Hydrogen diffusion into the subsurfaces of model metal catalysts from first principles

Area of Science:

• Surface Science
• Heterogeneous Catalysis
• Computational Chemistry

Background:

• Atomic hydrogen diffusion on catalyst surfaces is crucial for hydrogenation reactions.
• Understanding these pathways informs the design of novel catalysts.
• Previous studies have explored various aspects, but detailed pathway analysis across multiple transition metals is needed.

Purpose of the Study:

• To investigate and detail the diffusion pathways of atomic hydrogen on seven different model catalyst surfaces (Co, Ni, Pd, Pt, Cu, Ag, Au) and into their subsurfaces.
• To construct potential energy surfaces (PESs) for accurate modeling of hydrogen diffusion.
• To identify minimum energy diffusion pathways and analyze the influence of substrate relaxation.

Main Methods:

• First-principles calculations using ab initio density functional theory (DFT).
• Construction of thirteen potential energy surfaces (PESs) by interpolating DFT energy points.
• Global search for minimum energy diffusion pathways using a mesh method.
• Comparison with results from the nudged elastic band (NEB) method.

Main Results:

• Detailed diffusion pathways for atomic hydrogen on thirteen different transition metal crystal surfaces (Co(001), Ni(100)/(111), Pd(100)/(111), Pt(100)/(111), Cu(100)/(111), Ag(100)/(111), Au(100)/(111)) were identified.
• Potential energy surfaces (PESs) were constructed and used to accurately model hydrogen diffusion, showing excellent agreement with the nudged elastic band (NEB) method.
• Substrate relaxation was found to significantly decrease diffusion barriers for hydrogen entering catalyst subsurfaces.

Conclusions:

• The study provides a comprehensive understanding of atomic hydrogen diffusion mechanisms on various transition metal surfaces and into subsurfaces.
• Subsurface hydrogen diffusion is influenced by substrate relaxation, lowering energy barriers.
• The residual energy of subsurface hydrogen emerging onto the surface contributes to the high reactivity of subsurface species.