Single-Site Metal–Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2H4

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO₂ reduction reaction (CO₂RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal–organic framework (MOF), named as Cu–MOF–CF, to realize improved electrochemical CO₂RR performance, is reported. The Cu–MOF–CF shows suppression of CH₄, great increase in C₂H₄ selectivity (48.6%), and partial current density of C₂H₄ at −1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu–MOF–CF for CO₂RR results from the improved microenvironment of the Cu active sites that inhibits CH₄ production, more CO intermediate produced by single-site Cu–MOF in situ for CF, and the enlarged active surface area by porous Cu–MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO₂RR.     

AuCu Alloy Nanoparticle Embedded Cu Submicrocone Arrays for Selective Conversion of CO2 to Ethanol

The CO₂ reduction reaction (CO₂RR) driven by renewable electricity represents a promising strategy toward alleviating the energy shortage and environmental crisis facing humankind. Cu species, as one type of versatile electrocatalyst for the CO₂RR, attract tremendous research interest. However, for C₂ products, ethanol formation is commonly less favored over Cu electrocatalysts. Herein, AuCu alloy nanoparticle embedded Cu submicrocone arrays (AuCu/Cu‐SCA) are constructed as an active, selective, and robust electrocatalyst for the CO₂RR. Enhanced selectivity for EtOH is gained, whose Faradaic efficiency (FE) reaches 29 ± 4%, while ethylene formation is relatively inhibited (16 ± 4%) in KHCO₃ aqueous solution. The ratio between partial current densities of EtOH and C₂H₄ (j_EtOH/j_C2H4) can be tuned in the range from 0.15 ± 0.27 to 1.81 ± 0.55 by varying the Au content of the electrocatalysts. The combined experimental and theoretical calculation results identify the importance of Au in modifying binding energies of key intermediates, such as CH₂CHO*, CH₃CHO*, and CH₃CH₂O*, which consequently modify the activity and selectivity (j_EtOH/j_C2H4) for the CO₂RR. Moreover, AuCu/Cu‐SCA also shows high durability with both the current density and FE_EtOH being largely maintained for 24 h electrocatalysis.     

Less-Coordinated Atomic Copper-Dimer Boosted Carbon–Carbon Coupling During Electrochemical CO2 Reduction

This work reports a metal–organic framework (MOF) with less-coordinated copper dimers, which displays excellent electrochemical CO₂ reduction (eCO₂RR) performance with an advantageous current density of 0.9 A cm⁻² and a high Faradaic efficiency of 71% to C₂ products. In comparison with MOF with Cu monomers that are present as Cu₁ O₄ with a coordination number of 3.8 ± 0.2, Cu dimers exist as O₃Cu₁···Cu₂O₂ with a coordination number of 2.8 ± 0.1. In situ characterizations together with theoretical calculations reveal that two *CO intermediates are stably adsorbed on each site of less-coordinated Cu dimers, which favors later dimerization via a key intermediate of *CH₂CHO. The highly unsaturated dual-atomic Cu provides large-quantity and high-quality actives sites for carbon–carbon coupling, achieving the optimal trade-off between activity and selectivity of eCO₂RR to C₂ products.     

Designing N-Confused Metalloporphyrin-Based Covalent Organic Frameworks for Enhanced Electrocatalytic Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO₂) into value-added products is promising to alleviate greenhouse gas emission and energy demands. Metalloporphyrin-based covalent organic frameworks (MN₄-Por-COFs) provide a platform for rational design of electrocatalyst for CO₂ reduction reaction (CO₂RR). Herein, through systematic quantum-chemical studies, the N-confused metallo-Por-COFs are reported as novel catalysts for CO₂RR. For MN₄-Por-COFs, among the ten 3d metals, M = Co/Cr stands out in catalyzing CO₂RR to CO or HCOOH; hence, N-confused Por-COFs with Co/CrN₃C₁ and Co/CrN₂C₂ centers are designed. Calculations indicate CoN_xC_y-Por-COFs exhibit lower limiting potential (−0.76 and -0.60 V) for CO₂-to-CO reduction than its parent CoN₄-Por-COFs (−0.89 V) and make it feasible to yield deep-reduction degree C₁ products CH₃OH and CH₄. Electronic structure analysis reveals that substituting CoN₄ to CoN₃C₁/CoN₂C₂ increases the electron density on Co-atom and raises the d-band center, thus stabilizing the key intermediates of the potential determining step and lowering the limiting potential. For similar reason, changing the core from CrN₄ to CrN₃C₁/CrN₂C₂ lowers the limiting potential for CO₂-to-HCOOH reduction. This work predicts N-confused Co/CrN_xC_y-Por-COFs to be high-performance CO₂RR catalyst candidates. Inspiringly, as a proof-of-concept study, it provides an alternative strategy for coordination regulation and theoretical guidelines for rational design of catalysts.     

