a standard spectrometer (Horiba, Spex 1681) with the excitation at 410 nm. TEM. The morphology of NPs has been characterized by using a high resolution analytical transmission electron microscopy (HR-TEM) (JEOL 3000F equipped with Oxford SDD x-ray analyzer). Samples were prepared by directly depositing the NP suspension onto the carbon grid. FTIR. The FT-IR measurement was conducted at Beamline D7 in MAX IV Laboratory (Sweden). For sample preparation, MCs and NPs were diluted with KBr, and were pelletised. The distance between the light source and the sample was held constant (25 cm).
International Journal of Hydrogen Energy
The fuel cell performance of membrane electrode assemblies with a Pt anode and Pd, PdCu or Pd5Cu4... more The fuel cell performance of membrane electrode assemblies with a Pt anode and Pd, PdCu or Pd5Cu4Pt cathodes has been tested during 116 h (beginning of life). The incorporation of Cu to Pd increases the fuel cell performance. Incorporation of Pt leads to further improvement. SEM micrographs of the as-prepared and the fuel cell-tested assemblies show the effects of the 116 h of continuous operation. Nafion membranes were characterized by small angle X-ray scattering. The results show a reduction of the size of the lamellar domains in the perfluorinated matrix after fuel cell testing, but no correlation with the cathode electrocatalyst material. The cathode electrocatalysts were characterized by ex-situ synchrotron radiation X-ray diffraction and X-ray absorption spectroscopy at the Pd L-3, Cu K and Pt L-3 edges. Re-organization of Pd5Cu4Pt electrocatalyst after fuel cell testing was observed. The Cu in the electrocatalyst can be described as a nano-mixture of metallic Cu, alloyed Cu ...
The Journal of Physical Chemistry C, 2010
A new alkaline transition-metal borohydride, NaSc(BH 4 ) 4 , is presented. The compound has been ... more A new alkaline transition-metal borohydride, NaSc(BH 4 ) 4 , is presented. The compound has been studied using a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. NaSc(BH 4 ) 4 forms at ambient conditions in ball-milled mixtures of sodium borohydride and ScCl 3 . A new ternary chloride Na 3 ScCl 6 (P2 1 /n, a ) 6.7375(3) Å, b ) 7.1567(3) Å, c ) 9.9316(5) Å, ) 90.491(3)°, V ) 478.87(4) Å 3 ), isostructural to Na 3 TiCl 6 , was identified as an additional phase in all samples. This indicates that the formation of NaSc(BH 4 ) 4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (22 wt %) was obtained with a reactant ratio of ScCl 3 /NaBH 4 of 1:2. NaSc(BH 4 ) 4 crystallizes in the orthorhombic crystal system with the space group symmetry Cmcm (a ) 8.170(2) Å, b ) 11.875(3) Å, c ) 9.018(2) Å, V ) 874.9(3) Å 3 ). The structure of NaSc(BH 4 ) 4 consists of isolated homoleptic scandium tetraborohydride anions, [Sc(BH 4 ) 4 ] -, located inside slightly distorted trigonal Na 6 prisms (each second prism is empty, triangular angles of 55.5 and 69.1°). The experimental results show that each Sc 3+ is tetrahedrally surrounded by four BH 4 tetrahedra with a 12-fold coordination of H to Sc, while Na + is surrounded by six BH 4 tetrahedra in a quite regular octahedral coordination with a (6 + 12)-fold coordination of H to Na. The packing of Na + cations and [Sc(BH 4 ) 4 ]anions in NaSc(BH 4 ) 4 is a deformation variant of the hexagonal NiAs structure type. NaSc(BH 4 ) 4 is stable from RT up to ∼410 K, where the compound melts and then releases hydrogen in two rapidly occurring steps between 440 and 490 K and 495 and 540 K. Thermal expansion of NaSc(BH 4 ) 4 between RT and 408 K is anisotropic, and lattice parameter b shows strong anomaly close to the melting temperature.
