Regulation And Mechanism Study On Hydrogen Production Performance Of Al-Ga-In-Sn Based Alloys For On-demand Hydrogen Supply

As a sustainable,clean and pollution-free ideal new energy source,hydrogen energy has attracted much attention.However,due to its low volume energy density,hydrogen is confronted with such problems as high energy consumption,high equipment requirements and high risks in the storage and transportation process,which restrict the large-scale development of hydrogen energy.The on-demand hydrogen supply mode that integrates production and hydrogen storage can avoid the hydrogen storage and transportation links,and it also has a broad application prospect in the fields of emergency power supply,military field equipment,small unmanned equipment,and portable equipment.Using low melting point metals(Ga,In,Sn,etc.),the alloyed aluminum-rich bulk material block is an ideal on-demand hydrogen supply material.It has significant advantages such as high-volume energy density,convenient storage and transportation,and high purity of hydrogen production.However,there is still a gap between the on-line hydrogen supply performance of such alloys and the ideal state at present.Based on the currently recognized liquid diffusion activation mechanism,the effect of further improving the hydrolysis hydrogen production performance of the alloy is insufficient.Therefore,on the basis of the traditional low melting point metal activation mechanism model of aluminum alloy,other activation forms of aluminum,including galvanic mechanism and dissolution-redeposition mechanism,are introduced as a cooperative activation mechanism to promote the Al-H₂O reaction of the alloy to comprehensively improve the material's performance.At the same time,systematically explore the structure-activity relationship between the microstructure characteristics and its hydrogen production performance,and improve the activation mechanism during the hydrolysis of this type of alloy.In this paper,based on the Al-Ga-In-Sn quaternary alloy,Cu,Zn,and NaCl were selected as dopants to prepare an aluminum-rich on-demand hydrogen supply alloy.The hydrogen production performance,phase composition,microscopic morphology,element distribution and the change law of thermal effect temperature of the alloy under the condition of doping with different substances were systematically studied.The changes in hydrogen production performance of alloys under two types of synergistic activation modes:liquid phase activation and galvanic cell,liquid phase activation and dissolution redeposition were explored respectively,and the traditional Al-based hydrolysis hydrogen production mechanism was supplemented and improved,and the effect of the synergistic activation mechanism of aluminum alloy hydrolysis is clarified.The main research contents of the thesis are as follows:1.The preparation,performance analysis and mechanism of Al-Ga-In Sn₄-Cu hydrogen-producing alloy were studied.When Cu is doped in Al-Ga-In Sn₄ alloy in the form of inclusions,the increase in the number of Cu particles will lead to an increase in Al grain cracks,and pores are easy to form inside the ingot.Fragmented Al grains easily lead to an increase in the area of grain boundary phase grains.With the increase of Cu doping amount(0-3wt.%),the Al grain cracks caused by Cu particles lead to the increase of grain boundary phase grain size,and the more heat generated by the low melting point grain boundary phase particles is easier to activate the high melting point grain boundary Phase particles increase the hydrogen yield of the alloy.When the Cu doping amount is 3wt.%,the hydrogen yield can reach the theoretical value.However,continuing to increase the replacement ratio of Cu has led to a decrease in the total area and number of grain boundary phase particles,an increase in the average spacing of grain boundary phase particles,and a significant decrease in hydrogen production rate.In addition,Cu and Al undergo galvanic corrosion.Under this synergistic effect,the conversion efficiency of aluminum is improved,and maximum hydrogen production rate of the alloy can be controlled within a relatively small range.2.The preparation,performance analysis and mechanism study of Al-Ga-In₃Sn-Zn hydrogen-producing alloy were studied.Zn in the alloy mainly exists in the form of Al(Zn)solid solution,and particles with high Zn content will appear in local areas.With the increase of Zn addition,the total area of grain boundary phase grains,the number of grains and the average area of single grain boundary phase grains all have a significant downward trend.The melting point of grain boundary phase grains increases,which increases the difficulty of the alloy hydrolysis reaction.On the other hand,a large amount of Zn in the form of solid solution promotes the Al-H₂O reaction through dissolution and redeposition.Under the combined force of the above two effects,the Al-Ga-In₃Sn-(2wt.%)Zn alloy has a high hydrogen production rate at 40°C,and the average hydrogen production rate is the smallest.At the same time,the ratio of In and Sn elements is minimized,and the cost is reduced to a certain extent.3.The preparation,performance analysis and mechanism of Al-Ga-In₃Sn-NaCl hydrogen-producing alloy were studied.With the doping of NaCl,the effect of adjusting the hydrogen production performance of Al-Ga-In-Sn alloy is obvious.Among them,Al-Ga-In₃Sn-2wt.%NaCl alloy not only has a high hydrogen production rate(96.7%),but also realizes a gentle and stable rate of hydrolysis hydrogen production.The NaCl doped in the alloy is continuously released and dissolved to form ions during the hydrolysis process,which changes the composition of the electrolyte.The Cl^-released when the NaCl attached to the surface of the Al matrix is dissolved helps to accelerate the corrosion of aluminum and advance the peak of the hydrogen production rate.However,as the addition of NaCl increases and replaces more In₃Sn,the total area and number of grain boundary phase particles decrease,which will have a negative impact on the Al-H₂O reaction.Therefore,proper introduction of NaCl can effectively adjust the macroscopic hydrogen production performance of the alloy under the synergistic effect of the galvanic cell activation mechanism.4.The activation energy is related to the melting point,content and quantity of grain boundary phase particles.The activation energy can be used as a basis for the selection of hydrogen-producing alloy materials,which reflects the overall hydrogen-producing performance of the alloy.Based on the comparative analysis results of activation energy,for the bulk alloy of the Al-Ga-In-Sn system,the liquid phase activation mechanism of the low melting point metal plays a key role in the activation of Al,which is far greater than the synergistic effect of the galvanic cell and the dissolved redeposition.From the perspective of synergistic mechanism,the activation effect of galvanic battery is obviously better than that of dissolution redeposition.Based on the traditional Al-based hydrogen-producing alloy reaction model,two types of synergistic activation modes for hydrogen production aluminum alloys,"liquid phase activation and galvanic cell"and"liquid phase activation and dissolution-redeposition"have been developed respectively.The synergistic mechanism of"liquid phase activation and galvanic cell",it is possible to increase the reactivity of Al itself by introducing high electrode potential elements,or to introduce inorganic salts and spontaneously form an ionic electrolyte during the hydrolysis process to accelerate the Al-H₂O reaction;The synergistic mechanism of"liquid phase activation and dissolution-redeposition"can form a solid solution with Al through the introduction of high solid solubility elements,thereby improving the hydrolysis reaction activity of the matrix.After research,the above two methods can effectively improve the hydrolysis performance of the Al-Ga-In-Sn alloy,and appropriately reduce the cost,so that the material shows higher applicability.