Organometallic Frameworks for Efficient Electrocatalytic CO₂ Reduction Reactions

ABSTRACT

The electrocatalytic conversion of CO₂ to value‐added chemicals driven by renewable electricity offers a viable strategy to reduce atmospheric CO₂ concentration and realize energy storage. Crystalline porous metal‐organic frameworks (MOFs) with periodically ordered isolated metal active sites and large surface areas represent promising CO₂ reduction reaction (CO₂RR) catalysts due to their rapid CO₂ adsorption kinetics. However, conventional MOFs typically exhibit insufficient CO₂RR current densities stemming from inherent low electrical conductivity and sluggish electron transfer kinetics. Introducing Metal‐C bonds into the framework can directly regulate the electronic structure of the metal center, optimizing intermediate adsorption. Herein, we synthesized two organometallic frameworks featuring carbon‐silver connectivity to enhance the CO₂RR performances. The distinctive σ‐π coordination motif between alkyne moieties and metal centers endows these frameworks with enhanced electron transfer capability, superior CO₂ activation ability, and significantly improved CO₂RR performance. Crucially, these materials achieve exceptional CO Faraday efficiencies (FE_CO) exceeding 90% when operated at industrially relevant current densities (> 500 mA cm⁻²), surpassing most reported MOF‐based systems. This work establishes a novel design paradigm for organometallic frameworks and accelerates their practical deployment in industrial CO₂ electroreduction processes.

Organometallic framework featuring unique σ‐π coordination patterns based on carbon‐silver bonds have been synthesized, achieving exceptional Faradaic efficiency of over 90% toward CO for CO₂ electrocatalytic reduction reaction under industrial current densities.

1. Introduction

The excessive use of fossil fuels has resulted in a significant increase of carbon dioxide (CO₂) in the atmosphere, causing serious challenges such as global climate changes and disruption of carbon balance [1, 2]. To mitigate these problems and achieve carbon neutrality, the recovery and conversion of CO₂ to valued‐added chemicals are particularly crucial [3, 4]. In recent years, various strategies have been developed to convert CO₂ into high‐value carbon products, including photocatalysis, electrocatalysis, biological and chemical methods, and so forth [5, 6, 7, 8]. The electrocatalytic CO₂ reduction reaction (CO₂RR) has become one of the most attractive strategies due to its mild reaction conditions, adjustable product selectivity, and simple device operation [9, 10]. However, owing to the difficulty in activating CO₂ and the complexity of product types, developing catalysts with high activity and selectivity for the CO₂RR is currently a severe challenge [11]. Carbon monoxide (CO) is one of the most important products of CO₂RR [12]. Various electrode materials have been developed to promote CO₂RR toward CO, such as noble metals, metal oxides, metal alloy, single‐atomic catalyst, and porous crystalline materials, including metal‐organic frameworks (MOFs) and covalent organic frameworks [13, 14, 15, 16]. However, the high selectivity for most of the catalysts is achieved only at low current densities, which makes it difficult to meet industrial requirements [17]. Therefore, finding well‐defined and rationally designed catalysts with low overpotential, large current density, and high Faraday efficiency (FE) is a key issue to promote the industrialization of CO₂RR.

MOFs are one class of crystalline porous materials with regular framework structures and uniform pores constructed by bridging organic ligands and metal centers [18]. Thus, MOFs have been applied in many fields, including biomedical, energy storage, gas adsorption/separation, sensing, and catalysis [19, 20, 21, 22, 23, 24]. Particularly, the tunable well‐defined chemical and porous structure, high porosity, and multifunctional synergy make MOFs ideal electrocatalysts for CO₂RR [25, 26]. Nevertheless, most MOFs are typically constructed through metal ions with oxygen or nitrogen atoms of the redox‐inactive organic ligands [27, 28]. These MOFs usually exhibit low conductivity due to the poor overlap between π orbitals of the ligands and metal ion orbitals [29, 30]. The low electron transfer ability of these conventional MOFs typically results in low current density and energy conversion efficiency for CO₂RR. By enhancing conjugation or introducing electron‐rich units, the structure of MOFs can be effectively engineered to increase their carrier mobility. This facilitates faster electron transfer to active sites and substrates, thereby enabling higher current densities in CO₂RR [31, 32, 33, 34]. Recently, several types of conductive MOFs have been reasonably designed and synthesized by constructing a d‐π conjugation system through the enhancement of in‐plane charge delocalization and extending π‐conjugation or integrating electron rich units [35, 36]. For example, various transition metal (e.g., Ni, Co, Cu, and Fe)‐based conductive MOFs are constructed by connecting hexahydroxyl‐, hexamino‐, and hydrosulphonyl‐substituted benzene/benzene ligands [37, 38]. However, these MOFs are difficult to obtain due to the complex and tedious synthesis of these ligands. Moreover, at higher industrial current densities, the selectivity of the product inevitably decreases. Therefore, it is crucial to design new types of MOFs with high electron transfer ability for CO₂RR to improve the selectivity and current density.

