Carbon- and energy-efficient ethanol electrosynthesis via interfacial cation enrichment

The use of acidic electrolytes in CO₂ reduction avoids costly carbonate loss. However, the energy efficiency of acid-fed electrolysers has been limited by high hydrogen production and operating potentials. We find that these stem from the lack of alkali cations at the catalyst surface, limiting CO₂ and CO adsorption. In acid-fed membrane electrode assembly systems, the incorporation of these cations is challenging as there is no flowing catholyte. Here an interfacial cation matrix (ICM)–catalyst heterojunction is designed that directly attaches to the catalyst layer. The negatively charged nature of the ICM enriches the alkali cation concentration near the cathode surface, trapping generated hydroxide ions. This increases the local electric field and pH, increasing multi-carbon production. Integrating the ICM strategy with a tailored copper–silver catalyst enables selective ethanol production through a proton-spillover mechanism. We report a 45% CO₂-to-ethanol Faradaic efficiency at 200 mA cm⁻², carbon efficiency of 63%, full-cell ethanol energy efficiency of 15% (3-fold improvement over the best previous acidic CO₂ reduction value) and energy cost of 260 GJ per tonne ethanol, the lowest among reported ethanol-producing CO₂ electrolysers. (Figure presented.)