A group of academics has discovered a major stumbling barrier in the development of a standard solid-state hydrogen storage material, clearing the path for future design guidelines and broad commercial usage. Their results were detailed in the Journal of Materials Chemistry A, where the research was highlighted on the front cover. Hydrogen will be critical in powering our future. It is plentiful and has no hazardous pollutants when burnt. However, storing and transporting hydrogen is both expensive and unsafe.
There are currently three ways for storing hydrogen: high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and solid-state hydrogen storage. Solid-state materials are typically the safest and have the highest hydrogen storage density among solid-state hydrogen storage technologies.
Metal hydrides have long been studied due to their high hydrogen storage capacity and inexpensive cost. Hydrogen is absorbed onto the surface of certain metals when they come into contact with gaseous hydrogen. Further energy input causes hydrogen atoms to enter the metal’s crystal lattices, causing the metal to become hydrogen-saturated. From then, the substance may absorb and desorb more hydrogen.
Magnesium hydride (MgH2) has showed great potential in terms of better hydrogen storage capacity. However, for MgH2 to breakdown and create hydrogen, a high temperature is required. Furthermore, the material’s complicated hydrogen migration and desorption, which results in slow dehydrogenation kinetics, has hampered commercial adoption.
Scientists have been debating why MgH2 dehydrogenation is so difficult for decades. However, the study team has discovered a solution.
They discovered a “burst effect” during MgH2 dehydrogenation using calculations based on spin-polarized density functional theory with van der Waals corrections. The initial dehydrogenation barriers were 2.52 and 2.53 eV, respectively, whereas the succeeding reaction barriers were 0.12-1.51 eV. The researchers performed further bond analysis using the crystal orbital Hamilton population approach, confirming that the magnesium-hydride bond strength dropped as the dehydrogenation process progressed.
“After the first burst effect, hydrogen migration and desorption are significantly simpler,” says Hao Li, associate professor at Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR) and corresponding author of the work. “Structural engineering modifications that facilitate this desorption process may be the key to promoting MgH2 hydrogen desorption.”
When the initial layer of atomic hydrogen exists, Li and his colleagues proved that hydrogen vacancies retain a high degree of electronic localisation. Additional evidence was supplied by ab initio molecular dynamics simulations of the kinetic properties of MgH2 following surface dehydrogenation.
“Our results establish a theoretical foundation for the dehydrogenation kinetics of MgH2, giving crucial suggestions for redesigning MgH2-based hydrogen storage materials,” Li adds.
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