Achieving High Selectivity and Stability in Electrocatalytic CO 2 Reduction in Acidic Media via Ion Confinement

ABSTRACT Immobilizing cation‐type organic molecules at the cathode represents a transformative strategy for enhancing the electrocatalytic CO 2 reduction reaction (CO 2 RR) in acidic or pure water. However, the investigation of anion‐type organic molecules is missing, and the roles of cations and anions are not well understood, especially in the membrane electrode assembly (MEA) configuration. Employing an ionic‐confinement strategy mediated by a solid‐state electrolyte, we systematically investigate the influence of cation‐ and anion‐type organic molecules on CO 2 RR. Our findings show that cations in both cation‐ and anion‐type molecules play a crucial role in inhibiting the hydrogen evolution reaction and promoting CO 2 RR in MEA. Utilizing an anion‐type organic molecule, we achieved exceptional CO Faradaic efficiencies of 98.4% in H 2 SO 4 media (pH = 1) and 95.8% in pure water‐fed MEAs on Ag. Additionally, with cation‐type organic molecules, we demonstrated robust operational stability of 150 h in H 2 SO 4 (pH = 1) electrolyte and 460 h in an ultra‐low potassium concentration (2 mM) acidic electrolyte in MEA configuration. This work establishes a versatile framework for achieving high‐efficiency, long‐term CO 2 electrolysis across diverse electrolyte environments, highlighting its potential for industrial‐scale application.