Boosting CO 2 Electroreduction over a Covalent Organic Framework in the Presence of Oxygen.

Herein, we propose an oxygen-containing species coordination strategy to boost CO 2 electroreduction in the presence of O 2 . A two-dimensional (2D) conjugated metal-covalent organic framework (MCOF), denoted as NiPc-Salen(Co) 2 -COF that is composed of the Ni-phthalocyanine (NiPc) unit with well-defined Ni-N 4 -O sites and the salen(Co) 2 moiety with binuclear Co-N 2 O 2 sites, is developed and synthesized for enhancing the CO 2 RR under aerobic condition. In the presence of O 2 , one of the Co sites in the NiPc-Salen(Co) 2 -COF that coordinated with the intermediate of *OOH from ORR could decrease the energy barrier of the activation of CO 2 molecules and stabilize the key intermediate *COOH of the CO 2 RR over the adjacent Co center. Besides, the oxygen species axially coordinated Ni-N 4 -O sites can favor in reducing the energy barrier of the intermediate *COOH formation for the CO 2 RR. Thus, NiPc-Salen(Co) 2 -COF exhibits high oxygen-tolerant CO 2 RR performance and achieves outstanding CO Faradaic efficiency (FE CO ) of 97.2 % at -1.0 V vs. the reversible hydrogen electrode (RHE) and a high CO partial current density of 40.3 mA cm -2 at -1.1 V in the presence of 0.5 % O 2 , which is superior to that in pure CO 2 feed gas (FE CO =94.8 %, j CO =19.9 mA cm -2 ). Notably, the NiPc-Salen(Co) 2 -COF achieves an industrial-level current density of 128.3 mA cm -2 in the flow-cell reactor with 0.5 % O 2 at -0.8 V, which is higher than that in pure CO 2 atmosphere (j CO =104.8 mA cm -2 ). It is worth noting that an excellent FE CO of 86.8 % is still achieved in the presence of 5 % O 2 at -1.0 V. This work provides an effective strategy to enable the CO 2 RR under O 2 atmosphere by utilizing the *OOH intermediates of ORR to boost CO 2 electroreduction.