Recently, a research group led by Prof. YANG Yong from Hefei Institutes of Physical Science (HFIPS), Chinese Academy of Sciences (CAS), unveiled the role of neighboring adsorbate and quantum tunneling on the diffusion of hydrogen on graphene surface.
The research results were published in The Journal of Physical Chemistry C.
Hydrogen, being the lightest element, exhibits quantum motions known as nuclear quantum effects (NQEs) during its dynamical processes. The research conducted by Professor Yang's team demonstrates the crucial role played by quantum tunneling in the activation of dissociation and diffusion processes of hydrogen on copper surfaces. On graphene surfaces, hydrogen shows different aggregation states depending on the coverage.
To investigate the diffusion of hydrogen in various aggregation states on graphene surface, the researchers utilized first-principles calculations along with the transfer matrix method. They examined the quantum tunneling effects on hydrogen diffusion, calculating transmission probabilities, rate constants, and diffusion coefficients while considering respectively hydrogen atoms as classical and quantum particles.
The adsorption of hydrogen atoms on neighboring adsorption sites will significantly change the kinetic properties of the diffusing hydrogen atoms on graphene surface. The interaction between neighboring hydrogen atoms is found to be a key factor leading to the variation of the diffusion barrier height. In the diffusion of hydrogen atoms in different aggregation states, the comparison of the diffusion probability, reaction rate constant and diffusion coefficient of hydrogen as classical particle and quantum particle shows that quantum tunneling plays a key role in the diffusion at room temperature and below. Even in the higher temperature region (around 600 K), the contribution is still not negligible.
"Our findings provide new insights for understanding the diffusion dynamics of hydrogen atoms on the graphene surface," said Prof. YANG Yong.
Quantum tunneling of hydrogen on graphene surface (left panel); and comparison of diffusion coefficients in classical and quantum processes (right panel). (Image by YANG Yong)