Novel first-principles insights into graphene fluorination.

Area of Science:

• Materials Science
• Surface Chemistry
• Computational Chemistry

Background:

• Graphene derivatives, such as fluorographene, exhibit unique electronic properties.
• Fluorination of graphene with xenon difluoride results in a wide bandgap material.
• Experimental studies reveal a two-stage fluorination mechanism: rapid half-fluorination and slow full-fluorination.

Purpose of the Study:

• To elucidate the microscopic mechanisms behind the differing rates of half- and full-fluorination of graphene.
• To identify the chemical species responsible for hindering the full-fluorination stage.
• To propose a mechanism for overcoming the fluorination bottleneck and discuss potential applications.

Main Methods:

• Density functional theory (DFT) calculations were employed to model the fluorination process.
• Minimum energy pathways for both half- and full-fluorination were computed.
• Binding energies and stability of potential contaminants (H2, O2, N2, Xe) were assessed.

Main Results:

• DFT calculations initially suggested faster fluorine adsorption after half-fluorination, contradicting experimental observations.
• Chemical activation of the graphene sheet post-half-fluorination was identified as a key factor.
• Oxygen-fluorine ligands were determined to be the most probable contaminants impeding full fluorination.
• An oxygen desorption mechanism was proposed to explain accelerated full-fluorination at elevated temperatures.

Conclusions:

• The slower rate of full-fluorination is attributed to the formation of chemical contaminants, primarily oxygen-fluorine ligands, on the graphene surface.
• Elevated temperatures facilitate oxygen desorption, enhancing the rate of full fluorination.
• Pristine and defected fluorographene samples show potential for photocatalytic applications in water splitting and CO2 reduction.