Tailoring Polymeric Binder of Permselective Gas Diffusion Electrode for Low-Concentration CO₂ Electrolysis

Electrochemical CO₂ reduction (eCO₂R) offers a promising route to convert industrial CO₂ emissions into value-added chemicals. However, direct electrolysis of low-concentration CO₂ streams from flue gas suffers from mass transport limitation, resulting in poor Faradaic efficiency (FE). To address this challenge, a gas diffusion electrode featuring a permselective layer is developed that selectively concentrates CO₂ at the catalyst interface. The permselective layer integrates a hybrid CO₂-philic metal-organic framework Calgary Framework-20 (CALF-20) filler embedded within a tailored polymer matrix. Three polymers-Nafion, polysulfone (PSF), and styrene-ethylene-butylene-styrene-as the polymer matrix to optimize CO₂/N₂ selectivity and permeability are systematically tested. The CALF-20/PSF composite in the permselective layer achieves a CO₂/N₂ selectivity of ≈40, enabling a threefold increase in CO partial current density (j_CO of -42.7 mA cm^-2) with a dilute CO₂ feed (10 volume percentage) compared to unmodified electrodes at an applied current density of -50 mA cm^-2. In a membrane electrode assembly, the optimized electrode maintains a stable FE_CO of ≈70% for over 20 h. CO₂ uptake studies and structural characterization reveal that strong interactions between the triazole ligands of CALF-20 and the sulfonyl/ether groups of PSF enhance both CO₂ transport and electrode durability.