Performance And Regulation Of Hydrogen Production From Magnesium-based Alloys And Hydrides

Hydrogen as a globally accepted clean and renewable energy carrier,with the advantage of high energy density,abundance and environment friendly,is one of the potential candidates for replacing fossil fuels.Hydrogen generation by hydrolysis of Mg-based alloys or hydrides is a real-time hydrogen supply technology,which integrates hydrogen storage and generation.It is considered as one of the most promising hydrogen production methods due to its abundant source of raw materials,high purity of hydrogen production,high hydrogen yield.However,the hydrolysis reaction of Mg/Mg H2 is rapidly inhibited by the formation of a magnesium hydroxide passivation layer and shows sluggish kinetics,limited its commercial application.In this thesis,starting from the hydrolysis of Mg and its hydrides,magnesium calcium and magnesium silicon alloys and Mg-based hydrides composites are studied.Ball milling,alloying and composite system construction are used for improving the hydrogen generation properties of Mg/Mgmaterials in pure water.In addition,the hydrolysis and alcoholysis properties of Mg and its hydride composite system are examined by using an alcohol or alcohol-water mixed solution as a reaction solution from room temperature to-20°C to match the demand for the controlled real-time hydrogen release in real time and in all weather.Firstly,based on the CaH₂ can significantly enhance the hydrolysis properties of Mg or Mg H₂,but the Ca and Mg are difficult to be hydrogenated unless under the condition of high temperature and high pressure.Such,the high-cost of Mg H₂-CaH₂ composite make it not propitious for commercial application.In order to reduce costs,the Mg H₂-CaH₂ composite was prepared in-situ by ball-milling of Ca-Mg alloy under 3 MPaH₂.The introduction of Ni element can catalyze hydrogen decomposition to accelerate the hydrogenation of Ca Mg₂ alloy with completely hydrogenated in 3 h.The hydrogen production performance of CaH₂-Mg H₂composites prepared at different temperatures was explored.It also shows rapid hydrogen production performance even at 0°C.Secondly,in order to produce hydrogen controllable in real time and better adapt to the low temperature outdoor environment,methanol,ethanol or alcohol-water mixed solution were used as the reaction solution to investigate the hydrogen production performance of Ca Mg₂ alloy and CaH₂-Mg H₂ composite,especially at low temperature（<0°C）.The results show that the Ca Mg₂ alloy has excellent alcoholysis kinetics when react with methanol at room temperature,but is poor in ethanol solution.The hydrogen production can reach up to alcoholysis by-products of Ca Mg₂ alloy and CaH₂-Mg H₂ composites is Mg（CH₃O）₂ and Ca（CH₃O）₂,which can react with water and be converted into methanol,calcium hydroxide and magnesium hydroxide to realize the recycling of methanol.The Ca Mg₂ alloy can react with methanol at-20°C with the alcoholysis conversion rate of 70.7%.The hydrolysis conversion rate of CaH₂-Mg H₂ composite in the ethanol-water mixed solution was 78.6%at-10°C.In addition,the alcoholysis performance of Mg₂Si alloy in methanol was also investigated.The alcoholysis conversion rate of Mg₂Si ball-milled for 2 h was over 99%in 1min.Even at-10°C and-20°C,the alcoholysis conversion of Mg₂Si alloy was as high as94.8%and 89.8%,respectively.Finall,in order to improve the hydrogen production performance of Mg-based hydride materials,and improve its air stability,the Mg H₂-Li NH₂ composites are prepared by ball milling.The enrichment and coating effect of nano-Li NH₂ on the surface of Mg H₂ particles and its sensitivity to air were discussed,which laid a foundation for the development of magnesium-based hydride hydrolysis materials and more convenient use of practical hydrolysis.The 4Mg H₂-Li NH₂ composite prepared by ball milling can produce 887.2 m L·g^-1hydrogen in 1 min,and it also can react rapidly to produce a large amount of hydrogen even at low temperature（0°C）,which make it has a good application prospect.