Cu-MOF-74-Derived CuO-400 Material for CO₂ Electroreduction

Abstract

This study proposes a straightforward strategy utilizing metal–organic frameworks (MOFs) to obtain efficient electrocatalysts for synthesizing C2 products (C₂H₄ and C₂H₅OH) via a CO₂ reduction reaction. Cu-MOF-74 was chosen as the precursor, while copper oxide nanoparticles were obtained through a calcination method. During the calcination process, by controlling the calcination conditions, the porous structure of the MOF framework was successfully retained, leading to CuO-400 with a high catalytic activity and C2 production efficiency. Compared to CuO-n formed by the calcination of Cu(NO₃)₂, CuO-400 derived from MOFs exhibits a 1.6 times higher C2 activity as an electrocatalytic material at −1.15 V vs. RHE.

1. Introduction

With the improvement of living standards, the world’s demand for energy continuous to grow rapidly. However, due to the excessive exploitation of hydrocarbon resources, the emissions of carbon dioxide (CO₂) from fossil fuel combustion continue to rise, resulting in a series of impacts on the ecological environment. According to the latest research by the Global Carbon Budget scientific team, the global emissions of CO₂ from fossil fuels rose again in 2023, reaching a record level of 36.8 billion tons, an increase of 1.1% compared to 2022 [1]. In response to the environmental issues caused by the increase in CO₂ emissions, various CO₂ reduction and conversion technologies have been rapidly developed by researchers. Among these, electrochemical CO₂ reduction reactions (CO₂RRs) have attracted widespread attention due to their mild conditions, environmental friendliness, and the ability to produce a variety of valuable additional products [2]. However, electrochemical methods also face challenges such as noticeable competing reactions, high overpotential, and poor selectivity, which require further improvement. Electrochemical methods are influenced by various conditions, such as the electrolyzer, electrolyte, pH, and electrode materials [3]. Among the many influencing factors, the electrode materials are the most critical. Therefore, it is crucial to find efficient and selective catalysts.

Metal catalysts have been extensively studied by researchers due to their excellent conductivity and catalytic performance. In the early 20th century, metals such as mercury and zinc were discovered to be capable of CO₂ electroreductions. By the 1980s, it was found that copper-based catalysts could be used for the electrocatalytic reduction of CO₂, producing hydrocarbons and alcohols with high Faradaic efficiency (FE) [4]. Subsequently, an increasing number of metals were found to be capable of electrocatalytic CO₂ reduction. Among these metals, Cu-based catalysts demonstrate a superior catalytic performance compared to others. However, simple Cu catalysts still suffer from issues such as a poor selectivity for single-product and a low current efficiency in CO₂RR. To enhance the catalytic activity and product selectivity of Cu catalysts for CO₂RR, numerous scientific teams have conducted research focusing on copper-based catalysts, leading to the development of various types of Cu-based catalysts and their derivative catalysts. These catalysts include copper nanoparticles [5,6], copper alloy catalysts [7,8,9,10,11], single-atom catalysts [12,13,14], non-metal element-doped copper-based catalysts [15,16], and copper-based metal–organic framework (Cu-MOF) catalysts [17,18,19,20].

