2D Copper Tetrahydroxyquinone Conductive Metal-Organic Framework for Selective CO2 Electrocatalysis at Low Overpotentials

Increasing electrochemical carbon dioxide reduction to methane via a novel copper-based conductive metal organic framework

The development of a new system for the electrochemical carbon dioxide reduction reaction (ECO2RR) to methane (CH4) is challenging, and novel conductive metal organic frameworks (c-MOFs) for efficient ECO2RR to CH4 are critical to this system. Here, we report a novel c-MOF, copper-pyromellitic dianhydride-2-methylbenzimidazole (Cu-PD-2-MBI), in which the introduction of electron-withdrawing 2-methylbenzimidazole (2-MBI) into the copper-pyromellitic dianhydride (Cu-PD) interlayer elevated the valence of copper (Cu) ions, which improved the ECO2RR performance of Cu-PD-2-MBI. Cu-PD-2-MBI was tested in a flow cell, and the Faradaic efficiency of CH4 reached 73.7 %, with a corresponding partial current density of -428.3 mA·cm-2 at -1.3 V, which was higher than those of most reported Cu-based catalysts. Further exploration via theoretical calculations indicated that the intercalated 2-MBI in Cu-PD-2-MBI induced a shift in the d-band center in the Cu sites from -2.63 to -1.86 eV and reduced the formation energy of the *COOH and *CHO intermediates in the process of generating CH4 compared with those of the reference Cu-PD catalyst.

Efficient solar-driven: Photothermal catalytic reduction of atmospheric CO2 at the gas-solid interface by CuTCPP/MXene/TiO2

Directly capturing atmospheric CO2 and converting it into valuable fuel through photothermal synergy is an effective way to mitigate the greenhouse effect. This study developed a gas-solid interface photothermal catalytic system for atmospheric CO2 reduction, utilizing the innovative photothermal catalyst (Cu porphyrin) CuTCPP/MXene/TiO2. The catalyst demonstrated a photothermal catalytic performance of 124 μmol·g-1·h-1 for CO and 106 μmol·g-1·h-1 for CH4, significantly outperforming individual components. Density functional theory (DFT) results indicate that the enhanced catalytic performance is attributed to the internal electric field between the components, which significantly enhances carrier utilization. The introduction of CuTCPP reduces free energy of the photothermal catalytic reaction. Additionally, the local surface plasmon resonance (LSPR) effect and high-speed electron transfer properties of MXene further boost the catalytic reaction rate. This well-designed catalyst and catalytic system offer a simple method for capturing atmospheric CO2 and converting it in-situ through photothermal catalysis.

Asymmetric Cu-N1O3 Sites Coupling Atop-type and Bridge-type Adsorbed *C1 for Electrocatalytic CO2-to-C2 Conversion

2D functional porous frameworks offer a platform for studying the structure-activity relationships during electrocatalytic CO2 reduction reaction (CO2RR). Yet challenges still exist to breakthrough key limitations on site configuration (typical M-O4 or M-N4 units) and product selectivity (common CO2-to-CO conversion). Herein, a novel 2D metal-organic framework (MOF) with planar asymmetric N/O mixed coordinated Cu-N1O3 unit is constructed, labeled as BIT-119. When applied to CO2RR, BIT-119 could reach a CO2-to-C2 conversion with C2 partial current density ranging from 36.9 to 165.0 mA cm-2 in flow cell. Compared to the typical symmetric Cu-O4 units, asymmetric Cu-N1O3 units lead to the re-distribution of local electron structure, regulating the adsorption strength of several key adsorbates and the following catalytic selectivity. From experimental and theoretical analyses, Cu-N1O3 sites could simultaneously couple the atop-type (on Cu site) and bridge-type (on Cu-N site) adsorption of *C1 species to reach the CO2-to-C2 conversion. This work broadens the feasible C-C coupling mechanism on 2D functional porous frameworks.

Altering the CO2 Electroreduction Pathways Towards C1 or C2+ Products via Engineering the Strength of Interfacial Cu-O Bond

Copper (Cu)-based catalysts have established their unique capability for yielding wide value-added products from CO2. Herein, we demonstrate that the pathways of the electrocatalytic CO2 reduction reaction (CO2RR) can be rationally altered toward C1 or C2+ products by simply optimizing the coordination of Cu with O-containing organic species (squaric acid (H2C4O4) and cyclohexanehexaone (C6O6)). It is revealed that the strength of Cu-O bonds can significantly affect the morphologies and electronic structures of derived Cu catalysts, resulting in the distinct behaviors during CO2RR. Specifically, the C6O6-Cu catalysts made up from organized nanodomains shows a dominant C1 pathway with a total Faradaic efficiency (FE) of 63.7 % at -0.6 V (versus reversible hydrogen electrode, RHE). In comparison, the C4O4-Cu with an about perfect crystalline structure results in uniformly dispersed Cu-atoms, showing a notable FE of 65.8 % for C2+ products with enhanced capability of C-C coupling. The latter system also shows stable operation over at least 10 h with a high current density of 205.1 mA cm-2 at -1.0 VRHE, i.e., is already at the boarder of practical relevance. This study sheds light on the rational design of Cu-based catalysts for directing the CO2RR reaction pathway.

