Species Crossover in Electrochemical CO₂ Reduction

Catalyst studies have improved the overall CO 2 R (electrochemical CO 2 reduction) faraday efficiency (FE) 1 , however, the experimental FE can be deteriorated by product crossover through the membrane in a practical electrochemical CO 2 R cell. The CO 2 R product molecules generated at the cathode are subject to oxidation at the anode if they permeate through the membrane, thus decreasing the practical CO 2 R product collection. The product loss at the anode also poses a challenge for quantification and study of the crossover behavior 2–4 . In this work, we will present experimental designs that effectively overcome the oxidation at the anode to reveal the CO 2 R product crossover. The CO 2 R product crossover can be driven by electromigration and the concentration gradient across the membrane. Although the electromigration plays a significant role based on the current density of CO 2 R operation, the later can be varied by membrane design parameters. The membrane thickness and non-ionic reinforcement layers can effectively change the permeability of various CO 2 R product species. The CO 2 R product crossover measurements of commercially available anion exchange membranes will be presented. From a fundamental perspective, CO 2 R product crossover is a reflection of membrane selectivity. We also extend the component study to the cell level where parameters like electrolyte concentration/conductivity and electrolyte/CO 2 flow rate also affect the crossover. The species other than products in CO 2 R can have impact on both catalyst performance and crossover. We will discuss the crossover behavior in our standard CO 2 R setup 5,6 . Overall, we aim to address the CO 2 R product crossover by bridging the fundamental study of a component and CO 2 R integration efforts at NREL. Ge, L. et al. Electrochemical CO 2 reduction in membrane-electrode assemblies. Chem 8 , 663–692 (2022). McCallum, C. et al. Reducing the crossover of carbonate and liquid products during carbon dioxide electroreduction. Cell Rep. Phys. Sci. 2 , 100522 (2021). Wang, N. et al. Suppressing the liquid product crossover in electrochemical CO 2 reduction. SmartMat 2 , 12–16 (2021). Zhang, J., Luo, W. & Züttel, A. Crossover of liquid products from electrochemical CO 2 reduction through gas diffusion electrode and anion exchange membrane. J. Catal. 385 , 140–145 (2020). Chen, Y. et al. A Robust, Scalable Platform for the Electrochemical Conversion of CO 2 to Formate: Identifying Pathways to Higher Energy Efficiencies. ACS Energy Lett. 5 , 1825–1833 (2020). Chen, Y. et al. The effect of catholyte and catalyst layer binders on CO 2 electroreduction selectivity. Chem Catal. 2 , 400–421 (2022).