Organometallic compounds constructed by metal‐carbon (M‐C) bonds are important materials that have been applied in many fields, including luminescence, energy storage, and catalysis [39, 40, 41]. Carbonyl, alkene, alkyne, and carbene‐based ligands are usually employed to construct organometallic compounds [42, 43]. Among them, the metal‐alkynyl‐based organometallic compounds are formed by the metal with fully filled electrons and an alkynyl group with an empty pπ^* orbital [44]. In metal‐alkynyl compounds, the overlap between d‐pπ hybridized orbitals occupied by metal electrons and the empty pπ* orbitals of the alkynyl groups could lead to the formation of feedback π‐bonds [45, 46]. The unique bonds can regulate electron transport and increase the energy level of metal center orbitals, effectively adjusting the electronic structure of the metal sites and promoting electron transfer from metal sites [47]. Therefore, by strategically designing alkynyl ligands possessing extensive π‐conjugation, it is possible to construct novel MOFs with good charge transport ability via metal‐alkynyl bonds [48, 49]. Moreover, beyond enhancing electronic ability, the adsorption activity of MOFs is intrinsically linked to the electronic structure of the metal centers, specifically the energy and occupancy of the d orbitals. Strategic modulation of the active d orbitals enables preferable adsorption strength of CO₂. The formation of feed‐back π‐bonds from the metal to alkyne ligands provides an effective strategy to tune the d‐electron configuration of the metal centers. This electronic redistribution facilitates electron transfer from the metal to reaction intermediates, strengthens reactant adsorption, and consequently enhances the electrocatalytic activity of the MOFs. However, the construction of MOFs via M‐C bonds remains challenging due to the relatively poor dynamic reversibility of M‐C bonds, hindering the self‐assembly processes in the synthesis of MOFs. Additionally, the M‐C bonds usually involve diverse and unconventional coordination geometries that distinct from the common modes observed in traditional MOFs, further complicating the design and crystallization of frameworks.

Herein, we designed and synthesized two 3D organometallic frameworks (denoted as TEPB‐Ag and TEPM‐Ag (TEPB: 1,3,5‐Tris(4‐ethynylphenyl) benzene; TEPM: tetrakis(4‐ethynylphenyl) Methane) constructed by rigid alkynyl ligands and trinuclear Ag(I) clusters through Ag‐carbon bonds (Figure 1). The unique σ‐π coordination model between the alkyne group and the metal sites endows the TEPB‐Ag with high electronic conductivity up to 1.4×10⁻¹ S cm⁻¹, which is comparable to typical conductive MOFs and 2–4 magnitude orders higher than that of conventional MOFs constructed by M‐N and M‐O bonds. Thus, the obtained 3D Ag‐carbon‐based MOFs possessing good CO₂ active ability showed excellent CO₂RR performance. Especially, excellent FE_CO > 90% can be achieved when tested at industrial current densities (> 500 mA cm⁻²), higher than most MOFs. This work provides an approach to design novel organometallic frameworks and enhance the CO₂ electroreduction reaction performance.

FIGURE 1.

(a) The coordination mode of a typical σ and feedback π bond. (b) Formation of Ag(I) trinuclear clusters and determination of alkynyl configuration. (c) Schematic diagram of enhancing electron transport through organometallic framework (TEPB‐Ag) in electrocatalytic CO₂ reduction reaction.

