Exploration On NaBH₄ Regeneration Combining Hydrogen Storage And Production

NaBH₄ is considered to have a promising future in the field of new energy due to high gravimetric hydrogen density,controllable hydrolysis,high-purity hydrogen,environmentally friendly and recycling of by-product.However,tough regeneration process,high cost,requesting noble metal catalyst and low hydrogen generation rate in the system for producing hydrogen by hydrolysis of NaBH₄ fuel solution impede its development and practical application.So far,typical NaBH₄ regeneration methods include thermochemical and mechanochemical synthesis.But the former has many disadvantages including high energy consumption,unsafety and complex process,whose situation is not optimistic.Moreover,the previous methods with high-energy ball milling fail to use the real hydrolysis by-product as raw material and to meet practical requirement due to low regeneration rate of NaBH₄.Based on that,this research uses real hydrolysis by-product（NaBO₂?xH₂O）and magnesium or magnesium hydride as raw materials and deeply investigates NaBH₄ regeneration mechanism and yield via high-energy ball milling.In the meantime,the preliminary study on the hydrolysis of regeneration product（NaBH₄）is also conducted.The research shows that not only single reducing agent and oxidizing agent such as MgH₂ and NaBO₂?xH₂O or Mg and NaBO₂?xH₂O are able to realize the regeneration of NaBH₄ by high-energy ball milling under inert atmosphere,but also the mixture of MgH₂,Mg and NaBO₂?xH₂O or of NaBO₂?2H₂O（also written as NaB（OH）₄）,NaBO₂?4H₂O（also written as NaB（OH）₄?2H₂O）and single reducing agent could achieve NaBH₄ regeneration under homologous conditions.The regeneration mechanism of “MgH₂+NaBO₂?2H₂O” system and “Mg+NaBO₂?2H₂O” system is studied using characterization of XRD,FT-IR and NMR.The result shows that both systems have similar hydrogen transformation process,in which [OH]– is replaced by H– to form intermediate [BH₃（OH）]^-before NaBH₄ generates.The yield research shows a close relationship between the yield of NaBH₄ and ball milling time,as well as the mole ratio of two reactants.Firstly,extending ball milling time could increase the yield of NaBH₄ but its trend would become slower and slower.Secondly,with more reducing agent,the yield of “MgH₂+NaBO₂?2H₂O” system demonstrates a rapid increase and a slow decrease while the other system presents two different trends because of the “critical time”.When ball milling time is longer than the “critical time”,the yield of NaBH₄ increases along with the increasing amount of Mg.Conversely,the larger the excess amount of Mg is,the fewer the yield of NaBH₄ is.With optimal yield,“MgH₂+NaBO₂?2H₂O” system is up to 90% while “Mg+NaBO₂?2H₂O” system is approaching 70%.NaBH₄ is hydrolyzed through the so-called controlling water amount method achieving 6.75 wt.% of gravimetric hydrogen yield（the theoretical value is 7.28 wt.%）,which is the best result and has a huge advantage compared with the reported method by catalytic hydrolysis of NaBH₄ fuel solution.