The Journal of Physical Chemistry C, 2010
ABSTRACT A new potassium scandium borohydride, KSc(BH 4) 4 , is presented and characterized by a ... more ABSTRACT A new potassium scandium borohydride, KSc(BH 4) 4 , is presented and characterized by a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. The title compound, KSc(BH 4) 4 , forms at ambient conditions in ball milled mixtures of potassium borohydride and ScCl 3 together with a new ternary chloride K 3 ScCl 6 , which is also structurally characterized. This indicates that the formation of KSc(BH 4) 4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (∼31 mol %) can be obtained with a reactant ratio KBH 4 :ScCl 3 of 2:1. KSc(BH 4) 4 crystallizes in the orthorhombic crystal system, a) 11.856(5), b) 7.800(3), c) 10.126(6) Å, V) 936.4(8) Å 3 at RT, with the space group symmetry Pnma. KSc(BH 4) 4 has a BaSO 4 type structure where the BH 4 tetrahedra take the oxygen positions. Regarding the packing of cations, K + , and complex anions, [Sc(BH 4) 4 ] -, the structure of KSc(BH 4) 4 can be seen as a distorted variant of orthorhombic neptunium, Np, metal. Thermal expansion of KSc(BH 4) 4 in the temperature range RT to 405 K is anisotropic, and the lattice parameter b shows strong nonlinearity upon approaching the melting temperature. The vibrational and NMR spectra are consistent with the structural model, and previous investigations of the related compounds ASc(BH 4) 4 with A) Li, Na. KSc(BH 4) 4 is stable from RT up to ∼405 K, where the compound melts and then releases hydrogen in two rapid steps approximately at 460-500 K and 510-590 K. The hydrogen release involves the formation of KBH 4 , which reacts with K 3 ScCl 6 and forms a solid solution, K(BH 4) 1-x Cl x . The ternary potassium scandium chloride K 3 ScCl 6 observed in all samples has a monoclinic structure at room temperature, P2 1 /a, a) 12.729(3), b) 7.367(2), c) 12.825(3) Å,) 109.22(2)°, V) 1135.6(4) Å 3 , which is isostructural to K 3 MoCl 6 . The monoclinic polymorph transforms to cubic at 635 K, a) 10.694 Å (based on diffraction data measured at 769 K), which is isostructural to the high temperature phase of K 3 YCl 6 .
![Research paper thumbnail of Evidence for structural transition in hairy-rod poly[9,9-bis(2-ethylhexyl)fluorene] under high pressure conditions](https://attachments.academia-assets.com/41320501/thumbnails/1.jpg)
](Physical Review E, 2010
We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under qua... more We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under quasihydrostatic pressure from 1 to 11 GPa at room temperature. The scattering pattern of high molecular weight ͑HMW͒ polyfluorene ͑Ͼ10 kg/ mol͒ undergoes significant changes between 2 and 4 GPa in the bulk phase. The 110 reflection of the hexagonal unit cell disappears, indicating a change in equatorial intermolecular order. The intensity of the 00 21 reflection drops, with a sudden move toward higher scattering angles. Beyond these pressures, the diminished 00 21 reflection tends to return toward lower angles. These changes may be interpreted as a transition from crystalline hexagonal to glassy nematic phase ͑perceiving order only in one direc-tion͒. This transition may be rationalized by density arguments and the underlying theory of phase behavior of hairy-rod polyfluorene. Also the possible alteration of the 21-helical main chain toward more planar main chain conformation is discussed. The scattering of low molecular weight polyfluorene ͑Ͻ10 kg/ mol͒, which is glassy nematic in ambient pressure, is reminiscent with that of HMW polymer above 2-4 GPa.
Scientific Reports, 2015
Quantum dots (QDs) and graphene are both promising materials for the development of new-generatio... more Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 10 9 s −1 . Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications.
