| 1. |
- Biendicho, Jordi Jacas, et al.
(författare)
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New in-situ neutron diffraction cell for electrode materials
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 248, s. 900-904
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Tidskriftsartikel (refereegranskat)abstract
- A novel neutron diffraction cell has been constructed to allow in-situ studies of the structural changes in materials of relevance to battery applications during charge/discharge cycling. The new design is based on the coin cell geometry, but has larger dimensions compared to typical commercial batteries in order to maximize the amount of electrode material and thus, collect diffraction data of good statistical quality within the shortest possible time. An important aspect of the design is its modular nature, allowing flexibility in both the materials studied and the battery configuration. This paper reports electrochemical tests using a Nickel-metal-hydride battery (Ni-MH), which show that the cell is able to deliver 90% of its theoretical capacity when using deuterated components. Neutron diffraction studies performed on the Polaris diffractometer using nickel metal and a hydrogen-absorbing alloy (MH) clearly show observable changes in the neutron diffraction patterns as a function of the discharge state. Due to the high quality of the diffraction patterns collected in-situ (i.e. good peak-to-background ratio), phase analysis and peak indexing can be performed successfully using data collected in around 30 min. In addition to this, structural parameters for the beta-phase (charged) MH electrode obtained by Rietveld refinement are presented. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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| 2. |
- Dong, Hanwu, et al.
(författare)
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An air-metal hydride battery using MmNi(3.6)Mn(0.4)Al(0.3)Co(0.7) in the anode and a perovskite in the cathode
- 2010
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 35:9, s. 4336-4341
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen storage alloy MmNi(3.6)Mn(0.4)Al(0.3)Co(0.7) (MH) was tested as anode material in a metal hydride-air cell. The cathode was a non-noble metal air electrode based on a mixture of perovskite and pyrolyzed macrocycles on carbon. Polarization and discharge capacities of the electrodes were measured and compared at 22 degrees C and 40 degrees C using air or oxygen at the cathode. Discharge capacity reaching 330 mAh/g MH with pure oxygen at 40 degrees C and 305 mAh/g MH with air at 22 degrees C were obtained. Power densities and/or energy densities were found to significantly depend on the increase of the electrode kinetics on both the ORR (oxygen reduction reaction) and HOR (hydrogen oxidation reaction). However, for air electrode, an increase of oxygen concentration by using pure oxygen gas plays a more important role than an 18 degrees C temperature increase. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
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| 3. |
- Fahlquist, Henrik, 1983-, et al.
(författare)
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Cs10H[Ga3H8]3 : A Hydrogenous Zintl Phase Containing Propane-Like Polyanions [Ga3H8]3- and Interstitial Hydrogen
- 2013
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 52:12, s. 7125-7129
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogenous Zintl-phase Cs10H[Ga3H8](3) containing propane-like polyanions [Ga3H(D)(8)](3-) was successfully synthesized by direct hydrogenation of a 1:1 Cs/Ga metal mixture and characterized by powder X-ray and neutron diffraction. The charge of the polyanions is balanced by two different species of cations, hydrogen-centered octahedra [H(D)Cs-6](5+) and isolated Cs+. The structure crystallizes in the hexagonal space group P6(3)/mcm (193) with the cell parameters a = 11.1108(3) angstrom, c = 18.2149(5) angstrom, Z = 2.
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| 4. |
- Fahlquist, Henrik, et al.
(författare)
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Structural characterization of Sr4Mg4H4[CoH5](3) shows the importance of support from polarizing counter ions to 3d transition metal hydrido complexes
- 2013
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 579, s. 31-33
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the title compound was refined from neutron powder diffraction data in the cubic space group P-43m (215). The unit cell contains one formula unit with 3 structurally equivalent [Co(I)H-5](4)-complexes as well as 4 interstitial hydride (H-) ions. The presence of the larger and less polarizing Sr2+ ions weakens the bond in the complexes and probably also the stability of the structure. Attempts to synthesize the corresponding Ba analogue failed in contrast to using smaller and more polarizing Ca2+ and Yb2+ counterions.
