Adsorption and diffusion behavior of hydrogen on the M-doped (M=Zr, Mo, Y, Cu, Pd, Ir, Mg, Al, Si) Ti(0001) surfaces: A first-principles study

The adsorption and diffusion behaviors of hydrogen on M-doped Ti(0001) surfaces are investigated by firstprinciples calculations. The surface energies of M-doped surfaces follow the ordering of Mo > Ti > Zr > Cu > Mg > Y > Al > Pd > Ir > Si. In all the M-doped systems, H atom adsorbed at the next nearest neighboring site is more stable than the nearest neighboring site. All involved M dopants prevent the H adsorption at the nearest neighboring site, and the Si dopant has a significant repulsive effect on it. Both the surface stability and H adsorption behavior are interpreted successfully by the doping effects of s-d hybridization (Al, Si), D-band contribution (Pd, Cu, Ir), and the relative electronegativity (Mo, Zr, Y, Mg). H prefers to penetrate from the surface hcp site to the subtet site and finally to the suboct site, except for the Mo-doped and clean Ti surfaces with the path from the surface fcc site directly to the suboct site. Among these dopants, Mo promotes the H in-plane surface diffusion and Pd promotes the H penetration process most significantly.