Tunable Catalytic Platforms: Metal–Organic Frameworks for Electrocatalytic Carbon Dioxide Reduction Toward Value-Added Chemicals

Abstract

The electrochemical reduction of carbon dioxide (CO₂RR) into value-added chemicals using renewable electricity is a pivotal strategy for achieving a sustainable carbon cycle. However, this process is plagued by intrinsic challenges, including poor product selectivity, competing hydrogen evolution, and catalyst instability. Metal–organic frameworks (MOFs), with their highly designable periodic structures, atomically dispersed active sites, and tunable pore microenvironments, have emerged as a uniquely versatile platform to address these issues. This review articulates a multi-scale design philosophy that enables precise steering of the CO₂RR pathway. We systematically elaborate on hierarchical tuning strategies, beginning with molecular-scale engineering of active sites (metal nodes and organic ligands) to define intrinsic activity and intermediate binding. This is synergistically integrated with the optimization of electronic structure and charge transport to overcome conductivity bottlenecks, meso-scale modulation of crystal morphology and defects to enhance mass transport and site accessibility, and the construction of heterogeneous interfaces for tandem catalysis and synergistic effects. Through this coherent, cross-scale design framework, MOF-based catalysts demonstrate exceptional capability in the precise control of reaction pathways, leading to remarkably selective synthesis of target high-value products, from C₁ compounds (CO, HCOOH, CH₄, CH₃OH) to C₂⁺ species (C₂H₄, C₂H₅OH) and urea. Finally, we outline future directions centered on dynamic mechanistic understanding, electrode engineering for industrial current densities, and stability enhancement, thereby providing a comprehensive material design guideline to advance CO₂RR technology. This work positions MOFs as a quintessential tunable catalytic platform for the sustainable conversion of CO₂.

1. Introduction

Since the Industrial Revolution, the continuous consumption of fossil fuels such as coal, oil, and natural gas has supported global economic and population growth, but has also led to a sharp increase in atmospheric carbon dioxide (CO₂) concentrations, triggering a series of climate change and environmental issues [1,2,3,4]. There is a broad international consensus that annual CO₂ emissions must be drastically reduced to near-zero levels by 2050, making carbon reduction an urgent imperative [5,6]. Achieving this systemic goal relies on a multi-level carbon emission reduction technology framework, primarily including low-carbon technologies (e.g., energy efficiency improvements and energy substitution), zero-carbon technologies (e.g., wind, solar photovoltaic and nuclear power), and negative-emission technologies (e.g., carbon capture and utilization) [7,8,9,10]. Among these, carbon capture, utilization, and storage (CCUS) technology not only enables CO₂ sequestration but also converts it into high-value fuels and chemicals, thereby synergistically alleviating energy and environmental pressures. It is regarded as one of the most promising negative-emission pathways [11,12]. The main conversion routes for CO₂ into valuable products include:

(1)

Thermocatalytic conversion, which utilizes heat and catalysts to drive reactions such as methanation and reverse water–gas shift, offering high reaction rates but often requiring high temperatures and pressures [13,14];

(2)

Photocatalytic conversion, which harnesses solar energy to drive CO₂ reduction, providing a sustainable approach; however, it is currently limited by low efficiency and selectivity [15,16];

(3)

Electrocatalytic conversion (CO₂RR), the focus of this review, which uses renewable electricity to drive reduction at ambient conditions, offering excellent controllability and compatibility with intermittent renewable energy sources [17,18];

(4)

Biological conversion, which employs microorganisms or enzymes for CO₂ fixation, offering high selectivity but facing challenges in reaction rates and scalability [19,20,21];

Each approach has distinct advantages and limitations, and the choice of technology depends on factors including energy source availability, desired products, and scale of operation.

Among various CO₂ conversion technologies, the CO₂RR reduction reaction has become a leading research focus in energy and catalysis due to its distinct advantages [22,23]. CO₂RR utilizes renewable electricity to directly convert CO₂ into target products, offering a clean process, controllable product distribution, and compatibility with renewable energy sources. Key features include operation under mild conditions, which reduces equipment demands and enhances operational safety; the ability to tune product selectivity by adjusting applied potential and catalyst structure; and the potential for direct integration with intermittent renewable power sources like solar and wind, enabling the transformation of “green electricity” into “green chemicals” [24,25,26]. The macroscopic concept of this sustainable process is illustrated in the electrocatalytic CO₂ reduction cycle (Figure 1).

At the microscopic level, the electroreduction process is highly complex. It mainly includes the adsorption of CO₂ on the catalyst surface, the multistep electron–proton transfer and reduction at the interface, and the desorption of final products. The intricacies of optimizing these pathways, particularly for C₁ products, have been systematically reviewed by Ahmed et al. [27], who emphasized structure–activity relationships and the critical challenges of high overpotential, competing hydrogen evolution, and limited selectivity. Indeed, these significant challenges remain broadly applicable across current CO₂RR systems:

(1)

Product selectivity: The similar reduction potentials for many CO₂RR products, combined with the competing hydrogen evolution reaction (HER), make it difficult to achieve high selectivity toward a single desired product. This is particularly challenging for deep reduction products requiring multiple electron transfers.

(2)

Activity and overpotential: The high thermodynamic barrier for initial CO₂ activation (forming CO₂⁻ at −1.9 V vs. SHE) necessitates substantial overpotentials, reducing energy efficiency. Even state-of-the-art catalysts often require 300–500 mV overpotential to achieve appreciable current densities.

(3)

Catalyst stability: Many catalysts undergo structural degradation under reducing conditions, leading to performance decay over time. This includes metal leaching, ligand decomposition, and active site agglomeration.

(4)

Mass transport limitations: At high current densities, CO₂ supply to the catalyst surface becomes rate-limiting due to its limited solubility in aqueous electrolytes, necessitating advanced electrode designs such as gas diffusion electrodes. To address this, high-pressure CO₂RR (conducted usually above 1 atm) is an effective strategy to bridge the gap between lab-scale CO₂ electrolysis and industrial applications, as elevating the pressure significantly increases the solubility and surface concentration of CO₂, boosting reaction kinetics, current density, and selectivity toward multi-carbon products (C₂⁺) [28,29].

(5)

Electrolyte effects: The choice of electrolyte (pH, cation identity, buffer capacity) profoundly affects reaction kinetics and selectivity, adding another layer of complexity to system optimization [30,31,32]. Therefore, the development of electrocatalysts that simultaneously offer high activity, selectivity, and stability is paramount for achieving efficient and sustainable CO₂ conversion.

To overcome these intrinsic catalytic challenges, metal–organic frameworks (MOFs) have emerged as a frontier catalytic platform for CO₂RR [33]. While traditional heterogeneous catalysts (such as metallic Cu, Ag, and Au) face inherent limitations including limited tunability and ill-defined active sites, MOFs uniquely bridge the gap between homogeneous and heterogeneous catalysis through their highly programmable structural nature [34]. Composed of metal nodes and organic ligands, their exceptional tunability allows for rational design at the atomic scale, enabling precise control over the coordination environment and spatial geometry [35]. By systematically tuning ligand size and functional groups, researchers can precisely modulate pore microenvironments to enhance CO₂ adsorption and steer reaction pathways toward specific products (e.g., C₁ or C₂⁺ compounds) [36,37]. Furthermore, MOFs typically possess exceptionally high specific surface areas [38] and hierarchical pore structures that facilitate rapid mass transport, mitigating a common limitation in conventional carbon-based materials [39]. Beyond structural precision, MOFs offer multifunctional capabilities by integrating catalytic centers and proton relays within a single framework, while their stability in demanding environments can be engineered through strengthened metal–ligand bonds [40,41,42]. Even when transforming under reaction conditions, ordered MOF structures serve as excellent precursor templates for generating highly dispersed, stable active phases [43,44]. Finally, their well-defined, crystalline structures provide an ideal model system for combining advanced in situ spectroscopy with theoretical calculations to establish clear structure–performance correlations [45,46]. Compared with conventional catalysts, MOFs exhibit outstanding advantages including precise structure, excellent tunability, multifunctional synergy, clear mechanism, and high-quality precursor template potential, making them superior to traditional metal and carbon-based catalysts for CO₂ electroreduction and serving as tunable platforms bridging homogeneous and heterogeneous catalysis.

