Reversible hydrogen storage in Mg(HxF1-x)(2) solid solutions

摘要

Mg( HxF1-x)(2) solid solutions have been synthesized by mechanical milling MgF2 and MgH2 under H-2 atmosphere. Complete solubility has been observed at 475 degrees C. The solid solution presents a rutile-type structure with the anion site randomly occupied by H- or F- and with lattice parameters showing positive deviations from Vegard's law. The solution can be decomposed and re-formed reversibly by changing H-2 pressure. For example, Mg( H0.9F0.1)(2) reversibly stores 5.5 wt. % H-2 in less than 3 min at 440 degrees C. During decomposition H2 is released, and Mg and a solution rich in F appear as products. This process takes place in two clearly marked stages controlled by F- concentration in the material. The decomposition enthalpy of the first one is close to that of MgH2 for Mg( H0.9F0.1)(2), and decreases with the H content in the solution. (C) 2017 Elsevier B.V. All rights reserved.