Enhanced Hydrogen Generation Properties of MgH2-Based Hydrides by Breaking the Magnesium Hydroxide  Passivation Layer

Minghong Huang,Miaolian Ma,Liuzhang Ouyang,Min Zhu,Ruoming Duan,Lixian Sun,Hui Wang

doi:10.3390/en8054237

Abstract

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH2) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH2 is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH2-based hydrides we investigated three different approaches: ball milling, synthesis of MgH2-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH2/LaH3 composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH2 in pure water. Furthermore, the addition of Ni to the MgH2/LaH3 composite resulted in the synthesis of LaH3/MgH2/Ni composites. The LaH3/MgH2/Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H2 in the first 5 min—than the MgH2/LaH3 composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH2 was also improved by optimizing the solution. The MgH2 produced 1711.2 mL/g of H2 in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%.

Highlights

The global energy crisis and our current ecological problems have stimulated the development of new clean energies [1,2,3,4]
The hydrolysis reaction of MgH2 is interrupted by the formation of a magnesium hydroxide passivation layer
To improve the hydrolysis performance of MgH2-based materials, a composite structure of MgH2 with a different hydride was synthesized through ball milling

Summary

Introduction

The global energy crisis and our current ecological problems have stimulated the development of new clean energies [1,2,3,4]. MgH2-based materials have higher theoretical hydrogen content (15.2%) and Mg element is abundant in the earth’s crust (2.4%) They are low cost, have a high hydrogen yield, and are gentle on the environment, making them a potential candidate for high-quality hydrogen generation material. In order to improve the hydrolysis efficiency and the reaction rate, the main methods such as ball milling, alloying, changing hydrolysis solution composition, catalyst introduction, etc. We review our recent research results about hydrolysis of MgH2-based hydrides and confirm the effect of the ball-milling and catalyst-introducing methods to break the magnesium hydroxide passivation layer to enhance the hydrolysis rate and hydrogen generation yield. It eliminates the introduction of impure gas and byproduct, and simplifies the regeneration process Such a result opens a promising route for improving hydrolysis properties for commercial hydrogen production

Sample Preparation

Hydrolysis Experiment

Sample Characterization

Results and Discussion

Conclusions