Redox-dependent spatially resolved electrochemistry at graphene and graphite step edges

Area of Science:

• Electrochemistry
• Materials Science
• Surface Science

Background:

• Understanding the electrochemical (EC) behavior of graphene and graphite is crucial for their application in various fields.
• The intrinsic Fermi level of these materials influences their interaction with redox probes.
• Previous studies have shown varied EC responses depending on surface properties and redox couples.

Purpose of the Study:

• To investigate the high spatial resolution electrochemical behavior of graphene and highly oriented pyrolytic graphite (HOPG).
• To elucidate the time-dependent EC activity differences between basal planes and step edges.
• To understand the impact of HOPG delamination on electrochemical response.

Main Methods:

• Scanning electrochemical cell microscopy (SECCM) at high spatial resolution.
• Complementary techniques: Atomic Force Microscopy (AFM) and micro-Raman spectroscopy.
• Macroscopic voltammetric measurements and conductive AFM.

Main Results:

• Ru(NH3)6(3+/2+) redox probe reveals time-dependent EC activity differences between graphene/graphite basal planes and step edges.
• Other redox couples show uniform, high activity, indicating probe-specific behavior.
• HOPG delamination leads to partially coupled graphene layers, impacting the density of states near the Fermi level.
• Improved SECCM reveals subtle, enhanced activity at step edges for Ru(NH3)6(3+/2+).

Conclusions:

• The electrochemical response of graphene and graphite is sensitive to their electronic structure and surface morphology.
• Spontaneous delamination of HOPG significantly alters its electrochemical properties.
• A microscopic model is proposed to explain the EC response based on electronic band structure and surface features.