2. Results and Discussion

2.1. The Synthesis and Characterization of Organometallic Frameworks

Two crystalline organometallic frameworks, TEPB‐Ag and TEPM‐Ag, based on Ag‐carbon bonds were obtained through the reaction of silver salts and 1,3,5‐tris(4‐ethylphenyl) benzene (TEPB) or tetrakis(4‐ethynylphenyl) methane (TEPM), respectively, in the presence of triethylamine (Figure 2a). Their crystalline structures were confirmed by powder x‐ray diffraction (PXRD) in combination with Material Studio analysis. The TEPB‐Ag has intense peaks at 2θ = 5.4° and 9.4°, which are assigned to the (100) and (200) reflections, respectively. Notably, there was no peak of Ag₂O or Ag nanoparticles (Figure 2b), indicating the formation of the pure phase of the TEPB‐Ag and TEPM‐Ag. The experimental pattern of TEPB‐Ag is matched well with the simulated curve, with a reasonable unweighted‐profile R factor (R _p = 5.52%) and a weighted‐profile R factor (R _wp = 7.44%), suggesting the validity of the proposed model (Figure 2a,b). TEPB‐Ag crystallizes in the P3 space group with the parameters of a = 18.64 Å, b = 18.64 Å, c = 3.74 Å, α = β = 90°, γ = 120°. As shown in Figure 2a, each TEPB ligand coordinates with three trinuclear Ag₃ clusters through the σ and π coordination modes of Ag‐C bonds to generate 3D framework, in which 1D hexagonal channel with a theoretical pore size of 1.6 nm along c direction is formed. Different from TEPB‐Ag, TEPM‐Ag adopts ctn network with Td symmetry and triangular Ag₃ cluster, which shows a larger crystal cell with a = b = c = 39.58 Å, α = β = γ = 90° (Figure S1). The peaks in the PXRD pattern at 2θ = 7.0°, 11.9°, and 19.5° can be sequentially assigned to 100, 110, and 200 reflections. To further elucidate the orientation and crystallinity information of TEPB‐Ag and TEPM‐Ag, grazing‐incidence wide‐angle x‐ray scattering (GIWAXS) and small‐angle x‐ray scattering (SAXS) experiments were conducted. The GIWAXS 2D patterns reveal anisotropic scattering patterns for TEPB‐Ag and TEPM‐Ag (Figure S2). The SAXS curve of TEPB‐Ag exhibits an orientation signal at the inflection point at q = 0.39 Å^{− 1}, corresponding to the (100) crystal plane of the crystal model (Figure S3).

FIGURE 2.

The characterizations of TEPB‐Ag and TEPM‐Ag. (a) The synthesis scheme and structure of TEPB‐Ag and TEPM‐Ag. (b) The PXRD patterns and Pawley refinement of TEPB‐Ag. (c) The FT‐IR spectra of TEPB‐Ag and TEPB. (d) STEM dark‐field image of TEPB‐Ag (insert: IFFT‐STEM image based on the red box).

The Fourier transform infrared (FT‐IR) spectroscopy and solid‐state ¹³C NMR spectroscopy confirmed the formation of TEPB‐Ag and TEPM‐Ag. As shown in Figures 2c and S4, the FT‐IR indicated the disappearance of the characteristic alkynyl C‐H stretching vibration band (3270–3290 cm⁻¹) and C‐H bending vibration band (660–665 cm⁻¹) of the ligand, indicating the alkynyl ligands were coordinated with the Ag atoms. The characteristic peak at 2011–2021 cm⁻¹ was designated as the C≡C‐Ag vibration, confirming the successful coordination of alkynyl ligands and metal in MOFs (Figure S4). Meanwhile, the presence of alkynyl in two MOFs was confirmed by ¹³C solid‐state nuclear magnetic resonance spectroscopy (Figure S5). The chemical shifts of 127–153 ppm are attributed to the sp² carbon of the aromatic ring, while the chemical shift of 90–99 ppm is assigned to the sp carbon of the alkyne group. X‐ray photoelectron spectroscopy (XPS) analysis was performed to investigate the surface electronic states and elemental composition of the two MOFs, revealing the presence of C and Ag. The characteristic peaks of Ag 3d were located at 368.7 and 374.7 eV, indicating that Ag is in the +1 state (Figures S6, S7) [50, 51]. Moreover, the Ag content in TEPB‐Ag and TEPM‐Ag is 23 wt.% and 25 wt.%, respectively, as determined by inductively coupled plasma optical emission spectroscopy (ICP‐OES). The high metal contents can provide more CO₂ adsorption catalytic sites and promote the CO₂RR. Thermogravimetric analysis showed that both TEPB‐Ag and TEPM‐Ag exhibited good thermal stability up to 300°C (Figure S8). More importantly, TEPB‐Ag and TEPM‐Ag remain stable in 1 M KOH (Figure S9), which is suitable for the CO₂RR in alkaline electrolytes.

