Regeneration Of Sodium Borohydride By Hydrated Sodium Metaborate In Presence Of Magnesium Base Alloy

The hydrogen content of sodium borohydride is about 10.6 wt%,and hydrolysis of sodium borohydride is fast and controllable.In addition,hydrogen from hydrolysis is pure enough to be used directly by fuel cell,so sodium borohydride is suitable for hydrogen storage.However,the high cost of industrial production and complicated regeneration process prevent it from practically application.Therefore,reducing the cost of sodium borohydride is the main issue in its commercialization.Considering the direct hydrolysis byproduct sodium metaborate hydrate,sodium metaborate hydrate,magnesium,magnesium silicide,silicon and magnesium-aluminum alloy are used as raw materials.Shaker mill is the main method for in these reactions.Furthermore,mechanism and yield of regeneration are deeply investigated.At the same time,hydrolysis of NaBH4 has also been studied.Firstly,XRD,FT-IR,NMR are used to characterized the NaBH4 regenerated by Mg,Mg2Si,Si,Mg17Al12 and NaBO2·xH2O.In this study,the mole ratio and ball milling time are modified to study the feasibility of NaBH4 regeneration,and figure out the optimal conditions to achieve highest yield.The result of yield shows that the addition of Mg2Si or Si can promote the regeneration of NaBH4 when Mg is used as reducing agent.The yield is affected by ball milling time.A critical time point is found and the yield of NaBH4 increase with the ball milling time increase before this point,then NaBH4 yield decline if the ball milling time is further prolonged.Among the three system,the highest yield is achieved in the Mg-Mg2Si-NaBO2·2H2O system,which is 86%.Secondly,the regeneration mechanism of NaBH4 is studied by FT-IR and NMR.During the regeneration process,the intermediate product[BH3(OH)]-is detected.It can be speculated the conversion process is a substitution reaction.In detail,the sequence of transformations is[B(OH)4]-to[BH(OH)2]-and finally to[BH4]-.Finally,the hydrolysis properties of purified NaBH4 and commercial NaBH4 using catalyst are also studied.According to the hydrolysis curve,the purified NaBH4 exhibits fast hydrogen generation kinetics.The hydrogen production of regenerated NaBH4 reaches 2211 mL·g-1,similarly to commercial NaBH4.