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| 5. |
- Fahlquist, Henrik, 1983-
(författare)
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Transition Metal Hydride Complexes and Hydrogenated Gallium Clusters : Synthesis and Structural Properties
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis and structural characterisation of metal hydrides in two important systems are presented. The first system presented is low valent cobalt and nickel complex hydrides with the compositions BaMg5Co2H10, RbMg5CoNiH10, SrMg2CoH7and Sr4Mg4Co3H19 featuring nickel with oxidation state of 0 and cobalt with oxidation state +I and -I. The second system presented is polyanionic gallium complex hydrides with the compositions RbGaH2, RbxK(1−x)GaH2 (0.5≤x≤1), CsxRb(8−x)Ga5H15 (0≤x≤8) and Cs10Ga9H25 featuring novel hydrogenous polyanionic gallium hydride clusters mimicking common hydrocarbons. The syntheses of the compounds were performed at elevated temperatures and at moderate hydrogen pressures (50-100 bar). The structural investigations were mainly done by X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD). The metal-hydrogen bond was investigated by vibrational spectroscopy using Fourier Transform IR-spectroscopy (FTIR) and Inelastic Neutron Scattering (INS).By subtle changes in the compositions of the hydrides it was possible to induce major changes in band gaps, oxidation states and structures.
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| 6. |
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| 7. |
- Fahlquist, Henrik, et al.
(författare)
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Varying the Alkali-Metal Radii in (KxRb1−x)n[GaH2]n (0 ≤ x ≤ 1)Reorients a Stable Polyethylene-Structured [GaH2]nn− Anionic Chain
- 2013
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 52:9, s. 4771-4773
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Tidskriftsartikel (refereegranskat)abstract
- The stability of a negatively chargedpolyethylene-structured [GaH2]nn−cluster ion was inves-tigated by varying the K+/Rb+ratio in (KxRb1−x)n[GaH2]n(0≤x≤1). Neutron, X-ray, and IR spectroscopies wereused to characterize the new phases. Between the limitingcompositions Kn[GaH2]nand Rbn[GaH2]n, the [GaH2]nn−chains remained almost identical, indicating a stable specie.For rubidium-rich samples up to a potassium contentcorresponding to (K0.5Rb0.5)n[GaH2]n, two phases coexistin the samples, RbGaH2and (K0.5Rb0.5)n[GaH2]n, with aratio mirroring the relative alkali-ion content. The twophases have a different alignment of the [GaH2]nn−chains.For potassium-rich samples beyond (K0.5Rb0.5)n[GaH2]n,the samples were single-phased. The unit cell volume ofthe new (K0.5Rb0.5)n[GaH2]nstructure type shrinksaccording to Vegard’s law as smaller K+ions substitutefor larger Rb+ions. The [GaH2]nn−chains remained,however, almost identical. IR spectra from the differentphases were very similar, exhibited stretching, scissoring,and rocking modes similar to those in ordinary poly-ethylene, but shifted to lower frequencies, reflectingweaker Ga−H bonds. The existence of stable Kn[GaH2]nand Rbn[GaH2]n, would help to dehydrogenate KGaH4and RbGaH4upon heating. If this could be transferred tolighter alanates and borohydrides, it could be possible todevelop more functional hydrogen-storage systems.
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| 8. |
- Hu, Wei-Kang, et al.
(författare)
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Lab-size rechargeable metal hydride-air cells
- 2010
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 195:17, s. 5810-5813
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Tidskriftsartikel (refereegranskat)abstract
- Lab-size rechargeable metal hydride-air (MH-air) cells with a gas management device were designed in order to minimize the loss of electrolyte. An AB(5)-type hydrogen storage alloy was used as anode materials of the MH-air. The thickness of the metal hydride electrodes was in the range of 3.0-3.4 mm. Porous carbon-based air electrodes with Ag2O catalysts were used as bi-functional electrodes for oxygen reduction and generation. The electrodes were first examined in half-cells to evaluate their performance and then assembled into one MH-air cell. The results showed the good cycling stability of the rechargeable MH-air cell with a capacity of 1990 mAh. The discharge voltage was 0.69 V at 0.05-0.1 C. The charge efficiency was about 90%. The specific and volumetric energy densities were about 95 Wh kg(-1) and 140 Wh L-1, respectively.
