Metal-Organic Frameworks and Covalent Organic Frameworks for CO₂ Electrocatalytic Reduction: Research Progress and Challenges

Abstract

This paper provides a systematic review of the latest advancements in metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) for electrocatalytic carbon dioxide reduction. Both materials exhibit high specific surface areas, tunable pore structures, and abundant active sites. MOFs enhance CO₂ conversion efficiency through improved conductivity, optimized stability, and selective regulation—including bimetallic synergy, pulse potential strategies, and tandem catalysis. COFs achieve efficient catalysis through precise design of single or multi-metal active sites, optimization of framework conjugation, and photo/electro-synergistic systems. Both types of materials demonstrate excellent selectivity toward high-value-added products (CO, formic acid, C₂⁺ hydrocarbons), but they still face challenges such as insufficient stability, short operational lifespan, high scaling-up costs, and poor electrolyte compatibility. Future research should integrate in situ characterization with machine learning to deepen mechanistic understanding and advance practical applications.

1. Introduction

Since the Industrial Revolution, human activities have caused a sharp increase in carbon dioxide (CO₂) emissions, profoundly reshaping the Earth’s atmospheric composition and climate patterns [1]. According to the latest report from the International Energy Agency (IEA), global energy-related CO₂ emissions rose to 37.8 billion tons in 2024. Global energy demand grew by 2.2% in 2024, exceeding the average growth rate of the past decade. Energy-related carbon emissions continued to decouple from global economic growth, with the growth rate of global carbon emissions slowing to 0.8%, while global economic growth exceeded 3%. In 2024, growth rates varied significantly across different components of the global energy system, reflecting both short-term factors and deeper structural trends. In 2024, global energy demand grew by 2.2%, significantly faster than the average annual growth rate of 1.3% from 2013 to 2023. This growth was partly due to the impact of extreme weather, which we estimate contributed 0.3 percentage points to the 2.2% growth. Nevertheless, the growth rate of energy demand remains below that of the global economy, which grew by 3.2% in 2024, approaching the long-term average [2]. Meanwhile, according to the C3S bulletin, the global average temperature has been at least 1.5 degrees Celsius above pre-industrial levels (1850–1900) for 12 consecutive months as of June this year. The global average temperature from July 2023 to June 2024 has already reached the highest recorded value, 1.64 degrees Celsius above the pre-industrial average temperature. Effectively curbing the rise in CO₂ concentrations and achieving the “dual carbon” goals (carbon peaking and carbon neutrality) have become core issues concerning the future of humanity [3].

The global realization of the “dual carbon” strategy cannot be achieved without addressing the behind-the-scenes driving force—CO₂. Reducing CO₂ emissions is crucial for mitigating the greenhouse effect, addressing climate change, and curbing global temperature rise. Catalytic reduction technology, especially electrocatalysis [4], is the most effective method to significantly reduce the level of carbon dioxide in the atmosphere by converting carbon dioxide into valuable carbon-based chemicals and fuels, thereby reducing reliance on fossil energy and promoting a circular carbon economy. Among the materials involved in traditional electrocatalytic reduction, such as metals, metal oxides, semiconductors, and carbon-based materials, certain limitations are observed in terms of surface area, adjustment capacity, and overall catalytic performance. This lays the foundation for the development of new catalytic materials for electrocatalytic CO₂RR to enhance catalytic efficiency and performance.

In electrocatalytic carbon dioxide reduction reactions, metal-organic frameworks and covalent organic frameworks, as two important types of porous crystalline materials, have attracted much attention due to their high surface area, adjustable pore structure, and ability to accommodate multiple catalytic sites. However, they each have their own focuses in terms of structural essence and application characteristics. The electrocatalytic mechanism of MOFs [5] involves complex interactions among metal centers, organic linkers, and CO₂ molecules, which is similar to traditional metal catalysts in the processes of CO₂ activation adsorption and multi-step electron transfer. However, MOFs stand out due to their highly adjustable structure, unique coordination environment, and ability to control the microenvironment within the channels, but they often face challenges in terms of relatively poor conductivity. These characteristics shape their unique reaction pathways, enabling MOFs to function both directly as electrode materials and as electrocatalysts. By precisely regulating the electronic structure of metal centers (such as Fe, Co, Ni, Cu, Zn, and their combinations), optimizing ligand-metal interactions, improving electron conduction pathways, and fully utilizing their high surface area and abundant active sites, MOFs can effectively enhance electron transfer and promote the conversion of CO₂ into target products under mild conditions. Organic linkers also play a key role in regulating the electronic environment of the metal center, providing proton transfer sites and stabilizing reaction intermediates. Their porosity further optimizes the mass transfer of CO₂ and intermediates. In contrast, COFs are entirely composed of light elements (B, C, Si, N, O) connected to organic units through strong covalent bonds (such as B-O, C-N, C=N, C=C-N), and their building units need to maintain structural rigidity after synthesis to maintain a highly ordered porous framework. Although the design flexibility and performance diversity of COFs [6] are also developing rapidly, the dynamic reversibility of the linking bonds is a double-edged sword: it is not only a necessary condition for achieving high-crystallinity synthesis, but also one of the main factors that may lead to structural depolymerization and performance degradation of COFs in practical applications such as electrocatalysis. Therefore, one of the core strategies for enhancing the stability of COFs at present is to combine reversible polymerization with irreversible cyclization reactions to construct stable linkage units containing heterocyclic structures. In conclusion, MOFs have significant advantages in utilizing the activity of metal centers and structural tunability, while COFs are seeking fully organic and highly stable covalent frameworks. The two demonstrate complementary research directions and application potential in the field of electrocatalytic CO₂RR.

The core contributions of this review are mainly reflected in the following two dimensions:

First, regarding the systematic organization of MOF (metal-organic framework) catalysts: Centering on the “core requirement of improving catalytic performance”, it systematically introduces the design strategies of different types of MOF catalysts from three key directions—how to enhance catalyst stability, improve electrical conductivity, and optimize product selectivity. Meanwhile, it synchronously analyzes the catalytic efficiency and performance of various catalysts in their corresponding reactions.

Second, concerning the analysis of the design logic for COF (covalent organic framework) catalysts: Focusing on the “catalyst structure-performance relationship”, it elaborates in depth on the construction ideas of COF catalysts from core design dimensions, such as the screening and regulation of central metals and the design and selection of framework structures. Furthermore, it clearly points out the catalytic performance characteristics and advantages of COF catalysts under different design schemes.

2. The Mechanism of Electrocatalytic Reduction of CO₂

Electrocatalytic CO₂ reduction reaction (CO₂RR) involves the conversion of CO₂ into value-added chemicals such as carbon monoxide, formic acid, methanol, methane, and ethylene under an applied potential. Typically conducted in aqueous media, the process entails CO₂ adsorption and activation at the cathode, where it undergoes multi-step proton-coupled electron transfer, while water oxidation occurs at the anode to produce O₂ [7]. The coordination transition of CO₂ on the catalyst surface is a direct result of the proton-electron coupling transfer (EPCR) after CO₂ activation. The core is the intermediate evolution from “carbon-end adsorption” to “oxygen-end adsorption”, which can be specifically divided into three key steps:

(1).

Initial carbon coordination: Adsorption and activation of CO₂

The CO₂ molecule is chemically inert due to its linear structure (O=C=O) and high bond energy (C=O bond energy~750 kJ/mol), and needs to be adsorbed and activated at the active sites of the catalyst (such as metal atoms, defect sites) first.

CO₂ accepts electrons from the catalyst or external circuit, and its linear structure bends into a “V shape”, forming a carbon coordination intermediate—*CO₂⁻ (adsorbed carbonate anion)—with the carbon terminal bound to the active site. At this point, the C atoms in the CO₂ molecule directly bond with the active sites of the catalyst (such as the surface atoms of metals like Cu, Au, and Ag), with the O atoms facing outward, which is known as “carbon coordination”. A typical scenario is as follows: On the surfaces of metals such as Cu (100) and Au (111), CO₂ is adsorbed through electrostatic interaction or coordination bonds, and electrons are transferred from the active sites of the metal to the 2π antibond orbital of CO₂, stabilizing the CO₂⁻ intermediate. At this time, the coordination interaction is mainly the C-metal bond.

(2).

Key Transformation: Protonation drives oxygen-terminal binding (formation of oxygen coordination intermediates)

CO₂⁻ is an unstable intermediate state that requires further transformation through proton transfer (from the electrolyte H₂O or HCO₃⁻). During this process, the coordination center of gravity shifts from C atoms to O atoms, forming an oxygen coordination intermediate. Specifically, there are two pathways for this:

Path 1: Generate *COOH

One O atom in CO₂⁻ accepts a proton (H⁺) to form COOH (hydroxyl carbonyl intermediate). At this point, the O atoms connected to C in *COOH (C=O of O) form a stronger coordination interaction (O-metal bond) with the active site of the catalyst, and the binding of C atoms to the active site weakens, completing the transformation from “carbon coordination to oxygen coordination”.

For example, on Cu-based catalysts, *COOH is a key intermediate for the formation of CO (2-electron product) or C₂H₄ (8-electron product) from CO₂RR. Its oxygen coordination structure can be detected by in-situ Raman spectroscopy at 1200–1300 cm⁻¹ as a C-O stretching vibration peak.

Path 2: Generation of OCHO/HCOO⁻ (oxygen coordination, tending towards C1 product)

If a proton binds to another O atom of CO₂⁻, OCHO will be formed and further protonated or desorbed into HCOO⁻. At this point, the O atoms in OCHO/HCOO⁻ (the two O atoms connected to C) both have coordination effects with the active sites of the catalyst, which is a typical case of “oxygen coordination”. Metal catalysts such as Sn, Pb, and In have a stronger affinity for O atoms and are more likely to guide CO₂⁻ to the OCHO pathway, ultimately generating HCOOH with FE (The FE mentioned below all refer to this faradaic efficiency and will not be explained repeatedly) reaching over 80%, while Cu-based catalysts are more inclined towards the COOH pathway.

(3).

Subsequent evolution: Oxygen coordination intermediates determine product branching

The stability of oxygen coordination intermediates and the reaction pathways directly determine the final product, further demonstrating the irreversibility of coordination transitions:

COOH can break the O-H bond through electron transfer, regenerate carbon-coordinated CO (C atoms then bind to the active site), and subsequently generate C₂ products (such as C₂H₄ and C₂H₅OH) through *CO dimerization (C–C coupling).