The morphology of the two MOFs was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As shown in Figure S10, TEPB‐Ag was composed of sheet particles with a diameter of ∼60 nm. Similarly, TEPM‐Ag also exhibited an irregular agglomerated nanosheet morphology of ∼42.5 nm (Figure S10). The high‐resolution transmission electron microscopy (HR‐TEM) shows the lattice fringes of 16.3 Å for TEPB‐Ag (Figures 2d and S11), which is close to the pore size of the simulated framework. Energy‐dispersive x‐ray spectroscopy (EDS) mapping showed that Ag and C elements were uniformly distributed over TEPB‐Ag and TEPM‐Ag (Figures S11 and S12). Additionally, aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) revealed uniformly arranged Ag atoms (Figure S13).

To elucidate the coordination environment of Ag centers in the TEPB‐Ag and TEPM‐Ag, we performed X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS) measurements. As shown in Figure 3a, the white line peak of Ag K‐edge in TEPB‐Ag and TEPM‐Ag is located between Ag₂O and Ag foil, very close to Ag₂O, indicating that the valence state of Ag species is +1, which is in accordance with the XPS results. To obtain more detailed information about the local coordination of Ag in TEPB‐Ag and TEPM‐Ag, EXAFS analysis was conducted. The Ag K‐edge EXAFS curves of TEPB‐Ag showed a main peak at 1.41 Å in R‐space (Figure 3b), which can be assigned to the organometallic Ag‐C bond. Notably, this position is different from the distance of the Ag‐O bond in Ag₂O (1.68 Å), indicating the absence of Ag₂O particles. In addition, the peak at 2.60 Å was attributed to the Ag‐Ag bond, indicating the formation of Ag cluster nodes within the MOF. Furthermore, the wavelet‐transform spectrum of the k³‐weighted EXAFS (WT‐EXAFS) revealed that the intensity maxima at 3.7 and 10.1 Å^{− 1} corresponding to Ag‐C and Ag‐Ag scattering paths were observed for TEPB‐Ag and TEPM‐Ag (Figure 3c), which was consistent with the EXAFS results. The above peaks are different from the intensity peak at 6.6 Å^{− 1} for the Ag‐O contribution in Ag₂O, indicating the absence of Ag₂O particles. Similarly, TEPM‐Ag also has a peak at 1.41 Å in R‐space, which can be assigned to the Ag‐C bond, while the peak at 2.64 Å is attributed to the Ag‐Ag bond (Figure 3b). Using the least squares curve parameter method to fit the EXAFS spectra, the coordination number of the Ag‐C bond for both the TEPB‐Ag and TEPM‐Ag fits is approximately 3 and the coordination number of the Ag‐Ag bond was approximately 2 (Figure 3d,e). Therefore, based on the coordination numbers of Ag‐C and Ag‐Ag, as well as the universal σ‐π co‐coordination mode between Ag(I) and alkynyl groups, we propose the formation of a trinuclear Ag(I) cluster surrounded by three alkyne groups, which is in agreement with the analysis result of PXRD. In this structure, Ag(I) cluster connects to the carbonyl carbon via σ bonds, while there is a feedback π bond formed through the d orbital electrons of Ag(I) and the empty π orbitals of alkynyl, forming a σ‐π co‐coordination mode.

FIGURE 3.

