Electrosynthesis of acetate from CO offers the prospect of a low-carbon-intensity route to this valuable chemical––but only once sufficient selectivity, reaction rate and stability are realized. It is a high priority to achieve the protonation of the relevant intermediates in a controlled fashion, and to achieve this while suppressing the competing hydrogen evolution reaction (HER) and while steering multicarbon (C₂₊) products to a single valuable product––an example of which is acetate. Here we report interface engineering to achieve solid/liquid/gas triple-phase interface regulation, and we find that it leads to site-selective protonation of intermediates and the preferential stabilization of the ketene intermediates: this, we find, leads to improved selectivity and energy efficiency toward acetate. Once we further tune the catalyst composition and also optimize for interfacial water management, we achieve a cadmium-copper catalyst that shows an acetate Faradaic efficiency (FE) of 75% with ultralow HER (<0.2% H₂ FE) at 150 mA cm⁻². We develop a high-pressure membrane electrode assembly system to increase CO coverage by controlling gas reactant distribution and achieve 86% acetate FE simultaneous with an acetate full-cell energy efficiency (EE) of 32%, the highest energy efficiency reported in direct acetate electrosynthesis.

Reactive capture – the integration of CO₂ capture with electrochemical upgrade – offers the prospect of improving overall energy efficiency in captured-CO₂-to-fuels by eliminating the gas-phase CO₂ desorption step, and by further offering a CO₂-free gas product stream. Two related challenges limit the potential impact of electrified reactive capture today: its propensity to produce lower-value C₁ products (carbon products containing one carbon atom per molecule); and its failure to retain performance when fed dilute streams (e.g. ~1-10% CO₂). We posit that these could be addressed using catalysts that locally concentrate and activate in-situ generated CO₂: we integrate a redox-active polymeric network whose polymer fragments undergo reversible reduction during the electrochemical conversion process, enabling electron transfer to CO₂ molecules generated in-situ from carbonate capture liquid. We report as a result a 55 ± 5% C₂₊ (carbon products containing two or more carbon atoms per molecule) Faradaic efficiency (FE) at 300 mA/cm² in an electrochemical reactive capture system in which the electrolysis stage is fed with 1 M K₂CO₃. We obtain 56 ± 4 wt% C₂H₄ in the product gas stream. When we use a dilute stream consisting of 1% CO₂ in N₂ at the KOH capture stage, we retain the C₂₊ FE to within 85% (relative) of its value achieved in the case of pure CO₂.