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| 9. |
- Kadir, Abdulkarim, et al.
(författare)
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Investigation of Counterion Influence on an Octahedral IrH(6)-Complex in the Solid State Hydrides AAeIrH(6) (A = Na, K and Ae = Ca, Sr, Ba, and Eu) with a New Structure Type
- 2011
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:23, s. 11890-11895
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Tidskriftsartikel (refereegranskat)abstract
- A number of new quaternary iridium based hydrides and deuterides AAeIrH/D(6) (where A = Na and K; Ae = Ca, Ba, Sr, and Eu) have been synthesized by direct combination of the alkali, alkaline earth or europium binary hydrides/deuterides and iridium powder. The crystal structures were determined by Guinier-Hagg X-ray and neutron powder diffraction and a new cubic structure type was found. The structure is described in space group F (4) over bar 3m, but related to the K(2)PtCl(6) type structure. The new structure can be described as consisting of cubes of A(+) and Ae(2+) ions, where the A(+) and Ae(2+) ions alternates so that they occupy opposite corners in the cube. Every second cube contains a regular octahedral [Ir(III)H(6)](-3)-complex and the adjacent is empty. Solid-state IR spectroscopy was used to determine the Ir-allowed stretching and bending frequencies for the [Ir(III)H(6)](-3) complex with different counterions. These were also compared with the corresponding stretching frequencies for Fe(II)H(6), Ru(II)H(6), Os(II)H(6), and Ir(II)H(5) complexes in similar solid state hydrides, which increased when going from Fe through Ru, Os to Ir. The frequencies scaled almost linearly with the inverse of size of the cube surrounding the complexes but showed no significant dependence of the formal oxidation state or the experimentally obtained Ir-D distances. However, this was mainly because of difficulties in obtaining enough accurate atomic positions. The ab initio DFT calculations could reproduce the stretching frequencies within a few 10 cm(-1), indicating that experimental vibrational frequencies offer a sensitive test of DFT results.
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| 10. |
- Lelis, Martynas, et al.
(författare)
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A mechanically switchable metal-insulator transition in Mg2NiH4 discovers a strain sensitive, nanoscale modulated resistivity connected to a stacking fault
- 2010
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 496:02-jan, s. 81-86
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Tidskriftsartikel (refereegranskat)abstract
- The band gap in semiconducting Mg2NiH4 was found to be dependent on subtle structural differences. This was discovered when investigating if thin film samples of Mg2NiH4 could be used in a switchable mirror or window device by utilizing a high to low temperature transition at about 510K. In powder samples; this transition between an FCC high temperature phase, with dynamically disordered NiH4-complexes, and a monoclinic distorted low temperature phase, with ordered Mg2NiH4-complexes, has been demonstrated in a mechanical reversible conductor-insulator transition (Blomqvist and Noreus (2002) [7]). Black monoclinic Mg2NiH4 powders were found to have a band gap of 1.1 eV. Pressed tablets of black monoclinic Mg2NiH4 powders are conductive, probably from doping by impurities or non-stoichiometry. Thin film Mg2NiH4 samples were produced by reacting hydrogen with magnetron sputtered Mg2Ni films on quartz glass or CaF2 substrates. The Mg2NiH4 films on the other hand were orange, transparent with a band gap of 2.2 eV and a cubic unit cell parameter almost identical to the disorder HT phase but with lower symmetry. If black Mg2NiH4 powder is heated above the phase transition at 510K and subsequently cooled down, the conductivity is lost and the powder turns brown. After this heat treatment TEM pictures revealed a multiple stacking fault having a local pseudo-cubic arrangement separating regions of monoclinic symmetry. The loss of conductivity and colour change is attributed to a higher band gap in the strained areas. The structure on each side of the stacking fault is related by a mirror plane as a consequence of the possibility for the NiH4-complexes to order with different orientations. This leads to a mismatch in the long range ordering and strain is probably creating the stacking faults. Strain is important for forming the cubic modification. A severely strained film was revealed with optical microscopy in reflected light, indicating that strain prevents it from relaxing back into the monoclinic structure. This was supported by multiple twinned red translucent Mg2NiH4 crystals grown with cubic symmetry at elevated temperatures in a LiH flux. When cooled to ambient conditions, the ""crystals"" had the same cubic symmetry as the films, probably held together by their neighbours. When they were ground to a fine powder to prepare TEM samples, they relaxed and reverted back to the conventional monoclinic unit cell. This interesting nanoscale modulated resistance could possibly be developed into novel memory devices if properly controllable.
