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6. Hydrogen storage

Highlights: (1) and (2) hydrogen sorption in metastable Mg hydride at low T; (3) and (4) bcc Mg stabilization; (5) Mg pillar; (6) Mg/Nb multilayers
(1) Hydrogen sorption in metastable Mg hydride at low T





(2) Size and stress dependent hydrogen desorption in metastable Mg hydride films

(3) Stabilization of bcc Mg in Thin Films at Ambient Pressure




(4) Tailoring the formation of metastable Mg through interface

(5) porous and pillar-shaped Mg


(6) Mg/Nb mechanical properties

Hydrogen sorption in orthorhombic Mg hydride at ultra-low temperature

International Journal of Hydrogen Energy 2013


Highlights:
  • For the first time, the formation of metastable orthorhombic-MgH2 (O-MgH2) is observed. 
  • T
    he metastable O-MgH2 has ultra-low hydrogen desorption temperature, varying from room temperature to ~ 373K.
  • Two types of O-MgH2 were formed in both hydrided single layer Mg films and multilayer Mg/Nb films with different lattice parameters.
  • Density function theory (DFT) calculations confirmed that distortion in O-MgH2 due to either tensile or compressive stress can reduce the hydrogen desorption temperature significantly.

Size and stress dependent hydrogen desorption in 
metastable Mg hydride films

International Journal of Hydrogen Energy 2014


Highlights:
  • Explored the hydrogen storage performance of porous and dense Mg films prepared by magnetron sputtering.
  • Thinner dense Mg films have lower hydrogen desorption temperature than thicker porous films.
  • Mg 45 pillar films also shows improved hydrogen sorption performance than the more porous 5. pillar films.
  • Stress plays a critical rol to induce metastable orthorhombic Mg hydride






Stabilization of bcc Mg in Thin Films at Ambient Pressure: Experimental Evidence 
and ab initio Calculations

Materials Research Letter 2013


Highlights:
  • bcc Mg can be stabilized when grown together with bcc Nb in Mg/Nb multilayer films. 
  • Density functional theory calculations were performed to gain insight into the stability of Mg in the bcc structure.
  • Calculations show that bcc Mg structure is in fact metastable under thin film conditions.




Tailoring the formation of metastable Mg through interfacial 
engineering: Aphasestabilityanalysis

CALPHAD: Computer Coupling of Phase Diagrams and
Thermochemistry 2014


Highlights:
  • bcc and hcp Nb can be stabilize under Mg/Nb multilayers.
  • The reduction in the interfacial energy is the dominate effect that control the phase.
  • For the same bilayer thickness, the magnitude of the lattice distortion of metastable phase is related to the volume fraction



Fabrication of porous and pillar-shaped Mg by magnetron sputtering

Thin Solid Films 2014


Highlight:
  • Mg films deposited by RFs sputtering have mirror like surfaces and dense structure, in drastic contrast to highly porous DC sputtered Mg films
  • First principle calculations show that the diffusion distance during relaxation in RF sputtering 
    process is sufficiently large to remove growth defects and reduce film 
    porosity
  • Single crystal porosity-free Mg films can grow epitaxially on 
    Si(111) substrate by domain matching epitaxy. Glancing angle deposition 
    will lead to the formation of Mg nanopillars.

High strength Mg/Nb nanolayer composites

Materials Science and Engineering A (2011)


Highlight

  • The microstructure and mechanical behavior of sputter deposited 
    Mg/Nb multilayer films were investigated and the 
    hardness of Mg/Nb was compared to those of Mg and Cu/Nb 
    and Al/Nb multilayer systems.
  • Metastable structure of bcc Mg at 
    interface was revealed in Mg/Nb 5 nm multilayers.
  • The interface 
    barrier strength computed from Hall–Petch slope shows interphase 
    interfaces in Mg/Nb is a strong barrier to slip transmission.