Synthesis And Hydrolysis Performance For MgLi Based Hydrides

Magnesium or Aluminum-based materials have been considered as very promising materials for hydrogen production via hydrolysis,for the advantages of abundant reserves,high theoretical hydrogen yield,high-level purity,and environment-friendly hydrolysates.However,the formed passivation layers of magnesium hydroxide or alumina during hydrolysis,will hinder the further contact between the magnesium or aluminum and solution resulting in sluggish kinetics and depressed hydrogen yields.This paper prepared Mg Li-expanded graphite?EG?composite,Mg Li-Al/-Mg Cl₂ composite and Mg Li based hydrides?H-Mg Li?by ball milling.The hydrogen production performance via hydrolysis was discussed.The advantages of product recovery for different composites were also clarified.In order to provide alternatives for on-site hydrogen supply demands of portable electronic devices,this article aims to obtain Mg Li composite hydrogen production materials qualified with excellent hydrolysis kinetics and high hydrogen density.First,based on the features of low price and specific surface area of graphite as well as its ability to form a galvanic cell with the alloy,which can optimize hydrolysis performance,this paper introduced EG as a modified addition of Mg Li,and optimized the effects of hydrolysis solutions,ball milling time and the amount of introduced EG on hydrolysis performance.The hydrogen production performance of Mg Li-EG composite was discussed.The contributions of Cl^-and EG on boosting hydrolysis kinetics and the effects of the amount of introduced EG on chemical stability of Mg Li were clarified.The experiments indicate that Mg-10 wt%EG can generate 964 m L/g?8.6 wt%?hydrogen at 2 min.After exposed in air for10 min,it was tested that the composite suffered less hydrogen yield loss.The hydrolysis by-products of Mg Li-EG composite can be isolated automatically and easily recovered.Second,based on the facts of hydrogen non-supplied EG and the high cost of Mg H₂ and Li H.To further elevate the hydrogen yield,the corresponding hydrides?H-Mg Li?were synthesized by reaction ball milling under hydrogen atmosphere.The hydrogenation mechanism of reaction ball milling and hydrolysis mechanism were clarified.In order to eliminate the influence of ions in the solution,the hydrolysis kinetics performance H-Mg Li was detected in deionized water,with 1250 m L/g?11.1 wt%?hydrogen released in 1 min.Moreover,the special particle refinement of"from large to small"and hydrides synthesis during reaction ball milling were clarified.Numerous refined particles with the size of 2.0?m and 0.3?m can be obtained when the initial 1mm Mg Li particles were under reaction ball milling,then the morphology of the small particles gradually evolved into a spherical shape,and the ultimate H-Mg Li particle size was less than 30?m;the specific surface area increased and contributed to the synthesis of hydrides when the particles were refined.The metal hydrides with high hydrogen production density and excellent hydrolysis kinetics can be synthesized by reaction milling.With the feature of the low-requirement to the initial particle size,it is convenient for simple applications.To further promote the hydrogenation degree of H-Mg Li obtained from reaction ball milling,Mg Li alloy was hydrogenated at the condition of high temperature and hydrogen pressure.It can produce 1773 m L/g hydrogen in 5 min,with a high hydrogen production density of 15.8 wt%and the feature of"quick start and stable operation".Finally,in order to take full advantages of Al-rich content,lightweight,low cost and higher hydrogen yield than that of Mg,this paper maintains the hydrogen production performance of Mg Li while compounding Al.The Mg Li-Al composite,Mg Li-Al-5 wt%Mg Cl₂ composite was constructed for hydrogen production,and the hydrolysis performance of Mg Li-Al composites?H-Mg Li-Al?obtained from reaction ball milling was tested.The hydrolysis mechanism was also clarified.The hydrogen production via hydrolysis of Al without the presence of halogenation salts was improved.H-Mg Li-Al had excellent hydrolysis kinetics,and the conversion rate of Al was 78%at least.Li can combine with Al and be precipitated in the hydrolysate precipitates as Li Al₂?OH?₇·2H₂O.