A systematic search of Web of Science and Scopus (2015–2026) using keywords related to MOF-based CO₂ reduction (e.g., “active site engineering,” “C₂⁺ products”) yielded 135 key references. We prioritized studies with clear structure–performance relationships, mechanistic insights, and representative metrics. In addition to a thorough analysis of original research articles, this review also provides a detailed discussion of the most up-to-date reviews, offering readers a comprehensive entry point into the field. This review aims to systematically present recent advances in the rational design, advanced characterization, and performance optimization of MOF-based materials for CO₂RR. Following an overview of the fundamental mechanisms and pathways of CO₂RR, the discussion is structured around four key design dimensions: (1) molecular-scale engineering of active sites (including mono-/bimetallic nodes and ligand modulation); (2) optimization of electronic structure and strategies for charge transport enhancement; (3) mesoscale control of crystal morphology, dimensionality, and defect structures; and (4) heterogeneous interface synergy and tandem catalysis mechanisms. By examining selected representative studies, we highlight the excellent performance of MOFs in the efficient and selective production of high-value chemicals such as CO, CH₄, CH₃OH, HCOOH, C₂H₄, C₂H₅OH, urea, and multi-carbon (C₂⁺) products. Finally, we outline current challenges and future research directions, including electrode engineering for industrial-scale current densities, dynamic mechanistic understanding of active sites, and strategies for long-term stability.

The primary contribution and highlight of this review lies in its articulation of a coherent, cross-scale design philosophy—from atomic-level engineering to device-level integration. By systematically elaborating on the multi-level structure–activity relationships, we position MOFs not merely as alternative catalysts, but as a uniquely “tunable catalytic platform”. Ultimately, this work provides a comprehensive theoretical framework and actionable material design guidelines to inform the rational development of next-generation CO₂ electroreduction catalysts toward the goal of global carbon neutrality.

2. CO₂RR Reaction Mechanisms and Pathways

Carbon dioxide is a thermodynamically stable and chemically inert molecule, presenting significant kinetic and thermodynamic challenges for its electrocatalytic reduction [47,48,49]. CO₂RR involves the transfer of multiple protons and electrons, driven by an applied potential and facilitated by a catalyst surface, to convert CO₂ into various carbon-containing products [50,51]. The CO₂RR mechanism involves multiple steps. Different pathways and numbers of transferred electrons produce different products, depending on the catalyst’s ability to stabilize key intermediates [52,53,54].

CO₂RR is typically carried out in an electrochemical cell where the applied potential between the anode and cathode provides the driving force. Depending on the catalyst and specific reaction conditions (e.g., electrolyte, pH), the process can proceed via different mechanistic pathways [55,56]. The overall stoichiometry for CO₂ reduction can be represented as a xCO₂ + yH₂O → product + zO₂ CO₂ recycling reaction [57].

Although mechanistic details continue to be refined, a general framework for CO₂RR has been established through combined experimental and theoretical efforts.

Table 1. Standard electrochemical potential (E⁰ vs. RHE) for CO₂ reduction reactions under standard conditions (1 atm, 25 °C).

Reaction	E0 vs. SHE(V)
Half-electrochemical thermodynamic reactions	Electrode potentials (V vs. SHE) under standard conditions
CO2 (g) + e− → CO2− (aq)	−1.900
CO2 (g) +2 H+ + 2 e− → HCOOH (l)	−0.250
2CO2 (g) + 2 H+ + 2 e− → H2C2O4 (aq)	−0.500
CO2 (g) +2 H2O (l) + 2 e− → HCOO-(aq) + OH−	−1.078
2 CO2 (g) + 2 e− → C2O42− (aq)	−0.590
CO2 (g) + 2 H+ + 2 e− → CO (g) + H2O (l)	−0.106
CO2 (g) + 2 H2O (l) + 2 e− → CO (g) + 2 OH−	−0.934
CO2 (g) + 4 H + + 4 e− → C (s) + 2 H2O (l)	0.210
CO2 (g) + 2 H2O (l) + 4 e− → C (s) + 4 OH−	−0.627
CO2 (g) + 3 H2O (l) + 4 e− → CH2O (l) + 4 OH−	−0.898
CO2 (g) + 6 H + + 6 e− → CH3OH (l) + H2O (l)	0.016
CO2 (g) + 5 H2O (l) + 6 e− → CH3OH (l) + 6 OH−	−0.812
CO2 (g) + 8 H+ + 8 e− → CH4 (g) + 2 H2O (l)	0.169
CO2 (g) + 6 H2O (l) + 8 e− → CH4 (g) + 8 OH−	−0.659
2 CO2 (g) + 12 H+ + 12 e− → CH2CH2 (g) + 4 H2O (l)	0.064
2 CO2 (g) + 12 H+ + 12 e− → CH3CH2OH (l) + 3 H2O (l)	0.084
2 CO2 (g) + 9 H2O (l) + 12 e− → CH3CH2OH (l) + 12 OH−	−0.744

[58] shows the equations for different reduction products and their corresponding standard potentials versus the standard hydrogen electrode (SHE) under various conditions. The extremely high stability of the CO₂ molecule, which makes its chemical bonds difficult to break, is determined by its linear symmetric structure (O=C=O) and its three-center four-electron delocalized π bond (π₃⁴) [59]. In CO₂RR, this characteristic is directly reflected in the high thermodynamic barrier for the initial one-electron reduction step (forming the CO₂·⁻ radical anion) [60]. Theoretical calculations indicate that the standard potential for this step is approximately −1.9 V (vs. SHE), which often acts as the rate-determining step, necessitating a high overpotential for the overall process [61,62]. Therefore, designing catalysts to stabilize the CO₂⁻ intermediate and lower this initial energy barrier is key to improving CO₂RR efficiency. Across the entire potential window, the hydrogen evolution reaction (HER) consistently competes with CO₂RR for protons (H⁺) and electrons (e⁻). The electrolyte composition, local pH, proton supply rate, and the catalyst’s adsorption strength for H* collectively determine the competitive selectivity between HER and CO₂RR [63,64]. Understanding the complex mechanism of product formation during CO₂RR, especially the key selectivity-determining steps and descriptors, is crucial for the rational design of catalysts with satisfactory performance for target products.

CO₂RR is a complex multi-step process typically involving three fundamental stages: the adsorption of CO₂ onto the catalyst surface, multi-step electron–proton transfer and reduction at the interface, and the desorption of the final product [65]. The reaction pathway and product distribution are strongly governed by the interaction strength between the catalyst surface and key reaction intermediates (e.g., *COOH, *OCHO, *CO). An efficient catalyst effectively lowers the activation energy barriers for these interactions [66]. In the adsorption stage, the CO₂ molecule is activated at the electrode interface to form the *CO₂⁻ radical anion intermediate. The subsequent reaction and activation of adsorbed *CO₂⁻ can proceed via two primary mechanisms: the first is activation induced by the concerted proton–electron transfer (CPET) mechanism, where a proton and an electron are transferred synchronously to the CO₂ molecule. This pathway often effectively lowers the activation barrier and promotes C–O bond scission. The second is the stepwise proton-electron transfer (SPET) mechanism, which involves initial electron transfer to form an intermediate, followed by protonation. The energy barrier in SPET is highly dependent on the catalyst’s adsorption strength for the intermediate [53,67,68,69]. The competition and balance between these two mechanisms fundamentally dictate the overall reaction rate, selectivity, and energy efficiency. The distinct activation routes lead to the generation of various intermediates (e.g., *CO, *COOH, *OCCO), ultimately yielding a diverse array of carbon-containing products ranging from C₁ to C₃ species. These include carbon monoxide (CO), formic acid (HCOOH), methanol (CH₃OH), methane (CH₄), ethylene (C₂H₄), acetic acid (CH₃COOH), ethanol (CH₃CH₂OH), n-propanol (CH₃CH₂CH₂OH), and acetone (CH₃COCH₃), among others [70,71,72,73,74,75,76,77,78,79].

To date, the efficient and rapid synthesis of C₁ and C₂ products has been demonstrated, but achieving high conversion rates for higher-carbon (C₃⁺) products remains challenging [80]. A schematic representation of the possible reaction pathways is illustrated in the figure [81].

The formation pathway for C₁ products is highly dependent on the initial activation mode of CO₂ [82,83]. As shown in Figure 2, on catalyst surfaces that favor adsorption via the oxygen atom (e.g., p-block metals), CO₂ tends to form the *OCHO intermediate, which subsequently protonates to generate formic acid. Conversely, on transition metal surfaces that favor carbon-atom adsorption, CO₂ proceeds via the formation of the *COOH intermediate followed by deoxygenation, yielding the pivotal *CO intermediate. The binding energy of *CO on the catalyst serves as a “watershed” for subsequent pathways: weakly adsorbed *CO tends to desorb directly, producing gaseous CO, while strongly adsorbed *CO can undergo further hydrogenation. Subsequent pathways involve hydrogenated intermediates such as *COH or *CHO, and subtle differences in protonation sites ultimately steer the product distribution toward different C₁ molecules like methane or methanol. As this path involves multiple steps with comparable energy barriers, achieving high selectivity toward a single C₁ oxygenate (e.g., methanol) remains a significant challenge [84].

