The Preparation And Application Of Al-based Micro/Nano Composite Materials For Hydrogen Generation In Pure Water

The hydrogen ec onomy has been identified as an alternative to substitute the non-sustainable fossil fuel based economy. Ongoing research is underway to develop environmentally friendly and economical hydrogen production technologies that are essential for the hydrogen economy. One of the promising ways to produce hydrogen is to use aluminum or its alloys to reduce water to hydrogen. In this article, a kind of environment-friendly Al-based composite materials, Al-Ce and Al-BiCl3composite, has been developed via a convenient ball milling method. The two kinds of hydrogen production materials are based on a different activation mechanism. The positive effect of cerium is explained in the following two points:Firstly, cerium can damage the dense oxide layer of aluminum during the ball milling process. Secondly, cerium has an important influence on the morphology of the products generated in the reaction of Al-Ce composites with water. Using BiCl3as na no-miller causes the aluminum particles to reach smaller sizes in Al-BiCl3composite materials. Also, because of salt, there is a little chance foraluminum particlesto meet and cold-weld. Meanwhile, the Biis relatively uniformly distributed into the Al, resulting in the creation of more microgalvanic cellsbetween Al and dispersed Bi elements. Based on these theories, the structures and properties of as-prepared materials were thoroughly characterized using FESEM, XPS, XRD and BET, respectively. The results are summarized as follows.（1） Al-Ce composite materials have been prepared by the ball-milling method. The as-prepared Ce activated Al-Ce composite materials can produce hydrogen completely and quickly in pure neutral water. Typically, Al-13wt%Ce has a total production of1134mL/g and a conversion yield of92.42%within60minutes. Adding Ce plays a critical role in increasing the activity of Al-Ce composite. Firstly,Ce can damage the oxide layer much more effectively through theoxidation and reduction reaction during the ball-milling process.Secondly, Al-Ce composite layer can generate porous and flake oxideproducts and keep inside Al continuing to react with water. In addition,effects of the milling time and the additions of the chlorides （NaCl andKCl） on the Al-Ce composite reactivity have been investigated. Theaddition of chlorides can further prevent products deposition andaccelerate the reaction rate, such as Al-5wt%Ce-10wt%KCl has a totalproduction of1101mL/g and a conversion yield of93.86%.（2） Al-BiCl₃composite materials. Due to their brittle nature, saltparticles are fractured during milling and their sharp edges chopaluminum particles into pieces. This leads to an increment in hydrolysiskinetics. Meantime, the displacement reaction in the Al-BiCl₃systemproduces metal Bi. Al-10wt%BiCl₃has a total production of1201mL/gand a conversion yield of98.20%within60minutes. In addition, effectsof the milling time and the additions of the chlorides （NaCl and NaBH4）on the Al-BiCl₃composite reactivity have been investigated. Withincreasing milling time, the hydrogen generation rate and the hydrogenproduction of Al-10wt%BiCl₃composite are improved. The addition ofchloride evidently improves reaction rate and hydrogen production ofthe composites. Brittle addition plays a role of nano-miller in the processof ball milling. When the composite continuously reacts with water,causing more corrosion pits, and micro hydrogen bubble graduallyforms under the aluminum oxide layer. These micro hydrogen bubblescan break down the aluminum oxide layer, resulting in the continuousreaction of aluminum with water， such as Al-5wt%BiCl₃-5wt%NaBH4hasa total production of1351mL/g and a conversion yield of99.93%.