Hydrogen storage capacity of NH۲Be+, NH۲Li+, NH۲Sc+, NH۲Ti+, NH۲V+ and NH۲Ca+ complexes: a first-principles outlook

Hydrogen is the third most abundant element on the Earth's surface. Its potential as a fuel for hydrogen storage has garnered significant interest from researchers in recent years, owing to its unique properties as a renewable energy carrier, safety, and suitability as an ideal fuel. Hydrogen has the potential to replace fossil fuels, which contribute to air pollution and degrade the valuable ozone layer. This work presents the hydrogen storage capacity of NH۲M+ complexes, where M represents Be, Li, Sc, Ti, V, and Ca. The study employs density functional theory (DFT) and second-order Møller-Plesset (MP۲) methods, and also utilizing the wB۹۷XD functional and the ۶-۳۱++G(d,p) basis set within the Gaussian۰۹ code. The results indicate that the NH۲Be+, NH۲Li+, NH۲Sc+, NH۲Ti+, NH۲V+, and NH۲Ca+ complexes can interact with a maximum of three, five, six, six, five, and eight H۲ molecules, respectively, yielding gravimetric hydrogen uptake capacities of ۱۹.۳%, ۳۰.۳%, ۱۶.۴%, ۱۵.۸%, ۱۲.۹%, and ۲۲.۲%. Notably, the hydrogen uptake capacities for all complexes studied exceed the target established by the U.S. Department of Energy, which is ۵.۵ wt% by ۲۰۲۵. Based on Gibbs free energy-corrected adsorption energy plots, we conclude that H۲ adsorption on the NH۲Be+, NH۲V+, and NH۲Ti+ complexes is thermodynamically and energetically favorable at room temperature across a wide range of pressures and temperatures, from ۵۰ K to ۴۰۰ K and ۵۰ atm to ۴۰۰ atm. Conversely, the adsorption of H۲ on the NH۲Li+, NH۲Sc+, and NH۲Ca+ complexes is favorable only at temperatures below ۸۵ K, ۱۳۵ K, and ۷۵ K, respectively. The desorption temperature for the NH۲Ti+ complex, measured at ۳۲۹ K at the wB۹۷XD/۶-۳۱++G(d,p) level, indicates that it is thermodynamically favorable under ambient conditions. In contrast, the high desorption temperatures for the NH۲Be+, NH۲Sc+, NH۲Ti+, and NH۲V+ complexes reflect their strong interactions with H۲ molecules in comparison to other NH۲M+ complexes. In summary, the NH۲Be+, NH۲V+, and NH۲Ti+ complexes are promising candidates for hydrogen storage applications.

کلیدواژه ها:

Hydrogen storage ، Amide ، DFT and MP۲ ، Desorption temperature