Selective Electrochemical Reduction of Carbon Dioxide Using Cu Based Metal Organic Framework for CO2 Capture

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.

Al-Sehemi A, Alargarsamy S, Gajendran P, Ramachandran R. Development of Different Kinds of Electrocatalyst for the Electrochemical Reduction of Carbon Dioxide Reactions: An Overview

Significant advancements have been made in the development of CO2 reduction processes for applications such as electrosynthesis, energy storage, and environmental remediation. Several materials have demonstrated great potential in achieving high activity and selectivity for the desired reduction products. Nevertheless, these advancements have primarily been limited to small-scale laboratory settings, and the considerable technical obstacles associated with large-scale CO2 reduction have not received sufficient attention. Many of the researchers have been faced with persistent challenges in the catalytic process, primarily stemming from the low Faraday efficiency, high overpotential, and low limiting current density observed in the production of the desired target product. The highlighted materials possess the capability to transform CO2 into various oxygenates, including ethanol, methanol, and formates, as well as hydrocarbons such as methane and ethane. A comprehensive summary of the recent research progress on these discussed types of electrocatalysts is provided, highlighting the detailed examination of their electrocatalytic activity enhancement strategies. This serves as a valuable reference for the development of highly efficient electrocatalysts with different orientations. This review encompasses the latest developments in catalyst materials and cell designs, presenting the leading materials utilized for the conversion of CO2 into various valuable products. Corresponding designs of cells and reactors are also included to provide a comprehensive overview of the advancements in this field.

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.

Predesign of Catalytically Active Sites via Stable Coordination Cluster Model System for Electroreduction of CO2 to Ethylene

Purposefully designing the well-defined catalysts for the selective electroreduction of CO₂ to C₂ H₄ is an extremely important but challenging work. In this work, three crystalline trinuclear copper clusters (Cu₃ -X, X=Cl^- , Br^- , NO₃ ^- ) have been designed, containing three active Cu sites with the identical coordination environment and appropriate spatial distance, delivering high selectivity for the electrocatalytic reduction of CO₂ to C₂ H₄ . The highest faradaic efficiency of Cu₃ -X for CO₂ -to-C₂ H₄ conversion can be adjusted from 31.90 % to 55.01 % by simply replacing the counter anions (NO₃ ^- , Cl^- , Br^- ). The DFT calculation results verify that Cu₃ -X can facilitate the C-C coupling of identical *CHO intermediates, subsequently forming molecular symmetrical C₂ H₄ product. This work provides an important molecular model system and a new design perspective for electroreduction of CO₂ to C₂ products with symmetrical molecular structure.

Recent Development of Electrocatalytic CO2 Reduction Application to Energy Conversion

Carbon dioxide (CO₂ ) emission has caused greenhouse gas pollution worldwide. Hence, strengthening CO₂ recycling is necessary. CO₂ electroreduction reaction (CRR) is recognized as a promising approach to utilize waste CO₂ . Electrocatalysts in the CRR process play a critical role in determining the selectivity and activity of CRR. Different types of electrocatalysts are introduced in this review: noble metals and their derived compounds, transition metals and their derived compounds, organic polymer, and carbon-based materials, as well as their major products, Faradaic efficiency, current density, and onset potential. Furthermore, this paper overviews the recent progress of the following two major applications of CRR according to the different energy conversion methods: electricity generation and formation of valuable carbonaceous products. Considering electricity generation devices, the electrochemical properties of metal-CO₂ batteries, including Li-CO₂ , Na-CO₂ , Al-CO₂ , and Zn-CO₂ batteries, are mainly summarized. Finally, different pathways of CO₂ electroreduction to carbon-based fuels is presented, and their reaction mechanisms are illustrated. This review provides a clear and innovative insight into the entire reaction process of CRR, guiding the new electrocatalysts design, state-of-the-art analysis technique application, and reaction system innovation.

A Facile Strategy for Constructing a Carbon-Particle-Modified Metal-Organic Framework for Enhancing the Efficiency of CO2 Electroreduction into Formate

Electrocatalytic reduction of CO₂ by metal-organic frameworks (MOFs) has been widely investigated, but insufficient conductivity limits application. Herein, a porous 3D In-MOF {(Me₂ NH₂ )[In(BCP)]⋅2 DMF}_n (V11) with good stability was constructed with two types of channels (1.6 and 1.2 nm diameter). V11 exhibits moderate catalytic activity in CO₂ electroreduction with 76.0 % of Faradaic efficiency for formate (FE_HCOO- ). Methylene blue molecules of suitable size and pyrolysis temperature were introduced and transformed into carbon particles (CPs) after calcination. The performance of the obtained CPs@V11 is significantly improved both in FE_HCOO- (from 76.0 % to 90.1 %) and current density (2.2 times). Control experiments show that introduced CPs serve as accelerant to promote the charges and mass transfer in framework, and benefit to sufficiently expose active sites. This strategy can also work on other In-MOFs, demonstrating the universality of this method for electroreduction of CO₂ .

