High-rate and Selective CO2 Electrolysis to Ethylene via Metal-Organic Framework-augmented CO2 Availability

High-rate carbon dioxide (CO2)-to-ethylene (C2H4) conversion 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 electrolyte. Here, we present a metal-organic framework (MOF)-functionalized GDE design, one based on a catalysts:MOFs:hydrophobic substrate materials layered architecture, that leads to high-rate and selective C2H4 production in flow cell and membrane electrode assembly (MEA) electrolyzers. We find, using electroanalysis and operando X-ray absorption spectroscopy (XAS), that MOF-induced organic layers in GDEs augment local CO2 concentration near the active sites of the Cu catalysts. We use MOFs with different CO2 adsorption abilities and vary the stacking ordering of MOFs in the GDE. While sputtered Cu on PTFE (Cu/PTFE) exhibited 43% C2H4 Faradaic efficiency (FE) at a current density of 200 mA/cm2 in a flow cell, 49% C2H4 FE at 1 A/cm2 was achieved on MOF-augmented GDEs in CO2RR. We further evaluate MOF-augmented GDEs in MEA electrolyzer, achieving a C2H4 partial current density of 220 mA/cm2 for CO2RR and 121 mA/cm2 for 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.