First-principles study of adsorption, dissociation and diffusion of hydrogen on α-U (110) surface

According to the equilibrium crystal shape of α-U, the surface of α-U (110) is more stable and has a larger area fraction than that of α-U (001). Therefore, the reaction of H atoms and H₂ molecules on the α-U (110) surface were systematically studied by first-principles calculations. The results show that there are only two stable adsorption sites for H atom: the surface short-bridge site and the subsurface short-bridge site. The adsorption of H₂ molecules is divided into chemical adsorption of dissociated H₂ molecules and physical adsorption of undissociated H₂ molecules and the LB2-ParL adsorption configuration is the most stable adsorption configuration for H₂ molecule adsorption, with an adsorption energy of -0.250 eV. The work function and charge transfer show that adsorption of H atom or H₂ molecule leads to an increase in the work function value of α-U (110) surface, which enhances the electronic stability of the α-U (110) surface. The projected density of states (PDOS) shows that when the H atom or H₂ molecule is close to the α-U (110) surface, the 1s orbital electrons of H atom will hybridize with the 5f/6d orbital electrons of the nearby surface and subsurface U atoms, and new hybridized orbital peaks appear near the -4.5 eV or -7.3 eV energy level. The CI-NEB study shows that the surface free H atoms are very easy to diffuse between the surface short-bridge sites and the subsurface short-bridge sites, but the diffusion between the short-bridge site and the triangular center site is extremely difficult.