In recent years, metal–organic frameworks (MOFs) have become popular due to their novel properties. MOFs are a type of porous coordination polymer composed of metal ions/clusters and organic ligands, characterized by their high permanent porosity, high crystallinity, and order [21,22,23]. Compared to inorganic catalytic materials, nano-materials derived from MOFs exhibit an excellent catalytic activity in CO₂ electroreduction due to their high surface area, tunable geometric structures, and controllable pore sizes. This type of material is also frequently used in the modification of Cu-based catalysts. Among these, Cu-MOFs and their derivative catalytic materials have played a significant role in CO₂RR reactions [24,25]. Research has found that Cu-MOFs and their derivatives exhibit an excellent selectivity and high performance for C2 products. Xiao et al. [26] prepared Cu-MOF material Cu-BTC using 1,3,5-benzenetricarboxylic acid as the ligand. A series of different catalysts were prepared under various calcination conditions to modulate the oxidation states of Cu, resulting in a range of catalysts with different Cu oxidation states derived from Cu-BTC. The Cu/C-T-air catalyst, obtained by calcining in air, showed a preference for producing C₂H₄; in particular, the Cu/C-450-air catalyst calcined at 450 ℃ achieved an FE of 34.8%. Sargent et al. [27] used a thermochemical method to deform the symmetrical paddle-wheel Cu dimers of HKUST-1 (the alias of Cu-BTC) into asymmetrical forms, by changing the calcination isothermal time and maintaining the calcination temperature at 250 °C, thus controlling the deformation of the copper dimers, while preserving the HKUST-1 structure. Studies on the crystal structure showed that most of the paddle-wheel copper Cu dimers were located within the (111) plane. The loss of crystallinity on the (111) face could be explained by the structural distortion and loss of order of the Cu dimers in the paddle-wheel dimers. This method provides an effective strategy to maintain the MOF structure.

Cu-MOF-74 is an MOF material with a large specific surface area, containing highly dispersed and fully exposed unsaturated metal centers, which also has advantages in the form of nanocrystals in CO₂RR [28]. In this study, we subjected Cu-MOF-74 material to calcination to prepare CuO-400. By controlling the calcination conditions, we preserved the original rod-like structure of CuO-400 from the MOF. The calcined material was then employed in CO₂RR.

2. Results and Discussion

2.1. Electrochemical Performance of Cu-MOF-74 and CuO-400

According to reference [29], Cu-MOF-74 was synthesized using Cu(NO₃)₂·3H₂O as the copper precursor and H₄DOBDC as the organic linker, via a hydrothermal method. Subsequently, CuO-400 was obtained by calcination in air at 400 °C. To investigate the electrocatalytic performance of the MOF materials before and after calcination, linear sweep voltammetry (LSV) tests were conducted on both Cu-MOF-74 and CuO-400. Compared to the values in the N₂ environment, both Cu-MOF-74 (Figure 1a) and CuO-400 (Figure 1b) exhibited higher current densities in the CO₂ environment, indicating that both materials are conducive to CO₂ reduction. Moreover, CuO-400 showed an even higher current density, which indicates a faster electron transfer rate and a better electrocatalytic performance.

According to the LSV results, constant potential electrolysis of CO₂ on Cu-MOF-74 and CuO-400 materials was conducted within the potential range of −0.95 to −1.35 V vs. RHE. Gas and liquid products were detected using GC and ¹H NMR after electrolysis. When Cu-MOF-74 was used as the catalyst, the main product detected was HCOOH, with a maximum FE of 44.6% at −1.05 V vs. RHE (Figure 1c). However, the hydrogen evolution reaction of this catalyst was very severe, resulting in an overall low FE for CO₂RR. On the other hand, when CuO-400 was used as the catalyst, economically more favorable C2 species (C₂H₄ and C₂H₅OH) were the main products (Figure 1d). With the electrolysis potential shifting from −0.95 V to −1.35 V vs. RHE, there was an initial increase followed by a decrease in the FE of C2 products. At −1.15 V vs. RHE, the FE_C2 on CuO-400 reached a maximum of 51.7%, with 39.1% for C₂H₄ and 12.6% for C₂H₅OH; the hydrogen evolution reaction was partially suppressed, with an FE_H2 of only 18.6%. Comparatively, both the FE_C2 and partial current density of C2 products on CuO-400 were significantly higher than those on Cu-MOF-74 (Figure S1). Comparison of the electrolysis results of the materials before and after calcination shows that the CO₂ electrocatalytic performance of the calcined material is enhanced and the overall FE is improved, along with the increase in the FE of the C2 product and a significant reduction in the generation of H₂. Therefore, this derivatization strategy proves to be effective for modifying Cu-MOF-74.