The x‐Ray absorption spectroscopy characterizations of TEPB‐Ag and TEPM‐Ag. (a) Ag K‐edge of XANES spectra of TEPB‐Ag, TEPM‐Ag, Ag foil, and Ag₂O. (b) Ag K‐edge of EXAFS spectra of TEPB‐Ag, TEPM‐Ag, Ag foil, and Ag₂O. (c) Ag K‐edge WT‐EXAFS spectra of TEPB‐Ag, TEPM‐Ag, Ag foil, and Ag₂O. (d) EXAFS fitting curves of TEPB‐Ag in R‐space. (e) EXAFS fitting curves of TEPM‐Ag in R‐space.

The permanent porosity and carbon dioxide affinity of the TEPB‐Ag and TEPM‐Ag were determined by N₂ and CO₂ adsorption measurements. The N₂ adsorption isotherm at 77 K showed a Brunauer‐Emmett‐Teller (BET) specific surface area of 147 and 204 m²g for TEPB‐Ag and TEPM‐Ag, respectively (Figure S14). Moreover, the CO₂ uptake value for TEPB‐Ag and TEPM‐Ag was 26 and 24 cm³g⁻¹ at 25°C under 1 bar, respectively (Figure S15). The good CO₂ affinity would be beneficial for improving the electrocatalytic activity of CO₂RR. The coordination of the alkyne group with Ag endowed the materials with higher electronic conductivity than traditional MOF materials. To study its intrinsic conductivity, TEPB‐Ag and TEPM‐Ag thin films deposited on ITO glass were prepared. As expected, the conductivity of TEPB‐Ag reached 1.4×10⁻¹ S cm⁻¹ as well as 7.0×10⁻² S cm⁻¹ for TEPM‐Ag (Figure S16). The high conductivity is attributed to the special coordination mode between the alkyne group and Ag in the MOFs. Among them, Ag(I) is connected to alkynyl carbon through a σ bond, and there is a feedback π bond formed through the d orbital electrons of Ag(I) and the empty π orbitals of alkynyl, forming a σ‐π co‐coordination mode.

2.2. The Electrocatalytic CO₂RR Performances

The unique organometallic coordination mode of alkynyl and Ag effectively modulates the electronic structure of metal sites, which would promote electron transfer from these sites to enhance catalysis. This endows TEPB‐Ag and TEPM‐Ag as potential promising candidates for CO₂RR under high current density. The CO₂RR performances of TEPB‐Ag and TEPM‐Ag were evaluated using a gas diffusion electrode (GDE) under 1 M KOH electrolyte conditions (Figure 4a). From the linear scanning voltammetry (LSV) curves (Figure 4b), both catalysts showed higher current densities in a CO₂ atmosphere than in Ar‐saturated electrolytes, demonstrating the predominant reduction of CO₂ at the cathode. The reduction products under different potentials were identified by gas chromatography (GC) and ¹H NMR. CO and H₂ were the main products, and no liquid product was detected in the electrolyte (Figure S17). Both TEPB‐Ag and TEPM‐Ag showed efficient CO₂ reduction to CO over a wide potential range from −0.5 to −1.1 V (vs. RHE) (Figures S18 and S19). An excellent CO Faradaic efficiency (FE_CO) of 92% was achieved for TEPB‐Ag at −0.6 V (vs. RHE), with the corresponding CO partial current density (j _CO) of 111.3 mA cm⁻². Impressively, the TEPM‐Ag still achieved an outstanding FE_CO of 86% with a j _CO of 134.7 mA cm⁻² at ‐1.1 V (Figure S19). More importantly, the FE_CO of TEPB‐Ag remained over 90% in the range of large current density of 100–500 mA cm⁻². Particularly, the TEPB‐Ag achieved 97% FE_CO at 400 mA cm⁻² (Figure 4c). This performance is slightly superior to TEPM‐Ag (FE_CO = 91.9% at 400 mA cm⁻²), which may be attributed to the better electron transport ability of its in‐plane conjugated framework. It is noteworthy that the FE_CO and j _CO of both TEPB‐Ag and TEPM‐Ag exceeded most of the reported Ag‐based molecular catalysts and porous framework materials (Figure 4d). Notably, only H₂ was detected by GC over the ligands, which indicated the Ag species acted as the active center in the CO₂RR (Figure S20). The superior activity of TEPB‐Ag and TEPM‐Ag can be reasonably attributed to the strong electron‐transfer ability from Ag to the alkyne carbon. Additionally, the positive correlation between the double‐layer capacitance (C _dl) and the electrochemical active surface area (ECSA) of the catalyst was investigated to gain deeper insights into the electrocatalytic activity. As shown in Figure S21, the C _dl of TEPB‐Ag is similar to that of TEPM‐Ag, with values of 3.6 and 3.7 mF cm⁻², respectively. The enhanced performance of TEPB‐Ag may be attributed to its improved kinetic activity for CO₂RR and increased electrical conductivity. As shown in the electrochemical impedance spectroscopy (EIS) Nyquist plot in Figure S22, TEPB‐Ag exhibits a smaller semicircle compared to TEPM‐Ag, indicating faster electron transfer from the electrode to CO₂. The high orbital matching of the alkyne group and Ag in the MOF framework as well as the formation of d‐π bonds enhanced the electronic conductivity of the material. To illustrate the kinetic activity of the catalysts, we then tested the Tafel curves (overpotential versus log |j _CO|) (Figure S23). Both TEPB‐Ag and TEPM‐Ag exhibited Tafel slopes exceeding the theoretical value of 118 mV dec⁻¹, indicating that the conversion of adsorbed CO₂ receiving an electron and combining with H⁺ from the electrolyte to form *COOH is the rate‐determining step (RDS). Compared to TEPM‐Ag (323 mV dec⁻¹), TEPB‐Ag exhibits a significantly reduced Tafel slope (280 mV dec⁻¹), indicating enhanced kinetic activity for CO₂RR.

