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H2 Dissociation on H‑Precovered Ni(100) Surface: Physisorbed State and Coverage Dependence
journal contribution
posted on 2019-02-13, 00:00 authored by Ying He, Wenji WangHydrogen molecule
dissociation on metal surfaces is a prototypical
reaction for investigating the gas–surface interaction. To
investigate the effect of lattice motion, the embedded cluster model
is adopted to construct the quantum Ni(100) lattice, in which 11 Ni
atoms are treated quantum mechanically. The direct and steady-state
dissociation rates of H2 on H-precovered Ni(100) surface
are calculated by quantum instanton method. Both the direct and steady-state
dissociation rates on H-precovered Ni(100) are smaller than those
on the clean Ni(100). This is because the repulsive interaction between
H2 and the preadsorbed H raises the potential energy barrier.
Moreover, this repulsive interaction is inversely proportional to
the distance between H2 and the preadsorbed H. Owing to
the classical relaxation and entropy effect of Ni atoms, the lattice
motion promotes H2 dissociation by lowering the free-energy
barrier but it hinders H2 recombination by raising the
free-energy barrier. There are remarkable kinetic isotope effects
for the dissociation process, which is due to the entropy and quantum
tunneling effects. However, no kinetic isotope effect is obtained
for the recombination process.