Enhancing the hydrogen storage properties of (Ti, M)C1−x materials (M = W, Mg, Ni, and Al) depends on the carbon vacancies: Potential for the recycling of scraps

Abstract

New energy storage systems and recycling schemes are required to solve the increasing environmental and energy problems. Owing to the increasing cost of raw materials, scraps need to be recycled. Carbides can be used as hydrogen storage materials; however, their mechanical properties remain unclear. To fabricate high-quality carbides from scraps as potential candidates for hydrogen storage materials, it is necessary to understand the mechanical properties of the carbides when absorbing hydrogen atoms. In this study, we evaluated the thermodynamic stabilities, mechanical properties, and electronic structures of (Ti, M)C1-x materials (M = W, Mg, Ni, and Al, x=0–1. The effects of the carbon vacancies were examined using density functional theory calculations. Based on the results, the TiC0.625 composition was stable at ambient temperature and pressure. Titanium carbides have shown potential for use in hydrogen storage applications at 0≤x≤0.375, as the hardness decreases rapidly when x≥0.375. In addition, the results indicate that (Ti, Al)C should mainly be used in the target hydrogen storage materials at a composition below x=0.25. These findings support the design of hydrogen storage materials based on recycled carbides.