Acta Crystallographica Section A Foundations of Crystallography, 2012
The European Physical Journal Plus, 2015
ChemInform, 2010
Thermal Polymorphism and Decomposition of Y(BH 4 ) 3 . -The structure and thermal decomposition o... more Thermal Polymorphism and Decomposition of Y(BH 4 ) 3 . -The structure and thermal decomposition of the title compound is characterized by in situ synchrotron powder XRD, 11 B MAS NMR spectroscopy, and thermal analysis. A new high-temperature polymorph, β-Y(BH4)3 which crystallizes in the cubic space group Pm3m with Z = 1 is reported. The new polymorph exhibits a regular ReO3-type structure in which the Y 3+ cations form cubes with anions located on the edges. The new phase forms in small amounts during ball milling of LiBH4 and YCl3, and in larger amounts from α-Y(BH4)3 via a phase transition under moderate hydrogen pressure at about 180°C. Upon further heating, β-Y(BH4)3 decomposes at about 190°C to YH3, which transforms to YH2 at 270°C. An unidentified compound exists in the temperature range of 215-280°C. The final decomposition product is YB 4 . Formation of metal borides during decomposition is an important indication of possible reversibility. Thus, it is concluded that Y(BH 4 ) 3 may be a reversible hydrogen storage material. -(RAVNSBAEK, D. B.; FILINCHUK, Y.; CERNY, R.; LEY, M. B.; HAASE, D.; JAKOBSEN, H. J.; SKIBSTED, J.; JENSEN*, T. R.; Inorg. Chem. 49 (2010) 8, 3801-3809; Dep. Chem., Univ. Aarhus, DK-8000 Aarhus, Den.; Eng.) -W. Pewestorf 29-009 BH -4
The Journal of Physical Chemistry C, 2013
A composite material in the LiH−LiF−MgB 2 system has been synthesized by high-energy ball milling... more A composite material in the LiH−LiF−MgB 2 system has been synthesized by high-energy ball milling. Some peaks in addition to that of the binary 2LiH−MgB 2 and 2LiF−MgB 2 systems are observed for the composite material by high-pressure differential scanning calorimetry (HP-DSC), indicating the formation of intermediate phases. In situ synchrotron radiation powder X-ray diffraction (SR-PXD) performed at 60 bar of H 2 and 390°C shows a superposition of both reaction pathways that are typical for 2LiH− MgB 2 and 2LiF−MgB 2 . After hydrogen absorption of the LiH−LiF− MgB 2 composite the vibrational modes of LiBH 4 were observed by attenuated total reflection infrared (ATR-IR) spectroscopy. The 19 F MAS NMR spectrum of the LiF−LiBH 4 sample after heat treatment in hydrogen is strongly dominated by the centerband and spinning sidebands from LiF; in addition, a low-intensity resonance, very similar to that of [BF 4 ] − ion, is identified.
Review of Scientific Instruments, 2011
A detector with high dynamic range designed for combined small- and wide-angle x-ray scattering e... more A detector with high dynamic range designed for combined small- and wide-angle x-ray scattering experiments has been developed. It allows measurements on single events and reactive systems, such as particle formation in flames and evaporation of levitating drops. The detector consists of 26 channels covering a region from 0.5° to 60° and it provides continuous monitoring of the sampled signal without readout dead time. The time resolution for fast single events is about 40 μs and for substances undergoing slower dynamics, the time resolution is set to 0.1 or 1 s with hours of continuous sampling. The detector has been used to measure soot particle formation in a flame, burning magnesium and evaporation of a toluene drop in a levitator. The results show that the detector can be used for many different applications with good outcomes and large potential.
