Modification Of Nano-sized Fe-based Additions For MgH₂ On The Hydrogen Storage Performance

According to statistics,the building energy consumption accounts for 30%of the total global energy consumption.Researchers are actively implementing the new energies to the construction industry.Therein,the hydrogen-based fuel cell does not generate any pollutants while supplying energy to the building,providing a choice for the development of green buildings.At present,a safe and efficient way to store hydrogen still remains to be a key technology in the application of hydrogen-based fuel cell.As one of the most promising hydrogen storage materials,magnesium hydride（MgH₂）has attracted extensive attention due to its high hydrogen storage capacities（110 g/L and 7.6 wt%）,cheap cost and excellent reversibility.Nevertheless,the sluggish hydrogen sorption rate and high operational temperature greatly hinder its practical application in the field of hydrogen energy bulidings.In order to solve this problem,the modification method of catalytic doping is adopted in this paper,which can significantly improve the hydrogen storage performance of MgH₂,and its mechanism is analyzed in detail.（1）A two-dimensional layered Fe nanosheet was prepared by wet chemical ball milling in this paper,and its modification effect on the hydrogen storage performance of MgH₂was explored.The research found that minor addition of 5 wt%Fe nanosheets to MgH₂enables a quick release of 5.44 wt%H₂within 10 min at 300oC.In addition,the dehydrogenated sample takes up 6 wt%H₂in 10 min at 200oC and 32bar hydrogen pressure.Further analysises revealed that Fe nanosheets turned to be numberous ultrafine nanoparticles during the first dehydrogenation and rehydrogenation processes,thus providing more active sites and hydrogen diffusion channels to improve the kinetics properties.（2）An intermetallic Fe Co alloy catalyst with a synergistic effect on the hydrogen desorption performance of MgH₂was also synthesized in this paper.The results show that the hydrogen desorption process of nano-Fe Co-catalyzed MgH₂occurs at200-320oC.The reduction of the energy barriers is a directly reason to the improvement on the kinetic property of MgH₂,and the apparent activation energy of hydrogen desorption for this composite is dramatically reduced to 65.3±4.7 k J/mol.Combined with the characterization analysis,it was found that Fe Co nanosheets were uniformly distributed on the surface of MgH₂and stably existed during the hydrogen sorption process,thus remarkably promoting the decomposition and recombination of hydrogen molecules.（3）In order to further improve the cycling hydrogen storage performances of the composite system,Fe Ni nanoparticles dispersed on reduced graphene oxide nanosheets（Fe Ni/r GO）were prepared by hydrothermal carbonizationand process,and it was used as the catalyst of MgH₂.A hydrogen capacity of MgH₂added by 5 wt%Fe Ni/r GO was 6.9 wt%after 50 cycles,and the retention rate was 100%.A catalytic mechanism has been proposed that the synergetic effects between the in-situ formed Mg₂Ni/Mg₂Ni H₄,Fe and r GO,helped to promote the hydrogen dissociation and diffusion along the Mg/MgH₂interface,anchored the catalyst and prevented Mg/MgH₂particles from aggregation and growth.This three Fe-based catalysts prepared in this paper improved the hydrogen kinetics performance and cycle stability of MgH₂step by step,and the research of this paper can provide references for the designing and producing catalysts in hydrogen storage or other energy-related fields.