The generation of C₂⁺ products begins with carbon–carbon (C–C) coupling between two C₁ intermediates [85,86]. It is widely accepted that the dimerization of CO to form *OCCO is a critical, high-barrier initial step, which directly limits the total current density for C₂⁺ products. The dominance of one pathway over the other depends strongly on the local reaction microenvironment, including pH, potential, and *CO surface coverage. Recent theoretical and experimental studies have provided deeper insights into the C–C coupling mechanism. Two primary pathways have been proposed: (i) direct dimerization of two *CO species to form *OCCO, and (ii) coupling between *CO and *CHO to form *OCCHO. The preferred pathway depends on the applied potential and local reaction conditions. At low overpotentials where *CO coverage is high, direct *CO dimerization dominates. At higher overpotentials where hydrogenation becomes more favorable, the CO–CHO coupling pathway may contribute significantly.

The coupling barrier is highly sensitive to the local coordination environment. Density functional theory (DFT) calculations reveal that undercoordinated sites—such as steps, edges, and grain boundaries—can substantially lower the activation energy for C–C coupling by stabilizing the transition state. For example, Cu(100) facets exhibit significantly lower *CO dimerization barriers compared to Cu(111) due to their square atomic arrangement, which facilitates lateral interactions between adsorbed *CO molecules [18]. This facet-dependent behavior explains the experimentally observed higher C₂⁺ selectivity on Cu(100)-dominant surfaces.

Beyond the catalyst surface, the local reaction microenvironment plays a crucial role. High local *CO concentration, achieved through tandem catalyst design or confinement effects, increases the probability of two *CO species encountering each other. Additionally, alkali metal cations (e.g., K⁺, Cs⁺) in the electrolyte have been shown to stabilize the *OCCO transition state through electrostatic interactions, further lowering the coupling barrier [64].

After successful C–C bond formation, subsequent multi-step proton–electron transfer processes finely tune the final product distribution, selecting among different C₂ products like ethylene, ethanol, and acetate. It must be emphasized that the C–C coupling step imposes extremely high demands on the spatial proximity and local concentration of the two reaction intermediates [87]. This characteristic provides a crucial design rationale for catalysts with well-defined active site arrangements and adsorption properties, such as metal–organic frameworks. C₁ and C₂⁺ reaction pathways are shown in Figure 2 [81].

The mechanistic framework outlined above provides crucial design principles for MOF-based CO₂RR catalysts. First, the identification of *CO as the central branching point implies that precise control over *CO binding strength is key to steering product selectivity. MOFs offer unparalleled opportunities in this regard through atomic-level engineering of metal nodes—tuning their composition, oxidation state, and coordination environment can systematically modulate *CO adsorption energy, enabling selective promotion of CO, C₁, or C₂⁺ pathways.

Second, the high energy barrier for C–C coupling via *OCCO formation demands reaction microenvironments that enhance local *CO concentration and stabilize the coupling transition state. The confined nanospaces within MOF pores can effectively concentrate *CO intermediates and restrict their spatial orientation, lowering the entropic barrier for dimerization. This confinement effect is particularly pronounced in MOFs with pore dimensions comparable to the molecular size of reaction intermediates.

Third, the complex, multi-step nature of CO₂RR, especially for C₂⁺ products, calls for multifunctional catalytic systems. MOFs can integrate spatially organized tandem active sites within a single framework—for example, CO-generating sites adjacent to C–C coupling sites—to facilitate directional intermediate migration and sequential conversion, mimicking the efficiency of enzymatic cascades.

These mechanistic insights directly inform the design strategies elaborated in Section 3, where we discuss how molecular-scale engineering, electronic structure modulation, morphology control, and interfacial synergy in MOFs translate into precise control over CO₂RR pathways.

In summary, the CO₂RR mechanism is a cascade process starting from the formation of the CO₂•⁻ radical anion, branching via the *CO hub intermediate. The fundamental role of the catalyst is to steer the reaction flux toward specific product channels by modulating the adsorption energies of these key intermediates (especially the initial CO₂•⁻ and the branching point *CO) and their subsequent protonation rates on its surface. An atomic-level understanding of the above mechanisms forms the theoretical cornerstone for designing efficient catalysts.

3. Design Strategies for MOF-Based Electrocatalysts

Metal–organic frameworks (MOFs) exhibit unique catalytic potential for the electrochemical CO₂ reduction reaction (CO₂RR). Their precisely tailorable periodic structures, high surface areas, and atomically dispersed metal sites enable systematic tuning of the electronic structure of active sites and their surrounding chemical microenvironment at the molecular level, providing an ideal platform for establishing clear structure–performance relationships [88]. Compared to conventional solid catalysts, MOFs allow for the systematic tuning of the electronic structure of active sites and their surrounding chemical microenvironment at the molecular level, thereby providing an ideal platform for establishing clear structure–performance relationships.

3.1. Molecular-Scale Active Site Engineering

Molecular-scale active site engineering directly controls the adsorption behavior of key reaction intermediates (e.g., *COOH, *CO, *OCCO) by precisely modifying metal nodes and organic ligands, thereby governing the reaction pathway and product selectivity [89].

3.1.1. Metal Node Engineering: From Single Atoms to Bimetallic Synergy

The type, oxidation state, and coordination environment of metal nodes directly determine the adsorption energy of intermediates and the overall reaction pathway in CO₂RR [90]. Their type, oxidation state, and coordination environment directly influence the binding energy of intermediates and reaction barriers. Lv et al. [91] synthesized a two-dimensional conductive MOF (2D-vc-MOF(Cu)) with a vertically extended structure by coordinating Cu²⁺ ions with a vertically oriented triphenylene-based ligand (HHTC) (Figure 3a). Experimental data reveal that the unique vertically extended architecture maximally exposes Cu active sites, endowing the catalyst with outstanding CO₂ reduction performance. In flow cell tests, 2D-vc-MOF(Cu) achieved a high Faradaic efficiency of 73.4% for methane (CH₄) at −1.4 V (vs. Ag/AgCl), with a partial current density of 13.4 mA cm⁻² for CH₄, significantly outperforming its planar counterpart, 2D-c-MOF(Cu).

However, single-metal sites are often constrained by linear scaling relationships between the adsorption energies of different intermediates, making it difficult to optimize multiple steps simultaneously. A multi-metal strategy, by introducing other metal components, can break this limitation through electronic synergy [92]. For instance, Huang et al. [93] constructed an asymmetric Ni–Cu hybrid-site catalyst (Cu₁Ni-BDP) stabilized by pyrazolate groups, by introducing Cu atoms into a Ni-based MOF (Figure 3b). This unique asymmetric bimetallic site structure effectively modulates the electronic structure of the active center. Electrochemical tests demonstrated its exceptional performance for CO₂ reduction to ethylene (C₂H₄). At a cathodic potential of −1.3 V (vs. RHE), Cu₁Ni-BDP achieved a high ethylene Faradaic efficiency (FE) of 52.7% with a total current density of 0.53 A cm⁻². Moreover, the catalyst exhibited high stability during 25 h of continuous electrolysis, with only a 4.5% decrease in FE, significantly surpassing conventional copper-based catalysts.

3.1.2. Ligand Engineering: Electronic Tuning and Microenvironment Design

Organic ligands serve not only as structural supports in MOFs but also as effective tools for modulating the electron density and spatial environment of metal centers. By modifying ligands with different functional groups, catalytic activity and selectivity can be significantly influenced [94,95].

Metalloporphyrins and phthalocyanines are classical ligands for constructing conductive MOFs and biomimetic catalysts. Kornienko et al. [96] selected a catalytically active cobalt-metalated porphyrin derivative (Co-TCPP) as the organic ligand and assembled it with aluminum-based inorganic nodes to form an Al₂(OH)₂TCPP-Co thin-film catalyst with nanoporous channels. This design successfully integrated the homogeneous high activity of molecular porphyrin catalysts with the heterogeneous stability conferred by the MOF framework. Experimental data showed that, benefiting from the well-defined metalloporphyrin units as active sites, this MOF catalyst achieved a high CO Faradaic efficiency (FE) of 76% at −0.7 V (vs. RHE), maintained stability for over 7 h, and reached a turnover number (TON) of 1400 per active site.

Leveraging this concept, Yi et al. [97] coordinated nickel phthalocyanine (NiPc) with nickel-catecholate to successfully prepare 2D conductive MOF nanosheets (NiPc-NiO₄) featuring a fully π-conjugated structure (Figure 3c). Electrochemical tests demonstrated that at −1.0 V (vs. RHE), NiPc-NiO₄ achieved a CO Faradaic efficiency (FE) as high as 98.4% for CO₂ reduction to carbon monoxide (CO), with a corresponding CO partial current density of 34.5 mA cm⁻². Its performance significantly surpassed that of traditional MOF catalysts and molecular phthalocyanine counterparts, while also exhibiting long-term stability exceeding 10 h.

