High-Rate and Selective CO 2 Electrolysis to Ethylene via Metal-Organic-Framework-Augmented CO 2 Availability.

High-rate conversion of carbon dioxide (CO 2 ) to ethylene (C 2 H 4 ) in the CO 2 reduction reaction (CO 2 RR) requires fine control over the phase boundary of the gas diffusion electrode (GDE) to overcome the limit of CO 2 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 C 2 H 4 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 CO 2 concentration near the active sites of the Cu catalysts. MOFs with different CO 2 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% C 2 H 4 Faradaic efficiency (FE) at a current density of 200 mA cm - 2 in a flow cell, 49% C 2 H 4 FE at 1 A cm - 2 is achieved on MOF-augmented GDEs in CO 2 RR. MOF-augmented GDEs are further evaluated in an MEA electrolyzer, achieving a C 2 H 4 partial current density of 220 mA cm -2 for CO 2 RR and 121 mA cm -2 for the carbon monoxide reduction reaction (CORR), representing 2.7-fold and 15-fold improvement in C 2 H 4 production rate, compared to those obtained on bare Cu/PTFE.