OCHO/ HCOO⁻, due to its stable oxygen coordination structure, is less likely to undergo C–C coupling and is usually either directly desorbed into HCOOH (C1 product) or further protonated to form HCHO [8]. The selectivity toward specific C₂⁺ products is governed by the relative rates and thermodynamics of competing hydrogenation and deoxygenation pathways. Following reduction, the final products—including CO, HCOOH, CH₄, C₂H₄, and C₂H₅OH—must desorb from the catalyst surface into the electrolyte or evolve as gas. Product desorption is the terminal step of CO₂RR and plays a critical role in determining overall reaction efficiency and turnover frequency. If product binding is too strong, active sites may become blocked, inhibiting fresh CO₂ adsorption and leading to catalyst deactivation. Conversely, overly weak binding may hinder the reaction’s progression. Therefore, an ideal catalyst must strike a balance—providing sufficient affinity to stabilize intermediates and enable product formation, while allowing for efficient product release and active site regeneration. This delicate balance is essential for maintaining long-term catalytic activity and stability [9]. As shown in Figure 1, this section provides a schematic overview of the key pathways for CO₂ reduction, which is crucial for understanding the reaction mechanism.

Copper (Cu) is currently the only known metal capable of efficiently catalyzing C–C coupling for C₂⁺ formation. Its surface provides an optimal binding energy landscape for intermediates such as CO and OCCO, enabling both stabilization and reactivity.

The core challenge of the carbon dioxide reduction reaction (CO₂RR) lies in the effective cleavage of its highly stable C=O double bond [10]. The extremely high bond energy (approximately 750 kJ/mol) of this bond, the linear symmetrical structure of the CO₂ molecule, and the low energy level of the lowest unoccupied molecular orbital (LUMO) jointly result in significant thermodynamic stability and kinetic inertness, causing the initial activation energy barrier to be high. In addition, the generation of high-value-added products (such as CO, formic acid, methanol, or hydrocarbons) usually involves complex multi-electron/proton transfer processes, further increasing the difficulty of reaction regulation. The core function of the catalyst lies in overcoming this initial activation barrier and guiding the reaction path: inducing the bending of the CO₂ molecular configuration through adsorption, effectively weakening the C=O bond and reducing its LUMO energy level, and promoting electron injection; at the same time, it provides stable sites for key intermediates (such as COOH and CO), coordinates multi-step electron/proton coupled transfer (PCET), and ultimately regulates product selectivity [11]. In view of the urgent need for efficient CO₂ adsorption, precise design of active sites, and microenvironment regulation, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have become highly promising catalyst design platforms due to their unique structural characteristics. Their ultra-high specific surface area and ordered pore structure allow for efficient CO₂ adsorption and subsequent enrichment, thereby enhancing the overall CO₂ enrichment capacity.

The promoting effect of this ultra-high specific surface area (2370 m²/g) and ordered pore structure on CO₂ enrichment can be further analyzed through the difference in packaging structure (AA/AB):

AA-type cubic stacking (such as PMO nanocube) forms long-range ordered cubic mesoporous pores (pore size 4.2 nm) through surfactant templates. The strictly aligned pore network between layers enables the mesoporous order to reach 92% (XRD (111) peak half-height width < 0.3). However, micropores account for only 30% (confirmed by TEM and CO₂ adsorption). This structure is mainly characterized by mesoporous diffusion and is suitable for rapid mass transfer of low-concentration CO₂ (such as flue gas, 1.42 mmol/g, 273 K).

AB-type dislocation accumulation (such as coco peat-derived carbon, introduces grain boundary defects due to 60° interlayer dislocation, forming graded pores (70% of ultrafine pores < 0.7 nm, SSA 1702 m²/g). The ultrafine pores enhance the adsorption energy of CO₂ through the curvature of the pore wall (ΔH adsorption = −25 kJ/mol), and the adsorption capacity reaches 4.8 mmol/g at 298 K and 1 bar, which is 3.4 times that of the AA structure.

The differences between the two types of structures confirm the conclusion of reference [12]: ordered mesoporous pores (AA) enhance mass transfer efficiency, and ultrafine pores (AB) strengthen adsorption capacity. The synergy of the two (such as the AB-type graded pores in this study) can maximize the CO₂ enrichment capacity.

The tunable metal nodes in MOFs (such as unsaturated coordination metal clusters) and the directionally modified organic skeletons in COFs provide ideal carriers for constructing atomically precise catalytic active centers. The high degree of modularization and functionalization flexibility facilitates the optimization of the electronic structure of the active site, the introduction of co-catalytic groups, and the regulation of the reaction microenvironment, thereby systematically enhancing the CO₂ activation efficiency and the selectivity of the target product.

3. The Application of MOFs in CO₂ Electrocatalysis

MOFs have become promising electrocatalysts for CO₂RR due to their high specific surface area, significant catalyst activity, and unique structure with excellent tunability; thanks as well to their adjustable structure, high surface area and extensive catalytic sites.

Metal-organic frameworks (MOFs) are assembled from metal ions or metal clusters and organic ligands through coordination. This unique structure endows them with significant advantages and great potential in the implementation of various modification strategies. The specific structure of the basic MOF used in the electrocatalytic carbon dioxide reduction reaction (CO₂RR) is shown in Figure 2 [13]. Based on these structural characteristics, researchers are continuously improving the MOF by regulating the types of metal ions, optimizing the structure of coordination clusters, and adjusting the microscopic morphology, aiming to enhance its selectivity, stability, and efficiency in the electrocatalytic CO₂RR process [14].

3.1. Improve Electrical Conductivity

Metal-organic frameworks (MOFs) exhibit great potential in electrocatalytic CO₂ reduction reactions (CO₂RR) due to their high specific surface area, tunable pore structure, and abundant active sites. However, in practical applications, they suffer from poor conductivity and low electron transfer efficiency. This is because MOF materials are typically formed by organic ligands and metal ions connected via coordinate bonds, resulting in weak intermolecular forces and inherently poor conductivity (conductivity often below 10⁻⁸ S/cm). During electrocatalysis, electrons struggle to efficiently transfer from the electrode substrate to the active sites of the MOF, leading to increased overpotential (requiring higher voltages to drive the reaction), reduced catalytic activity, and potential side reactions (such as hydrogen evolution reaction, HER) due to electron accumulation. Conductivity can be improved by doping with conductive materials (such as carbon nanotubes or graphene), which also affects CO₂ diffusion and the exposure of active sites.

Xin et al. [15] proposed a novel approach to mitigate conductivity limitations: they prepared MOF-545-Cu/PAN (MCP) nanofibers via electrospinning, followed by carbonization to form porous nanofibers embedded with well-dispersed copper clusters. This MCP composite exhibits exceptional catalytic performance in CO₂RR, attributed to three synergistic structural advantages: high porosity, improved electrical conductivity, and uniform dispersion of copper clusters. Among the synthesized MCP variants, MCP-500 demonstrates the most prominent activity: it achieves a Faradaic efficiency for CO (FE_CO) of 98% at −0.8 V vs. RHE and maintains FE_CO above 95% even after 10 h of continuous electrocatalysis. Furthermore, MCP-500 exhibits remarkable selectivity over a broad potential range: as the applied voltage varies from −0.6 V vs. RHE to −1.0 V vs. RHE, FE_CO remains at a high level (80–98%). The authors attribute this superior performance to the synergistic interaction between the layered graphene framework (derived from carbonized PAN) and the uniformly dispersed copper clusters—this synergy not only enhances electronic conductivity but also improves mass transfer capability and strengthens the accessibility of active sites, collectively boosting catalytic efficiency.

An alternative strategy to enhance MOF conductivity is the design of conductive π-d MOFs, whose inherent conductivity stems from π-d conjugation between metal nodes and organic linkers. This conjugation facilitates electron transfer and accelerates reaction kinetics, addressing the core limitation of traditional MOFs. In π-d MOFs, transition metals (e.g., Fe, Co, Ni, Cu, Zn) are predominantly selected as metal nodes; these metals are favored for their excellent redox properties and ability to stabilize key CO₂RR intermediates [16,17,18]. For organic linkers, aromatic or conjugated systems (such as porphyrins and phthalocyanines) are preferred, as they provide π electrons to facilitate π-d conjugation, promote long-range electron transfer, and enhance the interaction between CO₂ molecules and active sites [19,20,21]. The synergistic interplay between transition metal nodes and conjugated linkers endows π-d MOFs with a customizable electronic structure, enabling precise tuning of catalytic properties and superior performance under electrocatalytic conditions. A key advantage of π-d MOFs is their enhanced charge transport capability, which supports higher current densities and reduces overpotential—two critical factors for improving CO₂RR efficiency.

Several studies have validated the efficacy of π-d MOFs in CO₂RR. For instance, Majidi et al. [22] reported the synthesis of 2D conjugated π-d MOF (c-MOF) nanosheets (Cu-THQ) with an average thickness of 5–10 nm and lateral dimensions of ~140 nm. As shown in Figure 3, these Cu-THQ nanosheets exhibit remarkable catalytic performance: they achieve an average FE_CO of 91% and a high turnover frequency (TOF) of 20.82 s⁻¹. When integrated into a flow cell, the Cu-THQ electrode further delivers a high current density of 173 mA cm⁻² at −0.45 V vs. RHE, highlighting its potential for practical applications.

π-d MOFs also demonstrate efficacy for CO₂RR toward formate (HCOO⁻). Hu’s group [23] utilized an indium-based porphyrin π-d MOF (In-TCPP), which features a well-defined structure, highly dispersed In active centers, and robust stability. This In-TCPP catalyst efficiently converts CO₂ to HCOO⁻, achieving an FE_HCOO⁻ of 90% and a cathode efficiency of 63.8% in a flow cell. Similarly, Wang’s team [24] designed a 2D π-d MOF (PML-Cu), which attains an FE_HCOO⁻ of 80.86% at −0.7 V vs. RHE. Gu’s group further corroborated this trend with their Cu₂(Cu-TCPP) nanosheets, which exhibit an FE_HCOO⁻ of 68.4% at −0.94 V vs. RHE [25]. Importantly, all these π-d MOFs maintain excellent stability under CO₂RR conditions, which further contributes to their sustained activity and selectivity. Collectively, these findings underscore the design flexibility of π-d MOFs, positioning them as ideal candidates for efficient and selective CO₂RR electrocatalysts [26].

3.2. Improve Stability

Metal-organic frameworks (MOFs) face critical stability limitations that hinder their practical application in electrocatalytic CO₂ reduction reactions (CO₂RR): they are prone to structural decomposition under typical reaction conditions. A primary cause is the use of aqueous electrolytes with variable pH in CO₂RR—MOF coordination bonds are susceptible to erosion by water or ions, and pH fluctuations can break these bonds, leading to framework collapse. Additionally, electrocatalytic processes introduce multiple destabilizing factors: high applied voltages, electron transfer dynamics, and the adsorption of reaction intermediates (e.g., *CO, *HCOO⁻) further exacerbate structural damage. These issues result in the loss of active sites, causing rapid degradation of catalytic performance over time; most conventional MOFs exhibit stability windows of less than 10 h. Environmental factors (e.g., water, acids, alkalis) also induce decomposition: for instance, classic MOF-5 degrades rapidly in water, while HKUST-1 undergoes structural transformation in alkaline environments.

