Complex hydrides Mg2(Fe,Co)Hy for hydrogen storage

MARCOS MEYER; LUIS MENDOZA ZELIS; LORENA BAUM

Rio de Janeiro

Conferencia; ICAM Internatioan Conference on Advanced Materials; 2009

SBPMat (Brazil-MRS)

Mg-based ternary hydride complexes and transition metal type Mg2THy are very attractive materials for hydrogen storage due to its high volumetric capacity: up to 150 kgH2/m3 in Mg2FeH6. They form complex anions [THY]-4 leading to ionic-covalent bonds to hydrogen and thus have high enthalpies of dissociation. These compounds can be obtained by sintering at high temperatures and high pressures of hydrogen and in the last decade have achieved remarkable improvements in the yield of the synthesis from mechanically alloyed in hydrogen atmosphere constituents. This technique has also allowed us to explore the synthesis of complex quaternary Mg2T1-zT'zHy combining two transition metals towards optimizing the properties of the resulting hydride. In this paper we discuss the collection of family compounds Mg2Fe1-zCozHy (0 ≤ z ≤ 1) via mechanical milling in hydrogen atmosphere at room temperature and its properties as hydrogen storage materials. From mixtures of Mg, Fe and Co in appropriate quantities and at a pressure of 0.3 MPa of H2, we study the progress of the synthesis mechanism through analysing  the kinetic curves of hydrogen absorption. Samples taken after reaching a final steady state and representative intermediate stages were characterized by X-ray diffraction, differential calorimetry and Mössbauer spectroscopy. The hydrogen sorption properties of some of them were analyzed in a volumetric equipment. Finally we discuss the different steps in the synthesis of these hydride complex mechanical and thermal properties of hydrogen sorption of the resulting phases, depending on the composition of them.