MOFs-Based Materials with Confined Space: Opportunities and Challenges for Energy and Catalytic Conversion

Metal-Organic Frameworks (MOFs) are a very promising material in the fields of energy and catalysis due to their rich active sites, tunable pore size, structural adaptability, and high specific surface area. The concepts of "carbon peak" and "carbon neutrality" have opened up huge development opportunities in the fields of energy storage, energy conversion, and catalysis, and have made significant progress and breakthroughs. In recent years, people have shown great interest in the development of MOFs materials and their applications in the above research fields. This review introduces the design strategies and latest progress of MOFs are included based on their structures such as core-shell, yolk-shell, multi-shelled, sandwich structures, unique crystal surface exposures, and MOF-derived nanomaterials in detail. This work comprehensively and systematically reviews the applications of MOF-based materials in energy and catalysis and reviews the research progress of MOF materials for atmospheric water harvesting, seawater uranium extraction, and triboelectric nanogenerators. Finally, this review looks forward to the challenges and opportunities of controlling the synthesis of MOFs through low-cost, improved conductivity, high-temperature heat resistance, and integration with machine learning. This review provides useful references for promoting the application of MOFs-based materials in the aforementioned fields.

Modulating Electronic States of Cu in Metal-Organic Frameworks for Emerging Controllable CH4/C2H4 Selectivity in CO2 Electroreduction

The intensive study of electrochemical CO2 reduction reaction (CO2RR) has resulted in numerous highly selective catalysts, however, most of these still exhibit uncontrollable selectivity. Here, it is reported for the first time the controllable CH4/C2H4 selectivity by modulating the electronic states of Cu incorporated in metal-organic frameworks with different functional ligands, achieving a Faradaic efficiency of 58% for CH4 on Cu-incorporated UiO-66-H (Ce) composite catalysts, Cu/UiO-66-H (Ce) and that of 44% for C2H4 on Cu/UiO-66-F (Ce). In situ measurements of Raman and X-ray absorption spectra revealed that the electron-withdrawing ability of the ligand side group controls the product selectivity on MOFs through the modulation of the electronic states of Cu. This work opens new prospects for the development of MOFs as a platform for the tailored tuning of selectivity in CO2RR.

Molecular enhancement of Cu-based catalysts for CO2 electroreduction

The electrochemical carbon dioxide reduction reaction (eCO2RR) represents an effective means of achieving renewable energy storage and a supply of carbon-based raw materials. However, there are still great challenges in selectively producing specific hydrocarbon compounds. The unique ability of the copper (Cu) catalyst to promote proton-coupled electron transfer processes offers clear advantages in generating value-added products. This review presents molecular enhancement strategies for Cu-based catalysts for CO2 electroreduction. We also elucidate the principles of each strategy for enhancing eCO2RR performance, discuss the structure-activity relationships, and propose some promising molecular enhancement strategies. This review will provide guidance for the development of organic-inorganic hybrid Cu-based catalysts as high-performance CO2 electroreduction catalysts.

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.

Carbon Dioxide Capture and Conversion Using Metal-Organic Framework (MOF) Materials: A Comprehensive Review

The escalating threat of anthropogenic climate change has spurred an urgent quest for innovative CO2 capture and utilization (CCU) technologies. Metal-organic frameworks (MOFs) have emerged as prominent candidates in CO2 capture and conversion due to their large specific surface area, well-defined porous structure, and tunable chemical properties. This review unveils the latest advancements in MOF-based materials specifically designed for superior CO2 adsorption, precise separation, advanced photocatalytic and electrocatalytic CO2 reduction, progressive CO2 hydrogenation, and dual functionalities. We explore the strategies that enhance MOF efficiency and examine the challenges of and opportunities afforded by transitioning from laboratory research to industrial application. Looking ahead, this review offers a visionary perspective on harnessing MOFs for the sustainable capture and conversion of CO2.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In Situ Evolved Ligand Defects

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05 : 1-4.3 : 1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

A Rhombic 2D Conjugated Metal-Organic Framework as Cathode for High-Performance Sodium-Ion Battery

2D conjugated metal-organic frameworks (2D c-MOFs) have garnered significant attention as promising electroactive materials for energy storage. However, their further applications are hindered by low capacity, limited cycling life, and underutilization of the active sites. Herein, Cu-TBA (TBA = octahydroxyltetrabenzoanthracene) with large conjugation units (narrow energy gap) and a unique rhombus topology is introduced as the cathode material for sodium-ion batteries (SIBs). Notably, Cu-TBA with a rhombus topology exhibits a high specific surface area (613 m2 g-1) and metallic band structure. Additionally, Cu-TBA outperforms its hexagonal counterpart, Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxyltriphenylene), demonstrating superior reversible capacity (153.6 mAh g-1 at 50 mA g-1) and outstanding cyclability with minimal capacity decay even after 3000 cycles at 1 A g-1. This work elucidates a new strategy to enhance the electrochemical performance of 2D c-MOFs cathode materials by narrowing the energy gap of organic linkers, effectively expanding the utilization of 2D c-MOFs for SIBs.