2.2. Morphological and Structural Characterization of Cu-MOF-74 and CuO-400

To investigate the morphological characteristics of Cu-MOF-74 and CuO-400, the morphology and structure of the catalysts were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). According to the XRD results, characteristic XRD peaks of Cu-MOF-74 were observed at 6.76° and 11.66°, which were in excellent agreement with the theoretical values of the MOF-74 structure [30]. Meanwhile, characteristic diffraction peaks of CuO-400 observed at 2θ values of 32.2°, 35.2°, 38.5°, 48.5°, 53.3°, 61.3°, and 65.9°matched well with the standard PDF card for CuO (PDF#44-0706) [31], corresponding to the (110), (002), (111), (202), (020), (113), and (311) planes of CuO (Figure 2).

From the SEM image, it can be observed that Cu-MOF-74 exhibits a rod-like structure with no apparent pores present (Figure 3a). After calcination, the resulting CuO-400 material maintains the rod-like structure of Cu-MOF-74, with CuO nanoparticles aggregated on the surface and the emergence of larger pores. The presence of these pores may provide more reaction sites during the electrocatalytic process, thereby enhancing the efficiency of electrocatalysis (Figure 3b).

2.3. Electrochemical Performance of CuO-400, CuO-n, and CuO-c

Through electrolysis and characterization analysis, it was found that the CuO material obtained from the derivatization strategy employed for Cu-MOF-74 indeed gave good catalytic results in the CO₂RR reaction. However, how does its performance compare to CuO synthesized in other ways? To address this question, we selected CuO-n obtained using calcination, using Cu(NO₃)₂·3H₂O as the precursor and commercial CuO-c for comparison.

Firstly, the electrochemical behavior of CuO-400, CuO-n, and CuO-c catalysts in the electrocatalytic reduction of carbon dioxide was tested using LSV. As shown in Figure 4a, compared to CuO-n and CuO-c samples, the CuO-400 catalyst exhibited the highest current density, indicating faster electron transfer kinetics and a better electrocatalytic performance in the CO₂RR reaction. The LSV curves for the CuO-n and CuO-c samples under N₂ and CO₂ atmospheres are shown in Figure S2. Next, constant potential electrolysis on CuO-400, CuO-n, and CuO-c was conducted in a 0.2 M KI electrolyte solution within the potential of −1.15 V vs. RHE. The electrolytic products on CuO-n and CuO-c materials are similar to those on CuO-400, predominantly C2 products. However, the FE_C2 for both CuO-n and CuO-c was significantly lower than that of CuO-400, with 35.9% and 35.5%, respectively (Figure 4b).

2.4. Morphological and Structural Characterization of CuO-400, CuO-n, and CuO-c

To determine whether there are morphological differences in CuO materials prepared using different methods, XRD, XPS, and SEM characterization were performed on CuO-400, CuO-n, and CuO-c. It can be seen from the figures that all three methods produced pure CuO substances without characteristic diffraction peaks of other materials (Figure S3a). XPS characterization (Figure S3b–d) reveals that the elemental Cu in CuO-400, CuO-n, and CuO-c are all in the Cu²⁺ oxidation state, consistent with the characterization results obtained from XRD. From the SEM images, it can be observed that CuO-n exhibits a rod-like aggregated morphology, and no obvious pores are observed (Figure 5a). CuO-c presents a block-like aggregated structure with a smooth surface and, similarly, no pores are observed (Figure 5b). In contrast, the excellent performance exhibited by the CuO-400 catalyst may be attributed to its retention of the rod-like structure of Cu-MOF-74 and its large pores (Figure 3b).

To obtain more specific pore size data, the pore size and BET surface area of CuO-400, CuO-n, and CuO-c were studied through N₂ adsorption–desorption isotherms. As shown in Figure 5c, the CuO-400 sample exhibits an upwardly convex curve in the low P/P₀ region, as well as a rapid increase in the isotherm at higher P/P₀ due to the capillary condensation of the adsorbate. The occurrence of capillary condensation leads to hysteresis in this region, characteristic of Type IV isotherms. On the other hand, the CuO-n and CuO-c samples exhibit downwardly convex curves throughout the entire pressure range, without any inflection point in the low P/P₀ region, indicating relatively weak interactions between the adsorbate and the adsorbent under these conditions [32]. The BET surface areas of the CuO-400, CuO-n, and CuO-c samples are 11.23, 5.04, and 9.06 m² g⁻¹, respectively, with average pore sizes of 4.2, 2.0, and 1.9 nm, and pore volumes of 0.025, 0.008, and 0.009 cm³ g⁻¹, respectively (Figure 5c,d, Table S1). This indicates that CuO-400 obtained via calcination from the MOF precursor has a larger BET surface area, pore size, and pore volume compared to CuO-n and CuO-c, which have almost no pores, consistent with the analysis results from SEM images.

