High Indirect Energy Consumption in AEM-Based CO₂ Electrolyzers Demonstrates the Potential of Bipolar Membranes

Abstract

Typically, anion exchange membranes (AEMs) are used in CO₂ electrolyzers, but those suffer from unwanted CO₂ crossover, implying (indirect) energy consumption for generating an excess of CO₂ feed and purification of the KOH anolyte. As an alternative, bipolar membranes (BPMs) have been suggested, which mitigate the reactant loss by dissociating water albeit requiring a higher cell voltage when operating at a near-neutral pH. Here, we assess the direct and indirect energy consumption required to produce CO in a membrane electrode assembly with BPMs or AEMs. More than 2/3 of the energy consumption for AEM-based cells concerns CO₂ crossover and electrolyte refining. While the BPM-based cell had a high stability and almost no CO₂ loss, the Faradaic efficiency to CO was low, making the energy requirement per mol of CO higher than for the AEM-based cell. Improving the cathode-BPM interface should be the future focus to make BPMs relevant to CO₂ electrolyzers.