The fundamental approach to improving MOF stability revolves around three key objectives: strengthening metal-ligand coordination bonds, optimizing framework structural integrity, and mitigating damage from external stimuli (e.g., water, acids, heat). For CO₂RR and other catalytic processes, a critical prerequisite for sustained activity is the catalyst’s tolerance to reaction media (e.g., acidic/basic electrolytes, aqueous systems). To meet this requirement, three targeted strategies have been developed:

(1) 

Selection of Stable Metal Nodes and Intrinsically Robust MOF Platforms

Prioritizing metal ions with high charge density (defined as valence/ionic radius ratio) is thermodynamically favorable for strengthening metal-ligand coordination. Metals with small ionic radii and high valences—such as Zr⁴⁺, Hf⁴⁺, Al³⁺, and Cr³⁺—are preferred, as their high charge density enhances bond strength and framework resistance to corrosion. Zr- or Hf-based MOFs are representative examples of this strategy, leveraging robust metal-ligand coordination for intrinsic stability. The UiO series (e.g., UiO-66, UiO-67) is a classic family of Zr-based MOFs, renowned for exceptional stability in water, acids, and alkalis [27]. Beyond intrinsic stability, UiO MOFs exhibit structural features tailored for CO₂RR: their Zr nodes provide effective CO₂ adsorption sites, reduce reaction energy barriers, and facilitate electron transfer, while their dicarboxylic acid linkers can be functionalized to further enhance activity and selectivity.

(2) 

Ligand Design for Mechanical and Chemical Stability

Ligand selection directly impacts MOF stability: rigid, chemically inert ligands with aromatic rings (e.g., benzene, naphthalene) or conjugated systems are preferred, as their rigidity enhances framework mechanical stability. Conversely, ligands prone to hydrolysis or protonation (e.g., those with amide or ester groups) should be avoided; instead, ligands with strong coordinating groups (e.g., carboxyl (-COOH), phosphonic acid (-PO₃H₂), imidazole) are used to reinforce metal-ligand bonds. For example, MOFs constructed with benzoic acid (BDC) or trimellitic acid (BTC) ligands exhibit significantly higher stability than those with flexible ligands. This design principle is exemplified by Cu-btca MOF (btca = benzotriazole-5-carboxylic acid), developed by Yu et al. [28] for stable CO₂RR in acidic environments. The benzotriazole-carboxylic acid ligand balances strong coordination with chemical inertness, allowing the Cu-btca network to maintain structural integrity in strong acidic electrolytes: at 300 mA/cm², it achieves 51.2% Faradaic efficiency (FE) for ethylene and 81.9% FE for polycarbonate products. Its porous structure further enables efficient mass transfer while suppressing proton reduction, minimizing the competitive hydrogen evolution reaction (HER).

(3) 

Compositional Modification and Structural Engineering

a. 

Doping and Ion Exchange

Ion exchange strategies can enhance both stability and catalytic performance by modifying active sites without compromising framework integrity. For instance, Pd was incorporated into Cu-based HKUST-1 [Cu₃(BTC)₂] (BTC = benzenetricarboxylate) via ion exchange, forming Cu-Pd paddlewheel dimers [29]. In CO₂-saturated 0.5 M KHCO₃, this modification increased FE from 28.7% to 84.8% at −0.77 V vs. reversible hydrogen electrode (RHE), while the BTC ligand’s strong coordination preserved framework stability.

b. 

Surface Modification

Surface modification targets environmental corrosion (e.g., water, electrolyte ions) by tuning surface properties. Hydrophobic modification, for example, mitigates water-induced degradation of active sites. A representative case is the PTFE-modified core-shell HKUST-1@Cu₂O nanocomposite [30]: HKUST-1 provides a high specific surface area and abundant active sites for CO₂ adsorption, while the PTFE-derived hydrophobic interface inhibits HER. At −1.0 V vs. RHE, HKUST-1@Cu₂O/PTFE-1 achieves 67.41% hydrocarbon efficiency and 46.08% FE_C₂H₄ (outperforming most Cu-based catalysts) and maintains stability over 12 h, with negligible current decay and consistent ethylene selectivity.

c. 

Core-Shell Architectures

Core-shell structures leverage synergistic interactions between core and shell components to boost stability, electron transfer efficiency, and product selectivity—key advantages for CO₂RR. The Cu₂O@Cu-TCPP (M) catalyst (M = Co, Fe, Ni; TCPP = tetrakis(4-carboxyphenyl)porphyrin) exemplifies this strategy for ethylene production in neutral electrolytes [31]. The Cu-TCPP shell protects the Cu₂O core, preserving its crystalline structure and valence state to extend long-term stability (Figure 4). Electrochemically, as the applied voltage ranges from −0.2 V to −1.6 V vs. RHE, FE for C₂H₄ and total C₂ products increases gradually; in 1 M KCl at 500 mA/cm², peak FEs reach 54 ± 2% (C₂H₄) and 69 ± 4% (total C₂ products).

Stable MOF platforms have been tailored for specific CO₂RR performance metrics, as demonstrated by the following examples:

UiO-66 derivatives: Liu’s group [32] synthesized HP-UiO-66-NH₂—a UiO-66 variant with hierarchical porosity and polar amino groups—for HCOO⁻ production. After pore modification, HP-UiO-66-NH₂ retained over 90% of its CO₂ adsorption capacity; optimized conditions yielded >6000 μmol gcat⁻¹h⁻¹ of HCOO⁻ within 3 h (5.6 times higher than free enzyme systems), reaching an HCOO⁻ concentration of 1.83 mM. Hod’s group [33] further functionalized UiO-66 with cyano groups (-CN) to form UiO-66-CN, which was integrated with a bismuth-based current collector. This catalyst achieved 93% FE_HCOOH at −0.75 V vs. RHE in Figure 5.

UiO-67-based catalysts: UiO-67’s larger pore size (vs. UiO-66) enables advanced functionalization. Wang’s group [34] developed 2Bn-Cu@UiO-67, which embeds N-heterocyclic carbene-linked Cu single-atom catalysts in interconnected nanoreactors. For CH₄ electrolysis (Figure 6), this catalyst exhibits exceptional activity: at −1.5 V vs. RHE, FE_CH₄ reaches 81% (with 420 mA cm⁻² current density), maintains >70% FE_CH₄ across all tested potentials, and achieves an unprecedented turnover frequency of 16.3 s⁻¹.

Collectively, these strategies—stable metal/ligand selection, compositional modification, and structural engineering—address the core stability limitations of MOFs for CO₂RR. By balancing stability with catalytic performance, these designs position MOFs as viable candidates for practical electrocatalytic applications.

3.3. Difficulties in Selectively Regulating Products

CO₂ reduction involves multi-electron transfer processes, potentially yielding various products such as CO, HCOOH, CH₄, and C₂H₄. However, the active sites of MOFs (metal centers and ligand functional groups) exhibit minimal differences in adsorption energy for intermediates, making it challenging to precisely control the reaction pathway. Low-valent metal centers (e.g., Cu²⁺ reduced to Cu⁰) tend to catalyze the formation of multi-carbon products, but their selectivity is often lower than that of pure Cu-based catalysts; high-valent metal centers (e.g., Co³⁺, Ni²⁺) are more inclined to produce CO or HCOOH, but their selectivity may fluctuate due to the instability of the microenvironment around the active sites (e.g., pore size, ligand electronic effects).

The pores of MOFs readily adsorb H₂O molecules. In a proton-rich environment, active sites may preferentially catalyze the reduction of H⁺ to H₂, thereby reducing the FE of CO₂RR. The following sections introduce some methods to address the challenges of controlling product selectivity: pulse potential strategies can be used to control structural reconstruction; bimetallic synergistic regulation can enhance the selectivity and activity of catalytic products; tandem catalysts can be employed to achieve stepwise synergistic and efficient production of target products; structural innovations can also be utilized to lower energy barriers and improve efficiency, among other approaches.

3.3.1. Pulse Potential Strategy

Although MOFs have promising prospects, during CO₂RR, especially under long-term electrolysis conditions, MOFs tend to undergo uncontrolled structural reconstruction, leading to blurred active site recognition and poor performance in actual electrocatalytic applications.

Pulse potential control is an innovative strategy for precisely regulating MOF reconstruction and designing its active sites, thereby overcoming the limitations of traditional material design methods. The structural fragility of MOFs, especially that associated with weak coordination bonds, also significantly contributes to their structural degradation [19]. Therefore, Huang et al. proposed a pulse potential strategy with optimized parameters to guide the structural evolution of Cu-MOFs and customize their active sites for CO₂RR. Under conventional constant-potential electrolysis, Cu-DMTZ MOF initially achieved a FE_CH₄ of 47.4%. Reasonably designed pulsed electrolysis can induce controlled reconstruction of Cu-DMTZ into active Cu₂O/CuO nanoclusters, thereby suppressing the formation of metallic Cu. Mechanistic studies using in situ Raman spectroscopy and controlled experiments involving H₂O₂ participation revealed that the oxidation process during pulsed electrolysis promotes the formation of CuO_x active sites, thereby enhancing the adsorption of the key *CO intermediate. As a result, the FE_CH₄ achieved 82.9% under the pulsed electrolysis strategy, significantly outperforming the constant-potential counterpart, representing state-of-the-art technology, and maintained over 60% FE_CH₄ during continuous operation for 12 h [35].

3.3.2. Bimetallic Catalyst

The synergy between two distinct metal atoms enhances catalytic efficiency by enabling multiple pathways for CO₂ activation and reduction, thereby improving both reaction kinetics and product selectivity. In electrochemical CO₂ reduction reactions (eCO₂RR), catalyst activity and target product selectivity are critically governed by the binding interactions between reaction intermediates and active sites. A viable strategy to optimize such interactions is the incorporation of transition metals into metal-organic frameworks (MOFs).

An ion exchange strategy was employed to incorporate Pd into Cu-based MOF HKUST-1 [Cu₃(BTC)₂, BTC = benzenetricarboxylate], forming Cu-Pd paddle-wheel dimers [30]. In CO₂-saturated 0.5 M KHCO₃, this modification elevated FE from 28.7% to 84.8% at −0.77 V vs. RHE; the bimetallic catalyst showed maximum CO FE at −0.77 V vs. RHE (FE decreased with more negative potential), while H₂ FE increased significantly when potential <−0.77 V vs. RHE. To further enhance catalytic performance, transition metal ions were systematically doped into MOFs. For instance, Ni²⁺, Fe²⁺, Cu²⁺ were doped into ZIF-8 at different ratios; Cu doping exerted a notable effect, with Cu_0.5Zn_0.5/ZIF-8 achieving 11.57 mA/cm² high partial current density and 88.5% maximum FE at −1.0 V vs. RHE [36].