![Research paper thumbnail of Evidence for structural transition in hairy-rod poly[9,9-bis(2-ethylhexyl)fluorene] under high pressure conditions](https://attachments.academia-assets.com/42884811/thumbnails/1.jpg)
](Physical Review E, 2010
We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under qua... more We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under quasihydrostatic pressure from 1 to 11 GPa at room temperature. The scattering pattern of high molecular weight ͑HMW͒ polyfluorene ͑Ͼ10 kg/ mol͒ undergoes significant changes between 2 and 4 GPa in the bulk phase. The 110 reflection of the hexagonal unit cell disappears, indicating a change in equatorial intermolecular order. The intensity of the 00 21 reflection drops, with a sudden move toward higher scattering angles. Beyond these pressures, the diminished 00 21 reflection tends to return toward lower angles. These changes may be interpreted as a transition from crystalline hexagonal to glassy nematic phase ͑perceiving order only in one direc-tion͒. This transition may be rationalized by density arguments and the underlying theory of phase behavior of hairy-rod polyfluorene. Also the possible alteration of the 21-helical main chain toward more planar main chain conformation is discussed. The scattering of low molecular weight polyfluorene ͑Ͻ10 kg/ mol͒, which is glassy nematic in ambient pressure, is reminiscent with that of HMW polymer above 2-4 GPa.
Physical Review E, 2013
We report on an x-ray diffraction (XRD) study of helical poly[9,9-bis(2-ethylhexyl)fluorene] (PF2... more We report on an x-ray diffraction (XRD) study of helical poly[9,9-bis(2-ethylhexyl)fluorene] (PF2/6) under high quasihydrostatic pressure and show an effect of pressure on the torsion angle (dihedral angle) between adjunct repeat units and on the hexagonal unit cell. A model for helical backbone conformation is constructed. The theoretical position for the most prominent 00l x-ray reflection is calculated as a function of torsion angle. The XRD of high molecular weight PF2/6 (M(n)=30 kg/mol) is measured through a diamond anvil cell upon pressure increase from 1 to 10 GPa. The theoretically considered 00l reflection is experimentally identified, and its shift with the increasing pressure is found to be consistent with the decreasing torsion angle between 2 and 6 GPa. This indicates partial backbone planarization towards a more open helical structure. The h00 peak is identified, and its shift together with the broadening of 00l implies impairment of the ambient hexagonal order, which begins at or below 2 GPa. Previously collected high-pressure photoluminescence data are reanalyzed and are found to be qualitatively consistent with the XRD data. This paper provides an example of how the helical π-conjugated backbone structure can be controlled by applying high quasihydrostatic pressure without modifications in its chemical structure. Moreover, it paves the way for wider use of high-pressure x-ray scattering in the research of π-conjugated polymers.
We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge ... more We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O 2 , with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O 2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co 3 O 4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.
Left – A schematic view of the XAS microfluidic set up at the beamline; fluorescence detector at ... more Left – A schematic view of the XAS microfluidic set up at the beamline; fluorescence detector at 90° angle to the X-ray beam (green line); right – microfluidic device setup on Balder beamline mounted perpendicular to beam path.
Journal of Polymer Science Part B: Polymer Physics, 2019
We report on X-ray scattering measurements of helical poly[9,9-bis(2ethylhexyl)-fluorene-2,7-diyl... more We report on X-ray scattering measurements of helical poly[9,9-bis(2ethylhexyl)-fluorene-2,7-diyl] by mapping the sample with 10 µm spatial resolution from 0.3 GPa to 36 GPa. We follow the strongest 00l reflection, which moves towards higher scattering angles with pressure indicating planarization of helical polyfluorene. Lateral inhomogeneity is increased for > 10 GPa concomitant with the solidification of the pressure transmitting medium (a 4:1 mixture of methanol and ethanol). We also follow the 00l reflection with increasing temperature at the constant pressure of 4.3 GPa in neon. We observe a sharp shift towards higher scattering angles indicative of a phase transition at 167-176 °C.
Physical Review E, 2016
Users may download and print one copy of any publication from the public portal for the purpose... more Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Phys. Chem. Chem. Phys., 2016
In situSR-PXD experiments revealed a new reaction mechanism of amide–hydride anionic exchange for... more In situSR-PXD experiments revealed a new reaction mechanism of amide–hydride anionic exchange for the K–Mg–N–H system.
