Hydrogen Generation Via Hydrolysis Of Al And Mg-based Materials

Hydrogen generation via hydrolysis is one of the most promising solutions for hydrogen storage.However,passivation during hydrolysis reaction becomes one of the biggest barriers to the commercial application of hydrogen generation by metal hydrolysis.This thesis presents a novel and up to scale high energy ball milling method to optimize the hydrogen generation property of the hydrolysis of Mg-based and Al-based materials,in order to provide an economical modification strategy to achieve an on-site hydrogen generation method with high yield and controllable kinetics.The modified precursors include low-cost alloys Al₃Mg₂,Al₁₂Mg₁₇,and pure-Mg.First,in order to improve the hydrogen generation kinetics of Al hydrolysis without reducing the hydrogen yield,an Al-Mg H₂ composite is obtained via ball milling from a fully hydrogenated Al₃Mg₂ alloy combined with Na OH.Al is better activated and refined into smaller particles during ball milling when Mg H₂ and a small quantity of Na OH are added.Moreover,the hydrogen generated during hydrolysis can also be enlarged by the contribution of Mg H₂hydrolysis.The composition has favourable hydrolysis characteristics after 2 h ball milling in aqueous solutions of Na OH and KOH,yielding 1488.2 and 1452.8 m L/g of hydrogen in 60 min at328 K,respectively.In the Na OH and KOH solutions,the hydrolysis activation energy decreased to 29.3 and 32.19 k J/mol,respectively.The accelerated Mg H₂ hydrolysis and the subsequent generation of the non-compact by-product Mg₂Al（OH）₇ in the alkaline solutions,which in turn stimulates the hydrolysis process may be the cause of excellent performance.In the second step,the mixture of Al and Mg H₂ is obtained from the fully hydrogenation of a cost-efficient alloy Al₁₂Mg₁₇.The major subjects of discussion are the properties of MHA hydrolysis with grinding agent additives light transition metal（TM）Mo and oxides B₂O₃ in various solutions.Al Cl₃ solution used in this work for hydrolysis is to prevent the serious corrosion of the alkali solution.The effect of different aqueous solutions on the hydrogen generation rate of MHA hydrolysis was investigated with 0.1,0.5,and 1 M concentrations.It has been demonstrated that the H₂ yield rises along with the solution concentrations.A decrease in the activation energy to 9.4k J/mol and the production of 1420.2 m L/g in 50 minutes at room temperature in a 1 M Al Cl₃solution is evidence of excellent hydrolysis capabilities.The generation of H₃BO₃ from the hydrolysis of B₂O₃,the development of an incompact Mg Al₂O₄ by-product,and the effective refining of Al and Mg H₂ all have an impact on the kinetic properties of the hydrolysis of Mg H₂and Al.Finally,to improve the kinetics of Mg hydrolysis,a low-cost metal carbide catalyst was employed via an up to scale ball milling method.With a large hydrogen capacity,magnesium hydrolysis offers a cost-effective method for on-site hydrogen supply.At standard temperature,a yield of 851.2 m L/g of hydrogen was attained after 10 minutes.Importantly,Mo₂C has great stability after recycling,and over 90%of the hydrogen yield is still obtainable after five reusing cycles.According to catalytic mechanism research,the performance of the hydrolysis is considerably improved by the specific Mg-Mo₂C interface and micro galvanic cells that is generated during ball milling.