Promoting Electrocatalytic CO2 Reduction to CH4 by Copper Porphyrin with Donor–Acceptor Structures

Molecular catalysts have been receiving increasingly attention in the electrochemical CO₂ reduction reaction (CO₂RR) with attractive features such as precise catalytic sites and tunable ligands. However, the insufficient activity and low selectivity of deep reduction products restrain the utilization of molecular catalysts in CO₂RR. Herein, a donor–acceptor modified Cu porphyrin (CuTAPP) is developed, in which amino groups are linked to donate electrons toward the central CuN₄ site to enhance the CO₂RR activity. The CuTAPP catalyst exhibited an excellent CO₂-to-CH₄ electroreduction performance, including a high CH₄ partial current density of 290.5 mA cm⁻² and a corresponding Faradaic efficiency of 54.8% at –1.63 V versus reversible hydrogen electrode in flow cells. Density functional theory calculations indicated that CuTAPP presented a much lower energy gap in the pathway of producing *CHO than Cu porphyrin without amino group modification. This work suggests a useful strategy of introducing designed donor–acceptor structures into molecular catalysts for enhancing electrochemical CO₂ conversion toward deep reduction products.     

Morphological and Compositional Design of Pd–Cu Bimetallic Nanocatalysts with Controllable Product Selectivity toward CO2 Electroreduction

Electrochemical conversion of carbon dioxide (electrochemical reduction of carbon dioxide) to value‐added products is a promising way to solve CO₂ emission problems. This paper describes a facile one‐pot approach to synthesize palladium–copper (Pd–Cu) bimetallic catalysts with different structures. Highly efficient performance and tunable product distributions are achieved due to a coordinative function of both enriched low‐coordinated sites and composition effects. The concave rhombic dodecahedral Cu₃Pd (CRD‐Cu₃Pd) decreases the onset potential for methane (CH₄) by 200 mV and shows a sevenfold CH₄ current density at ?1.2 V (vs reversible hydrogen electrode) compared to Cu foil. The flower‐like Pd₃Cu (FL‐Pd₃Cu) exhibits high faradaic efficiency toward CO in a wide potential range from ?0.7 to ?1.3 V, and reaches a fourfold CO current density at ?1.3 V compared to commercial Pd black. Tafel plots and density functional theory calculations suggest that both the introduction of high‐index facets and alloying contribute to the enhanced CH₄ current of CRD‐Cu₃Pd, while the alloy effect is responsible for high CO selectivity of FL‐Pd₃Cu.     

Porous Copper Microspheres for Selective Production of Multicarbon Fuels via CO2 Electroreduction

The electroreduction of carbon dioxide (CO₂) toward high‐value fuels can reduce the carbon footprint and store intermittent renewable energy. The iodide‐ion‐assisted synthesis of porous copper (P‐Cu) microspheres with a moderate coordination number of 7.7, which is beneficial for the selective electroreduction of CO₂ into multicarbon (C₂₊) chemicals is reported. P‐Cu delivers a C₂₊ Faradaic efficiency of 78 ± 1% at a potential of ?1.1 V versus a reversible hydrogen electrode, which is 32% higher than that of the compact Cu counterpart and approaches the record (79%) reported in the same cell configuration. In addition, P‐Cu shows good stability without performance loss throughout a continuous operation of 10 h.     

Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation

Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C₂H₂ capacity and selectivity over CO₂ and C₂H₄ than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C₂H₂/CO₂ (50/50, v/v) and C₂H₂/C₂H₄ (1/99, v/v), which can selectively remove C₂H₂ with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.     