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.

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.

Density Functional Study of Electrocatalytic Carbon Dioxide Reduction in Fourth-Period Transition Metal-Tetrahydroxyquinone Organic Framework

This study investigates the utilisation of organometallic network frameworks composed of fourth-period transition metals and tetrahydroxyquinone (THQ) in electrocatalytic CO2 reduction. Density functional theory (DFT) calculations were employed in analysing binding energies, as well as the stabilities of metal atoms within the THQ frameworks, for transition metal TM-THQs ranging from Y to Cd. The findings demonstrate how metal atoms could be effectively dispersed and held within the THQ frameworks due to sufficiently high binding energies. Most TM-THQ frameworks exhibited favourable selectivity towards CO2 reduction, except for Tc and Ru, which experienced competition from hydrogen evolution reaction (HER) and required solution environments with pH values greater than 5.716 and 8.819, respectively, to exhibit CO2RR selectivity. Notably, the primary product of Y, Ag, and Cd was HCOOH; Mo produced HCHO; Pd yielded CO; and Zr, Nb, Tc, Ru, and Rh predominantly generated CH4. Among the studied frameworks, Zr-THQ displayed values of 1.212 V and 1.043 V, corresponding to the highest limiting potential and overpotential, respectively, while other metal-organic frameworks displayed relatively low ranges of overpotentials from 0.179 V to 0.949 V. Consequently, it is predicted that the TM-THQ framework constructed using a fourth-period transition metal and tetrahydroxyquinone exhibits robust electrocatalytic reduction of CO2 catalytic activity.

Metal-Organic Framework-Based Nanovaccine for Relieving Immunosuppressive Tumors via Hindering Efferocytosis of Macrophages and Promoting Pyroptosis and Cuproptosis of Cancer Cells

Current cancer vaccines face challenges due to an immunosuppressive tumor microenvironment and their limited ability to produce an effective immune response. To address the above limitations, we develop a 3-(2-spiroadamantyl)-4-methoxy-4-(3-phosphoryloxy)-phenyl-1,2-dioxetane (alkaline phosphatase substrate) and XMD8-92 (extracellular signal-regulated kinase 5 inhibitor)-codelivered copper-tetrahydroxybenzoquinone (Cu-THBQ/AX) nanosized metal-organic framework to in situ-generate therapeutic vaccination. Once inside the early endosome, the alkaline phosphatase overexpressed in the tumor cells' membrane activates the in situ type I photodynamic effect of Cu-THBQ/AX for generating •O2-, and the Cu-THBQ/AX catalyzes O2 and H2O2 to •O2- and •OH via semiquinone radical catalysis and Fenton-like reactions. This surge of ROS in early endosomes triggers caspase-3-mediated proinflammatory pyroptosis via activating phospholipase C. Meanwhile, Cu-THBQ/AX can also induce the oligomerization of dihydrolipoamide S-acetyltransferase to trigger tumor cell cuproptosis. The production of •OH could also trigger the release of XMD8-92 for effectively inhibiting the efferocytosis of macrophages to convert immunosuppressive apoptosis of cancer cells into proinflammatory secondary necrosis. The simultaneous induction of pyroptosis, cuproptosis, and secondary necrosis effectively converts the tumor microenvironment from "cold" to "hot" conditions, making it an effective antigen pool. This transformation successfully activates the antitumor immune response, inhibiting tumor growth and metastasis.

A Conductive 3D Dual-Metal π-d Conjugated Metal-Organic Framework Fe3(HITP)2/bpm@Co for Highly Efficient Oxygen Evolution Reaction

Although 2D π-d conjugated metal-organic frameworks (MOFs) exhibit high in-plane conductivity, the closely stacked layers result in low specific surface area and difficulty in mass transfer and diffusion. Hence, a conductive 3D MOF Fe3(HITP)2/bpm@Co (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) is reported through inserting bpm (4,4'-bipyrimidine) ligands and Co2+ into the interlayers of 2D MOF Fe3(HITP)2. Compared to 2D Fe3(HITP)2 (37.23 m2 g-1), 3D Fe3(HITP)2/bpm@Co displays a huge improvement in the specific surface area (373.82 m2 g-1). Furthermore, the combined experimental and density functional theory (DFT) theoretical calculations demonstrate the metallic behavior of Fe3(HITP)2/bpm@Co, which will benefit to the electrocatalytic activity of it. Impressively, Fe3(HITP)2/bpm@Co exhibits prominent and stable oxygen evolution reaction (OER) performance (an overpotential of 299 mV vs RHE at a current density of 10 mA cm-2 and a Tafel slope of 37.14 mV dec-1), which is superior to 2D Fe3(HITP)2 and comparable to commercial IrO2. DFT theoretical calculation reveals that the combined action of the Fe and Co sites in Fe3(HITP)2/bpm@Co is responsible for the enhanced electrocatalytic activity. This work provides an alternative approach to develop conductive 3D MOFs as efficient electrocatalysts.

