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Nanoscale Mg-B via Surfactant Ball Milling of MgB2: Morphology, Composition, and Improved Hydrogen Storage Properties

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DOI

  • Y. S. Liu, Lawrence Berkeley National Laboratory
  • ,
  • K. G. Ray, Lawrence Livermore National Laboratory
  • ,
  • M. Jørgensen
  • ,
  • T. M. Mattox, Lawrence Berkeley National Laboratory
  • ,
  • D. F. Cowgill, Sandia National Laboratories CA
  • ,
  • H. V. Eshelman, Lawrence Livermore National Laboratory
  • ,
  • A. M. Sawvel, Lawrence Livermore National Laboratory
  • ,
  • J. L. Snider, Sandia National Laboratories CA
  • ,
  • W. York, Sandia National Laboratories CA
  • ,
  • P. Wijeratne, Sandia National Laboratories CA
  • ,
  • A. L. Pham, Lawrence Berkeley National Laboratory
  • ,
  • H. Gunda, Indian Institute of Technology Gandhinagar
  • ,
  • S. Li, Lawrence Livermore National Laboratory
  • ,
  • T. W. Heo, Lawrence Livermore National Laboratory
  • ,
  • S. Kang, Lawrence Livermore National Laboratory
  • ,
  • T. R. Jensen
  • V. Stavila, Sandia National Laboratories CA
  • ,
  • B. C. Wood, Lawrence Livermore National Laboratory
  • ,
  • L. E. Klebanoff, Sandia National Laboratories CA

Metal borides have attracted the attention of researchers due to their useful physical properties and unique ability to form high hydrogen-capacity metal borohydrides. We demonstrate improved hydrogen storage properties of a nanoscale Mg-B material made by surfactant ball milling MgB2 in a mixture of heptane, oleic acid, and oleylamine. Transmission electron microscopy data show that Mg-B nanoplatelets are produced with sizes ranging from 5 to 50 nm, which agglomerate upon ethanol washing to produce an agglomerated nanoscale Mg-B material of micron-sized particles with some surfactant still remaining. X-ray diffraction measurements reveal a two-component material where 32% of the solid is a strained crystalline solid maintaining the hexagonal structure with the remainder being amorphous. Fourier transform infrared shows that the oleate binds in a "bridge-bonding"fashion preferentially to magnesium rather than boron, which is confirmed by density functional theory calculations. The Mg-B nanoscale material is deficient in boron relative to bulk MgB2 with a Mg-B ratio of ∼1:0.75. The nanoscale MgB0.75 material has a disrupted B-B ring network as indicated by X-ray absorption measurements. Hydrogenation experiments at 700 bar and 280 °C show that it partially hydrogenates at temperatures 100 °C below the threshold for bulk MgB2 hydrogenation. In addition, upon heating to 200 °C, the H-H bond-breaking ability increases ∼10-fold according to hydrogen-deuterium exchange experiments due to desorption of oleate at the surface. This behavior would make the nanoscale Mg-B material useful as an additive where rapid H-H bond breaking is needed.

OriginalsprogEngelsk
TidsskriftJournal of Physical Chemistry C
Vol/bind124
Nummer39
Sider (fra-til)21761-21771
Antal sider11
ISSN1932-7447
DOI
StatusUdgivet - okt. 2020

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