Efficient Forward‐Bias Bipolar Membrane CO2 Electrolysis in Absence of Metal Cations

Abstract The acid‐base reaction of CO 2 with hydroxide ions to (bi)carbonate anions at the cathode of alkaline exchange membrane (AEM) CO 2 electrolyzer has detrimental impact on their performance. (Bi)carbonate buffers the local cathode pH, and in combination with metal cations, may lead to precipitation of salts at the cathode. This non‐electrochemical conversion of CO 2 significantly reduces the CO 2 utilization efficiency and limits the CO 2 single pass conversion of AEM CO 2 electrolyzer to 50% if CO is desired. Acidic metal cation‐free CO 2 electrolysis has the potential to address and mitigate these problems. Here, CO 2 valorization is demonstrated at faradaic CO efficiencies (FE) of up to 80% FE CO in forward‐bias BPM cell architectures using actual neutral pure water feeding at the anode. This study demonstrates how immobilized anion exchange ionomer layers thereby facilitate the metal cation‐free CO 2 valorization thanks to their positively charged functional NR 4 groups. Unlike metal cations, the immobilized positively charged groups are not washed out of the reactor. This study shows that careful design of the distribution and location of the anion exchange ionomer molecules within the Gas Diffusion Electrode is key to efficient CO 2 ‐to‐CO electrolyzer cell.