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Quantum instanton evaluations of surface diffusion, interior migration, and surface-subsurface transport for H/Ni
1Department of Chemistry, State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China.
The Journal of Chemical Physics
|February 16, 2010
Summary
This study explores hydrogen diffusion in nickel using quantum mechanics. Hydrogen enters bulk nickel more easily from fcc sites, and its diffusion mechanism changes with temperature.
Area of Science:
- Computational Chemistry
- Materials Science
- Surface Science
Background:
- Understanding hydrogen diffusion in metals is crucial for catalysis and energy applications.
- Nickel is a key material in many catalytic processes involving hydrogen.
Purpose of the Study:
- To investigate the dynamics of hydrogen diffusion on and within nickel lattices.
- To elucidate the influence of lattice vibrations and site-specific binding on hydrogen mobility.
Main Methods:
- Utilized the quantum instanton approximation combined with path integral Monte Carlo and adaptive umbrella sampling.
- Calculated free energy profiles, temperature-dependent rates, and diffusion coefficients for various hydrogen migration pathways.
Main Results:
- Hydrogen diffusion on Ni(111) is minimally affected by nickel atom motion.
- Hydrogen preferentially diffuses into bulk nickel from the fcc site compared to the hcp site.
- Lattice relaxation significantly lowers energy barriers, except for surface diffusion.
- Quantum lattice atom motion slightly impacts free energy but reduces rates by 20-40% at 300 K.
Conclusions:
- The study reveals distinct pathways and energy landscapes for hydrogen migration in nickel.
- Temperature-dependent instability of hydrogen in subsurface and interior sites suggests a variable reaction mechanism.
- Quantum effects of lattice atoms play a role in hydrogen diffusion kinetics, particularly at lower temperatures.
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