Highly Selective CO 2 Electroreduction to CH 4 by In Situ Generated Cu 2 O Single‐Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding

Metal-Organic Framework Supported Low-Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol

It is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF-based supported low-nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three-dimensional (3D) microporous Cu-based MOF, that achieves a single-product Faradaic efficiency (FE) of 82.5 % at -1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm-2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi-site synergism of Cu LNCCs can increase the C-C coupling effect, and thus achieve high FE of CO2-to-ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2-to-EtOH.

Regulated Cu Diatomic Distance Promoting Carbon-Carbon Coupling During CO2 Electroreduction

To address the bottle-neck carbon-carbon coupling issue during electrochemical carbon dioxide reduction (eCO2RR) to multicarbon (C2+) products, this work develops an anion-directed strategy (Cl-, NO3 -, and SO4 2-) to regulate interatomic distance of Cu diatoms. In comparison to pristine Cu (with a typical Cu-Cu distance of 2.53 Å), Cu-boroimidazole frameworks (BIF)/SO4, NO3, and Cl material shows elongated diatomic distance of 3.90 Å, 4.21 Å, and 3.30 Å, respectively. Among them, the Cu-BIF/Cl exhibits an outstanding eCO2RR performance with a Faradaic efficiency of 72.12% for C2+ products and an industrial-level current density of 539.0 mA cm-2 at -1.75 V versus RHE. Significantly, according to theoretical and in situ experimental investigation, the highly electronegative Cl- ion lifts d-band center of Cu sites of Cu-BIF/Cl, facilitating *CO adsorption with a low Gibbs free energy and its later dimerization overcoming a small energy barrier. In addition, this strategy to manipulate interatomic distance for diatomic catalysts, can also be adaptable to other reactions involving intermediate coupling and following the Langmuir-Hinshelwood mechanism, such as carbon-nitrogen coupling, nitrogen-nitrogen coupling, etc.

Construction of coherent interface between Cu2O and CeO2via electrochemical reconstruction for efficient carbon dioxide reduction to methane

Developing an efficient electrocatalyst that enables the efficient electrochemical conversion from CO2 to CH4 across a wide potential range remains a formidable challenge. Herein, we introduce a precatalyst strategy that realizes the in situ electrochemical reconstruction of ultrafine Cu2O nanodomains, intricately coupled on the CeO2 surface (Cu2O/CeO2), originating from the heterointerface comprised of ultrafine CuO nanodomains on the CeO2 surface (CuO/CeO2). When served as the electrocatalyst for the electrochemical CO2 reduction reaction, Cu2O/CeO2 delivers a selectivity higher than 49 % towards CH4 over a broad potential range from -1.2 V to -1.7 V vs. RHE, maintaining negligible activity decay for 20 h. Notably, the highest selectivity for CH4 reaches an impressive 70 % at -1.5 V vs. RHE. Through the combination of comprehensive analysis including synchrotron X-ray absorption spectroscopy, spherical aberration-corrected high-angle annular dark field scanning transmission electron microscope as well as the density functional theoretical calculation, the efficient production of CH4 is attributed to the coherent interface between Cu2O and CeO2, which could converted from the original CuO and CeO2 interface, ensuring abundant active sites and enhanced intrinsic activity and selectivity towards CH4.

Highly Selective Conversion of Carbon Dioxide to Methane by Copper Single Atom Electrocatalysts

Electrocatalytic carbon dioxide reduction into high-value chemicals is one of the important solutions to the greenhouse effect and energy crisis. However, the slow kinetic process of eight electrons requires the development of efficient catalysts to improve the yields. Single atom catalysts (SACs) with high activity and selectivity have become an emerging research frontier in the field of heterogeneous catalysis. Herein, a catalyst comprised of Cu single atoms loaded on carbon substrate (Cu-NC) is developed for highly selective electrocatalytic reduction of CO2 to methane (CH4). The optimal catalyst (Cu-NC-1-4) exhibits a faradaic efficiency (FE) of over 50 % for CH4 within a wide potential window from -1.3 V to -1.8 V (vs. RHE) and the highest FE of CH4 is up to 67.22 % at -1.6 V (vs. RHE). Meanwhile, the product selectivity of CH4 among all the carbon products reaches 93.00 %, and the activity decay can be negligible via the 70-hour-stability-test. The existence of atomic dispersed Cu-N3 sites was verified by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption near edge structure (XANES). Density functional theory (DFT) calculations show that the effective adsorption of the key intermediate *CO on Cu-N3 sites prompts the generation of CH4.

Recent advancements in carbon/metal-based nano-catalysts for the reduction of CO2 to value-added products

Due to the increased human activities in burning of fossil fuels and deforestation, the CO2 level in the atmosphere gets increased up to 415 ppm; although it is an essential component for plant growth, an increased level of CO2 in the atmosphere leads to global warming and catastrophic climate change. Various conventional methods are used to capture and utilize CO2, among that a feasible and eco-friendly technique for creating value-added products is the CO2RR. Photochemical, electrochemical, thermochemical, and biochemical approaches can be used to decrease the level of CO2 in the atmosphere. The introduction of nano-catalysts in the reduction process helps in the efficient conversion of CO2 with improved selectivity, increased efficiency, and also enhanced stability of the catalyst materials. Thus, in this mini-review of nano-catalysts, some of the products formed during the reduction process, like CH3OH, C2H5OH, CO, HCOOH, and CH4, are explained. Among different types of metal catalysts, carbonaceous, single-atom catalysts, and MOF based catalysts play a significant role in the CO2 RR process. The effects of the catalyst material on the surface area, composition, and structural alterations are covered in depth. To aid in the design and development of high-performance nano-catalysts for value-added products, the current state, difficulties, and future prospects are provided.

Metal-Organic Frameworks for Electrocatalytic CO2 Reduction: From Catalytic Site Design to Microenvironment Modulation

The electrochemical reduction of CO2 to high-value carbon-based chemicals provides a sustainable approach to achieving an artificial carbon cycle. In the decade, metal-organic frameworks (MOFs), a kind of porous crystalline porous materials featuring well-defined structures, large surface area, high porosity, diverse components, easy tailorability, and controllable morphology, have attracted considerable research attention, serving as electrocatalysts to drive CO2 reduction. In this review, the reaction mechanisms of electrochemical CO2 reduction and the structure/component advantages of MOFs meeting the requirements of electrocatalysts for CO2 reduction are analyzed. After that, the representative progress for the precise fabrication of MOF-based electrocatalysts for CO2 reduction, focusing on catalytic site design and microenvironment modulation, are systemically summarized. Furthermore, the emerging applications and promising research for more practical scenarios related to electrochemical CO2 conversion are specifically proposed. Finally, the remaining challenges and future outlook of MOFs for electrochemical CO2 reduction are further discussed.

Stabilized Cuδ+-OH species on in situ reconstructed Cu nanoparticles for CO2-to-C2H4 conversion in neutral media

Achieving large-scale electrochemical CO2 reduction to multicarbon products with high selectivity using membrane electrode assembly (MEA) electrolyzers in neutral electrolyte is promising for carbon neutrality. However, the unsatisfactory multicarbon products selectivity and unclear reaction mechanisms in an MEA have hindered its further development. Here, we report a strategy that manipulates the interfacial microenvironment of Cu nanoparticles in an MEA to suppress hydrogen evolution reaction and enhance C2H4 conversion. In situ multimodal characterizations consistently reveal well-stabilized Cuδ+-OH species as active sites during MEA testing. The OH radicals generated in situ from water create a locally oxidative microenvironment on the copper surface, stabilizing the Cuδ+ species and leading to an irreversible and asynchronous change in morphology and valence, yielding high-curvature nanowhiskers. Consequently, we deliver a selective C2H4 production with a Faradaic efficiency of 55.6% ± 2.8 at 316 mA cm-2 in neutral media.

