Unlocking Catalyst Secrets: How Kinetic Analysis Reveals CO Adsorption Energies in CO2 Electroreduction

Revolutionizing Catalyst Analysis Through Kinetic Modeling

Researchers have developed a groundbreaking approach to determine CO adsorption free energies on active sites during CO2 electroreduction (COR) to CO. This innovative method, detailed in Nature Catalysis, provides a universal kinetic expression that enables scientists to estimate adsorption energies across various catalyst materials without requiring complex surface characterization techniques. The breakthrough could accelerate the development of more efficient catalysts for converting CO2 to valuable chemicals and fuels.

The Kinetic Model Foundation

The research team established a kinetic framework that assumes the first electron transfer step serves as the rate-limiting step (RLS) during CO2-to-CO conversion. This assumption holds true for several well-known heterogeneous electrocatalysts, including polycrystalline gold, silver, copper, and glassy carbon-supported cobalt phthalocyanine. Interestingly, the model demonstrates remarkable robustness—whether the RLS includes proton transfer or not, the derived kinetic expression for estimating adsorption free energy remains consistent within a mean-field kinetic framework.

The researchers considered two primary reaction pathways: one where CO adsorption coupled with electron transfer serves as the RLS, and another where the first concerted proton-coupled electron transfer (CPET) step is rate-limiting. Through careful mathematical derivation, they arrived at a universal expression connecting CO adsorption free energy with measurable experimental parameters., according to related coverage

The Universal Kinetic Expression

The core achievement of this research lies in establishing a direct relationship between CO adsorption free energy (ΔG_CO), reaction order, and local CO concentration. The derived expression shows that ΔG_CO can be determined from the reaction order and local CO concentration, regardless of whether the RLS involves CO adsorption or CPET steps during COR to CO.

The key insight: Active sites with more negative ΔG_CO values tend to exhibit more negative CO reaction orders at lower local CO concentrations during COR. This relationship provides researchers with a powerful tool to characterize catalyst behavior under actual operating conditions rather than relying on ultra-high vacuum measurements that may not reflect electrochemical environments., according to recent research

Experimental Methodology and Validation

The team employed rotating ring-disk electrode (RRDE) voltammetry as their primary experimental technique, leveraging its unique capability to simultaneously quantify both CO reaction orders and local CO concentrations during COR. The method utilizes a gold ring electrode as a highly sensitive CO detector, enabling precise measurement of CO evolution rates from the disk electrode., according to market insights

Critical to the method’s success is maintaining kinetic control during measurements. The researchers used a rotation rate of 1,600 rpm to minimize mass transport limitations, carefully avoiding conditions where hydrogen evolution reaction interference could compromise data quality. This attention to experimental detail ensures the reliability of the obtained kinetic parameters.

Catalyst-Specific Findings

The methodology was validated across three different catalyst systems: gold, copper, and cobalt phthalocyanine supported on glassy carbon (CoPc/GC). The results revealed significant differences in CO adsorption behavior:, according to technological advances

• Gold and CoPc/GC exhibited comparable ΔG_CO values, consistent with their high efficiency as CO-producing catalysts
• Copper electrodes showed more negative ΔG_CO, with a reaction order of -0.82 ± 0.09 at -0.6 V, indicating steady-state fractional CO coverage between 0.7 and 0.9 on active sites
• Notably, the determined ΔG_CO for copper at -0.6 V was -0.28 ± 0.03 eV, significantly different from the -0.55 ± 0.05 eV measured under ultra-high vacuum conditions

Electrolyte Composition Effects

The research extended to investigating how electrolyte composition influences CO adsorption behavior. Systematic measurements in different bicarbonate electrolytes (LiHCO₃, NaHCO₃, and KHCO₃) revealed that cation identity significantly affects CO adsorption strength on gold electrodes.

Interestingly, lithium cations promoted stronger CO adsorption compared to potassium cations, as evidenced by more negative reaction orders in LiHCO₃ electrolytes. Furthermore, increasing sodium cation concentration from 0.1 M to 0.5 M caused the reaction order to shift from -0.50 to -0.94, indicating progressively stronger CO adsorption with higher cation concentrations., as related article

Practical Implications and Limitations

This kinetic analysis method offers several advantages for industrial catalyst development. It provides real-time information about catalyst behavior under operating conditions, enables comparison across different catalyst materials, and reveals how electrolyte composition affects catalytic performance. However, the approach has specific limitations that researchers must consider:

• The method is unsuitable for catalysts like platinum that produce minimal desorbed CO during COR
• It cannot be applied in potential windows where surface-adsorbed CO undergoes further reduction to multicarbon products
• For catalysts capable of reversible CO/CO₂ interconversion near equilibrium potential, kinetic data must be analyzed on an overpotential scale

Future Research Directions

The established methodology opens numerous possibilities for advancing electrocatalyst design. Future research could extend this approach to other reduction products, investigate temperature effects on adsorption energies, and explore how catalyst morphology influences local CO concentration and reaction kinetics. The ability to quantitatively compare adsorption energies across different catalyst systems under operational conditions represents a significant step toward rational catalyst design for CO2 utilization technologies.

This research demonstrates how sophisticated kinetic analysis can provide deep insights into catalyst behavior that were previously accessible only through complex surface science techniques. As the field of CO2 electroreduction advances, such methodologies will become increasingly valuable for developing efficient, selective, and stable catalysts for sustainable chemical production.

This article aggregates information from publicly available sources. All trademarks and copyrights belong to their respective owners.

Note: Featured image is for illustrative purposes only and does not represent any specific product, service, or entity mentioned in this article.