Armazenagem de hidrogênio em ligas Mg – Ni preparadas por metalurgia do pó seguida de limagem

Abstract

The advancement of hydrogen storage technologies is essential to enable the use of H2 as a clean and sustainable energy carrier. Magnesium hydride exhibits a high gravimetric capacity (7.6 wt%) and good reversibility; however, it shows slow hydrogen absorption/desorption kinetics and high thermodynamic stability. The addition of nickel to magnesium is an effective strategy to overcome these limitations, mainly due to the formation of the Mg2Ni intermetallic compound, which acts as a “hydrogen pump” for Mg, since its reversible conversion to Mg2NiH4 occurs with faster kinetics than the hydrogenation of pure Mg, promoting H2 dissociation and the transport of atomic hydrogen into the Mg matrix. In this work, a mixture of Mg with 22 wt.% Ni was processed by powder metallurgy, and sintering at 500°C for 30 minutes resulted in the formation of a composite containing Mg–39.5wt.% Mg2Ni, which was subsequently pulverized by rotary filing prior to hydrogenation tests. The composite exhibited hydrogen absorption and desorption performance superior to that of Mg processed under the same conditions (2.5 wt.% H₂ in 600 minutes). The initial activation showed an incubation time of approximately 40 minutes, reaching 4.0 wt.% H2 after 140 minutes; after the first cycle, a pronounced acceleration of the kinetics was observed, with the same capacity being achieved in only 5 minutes during the second absorption. Air exposure tests indicated good oxidation resistance, and after 30 days the composite maintained the ability to absorb 4.0 wt.% H2, reached in 220 and 5 minutes during the first and second absorptions, respectively. These results demonstrate that the combination of powder metallurgy and rotary filing constitutes a simple and efficient processing route for obtaining Mg–Mg2Ni composites with superior hydrogen storage properties.