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A microenvironment engineering strategy has been developed to switch the CO2 electroreduction reaction (CO2RR) selectivity from methane (CH4) to ethylene (C2H4) by adjusting the coordination microstructures of trinuclear copper cluster‐based metal‐covalent organic framework (MCOF). When Cu sites are oriented to channels in Cu‐PyCA‐MCOF, methane is the main product. Conversely, when trinuclear copper sites are coordinated with OH− and H2O molecules in Cu‐PyCAOH‐MCOF nanosheets, the main product switches from CH4 to C2H4 with 50.5% selectivity and 200.2 mA cm− partial current density at −1.2 V (vs RHE). This happens because CO2 molecules can only contact active sites perpendicular to the trinuclear copper cluster plane in Cu‐PyCAOH‐MCOF nanosheets, where the Cu─Cu distance between them is 3.2 Å, favoring the efficient conversion of CO2 to C2H4 through the C─C coupling reaction. Operando infrared spectroscopy, in situ X‐ray absorption near‐edge structure spectra, and DFT calculations reveal that changing the coordination environments of MCOFs significantly stabilizes key intermediates and reduces the energies of the CO2RR. This work offers an effective strategy for enhancing CO2RR performance toward C2H4 products by tuning the microenvironments of copper‐based electrocatalysts. [ABSTRACT FROM AUTHOR]

The use of flue gas (containing 3–4% O2) as the direct feed gas for the CO2 electroreduction reaction (CO2RR) is a promising protocol to reduce CO2 purification costs. However, the competitive oxygen reduction reaction (ORR) and cathodic carbonate salt precipitation severely hinder its practical application. Here, we realize efficient CO2RR towards CO under CO2 containing 5% O2 gas feed in conditions of acidic media. A conjugated cobalt polyphthalocyanine framework (CoPPc) shows outstanding performance in aqueous acidic electrolyte (H2SO4 + 0.4 M Cs2SO4, pH = 3.0) with a faradaic efficiency toward CO (FECO) exceeding 95% over a wide potential range from −1.0 to −1.9 V vs. a reversible hydrogen electrode (RHE), and a maximum CO partial current density (jCO) up to −294 mA cm−2 when using pure CO2 gas. After coating with polyaniline (PANI), CoPPc@PANI shows a high FECO of up to 87.4% and a maximum industrial level current density of −270 mA cm−2 at −2.1 V vs. RHE under 95% CO2 + 5% O2 feed gas in acidic media. The results of the oxygen reduction reaction, CO2 adsorption capacity and the isosteric heat of adsorption (Qst) demonstrate that CoPPc@PANI can adsorb and enrich CO2 in comparison with oxygen, resulting in superior CO2 reduction performance in the presence of O2. This work will shed new light on the development of efficient electrocatalysts for CO2RR using flue gas, which can reduce separation costs and avoid the formation of cathodic carbonate salt precipitates. [ABSTRACT FROM AUTHOR]

Herein, 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. [ABSTRACT FROM AUTHOR]

The direct use of flue gas for the electrochemical CO2 reduction reaction is desirable but severely limited by the thermodynamically favorable oxygen reduction reaction. Herein, a photonicswitching unit 1,2-Bis(5'-formyl-2'-methylthien-3'-yl)cyclopentene (DAE) is integrated into a cobalt porphyrin-based covalent organic framework for highly efficient CO2 electrocatalysis under aerobic environment. The DAE moiety in the material can reversibly modulate the O2 activation capacity and electronic conductivity by the framework ring-closing/opening reactions under UV/Vis irradiation. The DAE-based covalent organic framework with ring-closing type shows a high CO Faradaic efficiency of 90.5% with CO partial current density of −20.1 mA cm−2 at −1.0 V vs. reversible hydrogen electrode by co-feeding CO2 and 5% O2. This work presents an oxygen passivation strategy to realize efficient CO2 electroreduction performance by co-feeding of CO2 and O2, which would inspire to design electrocatalysts for the practical CO2 source such as flue gas from power plants or air. Direct use of flue gas for the electrocatalytic CO2 reduction reaction is desirable but severely limited by the thermodynamically favorable oxygen reduction reaction. Here the authors report an oxygen passivation strategy to improve electrocatalytic CO2 reduction reaction under aerobic conditions using a covalent organic frameworks with a photoswitching unit. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) imine‐based covalent organic frameworks (COFs) hold potential for photocatalytic CO2 reduction. However, high energy barrier of imine linkage impede the in‐plane photoelectron transfer process, resulting in inadequate efficiency of CO2 photoreduction. Herein, we present a dimensionality induced local electronic modulation strategy through the construction of one‐dimensional (1D) pyrene‐based covalent organic frameworks (PyTTA‐COF). The dual‐chain‐like edge architectures of 1D PyTTA‐COF enable the stabilization of aromatic backbones, thus reducing energy loss during exciton dissociation and thermal relaxation, which provides energetic photoelectron to traverse the energy barrier of imine linkages. As a result, the 1D PyTTA‐COF exhibits significantly enhanced CO2 photoreduction activity under visible‐light irradiation when coordinated with metal cobalt ion, yielding a remarkable CO evolution of 1003 μmol g−1 over an 8‐hour period, which surpasses that of the corresponding 2D counterpart by a factor of 59. These findings present a valuable approach to address in‐plane charge transfer limitations in imine‐based COFs. [ABSTRACT FROM AUTHOR]