Zou et al. developed a novel BiCu bimetallic organic framework composite (SU-101-Cu@2.5 C) for efficient eCO₂RR to formate [37]. Synthesized in situ at room temperature using multi-walled carbon nanotubes (MWCNTs) with tannic acid as a binder, this catalyst exhibits outstanding performance: it has a low initial potential of −0.46 V vs. RHE, current densities exceeding 100 mA/cm², and formate FE that rises to nearly 100% as voltage increases from −0.76 V to −0.96 V vs. RHE. Notably, it maintains FE > 80% across a −0.86~−1.06 V vs. RHE window, demonstrating strong formate selectivity. Density functional theory (DFT) calculations confirm that Bi acts as the eCO₂RR active center, Cu optimizes the electronic structure to enhance efficiency, and MWCNTs facilitate rapid electron transfer. The catalyst retains good efficiency and stability after 30 h of continuous catalysis, showing potential for large-scale applications.

Similarly, Huang et al. reported a MIL-68(In)/CuO heterostructure for eCO₂RR to formate [38]. By introducing microcrystalline CuO(111) onto the MIL-68(In) surface, the catalyst achieves 89.7% formate FE at −0.7 V vs. RHE in a flow cell. This performance stems from In-Cu dual active sites, which facilitate *HCOO⁻ formation and maintain stability over 180 h in a membrane electrode assembly (MEA) cell. In situ and ex situ studies further reveal that CuO enhances *HCOO⁻ generation while suppressing the competitive hydrogen evolution reaction (HER).

An ultra-thin two-dimensional triphenyl MOF (Cu-HHTT) was designed and synthesized for highly selective eCO₂RR to CO [39]. Its nanosheets, which contain CuO₄ units, exhibit excellent performance: at −0.6 V vs. RHE, they achieve a CO FE of 96.6% with a current density of 18 mA/cm². DFT calculations indicate this high selectivity arises from a lower energy barrier for CO desorption compared to *CO intermediate hydrogenation. Long-term durability tests confirm Cu-HHTT’s stability, with only a slight decrease in CO FE after ≥ 4 h of continuous operation.

3.3.3. Series Catalyst

The core design of MOF-based tandem catalysts lies in leveraging the porous structure of MOFs to achieve spatially ordered arrangement of active sites, decompose complex eCO₂RR reactions into consecutive elementary steps, and utilize pore confinement effects to promote directed transfer of intermediates between active sites—ultimately generating target products efficiently via a “stepwise relay” process. This design is distinguished from the “synchronous synergistic activation” of bimetallic sites by its reliance on the synergy between “spatial partitioning” and “temporal stepwise progression,” making it a crucial strategy for efficient conversion of complex reactions in heterogeneous catalysis.

Su et al. [40] synthesized CuAg bimetallic catalysts using an Ag-anchored Cu-based MOF (NH₂-Cu-BDC, BDC = 1,4-benzenedicarboxylic acid) as the precursor. For the CuAg5@NC catalyst, ethanol FE peaked at 51.8% at −1.0 V vs. RHE, total C₂ product FE reached a maximum of 82.6% at −1.2 V vs. RHE, and, conversely, byproduct H₂ FE decreased with increasing potential negativity, minimizing at 12.1% at −1.2 V vs. RHE. This superior performance is attributed to abundant Cu-Ag biphasic boundaries, which facilitate migration of CO (generated at Ag sites) to Cu sites—enhancing CO coverage on Cu sites and promoting C–C coupling.

He et al. [41] reported a tandem catalyst (CuPOF-Bpy/Cu₂O@CNT) constructed via a synergistic strategy: it combines a bidentate Cu(II) porphyrin framework (CuPOF) with Cu₂O nanoparticles (NPs) supported on carbon nanotubes (CNTs). This catalyst exhibits excellent eCO₂RR selectivity for C₂H₄: ethylene FE (FE_C₂H₄) increases significantly in the −1.0 to −1.4 V vs. RHE range, peaking at 71.0% at −1.1 V vs. RHE, and remains above 40% across the entire tested potential window. The performance originates from synergy between dual active sites (CuPor and CuBpy in CuPOF) and Cu₂O NPs: CuPor/CuBpy sites reduce CO₂ to *CO intermediates, which are then transferred to adjacent Cu₂O sites for C–C coupling to form C₂H₄.

For the Cu@BIF-144(Zn) tandem catalyst [42], electrochemical results show that CO FE decreases sharply with increasing voltage (becoming negligible at higher potentials), while FEs of CH₄ and C₂H₄ (key eCO₂RR products) increase significantly: CH₄ FE peaks at 41.8% at −1.6 V vs. RHE, and C₂H₄ FE peaks at 12.9% at −1.5 V vs. RHE. This voltage-dependent selectivity highlights the critical role of potential regulation in tuning CO₂ deep reduction pathways.

The catalyst’s superior performance stems from a unique microenvironment: the Zn catalytic center in BIF-144(Zn) generates a CO-rich local atmosphere, which promotes deep reduction of CO₂ on Cu NP surfaces. Compared to standalone BIF-144(Zn), the BIF-144(Zn)/Cu NPs composite exhibits notable electrochemical advantages: higher current density (more efficient reaction kinetics), lower Tafel slope (faster electron transfer), and smaller charge transfer resistance (reduced energy loss at the catalyst-electrolyte interface)—collectively confirming the value of the tandem design.

CNTs play a key role in accelerating electron transfer for tandem catalysts, as exemplified by the CNTs/R-Cu-TAl catalyst [43], which has high CO₂ capture capacity and promotes eCO₂RR to CH₄. At −1.56 V vs. RHE, R-Cu-TAl-CNTs1 achieves 54% CH₄ FE (nearly twice that of CNT-free R-Cu-TAl, 30%); in the −0.96~−1.76 V vs. RHE range, its CH₄/C₂H₄ FE ratio reaches 9.5 (≈12 times higher than R-Cu-TAl), confirming CNTs’ effect on enhancing CH₄ selectivity.

Sun et al. [44] reported a Cu@ZIF-8 nanowire (NW) core-shell catalyst with highly exposed Cu-ZIF-8 interfaces—another example of MOF-metal heterogeneous interfaces boosting performance. This catalyst exhibits excellent stability and achieves 57.5% FE for hydrocarbons (CH₄, C₂H₄) at −0.7 V vs. RHE; the Cu-ZIF-8 interface optimizes intermediate adsorption (especially stabilizing *CHO formation), thereby promoting hydrocarbon preference.

Yan et al. [45] recently developed a Cu-MOF-CF tandem catalyst (CF = copper foil) by combining single-site MOFs with copper foil, enabling highly selective eCO₂RR to C₂H₄. The catalyst consists of porous Cu-MOF anchored on copper foil, with enhanced performance attributed to three factors: the Cu-MOF unit cell supplies abundant CO intermediates on the Cu foil surface (promoting C–C coupling and C₂H₄ selectivity), the Cu foil surface microenvironment is improved, and the porous Cu-MOF enriches active sites and expands the active area. At −1.11 V vs. RHE, Cu-MOF-CF achieves 48.6% C₂H₄ FE (significantly outperforming bare Cu foil, 22.4% at −1.16 V vs. RHE) and a C₂H₄ partial current density over 4 times that of Cu foil.

3.3.4. Structural Innovation

Structural innovations in MOFs—particularly dimensional control—have expanded their catalytic potential for eCO₂RR. Following the successful application of 2D MOFs in CO₂-to-CO conversion, researchers have further explored their utility in multi-carbon product synthesis. Additionally, post-synthesis modification, solvent modulation, metal doping, and valence regulation of active sites have emerged as effective strategies to tailor MOF catalytic performance, as detailed below.

A triphenyl-based 2D vertically conductive MOF (2D-vc-MOF(Cu)) was designed to enhance CO₂-to-CH₄ electrocatalysis [46]. Density functional theory (DFT) calculations reveal that its vertically extended structure reduces reaction energy barriers and improves kinetics. For 2D-vc-MOF(Cu), as potential ranges from −1.2 V to −1.4 V vs. RHE, CH₄ FE increases sharply from 20% to 65% (demonstrating voltage-dependent methane selectivity); however, further increasing potential to −1.6 V vs. RHE lowers FE_CH₄ to 33%, indicating an optimal voltage window for maximizing methane production. Encapsulating the MOF’s active sites in a carbon layer also effectively inhibits aggregation and enhances charge transfer.

Post-synthesis structural modification can further tune 2D MOF selectivity. Zheng et al. [47] showed that bending the local structure of 2D coordination polymers reverses electrocatalytic preference: from hydrogen evolution reaction (HER, 80%) to eCO₂RR (76%), with C₂H₄ selectivity reaching 52%. Computational simulations confirm the wavy structure enhances H-bonding between amino groups and key eCO₂RR intermediates (lowering C₂H₄ formation barriers) while steric hindrance between amino groups and HER intermediates suppresses competitive HER.

Solvent choice is critical for synthesizing single-metal Cu-based MOFs, as it significantly impacts their structure (e.g., exposed crystal facets) and eCO₂RR performance.

Lu et al. [48] synthesized Cu(I)-5-mercapto-1-methyl-tetrazole (Cu-MMT) nanostructures with different exposed faces via solvent modulation:

• Water as solvent yields Cu-MMT nanoribbons that primarily expose (100) facets, achieving 55.22% FE for CH₄.
• Isopropanol as solvent produces Cu-MMT cross-linked nanosheets with exposed (001) faces, exhibiting 73.75% FE for C₂ products (especially ethylene).

Wang et al. [49] further demonstrated that adjusting solvent conditions controls the size of CuTrz (HTrz = 1H,1,2,4-triazole) MOF nanostructures, which modulates eCO₂RR performance. Smaller CuTrz nanostructures—rich in grain boundaries and defects—outperform larger counterparts: at −1.15 V vs. RHE, CuTrz-109 nm achieves 55.4% FE_C₂H₄ and 81.8% FE for total C₂ products.

Doping Cu-based MOFs or Cu-derived catalysts with other metals adjusts electronic structure and reaction pathways, enhancing selectivity for specific products.

• Ce doping: Chen et al. [50] doped Cu lattices with Ce (larger ionic radius) to form atomically doped Ce-CuOx catalysts, which boost eCO₂RR performance and CH₄ selectivity. Within −1.4 to −1.75 V vs. RHE, FE_CH₄ remains above 62% (peaking at 67.4%), with a partial current density of 293 mA/cm² at −1.6 V vs. RHE.
• Co doping: Sun et al. [51] prepared atomically dispersed Co-Cu alloys via electrochemical reconstruction of Co-doped Cu-MOFs. This catalyst exhibits outstanding eCO₂RR activity and CH₄ selectivity: during CH₄ conversion, it achieves 60 ± 1% FE and 303 ± 5 mA/cm² partial current density, outperforming most reported Cu-based catalysts.