Physical Chemistry Chemical Physics, 2016
Supporting information: 1. Synthesis methods and characterization: Synthesis of precursors: methy... more Supporting information: 1. Synthesis methods and characterization: Synthesis of precursors: methylammonium (MA) bromide (CH3NH3Br) and octylammonium (OTA) bromide (CH3(CH2)7NH3Br) were synthesized by reaction of the corresponding amine in water/HBr accordingly to the previously reports. In brief, for (CH3NH3Br) 36.9 ml of HBr and 83.4 ml of CH3NH2 were stirred for two hours in ice bath. The resulting solution was evaporated untill the formation of white crystals. The white crystals then were recrystallized from ethanol solution and then used as a precursor for CH 3 NH 3 PbBr 3 colloidal nanoparticles. The same procedures were repeated in order to prepare (CH3(CH2)7NH3Br) where 33.5 ml of CH3(CH2)7NH2 and 22.6 ml of HBr were stirred for two hours in ice bath. Synthesis of CH 3 NH 3 PbBr 3 bulk-like crystals: MAPbBr3 microcrystals were prepared by spin coating MAPbBr3 precursors in DMF onto glass substrates with 2000 rpm for 30 sec. Substrates were then annealed in air at 85 o C for half an hour to form orange colored crystals. In order to verify the crystal size, different dilution of precursors (original, ×2, ×4, ×8, ×16, ×25) were used which produced crystals with mean size of 14.7, 6.2, 4.2, 2.0 and 0.4 μm, respectively. Synthesis of CH 3 NH 3 PbBr 3 colloidal nanoparticles: CH 3 NH 3 PbBr 3 colloidal nanoparticles were synthesized via hot injection of MABr/OTABr and PbBr 2 precursors in coordinator solvent analogous to previous reports. In brief, 0.5 mmol oleic acid in 10 ml of octadecene was stirred and heated at 80 °C followed by addition of 0.3 mmol OTABr in 1 ml DMF. Then 0.2 mmol of MABr in 1 ml DMF and 0.5 mmol PbBr2 in 1 ml DMF were injected subsequently. The yellow dispersion containing nanoparticles was directly precipitated by acetone. Finally, the nanoparticles were redispersed in toluene for use. Here the ratio between OTABr and MABr is 6:4. UV/Vis spectroscopy. The ground state optical absorption spectra of the nanoparticles and bulk samples have been measured using a UV/Vis absorption spectrophotometer (PerkinElmer, Lambda 1050) equipped with integrated sphere to exclude signal from light scattering. Steady-state photoluminescence was measured using a standard spectrometer (Horiba, Spex 1681) with the excitation at 410 nm. TEM. The morphology of NPs has been characterized by using a high resolution analytical transmission electron microscopy (HR-TEM) (JEOL 3000F equipped with Oxford SDD x-ray analyzer). Samples were prepared by directly depositing the NP suspension onto the carbon grid. FTIR. The FT-IR measurement was conducted at Beamline D7 in MAX IV Laboratory (Sweden). For sample preparation, MCs and NPs were diluted with KBr, and were pelletised. The distance between the light source and the sample was held constant (25 cm).
International Journal of Hydrogen Energy
The fuel cell performance of membrane electrode assemblies with a Pt anode and Pd, PdCu or Pd5Cu4... more The fuel cell performance of membrane electrode assemblies with a Pt anode and Pd, PdCu or Pd5Cu4Pt cathodes has been tested during 116 h (beginning of life). The incorporation of Cu to Pd increases the fuel cell performance. Incorporation of Pt leads to further improvement. SEM micrographs of the as-prepared and the fuel cell-tested assemblies show the effects of the 116 h of continuous operation. Nafion membranes were characterized by small angle X-ray scattering. The results show a reduction of the size of the lamellar domains in the perfluorinated matrix after fuel cell testing, but no correlation with the cathode electrocatalyst material. The cathode electrocatalysts were characterized by ex-situ synchrotron radiation X-ray diffraction and X-ray absorption spectroscopy at the Pd L-3, Cu K and Pt L-3 edges. Re-organization of Pd5Cu4Pt electrocatalyst after fuel cell testing was observed. The Cu in the electrocatalyst can be described as a nano-mixture of metallic Cu, alloyed Cu ...
