Thermodynamics and dynamics of the Mg-Fe-H system and its potential for thermochemical thermal energy storage

The reversible Mg2FeH6 and the mixed Mg2FeH6-MgH2 hydride systems [Eqs. (1) and (2)] turned out to be highly suitable materials for thermochemical thermal energy storage at around 500 degreesC, for example as the storage of solar or excess industrial heat. The systems are characterized by a high gravimetric and volumetric thermal energy density in comparison to sensible or latent heat storage materials (Table 1) and have excellent stability in cycle tests. Further advantages include low price of the starting materials, a free choice and constancy of the heat delivery temperature by controlling the applied hydrogen pressure, and the absence of heat losses with time. By means of combined TEM-EDX investigations essential features of the initial formation and the subsequent de- and rehydrogenation processes of Mg2FeH6 could be elucidated on a micro- or nanoscale level. (C) 2002 Elsevier Science B.V. All rights reserved.