The valence of Cu ions is a key factor in eCO₂RR performance. For example, a novel conjugated MOF (Cu-PD-2-MBI) was developed by introducing electron-withdrawing 2-methylbenzimidazole (2-MBI) into the interlayer of copper-pyranic acid anhydride (Cu-PD) [52]. For Cu-PD-2-MBI: at −1.3 V vs. RHE, FE_CH₄ reaches 73.7% with a partial current density of −428.3 mA/cm². As potential shifts from −1.1 V to −1.3 V vs. RHE, FE_CH₄ increases gradually while FE_H₂ decreases (indicating effective HER suppression); beyond −1.3 V vs. RHE, FE_CH₄ declines due to enhanced H₂ evolution, defining an optimal voltage range for CH₄ production.

4. Application of COFs in CO₂ Electrocatalysis

Covalent organic frameworks (COFs) have emerged as promising catalysts due to their high surface area, tunable porosity, and stability. COFs are composed of light elements such as carbon, hydrogen, boron, nitrogen, and oxygen, connected by covalent bonds [53,54]. Due to their high porosity, COFs are more readily applicable to CO₂ reduction processes. Additionally, these materials exhibit a large surface area. According to research, the specific surface area of COFs ranges from 711 to 4107 cm²/g [13]. Their significant specific surface area is considered a key characteristic for converting CO₂ into value-added products. COFs also exhibit high selectivity toward CO₂, surpassing competing reactions, including hydrogen evolution, which is crucial for the effective conversion of CO₂ [54].

4.1. Metal Center Design

In electrocatalytic CO₂ reduction reactions (CO₂RR), constructing efficient active centers is key to improving catalytic performance. COFs materials can precisely anchor metal ions or atoms through the programmable construction of organic ligands, forming stable, structurally defined active centers [7]. Such centers can be designed through single metal introduction, multi-metal synergy, and coordination environment control.

4.1.1. Single-Atom Active Sites

Single-atom catalysts (SACs) maximize metal utilization efficiency and exhibit exceptional catalytic activity due to their unique electronic structures and coordinative unsaturation [55]. Within COFs, single-atom metal sites maintain stability in highly symmetric and controllable organic coordination environments, effectively preventing metal atom aggregation and thus avoiding active site loss. Porphyrin and phthalocyanine units, featuring planar four-nitrogen coordination, are frequently employed as COF building blocks and metal ligands, forming well defined, single-atom catalytic centers such as Co–N₄ and Ni–N₄ [9]. These structures mimic enzymatic active sites at the atomic scale, providing efficient electron transfer pathways and activation sites for CO₂RR, demonstrating superior CO₂ conversion activity and product selectivity.

Dai et al. [56] exploited interlayer π–π stacking effects in bipyridine-based fully conjugated two-dimensional COFs to construct interlayer single-atom metal active sites (synthesis schematic shown in Figure 7). This catalyst significantly improved selectivity and efficiency for electrochemical CO₂ reduction to C₂ products. Cu@BTT-BPy-COF exhibited the highest current density and C₂ product selectivity at −0.8 V vs. RHE, with a FE reaching 46.7%, surpassing most framework-based electrocatalysts.

San et al. reported the first application of novel COF material COF-LZU1 in high-efficiency catalysis. This easily prepared imine-linked COF-LZU1 has a 2D exfoliated layered structure, enabling metal ion binding. Via simple post-treatment, Pd(II)-containing COF (Pd/COF-LZU1) was synthesized, which exhibits excellent catalytic activity in Suzuki-Miura coupling reaction—characterized by broad reactant scope, 96–98% product yield, high stability, and easy recoverability [57].

Harsh Vardhan realized the decoration of covalent organic frameworks (COFs) with vanadium via post-synthetic modification. Systematic studies on the catalytic behavior of vanadium-decorated COFs in Prins condensation and sulfide oxidation reactions showed that these materials exhibit excellent catalytic performance, including efficient activity, retained framework crystallinity, and good reusability [58].

4.1.2. Dual-/Multi-Metal Synergy Sites

While single-metal active sites are effective, introducing multiple metal centers can further diversify catalyst functionality and induce unique electronic structure modulation and adsorption behaviors, resulting in pronounced synergistic catalytic effects [59]. Different metal centers may play distinct roles in various reaction stages or cooperatively optimize adsorption and conversion of key intermediates. For example, charge distribution differences between dual metal sites might promote CO₂ adsorption and activation at one site, while facilitating *CO intermediate desorption or further reduction at the other, jointly enhancing reaction pathways, selectivity, and lowering overpotential.

Liu et al. [60] reported a multi-component synthetic strategy using precursors such as PMDA, urea, NH₄Cl, NiCl₃, and (NH₄)2Mo₂O₇ to prepare COFs with varied metal contents (H₂Pc-COF, 0.25NiPc-COF, 0.5NiPc-COF, 0.75NiPc-COF, NiPc-COF). The 0.75NiPc-COF exhibited the highest CO₂RR activity and selectivity, with a turnover frequency (TOF) of 4909.87 h⁻¹ and FE_CO up to 95.37%. Dong et al. [61] introduced lanthanum (La) into a dual-copper COF, which altered the coordination environment of Cu centers with N and O atoms, modifying Cu oxidation states and electronic properties. Electrochemical tests revealed that La incorporation enhanced methane selectivity while suppressing ethylene production, demonstrating controlled product selectivity from ethylene to methane via dual Cu site modulation combined with La doping [62].

4.1.3. Coordinate Environment and Metal Valence Control

Beyond metal species, the coordination environment and metal oxidation states significantly influence CO₂RR pathways and intermediate stability [63]. The modular synthesis of COFs enables precise control over metal active center coordination environments, such as N₄, N₂O₂, or N₃S configurations, each imparting unique electronic properties and catalytic behaviors. By varying the types, numbers, and spatial arrangement of coordinating atoms, electronic density, orbital energies, and interaction strength with reaction intermediates can be finely tuned [64].

Moreover, adjusting electron-donating or -withdrawing groups in the COF backbone indirectly modulates the charge density and redox behavior of metal centers. Incorporating strong electron-withdrawing groups (e.g., nitro –NO₂, cyano –CN) lowers the overall framework electron density, resulting in metal centers with higher positive charge or lower electron density [65]. This can weaken metal binding to intermediates like *CO, facilitating product desorption and promoting deeper CO₂ reduction. Conversely, electron-donating groups (e.g., methoxy –OCH₃, amino –NH₂) increase electron density on metal centers, enhancing adsorption of CO₂ or key intermediates, favoring specific product formation [66].

Li et al. [67] conducted theoretical studies on COF366-Co and its derivatives, calculating Gibbs free energy changes (ΔG) for elementary steps in CO₂RR and competing hydrogen evolution reaction (HER). They found electron-donating groups raised valence band maximum (VBM) energy levels, increasing Co center charge density via electron transfer from occupied N sp² orbitals to empty Co 3d orbitals. Electron-withdrawing groups lowered VBM and d-band center (ξd), bringing ξd closer to occupied VBM levels. This functionalization enhanced intermediate adsorption, particularly benefiting CO₂RR performance. The study highlights the pivotal role of local electronic environment modulation via chemical structure design in tuning CO₂RR catalytic activity.

4.2. Framework Optimization and CO₂ Adsorption Activation

COFs not only stabilize metal active centers but their backbone structure also profoundly affects CO₂ adsorption, diffusion, and activation processes [68]. Through precise tuning of framework conjugation, pore size distribution, and functionalization, reactive catalytic microenvironments can be constructed to optimize overall CO₂RR performance [69].

Jiang et al. showed that introducing electron-deficient units (triazine, carboxyl, fluorinated groups) into the COF framework sequentially reduces the material’s LUMO energy level and strengthens π-back-donation between the framework and CO₂, thereby increasing CO₂ adsorption capacity to 174 mg·g⁻¹ and adsorption heat (Qst) to 43.5 kJ·mol⁻¹. In situ infrared (IR) spectroscopy and density functional theory (DFT) calculations collectively confirm that the optimized framework lowers the formation energy barrier of the *COOH intermediate by 0.54 eV, significantly promoting CO₂ adsorption and activation. Additionally, the sub-nanometer molecular sieve effect of the dual-pore topology (1.27/1.55 nm) preferentially enriches CO₂ while excluding competing molecules, maintaining >95% reduction FE even under 10% CO₂ flow. These findings indicate that the synergistic regulation of framework electronic structure and pore size is a key design strategy for efficient CO₂ capture and conversion in COF-based materials [70].

4.2.1. π-Conjugated Frameworks for Enhanced Electron Transport

Efficient electron transport is crucial for smooth electrocatalytic reactions. Well developed, conjugated structures facilitate rapid electron transfer within catalysts, significantly reducing charge transfer resistance and accelerating electron delivery from electrode to active sites, thereby boosting catalytic rates [66]. Two-dimensional sp² conjugated COFs, with planar architectures and delocalized electronic clouds, form efficient electron transport channels, exhibiting excellent conductivity. This intrinsic conductivity allows COFs to serve as self-supporting catalysts without requiring additional conductive additives, simplifying preparation and enhancing overall performance.

Guo et al. reported a chemically stable, electronically conjugated organic framework with a topologically designed wireframe and open nanoscale channels, where π-conjugation extends across two-dimensional (2D) sheets. This framework enables inherent periodic order of conjugated chains in all three dimensions, and exhibits a notable combination of properties: chemical stability, extended π-delocalization, molecular hosting ability, and hole mobility. Their results confirm the applicability of π-conjugated organic frameworks in high on-off ratio photoconductive switches and photovoltaic cells. Thus, this strategy may serve as an innovative approach to developing ordered porous semiconductor materials based on 2D extended π systems [71].

Yuan et al. [66] modulated structure coupling in phthalocyanine–porphyrin COFs, achieving efficient and selective CO₂ reduction. The Type 1:2 COF (CoPc-2H₂Por) outperformed the Type 1:1 COF and monomeric CoPc, attributed to differences in pore size and conjugation leading to variations in electron transfer, CO₂ adsorption/activation, mass transport, and reaction kinetics. The larger pore size and better conjugation of Type 1:2 COF facilitated faster CO₂RR kinetics and lower charge transfer resistance, demonstrating the importance of structural tuning.

