Challenges in CO2 reduction selectivity measurements by hydrodynamic methods

Electrochemical reduction of carbon dioxide (CO2) offers a promising pathway for converting CO2 into higher-value products using electrocatalysts, which could revolutionize the chemical industry by enabling electrification. However, a significant challenge in this field is the poor selectivity, or faradaic efficiency, of CO2 reduction due to competition with the hydrogen evolution reaction in aqueous electrolytes. To address this issue, rotating ring-disk electrode (RRDE) experiments have become a popular method for quantifying faradaic efficiencies, particularly for gold electrocatalysts. Despite their utility, RRDE measurements have been plagued by poor inter-laboratory reproducibility, leading to inconsistent results across studies.

Recent research has identified the root causes of variability in RRDE selectivity measurements by comparing protocols, reagent purities, and glassware cleaning procedures. The study found that electroplating of electrolyte impurities onto the disk and ring surfaces of the RRDE setup is a major contributor to electrocatalyst deactivation. These impurities can interfere with the electrochemical reactions, leading to inaccurate measurements of faradaic efficiencies. The variability in RRDE measurements has significant implications for the broader CO2 reduction research community, as it undermines the reliability of results and hinders progress in developing efficient electrocatalysts.

The findings of this study emphasize the need for standardized and cross-laboratory validation of CO2 RR selectivity measurements using RRDE. By establishing consistent protocols and ensuring high reagent purity, researchers can minimize the impact of electrode deactivation and improve the accuracy of their measurements. This, in turn, will facilitate more meaningful comparisons between different electrocatalysts and advance the development of more efficient systems for CO2 reduction.

Researchers employing RRDE for CO2 RR selectivity measurements must be aware of the potential for electrode deactivation and its effects on faradaic efficiencies and overall experimental conclusions. Maria Kelly, a Jill Hruby Postdoctoral Fellow at Sandia National Laboratories, played a key role in this research. Kelly earned her PhD in Professor Wilson Smith’s research group at the University of Colorado Boulder and the National Renewable Energy Laboratory, focusing on characterizing CO2 conversion interfaces using analytical electrochemical and in situ scanning probe methods. Her research interests broadly encompass advancing experimental measurement techniques to investigate the near-electrode environment during electrochemical reactions.

In conclusion, the challenges in CO2 reduction selectivity measurements by hydrodynamic methods, particularly through RRDE, highlight the importance of standardization and careful experimental design. By addressing the issues of electrolyte purity and electrode deactivation, the research community can enhance the reliability of CO2 reduction studies and accelerate the development of efficient electrocatalysts for sustainable chemical production.