Hydrogen Evolution Intermediate in Two-Dimensionally Confined Space between Graphene and Au(111)

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Graphene-covered Au(111) (Gr/Au(111)) exhibits enhanced catalytic activity for hydrogen evolution compared to bare Au(111) or graphene.
• The enhanced activity is attributed to a unique state of hydrogen confined between the graphene and Au(111) layers.

Purpose of the Study:

• To investigate the mechanism behind the improved hydrogen evolution activity of Gr/Au(111) in alkaline electrolytes.
• To characterize the confined hydrogen species and determine the thermodynamic properties of its deposition.

Main Methods:

• Cyclic voltammetry (CV) to assess electrochemical activity and measure thermodynamic properties.
• Electrochemical Raman spectroscopy to identify and characterize reaction intermediates.
• Scanning tunneling microscopy (STM) to visualize the hydrogen deposition process.
• Temperature-controlled CV to determine Gibbs energy and entropy of hydrogen deposition.
• Statistical mechanics calculations to model the behavior of confined hydrogen.

Main Results:

• Hydrogen evolution is significantly enhanced on Gr/Au(111) compared to bare Au(111) or graphene in alkaline media.
• Hydrogen atoms deposit into the space between Au(111) and graphene when the electrode is biased below the H2O/H2 potential.
• Temperature-controlled CV revealed the Gibbs energy and entropy of hydrogen deposition.
• Statistical mechanics calculations indicate that hydrogen forms a 2D atomic gas within the confined space, acting as a reaction intermediate.
• The edges of the graphene layer are identified as the primary active sites for hydrogen evolution.

Conclusions:

• The enhanced hydrogen evolution activity of Gr/Au(111) is due to the formation of a space-confined 2D atomic gas of hydrogen between the graphene and Au(111) layers.
• This confined hydrogen acts as a highly active intermediate for the hydrogen evolution reaction.
• Graphene edges serve as the key active sites, suggesting that controlling graphene coverage can optimize catalytic performance.