Nanoengineering Metal-Organic Framework-Based Materials for Use in Electrochemical CO2 Reduction Reactions

Electrocatalytic reduction of carbon dioxide to valuable chemicals is a sustainable technology that can achieve a carbon-neutral energy cycle in the environment. Electrochemical CO₂  reduction reaction (CO₂ RR) processes using metal-organic frameworks (MOFs), featuring atomically dispersed active sites, large surface area, high porosity, controllable morphology, and remarkable tunability, have attracted considerable research attention. Well-defined MOFs can be constructed to improve conductivity, introduce active centers, and form carbon-based single-atom catalysts (SACs) with enhanced active sites that are accessible for the development of CO₂  conversion. In this review, the progress on pristine MOFs, MOF hybrids, and MOF-derived carbon-based SACs is summarized for the electrocatalytic reduction of CO₂ . Finally, the limitations and potential improvement directions with respect to the advancement of MOF-related materials for the field of research are discussed. These summaries are expected to provide inspiration on reasonable design to develop stable and high-efficiency MOFs-based electrocatalysts for CO₂ RR.

Nitrogen-doped porous carbon derived from digested sludge for electrochemical reduction of carbon dioxide to formate

Carbon-based materials have been applied as cost-effective electrocatalysts to reduce carbon dioxide (CO₂) into valuable chemicals. Here, an environment-friendly method is proposed to obtain nitrogen-doped porous carbons (NPCs) from digested sludge, which is an abundant waste product from sewage treatment plants. The materials were used as a metal-free electrocatalyst for electrochemical reduction of CO₂ to formate. The synthesized material (NPC-600) had a mesoporous and microporous structure with a specific surface area of 246.21 m² g^-1 and pore volume of 0.494 cm³ g^-1. Active sites based on nitrogen atoms accounted for 2.98 atom% of the content and included pyrrolic-, pyridinic-, and graphitic-N, which is useful for CO₂ adsorption and electron transfer in electrochemical reduction. The Faradaic efficiency for formate production from CO₂ in the presence of NPC-600 was 68% at the potential of -1.5 V vs. SCE. Tafel analysis indicated that the pathway of CO₂ conversion involved the reduction of CO₂ to CO₂*^- intermediate, which was then converted to HCOO*^- and finally formate.

Identifying the Types and Characterization of the Active Sites on M-X-C Single-Atom Catalysts

Single atom catalysts (SACs) have attracted much attention in recent years. As an essential group in SACs, M-X-C (X=nonmetallic element) materials have been demonstrated to be efficient in many reactions. However, identifying the active sites on M-X-C, especially under working conditions, is still challenging, which is crucial for chemists to further understand the mechanism underlying the reaction and better design proper SACs for specific reactions. Herein, the types and characterization of M-X-C are comprehensively summarized and discussed in this review. In addition to the basic information above, the challenges and opportunities remaining in this field will be also proposed to present a perspective to the research on the next step.

Understanding the Efficiency and Selectivity of Two-Electron Production of Metalloporphyrin-Embedded Zirconium-Pyrogallol Scaffolds in Electrochemical CO2 Reduction

Because of the high efficiency and mild reaction conditions, electrocatalytic CO₂ reduction (ECR) has attracted significant attention in recent years. However, the specific mechanism of the formation of the two-electron production (CO or HCOOH) in this reaction is still unclear. Herein, with density functional theory calculation and experimental manipulation, the specific mechanism of the selective two-electron reduction of CO₂ has been systematically investigated, employing the polyphenolate-substituted metalloporphyrinic frameworks, ZrPP-1-M (M = Fe, Co, Ni, Cu, and Zn), as model catalysts. Experimental observations and theoretical calculations discovered that ZrPP-1-Co is a more favorable catalyst for ECR among them. Compared with the formation of HCOOH, electroreduction of CO₂ into CO has more beneficial thermodynamic and kinetic routes with ZrPP-1-Co as a catalyst. After introducing the r-GO for improving the conductivity, the Faradaic efficiency for CO formation is 82.4% at -0.6 v (vs RHE).

