SIFT-MS Enables Product-Specific Insight into Electrochemical Pulsed CO2 Reduction in Membrane Electrode Assemblies

Abstract Pulsed electrolysis is a promising operating strategy for electrochemical CO2 reduction, but understanding how products form, accumulate, and are released during dynamic operation remains challenging, particularly in membrane electrode assemblies (MEAs). Conventional product analysis methods provide limited time resolution, making them poorly suited for resolving product-specific changes during pulses that are on the timescale of seconds. Here, selected-ion-flow-tube mass spectrometry (SIFT-MS) was used as a quasi-real-time analytical technique to measure the product concentrations during pulsed CO2 electrolysis in a MEA using a copper oxide nanoparticle-derived cathode catalyst. Methodology development for the SIFT-MS technique established the sampling and pulsing criteria required for reliable semi-quantitative analysis of the concentration of reaction products. Applying these methodology developments to pulsed electrolysis experiments unveiled how molecular structure influences product retention within the electrode and subsequent transport into the MEA outlet stream under pulsed CO2R conditions. A comparison of the measured concentrations of ethanol, ethylene, and acetaldehyde provided evidence that the formation of ethanol occurs through multiple contributing reaction pathways. The analysis of the measured concentrations of acetaldehyde, propionaldehyde, and 1-propanol provided evidence for the sequential formation of products through which the formation of aldehydes precedes the formation of 1-propanol. Overall, this work establishes SIFT-MS as a product-specific, quasi-real-time analytical technique for probing pulsed CO2R in membrane electrode assemblies that can unveil crucial information to aid in the development of future MEA electrolyzers and operational strategies.