Efficient electrochemical reduction of CO2 to CO in a flow cell device by a pristine Cu5tz6-cluster-based metal-organic framework

The electrochemical reduction of CO2 to CO is a powerful approach to achieving carbon neutrality. Herein, we report a five-nuclear copper cluster-based metal-azolate framework CuTz-1 as an electrocatalyst for the electrochemical CO2 reduction reaction. It achieved a faradaic efficiency (FE) of 62.7% for yielding CO with a partial current density of -35.1 mA cm-2 in flow cell device, which can be preserved for more than ten hours with negligible changes of the current density and FE(CO). Studies of electrocatalytic mechanism studies revealed that the distance of Cu-N was increased, and the coordination number of the Cu ion was reduced, while the oxidation state of Cu was decreased after the electrocatalysis. These findings offer valuable insights into structural changes that influence the performance of the catalyst during the process of the electrochemical reduction of CO2 process.

Large-Area Conductive MOF Ultrathin Film Controllably Integrating Dinuclear-Metal Sites and Photosensitizers to Boost Photocatalytic CO2 Reduction with H2O as an Electron Donor

Owing to the electrical conductivity and periodic porosity, conductive metal-organic framework (cMOF) ultrathin films open new perspectives to photocatalysis. The space-selective assembly of catalytic sites and photosensitizers in/on cMOF is favorable for promoting the separation of photogenerated carriers and mass transfer. However, the controllable integration of functional units into the cMOF film is rarely reported. Herein, via the synergistic effect of steric hindrance and an electrostatic-driven strategy, the dinuclear-metal molecular catalysts (DMC) and perovskite (PVK) quantum dot photosensitizers were immobilized into channels and onto the surface of cMOF ultrathin films, respectively, affording [DMC@cMOF]-PVK film photocatalysts. In this unique heterostructure, cMOF not only facilitated the charge transfer from PVK to DMC but also guaranteed mass transfer. Using H2O as an electron donor, [DMC@cMOF]-PVK realized a 133.36 μmol·g-1·h-1 CO yield in photocatalytic CO2 reduction, much higher than PVK and DMC-PVK. Owing to the excellent light transmission of films, multilayers of [DMC@cMOF]-PVK were integrated to increase the CO yield per unit area, and the 10-layer device realized a 1115.92 μmol·m-2 CO yield in 4 h, which was 8-fold higher than that of powder counterpart. This work not only lightens the development of cMOF-based composite films but also paves a novel avenue for an ultrathin film photocatalyst.

Molecularly Imprinted Heterostructure-Based Electrochemosensor for Ultratrace and Precise Detection of 2-Methylisoborneol in Water

Ultratrace 2-methylisoborneol (2-MIB, ∼ng/L) in source water is the main odorant in the algae-derived odor episodes, whose accurate on-site detection will have a promising application potential. Due to the chemical inertness of 2-MIB, sensitive and selective detection of 2-MIB remains much challenging. Herein, molecularly imprinted polymer cavities were polymerized on the heterostructure Ti3C2Tx@CuFc-metal-organic framework to selectively capture 2-MIB, where the heterostructure could catalyze the probe redox reaction of [Fe(CN)63-/4-] and amplify the corresponding current signals. The prepared electrochemical sensor showed higher sensitivity on 2-MIB detection than the reported ones. Excellent stability, reusability, and selectivity for 2-MIB detection were also verified. The linear range and limit of detection of our sensor for 2-MIB were optimized to 0.0001-100 μg/L and 30 pg/L, respectively, performing much better than the reported sensors. Comparable performance to gas chromatography-mass spectrometry was achieved when the sensor was applied to real water samples with or without 2-MIB standards. Overall, our research has made great progress in the application of an on-site sensor in 2-MIB detection and well advances the development of molecularly imprinted polymer-based electrochemical sensors.

Instructive Synergistic Effect of Coordinating Phosphorus in Transition-Metal-Doped β-Phosphorus Carbide Guiding the Design of High-Performance CO2RR Electrocatalysts

Developing efficient electrocatalysts for the CO2 reduction reaction (CO2RR) is the key and difficult point to alleviate energy and climate issues. The synergistic catalytic effects between metal and nonmetal elements have gained attention for the design of the CO2RR electrocatalysts. The realization of this effect requires a suitable combination of metal and nonmetal elements, as well as the support of suitable substrates. Based on this, the transition-metal-doped β-phosphorus carbide (TM-PC) (TM = 4d and 5d transition metals except Tc) catalysts are designed, and their structures, electronic properties, and CO2RR catalytic performances are studied in depth via first-principle calculations. The strong bonding ability and high reactivity brought by the moderate electronegativity and abundant electrons and orbitals of phosphorus are the key to the excellent catalytic performance of TM-PCs. Coordinating phosphorus atoms improve the catalyst activity in two ways: (1) regulating the electron transfer of the TM active site, and (2) acting as the active site and changing the reaction mechanism. With the participation of coordinating P atoms, the "relay" of active sites reduces the limiting potential values for the reduction from CO2 to CH4 catalyzed by Cr-PC and Mo-PC by 0.27 and 0.23 V, respectively, compared with pathways where only the TM atom is the active site, reaching -0.55 and -0.63 V, respectively. Regarding the coordinating P atom as the second active site, Cr-PC and Mo-PC can catalyze the production of CH3CH2OH at limiting potential values of -0.54 and -0.67 V, respectively. This study demonstrates the dramatic enhancement of catalytic activity caused by suitable nonmetal coordinating atoms such as P and provides a reference for the design of high-performance CO2RR electrocatalysts based on metal-nonmetal coordinating active centers.

