High-Rate and Selective CO₂ Electrolysis to Ethylene via Metal–Organic-Framework-Augmented CO₂ Availability

High-rate conversion of carbon dioxide (CO₂) to ethylene (C₂H₄) in the CO₂ reduction reaction (CO₂RR) requires fine control over the phase boundary of the gas diffusion electrode (GDE) to overcome the limit of CO₂ solubility in aqueous electrolytes. Here, a metal–organic framework (MOF)-functionalized GDE design is presented, based on a catalysts:MOFs:hydrophobic substrate materials layered architecture, that leads to high-rate and selective C₂H₄ production in flow cells and membrane electrode assembly (MEA) electrolyzers. It is found that using electroanalysis and operando X-ray absorption spectroscopy (XAS), MOF-induced organic layers in GDEs augment the local CO₂ concentration near the active sites of the Cu catalysts. MOFs with different CO₂ adsorption abilities are used, and the stacking ordering of MOFs in the GDE is varied. While sputtering Cu on poly(tetrafluoroethylene) (PTFE) (Cu/PTFE) exhibits 43% C₂H₄ Faradaic efficiency (FE) at a current density of 200 mA cm⁻² in a flow cell, 49% C₂H₄ FE at 1 A cm⁻² is achieved on MOF-augmented GDEs in CO₂RR. MOF-augmented GDEs are further evaluated in an MEA electrolyzer, achieving a C₂H₄ partial current density of 220 mA cm⁻² for CO₂RR and 121 mA cm⁻² for the carbon monoxide reduction reaction (CORR), representing 2.7-fold and 15-fold improvement in C₂H₄ production rate, compared to those obtained on bare Cu/PTFE.