Chemical Kinetic Method for Active-Site Quantification in Fe-N-C Catalysts and Correlation with Molecular Probe and...

Area of Science:

• Materials Science
• Catalysis
• Electrochemistry

Background:

• Atomically dispersed iron-nitrogen-carbon (Fe-N-C) materials are promising non-precious metal catalysts for oxygen reduction reactions.
• Current discovery of Fe-N-C catalysts relies on empirical methods, hindering quantitative structure-reactivity relationship development.
• Accurate quantification of Fe-N-C active sites is crucial for catalyst benchmarking and rational design.

Purpose of the Study:

• To develop a kinetic probe reaction method for quantifying atomically dispersed FeN4 active sites in Fe-N-C catalysts.
• To compare the developed kinetic method with established techniques like Mössbauer spectroscopy, CO pulse chemisorption, and NO electrochemical reductive stripping.
• To assess the reliability and challenges of different site quantification approaches across diverse Fe-N-C materials.

Main Methods:

• A kinetic method utilizing the aerobic oxidation of a model hydroquinone substrate to determine FeN4 site density.
• Comparative analysis with low-temperature Mössbauer spectroscopy, CO pulse chemisorption, and electrochemical reductive stripping of NO.
• Testing on a diverse suite of Fe-N-C catalysts prepared via various routes, including those with only FeN4 sites and those with aggregated Fe species.

Main Results:

• The kinetic probe reaction method provides FeN4 site densities that correlate well with those obtained from CO pulse chemisorption and Mössbauer spectroscopy.
• The study identified outliers and challenges associated with each quantification method across different Fe-N-C materials.
• The developed kinetic method requires no specialized equipment beyond standard analytical instrumentation and avoids pre-treatments that could alter active sites.

Conclusions:

• A robust and accessible kinetic method for quantifying FeN4 active sites in Fe-N-C catalysts has been successfully developed.
• This method facilitates the quantitative benchmarking and rational design of Fe-N-C catalysts, advancing their application in areas like fuel cells.
• The findings contribute to a deeper understanding of Fe-N-C catalyst characterization and promote the adoption of standardized quantification techniques.