Hydrogen atom absorption in hydrogen-covered Pd(110) (1 × 2) missing-row surface

•We report absorption of H atom in H-covered Pd(110) (1 × 2) missing-row surface.•H atom is adsorbed on ridge- and trough-site of the missing-row surface.•Absorption of H atom is assisted by approaching H atom from vacuum.•H2 dissociation is rate-limiting step while assisted absorption is non-activated.

The absorption of H atom in H-covered Pd(110) (1 × 2) missing-row surface is investigated using density functional theory based calculations. For 1.5 monolayer H coverage, interaction among the adsorbed H atoms is found to be negligible and was verified by analyzing the electronic structure of the system and by comparing the calculated binding energies with low H coverage case. Neither the monoatomic absorption of H nor the assistance from the initially adsorbed H atom explains the experimentally observed presence of subsurface H in Pd(110) at high H coverage. Instead, H absorption is realized through the assistance of incoming H atoms from vacuum. The absorption of H in the H-covered surface is non-activated while the dissociation of H2 is the rate-limiting process. Dissociation on ridge site is energetically more preferred than on trough site and the difference in the activation barrier is elucidated by investigating the electronic structures of the system.