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| 11. |
- Lelis, Martynas, et al.
(författare)
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Substrate effects on formation and hydrogenation of Mg-Ni films
- 2012
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 263, s. 202-209
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Tidskriftsartikel (refereegranskat)abstract
- Usually metallic films for metal hydrides research applications are deposited on hard and flat substrates such as silicon, magnesium oxide, fused silica or quartz glass. With the film thickness increases all films during hydrogenation deals with typical problems such as film brittleness and cracking. In this paper we demonstrate that metal Mg-Ni films for hydrogen storage can be successfully deposited on to the flexible low surface energy expanded PTFE substrates. The received results for soft substrates (expanded PTFE) are compared to films being deposited on crystalline silicon substrate with and without plasma pretreatment. It is observed that different interface zone between substrate and film has great affect on both film crystallinity and its reaction with hydrogen. It is also demonstrated that modifying surface of the substrate might have affect on film microstructure before and after hydrogenation.
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| 12. |
- Ma, Honglei, et al.
(författare)
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Synchrotron X-ray diffraction and infrared spectroscopy studies of C60H18 under high pressure
- 2010
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society. - 1948-7185. ; 1:4, s. 714-719
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Tidskriftsartikel (refereegranskat)abstract
- In situ high-pressure angle-dispersive synchrotron X-ray diffraction and high-pressure mid-infrared (IR) spectrum measurements of C60H18 were carried out up to 32 and 10.2 GPa, respectively. Our diffraction data indicated that the fcc structure of C60H18 was stable up to 32 GPa. The bulk modulus B0 was determined to be 21 ± 1.16 GPa, about 40% higher than that of C60. The C−H vibrations still existed up to 10.2 GPa, and the vibrational frequencies decreased with increasing pressure. IR-active vibrational frequencies and their corresponding eigenvectors of C60H18 were simulated by DMOL3. The effects of the hydrogen atoms attached to the fullerene molecular cage on the stability of the structure under high pressure are discussed.
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| 13. |
- Moser, D., et al.
(författare)
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An in situ neutron diffraction measurement of the pressure-temperature evolution of a MgD2:TiD2 mixture
- 2010
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 30:4, s. 643-652
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen storage capacity of Mg-Ti-H films is approximately five times that of conventional metal hydride electrodes in NiMH-batteries. Mg and Ti are considered to be immiscible in the bulk and the ambient pressure phase diagram of Mg and Ti indicates that no binary stable bulk compounds are formed. However, in the presence of hydrogen, an Mg-Ti-H phase has been obtained by Kyoi et al. using a high pressure synthesis - where magnesium hydride is compacted with different TM-hydrides in an anvil cell at pressures of the order several GPa (4-8GPa) and at a temperature of 873K. In this work, we have proved the feasibility of in situ powder diffraction using the Paris-Edinburgh high pressure cell for the observation of structural changes on this system and we propose modifications to improve the output of the experiment.
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| 14. |
- Moser, D., et al.
(författare)
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The pressure-temperature phase diagram of MgH(2) and isotopic substitution
- 2011
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:30, s. 305403-
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Tidskriftsartikel (refereegranskat)abstract
- Computational thermodynamics using density functional theory ab initio codes is a powerful tool for calculating phase diagrams. The method is usually applied at the standard pressure of p = 1 bar and where the Gibbs energy is assumed to be equal to the Helmholtz energy. In this work, we have calculated the Gibbs energy in order to study the release temperature and phase modifications of MgH(2) at high pressures up to 10 GPa (100 kbar). The isotopic substitution of hydrogen with deuterium (or tritium) does not bring about any strong effects on the phase diagram. These considerations are of extreme importance for (i) the synthesis of novel substitutional magnesium based materials at high pressure and (ii) the determination of the correct reference states for the calculation of phase diagrams at high pressure. The calculated results are compared with experimental data obtained with an in situ neutron diffraction measurement.