Promoting CO2 Electroreduction to Hydrocarbon Products via Sulfur-Enhanced Proton Feeding in Atomically Precise Thiolate-Protected Cu Clusters

Thiolate-protected Cu clusters with well-defined structures and stable low-coordinated Cu+ species exhibit remarkable potential for the CO2RR and are ideal model catalysts for establishing structure-electrocatalytic property relationships at the atomic level. However, extant Cu clusters employed in the CO2RR predominantly yield 2e- products. Herein, two model Cu4(MMI)4 and Cu8(MMI)4(tBuS)4 clusters (MMI=2-mercapto-1-methylimidazole) are prepared to investigate the synergistic effect of Cu+ and adjacent S sites on the CO2RR. Cu4(MMI)4 can reduce CO2 to deep-reduced products with a 91.0 % Faradaic efficiency (including 53.7 % for CH4) while maintaining remarkable stability. Conversely, Cu8(MMI)4(tBuS)4 shows a remarkable preference for C2+ products, achieving a maximum FE of 58.5 % with a C2+ current density of 152.1 mA⋅cm-2. In situ XAS and ex situ XPS spectra reveal the preservation of Cu+ species in Cu clusters during CO2RR, extensively enhancing the adsorption capacity of *CO intermediate. Moreover, kinetic analysis and theoretical calculations confirm that S sites facilitate H2O dissociation into *H species, which directly participate in the protonation process on adjacent Cu sites for the protonation of *CO to *CHO. This study highlights the important role of Cu-S dual sites in Cu clusters and provides mechanistic insights into the CO2RR pathway at the atomic level.

Manipulating Ferroelectric Polarization and Spin Polarization of 2D CuInP2S6 Crystals for Photocatalytic CO2 Reduction

Manipulating electronic polarizations such as ferroelectric or spin polarizations has recently emerged as an effective strategy for enhancing the efficiency of photocatalytic reactions. This study demonstrates the control of electronic polarizations modulated by ferroelectric and magnetic approaches within a two-dimensional (2D) layered crystal of copper indium thiophosphate (CuInP2S6) to boost the photocatalytic reduction of CO2. We investigate the substantial influence of ferroelectric polarization on the photocatalytic CO2 reduction efficiency, utilizing the ferroelectric-paraelectric phase transition and polarization alignment through electrical poling. Additionally, we explore enhancing the CO2 reduction efficiency by harnessing spin electrons through the synergistic introduction of sulfur vacancies and applying a magnetic field. Several advanced characterization techniques, including piezoresponse force microscopy, ultrafast pump-probe spectroscopy, in situ X-ray absorption spectroscopy, and in situ diffuse reflectance infrared Fourier transformed spectroscopy, are performed to unveil the underlying mechanism of the enhanced photocatalytic CO2 reduction. These findings pave the way for manipulating electronic polarizations regulated through ferroelectric or magnetic modulations in 2D layered materials to advance the efficiency of photocatalytic CO2 reduction.

Rational design of organic ligands for metal-organic frameworks as electrocatalysts for CO2 reduction

Electrocatalytic carbon dioxide (CO2) reduction to valuable chemical compounds is a sustainable technology with enormous potential to facilitate carbon neutrality by transforming intermittent energy sources into stable fuels. Among various electrocatalysts, metal-organic frameworks (MOFs) have garnered increasing attention for the electrochemical CO2 reduction reaction (CO2RR) owing to their structural diversity, large surface area, high porosity and tunable chemical properties. Ligands play a vital role in MOFs, which can regulate the electronic structure and chemical environment of metal centers of MOFs, thereby influencing the activity and selectivity of products. This feature article discusses the strategies for the rational design of ligands and their impact on the CO2RR performance of MOFs to establish a structure-performance relationship. Finally, critical challenges and potential opportunities for MOFs with different ligand types in the CO2RR are mentioned with the aim to inspire the targeted design of advanced MOF catalysts in the future to achieve efficient electrocatalytic CO2 conversion.

Highly Selective CO2 Electroreduction to C2H4 Using a Dual-Sites Cu(II) Porphyrin Framework Coupled with Cu2O Nanoparticles via a Synergetic-Tandem Strategy

Low *CO coverage on the active sites is a major hurdle in the tandem electrocatalysis, resulting in unsatisfied C2H4 production efficiencies. In this work, we developed a synergetic-tandem strategy to construct a copper-based composite catalyst for the electroreduction of CO2 to C2H4, which was constructed via the template-directed polymerization of ultrathin Cu(II) porphyrin organic framework incorporating atomically isolated Cu(II) porphyrin and Cu(II) bipyridine sites on a carbon nanotube (CNT) scaffold, and then Cu2O nanoparticles were uniformly dispersed on the CNT scaffold. The presence of dual active sites within the Cu(II) porphyrin organic framework create a synergetic effect, leading to an increase in local *CO availability to enhance the C-C coupling step implemented on the adjacent Cu2O nanoparticles for further C2H4 production. Accordingly, the resultant catalyst affords an exceptional CO2-to-C2H4 Faradaic efficiency (FEC2H4) of 71.0 % at -1.1 V vs reversible hydrogen electrode (RHE), making it one of the most effective copper-based tandem catalysts reported to date. The superior performance of the catalyst is further confirmed through operando infrared spectroscopy and theoretic calculations.

Modulating the D-π-A Interactions in Metal-Covalent Organic Frameworks for Efficient Electroreduction of CO2 into Formate

Crystalline porous framework materials have attracted tremendous interest in electrocatalytic CO2 reduction owing to their ordered structures and high specific surface areas as well as rich designability, however, still suffer from a lack of accuracy in regulating the binding strength between the catalytic sites and intermediates, which is crucial for optimizing the electrocatalytic activity and expanding the product types. Herein, we report three new kinds of vinylene-linked metal-covalent organic frameworks (TMT-CH3-MCOF, TMP-CH3-MCOF and TMP-MCOF) with continuously tunable D-π-A interactions by adjusting the structure of the monomers at the molecular level for realizing efficient electroreduction of CO2 to formate for the first time. Interestingly, compared with TMT-CH3-MCOF and TMP-MCOF, the TMP-CH3-MCOF exhibited the highest HCOO- Faradaic efficiency (FEHCOO-) of 95.6 % at -1.0 V vs RHE and displayed the FEHCOO- above 90 % at the voltage range of -1.0 to -1.2 V vs. RHE, which is one of the highest among various kinds of reported electrocatalysts. Theoretical calculations further reveal that the catalytic sites in TMP-CH3-MCOF with unique moderate D-π-A interactions have suitable binding ability towards the reaction intermediate, which is beneficial for the formation of *HCOO and desorption of *HCOOH, thus effectively promoting the electroreduction of CO2 to formate.

Anionic Metal-Organic Framework Derived Cu Catalyst for Selective CO2 Electroreduction to Hydrocarbons

Metal-organic frameworks (MOFs)-related Cu materials are promising candidates for promoting electrochemical CO2 reduction to produce valuable chemical feedstocks. However, many MOF materials inevitable undergo reconstruction under reduction conditions; therefore, exploiting the restructuring of MOF materials is of importance for the rational design of high-performance catalyst targeting multi-carbon products (C2). Herein, a facile solvent process is choosed to fabricate HKUST-1 with an anionic framework (a-HKUST-1) and utilize it as a pre-catalyst for alkaline CO2RR. The a-HKUST-1 catalyst can be electrochemically reduced into Cu with significant structural reconstruction under operating reaction conditions. The anionic HKUST-1 derived Cu catalyst (aHD-Cu) delivers a FEC2H4 of 56% and FEC2 of ≈80% at -150 mA cm-2 in alkaline electrolyte. The resulting aHD-Cu catalyst has a high electrochemically active surface area and low coordinated sites. In situ Raman spectroscopy indicates that the aHD-Cu surface displays higher coverage of *CO intermediates, which favors the production of hydrocarbons.

