Achieving High Selectivity and Stability in Electrocatalytic CO2 Reduction in Acidic Media via Ion Confinement.

Immobilizing cation-type organic molecules at the cathode represents a transformative strategy for enhancing the electrocatalytic CO2 reduction reaction (CO2RR) 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 CO2RR. Our findings show that cations in both cation- and anion-type molecules play a crucial role in inhibiting the hydrogen evolution reaction and promoting CO2RR in MEA. Utilizing an anion-type organic molecule, we achieved exceptional CO Faradaic efficiencies of 98.4% in H2SO4 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 H2SO4 (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 CO2 electrolysis across diverse electrolyte environments, highlighting its potential for industrial-scale application.