FIGURE 4.

The CO₂RR performances of TEPB‐Ag. (a) Schematic of gas diffusion electrode. (b) LSV of TEPB‐Ag and TEPM‐Ag in Ar and CO₂. (c) FE_CO of TEPB‐Ag and TEPM‐Ag under different current density in 1 M KOH in flow‐cell. (d) Comparison of our works with previous data in terms of the current density and FE.

To confirm the origin of the product CO, ¹³C isotope labelling experiments were performed to trace the carbon source of CO in 1 M KOH and 0.1 M KCl using ¹³CO₂ as the reaction gas. The ¹³C‐labeling CO₂ isotope experiments revealed that the CO was produced solely from CO₂ in a CO₂‐saturated KCl aqueous solution, rather than from the decomposition of the catalyst or any other source (Figure S24). The long‐term stability of TEPB‐Ag was studied by chronoamperometric test, which showed the corresponding FE_CO can be retained after 10 h (Figure S25). The PXRD and FT‐IR after testing remained consistent with the materials, indicating the excellent structural stability of MOFs (Figures S26 and S27). The XPS after electrolysis revealed that the valence state of Ag remained at +1 (Figure S28).

2.3. The Reaction Mechanism Study

To investigate the mechanism of the CO₂RR process, we performed operando electrochemical attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) measurements using a homemade cell (Figure S29). As shown in Figure 5a, the band located at 1396 cm⁻¹ was assigned to the C═O stretching vibration of *COOH, which was recognized as the key intermediate for the formation of CO in CO₂RR [52]. The result further indicated that the formation of *COOH is the RDS, which is in agreement with the Tafel analysis. The density functional theory (DFT) was further performed to deepening the understanding of the catalytic selectivity and providing insights into the mechanism of CO₂RR. The Gibbs free energy curve of CO₂RR on TEPB‐Ag is shown in Figure 5b. The intermediate model for the calculation of CO₂RR and HER is given in Figures 5c, S30, and S31. First, CO₂ molecules were adsorbed on the active Ag center to generate *CO₂ (where * denotes the active site), which then formed the key intermediate *COOH via the proton‐electron transfer process (Figure S30). Subsequently, *COOH was converted to *CO by the proton transfer process and CO was produced by desorption from the Ag site finally (Figure S30). As shown in Figure 5b, *COOH formation is the RDS of CO₂RR with free energies of 0.5 eV, which are lower than the free energies of H₂ formation by the *H process of HER. Thus, in aqueous electrolytes TEPB‐Ag is more prone to CO₂RR than HER.