Recent Advances and Challenges in Efficient Selective Photocatalytic CO2 Methanation

Solar-driven carbon dioxide (CO2) methanation holds significant research value in the context of carbon emission reduction and energy crisis. However, this eight-electron catalytic reaction presents substantial challenges in catalytic activity and selectivity. In this regard, researchers have conducted extensive exploration and achieved significant developments. This review provides an overview of the recent advances and challenges in efficient selective photocatalytic CO2 methanation. It begins by discussing the fundamental principles and challenges in detail, analyzing strategies for improving the efficiency of photocatalytic CO2 conversion to CH4 comprehensively. Subsequently, it outlines the recent applications and advanced characterization methods for photocatalytic CO2 methanation. Finally, this review highlights the prospects and opportunities in this area, aiming to inspire CO2 conversion into high-value CH4 and shed light on the research of catalytic mechanisms.

Anion Modulation of Ag-Imidazole Cuboctahedral Cage Microenvironments for Efficient Electrocatalytic CO2 Reduction

How to achieve CO2 electroreduction in high efficiency is a current challenge with the mechanism not well understood yet. The metal-organic cages with multiple metal sites, tunable active centers, and well-defined microenvironments may provide a promising catalyst model. Here, we report self-assembly of Ag4L4 type cuboctahedral cages from coordination dynamic Ag+ ion and triangular imidazolyl ligand 1,3,5-tris(1-benzylbenzimidazol-2-yl) benzene (Ag-MOC-X, X=NO3, ClO4, BF4) via anion template effect. Notably, Ag-MOC-NO3 achieves the highest CO faradaic efficiency in pH-universal electrolytes of 86.1 % (acidic), 94.1 % (neutral) and 95.3 % (alkaline), much higher than those of Ag-MOC-ClO4 and Ag-MOC-BF4 with just different counter anions. In situ attenuated total reflection Fourier transform infrared spectroscopy observes formation of vital intermediate *COOH for CO2-to-CO conversion. The density functional theory calculations suggest that the adsorption of CO2 on unsaturated Ag-site is stabilized by C-H⋅⋅⋅O hydrogen-bonding of CO2 in a microenvironment surrounded by three benzimidazole rings, and the activation of CO2 is dependent on the coordination dynamics of Ag-centers modulated by the hosted anions through Ag⋅⋅⋅X interactions. This work offers a supramolecular electrocatalytic strategy based on Ag-coordination geometry and host-guest interaction regulation of MOCs as high-efficient electrocatalysts for CO2 reduction to CO which is a key intermediate in chemical industry process.

Dimensionally Intact Construction of Ultrathin S-Scheme CuFe2O4/ZnIn2S4 Heterojunctional Photocatalysts for CO2 Photoreduction

The conversion of CO2 into carbon-neutral fuels such as methane (CH4) through selective photoreduction is highly sought after yet remains challenging due to the slow multistep proton-electron transfer processes and the formation of various C1 intermediates. This research highlights the cooperative interaction between Fe3+ and Cu2+ ions transitioning to Fe2+ and Cu+ ions, enhancing the photocatalytic conversion of CO2 to methane. We introduce an S-scheme heterojunction photocatalyst, CuFe2O4/ZnIn2S4, which demonstrates significant efficiency in CO2 methanation under light irradiation. The CuFe2O4/ZnIn2S4 heterojunction forms an internal electric field that aids in the mobility and separation of exciton carriers under a wide solar spectrum for exceptional photocatalytic performance. Remarkably, the optimal CuFe2O4/ZnIn2S4 heterojunction system achieved an approximately 68-time increase in CO2 conversion compared with ZnIn2S4 and CuFe2O4 nanoparticles using only pure water, with nearly complete CO selectivity and yields of CH4 and CO reaching 172.5 and 202.4 μmol g-1 h-1, respectively, via a 2-electron oxygen reduction reaction (ORR) process. The optimally designed CuFe2O4/ZnIn2S4 heterojunctional system achieved approximately 96% conversion of BA and 98.5% selectivity toward benzaldehyde (BAD). Additionally, this photocatalytic system demonstrated excellent cyclic stability and practical applicability. The photogenerated electrons in the CuFe2O4 conduction band enhance the reduction of Fe3+/Cu2+ to Fe2+/Cu+, creating a microenvironment conducive to CO2 reduction to CO and CH4. Simultaneously, the appearance of holes in the ZnIn2S4 valence band facilitates water oxidation to O2. The synergistic function within the CuFe2O4/ZnIn2S4 heterojunction plays a pivotal role in facilitating charge transfer, accelerating water oxidation, and thereby enhancing CO2 reduction kinetics. This study offers valuable insights and a strategic framework for designing efficient S-scheme heterojunctions aimed at achieving carbon neutrality through solar fuel production.

Modulating the Active Sites of VS2 by Mn Doping for Highly Selective CO2 Electroreduction to Methanol in a Flow Cell

Methanol is a valuable liquid C1 product in CO2 electroreduction (CO2ER); however, it is hard to achieve high selectivity and a large current density simultaneously. In this work, we construct Mn2+-doped VS2 multilayer nanowafers applied in a flow cell to yield methanol as a single liquid product to tackle this challenge. Mn doping adjusts the electronic structure of VS2 and concurrently introduces sulfur vacancies, forming a critical *COB intermediate and facilitating its sequential hydrogenation to methanol. The optimal Mn4.8%-VS2 exhibits methanol Faradic efficiencies of more than 60% over a wide potential range of -0.4 to -0.8 V in a flow cell, of which the maximal value is 72.5 ± 1.1% at -0.6 V along with a partial current density of 74.3 ± 1.1 mA cm-2. This work opens an avenue to rationally design catalysts for engineering C1 intermediates toward CO2ER to a single liquid methanol in a flow cell.

Stabilizing Ni2+ in Hollow Nano MOF/Polymetallic Phosphides Composites for Enhanced Electrochemical Performance in 3D-Printed Micro-Supercapacitors

Polymetallic phosphides exhibit favorable conductivities. A reasonable design of nano-metal-organic frame (MOF) composite morphologies and in situ introduction of polymetallic phosphides into the framework can effectively improve electrolyte penetration and rapid electron transfer. To address existing challenges, Ni, with a strong coordination ability with N, is introduced to partially replace Co in nano-Co-MOF composite. The hollow nanostructure is stabilized through CoNi bimetallic coordination and low-temperature controllable polymetallic phosphide generation rate. The Ni, Co, and P atoms, generated during reduction, effectively enhance electron transfer rate within the framework. X-ray absorption fine structure (XAFS) characterization results further confirm the existence of Ni-N, Ni-Ni, and Co-Co structures in the nanocomposite. The changes in each component during the charge-discharge process of the electrochemical reactions are investigated using in situ X-ray diffraction (XRD). Theoretical calculations further confirm that P can effectively improve conductivity. VZNPGC//MXene MSCs, constructed with active materials derived from the hollow nano MOF composites synthesized through the Ni2+ stabilization strategy, demonstrate a specific capacitance of 1184 mF cm-2, along with an energy density of 236.75 µWh cm-2 (power density of 0.14 mW cm-2). This approach introduces a new direction for the synthesis of highly conductive nano-MOF composites.

Layer-by-layer growth of Cu3(HHTP)2 films on Cu(OH)2 nanowire arrays for high performance ascorbic acid sensing

Growing three-dimensional (3D) metal organic frameworks (MOFs) via heterogeneous epitaxial growth on metal hydroxide arrays are effective for constructing electrochemical sensor. However, the growth of MOFs is difficult to control, resulting in thick and irregular morphologies and even damage the metal hydroxide template. In this work, Cu3(HHTP)2 (HHTP = 2, 3, 6, 7, 10, 11-hexahydroxytriphenylene) films with controllable thickness and morphology were successfully prepared on Cu(OH)2 nanowire arrays (NWAs) through layer-by-layer (LBL) growth method. We have discovered that the LBL cycle and the reaction solvent composition are crucial for growing homogenous MOF thin films. The Cu3(HHTP)2 based ascorbic acid (AA) sensor, fabricated in ethanol within 10 LBL cycles, generated an ultrahigh sensitivity of 821.64 μA mM-1 cm-2 in the range of 6-981.41 μM, a low detection limit of 60 nM as well as the great selectivity, stability and reproducibility. Moreover, the relative deviation for AA detection in two fruit juices were 3.22 % and 3.71 %, and the test result for human sweat fall within the normal AA concentration range, verifying the feasibility of as-prepared sensor for practical application.

