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.