Mg-TM (TM: Ti, Nb, V, Co, Mo or Ni) core-shell like nanostructures: synthesis, hydrogen storage performance and catalytic mechanism

Magnesium (Mg) was coated by different transition metals (TM: Ti, Nb, V. Co, Mo, or Ni) with a grain size in the nano-scale to form a core (Mg)-shell (TM) like structure by reaction of Mg powder in THF solution with TMClx. The thickness of the TM shell is less than 10 nm. TPD-MS results show the Mg-Ti sample can release hydrogen even under 200 degrees C. It is experimentally confirmed that the significance of the catalytic effect on dehydrogenation is in the sequence Mg-Ti, Mg-Nb, Mg-Ni, Mg-V, Mg-Co and Mg-Mo. This may be due to the decrease in electro-negativity (chi) from Ti to Mo. However, Ni is a special case with a high catalytic effect in spite of the electro-negativity. It is supposed that the formation of the Mg2Ni compound may play an important role in enhancing the hydrogen de/hydrogenation of the Mg-Ni system. It is also found that the larger the formation enthalpy, the worse the dehydrogenation kinetics.