Species Crossover in Electrochemical CO2 Reduction

Abstract

Catalyst studies have improved the overall CO2R (electrochemical CO2 reduction) faraday efficiency (FE)1, however, the experimental FE can be deteriorated by product crossover through the membrane in a practical electrochemical CO2R cell. The CO2R product molecules generated at the cathode are subject to oxidation at the anode if they permeate through the membrane, thus decreasing the practical CO2R product collection. The product loss at the anode also poses a challenge for quantification and study of the crossover behavior2–4. In this work, we will present experimental designs that effectively overcome the oxidation at the anode to reveal the CO2R product crossover.The CO2R 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 CO2R 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 CO2R product species. The CO2R product crossover measurements of commercially available anion exchange membranes will be presented.From a fundamental perspective, CO2R 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/CO2 flow rate also affect the crossover. The species other than products in CO2R can have impact on both catalyst performance and crossover. We will discuss the crossover behavior in our standard CO2R setup5,6. Overall, we aim to address the CO2R product crossover by bridging the fundamental study of a component and CO2R integration efforts at NREL. Ge, L. et al. Electrochemical CO2 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 CO2 reduction. SmartMat 2, 12–16 (2021).Zhang, J., Luo, W. & Züttel, A. Crossover of liquid products from electrochemical CO2 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 CO2 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 CO2 electroreduction selectivity. Chem Catal. 2, 400–421 (2022).