The Preparation And Activation Mechanism Of Al-based Composites Used For Hydrogen Generation And Recovery Of Hydrolysis By-product

Hydrogen generation from the reaction between Al-based composites and water is one of the effective ways to realize industrial utilization of hydrogen energy under the condition of imperfect hydrogen storage and transport systems.Recycling and reuse the hydrolysis by-product of Al-based composites is a possible way to reduce the cost of Al-based composites used for hydrogen generation,such as micro/nano sized materials preparation,metal element recovery.It is of great theoretical and practical significance to promote hydrogen economy development,metal recycling,and environmental protection.Al-based composites activated by low-melting-point metals,oxides,and salts were prepared by high-energy ball milling.Uniform and orthogonal designs were chosen to optimize components and mechanical alloying parameters of the Al-based composites,respectively.The results suggest that the Al-1.0 wt.%Ga-1.5 wt.%In-3.0 wt.%SnCl₂-1.0wt.%Bi₂O₃ composite prepared using the parameters A4B1C3D2,including a rotation speed of 480 rpm,a milling time of 120 min,a ball-to-powder mass ratio of 15:1,and a mass ratio of balls with?10 and?6 mm diameters of 1:1,exhibited a hydrogen yield of1172.3 m L?g^-1 and maximum hydrogen generation rate of 1030.5 m L?min^-1?g^-1 at 25°C and atmospheric pressure.The reason why Al-1.0 wt.%Ga-1.5 wt.%In-3.0 wt.%SnCl₂-1.0wt.%Bi₂O₃ composite has excellent hydrogen generation properties are as follows:the Gibbs energy change of the reaction is less than zero,which means the reaction could proceed spontaneously.Oxide film formation on the surface of Al particles is broken due to the plastic deformation of Al-based composites during milling process and the formation of substitution solid solution Al(Ga).The in-situ formation of In Sn₄ and Al Cl₃ could effectively improve the hydrolysis properties.HCl(protons)from Al Cl₃ hydrolysis and eutectic reaction of Al-In Sn₄ could accelerate the reaction.Reduction of Bi₂O₃ in the thermite reaction promotes hydration and dissolution of the oxide and transfer of hydrated oxide molecules to the Al surface.The presence of metals either in the raw materials,such as Ga and In,or in-situ formation,such as Sn and Bi,promote the negative displacement of corrosion potential.The combined action of those factors significantly improves hydrogen generation properties of Al-1.0 wt.%Ga-1.5 wt.%In-3.0 wt.%SnCl₂-1.0 wt.%Bi₂O₃composite.The effects of additives including Ga,In,Bi₂O₃,and SnCl₂ and parameters including rotation speed,milling time,ball-to-powder mass ratio,and a mass ratio of balls with?10and?6 mm diameters on hydrolysis properties of Al-Ga-in-Bi₂O₃-SnCl₂ composites were investigated using the control variate method.Ga could improve hydrolysis properties of Al-based composites,while it also has side effects with high content for agglomeration during milling process.The effect of In and SnCl₂ contents on hydrogen generation performance is significant,and SnCl₂improve the hydrogen generation rate.The hydrogen generation rate after reaction start-up is associated with Bi₂O₃ content.The hydrogen generation performance would decrease dramatically for ball milling with high rotation and long milling time because of agglomeration.Ball-to-powder mass ratio has a certain effect on hydrogen generation performance.Moreover,effect of mass ratio of balls on hydrogen generation performance is less than other three parameters for the reason that it just affects the energy that balls carrying.The by-product properties of Al-based composites reaction with water was characterized.Al OOH presents nanosheet-assembled micro/nano flowers where all the elements are homogeneously distributed.Phase transformations from?-to?-and?-Al₂O₃occur during the heating process.Its particles with a volume fraction more than 99.0%is micron with BET specific surface area of 276.77 m²/g,pore volume of 0.37 cm³/g,average pore diameter of 5.99nm.Alumina with high specific surface area is prepared by ball milling with the hydrolysis by-product of Al-based composites.The phase transformation from Al OOH to Al₂O₃ completed using the parameters with a rotation speed of 480 rpm,a milling time of 3h,a ball-to-powder mass ratio of 15:1,and a mass ratio of balls with?10 and?6mm diameters of 1:1,which the volume fraction of nanoscale particles changes from 0.20%before to 40.05%after milling.Sn element is separated from the hydrolysis by-product using its special properties of Sn(OH)₄ compared with other hydroxide in the product.The Al OOH was prepared by carbonation from the remaining liquid after Sn separation.In this paper,Al-based composites with high hydrogen generation performance were prepared by mechanical alloying.The effects of additive content and milling parameters on hydrolysis properties as well as the recovery and reuse of by-products were discussed,which provided ideas and references for the design of composite materials with different hydrogen generation performance and the cost reduction of hydrogen production technology by Al-based composites.