We also utilized double-layer capacitance testing to assess the electrochemical surface area of CuO-400, CuO-n, and CuO-c materials. The cyclic voltammetry curves for CuO-400, CuO-n, and CuO-c can be found in Figure S4. Linear fits of current versus scan rate were performed for the three materials, with the double-layer capacitance of CuO-400 (442 μF cm⁻², Figure 5e) exceeding the values of CuO-n (225 μF cm⁻²) and CuO-c (232 μF cm⁻²). This suggests that CuO-400 possesses a larger electrochemical active surface area, which is advantageous for promoting CO₂RR.

At the open circuit potential, impedance tests were conducted on CuO-400, CuO-n, and CuO-c to investigate the reaction kinetics of these materials. As shown in Figure S4d, it is apparent that CuO-400 exhibits a smaller diameter compared to CuO-n and CuO-c. This suggests that CuO-400 has a smaller charge transfer resistance and is more favorable for CO₂ reduction reactions. Meanwhile, the Tafel slope of CuO-400 was found to be 191 mV dec⁻¹ (Figure S4e), significantly lower than that of CuO-n (388 mV dec⁻¹) and CuO-c (298 mV dec⁻¹), indicating rapid CO₂RR kinetics.

2.5. The Influence of Calcination Conditions on Material Properties

To investigate the effect of calcination temperature on catalyst performance, a series of catalysts with different calcination temperatures (300, 400, and 500 °C) was prepared. The corresponding materials were named CuO-300, CuO-400, and CuO-500, respectively. Electrolysis was conducted on CuO-300, CuO-400, and CuO-500 at a potential of −1.15 V vs. RHE. According to the electrolysis results, the primary products on both CuO-400 and CuO-500 are C2 products, with the highest FE_C2 values of 51.7% and 31.6%, respectively (Figure 6a), whereas, on CuO-300, the major HCOOH and C2 products were produced with roughly equal FEs of 23.4% and 24.8%, respectively.

The electrolysis data suggest that CuO-400 obtained at a calcination temperature of 400 °C is the most favorable for CO₂RR (Figure 6a). XRD and SEM characterization tests were conducted on the above materials. XRD analysis (Figure S5a) revealed that when calcined at 300 °C, the material exhibited characteristic diffraction peaks of Cu₂O and CuO, indicating a mixture of both. However, upon increasing the calcination temperature to 400 °C and above, all transformed into CuO. A comparison of the SEM images of CuO-300, CuO-400, and CuO-500 revealed that at a calcination temperature of 300 °C, the material exhibited a rod-like structure similar to CuO-400, but no pores were observed on the surface (Figure S6a). When the calcination temperature reached 500 °C, the material structure began to collapse, showing a tendency to transform into CuO nanoparticles (Figure S6b). The BET surface areas of CuO-300, CuO-400, and CuO-500 samples are 11.86, 11.23, and 5.90 m² g⁻¹, respectively. The average pore diameters are 2.4, 4.2, and 2.7 nm, while the pore volumes are 0.026, 0.025, and 0.020 cm³ g⁻¹, respectively (Figure S7a,b, Table S1). The surface area and pore volume of CuO-300 are similar to those of CuO-400, but CuO-400 has a larger pore diameter, while all three parameters of CuO-500 are lower than those of CuO-400. This may be what gives CuO-400 a better electrocatalytic performance.