Furthermore, ligand engineering can modulate the physicochemical microenvironment of the material; for example, modifying alkyl chains can adjust pore hydrophobicity, thereby influencing the diffusion and enrichment behavior of reactants and intermediates, providing an additional dimension for selective catalysis [98].

Molecular-scale active site engineering achieves deep control over the intrinsic activity and selectivity of catalysis through precise design of metal nodes and organic ligands. Future research should further combine in situ spectroscopic characterization and theoretical calculations to reveal the dynamic evolution mechanism of active sites under real reaction conditions, and explore the synergistic design of multi-metal and multifunctional ligands to break current performance limitations and advance MOF-based CO₂RR catalysts toward higher activity, selectivity, and stability.

3.2. Optimization of Electronic Structure and Charge Transport Enhancement

The intrinsically low electrical conductivity of most metal–organic frameworks (MOFs) is a key bottleneck limiting their electrocatalytic performance, severely hindering efficient electron transport from the current collector to active sites, resulting in low utilization of intrinsic active sites and limited overall current density. Enhancing charge conduction hinges on constructing efficient, continuous electron transport pathways [99,100,101]. Current strategies mainly revolve around two approaches: (i) achieving intrinsic charge delocalization through molecular design of the framework, and (ii) constructing rapid interfacial charge transfer channels by compositing with highly conductive materials [102,103].

3.2.1. Molecular Design of Intrinsic Charge Transport Paths

Achieving intrinsic high conductivity in MOFs is a fundamental solution to their charge transport problem. This typically relies on constructing extended π-conjugated systems or metal–ligand orbital hybridization within the framework, forming delocalized electronic bands, thereby enabling a “band-like transport” mechanism akin to metals or semiconductors [104,105]. For instance, Meng et al. [106] constructed a series of two-dimensional conductive MOFs based on metallophthalocyanine (MPc) units connected by copper (Cu) nodes, whose electrical conductivity can be tuned within the range of 2.73 × 10⁻³ to 1.04 × 10⁻¹ S cm⁻¹. This high conductivity originates from the delocalized energy bands formed by strong hybridization between metal d-orbitals and ligand π-orbitals within the 2D plane, coupled with efficient interlayer charge-hopping pathways provided by close π-π stacking. Furthermore, studies indicate that an analog based on cobalt phthalocyanine with oxygen bridges (CoPc-Cu-O) exhibits optimal CO selectivity, which is attributed to a lower energy barrier in the crucial *COOH intermediate formation step (Figure 3d,e), thereby effectively promoting CO₂ activation and conversion.

3.2.2. Charge Transport Engineering in Heterogeneous Composite Interfaces

For the vast majority of classical MOFs lacking intrinsic high conductivity, compositing them with highly conductive materials (e.g., carbon materials, MXenes, conductive polymers) is an effective strategy to enhance overall charge transport capability [107,108]. For instance, Zhu et al. [109] successfully constructed an MXene/In-TCPP (denoted as In@M) heterostructure (Figure 3f) via in situ hybridization of highly conductive 2D MXene with an indium-based MOF (In-TCPP) that exhibits intrinsic selectivity toward the formate pathway. In this composite system, MXene not only serves as a three-dimensional conductive framework ensuring rapid electron transport but also induces significant electronic interactions through intimate interfacial contact with the MOF. These interactions optimize the electronic density of states of the In active centers and stabilize the key intermediate *OCHO for formate generation, thereby synergistically enhancing both reaction kinetics and selectivity. The composite catalyst demonstrated stable operation in a membrane electrode assembly (MEA) at a current density of approximately 160 mA cm⁻² (Figure 3g) and could continuously produce a pure formic acid solution with a concentration of 0.22 M, fully showcasing its potential for practical application.

Enhancing the charge transport capability of MOF electrocatalysts requires a synergistic approach combining molecular-scale electronic structure design and mesoscale interface engineering. Intrinsically conductive MOFs achieve efficient intrinsic charge transport through band engineering, representing an ideal model for pursuing ultimate catalytic performance, whereas the heterogeneous composite strategy endows a wide range of MOF materials with practicality by constructing functionalized conductive interfaces. Future research directions should focus on deeply understanding and precisely regulating the charge transfer mechanism and band alignment at heterogeneous interfaces; developing novel composite systems with both high conductivity and excellent catalytic activity; and evaluating the long-term operational stability and energy cost economics of these materials in practical electrolysis devices. Through cross-scale charge transport engineering, it is promising to ultimately solve the conductivity bottleneck of MOF catalysts in CO₂RR applications.

3.3. Crystal-Scale Morphology and Structure Modulation

Achieving designable morphology and predictable properties is a challenging goal in materials engineering. Precise control over the morphology, dimensionality, crystal facets, and defect structures of MOFs is a key strategy for optimizing their mass transport, active site accessibility, electron conduction, and structural stability [104,110,111]. Applying these engineering approaches at meso- and macro-scales can significantly influence the final performance of MOFs (e.g., directly affecting CO₂ diffusion, local concentration and residence time of intermediates, and surface reaction pathways), thereby systematically enhancing the catalytic efficiency and product selectivity of CO₂RR.

3.3.1. Morphology and Dimensionality Engineering

Controlling the physical dimensionality and macroscopic morphology of MOFs can significantly alter their mass transfer kinetics and charge transport behavior. Two-dimensional nanomaterials possess unique properties due to their ultrathin thickness and large lateral dimensions. Fabricating MOFs into 2D nanosheets maximizes the exposure of surface metal nodes and greatly shortens ion/electron transport distances, whereas constructing 3D hierarchical or porous structures can utilize their inherent confinement effects to enrich reactant CO₂ and stabilize key intermediates (e.g., *CO), promoting deep reduction processes like C–C coupling by increasing local concentration. For example, Cho et al. [110] successfully prepared a nickel single-atom catalyst (Ni SAC, denoted as Ni-NC-NS) based on two-dimensional nanosheet metal–organic frameworks (MOFs) via a combined strategy of solvent exchange, vacancy engineering, and morphology reconstruction. As shown in Figure 3h, this 2D morphology not only endowed the material with a high specific surface area and abundant edge active sites but also, due to its corresponding metastable crystalline structure, facilitated the evaporation of zinc species during subsequent pyrolysis. This process created numerous homogeneous nitrogen vacancies in the derived nitrogen-doped carbon material. Combined analysis from EXAFS fitting and DFT calculations revealed that these vacancies played a decisive role in stabilizing the highly active Ni–N₂–V₂ sites and lowering the reaction energy barrier, thereby significantly enhancing the CO₂ reduction performance. The catalyst exhibited a CO Faradaic efficiency approaching 100% in the tests.

3.3.2. Crystal Facet Engineering

For crystalline MOFs, the exposed crystal facets determine surface atomic arrangement, coordinative unsaturation, and electronic structure, profoundly affecting intrinsic catalytic activity. Crystal facet engineering, by controlling the crystallization process to selectively expose specific facets with higher reactivity, is an effective route for optimizing anisotropic catalytic performance. For example, Zhang et al. [112] successfully prepared a ZIF-8-5% catalyst by performing surface post-synthetic modification (introducing DOBDC ligands) on the zeolitic imidazolate framework ZIF-8 without compromising its primary structure. Combined experimental and theoretical studies indicate that the modified material exposes a greater number of coordinatively unsaturated sites, and its surface chemical microenvironment and electronic structure are optimized, thereby significantly enhancing CO₂ adsorption and activation capabilities. DFT calculations further confirm that this strategy reduces the Gibbs free energy barrier for the formation of the key intermediate *COOH by approximately 0.4 eV, effectively suppressing the competing hydrogen evolution reaction. Consequently, this catalyst achieved simultaneous improvement in CO selectivity and current density over a broad potential window. At −1.1 V vs. RHE, the CO Faradaic efficiency increased from 56% to 79%, and the partial current density was enhanced from −4 mA cm⁻² to −10 mA cm⁻².

3.3.3. Defect Engineering

Deliberately introducing structural defects into the MOF skeleton (e.g., coordinatively unsaturated metal sites, missing ligands, grain boundaries) is a powerful strategy for creating highly active catalytic centers and tuning their electronic properties. Defects can not only serve as active sites to participate directly in reactions, but can also optimize intermediate adsorption behavior by altering local charge distribution and band structure, while forming secondary pores beneficial for mass transport. For instance, by controlling synthesis kinetics, a series of size-uniform copper-based MOF (CuTrz) nanocrystals rich in grain boundaries were prepared. These grain boundaries, acting as highly active “line defects”, not only significantly increase the material’s specific surface area, but also induce surface electronic structure rearrangement, optimizing the adsorption of intermediates like *CO, thereby promoting C–C coupling. The grain-boundary-rich sample exhibited a high Faradaic efficiency of 55.4% for C₂H₄ and a total selectivity of 81.8% for all multi-carbon products in electrocatalytic tests, significantly outperforming perfect crystals [113].

