Achievement of excellent hydrogen sorption through swift hydrogen transport in 1:2 Mg(NH2)2–LiH catalyzed by Li4BH4(NH2)3and carbon nanostructures

Abstract

The present studies deal with the catalytic character of carbon nanostructure (Graphene (Gr) and single-wall carbon nanotubes (SWNTs), and their composite versions) on the hydrogen sorption behavior of 1:2 Mg(NH2)2–LiH/Li4BH4(NH2)3. The inclusion of an optimal quantity of 2 wt% SWNTs in Mg(NH2)2–2LiH/Li4BH4(NH2)3 resulted in superior hydrogen sorption over 2 wt% Gr and 2 wt% of (Gr and SWNT) composite. The onset desorption temperature for SWNTs catalyzed Mg(NH2)2–2LiH/Li4BH4(NH2)3 is 108 °C which is 32 °C, 44 °C lower compared to Gr catalyzed Mg(NH2)2–2LiH/Li4BH4(NH2)3 and uncatalyzed Mg(NH2)2–2LiH/Li4BH4(NH2)3 respectively. The de/re-hydrogenation kinetics of the SWNT catalyzed sample has been found to be 4.02 wt% and 4.63 wt% within 15min at 170 °C and 7 MPa H2 pressure, correspondingly. The activation energy for SWNT catalyzed Mg(NH2)2–2LiH/Li4BH4(NH2)3 has been found to be 69.75 kJ/mol. The SWNT catalyzed Mg(NH2)2–2LiH/Li4BH4(NH2)3 shows good cyclic stability (almost no degradation) up to 10 cycles. The better hydrogen sorption for SWNTs is attributed to the ballistic transport of hydrogen atoms within and across the amide/hydride matrix. In contrast, Gr sheets agglomerate, which adversely affects hydrogen sorption from Gr and Gr+SWNT composites. A hydrogen sorption mechanism has been proposed based on structural, microstructural, Fourier-transform infrared spectroscopy, and Raman characterization results.