Quantum Tunnelling Driven H₂ Formation on Graphene.

Area of Science:

• Physical Chemistry
• Surface Science
• Quantum Mechanics

Background:

• Previously assumed that adsorbed hydrogen atoms on carbonaceous surfaces require incident atoms for H2 formation.
• Low-temperature recombination of adsorbed H atoms was considered improbable due to high energy barriers.

Purpose of the Study:

• To investigate the low-temperature recombination of adsorbed H atoms on carbonaceous surfaces.
• To explore the role of quantum mechanical effects, specifically tunneling, in H2 formation.
• To challenge the conventional understanding of H2 formation kinetics on graphene and related materials.

Main Methods:

• Utilized ring-polymer instanton theory to model multidimensional tunneling effects.
• Employed ab initio electronic structure calculations to determine reaction pathways and barriers.
• Performed quantum-mechanical simulations to assess reaction rates.

Main Results:

• Quantum simulations demonstrate that adsorbed H atoms can recombine to form H2 even at low temperatures.
• Deep tunneling significantly enhances recombination rates, by orders of magnitude, contrary to prior beliefs.
• A novel recombination pathway facilitated by multidimensional tunneling was identified, missed by 1D models.

Conclusions:

• Hydrogen molecule formation from adsorbed H atoms on carbon surfaces is a faster process at low temperatures than previously thought.
• Quantum tunneling plays a crucial role in enabling H2 formation, even across high energy barriers.
• These findings necessitate a re-evaluation of hydrogen chemistry in low-temperature environments involving graphene and graphite.