Amorphizing of Cu Nanoparticles toward Highly Efficient and Robust Electrocatalyst for CO2 Reduction to Liquid Fuels with High Faradaic Efficiencies

Conversion of carbon dioxide (CO₂) into valuable chemicals, especially liquid fuels, through electrochemical reduction driven by sustainable energy sources, is a promising way to get rid of dependence on fossil fuels, wherein developing of highly efficient catalyst is still of paramount importance. In this study, as a proof‐of‐concept experiment, first a facile while very effective protocol is proposed to synthesize amorphous Cu NPs. Unexpectedly, superior electrochemical performances, including high catalytic activity and selectivity of CO₂ reduction to liquid fuels are achieved, that is, a total Faradaic efficiency of liquid fuels can sum up to the maximum value of 59% at ?1.4 V, with formic acid (HCOOH) and ethanol (C₂H₆O) account for 37% and 22%, respectively, as well as a desirable long‐term stability even up to 12 h. More importantly, this work opens a new avenue for improved electroreduction of CO₂ based on amorphous metal catalysts.     

Restricting Lattice Flexibility in Polycrystalline Metal–Organic Framework Membranes for Carbon Capture

Although polycrystalline metal‐organic framework (MOF) membranes offer several advantages over other nanoporous membranes, thus far they have not yielded good CO₂ separation performance, crucial for energy‐efficient carbon capture. ZIF‐8, one of the most popular MOFs, has a crystallographically determined pore aperture of 0.34 nm, ideal for CO₂/N₂ and CO₂/CH₄ separation; however, its flexible lattice restricts the corresponding separation selectivities to below 5. A novel postsynthetic rapid heat treatment (RHT), implemented in a few seconds at 360 °C, which drastically improves the carbon capture performance of the ZIF‐8 membranes, is reported. Lattice stiffening is confirmed by the appearance of a temperature‐activated transport, attributed to a stronger interaction of gas molecules with the pore aperture, with activation energy increasing with the molecular size (CH₄ > CO₂ > H₂). Unprecedented CO₂/CH₄, CO₂/N₂, and H₂/CH₄ selectivities exceeding 30, 30, and 175, respectively, and complete blockage of C₃H₆, are achieved. Spectroscopic and X‐ray diffraction studies confirm that while the coordination environment and crystallinity are unaffected, lattice distortion and strain are incorporated in the ZIF‐8 lattice, increasing the lattice stiffness. Overall, RHT treatment is a facile and versatile technique that can vastly improve the gas‐separation performance of the MOF membranes.     

TEM observations of diamond films produced by hot filament thermal CVD

Diamond films were provided by a hot filament thermal chemical vapour deposition method with an H₂-CH₄ gas mixture under various reaction conditions: CH₄/H₂ ratios of 0.5% and 1.0%, Si and Cu substrates, a substrate temperature of 750 °tC, a pressure of 7 torr and a reaction time of 12 h. TEM observation showed that the films produced have many defects such as twins, stacking faults and large distortion of lattices. These defects, which increase with increasing CH₄ concentration, seem to be introduced during the crystal growth process. Fivefold symmetry twinned crystals were often observed in the diamond films.     

Hybrid Cu0 and Cux+ as Atomic Interfaces Promote High‐Selectivity Conversion of CO2 to C2H5OH at Low Potential

The mixing of charge states of metal copper catalysts may lead to a much improved reactivity and selectivity toward multicarbon products for CO₂ reduction. Here, an electrocatalyst model composed of copper clusters supported on graphitic carbon nitride (g‐C₃N₄) is proposed; the connecting Cu atoms with g‐C₃N₄ can be oxidized to Cu^{x +} due to substantial charge transfer from Cu to N atoms, while others stay as Cu⁰. It is revealed that CO₂ can be captured and reduced into *CO on the Cu_t⁰ site, owing to its zero oxidation state. More importantly, C–C coupling reaction of two *CHO species on the Cu_t⁰–Cu_b^{x +} atomic interface can occur with a rather low kinetic barrier of 0.57 eV, leading to the formation of the final C₂ product, namely, C₂H₅OH. During the whole process, the limiting potential is just 0.68 V. These findings may open a new avenue for CO₂ reduction into high‐value fuels and chemicals.     