Morphology, crystal facet, and defect engineering reconstruct the mesostructure and surface properties of MOF catalysts from different dimensions, providing multi-level tools for tuning CO₂RR performance. Future research needs to pay more attention to the synergistic application of these strategies and, with the aid of advanced in situ characterization techniques, reveal the intrinsic link between structural evolution and the dynamic behavior of active sites under real reaction conditions, thereby guiding the rational design and controllable preparation of MOF materials with directed catalytic functions.

3.4. Interfacial Synergistic Effects: From Functional Composites to Electronic Coupling

Compositing metal–organic frameworks with other functional materials (e.g., conductive carbons, metal nanoparticles, semiconductors) to construct multicomponent heterostructures is a key strategy for synergistically addressing the intrinsic limitations of MOFs and achieving performance multiplication. Such synergistic effects originate from unique physicochemical interactions at the heterogeneous interface (e.g., charge transfer, band rearrangement, chemical bonding), enabling the integration of advantages from different components to precisely control reaction pathways while enhancing conductivity and stability, thereby improving energy conversion efficiency.

3.4.1. Tandem Catalysis and Interfacial Electronic Modulation

Tandem catalysis decouples and optimizes the multi-step CO₂ reduction reaction by spatially coupling active components with distinct functional specificities, forming an efficient “relay” pathway. For example, Ren et al. constructed a tandem catalyst (CuSn-TCA-1) comprising coexisting copper nanoparticles (Cu NPs) and tin single atoms (Sn SAs) within a MOF (TCA) via an in situ encapsulation strategy; its unique architecture is shown in Figure 3i. In this design, Sn SAs function as CO-generating sites that preferentially and selectively reduce CO₂ to CO. The generated CO intermediates subsequently migrate to the surfaces of neighboring Cu NPs for C–C coupling, ultimately yielding ethylene. This spatially separated yet functionally linked mechanism effectively increases the local CO coverage on Cu surfaces, thereby significantly enhancing the selectivity towards C₂ products. The high-performance catalyst achieved a C₂H₄ Faradaic efficiency of 64% at −1.5 V vs. RHE, demonstrating exceptional electrocatalytic capability for ethylene synthesis [114].

3.4.2. Inspiration from Band Engineering in Heterojunctions

Although the concepts of S-scheme or Z-scheme heterojunctions originate from the field of photocatalysis, their core principle—constructing a built-in electric field at the interface via band alignment to drive directional charge separation—provides profound inspiration for understanding and designing electrocatalytic heterojunctions. For example, In the Ni-MOF/g-C₃N₄ S-scheme heterojunction, the difference in the Fermi levels of the two materials leads to the formation of a built-in electric field directed from g-C₃N₄ to Ni-MOF upon contact. This field directs the recombination of photogenerated electrons and holes along an S-scheme pathway, thereby concentrating highly reductive electrons in the conduction band of g-C₃N₄ while retaining highly oxidative holes in the valence band of Ni-MOF. This mechanism suppresses charge recombination and simultaneously maximizes the redox capacity of the system. Ultimately, the optimized charge-separation behavior significantly enhances the photocatalytic performance. According to the test data presented in Figure 3j, the CO production rate reaches 3.7 times that of pure Ni-MOF [115].

This principle is also crucial in electrocatalytic systems. In MOF-based composite electrocatalysts, when different components (e.g., two MOFs, MOF and semiconductor) come into contact, differences in their band structures can also lead to interfacial charge rearrangement and band bending. The resulting built-in electric field or dipole layer can modulate the local electron density at active sites, optimizing their adsorption energy for key intermediates, thereby guiding the reaction pathway and enhancing selectivity. Therefore, drawing on and developing band engineering concepts provides an important theoretical framework for rationally designing heterojunction catalysts with efficient interfacial electronic synergy in electrocatalytic systems.

Constructing MOF-based heterostructures is an effective route to achieve synergistic catalysis. Tandem catalysis focuses on optimizing the reaction sequence through spatial organization, with its efficiency deeply regulated by interfacial EMSI, whereas band engineering in heterojunctions provides a universal physical picture for understanding and designing interfacial charge behavior. Future research needs to comprehensively utilize in situ interfacial characterization and theoretical simulations to precisely analyze the dynamic interfacial structure and charge transfer processes of composite catalysts under working conditions, and explore band-matching rules across material systems, thereby guiding the design of next-generation CO₂ reduction electrocatalysts with high activity, selectivity, and stability.

Figure 3. (a) The synthesis and structural model of 2D-vcMOF(Cu). Gray, red, blue, and white spheres represent C, O, Cu, and H atoms, respectively. Reproduced with permission [91]. Copyright 2023, National Library of Medicine. (b) Structural model of the cage structure in the Cu1Ni-BDP MOF. Reproduced with permission [93]. Copyright 2023, National Library of Medicine. (c) Illustration of the preparation of NiPc-NiO₄. Top and side view of their structures with 2 × 2 square grids in AA-stacking mode. Reproduced with permission [96]. Copyright 2015, ACS Publications. Free energy profiles for electrochemical reduction of CO₂ to CO catalyzed by CoPc-Cu-NH (red), CoPc-Cu-O (green), NiPc-Cu-NH (orange), and NiPc-Cu-O (blue) under the standard condition and electrode potential of 0 V (vs standard hydrogen electrode) through the reaction pathway of (d) route I and (e) route II. Reproduced with permission [97]. Copyright 2021, Wiley. (f) Schematic illustrating the synthesis process of In-TCPP@ MXene. (g) Stability test of In@M-2 in MEA-SSE. Reproduced with permission [109]. Copyright 2025, ACS Publications. (h) Schematic of the synthesis method and proposed vacancy-manipulated Ni–Nx active site architecture of Ni–NC–NS. Reproduced with permission [110]. Copyright 2023, Wiley. (i) Schematic illustration of the designed in situ generation of Sn SAs and Cu NPs-engineered MOF. Reproduced with permission [114]. Copyright 2026, ACS Publications. (j) Schematic of work function alignment before and after contact and the S-scheme charge transfer mechanism in the Ni-MOF/CN heterojunction under light irradiation. Reproduced with permission [116]. Copyright 2025, MDPI.

Figure 3. (a) The synthesis and structural model of 2D-vcMOF(Cu). Gray, red, blue, and white spheres represent C, O, Cu, and H atoms, respectively. Reproduced with permission [91]. Copyright 2023, National Library of Medicine. (b) Structural model of the cage structure in the Cu1Ni-BDP MOF. Reproduced with permission [93]. Copyright 2023, National Library of Medicine. (c) Illustration of the preparation of NiPc-NiO₄. Top and side view of their structures with 2 × 2 square grids in AA-stacking mode. Reproduced with permission [96]. Copyright 2015, ACS Publications. Free energy profiles for electrochemical reduction of CO₂ to CO catalyzed by CoPc-Cu-NH (red), CoPc-Cu-O (green), NiPc-Cu-NH (orange), and NiPc-Cu-O (blue) under the standard condition and electrode potential of 0 V (vs standard hydrogen electrode) through the reaction pathway of (d) route I and (e) route II. Reproduced with permission [97]. Copyright 2021, Wiley. (f) Schematic illustrating the synthesis process of In-TCPP@ MXene. (g) Stability test of In@M-2 in MEA-SSE. Reproduced with permission [109]. Copyright 2025, ACS Publications. (h) Schematic of the synthesis method and proposed vacancy-manipulated Ni–Nx active site architecture of Ni–NC–NS. Reproduced with permission [110]. Copyright 2023, Wiley. (i) Schematic illustration of the designed in situ generation of Sn SAs and Cu NPs-engineered MOF. Reproduced with permission [114]. Copyright 2026, ACS Publications. (j) Schematic of work function alignment before and after contact and the S-scheme charge transfer mechanism in the Ni-MOF/CN heterojunction under light irradiation. Reproduced with permission [116]. Copyright 2025, MDPI.

4. Product-Oriented Catalysis of CO₂RR Using MOFs

Leveraging their atomically tunable active sites, designable pore microenvironments, and functionalizable interfaces, metal–organic frameworks (MOFs) provide an ideal platform for precisely steering the CO₂RR pathway toward specific high-value products. Through rational design of metal nodes, organic ligands, dimensionality/morphology, and composite interfaces, the adsorption energies of key intermediates and reaction barriers can be systematically modulated to achieve highly selective synthesis of products ranging from C₁ to C₂⁺ species. This chapter focuses on CO, CH₄, CH₃OH, HCOOH, C₂H₄, C₂H₅OH, urea, and multi-carbon (C₂⁺) products, reviewing recent advances in the design strategies and performance of MOF-based catalysts for these transformations, while analyzing the underlying structure–performance relationships.

