Imaging Electrode Heterogeneity Using Chemically Confined Fluorescence Electrochemical Microscopy.

Area of Science:

• Electrochemistry
• Chemical Spectroscopy
• Surface Science

Background:

• Electrochemical reactions like hydrogen evolution and oxygen reduction involve local pH changes at the electrode interface.
• Visualizing these pH changes is crucial for understanding reaction mechanisms and electrode performance.
• Current methods may lack the spatial resolution to observe surface heterogeneity.

Purpose of the Study:

• To develop a method for selectively and optically studying hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) at electrochemical interfaces.
• To visualize local pH shifts driven by redox reactions using fluorescence imaging.
• To improve the spatial resolution of interfacial pH measurements for visualizing electrode surface heterogeneity.

Main Methods:

• Utilizing a pH-sensitive fluorescent dye (8-hydroxypyrene-1,3,6-trisulfonate) and varying concentrations of a strong acid (perchloric acid, HClO4).
• Employing fluorescence imaging to visualize the local pH changes at the electrochemical interface.
• Implementing chemical confinement of the fluorophore using finite acid concentrations to enhance resolution.

Main Results:

• Demonstrated selective optical study of both HER and ORR by adjusting dye and acid concentrations.
• Successfully visualized local pH shifts at the electrode interface through fluorescence imaging.
• Achieved micrometer-scale resolution, enabling visualization of surface heterogeneity due to chemical confinement.

Conclusions:

• The developed method allows for selective and high-resolution optical monitoring of electrochemical reactions.
• Chemical confinement of the pH-sensitive dye enhances the ability to study interfacial phenomena.
• This technique provides a powerful tool for investigating electrode surface heterogeneity and reaction mechanisms.