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. While membrane electrode assembly (MEA) CO electrolyzers are industrially relevant, they currently suffer from a low energy efficiency 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.