Bipolar membrane electrolyzers enable high single-pass CO 2 electroreduction to multicarbon products.

In alkaline and neutral MEA CO 2 electrolyzers, CO 2 rapidly converts to (bi)carbonate, imposing a significant energy penalty arising from separating CO 2 from the anode gas outlets. Here we report a CO 2 electrolyzer uses a bipolar membrane (BPM) to convert (bi)carbonate back to CO 2 , preventing crossover; and that surpasses the single-pass utilization (SPU) limit (25% for multi-carbon products, C 2+ ) suffered by previous neutral-media electrolyzers. We employ a stationary unbuffered catholyte layer between BPM and cathode to promote C 2+ products while ensuring that (bi)carbonate is converted back, in situ, to CO 2 near the cathode. We develop a model that enables the design of the catholyte layer, finding that limiting the diffusion path length of reverted CO 2 to ~10 μm balances the CO 2 diffusion flux with the regeneration rate. We report a single-pass CO 2 utilization of 78%, which lowers the energy associated with downstream separation of CO 2 by 10× compared with past systems.