Neutral Electrosynthesis of Methane from Diluted CO <sub>2</sub> on Dense Cu Sites Embedded Covalent Organic Frameworks
Yingjun Tan, Chenglong Sun, Guokang Han, Zhengyi Qian, Yu Gu, Na Ye, Zheng Lin, Qizheng Huang, Fei Liu, Changze Wei, Zhaoqi Dong, Heng Luo, Mingchuan Luo, Shaojun Guo
Abstract
Electrochemical upgrading of diluted CO 2, particularly in neutral media, offers a promising route to reduce the costs associated with purified/concentrated CO 2 streams. However, challenges, such as sluggish mass transport, competitive hydrogen evolution, and poor selectivity, remain unresolved. Herein, we design a covalent organic framework (COF) featuring dense (8.4 wt %) copper atomic sites (Cu-COFs) for boosting direct electroreduction of diluted CO 2 to methane. We demonstrate that the pyridinic N and microporous structure of Cu-COFs efficiently enrich local CO 2 through dominant van der Waals force and nano confinement, while the pyridinic nitrogen functional groups from Cu-COFs facilitate the formation of electron-deficient copper sites. In situ spectroscopic analysis and density functional theory calculations further reveal that the copper atomic sites can facilitate *CO adsorption, promote water dissociation, and suppress *CO dimerization, thereby selectively steering the reaction pathway toward methane. Benefiting from its tailored mass and charge transfer, the as-made Cu-COFs catalyst achieves a peak CH 4 Faradaic efficiency (FE) of 79.1% in 60 vol % CO 2 and maintains 61.1% even in a simulated flue gas (CO 2 /N 2 = 15:85, v/v), representing a record for methane electrosynthesis under low CO 2 concentrations. This coupling engineering of mass transport and catalytic sites opens a strategic pathway for the direct utilization of industrially dilute CO 2 streams.