Dual Engineering of Lattice Strain and Valence State of NiAl-LDHs for Photoreduction of CO2 to Highly Selective CH4

Converting CO₂ to clean-burning fuel such as natural gas (CH₄) with high activity and selectivity remains to be a grand challenge due to slow kinetics of multiple electron transfer processes and competitive hydrogen evolution reaction (HER). Herein, the fabrication of surfactants (C₁₁H₂₃COONa, C₁₂H₂₅SO₄Na, C₁₆H₃₃SO₄Na) intercalated NiAl-layered double hydroxides (NiAl-LDH) is reported, resulting in the formation of LDH-S1 (S1 = C₁₁H₂₃COO⁻), LDH-S2 (S2 = C₁₂H₂₅SO₄⁻) and LDH-S3 (S3 = C₁₆H₃₃SO₄⁻) with curved morphology. Compared with NiAl-LDH with a 1.53% selectivity of CH₄, LDH-S2 shows higher selectivity of CH₄ (83.07%) and lower activity of HER (3.84%) in CO₂ photoreduction reaction (CO₂PR). Detailed characterizations and DFT calculation indicates that the inherent lattice strain in LDH-S2 leads to the structural distortion with the presence of V_Ni/Al defects and compressed M O M bonds, and thereby reduces the overall energy barrier of CO₂ to CH₄. Moreover, the lower oxidation states of Ni in LDH-S2 enhances the adsorption of intermediates such as OCOH* and *CO, promoting the hydrogenation of CO to CH₄. Therefore, the coupling effect of both lattice strain and electronic structure of the LDH-S2 significantly improves the activity and selectivity for CO₂PR.     

Synergistic Catalysis over Iron‐Nitrogen Sites Anchored with Cobalt Phthalocyanine for Efficient CO2 Electroreduction

Simultaneously achieving high Faradaic efficiency, current density, and stability at low overpotentials is essential for industrial applications of electrochemical CO₂ reduction reaction (CO₂RR). However, great challenges still remain in this catalytic process. Herein, a synergistic catalysis strategy is presented to improve CO₂RR performance by anchoring Fe‐N sites with cobalt phthalocyanine (denoted as CoPc©Fe‐N‐C). The potential window of CO Faradaic efficiency above 90% is significantly broadened from 0.18 V over Fe‐N‐C alone to 0.71 V over CoPc©Fe‐N‐C while the onset potential of CO₂RR over both catalysts is as low as ?0.13 V versus reversible hydrogen electrode. What is more, the maximum CO current density is increased ten times with significantly enhanced stability. Density functional theory calculations suggest that anchored cobalt phthalocyanine promotes the CO desorption and suppresses the competitive hydrogen evolution reaction over Fe‐N sites, while the *COOH formation remains almost unchanged, thus demonstrating unprecedented synergistic effect toward CO₂RR.     

Selective and Stable CO2 Electroreduction to CH4 via Electronic Metal–Support Interaction upon Decomposition/Redeposition of MOF

The CO₂ electroreduction to fuels is a feasible approach to provide renewable energy sources. Therefore, it is necessary to conduct experimental and theoretical investigations on various catalyst design strategies, such as electronic metal–support interaction, to improve the catalytic selectivity. Here a solvent-free synthesis method is reported to prepare a copper (Cu)-based metal–organic framework (MOF) as the precursor. Upon electrochemical CO₂ reduction in aqueous electrolyte, it undergoes in situ decomposition/redeposition processes to form abundant interfaces between Cu nanoparticles and amorphous carbon supports. This Cu/C catalyst favors the selective and stable production of CH₄ with a Faradaic efficiency of ≈55% at −1.4 V versus reversible hydrogen electrode (RHE) for 12.5 h. The density functional theory calculation reveals the crucial role of interfacial sites between Cu and amorphous carbon support in stabilizing the key intermediates for CO₂ reduction to CH₄. The adsorption of COOH* and CHO* at the Cu/C interface is up to 0.86 eV stronger than that on Cu(111), thus promoting the formation of CH₄. Therefore, it is envisioned that the strategy of regulating electronic metal–support interaction can improve the selectivity and stability of catalyst toward a specific product upon electrochemical CO₂ reduction.     

Carbon Dioxide Promotes Dehydrogenation in the Equimolar C2H2‐CO2 Reaction to Synthesize Carbon Nanotubes

The equimolar C₂H₂‐CO₂ reaction has shown promise for carbon nanotube (CNT) production at low temperatures and on diverse functional substrate materials; however, the electron‐pushing mechanism of this reaction is not well demonstrated. Here, the role of CO₂ is explored experimentally and theoretically. In particular, ¹³C labeling of CO₂ demonstrates that CO₂ is not an important C source in CNT growth by thermal catalytic chemical vapor deposition. Consistent with this experimental finding, the adsorption behaviors of C₂H₂ and CO₂ on a graphene‐like lattice via density functional theory calculations reveal that the binding energies of C₂H₂ are markedly higher than that of CO₂, suggesting the former is more likely to incorporate into CNT structure. Further, H‐abstraction by CO₂ from the active CNT growth edge would be favored, ultimately forming CO and H₂O. These results support that the commonly observed, promoting role of CO₂ in CNT growth is due to a CO₂‐assisted dehydrogenation mechanism.     