To further investigate the effect of calcination time on catalyst performance, a series of catalysts with different calcination times (0.5, 1, 2, and 3 h) were prepared. The corresponding materials were named CuO-400-0.5, CuO-400, CuO-400-2, and CuO-400-3. Electrolysis was conducted on CuO-400-0.5, CuO-400, CuO-400-2, and CuO-400-3 at a potential of −1.15 V vs. RHE. According to the electrolysis results, the main product was C2, with maximum FE_C2 values of 34.4%, 51.7%, 34.2%, and 30.0%, respectively (Figure 6b). Therefore, CuO-400 prepared with a 1 h calcination exhibited a significantly higher CO₂ electrocatalytic performance in CO₂ reduction compared to the other materials. XRD analysis revealed that the materials after calcination were all CuO (Figure S5b). SEM comparison between CuO-400-0.5, CuO-400, CuO-400-2, and CuO-400-3 showed that the material calcined for 0.5 h had a rod-like structure but no pores (Figure S6c); CuO nanoparticles calcined for 2 h had a rod-like structure (Figure S6d) and were smaller compared to CuO-400 calcinated for 1 h (Figure 3), and pores were observed on both the cross-section and surface for CuO-400; after 3 h of calcination, the rod-like structure began to collapse extensively (Figure S6e). The BET surface areas of the CuO-400-0.5, CuO-400, CuO-400-2, and CuO-400-3 samples are 8.05, 11.23, 5.38, and 8.89 m² g⁻¹, respectively. The average pore diameters are 1.7, 4.2, 2.4, and 1.1 nm, while the pore volumes are 0.024, 0.025, 0.018, and 0.023 cm³ g⁻¹, respectively (Figure S7c,d, Table S1). CuO-400 exhibits the largest surface area, pore diameter, and pore volume among the four materials, which may contribute to its superior electrocatalytic performance.

Based on the electrolysis results and characterization analysis, we ultimately determined that calcination at 400 °C for 1 h in an air atmosphere was the optimal calcination condition for Cu-MOF-74. Under this calcination condition, Cu-MOF-74 could maintain its rod-like structure with abundant pores, resulting in the best FE_C2.

2.6. Electrode Stability in CO₂ Electroreduction

To assess the stability of the CuO-400 electrocatalytic material, we subjected the CuO-400 material to prolonged electrolysis and performed SEM characterization. The corresponding total current density–time curve (i-t curve) is shown below. From Figure 7a, it can be observed that during prolonged electrolysis, the current density remains relatively stable, at approximately 39.7 mA cm⁻². Within 6 h of electrolysis, the Faradaic efficiency of the C2 product remains at around 51%, indicating that the CuO-400 material exhibits an efficient and stable electrocatalytic CO₂ reduction performance during this period.

From the SEM image (Figure 7b), it can be seen that the material maintains its rod-like structure without collapsing even after electrolysis, indicating that the CuO-400 material possesses an efficient and stable electrocatalytic CO₂ reduction performance. As a comparison, SEM characterization was also conducted on CuO-n and CuO-c after electrolysis. The results show that CuO-n transformed entirely from its original solid nanorod-like structure to nano-spherical particles after electrolysis (Figure S8a). Although CuO-c remains as solid block-like particles after electrolysis, nano-spherical particles are also observed on its surface (Figure S8b). SEM analysis results indicate that the stability of CuO-n and CuO-c is comparably poorer than that of the CuO-400 material.

3. Materials and Methods

3.1. Materials

Copper nitrate trihydrate (Cu(NO₃)₂·3H₂O, >99%) and potassium iodide (KI, 95%) were purchased from Sinopharm (Shanghai, China). Cupric oxide (CuO, 98%) and 2,5-dihydroxyterephthalic acid (H₄DOBDC, 99%) were obtained from Innochem (Atlanta, GA, USA). Nafion solution (5 wt%) was supplied by Sigma-Aldrich Chemical Reagent Co., Ltd. (St. Louis, MO, USA). All chemicals were used without further purification.

