Characterizing CO₂ Reduction Catalysts on Gas Diffusion Electrodes: Comparing Activity, Selectivity, and Stability of...

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Electrochemical reduction of CO2 (CO2RR) performance depends on catalyst, environment, and system configuration.
• Existing CO2RR research is largely based on low current density (5 mA cm-2) benchmarks.
• An updated baseline at elevated current densities is needed to reflect current research advancements.

Purpose of the Study:

• To re-characterize the activity, selectivity, and stability of Ag, Au, Pd, Sn, and Cu catalysts for CO2RR at elevated current densities.
• To provide a renewed resource and point of comparison for CO2RR research.
• To evaluate the utility of reaction rates as a baseline metric.

Main Methods:

• Electrochemical operation and physical characterization of five transition metal catalysts (Ag, Au, Pd, Sn, Cu).
• Utilized a common cell architecture, controlled catalyst layer morphology/thickness, and fixed current densities across 88 experiments.
• Compared catalytic selectivity at 10 mA cm-2 versus 200 mA cm-2.

Main Results:

• Identified CO-limiting current densities for Au (72 mA cm-2) and Pd (50 mA cm-2) in CO-producing catalysts.
• Demonstrated the instability of Sn in highly alkaline conditions.
• Observed convergence of product selectivity for Cu catalysts in neutral and alkaline media at elevated current densities.

Conclusions:

• Elevated current densities reveal distinct performance limitations and behaviors for CO2RR catalysts.
• Reaction rates are a critical but not sole determinant of catalyst performance and selectivity.
• This work offers a valuable dataset for researchers establishing new CO2RR experiments.