Superior hydrogen performance of in situ formed carbon modified MgH2 composites.

Abstract

The MgH2-carbonic combustion product of the anthracene (CCPA) composite was synthesized by hydrogen combustion and mechanically ball-milled method to simultaneously achieve confinement by the in situ formed amorphous carbon. The amorphous carbon derived from the carbonic combustion product of anthracene in the MgH2-CCPA composite led to a significant increase in hydrogen sorption characteristics. The onset dehydrogenation temperature for the MgH2-CCPA composite was reduced to 589 K, which was 54 K less than that of pure milled MgH2. Regarding dehydrogenation kinetics, the MgH2-CCPA composite could release 5.933 wt% H2 within 3000 s at 623 K, while only 3.970 wt% H2 was liberated from the as-milled MgH2 within 3000 s at the same temperature. The MgH2-CCPA composite also exhibited excellent hydrogenation characteristics, absorbing 3.246 wt% of hydrogen within 3000 s at 423 K, which was three times higher than 0.818 wt% uptaken by the pure MgH2. The apparent activation energy (E a) for the dehydrogenation of the MgH2-CCPA composite was significantly reduced from 161.1 kJ mol-1 to 77.5 kJ mol-1. The notable improvement in sorption kinetics of the MgH2-CCPA nanocomposite is ascribed to the in situ formed amorphous carbon during the hydrogenation/dehydrogenation process.