Molecular Engineering of a Metal-Organic Polymer for Enhanced Electrochemical Nitrate-to-Ammonia Conversion and Zinc Nitrate Batteries

Metal-organic framework-based materials are promising single-site catalysts for electrocatalytic nitrate (NO3 - ) reduction to value-added ammonia (NH3 ) on account of well-defined structures and functional tunability but still lack a molecular-level understanding for designing the high-efficient catalysts. Here, we proposed a molecular engineering strategy to enhance electrochemical NO3 - -to-NH3 conversion by introducing the carbonyl groups into 1,2,4,5-tetraaminobenzene (BTA) based metal-organic polymer to precisely modulate the electronic state of metal centers. Due to the electron-withdrawing properties of the carbonyl group, metal centers can be converted to an electron-deficient state, fascinating the NO3 - adsorption and promoting continuous hydrogenation reactions to produce NH3 . Compared to CuBTA with a low NO3 - -to-NH3 conversion efficiency of 85.1 %, quinone group functionalization endows the resulting copper tetraminobenzoquinone (CuTABQ) distinguished performance with a much higher NH3 FE of 97.7 %. This molecular engineering strategy is also universal, as verified by the improved NO3 - -to-NH3 conversion performance on different metal centers, including Co and Ni. Furthermore, the assembled rechargeable Zn-NO3 - battery based on CuTABQ cathode can deliver a high power density of 12.3 mW cm-2 . This work provides advanced insights into the rational design of metal complex catalysts through the molecular-level regulation for NO3 - electroreduction to value-added NH3 .

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.

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 (eCO2 RR) 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 O3 Cu1 ···Cu2 O2 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 *CH2 CHO. 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 eCO2 RR to C2 products.

Computational Prediction of Stacking Mode in Conductive Two-Dimensional Metal-Organic Frameworks: An Exploration of Chemical and Electrical Property Changes

Conductive two-dimensional metal-organic frameworks (2D MOFs) have attracted interest as they induce strong charge delocalization and improve charge carrier mobility and concentration. However, characterizing their stacking mode depends on expensive and time-consuming experimental measurements. Here, we construct a potential energy surface (PES) map database for 36 2D MOFs using density functional theory (DFT) for the experimentally synthesized and non-synthesized 2D MOFs to predict their stacking mode. The DFT PES results successfully predict the experimentally synthesized stacking mode with an accuracy of 92.9% and explain the coexistence mechanism of dual stacking modes in a single compound. Furthermore, we analyze the chemical (i.e., host-guest interaction) and electrical (i.e., electronic structure) property changes affected by stacking mode. The DFT results show that the host-guest interaction can be enhanced by the transition from AA to AB stacking, taking H2S gas as a case study. The electronic band structure calculation confirms that as AB stacking displacement increases, the in-plane charge transport pathway is reduced while the out-of-plane charge transport pathway is maintained or even increased. These results indicate that there is a trade-off between chemical and electrical properties in accordance with the stacking mode.

Three dimensional cyclic trinuclear units based metal-covalent organic frameworks for electrochemical CO2RR

A three-dimensional metal-covalent organic framework (3D-MCOF) based on cyclic trinuclear units was synthesized using organic tetrahedral linkers and copper-based cyclic trinuclear complexes. The novel type of 3D-MCOF, named 3D-CTU-MCOF, with the ctn topology, is reported herein for the first time. Our study demonstrated enhanced electrocatalytic capacity for CO2 reduction reaction of 3D-CTU-MCOF compared to independent cyclic trinuclear units.

Applications of Metal-Organic Frameworks and Their Derivatives in Electrochemical CO2 Reduction

Electrochemically reducing CO2 to more reduced chemical species is a promising way that not only enables the conversion of intermittent energy resources to stable fuels, but also helps to build a closed-loop anthropogenic carbon cycle. Among various electrocatalysts for electrochemical CO2 reduction, multifunctional metal-organic frameworks (MOFs) have been employed as highly efficient and selective heterogeneous electrocatalysts due to their ultrahigh porosity and topologically diverse structures. Up to now, great progress has been achieved in the design and synthesis of highly active and selective MOF-related catalysts for electrochemical CO2 reduction reaction (CO2RR), and their corresponding reaction mechanisms have been thoroughly studied. In this review, we summarize the recent progress of applying MOFs and their derivatives in CO2RR, with a focus on the design strategies for electrocatalysts and electrolyzers. We first discussed the reaction mechanisms for different CO2RR products and introduced the commonly applied electrolyzer configurations in the current CO2RR system. Then, an overview of several categories of products (CO, HCOOH, CH4, CH3OH, and multi-carbon chemicals) generated from MOFs or their derivatives via CO2RR was discussed. Finally, we offer some insights and perspectives for the future development of MOFs and their derivatives in electrochemical CO2 reduction. We aim to provide new insights into this field and further guide future research for large-scale applications.