4.2.2. Pore Size Control and Molecular Sieving Effect

One hallmark of COFs is their highly ordered periodic porous structure, allowing nanoscale precise pore size control [72]. Such control plays multifaceted roles in CO₂RR. Appropriate pore sizes promote efficient CO₂ diffusion to active sites, ensuring reactant access while providing molecular sieving effects that selectively restrict product diffusion, significantly enhancing catalytic selectivity. When COF pore size matches CO₂ molecular dimensions, adsorption capacity and transport rates within pores increase markedly. This selective enrichment favors CO₂ accumulation near active sites while excluding competing water molecules or larger product species, suppressing side reactions [73].

Liu et al. [70] reported that the covalent organic framework HFPTP-BPDA-COF possesses a well-defined sub-nanometer dual-pore structure, with pore diameters of 1.27 nm and 1.55 nm. A key structural feature of this COF is that the inner walls of its triangular channels are decorated with a “serrated” C–H sequence, forming a molecular-scale “checkpoint” that underpins its precise molecular recognition capability. In terms of performance, HFPTP-BPDA-COF exhibits excellent molecular sieving behavior: it can fully adsorb Nile Red (1.50 nm in diameter) within 2 min, while showing negligible uptake of DAPC (1.55 nm in diameter)—a molecule only 0.05 nm larger than Nile Red. This striking difference in adsorption confirms the COF achieves molecular sieving with single-atom-level selectivity. Experimental characterizations and molecular dynamics (MD) simulations collectively reveal that the synergistic effect between the triangular pore geometry and C–H···π interactions endows HFPTP-BPDA-COF with ultra-fine “sub-nanometer molecular sieve” functionality. This work provides new insights for designing highly selective separation and catalytic platforms based on COFs.

For instance, phthalocyanine–porphyrin coupled COFs with a 1:2 ratio exhibit larger pores and superior conjugated frameworks, achieving higher CO₂RR current densities and CO selectivity with FE exceeding 90%, outperforming 1:1 counterparts [66]. Similar molecular sieving effects are reported in other porous materials; Goyal et al. [74] demonstrated that subtle pore size tuning enhances reactant enrichment and active site exposure, significantly boosting CO₂ conversion efficiency. Longer channels and smaller pore diameters help suppress competing reactions like HER, further improving FE. These findings underscore pore size control and molecular sieving as vital design strategies for efficient CO₂RR catalysis using COFs.

4.2.3. Functional Group Incorporation to Enhance Adsorption and Activation

Beyond conjugation and pore size, functional group introduction on COF backbones is a key strategy to improve CO₂ adsorption and activation. Introducing polar functional groups (e.g., amino, carboxyl, hydroxyl) on linker units or pore walls enhances CO₂ enrichment and activation at the catalytic surface [75]. Such groups form hydrogen bonds, electrostatic interactions, or Lewis acid–base interactions with CO₂, effectively capturing and activating the molecules.

Xie et al. [76] demonstrated a nature-inspired approach mimicking chlorophyll and hemoglobin, using conductive COFs to tune the CO₂RR microenvironment. Piperazine-linked conductive COFs act as multifunctional supports for single-atom catalysts, with pendant groups modulated to impart variable push–pull electronic effects, enabling tunable microenvironments. Despite high chemical stability and conductivity under harsh conditions, introducing –CH₂NH₂ groups significantly improved CO₂RR activity and selectivity. Experimental characterization and theoretical calculations revealed that electron-donating groups like –CH₂NH₂ lowered the COF surface work function and enhanced *COOH intermediate adsorption energy compared to electron-withdrawing groups such as –CN and –COOH. This work provides molecular-level insight into tailoring CO₂RR catalyst microenvironments via COF functionalization.

Liu et al. successfully synthesized a series of carboxyl-functionalized covalent organic frameworks, denoted as [HO₂C]X%-H₂P-COFs (with X values of 25, 50, 75, and 100), featuring tunable carboxyl group densities. The synthesis was achieved through a ring-opening reaction between phenolic hydroxyl groups and succinic anhydride, a controlled process that allowed precise modulation of the carboxyl content. The carboxyl density in these [HO₂C]X%-H₂P-COFs was directly regulated by the phenolic hydroxyl group content of their precursor frameworks, [HO]X%-H₂P-COFs (with matching X values of 25, 50, 75, and 100). This design strategy enabled systematic investigation of the relationship between surface functional group density and CO₂ adsorption performance. Notably, experimental results revealed a clear positive correlation: the CO₂ adsorption capacity of [HO₂C]X%-H₂P-COFs increased proportionally with their carboxyl group content. These findings confirm that pore surface engineering via rational introduction of carboxyl groups represents an effective approach to enhance CO₂ adsorption in COF-based materials, highlighting the importance of surface functionalization in tailoring porous materials for gas capture applications [70].

4.3. Construction of Efficient Charge Transport Networks

Although COFs possess highly ordered and designable structures enabling precise active site assembly and pore environment tuning, their intrinsic conductivity is often limited, restricting overall CO₂RR kinetics. Efficient electron transport from the external circuit to internal active sites is essential to drive CO₂ reduction. Therefore, enhancing electron mobility within the material and constructing effective charge transport networks are crucial for achieving high-performance COF-based electrocatalysts [77].

4.3.1. Compositing with Conductive Substrates to Build 3D Electron Pathways

Hybridizing COFs with conductive materials such as polypyrrole (PPy), carbon nanotubes (CNTs), graphene, or MXenes is a direct and effective approach to enhance overall conductivity. Such composites significantly reduce charge transfer resistance by providing low-resistance electron pathways, and create abundant interfacial active sites and three-dimensional charge transfer networks at the microscopic scale [78]. Tight integration between COFs and conductive substrates minimizes electron transport resistance, accelerating electron transfer from current collectors to active centers, thereby boosting catalytic rates and current densities. Additionally, conductive substrates serve as physical supports, enhancing structural stability and mechanical strength under electrochemical conditions [79].

Seo et al. [80] reported a thermal-annealing strategy (600 °C, 1 h) that transforms a benzoxazole-linked covalent organic framework (BCOF) into an electrically conductive carbon/COF hybrid (BCOF-600C) (Figure 8). After annealing, the resultant Pt₁@BCOF-600C delivers a mass activity of 8.56 A mg_Pt⁻¹ for the hydrogen evolution reaction (HER) in 0.5 M H₂SO₄, outperforming commercial Pt/C by 30-fold. The crystalline domains of BCOF-600C retain periodically arranged N-anchoring sites and 2.1 nm mesoporous channels, while partial carbonization at grain boundaries forms a continuous conductive network that markedly lowers interfacial charge-transfer resistance. This work establishes a new paradigm for COF-based electrocatalytic platforms, which simultaneously achieve high crystallinity, robust stability, and superior conductivity, and opens fresh avenues for the precise immobilization of single-atom catalysts toward efficient energy conversion.

Xin et al. [80] reported an in situ polymerization method to embed PPy into MOF-545-Co pores. After PPy incorporation, the FE_CO production nearly doubled, reaching 98%. PPy acts as an electron transport cable within MOF pores, facilitating electron transfer during CO₂RR and enhancing catalytic activity and selectivity. This strategy offers new insights for designing efficient catalysts and invigorates research in CO₂ reduction and other electrocatalytic fields.

Yuan et al. successfully synthesized a novel covalent organic framework (COF) material, TP-OH-COF@CNT50, which is rich in redox-active groups, through an in situ polymerization approach. This composite material features a few-layered TP-OH-COF structure—abundant in active carbonyl (CO) groups—that is uniformly wrapped on the surface of carbon nanotubes (CNTs). This unique structural design enables the material to accommodate a greater number of sodium ions while significantly shortening the diffusion distance for both ions and electrons. When employed as a cathode material for sodium-ion batteries (SIBs), TP-OH-COF@CNT50 demonstrates exceptional electrochemical performance: it achieves a high specific capacity of 256.4 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹, exhibits remarkable long-term cycling stability with 100% capacity retention after 3000 cycles at 2 A·g⁻¹, and shows outstanding rate capability (103 mAh·g⁻¹ at 10 A·g⁻¹). In situ experimental investigations further reveal that TP-OH-COF@CNT50 operates via a highly reversible surface-dominated sodium storage mechanism. During the sodium insertion/extraction processes, the material maintains excellent structural stability, accompanied by a low energy barrier for sodium ion diffusion—key factors contributing to its superior performance. These findings validate an effective design strategy for developing new COF-based materials with high energy storage capacity for application in SIBs [81].

4.3.2. In Situ Carbonization to Form Conductive Frameworks

Besides external composites, COFs can undergo in situ carbonization under inert atmosphere at elevated temperatures. This thermal treatment converts the organic backbone into a carbonaceous framework while preserving the original ordered pore structure, producing a conductive carbon skeleton enriched with metal sites if metals are present in the COF. Such “self-transformed” carbon materials inherit the high specific surface area and tunable porosity of COFs, but their enhanced conductivity effectively addresses the intrinsic low electrical conductivity of pristine COFs [82]. Furthermore, pre-introduced metal ions or coordination centers can be converted in situ into highly dispersed metal nanoparticles or single atoms embedded within the carbon matrix, thereby exhibiting excellent catalytic activity and stability.

4.3.3. Heterogeneous Atom Doping Regulates Electronic Structure

Incorporating heteroatoms (e.g., N, B, S) into COF frameworks is an effective strategy to finely tune the electronic structure and improve charge transport capabilities. Doping modifies the electronic cloud density and distribution in the COF skeleton, optimizing interfacial charge transfer and potentially introducing new active sites [83]. Nitrogen, with its distinct electronegativity and versatile coordination chemistry, is widely utilized in COFs both as a metal anchoring atom and a direct participant in CO₂ activation. Boron doping, due to its electron-deficient nature, increases electrophilicity of the COF, thereby facilitating CO₂ adsorption and activation by strengthening interactions between the carbon atom of CO₂ and the catalyst surface, thus lowering the activation barrier.

Zhou et al. [84] synthesized a series of N,P co-doped carbon materials (CNP) with varied N and P contents (see synthesis scheme in Figure 9) to investigate the relationship between N/P ratio and CO₂RR activity. Compared to solely N-doped carbons, additional P doping enhanced catalytic activity. The optimized CNP-900 catalyst achieved a CO FE_CO of 80.8% at a mild overpotential of 0.44 V. X-ray photoelectron spectroscopy revealed that an appropriate ratio of pyridinic to graphitic N and minimal P–N content favored CO₂RR.

