First-principles Investigation On Hydrogen Desorption Properties Of Doped LiNH₂ And Li₄BN₃H₁₀ Systems

The thermodynamic and hydrogen desorption properties of Li NH2 and Li4BN3H10 doped with catalysts have been investigated by first-principles calculations based on density functional theory. The work focuses on studying the effect of cation doping, anion doping and co-doping on the thermodynamic properties of the hydrides by calculating their formation and substitution enthalpies. At the same time, the diffusion processes of anion Cl into the hydride lattices are also investigated to interpret the difference of reduced dehydrogenation temperature of the doped hydrides found in experiments.The results are presented in the following:(1) By studying the thermodynamic properties of Ti-doped Li NH2 and Ni-doped Li4BN3H10, it is found that the stability of the doped Li NH2 and Li4BN3H10 decreases and it is easier for hydrogen to release from the hydrides.(2) By investigating the thermodynamic properties of Cl-doped Li NH2 and Li4BN3H10, it is shown that the resulting increased stability of the doped Li NH2 and suppresses the release of hydrogen from the hydrides.(3) Based on the above analysis, our study finds that the cation and anion co-doping on hydrides can compensate for the deficiencies of the cation or anion single doping. The co-doping not only increases the stability of the hydrides but also improves their hydrogen desorption properties.(4) By calculating the diffusion barrier of anion Cl into Li NH2 and Li4BN3H10, it is revealed that Cl diffuses into the host Li NH2 lattice with lower diffusion barrier while its diffusion into the host Li4BN3H10 lattice needs higher diffusion barrier, which interprets the difference of reduced dehydrogenation temperature of the doped hydrides found in experiments. Thus, not only reaction thermodynamics, but diffusion kinetics plays an important role in the dehydrogenation process as well.