Mg2FeH6-based nanocomposites for hydrogen storage

• Grant number: 08/09643-3
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date until: April 01, 2009
• End date until: July 31, 2010
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Walter José Botta Filho
• Grantee: Daniel Rodrigo Leiva
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 05/59594-0 - Properties of amorphous, metastable and nano-structured metallic alloys, AP.TEM

Abstract

The complex hydride Mg2FeH6 is a promising material for hydrogen storage in the solid state. Among the main attractive characteristics, we can point out the volumetric capacity for H2 storage (the largest known, of 150 kg of H2/m3), the reversibility for absorption / desorption cycles, and the low cost of the constituent elements. During the previous work of the candidate, we reached a great control of the synthesis of nanocrystalline Mg2FeH6 from 2Mg-Fe mixtures, using reactive milling under hydrogen atmosphere as a processing route, which is a relatively simple and cheap technique. Previous results in the literature pointed out the difficulties for the synthesis of such complex hydrides from the elements as one of the main barriers to their application, together with their relatively high thermal stability. We now consider the systematic study to de-stabilize such complex hydride through the production of nanocomposites by high energy milling, aiming to obtain faster hydrogen absorption/desorption kinetic and lower operating temperatures. Two distinct approaches will be explored: in a first stage, we will study the effect of additives selected among the catalyses elements which have already proved efficient for hydrogen absorption/desorption, as the transition metals, theirs oxides and fluorides; in a second stage, we will elaborate Mg2FeH6 and MgH2 nanocomposites containing the additives that presented the best results in the first stage. Using the combined effect of the surface activity of the catalysis elements with the presence of two types of different hydrides in the mixtures, we aim to obtain composite materials of relatively low cost with interesting properties for storage of H2. The structural characterization will be carried out by X-ray diffraction, transmission and scanning electron microscopy and X-Ray Photoelectron Spectroscopy. Phase transformations during heating will be studied by X-ray diffraction using synchrotron radiation and differential scanning calorimetry. The storage properties will be determined using a commercial hydrogen analyzer and a PCT (pressure-composition-temperature) equipment.