Chemical transformation of additive phase in MgH2/CeO2 hydrogen storage system and its effect on catalytic performance

• Published in: Applied surface science Vol. 561; p. 150062
• Main Authors: Pukazhselvan, D., Sandhya, K.S., Nasani, Narendar, Paul Fagg, Duncan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30-09-2021
• Subjects: Binary hydrides; Catalysis; Hydrogen Storage; X ray diffraction; Hydrogen Storage; Catalysis; Binary hydrides; X ray diffraction
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.150062

[Display omitted]
•MgH2 and CeO2 interact chemically and make CeO1.96 and Ce2O3 in situ products.•Crystalline to amorphous transformation of ceria occurs during mechanical milling.•Recrystallization occursduring de/re-hydrogenation of the ball milled samples.•The belief regarding CeH2 as the only active in situ product is questionable.•CeO1.66 seems to be overlooked as CeH2 in MgH2/CeO2 hydrogen storage system.
This study provides important information for understanding the hydrogen storage mechanism of ceria additive incorporated magnesium hydride (MgH2). It is observed that dehydrogenation activation energy of MgH2 can be lowered by at least 50 kJ/mol.H2 upon incorporating a small amount of CeO2 with MgH2. The ceria additive partially transforms to CeO1.96 and hcp Ce2O3 phases when we mechanically mix ceria with MgH2. Subsequently, upon further dehydrogenation at 300 °C, the remaining CeO2, CeO1.96 and hcp Ce2O3 phases transform to cubic Ce2O3. A substantial quantity of ceria undergoes crystalline to amorphous transformation upon intense mechanical milling but the crystallinity gets restored during hydrogenation/dehydrogenation reactions. With appropriate evidence, the current study also explains, “how reduced cerium oxide phase(s) may be mistaken as cerium hydride(s)” and “why the beliefs existing in the literature regarding CeH2 as the active in situ catalyst in MgH2/CeO2 hydrogen storage system needs to be further scrutinized”.