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| 15. |
- Parker, Stewart F., et al.
(författare)
-
Preface
- 2011
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 151, s. 9-9
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Tidskriftsartikel (refereegranskat)
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| 16. |
- Talyzin, Alexandr, 1969-, et al.
(författare)
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Hydrogenation, Purification, and Unzipping of Carbon Nanotubes by Reaction with Molecular Hydrogen : Road to Graphane Nanoribbons
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 5:6, s. 5132-5140
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of single-walled carbon nanotubes (SWNTs) with hydrogen gas was studied in a temperature interval of 400-550 degrees C and at hydrogen pressure of 50 bar. Hydrogenation of nanotubes was observed for samples treated at 400-450 degrees C with about 1/3 of carbon atoms forming covalent C-H bonds, whereas hydrogen treatment at higher temperatures (550 degrees C) occurs as an etching. Unzipping of some SWNTs Into graphene nanoribbons is observed as a result of hydrogenation at 400-550 degrees C Annealing in hydrogen gas at elevated conditions for prolonged periods of time (72 h) is demonstrated to result also in nanotube opening, purification of nanotubes from amorphous carbon, and removal of carbon coatings from Fe catalyst particles, which allows their complete elimination by acid treatment.
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| 17. |
- Ye, Zhou, et al.
(författare)
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Metal hydrides for high-power batteries
- 2013
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Ingår i: MRS bulletin. - : Springer Science and Business Media LLC. - 0883-7694 .- 1938-1425. ; 38:6, s. 504-508
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Tidskriftsartikel (refereegranskat)abstract
- Rechargeable batteries are essentially unstable systems with respect to charging/discharging. The main electrode reactions of all battery chemistries are well known but are valid and reversible only at small currents. When batteries are used with nonzero current, gradients in voltage, current, and temperature will arise and initiate a number of less understood parasitic reactions. If all these rather complicated and interconnected reactions are not reversible upon charging/discharging, the battery will derail after a number of charging/discharging cycles. This article describes two ways to improve performance. One is to choose applications where the battery is not deeply discharged, such as in hybrid electric vehicles. In battery electric vehicle applications, this would correspond to working with a significantly oversized battery. The second way is to improve uniformity and quality of design and materials of metal hydride electrodes; however, this will also drastically increase cost, and for a battery application, the total throughput of available energy over the lifetime cost of the battery must be maximized. Uniform metal hydride particles with a large and uniform reaction surface are examples of how to increase battery performance by making the electrodes work under more ideal conditions, which slows down the deteriorating influence from the parasitic reactions.
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| 18. |
- Ye, Zhou, et al.
(författare)
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Oxygen and hydrogen gas recombination in NiMH cells
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 208, s. 232-236
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of oxygen and hydrogen gas recombination on the metal hydride electrode in a NiMH cell is investigate as function of gas pressure, temperature, cycling and a hydrophobic additive. Both oxygen and hydrogen gas recombination rates in the NiMH cells are found to be linearly proportional to the gas pressure, indicating that surface processes with a constant number of reaction sites could be the rate limiting step. The rate of oxygen gas recombination is, however, more than 10 times faster than that of hydrogen at the same pressure. As the temperature increases, both reaction rates increase very rapidly, even though the solubilities of the gases in the KOH electrolyte decrease with temperature. The activation energies for oxygen and hydrogen gas recombination are 32.6 kJ mol(-1) and 27.0 kJ mol(-1), respectively. The reactions rates also increase as the cells are cycled. This indicates, that the number of active sites increases, as the surface area increases, due to the continuously decrepitating of the alloy particles. The hydrogen gas absorption rate increases dramatically after a large number of cycles due the drying of the MH electrode. A hydrophobic FTFE additive in the MH electrode can significantly improve hydrogen absorption efficiency in NiMH cells.
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