Constructing 2D Phthalocyanine Covalent Organic Framework with Enhanced Stability and Conductivity via Interlayer Hydrogen Bonding as Electrocatalyst for CO2 Reduction

Fabricating COFs-based electrocatalysts with high stability and conductivity still remains a great challenge. Herein, 2D polyimide-linked phthalocyanine COF (denoted as NiPc-OH-COF) is constructed via solvothermal reaction between tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato nickel(II) and 2,5-diamino-1,4-benzenediol (DB) with other two analogous 2D COFs (denoted as NiPc-OMe-COF and NiPc-H-COF) synthesized for reference. In comparison with NiPc-OMe-COF and NiPc-H-COF, NiPc-OH-COF exhibits enhanced stability, particularly in strong NaOH solvent and high conductivity of 1.5 × 10-3 S m-1 due to the incorporation of additional strong interlayer hydrogen bonding interaction between the O-H of DB and the hydroxy "O" atom of DB in adjacent layers. This in turn endows the NiPc-OH-COF electrode with ultrahigh CO2-to-CO faradaic efficiency (almost 100%) in a wide potential range from -0.7 to -1.1 V versus reversible hydrogen electrode (RHE), a large partial CO current density of -39.2 mA cm-2 at -1.1 V versus RHE, and high turnover number as well as turnover frequency, amounting to 45 000 and 0.76 S-1 at -0.80 V versus RHE during 12 h lasting measurement.

Sub-Nanometer Mono-Layered Metal-Organic Frameworks Nanosheets for Simulated Flue Gas Photoreduction

The dilemma between the thickness and accessible active site triggers the design of porous crystalline materials with mono-layered structure for advanced photo-catalysis applications. Here, a kind of sub-nanometer mono-layered nanosheets (Co-MOF MNSs) through the exfoliation of specifically designed Co3 cluster-based metal-organic frameworks (MOFs) is reported. The sub-nanometer thickness and inherent light-sensitivity endow Co-MOF MNSs with fully exposed Janus Co3 sites that can selectively photo-reduce CO2 into formic acid under simulated flue gas. Notably, the production efficiency of formic acid by Co-MOF MNSs (0.85 mmol g-1 h-1) is ≈13 times higher than that of the bulk counterpart (0.065 mmol g-1 h-1) under a simulated flue gas atmosphere, which is the highest in reported works up to date. Theoretical calculations prove that the exposed Janus Co3 sites with simultaneously available sites possess higher activity when compared with single Co site, validating the importance of mono-layered nanosheet morphology. These results may facilitate the development of functional nanosheet materials for CO2 photo-reduction in potential flue gas treatment.

Linkage Engineering in Covalent Organic Frameworks for Metal-Free Electrocatalytic C2H4 Production from CO2

Electrocatalytic carbon dioxide reduction reaction (CO2RR) to produce ethylene (C2H4) is conducive to sustainable development of energy and environment. At present, most electrocatalysts for C2H4 production are limited to the heavy metal copper, meanwhile, achieving metal-free catalysis remains a challenge. Noted piperazine with sp3 N hybridization is beneficial to CO2 capture, but CO2RR performance and mechanism have been lacking. Herein, based on linkage engineering, we construct a novel high-density sp3 N catalytic array via introducing piperazine into the crystalline and microporous aminal-linked covalent organic frameworks (COFs). Thanks to its high sp3 N density, strong CO2 capture capacity and great hydrophilicity, aminal-linked COF successfully achieves the conversion of CO2 to C2H4 with a Faraday efficiency up to 19.1 %, which is stand out in all reported metal-free COF electrocatalysts. In addition, a series of imine-linked COFs are synthesized and combined with DFT calculations to demonstrate the critical role of sp3 N in enhancing the kinetics of CO2RR. Therefore, this work reveals the extraordinary potential of linkage engineering in COFs to break through some catalytic bottlenecks.

Restructuring multi-phase interfaces from Cu-based metal-organic frameworks for selective electroreduction of CO2 to C2H4

Multi-phase interfaces are promising for surmounting the energy barriers of electrochemical CO2 reduction involving multiple electron transfer steps, but challenges still remain in constructing interfacial micro-structures and unraveling their dynamic changes and working mechanism. Herein, highly active Ag/Cu/Cu2O heterostructures are in situ electrochemically restructured from Ag-incorporating HKUST-1, a Cu-based metal-organic framework (MOF), and accomplish efficient CO2-to-C2H4 conversion with a high faradaic efficiency (57.2% at -1.3 V vs. RHE) and satisfactory stability in flow cells, performing among the best of recently reported MOFs and their derivatives. The combination of in/ex situ characterizations and theoretical calculations reveals that Ag plays a crucial role in stabilizing Cu(i) and increasing the CO surface coverage, while the active Cu/Cu2O interfaces significantly reduce the energy barrier of C-C coupling toward the boosted ethylene production. This work not only proves MOFs as feasible precursors to derive efficient electrocatalysts on site, but also provides in-depth understanding on the working interfaces at an atomic level.

Br, O-Modified Cu(111) Interface Promotes CO2 Reduction to Multicarbon Products

Electrochemical reduction of CO2 to multicarbon (C2+) products with added value represents a promising strategy for achieving a carbon-neutral economy. Precise manipulation of the catalytic interface is imperative to control the catalytic selectivity, particularly toward C2+ products. In this study, a unique Cu/UIO-Br interface is designed, wherein the Cu(111) plane is co-modified simultaneously by Br and O from UIO-66-Br support. Such Cu/UIO-Br catalytic interface demonstrates a superior Faradaic efficiency of ≈53% for C2+ products (ethanol/ethylene) and the C2+ partial current density reached 24.3 mA cm-2 in an H-cell electrolyzer. The kinetic isotopic effect test, in situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory calculations have been conducted to elucidate the catalytic mechanism. The Br, O co-modification on the Cu(111) interface enhanced the adsorption of CO2 species. The hydrogen-bond effect from the doped Br atom regulated the kinetic processes of *H species in CO2RR and promoted the formation of *COH intermediate. The formed *COH facilitates the *CO-*COH coupling and promotes the C2+ selectivity finally. This comprehensive investigation not only provides an in-depth study and understanding of the catalytic process but also offers a promising strategy for designing efficient Cu-based catalysts with exceptional C2+ products.

Electrochemical reconstruction of a 1D Cu(PyDC)(H2O) MOF into in situ formed Cu-Cu2O heterostructures on carbon cloth as an efficient electrocatalyst for CO2 conversion

Electrochemical carbon dioxide (CO2) conversion has enormous potential for reducing high atmospheric CO2 levels and producing valuable products simultaneously; however the development of inexpensive catalysts remains a great challenge. In this work, we successfully synthesised a 1D Cu-based metal-organic framework [Cu(PyDC)(H2O)], which crystallizes in an orthorhombic system with the Pccn space group, by the hydrothermal method. Among the different catalysts utilized, the heterostructures of cathodized Cu-Cu2O@CC demonstrate increased efficiency in producing CH3OH and C2H4, achieving maximum FE values of 37.4% and 40.53%, respectively. Also, the product formation rates of CH3OH and C2H4 reach up to 667 and 1921 μmol h-1 cm-2. On the other side, Cu-Cu2O/NC-700 carbon composites simultaneously produced C1-C3 products with a total FE of 23.27%. Furthermore, a comprehensive study involving detailed DFT simulations is used to calculate the energetic stability and catalytic activity towards the CO2 reduction of Cu(111), Cu2O(111), and Cu@Cu2O(111) surfaces. During the early phase of electrochemical treatment, Cu(II) carboxylate nodes (Cu-O) in the Cu(PyDC)(H2O) MOF were reduced to Cu and Cu2O, with a possible synergistic enhancement from the PyDC ligands. Thus, the improved activity and product enhancement are closely associated with the cathodized reconstruction of Cu-Cu2O@CC heterostructures on carbon cloth. Hence, this study provides efficient derivatives of Cu-based MOFs for notable electrocatalytic activity in CO2 reduction and gives valuable insights towards the advancement of practical CO2 conversion technology.

