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Improved NiMH performance by a surface treatment that creates magnetic Ni-clusters
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Number of Authors: 4
2016 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 23, 9933-9938 p.Article in journal (Refereed) Published
Abstract [en]

A surface treatment method has been developed to activate the surface of an AB(5) type (La-20 Ce-7 Pr-1 Nd-4 Al-2 Mn-5 Co-6 Ni-55) alloy. In the process the surface is covered with a porous surface layer containing needle shaped rare earth hydroxides after etching by a potassium hydroxide solution. TEM studies show in addition the presence of a denser surface oxide layer with embedded Ni containing clusters covering the bulk alloy. The magnetic properties of the alloy powders change with the surface treatment. In addition to a paramagnetic component of the bulk alloy, surface treated alloy also displays superparamagnetic and ferromagnetic properties. In electrochemical half-cell tests, the alloy shows better high-rate dischargeability with increasing presence of magnetic clusters in the metal hydride particles surface.

Place, publisher, year, edition, pages
2016. Vol. 41, no 23, 9933-9938 p.
Keyword [en]
Metal hydrides, NiMH batteries, Surface treatment, Ni clusters, Discharge kinetics, Rare earths hydroxides
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-132397DOI: 10.1016/j.ijhydene.2016.01.145ISI: 000378359400029OAI: oai:DiVA.org:su-132397DiVA: diva2:952570
Conference
1st International Symposium on Materials for Energy Storage and Conversion (ESC-IS), Middle East Technical University, Ankara, Turkey, September 07-09, 2015
Available from: 2016-08-15 Created: 2016-08-11 Last updated: 2017-08-14Bibliographically approved
In thesis
1. Structure determination of beam sensitive crystals by rotation electron diffraction: the impact of sample cooling
Open this publication in new window or tab >>Structure determination of beam sensitive crystals by rotation electron diffraction: the impact of sample cooling
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electron crystallography is complementary to X-ray crystallography. Single crystal X-ray diffraction requires the size of a crystal to be larger than about 5 × 5 × 5 μm3 while a TEM allows a million times smaller crystals being studied. This advantage of electron crystallography has been used to solve new structures of small crystals. One method which has been used to collect electron diffraction data is rotation electron diffraction (RED) developed at Stockholm University. The RED method combines the goniometer tilt and beam tilt in a TEM to achieve 3D electron diffraction data. Using a high angle tilt sample holder, RED data can be collected to cover a tilt range of up to 140o

Here the crystal structures of several different compounds have been determined using RED. The structure of needle-like crystals on the surface of NiMH particles was solved as La(OH)2. A structure model of metal-organic layers has been built based on RED data. A 3D MOF structure was solved from RED data. Two halide perovskite structures and two newly synthesized aluminophosphate structures were solved. For those beam sensitive crystals characterized here, sample cooling down to -170oC was used to reduce the beam damage. The low temperature not only reduces electron beam damage, but also keeps the structure more stable in the high vacuum in a TEM and improves the quality of the diffraction data. It is shown that cooling can improve the resolution of diffraction data for MOFs and zeolites, for samples undergoing phase changes at low temperature, the data quality could be worse by cooling. In summary, cooling can improve the ED data quality as long as the low temperature does not trigger structural changes. 

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2017
Keyword
electron crystallography, rotation electron diffraction, structure determination, cooling
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-145636 (URN)978-91-7649-856-9 (ISBN)978-91-7649-857-6 (ISBN)
Public defence
2017-10-11, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Submitted.

Available from: 2017-09-18 Created: 2017-08-14 Last updated: 2017-09-14Bibliographically approved

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