The Journal of Physical Chemistry C, 2010
A new alkaline transition-metal borohydride, NaSc(BH 4 ) 4 , is presented. The compound has been ... more A new alkaline transition-metal borohydride, NaSc(BH 4 ) 4 , is presented. The compound has been studied using a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. NaSc(BH 4 ) 4 forms at ambient conditions in ball-milled mixtures of sodium borohydride and ScCl 3 . A new ternary chloride Na 3 ScCl 6 (P2 1 /n, a ) 6.7375(3) Å, b ) 7.1567(3) Å, c ) 9.9316(5) Å, ) 90.491(3)°, V ) 478.87(4) Å 3 ), isostructural to Na 3 TiCl 6 , was identified as an additional phase in all samples. This indicates that the formation of NaSc(BH 4 ) 4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (22 wt %) was obtained with a reactant ratio of ScCl 3 /NaBH 4 of 1:2. NaSc(BH 4 ) 4 crystallizes in the orthorhombic crystal system with the space group symmetry Cmcm (a ) 8.170(2) Å, b ) 11.875(3) Å, c ) 9.018(2) Å, V ) 874.9(3) Å 3 ). The structure of NaSc(BH 4 ) 4 consists of isolated homoleptic scandium tetraborohydride anions, [Sc(BH 4 ) 4 ] -, located inside slightly distorted trigonal Na 6 prisms (each second prism is empty, triangular angles of 55.5 and 69.1°). The experimental results show that each Sc 3+ is tetrahedrally surrounded by four BH 4 tetrahedra with a 12-fold coordination of H to Sc, while Na + is surrounded by six BH 4 tetrahedra in a quite regular octahedral coordination with a (6 + 12)-fold coordination of H to Na. The packing of Na + cations and [Sc(BH 4 ) 4 ]anions in NaSc(BH 4 ) 4 is a deformation variant of the hexagonal NiAs structure type. NaSc(BH 4 ) 4 is stable from RT up to ∼410 K, where the compound melts and then releases hydrogen in two rapidly occurring steps between 440 and 490 K and 495 and 540 K. Thermal expansion of NaSc(BH 4 ) 4 between RT and 408 K is anisotropic, and lattice parameter b shows strong anomaly close to the melting temperature.
The Journal of Physical Chemistry C, 2010
ABSTRACT A new potassium scandium borohydride, KSc(BH 4) 4 , is presented and characterized by a ... more ABSTRACT A new potassium scandium borohydride, KSc(BH 4) 4 , is presented and characterized by a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. The title compound, KSc(BH 4) 4 , forms at ambient conditions in ball milled mixtures of potassium borohydride and ScCl 3 together with a new ternary chloride K 3 ScCl 6 , which is also structurally characterized. This indicates that the formation of KSc(BH 4) 4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (∼31 mol %) can be obtained with a reactant ratio KBH 4 :ScCl 3 of 2:1. KSc(BH 4) 4 crystallizes in the orthorhombic crystal system, a) 11.856(5), b) 7.800(3), c) 10.126(6) Å, V) 936.4(8) Å 3 at RT, with the space group symmetry Pnma. KSc(BH 4) 4 has a BaSO 4 type structure where the BH 4 tetrahedra take the oxygen positions. Regarding the packing of cations, K + , and complex anions, [Sc(BH 4) 4 ] -, the structure of KSc(BH 4) 4 can be seen as a distorted variant of orthorhombic neptunium, Np, metal. Thermal expansion of KSc(BH 4) 4 in the temperature range RT to 405 K is anisotropic, and the lattice parameter b shows strong nonlinearity upon approaching the melting temperature. The vibrational and NMR spectra are consistent with the structural model, and previous investigations of the related compounds ASc(BH 4) 4 with A) Li, Na. KSc(BH 4) 4 is stable from RT up to ∼405 K, where the compound melts and then releases hydrogen in two rapid steps approximately at 460-500 K and 510-590 K. The hydrogen release involves the formation of KBH 4 , which reacts with K 3 ScCl 6 and forms a solid solution, K(BH 4) 1-x Cl x . The ternary potassium scandium chloride K 3 ScCl 6 observed in all samples has a monoclinic structure at room temperature, P2 1 /a, a) 12.729(3), b) 7.367(2), c) 12.825(3) Å,) 109.22(2)°, V) 1135.6(4) Å 3 , which is isostructural to K 3 MoCl 6 . The monoclinic polymorph transforms to cubic at 635 K, a) 10.694 Å (based on diffraction data measured at 769 K), which is isostructural to the high temperature phase of K 3 YCl 6 .
