Hydrogen Storage in Magnesium-Based Metal Hydride Alloys and Theoretical Design of a Storage Tank for Magnesium Alloys
Abstract
The article addresses the issue of hydrogen storage in magnesium-based metal hydride alloys, the kinetic properties of various magnesium hydrides, and the potential applications of these metal hydride alloys in the transportation sector. The article also includes a theoretical design of an atypical metal hydride storage tank that uses magnesium-based alloys.
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Introduction
Hydrogen is receiving increasing attention both in Europe and around the world. The most important aspect is the fact that the energy recovery of green hydrogen in fuel cells does not produce any emissions into the atmosphere. It therefore represents a possible solution for partially decarbonizing industrial processes and economic sectors.
In the area of transport infrastructure, it is necessary to focus on alternative propulsion fuels and systems that are derived from renewable energy sources. Naturally, these systems will also contribute to the reduction of greenhouse gases. Currently, two technological platforms appear to be long-term fuel sources, namely electromobility and hydrogen-based transport systems. Slovakia has committed to ensuring that more than 20% of vehicles in public administration should be emission-free by 2021. Today, several EU member states, as well as other developed economies—such as the United States and Japan—are testing the possibilities of using hydrogen technologies in both individual and public transport through the implementation and deployment of hydrogen-based vehicle solutions. One of the key challenges is improving the safety of hydrogen fuel storage. At present, hydrogen fuel is stored at extremely high pressures of 35–95 MPa, which poses a safety risk.
Solid-state hydrogen storage materials, primarily metal hydrides, have proven to be promising candidates for storage applications due to their high volumetric density, low operating pressure—ranging from 1 bar to 3 MPa, which is significantly lower than that of high-pressure systems—and, last but not least, their high safety.
Conclusion
This article addresses the issue of hydrogen storage in magnesium-based metal hydride alloys. The advantage of this type of storage is their significantly higher hydrogen storage capacity—reaching values of up to 7.6 wt.%—compared to the most commonly used AB₅-type alloys based on Ti-Fe, which only offer a storage capacity of around 1.5 wt.%.
The biggest drawback of this form of hydrogen storage is that, for example, in the case of the binary magnesium hydride MgH₂, hydrogenation and dehydrogenation occur at very high temperatures, typically from around 300 °C. Therefore, it is necessary to design an efficient system to heat the storage tank to the required operating temperatures.
This article also includes a theoretical design of a metal hydride storage tank that utilizes magnesium-based alloys. The tank consists of two seam-welded tubes. A smaller-diameter tube is placed concentrically inside a larger-diameter tube. The pair of tubes is joined by an atypical bottom so that a flue gas pipe, directly connected to an internal combustion engine, can be routed through the inner tube. The exhaust gases flowing through the pipe will heat the alloy stored in the tank. This heating of the selected magnesium alloy with exhaust gases to the desired temperature is necessary to reach sufficient temperatures for hydrogen absorption into the structure of the magnesium alloy.
Subsequently, a static analysis of the atypical storage tank was performed to assess its strength characteristics at an operating temperature of 250 °C and an operating pressure of 3 MPa. Based on the analysis, it was determined that the tank meets the required operational parameters. The next step in the research will be the analysis of material creep under cyclic loading and the subsequent optimization of structural parameters.