Hydrogen-Bonded Organic Framework Supporting Atomic Bi-N2O2 Sites for High-Efficiency Electrocatalytic CO2 Reduction

Single atomic catalysts (SACs) offer a superior platform for studying the structure-activity relationships during electrocatalytic CO2 reduction reaction (CO2RR). Yet challenges still exist to obtain well-defined and novel site configuration owing to the uncertainty of functional framework-derived SACs through calcination. Herein, a novel Bi-N2O2 site supported on the (1 1 0) plane of hydrogen-bonded organic framework (HOF) is reported directly for CO2RR. In flow cell, the target catalyst Bi1-HOF maintains a faradaic efficiency (FE) HCOOH of over 90 % at a wide potential window of 1.4 V. The corresponding partial current density ranges from 113.3 to 747.0 mA cm-2. And, Bi1-HOF exhibits a long-term stability of over 30 h under a successive potential-step test with a current density of 100-400 mA cm-2. Density function theory (DFT) calculations illustrate that the novel Bi-N2O2 site supported on the (1 1 0) plane of HOF effectively induces the oriented electron transfer from Bi center to CO2 molecule, reaching an enhanced CO2 activation and reduction. Besides, this study offers a versatile method to reach series of M-N2O2 sites with regulable metal centers via the same intercalation mechanism, broadening the platform for studying the structure-activity relationships during CO2RR.

Atomic Design of Copper Active Sites in Pristine Metal-Organic Coordination Compounds for Electrocatalytic Carbon Dioxide Reduction

Electrocatalytic carbon dioxide reduction reaction (CO2RR) has emerged as a promising and sustainable approach to cut carbon emissions by converting greenhouse gas CO2 to value-added chemicals and fuels. Metal-organic coordination compounds, especially the copper (Cu)-based coordination compounds, which feature well-defined crystalline structures and designable metal active sites, have attracted much research attention in electrocatalytic CO2RR. Herein, the recent advances of electrochemical CO2RR on pristine Cu-based coordination compounds with different types of Cu active sites are reviewed. First, the general reaction pathways of electrocatalytic CO2RR on Cu-based coordination compounds are briefly introduced. Then the highly efficient conversion of CO2 on various kinds of Cu active sites (e.g., single-Cu site, dimeric-Cu site, multi-Cu site, and heterometallic site) is systematically discussed, along with the corresponding catalytic reaction mechanisms. Finally, some existing challenges and potential opportunities for this research direction are provided to guide the rational design of metal-organic coordination compounds for their practical application in electrochemical CO2RR.

High selective electrocatalytic reduction of carbon dioxide to ethylene enabled by regulating the microenvironment over Cu-Ag nanowires

Copper-based tandem catalysts are effective candidates for yielding multi-carbon (C2+) products in electrochemical reduction of carbon dioxide (CO2RR). However, these catalysts still face a significant challenge regarding in the low selectivity for the production of a specific product. In this study, we report a high selectivity of 77.8 %±2 % at -1.0 V (vs RHE) for the production of C2H4 by using a Cu88Ag12NW catalyst which is primarily prepared through a combined Cu-Ag co-deposition and wet chemical method, employing an attractive strategy focused on regulating the microenvironment over Cu-Ag nanowires. The experimental and computational studies show that the higher *CO coverage and lower intermediate adsorption energy are important reasons for achieving the high C2H4 selectivity of Cu88Ag12NW catalyst. Comsol simulation results indicate that dense nanowires exhibit a nano-limiting effect on OH- ions, thereby leading to an increase in local pH and promoting coupling reactions. The catalyst demonstrates no noticeable decrease in current density or selectivity even after 12 h of continuous operation. The Cu-Ag nanowire composite exhibits remarkable catalytic activity, superior faradaic efficiency, excellent stability, and easy synthesis, which highlights its significant potential for electro-reducing carbon dioxide into valuable products.

Cu-phen Coordination Enabled Selective Electrocatalytic Reduction of CO2 to Methane

Manipulation of selectivity in the catalytic electrochemical carbon dioxide reduction reaction (eCO2RR) poses significant challenges due to inevitable structure reconstruction. One approach is to develop effective strategies for controlling reaction pathways to gain a deeper understanding of mechanisms in robust CO2RR systems. In this work, by precise introduction of 1,10-phenanthroline as a bidentate ligand modulator, the electronic property of the copper site was effectively regulated, thereby directing selectivity switch. By modification of [Cu3(btec)(OH)2]n, the use of [Cu2(btec)(phen)2]n·(H2O)n achieved the selectivity switch from ethylene (faradaic efficiency (FE) = 41%, FEC2+ = 67%) to methane (FECH4 = 69%). Various in situ spectroscopic characterizations revealed that [Cu2(btec)(phen)2]n·(H2O)n promoted the hydrogenation of *CO intermediates, leading to methane generation instead of dimerization to form C2+ products. Acting as a delocalized π-conjugation scaffold, 1,10-phenanthroline in [Cu2(btec)(phen)2]n·(H2O)n helps stabilize Cuδ+. This work presents a novel approach to regulate the coordination environment of active sites with the aim of selectively modulating the CO2RR.

Metal-Organic Framework (MOF)-Based Clean Energy Conversion: Recent Advances in Unlocking its Underlying Mechanisms

Carbon neutrality is an important goal for humanity . As an eco-friendly technology, electrocatalytic clean energy conversion technology has emerged in the 21st century. Currently, metal-organic framework (MOF)-based electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), are the mainstream energy catalytic reactions, which are driven by electrocatalysis. In this paper, the current advanced characterizations for the analyses of MOF-based electrocatalytic energy reactions have been described in details, such as density function theory (DFT), machine learning, operando/in situ characterization, which provide in-depth analyses of the reaction mechanisms related to the above reactions reported in the past years. The practical applications that have been developed for some of the responses that are of application values, such as fuel cells, metal-air batteries, and water splitting have also been demonstrated. This paper aims to maximize the potential of MOF-based electrocatalysts in the field of energy catalysis, and to shed light on the development of current intense energy situations.

Cooperation of Different Active Sites to Promote CO2 Electroreduction to Multi-carbon Products at Ampere-Level

Electroreduction of CO2 to C2+ products provides a promising strategy for reaching the goal of carbon neutrality. However, achieving high selectivity of C2+ products at high current density remains a challenge. In this work, we designed and prepared a multi-sites catalyst, in which Pd was atomically dispersed in Cu (Pd-Cu). It was found that the Pd-Cu catalyst had excellent performance for producing C2+ products from CO2 electroreduction. The Faradaic efficiency (FE) of C2+ products could be maintained at approximately 80.8 %, even at a high current density of 0.8 A cm-2 for at least 20 hours. In addition, the FE of C2+ products was above 70 % at 1.4 A cm-2. Experiments and density functional theory (DFT) calculations revealed that the catalyst had three distinct catalytic sites. These three active sites allowed for efficient conversion of CO2, water dissociation, and CO conversion, ultimately leading to high yields of C2+ products.

