Boosting CO2 Electroreduction over a Covalent Organic Framework in the Presence of Oxygen

Abstract

AbstractHerein, we propose an oxygen‐containing species coordination strategy to boost CO2 electroreduction in the presence of O2. 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−N4−O sites and the salen(Co)2 moiety with binuclear Co−N2O2 sites, is developed and synthesized for enhancing the CO2RR under aerobic condition. In the presence of O2, 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 CO2 molecules and stabilize the key intermediate *COOH of the CO2RR over the adjacent Co center. Besides, the oxygen species axially coordinated Ni−N4−O sites can favor in reducing the energy barrier of the intermediate *COOH formation for the CO2RR. Thus, NiPc‐Salen(Co)2‐COF exhibits high oxygen‐tolerant CO2RR performance and achieves outstanding CO Faradaic efficiency (FECO) 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 % O2, which is superior to that in pure CO2 feed gas (FECO=94.8 %, jCO=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 % O2 at −0.8 V, which is higher than that in pure CO2 atmosphere (jCO=104.8 mA cm−2). It is worth noting that an excellent FECO of 86.8 % is still achieved in the presence of 5 % O2 at −1.0 V. This work provides an effective strategy to enable the CO2RR under O2 atmosphere by utilizing the *OOH intermediates of ORR to boost CO2 electroreduction.