Abstract
Magnesium hydride (MgH2) is one of the competitive hydrogen storage materials on account of abundant reserves and high hydrogen content. The hydrolysis of MgH2 is an ideal and controllable chemical hydrogen generation process. However, the hydrolyzed product of MgH2 is a passivation layer on the surface of the magnesium hydride, which will make the reaction continuity worse and reduce the rate of hydrogen release. In this work, hydrogen generation is controllably achieved by regulating the change of the surface tension value in the hydrolysis, a variety of surfactants were systematically investigated for the effect of the hydrolysis of MgH2 In the meantime, the passivation layer of MgH2 was observed by scanning electron microscope (SEM), and the surface tension value of the solution with different surfactants were monitored, investing the mechanism of hydrolysis adding different surfactants. Results show that different surfactants have different effects on hydrogen generation. The hydrogen generation capacity from high to low is as follows: tetrapropylammonium bromide (TPABr), sodium dodecyl benzene sulfonate (SDBS), Ecosol 507, octadecyl trimethyl ammonium chloride (OTAC), sodium alcohol ether sulfate (AES), and fatty methyl ester sulfonate (FMES-70). When the ratio of MgH2 to TPABr was 5 : 1, the hydrogen generation was increased by 52% and 28.3%, respectively, at the time of 100 s and 300 s. When hydrolysis time exceeds 80 s, the hydrogen generation with AES and FMES-70 began to decrease; it was reduced by more than 20% at the time of 300 s. SEM reveals that surfactants can affect the crystalline arrangement of Mg(OH)2 and make the passivation layer three-dimensionally layered providing channels for H2O molecules to react with MgH2.
Highlights
With the rapid development of industrial technology, the global demand for energy is growing exponentially
Eliminating the cladding effect of magnesium hydroxide passivation layer on MgH2 has become an urgent problem to be solved in the hydrogen yield of hydrolysis [23]
The reaction system is composed of a 250 mL three-necked flask, a condenser, a thermometer, and a water bath; the metering system is composed of a gas washing bottle, a beaker, and an analytical balance
Summary
With the rapid development of industrial technology, the global demand for energy is growing exponentially. The magnesium hydroxide is difficult to dissolve in water whose solubility product is 5:6 × 10−12 mol3 · L−3 It forms the passivation layer during the hydrolysis process, prevents the diffusion of water molecules toward the surface of magnesium hydride, reduces the rate, and shortens the duration of hydrolysis reaction [20–22]. Eliminating the cladding effect of magnesium hydroxide passivation layer on MgH2 has become an urgent problem to be solved in the hydrogen yield of hydrolysis [23]. Based on the above principles, this study selected several typical surfactants to study the influence on the quantity of hydrogen generation and the rate of hydrogen generation These data were combined with the surface tension value of the aqueous solution and the scanning electron micrograph of the product to analyze the corresponding mechanism. The study of interface control in this work provides the theoretical basis for the future researches of H2 generation by hydrolysis of MgH2
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