Control of evolution of porous copper-based metal-organic materials for electroreduction of CO2 to multi-carbon products

Electrochemcial reduction of CO2 to multi-carbon (C2+) products is an important but challenging task. Here, we report the control of structural evolution of two porous Cu(ii)-based materials (HKUST-1 and CuMOP, MOP = metal-organic polyhedra) under electrochemical conditions by adsorption of 7,7,8,8-tetracyanoquinodimethane (TNCQ) as an additional electron acceptor. The formation of Cu(i) and Cu(0) species during the structural evolution has been confirmed and analysed by powder X-ray diffraction, and by EPR, Raman, XPS, IR and UV-vis spectroscopies. An electrode decorated with evolved TCNQ@CuMOP shows a selectivity of 68% for C2+ products with a total current density of 268 mA cm-2 and faradaic efficiency of 37% for electrochemcial reduction of CO2 in 1 M aqueous KOH electrolyte at -2.27 V vs. RHE (reversible hydrogen electrode). In situ electron paramagnetic resonance spectroscopy reveals the presence of carbon-centred radicals as key reaction intermediates. This study demonstrates the positive impact of additional electron acceptors on the structural evolution of Cu(ii)-based porous materials to promote the electroreduction of CO2 to C2+ products.

Cu+-Mediated CO Coordination for Promoting C-C Coupling for CO2 and CO Electroreduction

Selective electrochemical upgrading of CO₂ to multicarbon (C₂₊) products requires a C-C coupling process, yet the underlying promoting mechanism of widely involved Cu oxidation states remains largely unclear, hindering the subtle design of efficient catalysts. Herein, we unveil the critical role of Cu⁺ in promoting C-C coupling via coordination with a CO intermediate during electrochemical CO₂ reduction. We find that, relative to other halogen anions, iodide (I^-) in HCO₃^- electrolytes accelerates the generation of strongly oxidative hydroxyl radicals that accounts for the formation of Cu⁺, which can be dynamically stabilized by I^- via the formation of CuI. The in situ generated CO intermediate strongly binds to CuI sites, forming nonclassical Cu(CO)_n⁺ complexes, leading to an approximately 3.0-fold increase of C₂₊ Faradaic efficiency at -0.9 V_RHE relative to that of I^--free Cu surfaces. Accordingly, a deliberate introduction of CuI into I^--containing HCO₃^- electrolytes for direct CO electroreduction brings about a 4.3-fold higher C₂₊ selectivity. This work provides insights into the role of Cu⁺ in C-C coupling and the enhanced C₂₊ selectivity for CO₂ and CO electrochemical reduction.

Copper-based catalysts for the electrochemical reduction of carbon dioxide: progress and future prospects

There is an urgent need for the development of high performance electrocatalysts for the CO₂ reduction reaction (CO₂RR) to address environmental issues such as global warming and achieve carbon neutral energy systems. In recent years, Cu-based electrocatalysts have attracted significant attention in this regard. The present review introduces fundamental aspects of the electrocatalytic CO₂RR process together with a systematic examination of recent developments in Cu-based electrocatalysts for the electroreduction of CO₂ to various high-value multicarbon products. Current challenges and future trends in the development of advanced Cu-based CO₂RR electrocatalysts providing high activity and selectivity are also discussed.

A Triptycene-Based 2D MOF with Vertically Extended Structure for Improving the Electrocatalytic Performance of CO2 to Methane

Two-dimensional conductive metal-organic frameworks (2D-c-MOFs) have attracted extensive attention owing to their unique structures and physical-chemical properties. However, the planarly extended structure of 2D-c-MOFs usually limited the accessibility of the active sites. Herein, we designed a triptycene-based 2D vertically conductive MOF (2D-vc-MOF) by coordinating 2,3,6,7,14,15-hexahydroxyltriptycene (HHTC) with Cu²⁺ . The vertically extended 2D-vc-MOF(Cu) possesses a weak interlayer interaction, which leads to a facile exfoliation to the nanosheet. Compared with the classical 2D-c-MOFs with planarly extended 2D structures, 2D-vc-MOF(Cu) exhibits a 100 % increased catalytic activity in terms of turnover number and a two-fold increased selectivity. Density functional theory (DFT) calculations further revealed that higher activity originated from the lower energy barriers of the vertically extended 2D structures during the CO₂ reduction reaction process.

