Bipolar Membrane with Porous Anion Exchange Layer for Efficient and Long‐Term Stable Electrochemical Reduction of CO2 to CO

Abstract Bipolar membranes in forward bias have the potential to address several challenges of alkaline zero‐gap CO 2 electrolyzers. However, the inevitable gas evolution of CO 2 at the membrane junction typically leads to delamination and failure of the membrane after a few hours, limiting its applicability in electrolyzers so far. In this work, a bipolar membrane with a perforated anion exchange layer is presented that allows the CO 2 gas to flow back to the cathode and thus preventing accumulation of gas at the junction. This configuration for the first time enables stable operation of a forward bias bipolar membrane showing a degradation rate of 0.5 mV h −1 in a 200 h constant current hold at 100 mA cm − 2 and 3.1 V. Highest reported energy efficiency of EE CO = 39% and Faradaic efficiency of FE CO = 96% at 200 mA cm − 2 among forward bipolar membranes prove that the perforated membrane does not compromise efficiency. A maximum CO 2 single‐pass conversion of 52% at 0.75 mL CO2 min −1 cm − 2 and a low specific energy consumption of 665 kJ mol −1 CO 2 shows that this concept is superior not only to other bipolar membranes in the literature, but potentially also to conventional anion exchange membrane‐based electrolyzers.