Bifunctional ionomers for efficient co-electrolysis of CO2 and pure water towards ethylene production at industrial-scale current densities

Many CO2 electrolysers under development use liquid electrolytes (KOH solutions, for example), yet using solid-state polymer electrolytes can in principle improve efficiency and realize co-electrolysis of CO2 and pure water, avoiding corrosion and electrolyte consumption issues. However, a key challenge in these systems is how to favour production of multicarbon molecules, such as ethylene, which typically necessitates a strong alkaline environment. Here we use bifunctional ionomers as polymer electrolytes that are not only ionically conductive but can also activate CO2 at the catalyst–electrolyte interface and favour ethylene synthesis, while running on pure water. Specifically, we use quaternary ammonia poly(ether ether ketone) (QAPEEK), which contains carbonyl groups in the polymer chain, as the bifunctional electrolyte. An electrolyser running on CO2 and pure water exhibits a total current density of 1,000 mA cm−2 at cell voltages as low as 3.73 V. At 3.54 V, ethylene is produced with the industrial-scale partial current density of 420 mA cm−2 without any electrolyte consumption.