FIGURE 5.

Density functional theory calculations and proposed schematic mechanism. (a) Operando ATR‐FTIR spectra of TEPB‐Ag collected in CO₂‐saturated 0.5 M KHCO₃ electrolyte. (b) Free energy diagrams of TEPB‐Ag for CO₂RR and HER pathways. (c) The DFT calculated TEPB‐Ag structures of various states for CO₂RR. (d) DOS of Ag, C atoms of TEPB‐Ag and C atom of TEPB. (e) DOS of different orbitals of Ag, C atoms in TEPB‐Ag.

In addition, the electronic structures of TEPB and TEPB‐Ag were investigated by XPS analysis and theoretical calculations. Figure S32 shows that the C 2p peak of TEPB‐Ag is significantly shifted to a higher binding energy (0.6 eV) compared to that of the ligand TEPB, suggesting the transfer of electrons from Ag to the TEPB alkyne carbon. The density of states (DOS) further revealed the electron transfer mechanism in TEPB‐Ag. Compared to the ligand TEPB (Figure 5d), the 𝜋* orbitals in TEPB‐Ag show a wider distribution and stronger off‐domains upon bonding to Ag (Figure 5d), which can be attributed to the electron filling from the d‐orbitals of Ag through the empty 𝜋* LUMOs from Ag to alkynyl carbon atom. In particular, for the alkyne bond, the p‐orbitals of the alkyne C atoms overlap the d‐orbitals of Ag, respectively (Figure 5e), which suggests the presence of a strong orbital hybridization between alkyne C and Ag, further revealing the presence of a feedback 𝜋 bond. Electronic structure analysis further elucidated the charge redistribution between Ag centers and alkynyl ligands in the coordination network. The charge density difference of TEPB‐Ag (Figure S33a) shows that electrons transfer from Ag to alkynyl C, where the blue and yellow equal surfaces represent charge accumulation and depletion, respectively. This charge redistribution confirms the binding of Ag and C. In addition, the electron localization in the doping site region of the electronic localization function (ELF) (Figure S33b) is significantly enhanced, which is verified by the strong covalent properties of Ag‐C. The feedback 𝜋‐bond effectively modulates the d‐electronic structure of the Ag center, reduces the electron filling of the d orbitals, and brings the d‐band center of the Ag atom closer to the Fermi energy level in TEPB‐Ag, which strengthens the catalytic performance.

3. Conclusion

In summary, two MOFs based on organometallic Ag‐C bonds were designed and synthesized via the unique σ‐π coordination mode between alkyne groups and Ag to promote CO₂RR performance. The unique σ‐𝜋 coordination mode between the alkyne and metal center effectively modulates electron transport, elevates the energy level of the metal center orbital, facilitates electron transfer from the metal to reaction intermediates, and enhances reactant adsorption, thereby improving the electrocatalytic CO₂RR activity of the MOFs. Crucially, these materials achieve an exceptional FE_CO exceeding 90% at large current densities (> 500 mA cm⁻²). DFT calculations reveal an electron transfer mechanism via the M‐C bond, where the feedback π bond effectively modulates the d‐electron structure of the Ag center. This reduces the electronic filling of the d orbitals, bringing the d‐band center of the Ag atom closer to the Fermi level, thereby enhancing catalytic performance. This work may provide new insights for the synthesis of novel organometallic frameworks and the selection and application of CO₂RR catalysts at industrial current densities.

Author Contributions

Yu‐Luan Zhang: data curation, investigation, validation, writing – original draft. Wei‐Xuan Chen: data curation. Hui Guo: data curation, formal analysis. Yi‐Ying Lan: data curation, formal analysis. Rong Cao: supervision, funding acquisition, writing – review and editing. Yuan‐Biao Huang: conceptualization, writing – review and editing, supervision.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Experimental details for the preparations, characterizations of materials, electrochemical measurements, and computational method.

Supporting file: anie72853‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.