Revealing the structure-activity relationship of two Cu-porphyrin-based metal-organic frameworks for the electrochemical CO2-to-HCOOH transformation

The eCO2RR activity is correlated to the internal structural character of the catalyst. We employed two types of structural models of porphyrin-based MOFs of PCN-222(Cu) and PCN-224(Cu) into heterogeneous catalysis to illustrate the effect of structural factors on the eCO2RR performance. The composite catalyst PCN-222(Cu)/C displays better activity and selectivity (η = 450 mV, FEHCOOH = 44.3%, j = 3.2 mA cm-2) than PCN-224(Cu)/C (η = 450 mV, FEHCOOH = 34.1%, j = 2.4 mA cm-2) for the CO2 reduction to HCOOH in the range of -0.7--0.9 V (vs. RHE) due to its higher BET surface area, CO2 uptake, and a larger pore diameter. It is interesting that PCN-224(Cu)/C displays better performance in the range of -0.4--0.6 V (vs. RHE) due to its greater heat of adsorption, Qst and a higher affinity for CO2 molecule, which could promote the capture of CO2 onto the exposed active sites. As a result, PCN-224(Cu)/C exhibits better stability for the long-term electrolysis.

Organic-Inorganic Hybrid Nanomaterials for Electrocatalytic CO2 Reduction

Electrochemical CO₂ reduction (ECR) to value-added chemicals and fuels is regarded as an effective strategy to mitigate climate change caused by CO₂ from excess consumption of fossil fuels. To achieve CO₂ conversion with high faradaic efficiency, low overpotential, and excellent product selectivity, rational design and synthesis of efficient electrocatalysts is of significant importance, which dominates the development of ECR field. Individual organic molecules or inorganic catalysts have encountered a bottleneck in performance improvement owing to their intrinsic shortcomings. Very recently, organic-inorganic hybrid nanomaterials as electrocatalysts have exhibited high performance and interesting reaction processes for ECR due to the integration of the advantages of both heterogeneous and homogeneous catalytic processes, attracting widespread interest. In this work, the recent advances in designing various organic-inorganic hybrid nanomaterials at the atomic and molecular level for ECR are systematically summarized. Particularly, the reaction mechanism and structure-performance relationship of organic-inorganic hybrid nanomaterials toward ECR are discussed in detail. Finally, the challenges and opportunities toward controlled synthesis of advanced electrocatalysts are proposed for paving the development of the ECR field.

The Origin of the Electrocatalytic Activity for CO2 Reduction Associated with Metal-Organic Frameworks

There has been a rapid growth in the use of metal-organic framework (MOF) materials as electrocatalysts. However, simple anodic stripping analysis reveals that some well-known previously reported stable MOFs are in fact unstable at the negative potentials used to catalytically reduce CO₂ in aqueous electrolyte media. Thus, it is the resulting metal nanoparticles derived from reduction of the MOFs rather than the MOFs themselves that are the electrocatalysts. The results reported herein therefore suggest that stability data and the origin of the activity for MOF electrocatalysts may need careful re-evaluation and that suitable strategies are needed to ensure that stable MOF electrocatalysts have been synthesized. The use of the readily accessible stripping analysis method provides a powerful tool to assess MOF stability under turnover conditions.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks

Transformation of CO₂ based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO₂ . In fact, it is the formation of new covalent bonds between CO₂ and substrate molecules that successfully result in CO₂ solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO₂ conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO₂ , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Bi-Doped SnO Nanosheets Supported on Cu Foam for Electrochemical Reduction of CO2 to HCOOH

Design and fabrication of efficient electrocatalysts is essential for electrochemical reduction of carbon dioxide (CO₂). In this work, bismuth (Bi)-doped SnO nanosheets were grown on copper foam (Bi-SnO/Cu foam) by a one-step hydrothermal reaction method and applied for the electrochemical reduction of CO₂ to formic acid (HCOOH). The experimental results indicated that Bi doping stabilized the divalent tin (Sn²⁺) existing on the surface of the electrocatalyst, making it difficult to be reduced to metallic tin (Sn⁰) during the electrochemical reduction process. In addition, combining with density functional theory (DFT) calculations, it is found that Bi doping and electron transfer from the catalyst to the Cu foam substrate could enhance the adsorption of *OOCH intermediates. As such, the Bi-doped SnO electrocatalyst exhibited a superior faradaic efficiency of 93% at -1.7 V (vs Ag/AgCl) for the reduction of CO₂ to HCOOH, together with a current density of 12 mA cm^-2 and excellent stability in at least 30 h of operation.

