Hydrogen Generation by the Hydrolysis of MgH 2
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HYDROGEN GENERATION BY THE HYDROLYSIS OF MgH 2 Yu. V. Verbovytskyy,1,2 V. V. Berezovets,1 A. R. Kytsya,1 I. Yu. Zavaliy,1 and V. A. Yartys3
UDC 546.3-19′11
Magnesium hydride ( MgH 2 ) is a hydrogen-rich compound generating significant amounts of hydrogen in the process of hydrolysis, i.e., in the course of its chemical interaction with water or with aqueous solutions. This process is of great interest for the on-site hydrogen generation aimed at application of H 2 as a fuel for PEM fuel cells. We propose a review of recent reference publications in the field and also present the results of our own research. The increase of the rates of H2 release and the completeness of transformation of MgH 2 are two important goals, which can be attained by optimizing the size of the powders of MgH 2 by ball milling, by using catalysts added to MgH 2 and to aqueous solutions, and by increasing the interaction temperature. The effect of these parameters on the degree of conversion and the rates of hydrogen evolution are analyzed in detail and the best systems to reach the efficient hydrolysis performance are identified. The mechanism of catalytic hydrolysis is proposed, while further improvements of the process of hydrolysis are required and additional studies of this important topic are needed. Keywords: hydrogen, magnesium hydride, composites, hydrolysis, hydrogen energy.
Introduction Magnesium hydride ( MgH 2 ) is obtained from magnesium, which is an inexpensive metal abundant on the Earth and characterized by a high theoretical hydrogen storage capacity of 7.6 wt.% H. Hydrogen can be obtained as a result of hydrolysis of MgH 2 , which gives double as much H 2 as compared with Mg according to the reaction:
Mg + 2H 2O = Mg(OH)2 + 2H 2 . The weight yield of released hydrogen is 6.4% when water is taken into account in calculations and even increases up to 15.2% if the water produced by the oxidation of H 2 in a fuel cell is collected and used for hydrolysis. It is worth noting that this reaction has an advantage of producing eco-friendly Mg(OH)2 . When using MgH 2 , the reaction of hydrolysis is rapidly terminated due to the formation of a compact layer of magnesium hydroxide on the surface of the reacting material. Several methods were proposed to increase the yield of hydrolysis [1–23]. The main techniques used for this purpose included ball milling, alloying, modification of the composition of solutions used for hydrolysis, and introduction of catalysts. In the present paper, our aim is to summarize recent advances in the investigations of hydrolysis of MgH 2 -based materials. 1 2 3
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail: [email protected]. Institute for Energy and Technology, Kjeller, Norway.
Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 56, No. 1, pp. 9–20, January–February, 2020. Original article submitted September 10, 2019. 1068-820X/20/5601–0001
© 2020
Springer Science+Business Media, LLC
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YU. V. VERBOVYTSKY
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