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.