Cycling behavior of Mg-Fe-H system hydrides

A. BARUJ; J. A. PUSZKIEL; F. C. GENNARI; P. ARNEODO LAROCHETTE

Reykjavik, Iceland

Simposio; International Symposium on Metal-Hydrogen Systems; 2008

Metal-Hydrogen Systems Association

In this work, samples of Mg-Fe elemental powders mixtures with three different compositions were studied, namely Mg Fe, Mg Fe and Mg Fe. All of them were synthesized via reactive ball milling under hydrogen atmosphere. Additionally, Mg Fe samples produced by means of ball milling in argon atmosphere were analyzed. The cycling process was carried out at constant temperatures of 375ºC and 400ºC in a closed loop device and the time elapsed between two consecutive absorption stages was approximately 15 minutes. The evolution of both storage capacity and reaction kinetics was monitored during hydrogen absorption and desorption cycling. The samples prior and after cycling were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). During cycling, we have found that the materials display two different behaviors. Through the first cycles number of cycles that depends on the sample characteristics and the temperature. After this initial stage, the materials slowly degrade with the increase in the number of pressure cycles. Typically, the storage capacity reduction after 1000 cycles at 400 C is more pronounced than that measured at 375 C.We discuss the possible reasons for this behavior and the differences observed at these two temperatures based on the formation of the different hydride phases, their associated hydrogen sorption kinetics and their relative stability.