The development, testing and optimization of energy storage materials based on the MgH2Mg system

Abstract

A systematic investigation was conducted detailing the kinetics, extent of hydrogen loading and cycling stability for both the Ni-doped and undoped MgH2-Mg systems as heat and hydrogen storage materials. Several methods for doping Mg powders with Ni were tested, in which commercial Ni compounds are used as doping agents. The storage properties of these Ni-doped materials are comparable with those of a so-called standard material, Mg doped via bis(1,5-cyclooctadiene)Ni in solution. The mechanical mixing of Mg powder with Ni powder in the dry state turned out to be by far the simplest and least expensive doping method. The storage materials obtained by mechanical mixing showed, besides satisfactory kinetics and hydrogen loading capacity, the highest cycling stability in long-term tests. The results of the cycling tests reveal a different behavior for the Ni-doped and undoped MgH2-Mg storage materials at low vs high H2 pressures and temperatures; an increase of hydrogen loading when cycling is carried out under close-to-equilibrium hydrogenation conditions; and reversibility of loading losses. The complete observations and results presented are of practical utility for the operation of heat or hydrogen stores on the MgH2-Mg basis.