Armazenamento de hidrogênio em compósito Mg-Fe produzido por reofundição e limagem

Abstract

One way to enable the use of renewable energy would be to produce hydrogen to act as an energy carrier. However, its storage is a challenge. An alternative would be to store it in a solid state using metal hydrides. Among the hydrides, MgH2 presents excellent gravimetric capacity and cyclability. However, its slow kinetics, associated with operating temperatures >300°C, limit its application. To overcome these limitations, additives are used along with processing techniques. Iron is already employed, showing remarkable performance depending on how it is incorporated. In this research, a magnesium composite with 8% at. Fe was synthesized by rheocasting. The ingot was characterized to verify the iron distribution, and the selected region was processed by manual and rotary filing. Part of the filings was exposed to air; the remainder was ground for 30, 60, and 120 minutes. The materials were characterized by XRD, SEM, DSC, TG, volumetric tests in a Sieverts-type apparatus, and TEM. Fe was heterogeneously distributed throughout the ingot, with the lower region having the highest content (average of ~10.42% wt. Fe). The material containing Fe exhibited superior kinetics and a negligible incubation period when compared to Mg; furthermore, it showed resistance to air exposure. The addition of graphite provided further improvement in kinetics, reaching a transformed fraction of approximately 0.4 in 120 minutes. The apparent activation energy was 160.91 kJ/mol and 135.65 kJ/mol for rotary-processed and manually processed Mg, respectively. For the material containing Fe, the apparent activation energy was 125.91 kJ/mol and 123.88 kJ/mol for rotary-processed and manually processed material, respectively. Therefore, the addition of Fe reduced the apparent activation energy of MgH2 desorption by ~23%.