Tailored water and hydroxide transport at a quasi-two-phase interface of membrane electrode assembly electrolyzer for CO electroreduction

Electrochemical CO reduction can potentially serve as an intermediate step for the efficient conversion of CO₂ to chemical fuels using renewable electricity. Although membrane electrode assembly (MEA) CO electrolyzers are industrially relevant, they currently suffer from a low energy efficiency (EE) due to a high-cell voltage (typically >3 V at 1,000 mA cm⁻²). In this work, we reveal that water and hydroxide transport at the quasi-two-phase interface of the cathode limits the performance of MEA electrolyzers at high current densities. By developing a system that allows for sufficiently rapid interfacial mass transport, we obtain an electrolyzer that has a cell voltage of only 2.4 V at 1,000 mA cm⁻². The electrolyzer has a Faradaic yield of more than 90% for C₂₊ products and demonstrates a stability of more than 100 h.