Prediction of M3 B4 -type MBenes as Promising Catalysts for CO2 Capture and Reduction

The rational design of novel catalysts with high activity and selectivity for carbon dioxide reduction reaction (CO2 RR) is highly desired. In this work, we have extensive investigations on the properties of two-dimensional transition metal borides (MBenes) to achieve efficient CO2 capture and reduction through first-principles calculations. The results show that all the investigated M3 B4 -type MBene exhibit remarkable CO2 capture and activation abilities, which proved to be derived from the lone pair of electrons on the MBene surface. Then, we emphasize that the investigated MBenes can further selectively reduce activated CO2 to CH4 . Moreover, a new linear scaling relationship of the adsorption energies of potential-determining intermediates (*OCH2 O and *HOCH2 O) versus ΔG(*OCHO) has been established, where the CO2 RR limiting potentials on MBenes are determined by the different fitting slopes of ΔG(*OCH2 O) and ΔG(*HOCHO), allowing significantly lower limiting potentials to be achieved compared to transition metals. Especially, two promising CO2 RR catalysts (Mo3 B4 and Cr3 B4 MBene) exist quite low limiting potentials of -0.48 V and -0.66 V, as well as competitive selectivity concerning hydrogen evolution reactions have been identified. Our research results make future advances in CO2 capture by MBenes easier and exploit the applications of Mo3 B4 and Cr3 B4 MBenes as novel CO2 RR catalysts.

Microwave-Assisted Rapid Synthesis of MOF-Based Single-Atom Ni Catalyst for CO2 Electroreduction at Ampere-Level Current

Carbon-based single-atom catalysts (SACs) have attracted tremendous interest in heterogeneous catalysis. However, the common electric heating techniques to produce carbon-based SACs usually suffer from prolonged heating time and tedious operations. Herein, a general and facile microwave-assisted rapid pyrolysis method is developed to afford carbon-based SACs within 3 min without inert gas protection. The obtained carbon-based SACs present high porosity and comparable carbonization degree to those obtained by electric heating techniques. Specifically, the single-atom Ni implanted N-doped carbon (Ni1 -N-C) derived from a Ni-doped metal-organic framework (Ni-ZIF-8) exhibits remarkable CO Faradaic efficiency (96 %) with a substantial CO partial current density (jCO ) up to 1.06 A/cm2 in CO2 electroreduction, far superior to the counterpart obtained by traditional pyrolysis with electric heating. Mechanism investigations reveal that the resulting Ni1 -N-C presents abundant defective sites and mesoporous structure, greatly facilitating CO2 adsorption and mass transfer. This work establishes a versatile approach to rapid and large-scale synthesis of SACs as well as other carbon-based materials for efficient catalysis.

Guiding the Driving Factors on Plasma Super-Photothermal S-Scheme Core-Shell Nanoreactor to Enhance Photothermal Catalytic H2 Evolution and Selective CO2 Reduction

Light-induced heat has a non-negligible role in photocatalytic reactions. However, it is still challenging to design highly efficient catalysts that can make use of light and thermal energy synergistically. Herein, the study proposes a plasma super-photothermal S-scheme heterojunction core-shell nanoreactor based on manipulation of the driving factors, which consists of α-Fe2 O3 encapsulated by g-C3 N4 modified with gold quantum dots. α-Fe2 O3 can promote carrier spatial separation while also acting as a thermal core to radiate heat to the shell, while Au quantum dots transfer energetic electrons and heat to g-C3 N4 via surface plasmon resonance. Consequently, the catalytic activity of Au/α-Fe2 O3 @g-C3 N4 is significantly improved by internal and external double hot spots, and it shows an H2 evolution rate of 5762.35 µmol h-1 g-1 , and the selectivity of CO2 conversion to CH4 is 91.2%. This work provides an effective strategy to design new plasma photothermal catalysts for the solar-to-fuel transition.

Tailoring the Hydrophobic Interface of Core-Shell HKUST-1@Cu2O Nanocomposites for Efficiently Selective CO2 Electroreduction

The electrochemical reduction of carbon dioxide (CO2) to ethylene creates a carbon-neutral approach to converting carbon dioxide into intermittent renewable electricity. Exploring efficient electrocatalysts with potentially high ethylene selectivity is extremely desirable, but still challenging. In this report, a laboratory-designed catalyst HKUST-1@Cu2O/PTFE-1 is prepared, in which the high specific surface area of the composites with improved CO2 adsorption and the abundance of active sites contribute to the increased electrocatalytic activity. Furthermore, the hydrophobic interface constructed by the hydrophobic material polytetrafluoroethylene (PTFE) effectively inhibits the occurrence of hydrogen evolution reactions, providing a significant improvement in the efficiency of CO2 electroreduction. The distinctive structures result in the remarkable hydrocarbon fuels generation with high Faraday efficiency (FE) of 67.41%, particularly for ethylene with FE of 46.08% (-1.0 V vs RHE). The superior performance of the catalyst is verified by DFT calculation with lower Gibbs free energy of the intermediate interactions with improved proton migration and selectivity to emerge the polycarbon（C2+） product. In this work, a promising and effective strategy is presented to configure MOF-based materials with tailored hydrophobic interface, high adsorption selectivity and more exposed active sites for enhancing the efficiency of the electroreduction of CO2 to C2+ products with high added value.

Cu and Zn promoted Al-fumarate metal organic frameworks for electrocatalytic CO2 reduction

Metal organic frameworks (MOFs) are attractive materials to generate multifunctional catalysts for the electrocatalytic reduction of CO2 to hydrocarbons. Here we report the synthesis of Cu and Zn modified Al-fumarate (Al-fum) MOFs, in which Zn promotes the selective reduction of CO2 to CO and Cu promotes CO reduction to oxygenates and hydrocarbons in an electrocatalytic cascade. Cu and Zn nanoparticles (NPs) were introduced to the Al-fum MOF by a double solvent method to promote in-pore metal deposition, and the resulting reduced Cu-Zn@Al-fum drop-cast on a hydrophobic gas diffusion electrode for electrochemical study. Cu-Zn@Al-fum is active for CO2 electroreduction, with the Cu and Zn loading influencing the product yields. The highest faradaic efficiency (FE) of 62% is achieved at -1.0 V vs. RHE for the conversion of CO2 into CO, HCOOH, CH4, C2H4 and C2H5OH, with a FE of 28% to CH4, C2H4 and C2H5OH at pH 6.8. Al-fum MOF is a chemically robust matrix to disperse Cu and Zn NPs, improving electrocatalyst lifetime during CO2 reduction by minimizing transition metal aggregation during electrode operation.

Steering CO2 Electroreduction Selectivity U-Turn to Ethylene by Cu-Si Bonded Interface

Copper (Cu), with the advantage of producing a deep reduction product, is a unique catalyst for the electrochemical reduction of CO2 (CO2RR). Designing a Cu-based catalyst to trigger CO2RR to a multicarbon product and understanding the accurate structure-activity relationship for elucidating reaction mechanisms still remain a challenge. Herein, we demonstrate a rational design of a core-shell structured silica-copper catalyst (p-Cu@m-SiO2) through Cu-Si direct bonding for efficient and selective CO2RR. The Cu-Si interface fulfills the inversion in CO2RR product selectivity. The product ratio of C2H4/CH4 changes from 0.6 to 14.4 after silica modification, and the current density reaches a high of up to 450 mA cm-2. The kinetic isotopic effect, in situ attenuated total reflection Fourier-transform infrared spectra, and density functional theory were applied to elucidate the reaction mechanism. The SiO2 shell stabilizes the *H intermediate by forming Si-O-H and inhibits the hydrogen evolution reaction effectively. Moreover, the direct-bonded Cu-Si interface makes bare Cu sites with larger charge density. Such bare Cu sites and Si-O-H sites stabilized the *CHO and activated the *CO, promoting the coupling of *CHO and *CO intermediates to form C2H4. This work provides a promising strategy for designing Cu-based catalysts with high C2H4 catalytic activity.

Br-doped Cu nanoparticle formed by in situ restructuring for highly efficient electrochemical reduction of CO2 to formate

Electrochemical conversion of CO2 into chemical feedstock, such as an energy-dense liquid product (formate), is desirable to address the excessive emission of greenhouse gases and store energy. Cu-based catalysts exhibit great advantages in electrochemical CO2 reduction reaction (eCO2RR) due to their low cost and high abundance, but suffer from low selectivity of formate. In this work, a facile one-pot approach is developed to synthesize CuBr nanoparticle (CuBr NP) that can conduct in situ dynamic restructuring during eCO2RR to generate Br-doped Cu NP. The in situ-formed Br-doped Cu NP can afford up to 91.6% Faradaic efficiency (FE) for formate production with a partial current density of 15.1 mA·cm-2 at -0.94 V vs. reversible hydrogen electrode (RHE) in an H-type cell. Moreover, Br-doped Cu NP can deliver excellent long-term stability for up to 25 h. The first-principles density functional theory (DFT) calculations show that the doped Br can regulate the electronic structure of Cu active sites to optimize the adsorption of the HCOO* intermediate, greatly hindering the formation of CO and H2. This work provides a strategy for electronic modulation of metal active site and suggests new opportunities in high selectivity for electrocatalytic reduction of CO2 to formate over Cu-based catalysts.

