MgH2 cathalyzed with Fe or Fe2O3 as hydrogen reservoir

MARCOS MEYER; LORENA BAUM; GIOVANNI PRINCIPI; LUIS MENDOZA ZELIS

Bariloche (Rio Negro)

Congreso; Solidos 05; 2005

Magnesium hydride is one of the the most interesting materials for solid state hydrogen storage ecase of its low cost, easy handling and high storage capacity (near to 0,075 mass). However, previous to practical use in mobile applications, considerable efforts must be done in order to  improve its absortion/desortion kinetics. High energy mechanical milling has been used to reduce the grain size to the nanometric scale, giving rise to charge/discharge times of some minutes at temperatures close to 300 ºC. However, at lower temperatures, the sluggish kinetics remains a problem to be solved for any technological application. Furthermore, it has been observed that the addition of small quantities of transition metals and/or their oxides have an important cathalitic effect in the sorption kinetics. Although this cathalitic effect is well documented very little is known about the precise mechanisms involved in the sorption rate improvement. In order to contribute to the understanding of such procresses we studied with M¨ossbauer spectroscopy the near neighbourhood of the Fe atoms in samples ofMg doped with Fe and Fe2O3, before and after some hydriding-dehydriding cycles. Several samples, with different ammount of additives were prepared by milling. The absorption/desorption properties were analyzed with a Sievert type aparatus. All the studied samples reached the stationary conditions after a few charge/discharge cicles of absorption desorption, indicating that reactive milling reduce the duration of the activation stage. Some   differences were found in the desorption kinetics that will be discussed in terms of the samples microstucture.