Estimating Reaction Rate Constants from Impedance Spectra: Combining Microkinetic Modeling and Experiments of the...

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Kinetics

Background:

• Understanding reaction rate constants is crucial for electrochemical mechanisms.
• First-principles methods like DFT have limitations due to idealized assumptions.
• Estimating rate constants directly from experimental electrochemical data offers an alternative approach.

Purpose of the Study:

• To demonstrate the estimation of reaction rate constants from electrochemical impedance spectroscopy (EIS) data.
• To apply this method to the oxygen evolution reaction (OER) using a hematite (Fe2O3) anode.
• To represent the OER electrochemistry using a microkinetic model and physicochemical quantities.

Main Methods:

• Estimation of rate constants from EIS data of the OER on a hematite anode.
• Utilizing a microkinetic model instead of traditional equivalent circuit fitting.
• Employing maximum likelihood estimation to optimize a single set of rate constants across multiple potentials.
• Validation with synthetic measurements and simulation of intermediate species coverages.

Main Results:

• Successfully estimated rate constants directly corresponding to OER reaction steps.
• Obtained a single set of rate constants optimized simultaneously for multiple potentials.
• Demonstrated the method's effectiveness with both synthetic and experimental EIS data.
• Acknowledged current accuracy limitations due to the model not accounting for all interfacial processes like diffusion.

Conclusions:

• The developed method effectively estimates reaction rates and intermediate species coverages from EIS data combined with microkinetic modeling.
• This approach aids in identifying reaction mechanisms directly from experimental results.
• The estimated rate constants are suitable for kinetic analysis, parameter studies, and comparing electrode materials.
• Enables validation of models and prediction of electrochemical data for different material systems, saving time and cost.