Physical Review E, 2010
We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under qua... more We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under quasihydrostatic pressure from 1 to 11 GPa at room temperature. The scattering pattern of high molecular weight ͑HMW͒ polyfluorene ͑Ͼ10 kg/ mol͒ undergoes significant changes between 2 and 4 GPa in the bulk phase. The 110 reflection of the hexagonal unit cell disappears, indicating a change in equatorial intermolecular order. The intensity of the 00 21 reflection drops, with a sudden move toward higher scattering angles. Beyond these pressures, the diminished 00 21 reflection tends to return toward lower angles. These changes may be interpreted as a transition from crystalline hexagonal to glassy nematic phase ͑perceiving order only in one direc-tion͒. This transition may be rationalized by density arguments and the underlying theory of phase behavior of hairy-rod polyfluorene. Also the possible alteration of the 21-helical main chain toward more planar main chain conformation is discussed. The scattering of low molecular weight polyfluorene ͑Ͻ10 kg/ mol͒, which is glassy nematic in ambient pressure, is reminiscent with that of HMW polymer above 2-4 GPa.
Scientific Reports, 2015
Quantum dots (QDs) and graphene are both promising materials for the development of new-generatio... more Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 10 9 s −1 . Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications.
Acta Crystallographica Section A Foundations of Crystallography, 2012
The European Physical Journal Plus, 2015
ChemInform, 2010
Thermal Polymorphism and Decomposition of Y(BH 4 ) 3 . -The structure and thermal decomposition o... more Thermal Polymorphism and Decomposition of Y(BH 4 ) 3 . -The structure and thermal decomposition of the title compound is characterized by in situ synchrotron powder XRD, 11 B MAS NMR spectroscopy, and thermal analysis. A new high-temperature polymorph, β-Y(BH4)3 which crystallizes in the cubic space group Pm3m with Z = 1 is reported. The new polymorph exhibits a regular ReO3-type structure in which the Y 3+ cations form cubes with anions located on the edges. The new phase forms in small amounts during ball milling of LiBH4 and YCl3, and in larger amounts from α-Y(BH4)3 via a phase transition under moderate hydrogen pressure at about 180°C. Upon further heating, β-Y(BH4)3 decomposes at about 190°C to YH3, which transforms to YH2 at 270°C. An unidentified compound exists in the temperature range of 215-280°C. The final decomposition product is YB 4 . Formation of metal borides during decomposition is an important indication of possible reversibility. Thus, it is concluded that Y(BH 4 ) 3 may be a reversible hydrogen storage material. -(RAVNSBAEK, D. B.; FILINCHUK, Y.; CERNY, R.; LEY, M. B.; HAASE, D.; JAKOBSEN, H. J.; SKIBSTED, J.; JENSEN*, T. R.; Inorg. Chem. 49 (2010) 8, 3801-3809; Dep. Chem., Univ. Aarhus, DK-8000 Aarhus, Den.; Eng.) -W. Pewestorf 29-009 BH -4
The Journal of Physical Chemistry C, 2013
A composite material in the LiH−LiF−MgB 2 system has been synthesized by high-energy ball milling... more A composite material in the LiH−LiF−MgB 2 system has been synthesized by high-energy ball milling. Some peaks in addition to that of the binary 2LiH−MgB 2 and 2LiF−MgB 2 systems are observed for the composite material by high-pressure differential scanning calorimetry (HP-DSC), indicating the formation of intermediate phases. In situ synchrotron radiation powder X-ray diffraction (SR-PXD) performed at 60 bar of H 2 and 390°C shows a superposition of both reaction pathways that are typical for 2LiH− MgB 2 and 2LiF−MgB 2 . After hydrogen absorption of the LiH−LiF− MgB 2 composite the vibrational modes of LiBH 4 were observed by attenuated total reflection infrared (ATR-IR) spectroscopy. The 19 F MAS NMR spectrum of the LiF−LiBH 4 sample after heat treatment in hydrogen is strongly dominated by the centerband and spinning sidebands from LiF; in addition, a low-intensity resonance, very similar to that of [BF 4 ] − ion, is identified.
