Exploration And Property Control Of Mg-based Materials For Hydrogen Generation Via Hydrolysis Reaction

Due to the high hydrogen capacity,abundance and mild reaction conditions,hydrogen generation via hydrolysis of Mg-based materials has been regarded as a promising controllable chemical hydrogen production technology,which is expected to be used in portable hydrogen production field.However,the reaction is easily interrupted by the formation of Mg?OH?₂ passive layer on the reactant surface during the hydrolysis process,leading to a failure of commercial application.In this paper,the hydrolysis of Mg-Mg₂Si materials was explored.Hydogen generation performance was optimized by high energy ball milling and changing the composition of aqueous solution.Characterizations,such as XRD,SEM and MS were adopted to analyze reaction products and clarify the reaction mechanism.The obtained hydrogen generation system by hydrolysis with enduring reaction kinetics may open a new avenue to the future mobile hydrogen fuel cell industry.Mg₂Si was introduced as an second phase to Mg.Mg-Mg₂Si composite material for hydrogen generation was prepared by introducing Si to Mg.Through melting,crushing and ball milling,the Mg-14 wt%Mg₂Si composite sample was obtained as the raw material for hydrogen generation.The effect of introduction of MgCl₂ and its concentration to the hydrolysis kinetics was studied in detail.The hydrolysis kinetics was enhanced by MgCl₂introducing and achieves its optimal performance when the concentration was 0.5 M,releasing 648 m L/g?74.1%?and 816 m L/g?93.3%?H₂ in 10 min and 1 h,respectively.The effects of temperature on hydrolysis performance were further studied.The fitting calculation showed that the activation energy of hydrolysis reaction was significantly affected by the introduction of MgCl₂.Besides,contrast analysis on the hydrolysis properties of the obtained Mg-Mg₂Si composite than commercial pure Mg and Mg adding Mg₂Si or MgO showed that the ways of addition of Mg₂Si and its concentration influenced the hydrolysis performance of composite material.The melted Mg-Mg₂Si composite shows an enhanced hydrolysis performance.In addition,the hydrolysis property of commercial Mg₂Si was further studied.NH₄F solution was used as the reaction media to build a Mg₂Si-NH₄F hydrogen generation system.Mg₂Si shown the best hydrolysis property when the concentration of NH₄F solution was 13.0wt%,releasing 617 mL/g H₂ within 30 min.The high energy ball milling was used to improve the conversion rate of Mg₂Si hydrolysis,resulting in a nice hydrogen generation performance in 5-35?.In the low temperature condition,the hydrolysis of Mg₂Si by ball milling process for 2 h and 5 h in 13.0 wt%NH₄F solution at 5?could generated 633 m L/g?49.5%?and 660mL/g?51.6%?in 1 h,respectively.Besides,in 35?,the hydrolysis kinetics was significantly promoted.The untreated Mg₂Si could generate 714 m L/g H₂,while the Mg₂Si milled for 2 h and 5 h could generate 852 m L/g?66.6%?and 936 m L/g?73.2%?,respectively.