Dual Cation-Exchange Membrane Solid Electrolyte Reactors for Organic Acid Separation and Alkali Cation Recovery from Neutral CO2 Electroreduction.

Electrochemical CO2 reduction (CO2RR) under near-neutral conditions offers enhanced operational stability and compatibility with reactive carbon capture, yet downstream separation of dissolved products from supporting alkali cations remains a major barrier to practical deployment. Here we report a dual-cation-exchange-membrane solid electrolyte reactor (SER) that enables simultaneous organic acid separation, alkali cation recovery, and CO2 regeneration from neutral CO2RR effluents through highly efficient ion transport. Compared with state-of-the-art flow-electrode capacitive deionization systems, the SER exhibits substantially enhanced ion-transport performance without requiring flow electrodes or supporting electrolytes. Organic acids are selectively retained in the separation chamber with efficiencies of up to 94.7%, whereas more than 95% of alkali cations are recovered in the cathode chamber. Mechanistic analyses reveal that proton-assisted conductivity enhancement governs cation transport, whereas organic acid crossover remains limited and is primarily associated with electro-osmotic drag accompanying cation migration through the membrane. Integration of the SER with a practical reactive-capture electrolyzer demonstrates stable continuous coupling of carbon capture, electrochemical conversion, product separation and electrolyte recovery. These findings establish solid electrolyte reactors as an energy-efficient platform for electrochemical separations and highlight their potential for scalable downstream processing in CO2 electrovalorization systems.