Metal–Organic Frameworks Toward Electrocatalytic Applications

Metal–organic frameworks (MOFs) are a class of porous materials constructed from metal-rich inorganic nodes and organic linkers. Because of their regular porosity in microporous or mesoporous scale and periodic intra-framework functionality, three-dimensional array of high-density and well-separated active sites can be built in various MOFs; such characteristics render MOFs attractive porous supports for a range of catalytic applications. Furthermore, the electrochemically addressable thin films of such MOF materials are reasonably considered as attractive candidates for electrocatalysis and relevant applications. Although it still constitutes an emerging subfield, the use of MOFs and relevant materials for electrocatalytic applications has attracted much attention in recent years. In this review, we aim to focus on the limitations and commonly seen issues for utilizing MOFs in electrocatalysis and the strategies to overcome these challenges. The research efforts on utilizing MOFs in a range of electrocatalytic applications are also highlighted.

Artificial photosynthesis with metal and covalent organic frameworks (MOFs and COFs): challenges and prospects in fuel-forming electrocatalysis

Mimicking photosynthesis in generating chemical fuels from sunlight is a promising strategy to alleviate society's demand for fossil fuels. However, this approach involves a number of challenges that must be overcome before this concept can emerge as a viable solution to society's energy demand. Particularly in artificial photosynthesis, the catalytic chemistry that converts energy in the form of electricity into carbon-based fuels and chemicals has yet to be developed. Here, we describe the foundational work and future prospects of an emerging and promising class of materials: metal- and covalent-organic frameworks (MOFs and COFs). Within this context, these porous and tuneable framework materials have achieved initial success in converting abundant feedstocks (H₂ O and CO₂ ) into chemicals and fuels. In this review, we first highlight key achievements in this direction. We then follow with a perspective on precisely how MOFs and COFs can perform in ways not possible with conventional molecular or heterogeneous catalysts. We conclude with a view on how spectroscopically probing MOF and COF catalysis can be used to elucidate reaction mechanisms and material dynamics throughout the course of reaction.

Emerging Carbon-Based Heterogeneous Catalysts for Electrochemical Reduction of Carbon Dioxide into Value-Added Chemicals

The electrocatalytic reduction of CO₂ provides a sustainable way to mitigate CO₂ emissions, as well as store intermittent electrical energy into chemicals. However, its slow kinetics and the lack of ability to control the products of the reaction inhibit its industrial applications. In addition, the immature mechanistic understanding of the reduction process makes it difficult to develop a selective, scalable, and stable electrocatalyst. Carbon-based materials are widely considered as a stable and abundant alternative to metals for catalyzing some of the key electrochemical reactions, including the CO₂ reduction reaction. In this context, recent research advances in the development of heterogeneous nanostructured carbon-based catalysts for electrochemical reduction of CO₂ are summarized. The leading factors for consideration in carbon-based catalyst research are discussed by analyzing the main challenges faced by electrochemical reduction of CO₂ . Then the emerging metal-free doped carbon and aromatic N-heterocycle catalysts for electrochemical reduction of CO₂ with an emphasis on the formation of multicarbon hydrocarbons and oxygenates are discussed. Following that, the recent progress in metal-nitrogen-carbon structures as an extension of carbon-based catalysts is scrutinized. Finally, an outlook for the future development of catalysts as well as the whole electrochemical system for CO₂ reduction is provided.

An MOF-derived copper@nitrogen-doped carbon composite: the synergistic effects of N-types and copper on selective CO2 electroreduction

N-doping carbon and copper derived from benzimidazole-modified Cu-BTC MOFs have synergistic effects on selective CO₂ electroreduction.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

This review summarizes recent advances and highlights the structure–property relationship on metal–organic framework-based materials for carbon dioxide capture and conversion.

Enhanced electrochemical CO2 reduction selectivity by application of self-assembled polymer microparticles to a silver electrode

The self-assembled PS-modified Ag electrodes increased the selectivity for CO₂ reduction to CO and inhibited H₂ generation.

Design, synthesis and characterization of copper-based coordination compounds with bidentate (N,N and N,O) ligands: reversible uptake of iodine, dye adsorption and assessment of their antibacterial properties

This work presents the synthesis of close-packed copper complexes with an uncommon ability for dye and iodine adsorption and antibacterial activities.

Trace water accelerating the CO2 cycloaddition reaction catalyzed by an indium–organic framework

A unique four-fold interpenetrated In–MOF is utilized as a catalyst in the chemical fixation of CO₂, and the catalytic activity is promoted by trace water.