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

• Published in: Nature energy Vol. 7; no. 9; pp. 835 - 843
• Main Authors: Li, Wenzheng, Yin, Zhenglei, Gao, Zeyu, Wang, Gongwei, Li, Zhen, Wei, Fengyuan, Wei, Xing, Peng, Hanqing, Hu, Xingtao, Xiao, Li, Lu, Juntao, Zhuang, Lin
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2022; Nature Publishing Group
• Subjects: 639/301/299/886; 639/4077/4057; 639/4077/909/4101/4102; Ammonia; Carbon dioxide; Carbonyl compounds; Carbonyl groups; Carbonyls; Catalysts; Chemical synthesis; Consumption; Current density; Economics and Management; Electrolysis; Electrolytes; Energy; Energy Policy; Energy Storage; Energy Systems; Ethylene; Ionomers; Ketones; Molten salt electrolytes; Polymers; Renewable and Green Energy; Running; Solid electrolytes; Solid state
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/s41560-022-01092-9

Many CO 2 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 CO 2 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 CO 2 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 CO 2 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. Solid-state polymers are promising electrolytes for CO 2 electrolysers, but when pure water is used as the feed, they typically cannot create a sufficiently alkaline environment to favour multicarbon products. Here the authors use bifunctional ionomers as polymer electrolytes that activate CO 2 at the catalyst–electrolyte interface, favouring ethylene synthesis, while running on pure water.