Accelerating Dynamics of H on Graphene by Coadsorbates

Area of Science:

• Surface Science
• Computational Chemistry
• Materials Science

Background:

• The dynamics of adsorbed atoms on surfaces are crucial for catalysis and materials science.
• Understanding hydrogen diffusion on carbon surfaces, like graphene, is essential for various applications.
• Factors influencing hydrogen atom mobility require detailed investigation.

Purpose of the Study:

• To investigate the effect of coadsorbed molecules on the diffusion dynamics of hydrogen atoms on graphene.
• To quantify the changes in hydrogen diffusion barriers in the presence of various H-containing molecules.
• To elucidate the mechanisms behind the observed changes in diffusion barriers.

Main Methods:

• Density functional theory (DFT) calculations were employed to model hydrogen adsorption and diffusion.
• Calculations focused on the diffusion of hydrogen atoms on a graphene surface.
• The influence of coadsorbed species, including water, ammonia, hydrogen fluoride, hydrogen sulfide, arsine, and phosphine, was systematically studied.

Main Results:

• The diffusion barrier for hydrogen on pristine graphene was calculated to be 0.94 eV.
• Coadsorption with water reduced the barrier to 0.85 eV, while ammonia reduced it significantly to 0.12 eV.
• The substantial reduction with ammonia was linked to the formation of a stable NH₄ intermediate state.
• Other coadsorbates like hydrogen fluoride, hydrogen sulfide, arsine, and phosphine were also examined, revealing a trend where stronger hydrogen-hydride bonds correlate with lower diffusion barriers.

Conclusions:

• Coadsorption is a critical factor modulating hydrogen atom diffusion on graphene.
• The nature of the coadsorbate dictates the extent of diffusion barrier modification, with ammonia showing a pronounced effect.
• A correlation exists between the strength of hydrogen-hydride bonds formed and the resulting diffusion barrier of hydrogen on graphene.