The Hydrogen Storage And Hydrolysis Properties Of Magnesium Based Ultrafine Powders Prepared By Arc Plasma Method

Magnesium is considered as one of the most promising hydrogen storage materials for its high hydrogen capacity?7.6 wt.%?,low cost,high abundance in the erath crust.However,the hydrogen absorption of Mg is sluggish and hydrogen desorption temperature of MgH₂ is very high,which have limited the wide application of Mg for hydrogen storage.Hydrogen generation from hydrolysis of MgH₂ is a simple and effective method which can produce hydrogen under mild conditions.However,the hydrolysis reaction will be stopped due to the formation of Mg?OH?₂ on the MgH₂particles.In order to solve these problems,metal fluorides,3d TM,boron,graphene and silicon was introduced into Mg powders using arc plasma method.The particle size distribution,phase components,microstructures,hydrogen sorption properties of these composites and hydrolysis properties of their corresponding hydrogenated powders are carefully investigated.It is shown that the addition of MF_x through arc plasma method can improve both the hydrogen absorption kinetics of Mg and the hydrolysis properties of corresponding hydrogenated powders.Among them,the Mg-NiF₂ composite shows the best hydrogen absorption properties at relatively low temperatures,which can absorb 3.26 wt.%of H₂ at 373 K in 2 h.Such rapid hydrogen absorption rate is mainly due to the formation of Mg₂Ni and MgF₂ on Mg particles during arc evaporation and condensation.In contrast,measurements also show that the hydrogenated Mg-VF₃ composite has the lowest peak desorption temperature and the fastest hydrolysis rate among all the hydrogenated Mg-MF_x composites.The less agglomeration tendency of Mg particles and VO₂ covered on MgH₂ particles account for the reduced hydrogen desorption temperature and enhanced hydrolysis rate.The investigations on the arc evaporated Mg with 3d TMs,boron,graphene and silicon showed that:the addition of 3d TMs can signicantly improve the hydrogen absorption kinetics of Mg.Among the added 3d TMs,Ni showed the best catalytic effect for hydrogen absorption in Mg.Mg-Ni powders can absorb about 6 wt.%H₂ within 500 s and reach its saturated hydrogen content in 1000 s.This is due to the fact that Mg₂Ni covered on Mg particles can act as the“hydrogen pump”,promoting the hydrogen absorption of Mg.Among hydrogenated Mg-X?X=B,Graphene,Si?powders,the addition of Si showed faster hydrolysis kinetics than other two additives.