Diffusion boundary layer of a rotating disk electrode as a thin-layer spectroelectrochemical cell.

Area of Science:

• Electrochemistry
• Spectroscopy
• Analytical Chemistry

Background:

• The ferrocyanide/ferricyanide redox couple is a common model system in electrochemistry.
• Understanding diffusion boundary layers is crucial for electrochemical reaction kinetics.
• Spectroscopic methods offer in-situ monitoring capabilities for electrochemical processes.

Purpose of the Study:

• To develop and validate a method for in-situ monitoring of electrochemical reactions using UV-Vis spectroscopy.
• To investigate the diffusion boundary layer of aqueous [Fe(CN)6]4- solutions during oxidation.
• To correlate spectroscopic absorbance with electrochemical parameters.

Main Methods:

• Coupling of a UV-visible rapid scan spectrophotometer (RSS) with a gold rotating disk electrode (RDE).
• Near-normal incidence reflection-absorption spectroscopy was used to monitor the diffusion layer.
• Electrochemical measurements were performed over a potential range for ferrocyanide oxidation.

Main Results:

• Well-defined spectra of ferricyanide ([Fe(CN)6]3-) were obtained at lambda(max) = 420 nm.
• Absorbance was found to be proportional to the electrochemical current.
• Absorbance also showed a proportional relationship with the square root of the electrode rotation rate (omega(1/2)).

Conclusions:

• The combined RSS-RDE system effectively monitors electrochemical reactions in real-time.
• Spectroscopic absorbance is a reliable indicator of ferricyanide concentration in the diffusion layer.
• The findings align with theoretical predictions for diffusion-controlled electrochemical processes.