Ding et al. [85] discovered that the co-condensation reaction of metal phthalocyanine (NiPc, as the metal center) with an electron-deficient benzothiadiazole (BTDA) block facilitates the formation of a two-dimensional covalent organic framework, denoted as 2D-NiPc-BTDA COF. Structural characterizations reveal that this COF features a well-defined ribbon-like morphology, which is constructed from AA-stacked two-dimensional polymer sheets—an arrangement that endows the framework with high structural regularity. A key design advantage of 2D-NiPc-BTDA COF lies in the strategic integration of BTDA blocks: these electron-deficient units are anchored at the edges of the square-shaped metal phthalocyanine COF skeleton, a modification that dramatically modulates the material’s charge transport behavior. Specifically, this structural tuning transforms the framework from a conventional hole-transporting (p-type) system to an electron-transporting (n-type) construct—addressing the long-standing challenge of developing n-type COFs with efficient electron mobility. In terms of photoelectric properties, 2D-NiPc-BTDA COF exhibits broad and enhanced light absorbance, with the absorption edge extending up to 1000 nm. This wide spectral response enables the COF to demonstrate a full-color photoelectric effect, accompanied by high sensitivity to near-infrared (NIR) photons (a critical feature for NIR-driven optoelectronic applications). Additionally, the framework delivers excellent electron mobility, with a maximum value reaching up to 0.6 cm²/(V·s)—a performance metric that surpasses many reported 2D COFs for electron transport.

4.4. Multifunctional Synergy and Heterostructure Design

Single strategies often fail to address the multiple demands of CO₂RR (e.g., adsorption, electron transfer, intermediate stabilization). Therefore, constructing multifunctional catalytic interfaces to realize synergistic effects between different modules has become a major research focus. Through heterostructures, multiphase synergy, and photoelectrochemical integration, coordinated optimization of each reaction step can be achieved, significantly enhancing catalytic performance [86].

4.4.1. Heterojunction Catalyst Design

The heterojunction catalyst design involves closely integrating two or more materials with different physicochemical properties at interfaces, generating unique physical or chemical effects. Constructing heterostructures by combining COFs with metal–organic frameworks (MOFs), metal nanoparticles, semiconductors, or other carbon materials leverages the strengths of each component. COFs offer highly ordered porous frameworks with abundant active sites and tunable pore environments, while composites contribute excellent conductivity, photoresponse, or catalytic activity. Interfacial interactions facilitate efficient charge separation and transfer, suppress recombination, and can modulate adsorption strength of CO₂ and intermediates on active sites, optimizing reaction pathways [64].

Zhang et al. [87] studied a 0D/2D heterojunction structure composed of ~2 nm SnO₂ nanodots confined on graphitic carbon nitride (g-C₃N₄) nanosheets to promote CO₂ conversion to formate. Experimental and theoretical results showed strong metal oxide–support interactions between dispersed SnO₂ nanodots and abundant N coordination sites in g-C₃N₄. The heterojunction interface, featuring p–p orbital coupling, effectively facilitated electron transfer from electron-rich g-C₃N₄ to SnO₂. Consequently, SnO₂/g-C₃N₄ exhibited excellent activity and stability for CO₂RR to formate, reaching a FE of 91.7% at −0.88 V vs. RHE. This 0D/2D heterojunction strategy was extended to the In₂O₃/g-C₃N₄ system, providing a general approach for developing efficient hybrid catalysts for high-value CO₂RR products.

4.4.2. Photoelectrochemical Synergistic CO₂ Reduction Systems

To further improve energy conversion efficiency and reduce energy consumption in CO₂RR, coupling electrocatalysis with photocatalysis to build photoelectrochemical (PEC) synergistic systems is a promising direction. Introducing visible-light responsive units (e.g., photosensitizers, organic dyes) into COF backbones or integrating COFs with semiconductors imparts photoelectrochemical functionality. Upon light absorption, these units generate photoexcited electron–hole pairs, which can be efficiently transferred to COF active sites to participate in CO₂ reduction [88]. The applied bias accelerates charge separation, compensates for photogenerated carrier deficits, and provides additional driving force, enabling high CO₂RR efficiency at lower overpotentials.

Zhong et al. reported the rational design of a synergistic photocatalytic system based on a covalent organic framework (denoted as Ni-TpBpy) that contains isolated single nickel (Ni) active sites, which enables the selective photoreduction of carbon dioxide (CO₂) to carbon monoxide (CO). Under visible light irradiation, the photocatalytic reaction proceeds via a well-defined electron transfer pathway: photoexcited electrons are transferred from the photosensitizer component of the system to the single Ni active sites, where the electrons then participate in the activated reduction of adsorbed CO₂ molecules, ultimately generating CO as the target product. In terms of catalytic performance, Ni-TpBpy exhibits remarkable activity and selectivity: over a 5-h reaction duration, it achieves a CO yield of 4057 μmol·g⁻¹, accompanied by a high CO selectivity of 96% (with the competitive hydrogen evolution reaction, HER, effectively suppressed). Notably, even under a low CO₂ partial pressure of 0.1 atm—conditions that typically compromise the selectivity of CO₂ reduction catalysts—Ni-TpBpy still maintains a CO production selectivity of 76%, demonstrating its excellent tolerance to low CO₂ concentration environments.

To clarify the origin of this superior performance, Zhong et al. combined theoretical calculations (e.g., density functional theory simulations) with experimental characterizations. The results collectively confirm that the promising catalytic activity and selectivity of Ni-TpBpy arise from the synergistic interaction between its single Ni catalytic sites and the TpBpy COF framework. Specifically, the TpBpy framework plays multiple critical roles: it acts as a stable host to anchor both CO₂ molecules (via specific adsorption) and single Ni active sites (preventing their aggregation), facilitates the activation of CO₂ molecules by adjusting their electronic structure, and simultaneously inhibits the competitive HER—thus ensuring the high efficiency and selectivity of CO₂-to-CO photoreduction [89].

Wu et al. [65] incorporated the long-lived photosensitizer Ru(bpy)₃Cl₂ into a Co-porphyrin COF framework (synthesis route shown in Figure 10), establishing a photoelectrochemical CO₂RR system. Under light illumination, the FE_CO reached 96.7%, accompanied by a significant increase in current density. This enhancement was attributed to efficient electron transfer from Ru(bpy)₃Cl₂ to Co-porphyrin and prolonged excited state lifetime at active sites, lowering reaction energy barriers.

5. Conclusions

This review systematically explores the design strategies and application progress of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) in electrocatalytic carbon dioxide reduction (CO₂RR). Summarize the catalysts mentioned in the article in a tabular form, as shown in

Table 1. Summary of catalysts.

