Researches On The Hydrogen Generation Properties Of Si Based Materials

Because of the advantages of high theoretical hydrogen capacity,low cost and rich resources,silicon is considered to be a promising new hydrolysis material,which can be used in portable hydrogen source or fuel cell system.However,the hydrolysis property of silicon is poor because of the slow hydrogen production rate and low yield,which restricts its application.In order to improve the reactivity of silicon,(1)Si/LiH(LiBH4)composites were prepared by ball milling,and NiCl2 was added to the composites to form ternary composites,the hydrogen-generation properties of these composites were systematically studied;(2)The porous silicon was prepared by chemical method and the hydrogen production performance of porous silicon was studied;(3)The hydrolysis properties of silicon and its composites in alkaline solution were studied.The synergistic effect of Si/LiBH4 composites hydrolyzed in the KOH solution was found.These samples were characterized by XRD,SEM,BET,XPS and other test methods,and the related mechanism is discussed.Firstly,the hydrolysis properties of ball-milled silicon,Si/LiH(LiBH4)compounds were systematically studied.The results show that the addition of LiH(LiBH4)is beneficial to the improvement of hydrolysis property of silicon.Hydrolysis for 1h at ambient conditions,hydrogen generation capacity of the Si/10%molLiH composite is about 37mL/g,and that of the Si/10%molLiBH4 composite reaches 126mL/g,while the Si/10%molLiH-3%molNiCl2 ternary complex reaches around 119mL/g,which is 12 times higher than the hydrolysis of silicon alone.Then porous silicon was prepared and its the hydrolysis properties were studied.The experimental results show that hydrogen generation capacity of the porous silicon etched for 5 hours is 20.5mL/g when it hydrolyzed for 1h at ambient conditions.The increase of temperature and appropriate amount of alcohol addition into deionized water is able to improve the hydrolysis yield of porous silicon.The hydrogen yield capacity of porous silicon hydrolyzed in the mixed solution reaches 37.5mL/g at 65?.Finally,the hydrolysis of silicon in KOH solution was systematically studied.The results show that the hydrogen yield of silicon hydrolyzed in the KOH solution increases at first and then decreases with increasing amount and concentration of KOH.The hydrogen yield of silicon hydrolyzed in the 15wt%KOH solution(molar ratio of Si:KOH=1:2)at ambient conditions for 1 hour reaches 85%.It is worth mentioning that when the molar ratio of Si:KOH = 1:0.5,the hydrogen yield of Si-3mol%LiBH4 compound hydrolyzed at ambient conditions for 1 hour in the KOH solution reaches 72.5%,100%higher than that of silicon alone,which may result from the synergistic effect of hydrolysis of LiBH4 and hydrolysis of silicon in the KOH solution.