Rigorous Evaluation of Liquid Products in High-Rate CO₂/CO Electrolysis

In this work, the water crossover in CO₂ electrolysis was systematically analyzed with hydrated ions transferring through ion-selective membranes as charge carriers in three-compartment devices. We demonstrate that the water crossover leads to a variation in the electrolyte volume, which plays an important role in the evaluation of the catalytic selectivity of liquid products. Without considering the water crossover, the catalytic selectivity of liquid products could be overestimated with the use of anion exchange membranes and underestimated with cation exchange membranes, especially when ions with large hydration numbers transport through membranes for long-term electrolysis. In addition, a protocol for reliably quantifying liquid products is proposed for high-rate CO₂/CO electrolysis in three-compartment flow electrolyzers.