Study On Bi And Bi₂O₂CO₃ For The Preparation Of Al-based Hydrogen-producing Materials

Hydrogen energy is regarded as the most potential clean energy in the 21st century.But hydrogen is easy to leak,small density,flammable and explosive,making it difficult to store and transport,which greatly restricts the development of hydrogen energy industry.One of the effective ways to solve the problem of hydrogen storage and transportation is to develop a hydrogen production material which is convenient for storage and transportation,high hydrogen production efficiency and environmental protection as mobile hydrogen source.It is considered to be a promising technology to produce hydrogen on demand in real-time by using the properties of aluminum or aluminum-based composite reacting with water.In this paper,a series of Al-based hydrogen-producing materials were prepared by mechanical ball milling and using inexpensive bismuth and sodium chloride as active agents.The effects of ball milling time and the content of active agent on the hydrogen generation performance of composites were systematically studied.Al-4%Bi-4%NaCl composite with the best hydrogen production efficiency was obtained under the parameters of ball milling time of 11 h and the content of bismuth and sodium chloride of 4%.The composite produced1156 mL g^-1 of H₂ in 1 h,and the hydrogen conversion rate was 92.5%.The mechanism of bismuth activating aluminum was explored.The test results showed that the activation of aluminum mainly comes from the following three reasons:?1?the formation of micro-galvanic cell between aluminum and bismuth during hydrolysis process accelerates the aluminum corrosion;?2?the brittle and hard bismuth will cause enough defects inside the aluminum powder during ball milling process,thereby increasing the activity of aluminum;?3?The addition of bismuth causes a large negative shift in the electrode potential of aluminum powder,making aluminum more easily oxidized.Under the synergistic effects of these aspects,the activity of aluminum is greatly improved,so it can be rapidly hydrolyzed to produce hydrogen at room temperature.Bi₂O₂CO₃ was found in the by-product of hydrolysis of Al-4%Bi-4%NaCl composite.After further understanding of the properties of Bi₂O₂CO₃,an attempt was made to use Bi₂O₂CO₃ as an active agent to prepare hydrogen-generating materials.The hydrolysis experiment shows that the Al-15%Bi₂O₂CO₃ composite prepared by ball milling can produce hydrogen rapidly at room temperature.The results of phase characterization show that with the decomposition of Bi₂O₂CO₃ in the ball milling process,Bi and Al₂O₃ are formed in situ.Al₂O₃ can effectively prevent agglomeration between Al-Bi,Al-Al,and Bi-Bi.In synergy with the active agent of bismuth,the activity of aluminum is greatly improved.On this basis,the effects of NaCl,AlCl₃,Na₂CO₃,CaO on the hydrogen production performance of the composite were studied.It was found that the addition of NaCl and AlCl₃ can significantly improve the activity of the composite.At 30°C,the maximum hydrogen generation rates of Al-15%Bi₂O₂CO₃-5%NaCl and Al-15%Bi₂O₂CO₃-5%AlCl₃ were 34.5 mL g^-1 s^-1 and32.5 mL g^-1 s^-1.In order to study the hydrolysis kinetics,the activation energies of Al-15%Bi₂O₂CO₃-5%NaCl and Al-15%Bi₂O₂CO₃-5%AlCl₃ composites were calculated by Arrhenius formula,which were 9.43 KJ mol^-1 and 6.87 KJ mol^-1 respectively.The lower activation energies suggested that the composites could react with water rapidly at low temperature.However,hydrogen-generating materials would gradually lose their activity when exposed to air,and vacuum packaging could effectively maintain their activity.