Equivalent Salt Concentration: A Quantitative Criterion for Predicting and Mitigating Salt Precipitation in MEA CO 2 Electrolysis

Membrane electrode assembly (MEA)-based CO 2 electrolyzers are promising for industrial applications due to high energy efficiency and scalability, yet their long-term stability is severely limited by cathode salt precipitation. This work innovatively uncovers the salt precipitation mechanism from the perspective of water dynamics. This study clarifies that water plays dual key roles in regulating salt precipitation: first, as the essential carrier for cation removal, and second, as a dynamic modulator of transmembrane water and cation fluxes. Based on this insight, the concept of equivalent salt concentration ( C eq ) is proposed, defined as the ratio of transmembrane potassium ion flux to liquid water flux. By comparing C eq with the saturation solubility of KHCO 3 (2.24 mol/L at 20 °C), a quantitative model is established to accurately predict the risk of salt precipitation under different anolyte concentrations, which is validated by long-term stability experiments. Systematic investigations show that membranes with high water permeability and low electro-osmotic drag (EOD) coefficients (e.g., X37–50 RT membrane reducing C eq by 62.8% vs A40), enhanced gas diffusion layer (GDL) hydrophobicity, and optimized CO 2 flow rates effectively mitigate salt precipitation. This work not only establishes a rapid prediction method for salt precipitation risk but also provides targeted strategies for the design of salt precipitation-resistant anion exchange membranes and GDLs in MEA CO 2 electrolyzers, which is of great significance for advancing the industrial application of this technology.