Probing the molecular structure at graphite-water interfaces by correlating 3D-AFM and SHINERS

Area of Science:

• Physical Chemistry
• Surface Science
• Materials Science

Background:

• Interfacial water structure is critical for numerous applications, including biological processes and energy conversion.
• Realistic conditions involving environmental and surface charge variations complicate the understanding of interfacial water.
• Existing methods struggle to resolve water structure at solid-liquid interfaces under varying conditions.

Purpose of the Study:

• To characterize the in situ graphite-water interfacial structure under varying potentials.
• To elucidate the dynamic configurations of water molecules at the solid-liquid interface.
• To resolve controversies regarding interfacial water behavior.

Main Methods:

• Combined three-dimensional atomic force microscopy (3D-AFM) for spatial density mapping.
• Utilized shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) for vibrational analysis.
• Correlative analysis of AFM density maps and SHINERS vibrational peaks within 2 nm of the graphite surface.

Main Results:

• Identified two distinct interfacial configurations at open circuit potential: a transient state with hydrogen bond breaking and a steady state dominated by hydrocarbons.
• Observed a transition to a stable structure with pristine water and diverse hydrogen bond configurations at negative potentials.
• Developed a three-state model explaining the observed interfacial water structures.

Conclusions:

• The study provides a comprehensive understanding of interfacial water structure at the graphite-water interface.
• The developed three-state model resolves key debates in the field of interfacial water.
• This work offers insights into controlling interfacial water properties for various applications.