Remarkable hydrogen properties of MgH2via combination of an in-situ formed amorphous carbon

Abstract

Carbon-based materials have been proposed as an ideal medium to reduce the reaction energy barriers and improve the (de)hydrogenation kinetics of magnesium-based hydrogen storage material (MgH2) in term of their excellent dispersion. However, tedious preparation process and uneven distribution of carbon restrict the application. Therefore, in this paper, we cover MgH2 by in-situ formed amorphous carbon via a facile approach of co-sintering Mg with fluorene followed by hydriding combustion and ball milling processes, named as MgH2-carbonization product of fluorene (MgH2-CPF). As a result, the MgH2-CPF composite prepared at 823 K initially dehydrogenates at 557 K, 94 K lower than the as-milled MgH2 (651 K). Meanwhile, the composite can release 5.67 wt% H2 within 1000 s at 623 K. Even at a lower temperature of 423 K, the MgH2-CPF composite still reabsorbs 5.62 wt% H2 within 3600 s, while the as-milled Mg can hardly absorb hydrogen under a same condition. Furthermore, by addition of CPF, the apparent activation energy of the system is decreased from 161.2 kJ/mol to 87.2 kJ/mol. Our finding suggests that the carbon layer can keep the MgH2 from aggregation, promote hydrogen transport and improve the efficiency of hydrogen absorption and desorption.