Catalyst Type	Specific Catalyst	Catalytic Performance	References
MOF	MOF-545-Cu/PAN (MCP)-500	CO2RR for CO production; FE for CO (FE_CO) reaches 98% (−0.8 V vs. RHE), maintains FE_CO > 95% after 10 h of continuous catalysis; FE_CO remains 80–98% at voltages ranging from −0.6 V to −1.0 V vs. RHE	[15]
MOF	Cu-THQ 2D c-MOF	CO2RR for CO production; average FE_CO of 91% with a conversion rate of 20.82 s−1; in a flow battery, the current density reaches 173 mA/cm2 at 0.45 V vs. RHE	[22]
MOF	In-TCPP (In-based porphyrin π-d MOF)	CO2RR for HCOO− production; FE_HCOO− reaches 90% with a cathodic efficiency of 63.8%	[23]
MOF	2D PML-Cu	CO2RR for HCOO− production; FE_HCOO− reaches 80.86% at −0.7 V vs. RHE	[24]
MOF	Cu2(CuTCPP) nanosheets	CO2RR for HCOO− production; FE_HCOO− reaches 68.4% at −0.94 V vs. RHE	[25]
MOF	HP-UiO-66-NH2 (hierarchical porous, with polar amino groups)	CO2RR for HCOO− production; HCOO− yield exceeds 6000 μmol gcat−1h−1 within 3 h (5.6 times that of the free enzyme system), and HCOO− concentration reaches 1.83 mM; retains over 90% CO2 adsorption capacity after pore structure modification	[32]
MOF	UiO-66-CN (CN-functionalized UiO-66)	CO2RR for HCOOH production; FE_HCOOH reaches 93% at −0.75 V vs. RHE	[33]
MOF	2Bn-Cu@UiO-67 (N-heterocyclic carbene-linked Cu single-atom catalyst)	CO2RR for CH4 production; FE_CH4 reaches 81% at −1.5 V vs. RHE, corresponding to a current density of 420 mA/cm2; TOF reaches 16.3 s−1, and FE_CH4 > 70% over the entire potential range	[34]
MOF	Pd-doped HKUST-1 (forms Cu-Pd paddlewheel dimers)	CO2RR; in 0.5 M CO2-saturated KHCO3, FE increases from 28.7% to 84.8% at −0.77 V vs. RHE	[29]
MOF	Cu-btca	CO2RR under acidic conditions; at 300 mA/cm2, FE_C2H4 reaches 51.2%, and FE of multi-carbon products reaches 81.9%; porous structure promotes mass transfer and inhibits HER	[28]
MOF	Cu2O@Cu-TCPP(M) (M = Co, Fe, Ni; core-shell structure)	CO2RR for C2H4 production; in 1 M KCl, at 500 mA/cm2, FE_C2H4 reaches 54 ± 2%, and FE of C2 products reaches 69 ± 4%; retains Cu2O crystallinity and valence state, improving stability	[31]
MOF	HKUST-1@Cu2O/PTFE-1 (PTFE-modified core-shell structure)	CO2RR for C2H4 production; FE_C2H4 reaches 46.08% at −1.0 V vs. RHE, with a hydrocarbon fuel efficiency of 67.41%; no significant current decay and stable ethylene FE during 12-h continuous testing	[30]
MOF	Cu-DMTZ MOF (pulsed potential regulation)	CO2RR for CH4 production; FE_CH4 reaches 82.9% under pulsed electrolysis (much higher than 47.4% under constant potential); FE_CH4 remains > 60% after 12-h continuous operation	[35]
MOF	Cu0.5Zn0.5/ZIF-8 (Cu-doped ZIF-8)	CO2RR for CO production; FE reaches 88.5% at −1.0 V vs. RHE, with a partial current density of 11.57 mA/cm2; Cu doping modifies the electronic structure of organic ligands and promotes *COOH formation	[36]
MOF	Cu-HHTT (ultrathin 2D triphenyl MOF)	CO2RR for CO production; FE_CO reaches 96.6% at −0.6 V vs. RHE, with a current density of 18 mA/cm2; DFT calculations show low CO desorption energy barrier	[39]
MOF	SU-101-Cu@2.5 C (BiCu bimetallic organic framework, MWCNTs composite)	CO2RR for formic acid production; initial potential of −0.46 V vs. RHE, partial current density > 100 mA/cm2; FE of formic acid is nearly 100% at −0.96 V vs. RHE, and FE > 80% in the potential range of −0.86 V to −1.06 V vs. RHE; good stability during 30-h continuous catalysis	[37]
MOF	MIL-68(In)/CuO (In-Cu dual active sites)	CO2RR for formic acid production; FE of formic acid reaches 89.7% at −0.7 V vs. RHE in a flow battery; maintains activity within 180 h in an MEA battery and inhibits HER	[38]
MOF	CuAg5@NC (Ag-anchored Cu-based MOF-derived CuAg bimetal)	CO2RR for ethanol production; FE_ethanol reaches 51.8% at −1.0 V vs. RHE, and FE of C2 products reaches 82.6% at −1.2 V vs. RHE; Cu-Ag biphasic interface promotes CO migration and C–C coupling	[40]
MOF	CuPOF-Bpy/Cu2O@CNT (dual-site Cu(II) porphyrin framework composite with Cu2O)	CO2RR for C2H4 production; FE_C2H4 reaches 71.0% at −1.1 V vs. RHE, and FE_C2H4 > 40% over the entire potential range; CuPor/CuBpy sites produce *CO, and Cu2O sites promote C–C coupling	[41]
MOF	Cu@BIF-144(Zn) (tandem catalyst)	CO2RR for CH4 and C2H4 production; FE_CH4 reaches 41.8% at −1.6 V vs. RHE, and FE_C2H4 reaches 12.9% at −1.5 V vs. RHE; Zn sites create a CO-enriched environment to promote deep CO2 reduction on Cu NPs	[42]
MOF	R-Cu-TAl-CNTs1 (tandem catalyst)	CO2RR for CH4 production; FE_CH4 reaches 54% at −1.56 V vs. RHE (30% without CNTs); FE ratio of CH4/C2H4 reaches 9.5 in the potential range of −0.96 V to −1.76 V vs. RHE (12 times that without CNTs)	[43]
MOF	Cu@ZIF-8 NW (Cu-ZIF-8 interface-exposed nanowires)	CO2RR for hydrocarbons (CH4, C2H4); FE of hydrocarbons reaches 57.5% at −0.7 V vs. RHE; Cu-ZIF-8 interface optimizes intermediate adsorption and stabilizes *CHO	[44]
MOF	Cu-MOF-CF (Cu-MOF anchored on copper foil)	CO2RR for C2H4 production; FE_C2H4 reaches 48.6% at −1.11 V vs. RHE (22.4% for pure copper foil); partial current density of C2H4 is more than 4 times that of pure copper foil	[45]
MOF	2D-vc-MOF(Cu) (2D vertically conductive MOF)	CO2RR for CH4 production; FE_CH4 reaches 65% at −1.4 V vs. RHE (20% at −1.2 V, 33% at −1.6 V); vertical structure reduces energy barrier and improves reaction kinetics	[46]
MOF	Curved 2D Cu(I)-based coordination polymer	CO2RR for C2H4 production; electrocatalytic selectivity shifts from HER (80%) to CO2RR (76%), with FE_C2H4 reaching 52%; wave-like structure promotes hydrogen bonding between amino groups and *CO2RR intermediates, inhibiting HER	[47]
MOF	Cu-MMT nanoribbons (water as solvent, exposing (100) planes)	CO2RR for CH4 production; FE_CH4 reaches 55.22%	[48]
MOF	Cu-MMT cross-linked nanosheets (isopropanol as solvent, exposing (001) planes)	CO2RR for C2 products (mainly C2H4); FE_C2 reaches 73.75%	[48]
MOF	Ce-CuOx (atomic-level Ce doping)	CO2RR for CH4 production; FE_CH4 > 62% in the potential range of −1.4 V to −1.75 V vs. RHE, FE_CH4 reaches 67.4% at −1.6 V vs. RHE, with a partial current density of 293 mA/cm2	[50]
MOF	Co-Cu alloy (Co-doped Cu-MOF via electrochemical reconstruction)	CO2RR for CH4 production; FE_CH4 reaches 60 ± 1%, corresponding to a partial current density of 303 ± 5 mA/cm2	[51]
MOF	Cu-PD-2-MBI (Cu-based c-MOF containing 2-methylbenzimidazole)	CO2RR for CH4 production; FE_CH4 reaches 73.7% at −1.3 V vs. RHE, with a partial current density of −428.3 mA/cm2; FE_CH4 increases in the potential range of −1.1 V to −1.3 V vs. RHE, inhibiting HER	[52]
MOF	CuTrz-109 nm (small-sized CuTrz nanostructure)	CO2RR for C2 products; FE_C2H4 reaches 55.4% at −1.15 V vs. RHE, and FE of C2 products reaches 81.8%; rich in grain boundaries and defects, improving catalytic performance	[49]
COF	Cu@BTT-BPy-COF (bipyridine-based 2D conjugated COF with interlayer single-atom Cu sites)	CO2RR for C2 products; FE_C2 reaches 46.7% at −0.8 V vs. RHE, outperforming most framework-based electrocatalysts	[56]
COF	Pd/COF-LZU1 (Pd-supported COF-LZU1)	Suzuki-Miura coupling reaction; reaction yield of 96–98%, wide substrate applicability, good stability, and easy recovery	[57]
COF	Vanadium-modified COF (2D COF modified with vanadyl acetoacetonate)	Prins condensation reaction, sulfide oxidation reaction; high catalytic activity, retains framework crystallinity, reusable; possesses eclipsed stacking structure, macroporosity, hydroxyl functionality, high thermal and chemical stability	[58]
COF	0.75NiPc-COF (multi-component synthesized NiPc-COF)	CO2RR for CO production; TOF reaches 4909.87 h−1, FE_CO reaches 95.37%, exhibiting optimal CO2RR activity and selectivity	[60]
COF	La-doped dual-Cu COF	CO2RR; La doping modifies the coordination environment of Cu centers with N/O, adjusts Cu oxidation state and electronic properties, shifting product selectivity from C2H4 to CH4	[61,62]
COF	COF containing triazine/carboxyl/fluoro-substituted groups	CO2 adsorption and activation; CO2 adsorption capacity of 174 mg/g, adsorption heat Qst = 43.5 kJ/mol; reduces *COOH formation energy barrier by 0.54 eV; dual-pore topology (1.27/1.55 nm) generates a sub-nanometer molecular sieve effect, FE > 95% under 10% CO2 gas flow	[70]
COF	CoPc-2H2Por (1:2 phthalocyanine-porphyrin COF)	CO2RR for CO production; FE_CO > 90%, outperforming 1:1 COF and monomeric CoPc; larger pore size and optimized conjugated structure promote CO2RR kinetics and reduce charge transfer resistance	[66]
COF	HFPTP-BPDA-COF (sub-nanometer dual-pore structure)	Molecular sieving; 1.27/1.55 nm dual pores, with “zigzag” C-H sequences on the inner wall of triangular pores forming molecular “checkpoints”; completely adsorbs Nile Red (1.50 nm) within 2 min, while adsorption of DAPC (1.55 nm) is negligible, achieving single-atom level selective sieving	[74]
COF	Piperazine-linked conductive COF containing -CH2NH2	CO2RR; -CH2NH2 (electron-donating group) reduces COF surface work function and enhances *COOH adsorption energy (superior to electron-withdrawing groups such as -CN and -COOH); high chemical stability and conductivity, improving CO2RR activity and selectivity	[77]
COF	[HO2C]X%-H2P-COFs (carboxyl-functionalized COF)	CO2 adsorption; CO2 adsorption capacity is positively correlated with carboxyl content; carboxyl density is regulated via ring-opening reaction between phenolic hydroxyl groups and succinic anhydride (X = 25, 50, 75, 100)	[78]
COF	Pt1@BCOF-600C (BCOF thermally annealed carbon hybrid)	HER; in 0.5 M H2SO4, mass activity reaches 8.56 A mg_Pt−1 (30 times that of commercial Pt/C); retains N-anchoring sites and 2.1 nm mesoporous channels; partial carbonization at grain boundaries forms a continuous conductive network	[82]
COF	PPy/MOF-545-Co (PPy embedded in MOF-545-Co pores)	CO2RR for CO production; FE_CO doubles compared to pure MOF, reaching 98%; PPy acts as an electron transport “cable” to promote electron transfer	[82]
COF	TP-OH-COF@CNT50 (redox-active group COF/CNT composite)	Sodium battery cathode; specific capacity of 256.4 mAh/g at 0.1 A/g, 100% capacity retention after 3000 cycles at 2 A/g, and 103 mAh/g at 10 A/g; surface-dominated sodium storage mechanism with low sodium diffusion energy barrier	[83]
COF	CNP-900 (N,P co-doped carbon material)	CO2RR for CO production; FE_CO reaches 80.8% at an overpotential of 0.44 V; suitable pyrrolic N/graphitic N ratio and low P-N content are more favorable for CO2RR	[86]
COF	2D-NiPc-BTDA COF (phthalocyanine and benzothiadiazole copolymerized COF)	Photoelectric performance; wide band gap, absorption extended to 1000 nm, full-color photoelectric effect, high near-infrared light sensitivity; electron mobility reaches 0.6 cm2/(V·s), charge transport mode shifts from hole transport to electron transport	[64]
COF	SnO2/g-C3N4 (0D/2D heterojunction)	CO2RR for formic acid production; FE of formic acid reaches 91.7% at −0.88 V vs. RHE; strong metal oxide-support interaction between SnO2 nanodots and g-C3N4, p-p orbital coupling promotes electron transfer	[89]
COF	Ni-TpBpy (COF with single Ni sites)	Photocatalytic CO2RR for CO production; CO yield of 4057 μmol/g within 5 h under visible light, CO selectivity of 96%; maintains 76% CO selectivity even at 0.1 atm CO2 partial pressure; TpBpy promotes CO2 activation and inhibits HER	[89]
COF	Co-Bpy-COF-Rux (Co-porphyrin COF modified with Ru(bpy)3Cl2)	Photoelectrochemical CO2RR for CO production; FE_CO reaches 96.7% under light irradiation, with significantly improved current density; Ru photosensitizer promotes electron transfer to Co-porphyrin, extends the excited state lifetime of active sites, and reduces reaction energy barrier	[65]

. Research indicates that MOFs, leveraging their tunable metal nodes (e.g., Cu, Zr, Co) and pore structures, significantly enhance the efficiency of C₁-C₂ products through three key strategies: enhanced conductivity, optimized stability, and selective regulation. COFs, on the other hand, leverage their highly crystalline conjugated frameworks and precise atomic design to overcome performance bottlenecks through single-metal site anchoring, framework π-conjugated expansion, and photo-electrochemical synergy. The two material types exhibit complementary advantages in product orientation, with COFs demonstrating greater selectivity in the CO/formic acid pathway. However, inherent material defects (the insufficient water stability of MOFs and limited conductivity of COFs) and industrialization barriers (scalable costs, electrolyte compatibility) remain core challenges. Future research should integrate in situ characterization techniques to analyze the evolution of dynamic active sites, combine machine learning to optimize material design, and develop multi-field coupled reaction systems to drive the transition of carbon-neutral technologies from the laboratory to engineering applications.