Bipolar membranes for intrinsically stable and scalable CO2 electrolysis

CO2 electrolysis allows the sustainable production of carbon-based fuels and chemicals. However, state-of-the-art CO2 electrolysers employing anion exchange membranes (AEMs) suffer from (bi)carbonate crossover, causing low CO2 utilization and limiting anode choices to those based on precious metals. Here we argue that bipolar membranes (BPMs) could become the primary option for intrinsically stable and efficient CO2 electrolysis without the use of scarce metals. Although both reverse- and forward-bias BPMs can inhibit CO2 crossover, forward-bias BPMs fail to solve the rare-earth metals requirement at the anode. Unfortunately, reverse-bias BPM systems presently exhibit comparatively lower Faradaic efficiencies and higher cell voltages than AEM-based systems. We argue that these performance challenges can be overcome by focusing research on optimizing the catalyst, reaction microenvironment and alkali cation availability. Furthermore, BPMs can be improved by using thinner layers and a suitable water dissociation catalyst, thus alleviating core remaining challenges in CO2 electrolysis to bring this technology to the industrial scale. The membrane separating anode from cathode in CO2 electrolysers plays a key role in determining the performance, stability and material selection of the device. Here the authors argue that bipolar membranes could become the primary choice for scarce-metal-free, stable and efficient CO2 electrolysers.