New Insight into the Electronic Effect for Cu Porphyrin Catalysts in Electrocatalytic of CO2 into CH4

Perturbation of the copper (Cu) active site by electron manipulation is a crucial factor in determining the activity and selectivity of electrochemical carbon dioxide (CO2 ) reduction reaction (e-CO2 RR) in Cu-based molecular catalysts. However, much ambiguity is present concerning their electronic structure-function relationships. Here, three molecular Cu-based porphyrin catalysts with different electron densities at the Cu active site, Cu tetrakis(4-methoxyphenyl)porphyrin (Cu─T(OMe)PP), Cu tetraphenylporphyrin (Cu─THPP), and Cu tetrakis(4-bromophenyl)porphyrin (Cu─TBrPP), are prepared. Although all three catalysts exhibit e-CO2 RR activity and the same reaction pathway, their performance is significantly affected by the electronic structure of the Cu site. Theoretical and experimental investigations verify that the conjugated effect of ─OCH3 and ─Br groups lowers the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbitals (LUMO) gap of Cu─T(OMe)PP and Cu─TBrPP, promoting faster electron transfer between Cu and CO2 , thereby improving their e-CO2 RR activity. Moreover, the high inductive effect of ─Br group reduces the electron density of Cu active site of Cu─TBrPP, facilitating the hydrolysis of the bound H2 O and thus creating a preferable local microenvironment, further enhancing the catalytic performance. This work provides new insights into the relationships between the substituent group characteristics with e-CO2 RR performance and is highly instructive for the design of efficient Cu-based e-CO2 RR electrocatalysts.

Asymmetric Cu-N-La Species Enabling Atomic-Level Donor-Acceptor Structure and Favored Reaction Thermodynamics for Selective CO2 Photoreduction to CH4

Photocatalytic CO2 reduction into ideal hydrocarbon fuels, such as CH4 , is a sluggish kinetic process involving adsorption of multiple intermediates and multi-electron steps. Achieving high CH4 activity and selectivity therefore remains a great challenge, which largely depends on the efficiency of photogenerated charge separation and transfer as well as the intermediate energy levels in CO2 reduction. Herein, we construct La and Cu dual-atom anchored carbon nitride (LaCu/CN), with La-N4 and Cu-N3 coordination bonds connected by Cu-N-La bridges. The asymmetric Cu-N-La species enables the establishment of an atomic-level donor-acceptor structure, which allows the migration of electrons from La atoms to the reactive Cu atom sites. Simultaneously, intermediates during CO2 reduction on LaCu/CN demonstrate thermodynamically more favorable process for CH4 formation based on theoretical calculations. Eventually, LaCu/CN exhibits a high selectivity (91.6 %) for CH4 formation with a yield of 125.8 μmol g-1 , over ten times of that for pristine CN. This work presents a strategy for designing multi-functional dual-atom based photocatalysts.

Evoking C2+ production from electrochemical CO2 reduction by the steric confinement effect of ordered porous Cu2O

Selective conversion of carbon dioxide (CO2) to multi-carbon products (CO2-to-C2+) at high current densities is in essential demand for the practical application of the resultant valuable products, yet it remains challenging to conduct due to the lack of efficient electrocatalysts. Herein, three-dimensional ordered porous cuprous oxide cuboctahedra (3DOP Cu2O-CO) were designed and synthesized by a molecular fence-assisted hard templating approach. Capitalizing on the merits of interconnected and uniformly distributed pore channels, 3DOP Cu2O-CO exhibited outstanding electrochemical CO2-to-C2+ conversion, achieving faradaic efficiency and partial current density for C2+ products of up to 81.7% and -0.89 A cm-2, respectively, with an optimal formation rate of 2.92 mmol h-1 cm-2 under an applied current density of -1.2 A cm-2. In situ spectroscopy and simulation results demonstrated that the ordered pores of 3DOP Cu2O-CO can effectively confine and accumulate sufficient *CO adsorption during electrochemical CO2 reduction, which facilitates efficient dimerization for the formation of C2+ products. Furthermore, the 3DOP structure induces a higher local pH value, which not only enhances the C-C coupling reaction, but also suppresses competing H2 evolution.

Enhanced CO2 Electroreduction Selectivity toward Ethylene on Pyrazolate-Stabilized Asymmetric Ni-Cu Hybrid Sites

Metal-organic frameworks (MOFs) possess well-defined, designable structures, holding great potential in enhancing product selectivity for electrochemical CO2 reduction (CO2R) through active site engineering. Here, we report a novel MOF catalyst featuring pyrazolate-stabilized asymmetric Ni/Cu sites, which not only maintains structural stability under harsh electrochemical conditions but also exhibits extraordinarily high ethylene (C2H4) selectivity during CO2R. At a cathode potential of -1.3 V versus RHE, our MOF catalyst, denoted as Cu1Ni-BDP, manifests a C2H4 Faradaic efficiency (FE) of 52.7% with an overall current density of 0.53 A cm-2 in 1.0 M KOH electrolyte, surpassing that on prevailing Cu-based catalysts. More remarkably, the Cu1Ni-BDP MOF exhibits a stable performance with only 4.5% reduction in C2H4 FE during 25 h of CO2 electrolysis. A suite of characterization tools─such as high-resolution transmission electron microscopy, X-ray absorption spectroscopy, operando X-ray diffraction, and infrared spectroscopy─and density functional theory calculations collectively reveal that the cubic pyrazolate-metal coordination structure and the asymmetric Ni-Cu sites in the MOF catalyst synergistically facilitate the stable formation of C2H4 from CO2.

Highly Efficient Electroreduction of CO2 to Ethanol via Asymmetric C-C Coupling by a Metal-Organic Framework with Heterodimetal Dual Sites

The electroreduction of CO2 into value-added liquid fuels holds great promise for addressing global environmental and energy challenges. However, achieving highly selective yielding of multi-carbon oxygenates through the electrochemical CO2 reduction reaction (eCO2RR) is a formidable task, primarily due to the sluggish asymmetric C-C coupling reaction. In this study, a novel metal-organic framework (CuSn-HAB) with unprecedented heterometallic Sn···Cu dual sites (namely, a pair of SnN2O2 and CuN4 sites bridged by μ-N atoms) was designed to overcome this limitation. CuSn-HAB demonstrated an impressive Faradic efficiency (FE) of 56(2)% for eCO2RR to alcohols, achieving a current density of 68 mA cm-2 at a low potential of -0.57 V (vs RHE). Notably, no significant degradation was observed over a continuous 35 h operation at the specified current density. Mechanistic investigations revealed that, in comparison to the copper site, the SnN2O2 site exhibits a higher affinity for oxygen atoms. This enhanced affinity plays a pivotal role in facilitating the generation of the key intermediate *OCH2. Consequently, compared to homometallic Cu···Cu dual sites (generally yielding ethylene product), the heterometallic dual sites were proved to be more thermodynamically favorable for the asymmetric C-C coupling between *CO and *OCH2, leading to the formation of the key intermediate *CO-*OCH2, which is favorable for yielding ethanol product.