A rational design of functional porous frameworks for electrocatalytic CO2 reduction reaction

The electrocatalytic CO₂ reduction reaction (ECO₂RR) is considered one of the approaches with the most potential to achieve lower carbon emissions in the future, but a huge gap still exists between the current ECO₂RR technology and industrial applications. Therefore, the design and preparation of catalysts with satisfactory activity, selectivity and stability for the ECO₂RR have attracted extensive attention. As a classic type of functional porous framework, crystalline porous materials (e.g., metal organic frameworks (MOFs) and covalent organic frameworks (COFs)) and derived porous materials (e.g., MOF/COF composites and pyrolysates) have been regarded as superior catalysts for the ECO₂RR due to their advantages such as designable porosity, modifiable skeleton, flexible active site structure, regulable charge transfer pathway and controllable morphology. Meanwhile, with the rapid development of nano-characterization and theoretical calculation technologies, the structure-activity relationships of functional porous frameworks have been comprehensively considered, i.e., metallic element type, local coordination environment, and microstructure, corresponding to selectivity, activity and mass transfer efficiency for the ECO₂RR, respectively. In this review, the rational design strategy for functional porous frameworks is briefly but precisely generalized based on three key factors including metallic element type, local coordination environment, and microstructure. Then, details about the structure-activity relationships for functional porous frameworks are illustrated in the order of MOFs, COFs, composites and pyrolysates to analyze the effect of the above-mentioned three factors on their ECO₂RR performance. Finally, the challenges and perspectives of functional porous frameworks for the further development of the ECO₂RR are reasonably proposed, aiming to offer insights for future studies in this intriguing and significant research field.

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu-O, Cu-S, Cu-Se, Cu-N, and Cu-P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal-air batteries, water-splitting, and CO₂ reduction reaction (CO₂ RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.

Graphite-like Charge Storage Mechanism in a 2D π-d Conjugated Metal-Organic Framework Revealed by Stepwise Magnetic Monitoring

Quasi-two-dimensional (2D) fully π-d conjugated metal-organic frameworks (MOFs) have been widely employed as active materials of secondary batteries; however, the origin of their high charge storage capacity is still unknown. Some reports have proposed a mechanism by assuming the formation of multiple radicals on one organic ligand, although there is no firm evidence for such a mechanism, which would run counter to the resonance theory. In this work, we utilized various magnetometric techniques to monitor the formation and concentration of paramagnetic species during the electrochemical process of 2D π-d conjugated Cu-THQ MOF (THQ = tetrahydroxy-1,4-benzoquinone). The spin concentration of the fully reduced (discharged 1.5 V) electrode was estimated to be around only 0.1 spin-1/2 per CuO₄ unit, which is much lower than that of the expected "diradical" form. More interestingly, a significant elevation of the temperature-independent paramagnetic term was simultaneously observed, which indicates the presence of delocalized π electrons in this discharged state. Such results were corroborated by first-principles density functional theory calculations and the electrochemically active density of states, which reveal the microscopic mechanism of the charge storage in the Cu-THQ MOF. Hence, a graphite-like charge storage mechanism, where the π-electron band accepts/donates electrons during the charge/discharge process, was suggested to explain the excessive charge storage of Cu-THQ. This graphite-like charge storage mechanism revealed by magnetic studies can be readily generalized to other π-d conjugated MOFs.

Heterogenization of Molecular Electrocatalytic Active Sites through Reticular Chemistry

The electrochemical conversion of small molecules, such as CO₂ , O₂ , and H₂ O, has received significant attention as a potential engine for sustainable life. Metal-organic frameworks (MOFs) are a promising class of electrocatalytic materials for such processes. An attractive aspect of utilizing this class of materials as electrocatalysts is that well-known molecular active sites can be introduced to well-defined crystalline heterogeneous catalytic systems with high tunability. This review offers strategic insights into recent studies on MOF-based electrocatalysts by discussing the notable active sites that have been utilized in both homogeneous and heterogeneous catalysts, while highlighting instances where such active sites have been introduced into MOFs. In addition, material design principles enabling the integration of electrochemically active components with the MOF platform are outlined. Viewpoints on the viability of MOFs as an alternative to currently used electrocatalysts are also discussed. Finally, the future direction of MOF-based electrocatalysis research is established.

Rational Design of Metal-Organic Frameworks for Electroreduction of CO2 to Hydrocarbons and Carbon Oxygenates

Since CO2 can be reutilized by using renewable electricity in form of product diversity, electrochemical CO2 reduction (ECR) is expected to be a burgeoning strategy to tackle environmental problems and the energy crisis. Nevertheless, owing to the limited selectivity and reaction efficiency for a single component product, ECR is still far from a large-scale application. Therefore, designing high performance electrocatalysts is the key objective in CO2 conversion and utilization. Unlike most other types of electrocatalysts, metal-organic frameworks (MOFs) have clear, designable, and tunable catalytic active sites and chemical microenvironments, which are highly conducive to establish a clear structure-performance relationship and guide the further design of high-performance electrocatalysts. This Outlook concisely and critically discusses the rational design strategies of MOF catalysts for ECR in terms of reaction selectivity, current density, and catalyst stability, and outlines the prospects for the development of MOF electrocatalysts and industrial applications. In the future, more efforts should be devoted to designing MOF structures with high stability and electronic conductivity besides high activity and selectivity, as well as to develop efficient electrolytic devices suitable for MOF catalysts.