A Chemically Stable Hofmann-Type Metal−Organic Framework with Sandwich-Like Binding Sites for Benchmark Acetylene Capture

The realization of porous materials for highly selective separation of acetylene (C₂H₂) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann-type metal−organic framework (MOF), Co(pyz)[Ni(CN)₄] (termed as ZJU-74a), that features sandwich-like binding sites for benchmark C₂H₂ capture and separation is reported. Gas sorption isotherms reveal that ZJU-74a exhibits by far the record C₂H₂ capture capacity (49 cm³ g⁻¹ at 0.01 bar and 296 K) and thus ultrahigh selectivity for C₂H₂/CO₂ (36.5), C₂H₂/C₂H₄ (24.2), and C₂H₂/CH₄ (1312.9) separation at ambient conditions, respectively, of which the C₂H₂/CO₂ selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU-74a can construct a sandwich-type adsorption site to offer dually strong and cooperative interactions for the C₂H₂ molecule, thus leading to its ultrahigh C₂H₂ capture capacity and selectivities. The exceptional separation performance of ZJU-74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C₂H₂/CO₂, 1/99 C₂H₂/C₂H₄, and 50/50 C₂H₂/CH₄ mixtures under ambient conditions.     

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution by Plasmonic Au/CdSe–Cu2O Hierarchical Nanostructures under Visible Light

Here, the photocatalytic CO₂ reduction reaction (CO₂RR) with the selectivity of carbon products up to 100% is realized by completely suppressing the H₂ evolution reaction under visible light (λ > 420 nm) irradiation. To target this, plasmonic Au/CdSe dumbbell nanorods enhance light harvesting and produce a plasmon‐enhanced charge‐rich environment; peripheral Cu₂O provides rich active sites for CO₂ reduction and suppresses the hydrogen generation to improve the selectivity of carbon products. The middle CdSe serves as a bridge to transfer the photocharges. Based on synthesizing these Au/CdSe–Cu₂O hierarchical nanostructures (HNSs), efficient photoinduced electron/hole (e^?/h⁺) separation and 100% of CO selectivity can be realized. Also, the 2e^?/2H⁺ products of CO can be further enhanced and hydrogenated to effectively complete 8e^?/8H⁺ reduction of CO₂ to methane (CH₄), where a sufficient CO concentration and the proton provided by H₂O reduction are indispensable. Under the optimum condition, the Au/CdSe–Cu₂O HNSs display high photocatalytic activity and stability, where the stable gas generation rates are 254 and 123 µmol g^?1 h^?1 for CO and CH₄ over a 60 h period.     

Multilayer-Cavity Tandem Catalyst for Profiling Sequentially Coupling of Intermediate CO in Electrocatalytic Reduction Reaction of CO2 to Multi-Carbon Products

Electrochemical CO₂ reduction reaction (CO₂RR) is an effective approach to address CO₂ emission, promote recycling, and synthesize high-value multi-carbon (C₂₊) chemicals for storing renewable electricity in the long-term. The construction of multilayer-bound nanoreactors to achieve management of intermediate CO is a promising strategy for tandem to C₂₊ products. In this study, a series of Ag@Cu₂O nanoreactors consisting of an Ag-yolk and a multilayer confined Cu shell is designed to profile electrocatalytic CO₂RR reactions. The optimized Ag@Cu₂O-2 nanoreactor exhibits a 74% Faradaic efficiency during the C₂₊ pathway and remains stable for over 10 h at a bias current density of 100 mA cm⁻². Using the finite element method, this model determines that the certain volume of cavity in the Ag@Cu₂O nanoreactors facilitates on-site CO retention and that multilayers of Cu species favor CO capture. Density functional theory calculations illustrate that the biased generation of ethanol products may arise from the (100)/(111) interface of the Cu layer. In-depth explorations in multilayer-bound nanoreactors provide structural and interfacial guidance for sequential coupling of CO₂RR intermediates for efficient C₂₊ generation.