4.1. Carbon Monoxide (CO)

The selective electrosynthesis of CO requires a catalyst that effectively lowers the energy barrier for the initial COOH formation while promoting the subsequent desorption of the CO intermediate to prevent its further reduction. MOFs demonstrate significant advantages in addressing this dual requirement through precise electronic structure and microenvironment design. Magnetic field coupling and multi-metal synergy offer a novel approach. Yin et al. [116] reported a one-dimensional Cu-ZnMg trimetal MOF, as shown in Figure 4a, where introducing non-magnetic Zn²⁺/Mg²⁺ ions achieves “magnetic dilution” of Cu²⁺ sites, converting them into isolated paramagnetic centers. This design enables effective coupling with an alternating magnetic field, facilitating energy transfer via spin-lattice relaxation, while Zn and Mg synergistically optimize *CO desorption and CO₂ adsorption, respectively. This catalyst achieved ~95% CO Faradaic efficiency (FE) at an ultralow overpotential of −0.2 V (vs. RHE), revealing the potential of external field stimulation and multi-metal synergy to overcome thermodynamic limitations. For more complex syngas precursors, a bimetallic site division of labor strategy shows unique value. Zhong et al. [117] reported a 2D conjugated MOF, PcCu-O₈-Zn, as shown in Figure 4b, where ZnO₄ nodes are responsible for CO₂ adsorption and reduction, while adjacent CuN₄ units act as efficient proton transfer mediators. This synergistic mechanism not only achieved 88% CO FE but also allowed precise tuning of the H₂/CO ratio between 1:7 and 4:1 by varying the potential or metal center, catering to different downstream Fischer-Tropsch synthesis processes. Addressing the intrinsic charge transport bottleneck of MOFs is key to achieving industrial-level current density. Constructing intrinsically conductive MOFs is a fundamental strategy. Yi et al. [97] developed nickel phthalocyanine-based 2D MOF (NiPc-NiO₄) nanosheets, as shown in Figure 4c, where strong hybridization between metal d-orbitals and ligand π-orbitals forms a highly delocalized band structure, granting significantly enhanced intrinsic conductivity. Benefiting from rapid electron transport and fully exposed Ni-N₄ active sites, this catalyst achieved a high CO partial current density of 34.5 mA·cm⁻² at −1.2 V while maintaining 98.4% FE.

Efficient CO generation using MOFs primarily relies on multi-metal synergy to optimize reactant adsorption/product desorption and band engineering to construct intrinsic fast charge channels. Future research should further explore the universality of external field coupling and strive to develop novel MOF systems combining ultra-high conductivity with excellent stability to meet the demands of industrial electrolyzers for high current density and long operational lifetime.

4.2. Methane (CH₄)

Achieving high selectivity towards CH₄, an eight-electron reduction product, necessitates a catalyst that can drive the deep hydrogenation and C–O bond cleavage of the CO intermediate while effectively suppressing the competing C–C coupling pathway. The core of MOF catalyst design for this purpose lies in stabilizing an appropriate Cu valence state to promote hydrogenation while constructing a spatial synergy mechanism to enrich and convert *CO. A dual-site design with intermediate directional migration strategy effectively addresses. Zhao et al. [118] constructed CuN₂–MgN₂ dual single-atom catalysts anchored on N-doped carbon. Theoretical and experimental evidence confirmed that Mg sites are responsible for efficient CO generation, while adjacent Cu sites exhibit strong adsorption for CO. Crucially, the migration of *CO from Mg to Cu sites is thermodynamically spontaneous (barrier: −0.95 eV), far more favorable than its gaseous desorption. This “generation–utilization separation” tandem mechanism achieved 78.3% CH₄ FE and a partial current density of 228.7 mA·cm⁻² at −1.1 V.

Another key to achieving high selectivity is stabilizing the active Cu(I) valence state, preventing its over-reduction to Cu(0), which is unfavorable for CH₄ formation. Jia et al. [119] successfully synthesized a Cu–C strong σ-bond-based MOF (Cu-TEPT) by selecting terminal alkynyl ligands, as shown in Figure 5a. This strong bonding effectively inhibits the reduction of Cu⁺ under cathodic potentials, maintaining the stability of the active center, and achieved 83.6% CH₄ FE at −1.5 V. Qian et al. [120] further utilized σ-π coordination between phenylacetylene and Cu⁺, as shown in Figure 5b, achieving 68.8% CH₄ FE even in a strongly acidic electrolyte (pH = 3), demonstrating the robustness of this strategy under harsh conditions.

High-selectivity CH₄ generation relies on atomic-scale spatial synergy for targeted intermediate transfer/conversion and strong chemical bonding to stabilize key active species. Future catalyst design needs to pay more attention to the dynamic stability of dual-site structures and the persistence of synergistic effects under real electrolysis conditions, especially at high current densities and during long-term operation.

4.3. Methanol (CH₃OH)

The efficient conversion of CO₂ to CH₃OH faces the complex challenge of guiding CO through multi-step protonation while selectively retaining the C–O bond, demanding exquisite control over the intermediate’s hydrogenation pathway. MOFs effectively steer the reaction toward methanol generation by constructing multifunctional active interfaces, tandem catalytic systems, and leveraging unique ionic environments. Constructing Metal/Metal Oxide Heterojunctions is an effective means. Yang et al. [121] used the classic Cu-BTC MOF as a precursor to derive core–shell Cu@Cu₂O nanoparticles coated with an N-doped carbon layer via controlled pyrolysis. The abundant Cu⁰/Cu⁺ interfaces in this catalyst provide moderate *CO adsorption strength, inhibiting CO desorption while avoiding catalyst poisoning from overly strong adsorption, thereby achieving 45% CH₃OH FE at −0.7 V. For more complex multi-step conversions, integrating molecular tandem catalysts within MOFs shows great potential. Ghatak et al. [122] covalently anchored cobalt phthalocyanine (CoPc) and iron protoporphyrin (hemin) on the nodes of a 2D Zr-BTB MOF, as shown in Figure 6a,b. They discovered a non-classical tandem pathway: CoPc reduces CO₂ to a formaldehyde (HCHO) intermediate, which is then hydrogenated to CH₃OH by hemin. This bimolecular synergistic system achieved 18% methanol FE and a current density of 25.4 mA·cm⁻² in a gas diffusion electrode. Furthermore, utilizing the ionic character of MOFs can create unique reaction microenvironments. Zhang et al. [123] reported a trinuclear Cu(I) ionic MOF (CuTz-1-300), where a powerful “electrostatic tension” field generated between the free BF₄⁻ anions and the cationic framework significantly enhances CO₂ adsorption and activation, leading to 56.4% CH₃OH FE at −0.97 V.

Efficient methanol synthesis requires catalysts capable of finely tuning the subsequent hydrogenation path of *CO. MOFs provide multi-level solutions to this challenge through derivative construction of multifunctional heterojunctions, integration of molecular catalytic units, and utilization of their intrinsic ionic properties. Future directions lie in deeply understanding the charge and mass transfer mechanisms at hetero-interfaces or between tandem sites and designing intelligent MOF catalytic systems with adaptive regulation capabilities.

4.4. Formic Acid (HCOOH)

The two-electron reduction of CO₂ to formic acid via the OCHO pathway is particularly favored on p-block metals (e.g., In, Bi), where the key challenge lies in optimizing the binding strength of this intermediate and ensuring catalyst durability under operating conditions. MOF catalyst design focuses on creating highly active, low-coordination single-atom sites and addressing material stability issues in electrochemical environments. Constructing low-coordination single-atom centers can break. Li et al. [124] anchored atomically dispersed In(III) sites on an ultra-thin 2D Zr-BTB MOF monolayer via post-synthetic modification, as shown in Figure 7a. X-ray absorption fine structure spectroscopy confirmed a rare low-coordination tetrahedral geometry for the In site. This unique geometry allows it to simultaneously stabilize two *HCOO key intermediates, triggering a bimolecular cooperative reduction pathway that significantly lowers the rate-determining step barrier from 0.89 eV (unimolecular path) to 0.49 eV. This catalyst achieved 95.7% formic acid FE and a current density of 213.3 mA·cm⁻² in a strongly acidic electrolyte (pH = 1.67). For MOFs with poor conductivity, employing them as pre-catalysts for electrochemical in situ reconstruction is an effective strategy. Lamagni et al. [125] used a porous Bi(btb) MOF as a precursor. Upon applying a reductive potential, Bi³⁺ in the framework was reduced and nucleated relying on a partially carbonized organic matrix, ultimately forming a composite of highly dispersed metallic Bi nanoparticles embedded in porous carbon, as shown in Figure 7b,c. This reconstruction process endowed the material with excellent conductivity and abundant active sites, achieving 95% formate FE at an overpotential of −0.97 V.

