R. Lober et D. Hennig, INTERACTION OF HYDROGEN WITH TRANSITION-METAL FCC(111) SURFACES, Physical review. B, Condensed matter, 55(7), 1997, pp. 4761-4765
The interaction of atomic hydrogen with the fcc(111) surfaces of Pd an
d Rh was investigated theoretically with an ab initio method, to find
out the differences and similarities between these neighboring metals.
At the Rh surface the hcp site of the threefold-coordinated adsorptio
n sites is preferred, while at Pd almost no difference between the hcp
and fee sites was found. For Pd, the occupation of subsurface positio
ns was calculated to be more stable than bulklike positions. The energ
y gain caused by hydrogen absorption in subsurface positions is only a
bout 100 meV lower than for hydrogen adsorption at the surface. In con
trast, for Rh, significant differences between adsorption and absorpti
on were calculated. The diffusion barrier for hydrogen diffusion from
surface to subsurface positions was calculated and compared to the dif
fusion barrier in bulk. The hydrogen-induced work-function changes for
the considered 4d transition-metal surfaces were positive for coverag
e theta=1.