Investigation on hydrogen production using multicomponent aluminum alloys at mild conditions and its mechanism
Highlights
► Al was activated using Ga, In, Sn for hydrogen generation with water. ► The activity of Al was related to the alloy elements, amount and composition. ► Al–3%Ga–3%In–5%Sn shows high reactivity at room temperature with tap water. ► Hydrogen conversion efficiency for activated Al–3%Ga–3%In–5%Sn alloy is nearly 100%. ► Highest hydrogen generation rate can reach 1560 mL/g min.
Introduction
The depletion of fossil fuel and environmental problems arising in the global has promoted an urgent demand for the clean and renewable energy supply nowadays. Among different fuels, hydrogen power has proved to be the cleanest and the most likely alternative energy to replace fossil fuel. In the past two decades, several methods including biological [1], water electrolysis [2], [3], water splitting [4], and steam/partial oxidation [5], [6] have been developed to produce hydrogen. However, the low conversion efficiency, high cost, non-clean preparation process, as well as the transportation and storage of hydrogen limited their applications. Recently, a method based on the interaction of lightweight metals and their hydrides with water for hydrogen generation has attracted more and more attention. It is considered as the most perspective and close to practical realization [7]. Among these substances, Al is the most potential candidate material for hydrogen generation as it is cheap, available, environmentally safe, and usable as the hydrogen generator for portable devices. In addition, the reactants of hydrolysis reaction of Al can be easily cycled via the Hall–Héroult process [8].
However, it is known that the thin oxide layer formed on the Al surface can prevent the interaction between Al and water, which inhibits the hydrogen generation. As a result, pure Al couldn't produce hydrogen at mild conditions, such as at room temperature or using neutral water. It was reported that Al could react with water to produce hydrogen with the assistance of alkaline [9], [10], [11] or at elevated temperature [12], [13]. However, the harsh condition can damage the apparatus where the reaction occurs, which makes it not suitable for portable and household applications. Therefore, it is important to study the methods using activated Al alloys to produce hydrogen at mild conditions.
At present, two methods have been developed to fabricate this kind of activated Al alloys. One way is to use mercury to moisten the surface of Al. The amalgamation effect between Al and mercury could prevent the formation of oxide layer on the surface [14], [15]. However, the mercury is very toxic and unsafe to people. The other way is to add low melting point metal, such as Ga, In, Zn, Sn, and Bi into Al [16], [17], [18], [19], [20], [21], [22]. Kravchenko et al. [17] found that the Al alloy containing Ga, In, Zn, Sn prepared by melting method could react with hot water at 75–82 °C. However, the Al alloy couldn't react with water at room temperature. Fan et al. [18] prepared Al–Bi (10%–30%Bi) alloy using mechanical alloying method. It was found that the Al–Bi alloy has higher reactivity than that prepared by the melting method. The addition of Bi could significantly enhance the reactivity of Al with water at room temperature. However, the activated Al alloy are expensive due to the high content of Bi and the rather low reaction rate at room temperature. In order to decrease the usage of low melting point metals, especially Ga and In, A.V. Ilyukhina et al. [22] prepared 2–3 wt.% gallium alloy (gallam) and found there was hydrogen produced at room temperature 20–25 °C. However, the hydrogen yields only reached 50–55% of the theoretical value. Furthermore, the gallam was fabricated before mechanical alloying, which increases the complexity and the cost of activated Al alloys. Thus how to increase the hydrogen conversion efficiency at mild conditions and simultaneously decrease the amount of Ga and In is still a challenging task.
In this work, we fabricated different Al alloys using Ga, In, Sn as alloy elements by mechanical alloying method. The hydrogen yields, generation rate and conversion efficiency at mild conditions were investigated. The phase compositions, morphologies of different aluminum alloys, and its reaction products were characterized. Through the analysis of hydrogen production property and the microstructure characteristics, the mechanism for activating Al was discussed.
Section snippets
Experimental
Al (200 mush, 99.99 wt.%), Ga (99.8 wt.%), In (200 mush, 99 wt.%), Sn (200 mush, 99.9 wt.%) were used as starting materials. The powders with different alloy elements and weight ratio were mixed and filled in an argon-filled glove box. The mechanical alloying was performed in planetary ball miller. The ball-to-powder ratio and milling time was set as 10:1 and 6 h, respectively. The products were stored in argon-filled specimen bottles at room temperature.
The hydrolysis reaction test was carried
Binary aluminum alloy
Binary Al alloys including Al–Ga, Al–In, and Al–Sn have been prepared. The content of alloy elements was 3 wt.%, 5 wt.%, 7 wt.%, and 10 wt.%, respectively. The corresponding hydrolysis ability of these Al alloys was examined in tap water at room temperature. The experiments revealed that no hydrogen yields were obtained, which indicated that single Ga, In, Sn alloy element couldn't activate Al to produce hydrogen at mild conditions in this experiment.
Ternary aluminum alloy
In order to further activate Al, ternary Al
Conclusions
Different Al alloys were fabricated using Ga, In, Sn as alloy elements by mechanical alloying method in this work. The hydrogen production property of activated Al with water was studied at room temperature. It was found that the final hydrogen production of activated Al depends on alloy elements, amount and composition.
For Al–Ga, Al–In, Al–Sn, and Al–Ga–Sn alloys, no hydrogen is produced at room temperature in tap water when the alloy elements weight ratio is less than 10%. However, Al–Ga–In
Acknowledgment
The authors gratefully acknowledge the financial support of Major State Basic Research Development Program of China (973 Program, 2010CB635107), the National Natural Science Foundation of China (No. 51202064, No. 51004046 and No. 51075129), and the National Natural Science Foundation of Hubei province of China (No. 2010CDB05806).
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