The application of MOFs in formic acid electrosynthesis highlights the importance of coordination environment engineering for enhancing intrinsic activity and the feasibility of dynamic structural evolution strategies for achieving practical performance. Future research should utilize advanced in situ characterization techniques to track the dynamic changes in low-coordination single-atom sites under reaction conditions in real-time and explore the reconstruction patterns of more p-block metal MOF pre-catalysts to build high-performance, long-lived catalytic systems.

4.5. Urea

Urea electrosynthesis represents a formidable challenge as it requires the simultaneous coupling of two distinct half-reactions—CO₂ reduction and nitrate reduction—involving multi-electron transfers and the critical formation of a C–N bond. The well-defined and spatially organizable multiple active sites in MOFs provide an ideal platform for integrating and synergistically catalyzing this complex reaction at the atomic scale. Constructing dual-functional active centers within a single MOF skeleton is a direct approach. Qiu et al. [126] designed a 2D conductive MOF (PcNi-Fe-O), where FeO₄ nodes preferentially catalyze NO₃⁻ reduction to NH₃, while adjacent NiPc centers are responsible for activating CO₂ and catalyzing subsequent C–N coupling, as shown in Figure 8a. This spatially proximate dual-site design allows rapid transfer of reaction intermediates, significantly lowering the reaction barrier, achieving 54.1% urea FE and a high production rate of 2.1 g h⁻¹ gcat⁻¹ under neutral conditions. Given the fluctuating nitrate concentration in actual wastewater, developing concentration-adaptive catalysts is of great practical significance. Tan et al. [127] revealed different adaptation mechanisms by comparing non-metallated porphyrin MOF (PMOF) with copper porphyrin MOF (Cu-PMOF): the porphyrin center in PMOF has weak adsorption for NO₂, suitable for stepwise coupling under high NO₃⁻ concentration, whereas the Cu site in Cu-PMOF exhibits strong adsorption for NO₂, promoting continuous NO and CO coupling reactions under low concentration, as shown in Figure 8b. Catalysts designed based on this principle maintained efficient urea synthesis over a wide concentration range (FE up to 52.7%).

The use of MOFs for urea synthesis successfully demonstrates their unique ability to integrate multifunctional catalytic centers at the molecular level. Precise control over the spatial arrangement and electronic properties of active sites enables accurate control of complex tandem reaction pathways. The future challenge lies in how to integrate such high-performance powder catalysts on a large scale into flow electrolysis cells and conduct economic assessments of the selectivity and energy consumption for urea synthesis from actual impurity-containing wastewater.

4.6. Ethylene (C₂H₄)

The generation of ethylene is fundamentally governed by the efficiency of the C–C coupling step between two adsorbed CO intermediates, a process demanding high local CO coverage and specific geometric configurations on the catalyst surface. MOF catalysts systematically enhance ethylene selectivity by constructing tandem systems to enrich *CO, modifying electrodes to enhance mass transfer, and tuning substrate crystal facets. Designing a tandem catalytic system for site-specific generation and enrichment of CO is an effective strategy. Xu et al. [128] constructed a copper–silver bimetallic covalent organic framework (MCOF), where Ag sites preferentially generate CO due to their high affinity for CO₂, as shown in Figure 9a. The generated CO then spontaneously migrates to adjacent Cu sites with stronger adsorption capability for CO. This thermodynamically driven “intermediate interlayer transfer” mechanism creates high local *CO coverage on Cu site surfaces, significantly promoting C–C coupling, achieving 51.5% C₂H₄ FE at −1.774 V. Yan et al. [129] grew an in situ layer of MOF with single Cu sites on copper foil, forming an MOF/Cu tandem electrode. The MOF layer acts as an efficient CO₂-to-CO converter, and the produced CO migrates to the underlying Cu foil surface for coupling. Simultaneously, the coverage of the MOF layer induced the exposure of more Cu(200) facets conducive to C₂ product formation on the Cu foil and completely suppressed the CH₄ pathway, achieving 48.6% C₂H₄ FE at −1.11 V. To achieve industrial-level current density, utilizing MOFs to optimize electrode gas-phase mass transfer is crucial. Nam et al. [130] integrated MOFs with high CO₂ adsorption capacity (e.g., HKUST-1) as a functional layer into a gas diffusion electrode (GDE), as shown in Figure 9b. This MOF layer acts as a local CO₂ “concentrator,” significantly increasing the gaseous reactant concentration near the Cu catalytic layer, thus maintaining 49% C₂H₄ FE even at an ultra-high current density of 1 A cm⁻².

Efficient ethylene synthesis at high current density is a systems engineering task requiring tandem catalytic design to enrich key intermediates, electrode microenvironment engineering to ensure reactant supply, and substrate surface engineering to expose favorable crystal facets. MOFs play multiple roles as active site designers, intermediate modulators, and mass transfer promoters. The future research focus is to integrate these lab-scale optimization strategies into scalable membrane electrode assemblies and investigate their performance degradation mechanisms over hundreds of hours of operation.

4.7. Ethanol (C₂H₅OH)

Selective ethanol production imposes even more stringent demands than ethylene, requiring not only successful C–C coupling, but also the subsequent retention and hydrogenation of the C–O bond, which calls for an active site with asymmetric electronic and geometric properties. MOFs achieve precise guidance of this complex pathway by constructing hetero-bimetallic sites and confining special cluster structures. Constructing hetero-bimetallic active sites can break the symmetry limitations. Zhao et al. [131] introduced Sn single atoms into a conductive Cu-HAB MOF via post-synthetic modification, forming a μ-N-bridged Sn···Cu hetero-bimetallic pair, as shown in Figure 10a. Theoretical calculations show that Sn sites strongly adsorb the oxygen-containing intermediate *OCH₂, while Cu sites adsorb *CO. Their combination enables the asymmetric coupling of *CO and *OCH₂. The barrier for this pathway (0.26 eV) is much lower than that for the C–O cleavage path leading to ethylene (2.72 eV), resulting in 56% ethanol FE at −0.57 V. Utilizing MOF channels to confine electrochemically reconstituted low-nuclearity clusters is another effective way to create highly active catalytic centers. Shao et al. [132] electrochemically reduced a 3D Cu-MOF, as shown in Figure 10b. Under conditions that preserved the main framework, some unstable Cu²⁺ ions migrated, reduced, and aggregated within the pores, forming atomically dispersed single atoms and low-nuclearity Cu clusters (2–10 atoms). These MOF-channel-confined low-nuclearity clusters were confirmed to be the primary active species catalyzing CO₂ to ethanol conversion, achieving 82.5% ethanol FE at −1.0 V.

The highly selective synthesis of ethanol signifies a higher level of control over the CO₂RR pathway. Its success relies on creating an active environment with asymmetric electron distribution at the atomic scale. The precise pore structure and modifiable sites of MOFs make it possible to customize such complex active centers. Future challenges lie in deeply understanding the electronic communication mechanism between hetero-bimetallic sites and how to controllably and scalably prepare metal-cluster@MOF composites with uniform nuclearity distribution.

4.8. Multi-Carbon (C₂⁺) Products

From an application perspective, the overarching challenge for C₂⁺ product generation is to maximize the total yield and energy efficiency at industrially relevant current densities, which requires catalysts that maintain high activity and structural stability under harsh reduction potentials. MOFs strive to meet this challenge through strategies like surface engineering to stabilize high-activity valence states and constructing heterojunctions to optimize overall reaction pathways. Stabilizing high-valence copper species (Cuδ⁺, 0 < δ < 2) is considered crucial. Jang et al. [133] used Cu-BDC MOF as a precursor, as shown in Figure 11a. Through a two-step method combining air thermal annealing and electrochemical activation, they constructed and stabilized enriched Cuδ⁺ species on the material surface. Quasi-in situ XPS and theoretical calculations indicated that these Cuδ⁺ sites effectively enhance *CO adsorption and lower its dimerization barrier. The optimized catalyst achieved a total C₂⁺ product FE of 78% at −1.06 V. Constructing metal oxide/MOF heterojunctions can synergistically regulate multiple reaction steps. Liu et al. [134] grew Cu₂O nanoparticles in situ on 2D Cu-BDC nanosheets, forming abundant Cu₂O/Cu-BDC hetero-interfaces, as shown in Figure 11b. This interface not only stabilizes active Cu⁺ species but its unique electronic structure also synergistically optimizes the adsorption strength of key intermediates like *CO and *CHO, placing them within the most favorable range for subsequent C–C coupling, thereby achieving 58.2% C₂⁺ FE at a high current density of 300 mA·cm⁻².

