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

Abstract 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.