Ag+ -Doped InSe Nanosheets for Membrane Electrode Assembly Electrolyzer toward Large-Current Electroreduction of CO2 to Ethanol

It is an appealing approach to CO2 utilization through CO2 electroreduction (CO2 ER) to ethanol at high current density; however, the commonly used Cu-based catalysts cannot sustain large current during CO2 ER despite their capability for ethanol production. Herein, we report that Ag+ -doped InSe nanosheets with Se vacancies can address this grand challenge in a membrane electrode assembly (MEA) electrolyzer. As revealed by our experimental characterization and theoretical calculation, the Ag+ doping, which can tailor the electronic structure of InSe while diversifying catalytically active sites, enables the formation of key reaction intermediates and their sequential evolution into ethanol. More importantly, such a material can well work for large-current conditions in MEA electrolyzers with In2+ species stabilized via electron transfer from Ag to Se. Remarkably, in an MEA electrolyzer by coupling cathodic CO2 ER with anodic oxygen evolution reaction (OER), the optimal catalyst exhibits an ethanol Faradaic efficiency of 68.7 % and a partial current density of 186.6 mA cm-2 on the cathode with a full-cell ethanol energy efficiency of 26.1 % at 3.0 V. This work opens an avenue for large-current production of ethanol from CO2 with high selectivity and energy efficiency by rationally designing electrocatalysts.

Dual-Function Precious-Metal-Free Metal-Organic Framework for Photocatalytic Conversion and Chemical Fixation of Carbon Dioxide

Highly efficient transformation of carbon dioxide (CO2) into value-added chemicals is considered a promising route for clean production and future energy sustainability, which is crucial for realizing a carbon-neutral economy. It remains a great challenge to develop highly stable and active catalysts with low-cost, environmentally friendly, and nontoxic materials for catalytic conversion of CO2. Herein, a precious-metal-free and heterogeneous MOF (LTG-FeZr) catalyst, composed of bis(terpyridine)iron(II) complexes and zirconium(IV) ions, was designed and prepared via a metalloligand approach. LTG-FeZr, with a robust framework and regular 1D channels not only can achieve the photocatalytic reduction of CO2 to HCOOH with a high conversion rate (up to 265 μmol·g-1·h-1) under visible-light irradiation but also exhibits exceptional catalytic activities toward the synthesis of cyclic carbonates via cycloaddition reactions of various epoxides and CO2 in the absence of light. Possible mechanisms for two different conversion processes of CO2 catalyzed by LTG-FeZr have been proposed. LTG-FeZr represents an ideal dual-function MOF platform for the catalytic conversion and utilization of CO2 in all weather conditions.

Multifunctional Roles of Clathrate Hydrate Nanoreactors for CO2 Reduction

In this study, we explore a possible platform for the CO2 reduction (CO2 R) in one of water's solid phases, namely clathrate hydrates (CHs), by ab initio molecular dynamics and well-tempered metadynamics simulations with periodic boundary conditions. We found that the stacked H2 O nanocages in CHs help to initialize CO2 R by increasing the electron-binding ability of CO2 . The substantial CO2 R processes are further influenced by the hydrogen bond networks in CHs. The first intermediate CO2 - in this process can be stabilized through cage structure reorganization into the H-bonded [CO2 - ⋅⋅⋅H-OHcage ] complex. Further cooperative structural dynamics enables the complex to convert into a vital transient [CO2 2- ⋅⋅⋅H-OHcage ] intermediate in a low-barrier disproportionation-like process. Such a highly reactive intermediate spontaneously triggers subsequent double proton transfer along its tethering H-bonds, finally converting it into HCOOH. These hydrogen-bonded nanoreactors feature multiple functions in facilitating CO2 R such as confining, tethering, H-bond catalyzing and proton pumping. Our findings have a general interest and extend the knowledge of CO2 R into porous aqueous systems.

Modulated synthesis of cesium phosphomolybdate encapsulated in hierarchical porous UiO-66 for catalysing alkene epoxidation

The hybrid composite of cesium phosphomolybdate (CsPM) encapsulated in hierarchical porous UiO-66 (HP-UiO-66) was synthesized using a modulated solvothermal method. A variety of characterization results demonstrated that the pore size distribution of CsPM@HP-UiO-66 is broader than traditional microporous CsPM@UiO-66 and cesium phosphomolybdate clusters are uniformly distributed in the octahedral cages of HP-UiO-66. The catalytic properties of the hybrid composite were investigated in alkene epoxidation reaction with tert-butyl hydroperoxide (t-BuOOH) as an oxidant. CsPM@HP-UiO-66 showed much higher catalytic activity for the alkene epoxidation reaction in comparison with the reference catalysts and could be easily reused by centrifugation and recycled for at least ten runs without significant loss in catalytic activity. The superior catalytic activity and stability of the hybrid composite CsPM@HP-UiO-66 should be mainly attributed to the hierarchical pores in the support HP-UiO-66 promoting the diffusion of alkene molecules, the uniform distribution of highly active CsPM clusters in the octahedral cages of HP-UiO-66, the introduction of cesium cations to form the insoluble cesium phosphomolybdate and the strong metal-support interactions (SMSI) between the CsPM clusters and the HP-UiO-66 framework.

Integration of MnO2 Nanosheets with Pd Nanoparticles for Efficient CO2 Electroreduction to Methanol in Membrane Electrode Assembly Electrolyzers

It remains a challenge to design a catalyst with high selectivity at a large current density toward CO2 electrocatalytic reduction (CO2ER) to a single C1 liquid product of methanol. Here, we report the design of a catalyst by integrating MnO2 nanosheets with Pd nanoparticles to address this challenge, which can be implemented in membrane electrode assembly (MEA) electrolyzers for the conversion of CO2ER to methanol. Such a strategy modifies the electronic structure of the catalyst and provides additional active sites, favoring the formation of key reaction intermediates and their successive evolution into methanol. The optimal catalyst delivers a Faradaic efficiency of 77.6 ± 1.3% and a partial current density of 250.8 ± 4.3 mA cm-2 for methanol during CO2ER in an MEA electrolyzer by coupling anodic oxygen evolution reaction with a full-cell energy efficiency achieving 29.1 ± 1.2% at 3.2 V. This work opens a new avenue to the control of C1 intermediates for CO2ER to methanol with high selectivity and activity in an MEA electrolyzer.

Intermediates Regulation via Electron-Deficient Cu Sites for Selective Nitrate-to-Ammonia Electroreduction

Ammonia (NH3 ), known as one of the fundamental raw materials for manufacturing commodities such as chemical fertilizers, dyes, ammunitions, pharmaceuticals, and textiles, exhibits a high hydrogen storage capacity of ≈17.75%. Electrochemical nitrate reduction (NO3 RR) to valuable ammonia at ambient conditions is a promising strategy to facilitate the artificial nitrogen cycle. Herein, copper-doped cobalt selenide nanosheets with selenium vacancies are reported as a robust and highly efficient electrocatalyst for the reduction of nitrate to ammonia, exhibiting a maximum Faradaic efficiency of ≈93.5% and an ammonia yield rate of 2360 µg h-1 cm-2 at -0.60 V versus reversible hydrogen electrode. The in situ spectroscopical and theoretical study demonstrates that the incorporation of Cu dopants and Se vacancies into cobalt selenide efficiently enhances the electron transfer from Cu to Co atoms via the bridging Se atoms, forming the electron-deficient structure at Cu sites to accelerate NO3 - dissociation and stabilize the *NO2 intermediates, eventually achieving selective catalysis in the entire NO3 RR process to produce ammonia efficiently.

Efficient electroreduction of CO to acetate using a metal-azolate framework with dicopper active sites

Electrochemical reduction of CO to value-added products, especially C2 products, provides a potential approach to achieve carbon neutrality and overcome the energy crisis. Herein, we report a metal-azolate framework (CuBpz) with dicopper active sites as an electrocatalyst for the electrochemical CO reduction reaction (eCORR). As a result, CuBpz achieved an impressive faradaic efficiency (FE) of 47.8% for yielding acetate with a current density of -200 mA cm-2, while no obvious degradation was observed over 60 hours of continuous operation at a current density of -200 mA cm-2. Mechanism studies revealed that the dicopper site can promote C-C coupling between two C1 intermediates, thereby being conducive to the generation of the key *CH2COOH intermediate.