C₂⁺ product generation for industrial applications demands that catalysts maintain structural stability and high-activity valence states under high overpotentials and strongly reducing environments. MOFs and their derived materials provide feasible solutions to this challenge through surface reconstruction and interface engineering design. Future research needs to proceed from a device-level perspective, systematically evaluating the mechanical stability, anti-poisoning ability, and product separation economics of such catalysts in membrane electrode assemblies during long-term operation, to propel them from basic research toward practical application.

Herein, we summarize the design strategies and representative electrocatalytic performance of metal–organic framework (MOF)-based catalysts for electrochemical CO₂ reduction (CO₂RR) toward diverse target products, as presented in

Table 2. Design strategies and representative performance of MOF-based CO₂RR catalysts for target products.

Representative Catalyst	Core Design Strategy	Key Performance (Faradaic Efficiency, FE)	Target Product	Ref.
Cu-ZnMg MOF	Magnetic field coupling and trimetallic synergy; magnetic dilution to lower overpotential	~95% FE @ −0.2 V vs. RHE	CO	[116]
PcCu-O8-Zn	Bimetallic site division of labor (ZnO4 for CO2 reduction, CuN4 for proton transfer); tunable syngas ratio	88% FE	CO/H2	[117]
NiPc-NiO4	Constructing intrinsically conductive 2D π-conjugated framework; optimizing charge transfer and *COOH formation barrier	98.4% FE @ −0.85 V vs. RHE	CO	[97]
CuN2-MgN2	Dual-site tandem catalysis; CO generation on Mg sites and spillover to Cu sites for hydrogenation	78.3% FE @ −1.1 V vs. RHE	CH4	[118]
Cu-TEPT	Ligand engineering; strong σ-bond from alkynyl groups stabilizes Cu+ active sites	83.6% FE @ −1.5 V vs. RHE	CH4	[119]
OMe-PhCu MOP	σ-π dative bonding stabilizes Cuδ+ sites; suitable for acidic environments	68.8% FE (pH = 3)	CH4	[120]
Cu@Cu2O/NC	MOF-derived core–shell heterojunction; abundant Cu0/Cu+ interfaces with moderate *CO adsorption	45% FE @ −0.7 V vs. RHE	CH3OH	[121]
CoPc/Hemin@Zr-BTB	Dual-molecular tandem catalysis; non-CO pathway (CO2 → formaldehyde → methanol)	18% FE (flow cell)	CH3OH	[122]
CuTz-1-300	Ionic framework creates an electrostatic tension field to enhance CO2 adsorption; low-temperature activation preserves Cu+ sites and conductivity	56.4% FE @ −0.97 V vs. RHE	CH3OH	[123]
Zr-BTB-In(monolayer)	Low-coordination In single atom enables dual *HCOO intermediate synergistic pathway	95.7% FE @ −1.8 V vs. RHE (pH = 1.67)	HCOOH	[124]
Bi(btb)-derived	MOF precatalyst in situ reconstructs into highly dispersed Bi nanoparticles/carbon composite	95% FE @ −0.97 V vs. RHE	HCOO−	[125]
PcNi–Fe–O 2D c-MOF	Dual active sites (FeO4 reduces NO3−, NiPc activates CO2 and couples); synergy lowers C–N bond formation barrier	54.1% FE @ −0.6 V vs. RHE	Urea	[126]
PMOF/Cu-PMOF	Concentration-adaptive design; porphyrin/metalloporphyrin centers match coupling mechanisms at different NO3− concentrations	Up to 52.7% FE	Urea	[127]
Ag0.5Cu0.5-CTC-TAPT	Alternating heterometallic layers enable directional CO migration from Ag to Cu sites, enriching *CO for dimerization	51.5% FE @ −1.774 V vs. RHE	C2H4	[128]
Cu-MOF-CF	MOF layer acts as CO generator; modulates Cu foil facets and completely suppresses CH4	48.6% FE @ −1.11 V vs. RHE	C2H4	[129]
MOF/GDE (HKUST-1)	MOF functional layer enriches local CO2 concentration at the electrode, overcoming mass-transfer limitations	49% FE @ 1 A cm−2 (flow cell)	C2H4	[130]
CuSn-HAB	Sn···Cu heterobimetallic sites guide asymmetric C–C coupling (CO + OCH2), preserving the C–O bond	56% FE @ −0.57 V vs. RHE	C2H5OH	[131]
Cu-MOF-20 (LNCCs)	Electrochemical reconstruction of MOF precursor yields confined Cu low-nuclearity clusters (2–10 atoms), enhancing C–C coupling	82.5% FE @ −1.0 V vs. RHE	C2H5OH	[132]
Cux-Act (Cu-BDC derived)	Combined thermal annealing and electrochemical activation stabilizes partially oxidized Cuδ+ species, promoting *CO dimerization	78% total C2+ FE @ −1.06 V vs. RHE	C2+	[133]
Cu2O@Cu-BDC	Rich heterointerfaces between MOF nanosheets and Cu2O nanoparticles synergistically stabilize intermediates and active sites	72.1% total C2+ FE @ −1.19 V vs. RHE (H-cell)	C2+	[134]

“*” denotes the adsorbed state.

.

5. Prospects and Outlook

Owing to their highly programmable structures and tunable functionalities, metal–organic frameworks (MOFs) have emerged as a promising platform for CO₂RR. Through atomic-level design of active sites and cross-scale optimization of charge transport and reaction microenvironments, MOFs enable precise control over reaction pathways, offering unprecedented opportunities for converting CO₂ into specific high-value chemicals. However, translating this potential from laboratory breakthroughs to practical applications requires addressing several critical challenges. Future research should focus on the following directions:

(1)

Rational design integrated with dynamic mechanistic understanding.

A closed-loop paradigm of “theoretical prediction–precise synthesis–in situ characterization” is essential. Machine learning and high-throughput computation can accelerate the screening of optimal metal nodes, organic ligands, and topologies. Concurrently, advancing in situ/operando techniques with high spatiotemporal resolution (e.g., time-resolved XAS, operando electrochemical microscopy) is imperative for real-time monitoring of framework evolution, metal valence states, coordination environments, and key intermediates under operating conditions. Such insights will clarify the true identity of active sites and their dynamic reconstruction mechanisms, guiding the design of more stable and active catalysts.

(2)

Electrode and device engineering for industrial-level performance.

Most MOF-based catalysts currently operate at relatively low current densities (<50 mA cm⁻²), far below industrial requirements (>200 mA cm⁻²). Achieving practical viability requires synergistic advances at both material and device levels:

Material design: Develop novel MOFs combining high intrinsic activity with excellent conductivity (e.g., extended 2D π-conjugated MOFs).

Architectural design: Construct three-dimensional hierarchical porous structures or macroscopic monolithic electrodes to maximize active site exposure and eliminate mass transport limitations.

Device integration: Optimize the integration of catalyst layers with gas diffusion electrodes and ion-exchange membranes to fabricate low-impedance, highly stable membrane electrode assemblies for efficient operation at high current densities.

(3)

Precise pathway control through multifunctional integration.

For multi-step reactions yielding C₂⁺ products or urea, single active sites are insufficient. Future efforts should focus on designing spatially ordered, multifunctional active centers within MOFs, such as tandem catalytic sites or hetero-bimetallic sites. By precisely tuning the distance, orientation, and electronic interaction between these sites, directional migration and relay conversion of intermediates can be achieved. Additionally, leveraging the confinement effect of MOF pores to tailor the local microenvironment (e.g., pH, water activity, ion concentration) can further suppress side reactions and enhance selectivity toward target products.

(4)

Long-term operational stability enhancement.

The structural stability of MOFs under electrochemical conditions remains a core bottleneck for practical application. Promising strategies include:

Designing MOFs with strong covalent metal–ligand bonds and high redox stability.

Developing dynamically stable frameworks with self-healing capabilities.

Using MOFs as precursors or protective shells to construct core–shell structures or composite interfaces, where their ordered nature serves as a template to generate highly active derived phases while inhibiting aggregation, leaching, or over-reduction of active components.

In summary, with their unparalleled structural tailorability, MOFs offer a promising platform to simultaneously address the intertwined challenges of activity, selectivity, and stability in CO₂RR. Through the deep integration of materials science, electrochemistry, theoretical computation, and chemical engineering, the rational design of next-generation, high-performance, and durable “intelligent” MOF electrocatalysts is within reach. Such advancements will be instrumental in propelling CO₂RR technology toward scalable applications and contributing to global carbon neutrality goals.