Two-Dimensional (2D) TM-Tetrahydroxyquinone Metal-Organic Framework for Selective CO2 Electrocatalysis: A DFT Investigation

The resource utilization of CO2 is one of the essential avenues to realize the goal of "double carbon". The metal-organic framework (MOF) has shown promising applications in CO2 catalytic reduction reactions due to its sufficient pore structure, abundant active sites and functionalizability. In this paper, we investigated the electrocatalytic carbon dioxide reduction reactions of single-atom catalysts created by MOF two-dimensional coordination network materials constructed from transition metal-tetrahydroxybenzoquinone using density function theory calculations. The results indicate that for 10 transition metals, TM-THQ single levels ranging from Sc to Zn, the metal atom binding energy to the THQ is large enough to allow the metal atoms to be stably dispersed in the THQ monolayer. The Ni-THQ catalyst does not compete with the HER reaction in an electrocatalytic CO2 reduction. The primary product of reduction for Sc-THQ is HCOOH, but the major product of Co-THQ is HCHO. The main product of Cu-THQ is CO, while the main product of six catalysts, Ti, V, Cr, Mn, Fe, and Zn, is CH4. The limit potential and overpotential of Ti-THQ are the highest, 1.043 V and 1.212 V, respectively. The overpotentials of the other monolayer catalysts ranged from 0.172 to 0.952 V, and they were all relatively low. Therefore, we forecast that the TM-HQ monolayer will show powerful activity in electrocatalytic carbon dioxide reduction, making it a prospective electrocatalyst for carbon dioxide reduction.

A stable metal-azolate framework with cyclic tetracopper(I) clusters for highly selective electroreduction of CO2 to C2 products

It is of great significance for constructing electrocatalysts with accurate structures and compositions to pinpoint the active sites, thereby improving the C 2 products (C 2 H 4 , C 2 H 5 OH and CH 3 COOH) selectivity during electrocatalytic CO 2 reduction raction. Here, we report a tetracopper(I) cluster-based metal-organic framework that exhibits long-term stability and remarkable performance for electroreduction CO 2 towards C 2 products in an H-type cell with a maximum Faradaic efficiency (FE) of 72%, and delivers a current density of 350 mA cm -2 with a FE(C 2 ) up to 46% in a flow cell device, outperforming most of the Cu-based electrocatalysts such as Cu derivatives and Cu nanostructured materials. Importantly, no obvious degradation was observed at 350 mA cm -2 over 20 hours of continuous operation, strengthening the practicability. In-situ infrared spectroscopy analysis showed the cooperative effect of adjacent Cu(I) ions in tetracopper(I) cluster may promote the C-C coupling to generate C 2 products.

Thousand-fold increase in O2 electroreduction rates with conductive MOFs

Molecular materials must deliver high current densities to be competitive with traditional heterogeneous catalysts. Despite their high density of active sites, it has been unclear why the reported O₂ reduction reaction (ORR) activity of molecularly defined conductive metal-organic frameworks (MOFs) have been very low: ca. -1 mA cm^-2. Here, we use a combination of gas diffusion electrolyses and nanoelectrochemical measurements to lift multiscale O₂ transport limitations and show that the intrinsic electrocatalytic ORR activity of a model 2D conductive MOF, Ni₃(HITP)₂, has been underestimated by at least 3 orders of magnitude. When it is supported on a gas diffusion electrode (GDE), Ni₃(HITP)₂ can deliver ORR activities >-150 mA cm^-2 and gravimetric H₂O₂ electrosynthesis rates exceeding or on par with those of prior heterogeneous electrocatalysts. Enforcing the fastest accessible mass transport rates using scanning electrochemical cell microscopy revealed that Ni₃(HITP)₂ is capable of ORR current densities exceeding -1200 mA cm^-2 and at least another 130-fold higher ORR mass activity than has been observed in GDEs. Our results directly implicate precise control over multiscale mass transport to achieve high-current-density electrocatalysis in molecular materials.

Cu-based Organic-Inorganic Composite Materials for Electrochemical CO2 Reduction

Electrochemical CO2 reduction reaction (CO2RR) is an attractive pathway to convert CO2 into value-added chemicals and fuels. Copper (Cu) is the most effective monometallic catalyst for converting CO2 into multi-carbon products, but suffers from high overpotentials and poor selectivity. Therefore, it is essential to design efficient Cu-based catalyst to improve the selectivity of specific products. Due to the combination of advantages of organic and inorganic composite materials, organic-inorganic composites exhibit high catalytic performance towards CO2RR, and have been extensively studied. In this review, the research advances of various Cu-based organic-inorganic composite materials in CO2RR, i.e., organic molecular modified-metal Cu composites, Cu-based molecular catalyst/carbon carrier composites, Cu-based metal organic framework (MOF) composites, and Cu-based covalent organic framework (COF) composites are systematically summarized. Particularly, the synthesis strategies of Cu-based composites, structure-performance relationship, and catalytic mechanisms are discussed. Finally, the opportunities and challenges of Cu-based organic-inorganic composite materials in CO2RR are proposed.