Enhanced dehydrogenation properties of Mg-Ni-Cu hydride after air exposure

• Published in: Journal of alloys and compounds 2025-01, Vol.1010, p.177989, Article 177989
• Main Authors: Zhang, Ruiming, Shi, Rui, Zhu, Yunfeng, Ni, Jinlian, Liu, Yana, Zhang, Jiguang, Wang, Jun, Ba, Zhixin
• Format: Article
• Language: English
• Subjects: Air stability; Dehydrogenation behavior; Mg-Ni-Cu hydrides
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.177989

It is difficult to strike the balance between air-stability and high reactivity of magnesium-based hydrogen storage materials. The high reactivity requires more fresh surface without oxidation, but this always comes with severe surface passivation since the fresh metal surface can react with the O2/H2O/CO2 in the air easily. In this work, a new strategy was investigated to improve the reactivity and air-stability by substituting part of nickel (Ni) in Mg-Ni hydride with copper (Cu). The hydrides with the composition Mg80Ni20-yCuy (y = 1, 2, 3, 4) were synthesized and analyzed, and the results demonstrated that Cu substitution enhanced the hydrogen storage properties of the hydrides. Notably, the Mg80Ni19CuHx hydride showed the best performance, including superior air stability, the highest hydrogen storage capacity, and the greatest improvement after air exposure. The onset dehydrogenation temperature of Mg80Ni19CuHx decreased from 310.0 °C to 237.5 °C after 3 months of air exposure. At 245 °C, the air-exposed Mg80Ni19CuHx released 4.15 wt% H2 within 1000 seconds, retaining more than 97 % of its initial capacity before air exposure. After 3 months of air exposure, the observation revealed that an Mg(OH)2 passivation layer formed and nickel particles were generated in situ on the surface of Mg80Ni19CuHx, where the passivation layer preserved the hydride's air stability, and the Ni particles enhanced the dehydrogenation kinetics. This work offers a promising approach for the large-scale production of highly reactive yet air-stable hydrides. •Cu substitution enhances dehydrogenation of Mg-Ni-Cu hydrides obviously.•Onset dehydrogenation temperature drops significantly after air exposure.•Mg-Ni-Cu hydrides maintain over 97 % capacity even after 3 months of air exposure.•Mg(OH)₂ layer and Ni particles improve air stability and reaction kinetics.