Review of Scientific Instruments, 2011
A detector with high dynamic range designed for combined small- and wide-angle x-ray scattering e... more A detector with high dynamic range designed for combined small- and wide-angle x-ray scattering experiments has been developed. It allows measurements on single events and reactive systems, such as particle formation in flames and evaporation of levitating drops. The detector consists of 26 channels covering a region from 0.5° to 60° and it provides continuous monitoring of the sampled signal without readout dead time. The time resolution for fast single events is about 40 μs and for substances undergoing slower dynamics, the time resolution is set to 0.1 or 1 s with hours of continuous sampling. The detector has been used to measure soot particle formation in a flame, burning magnesium and evaporation of a toluene drop in a levitator. The results show that the detector can be used for many different applications with good outcomes and large potential.
Physical Review E, 2010
We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under qua... more We report on an x-ray scattering experiment of bulk poly͓9,9-bis͑2-ethylhexyl͒fluorene͔ under quasihydrostatic pressure from 1 to 11 GPa at room temperature. The scattering pattern of high molecular weight ͑HMW͒ polyfluorene ͑Ͼ10 kg/ mol͒ undergoes significant changes between 2 and 4 GPa in the bulk phase. The 110 reflection of the hexagonal unit cell disappears, indicating a change in equatorial intermolecular order. The intensity of the 00 21 reflection drops, with a sudden move toward higher scattering angles. Beyond these pressures, the diminished 00 21 reflection tends to return toward lower angles. These changes may be interpreted as a transition from crystalline hexagonal to glassy nematic phase ͑perceiving order only in one direc-tion͒. This transition may be rationalized by density arguments and the underlying theory of phase behavior of hairy-rod polyfluorene. Also the possible alteration of the 21-helical main chain toward more planar main chain conformation is discussed. The scattering of low molecular weight polyfluorene ͑Ͻ10 kg/ mol͒, which is glassy nematic in ambient pressure, is reminiscent with that of HMW polymer above 2-4 GPa.
Physical Review E, 2013
We report on an x-ray diffraction (XRD) study of helical poly[9,9-bis(2-ethylhexyl)fluorene] (PF2... more We report on an x-ray diffraction (XRD) study of helical poly[9,9-bis(2-ethylhexyl)fluorene] (PF2/6) under high quasihydrostatic pressure and show an effect of pressure on the torsion angle (dihedral angle) between adjunct repeat units and on the hexagonal unit cell. A model for helical backbone conformation is constructed. The theoretical position for the most prominent 00l x-ray reflection is calculated as a function of torsion angle. The XRD of high molecular weight PF2/6 (M(n)=30 kg/mol) is measured through a diamond anvil cell upon pressure increase from 1 to 10 GPa. The theoretically considered 00l reflection is experimentally identified, and its shift with the increasing pressure is found to be consistent with the decreasing torsion angle between 2 and 6 GPa. This indicates partial backbone planarization towards a more open helical structure. The h00 peak is identified, and its shift together with the broadening of 00l implies impairment of the ambient hexagonal order, which begins at or below 2 GPa. Previously collected high-pressure photoluminescence data are reanalyzed and are found to be qualitatively consistent with the XRD data. This paper provides an example of how the helical π-conjugated backbone structure can be controlled by applying high quasihydrostatic pressure without modifications in its chemical structure. Moreover, it paves the way for wider use of high-pressure x-ray scattering in the research of π-conjugated polymers.