Catalyst derived from in situ-formed amorphous carbon to enhance the hydrogen sorption behavior of MgH2

Abstract

An MgH₂–anthraquinone carbonization product composite (denoted as MgH₂–ACP composites) was successfully prepared through a hydrogenation combustion and mechanical ball-milling method using the original Mg powder to simultaneously achieve modification via in situ-formed amorphous carbon. The amorphous carbon derived from the combustion of carbonic compounds significantly enhanced the hydrogen-absorption and -desorption performances of MgH₂. Results revealed that the onset decomposition temperature of the MgH₂–ACP composite decreased from 638 K to 587 K in the dehydrogenation stage. Moreover, the MgH₂–ACP sample delivered dehydrogenation capacities of 3.525 wt% at 598 K, whereas the as-milled MgH₂ decomposed only 0.763 wt% at the same temperature. The activation energies calculated using Kissinger analysis in the dehydrogenation process of MgH₂ were lowered by about 57.5 kJ mol⁻¹. For the absorption kinetic measurements at 473 K, the MgH₂-ACP sample could uptake about 4.629 wt% of H₂ in 3200 s compared to 1.804 wt% taken up by the as-milled MgH₂. The in situ-formed amorphous carbon and MgO were confirmed as the active species that contributed to the enhancement of hydrogen-storage properties of the composite.