We propose an effective highest occupied d‐orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO2 electroreduction from HCOOH/CO to higher‐valued hydrocarbons. An atomically well‐defined Cu6 NC with symmetry‐broken Cu−S2N1 active sites (named Cu6(MBD)6, MBD=2‐mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu−S3 sites, the Cu6(MBD)6 with Cu−S2N1 coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at −1.4 V versus the reversible hydrogen electrode (including 42.5 % CH4 and 23 % C2H4), with the hydrocarbons partial current density of −183.4 mA cm−2. Theoretical calculations reveal that the symmetry‐broken Cu−S2N1 sites can rearrange the Cu 3d orbitals with dx2-y2 ${d_{x^2 - y^2 } }$ as the highest occupied d‐orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C−C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO2RR towards highly‐valued products. [ABSTRACT FROM AUTHOR]

The development of single atom catalysts (SACs) for CO2 electroreduction in acidic electrolytes can greatly improve the CO2 utilization efficiency but remains challenging. We report a carbon-embedded atomic nickel catalyst prepared from carbon black, porphyrin and nickel(II) salts. The catalyst shows excellent activity for CO2 reduction with high CO faradaic efficiency of 99.9% and an industrial-level CO partial current density of 296.4 mA cm−2 in acidic media, which indicates the importance of carbon-supported SACs. [ABSTRACT FROM AUTHOR]

Although the highly porous crystalline metal–organic frameworks (MOFs) are promising candidates as active electrocatalysts for CO2 reduction reaction (CO2RR), their poor electronic conductivities severely limit their applications. Viologens (Vg) and their derivatives are able to act as electron-transfer mediators (ETMs) to facilitate rapid electron transfer to active sites but have not yet been integrated into MOFs for the CO2RR. Herein, viologen groups are integrated into cobalt porphyrin (Por(Co))-based MOFs for the first time to act as ETMs to enhance the electron-transfer capacity and thus improve the activity of the CO2RR. The obtained optimal Vg–Por(Co)–MOF(9 : 1) (Por(Co) : Vg = 9 : 1) showed excellent catalytic performance with a high faradaic efficiency of CO (FECO = 93.8%, 2.3 V) and large CO partial current density of (jCO) 111.1 mA cm−2 at 2.9 V in the CO2RR in a membrane electrode assembly (MEA) system. The FECO and jCO values for Vg–Por(Co)–MOF(9 : 1) are about 1.9 and 2 times larger than those of Por(Co)–MOF containing free Vg as the ETM (49.2% and 51.4 mA cm−2, respectively). Such excellent performance of Vg–Por(Co)–MOF(9 : 1) also surpasses that of the majority of other cobalt-based electrocatalysts, which make it stand out as being among the benchmark electrocatalysts for CO2 to CO generation. This work offers an efficient method for designing extremely effective porous frameworks for enhanced electrocatalysis through increasing electrical conductivity. [ABSTRACT FROM AUTHOR]

We present the first example of charged imidazolium functionalized porphyrin‐based covalent organic framework (Co‐iBFBim‐COF‐X) for electrocatalytic CO2 reduction reaction, where the free anions (e.g. F−, Cl−, Br−, and I−) of imidazolium ions nearby the active Co sites can stabilize the key intermediate *COOH and inhibit hydrogen evolution reaction. Thus, Co‐iBFBim‐COF‐X exhibits higher activity than the neutral Co‐BFBim‐COF, following the trend of F−