Construction Of Hydrogen Generation System Of Al-Bi/Carbon Nanotubes Or Al-Bi Containing Compounds And Mechanism Study

In this thesis,Al-Bi-CNTs,Al-BiOX(X=F,Cl,Br,I)and Al-Bi₂O₂CO₃,with good performances of hydrogen generation and antioxidant ability,have been prepared by combining ball-milling and spark plasma sintering.Their hydrogen generation performances are evaluated.Meanwhile,the hydrogen production mechanisms are also studied by XRD,SEM-EDS,TEM-SAED,XPS,and so on.Firstly,Al-Bi-CNTs material has been prepared combined ball-milling and spark plasma sintering.And it can be found that the Al-Bi-CNTs become to bulk material from powder.The results show that Al-3 wt%Bi-5 wt%CNTs bulk material has the best hydrogen generation performance,that is its volume of hydrogen generation and maximum hydrogen generation rate are 1182.4 mL·g^-1and 971.6 mL·g^-1·min^-1,respectively.It is superior that of Al-3 wt%Bi-5 wt%CNTs powder(such as 576.8 mL·g^-1).Meanwhile,the antioxidant ability of bulk material is significantly improved.For example,the conversion yield of the bulk material is 65.8%of its initial value after leaving in the air for 20 days;but it is only 11.0%for its powder material.The mechanism study shows that spark plasma sintering process can break the alumina inert film of aluminum,increase defects in Al crystals.Theoretical calculation demonstrates that the activity of Al is enhanced through increasing the lattice constant of Al in SPS process.In this process,part of Bi and CNTs fill in the crack of Al and another is on the surface of Al.the corrosion cell of Al-Bi and Al-CNTs form when the Al-3 wt%Bi-5 wt%CNTs bulk contacts water;at the same time,CNTs with good electrical conductivity can also enhance electronic transport in the hydrolytic process.Then,BiOF,BiOBr and BiOI were synthesized by solution method,and Al-BiOX(X=F,Cl,Br,I)composite have been prepared by ball-milled.The results show that the BiOX(X=F?Cl?Br?I)can greatly improve the hydrogen generation performance of Al.And the hydrogen generation performance of these composite obtained in the order of BiOF,BiOCl,BiOBr and BiOI is enhanced successively.Among them,Al-BiOI has the best hydrogen generation performance.When the doping amount of BiOI is 15 wt%,the volume of hydrogen generation and the maximum hydrogen generation rate are respectively 1101.6 mL·g^-1and 3451.8 mL·g^-1·min^-1,which is better than the hydrogen generation performance of Al-BiOCl^[86](1058.6 mL·g^-1and 491.4 mL·g^-1·min^-1).The mechanism study shows that BiOI will react with Al to produce Bi and Bi₂O₃during ball-milled process.That is four active sites of fresh surface of Al,Al-Bi,Al-Al I₃and Al-Bi₂O₃are produced,that greatly improved the hydrogen generation performance of Al-BiOI composite.Finally,Bi₂O₂CO₃,4Bi NO₅H₂·BiO(OH)and BiOHSO₄·H₂O are selected as additives,combined ball-milled and spark plasma sintering to prepared the Al-based bulk materials.The results show that Al-Bi₂O₂CO₃has the best hydrogen generation performance.The conversion yield and maximum hydrogen generation rate are 94.9%and 384.6mL·g^-1·min^-1.After early stage of rapid hydrogen production,the Al-Bi₂O₂CO₃releases hydrogen for 245 min at a rate of 3.5 mL·g^-1·min^-1,it is superior to Al-3wt%Bi-5wt%CNTs,which releases hydrogen for 225 min at a rate of 2.0 mL·g^-1·min^-1.Mechanism study shows that Bi₂O₂CO₃decomposes into Bi₂O₃and CO₂,and Bi₂O₃reacts with Al in situ to produce Bi and Al₂O₃under the spark plasma sintering process.The CO₂can create a large number of pores in the bulk material under the action of sintering pressure,and porous Al-Bi₂O₂CO₃bulk material is obtained.The hydrogen generation performance of Al-Bi₂O₂CO₃ bulk material has been greatly improved under the synergistic effect of these factors.