Nickel-decorated graphene nanoplates for enhanced H₂ sorption properties of magnesium hydride at moderate temperatures

Magnesium hydride is considered as an ideal candidate for effective hydrogen storage due to its high gravimetric hydrogen capacity and accessibility. But its use as a commercial material is hindered by its relatively high operating temperatures and slow release/uptake kinetics. To solve this, we first synthesized Ni decorated graphene nanoplate (Ni/Gn) catalysts with highly dispersed metal nano-particles (NPs) via a facile method, then the as-prepared Ni/Gn catalysts were introduced by using the hydriding combustion synthesis and mechanical milling (HCS + MM) method to obtain Mg-based composites. Remarkable enhancement of hydrogen sorption rates has been found for these composites in the presence of Ni/Gn additives, especially for the Mg@Ni₈Gn₂ sample: A hydrogen absorption amount of 6.28 wt% within 100 s at 373 K and a hydrogen desorption amount of 5.73 wt% within 1800 s at 523 K. A rather low activation energy (71.8 kJ mol^-1) for the dehydrogenation of MgH₂ was determined in the same sample, indicating that relatively moderate temperatures are required to absorb/desorb hydrogen. The excellent hydrogen sorption rates of the composites are thought to be associated with the high dispersity of in situ formed nanometric Mg₂NiH₄ particles during the HCS + MM process. In addition, a microstrain-induced synergetic hydrogen sorption mechanism is proposed, being correlated by the local introduction of a Mg₂Ni nano-catalyst into the Mg matrix.