This study presents a pure-water-fed, membrane-electrode-assembly (MEA) system for electrocatalytic CO₂ reduction to ethylene, which effectively suppresses carbonate formation and prevents salt precipitation. The system integrates an anion-exchange membrane (AEM) and a proton-exchange membrane (PEM) at the cathode and anode sides, respectively, under forward bias. This design maintains an alkaline cathode environment while preventing anion crossover, leading to over 1,000 hours of stability at a total current of 10 A with 50% Faradaic efficiency towards ethylene. The pure-H₂O system suppresses carbonate formation by preventing the reaction of CO₂ with electrogenerated OH- and by maintaining an alkaline environment. In situ Raman spectroscopy and isotope labeling experiments confirm the suppression of carbonate formation. The system's performance is comparable to that of conventional AEM-MEA systems with 1 M KOH as the anolyte, demonstrating its potential for industrial-scale operation.This study presents a pure-water-fed, membrane-electrode-assembly (MEA) system for electrocatalytic CO₂ reduction to ethylene, which effectively suppresses carbonate formation and prevents salt precipitation. The system integrates an anion-exchange membrane (AEM) and a proton-exchange membrane (PEM) at the cathode and anode sides, respectively, under forward bias. This design maintains an alkaline cathode environment while preventing anion crossover, leading to over 1,000 hours of stability at a total current of 10 A with 50% Faradaic efficiency towards ethylene. The pure-H₂O system suppresses carbonate formation by preventing the reaction of CO₂ with electrogenerated OH- and by maintaining an alkaline environment. In situ Raman spectroscopy and isotope labeling experiments confirm the suppression of carbonate formation. The system's performance is comparable to that of conventional AEM-MEA systems with 1 M KOH as the anolyte, demonstrating its potential for industrial-scale operation.