3.2. Catalyst Synthesis and Electrode Preparation

3.2.1. Synthesis of Cu-MOF-74

Using the classical synthetic method [29], 2.2 g of 2,5-dihydroxyterephthalic acid (H₄DOBDC) and 5.9 g of Cu(NO₃)₂·3H₂O were dissolved in 238 mL of DMF and 12 mL of isopropanol. After stirring until these were dissolved, the mixed solution was transferred to a 250 mL conical flask and kept in an 80 °C oven for 18 h. After synthesis, the resulting solid–liquid mixture was cooled to room temperature, washed and filtered with DMF three times, then soaked in anhydrous methanol solution; the solution was changed every 24 h and this was repeated 4 times. The reddish-brown powder was then placed in a vacuum drying oven and was dried at 60 °C for 12 h.

3.2.2. Synthesis of CuO-T with Different Calcination Temperatures

The Cu-MOF-74 was placed in an air atmosphere; was heated at a rate of 1 °C/min to temperatures of 300, 400, and 500 °C, respectively; and was held for 1 h at each temperature. The resulting materials were named CuO-300, CuO-400, and CuO-500, respectively.

3.2.3. Synthesis of CuO-400-X with Different Calcination Times

The Cu-MOF-74 was placed in an air atmosphere and heated at a rate of 1 °C/min and was then maintained at 400 °C for 0.5, 1, 2, and 3 h, respectively. The resulting materials were named CuO-400-0.5, CuO-400, CuO-400-2, and CuO-400-3, respectively.

3.2.4. Synthesis of CuO-n

For comparison, CuO-n was obtained by grinding Cu(NO₃)₂·3H₂O and placing it under an air atmosphere and keeping it at 400 °C for one hour at a heating rate of 1 °C/min.

3.2.5. Electrode Preparation

A total of 2 mg of catalyst was weighed and added to 20 µL of Nafion 117 solution and 100 µL of deionized water and was sonicated for 20 min to make a homogeneous mixture of the materials. The mixture was then uniformly applied to a 1 cm × 1 cm carbon paper and dried to obtain a working electrode. The method for preparing the working electrode described here is applicable to all materials prepared in this study. The prepared working electrode was utilized for linear sweep voltammetry, electrochemical surface area testing of the electrode, and constant potential electrolysis.

3.3. Material Characterization

The morphology and crystal structure of the samples were characterized by scanning electron microscopy (SEM) using a ZEISS Gemini 450 (Jena, Germany) operating at 2 kV and 100 mA. The crystal structure of the samples was characterized using X-ray diffraction (XRD), using an Ultima IV instrument (Rigaku, Akishima, Japan) with a Cu-Kα (λ = 1.5406 Å) X-ray source. Nitrogen adsorption–desorption isotherms were measured on a BELSORP-MAX instrument (BEL, Toyonaka, Japan). X-ray photoelectron spectroscopy (XPS) was performed using an AXIS Ultra DLD instrument (Shimadzu, Kyoto, Japan), with materials irradiated using an Al-Kα X-ray beam; the binding energy of C 1s at 284.8 eV was used as the standard.

3.4. Electrochemical Analysis

All electrochemical measurements were carried out using an electrochemical workstation (CHI660E, Shanghai, China). An H-type cell consisting of a working electrode, a platinum wire counter electrode, and a saturated calomel reference electrode was used. A 0.2 M potassium iodide (KI) electrolyte was chosen and carbon dioxide was introduced into the cell at a flow rate of 15 mL/min. Prior to each experiment, the working electrode was freshly prepared and linear sweep voltammetry (LSV) curves were used to evaluate the electrocatalytic performance of the prepared electrode. The measured potential (V vs. SCE) was converted to the RHE reference scale using the equation E_RHE = E_SCE + 0.0591 × pH + 0.241. The electrochemical active surface area was tested using the double-layer capacitance (C_dl) method, employing the same electrode system as in the Linear Sweep Voltammetry (LSV) electrode system. Prior to testing, the electrolysis cell was purged with N2 for 0.5 h. Different scan rates were applied from 0.83 V vs. RHE to 0.63 V vs. RHE to obtain cyclic voltammograms. The calculation method for C_dl is given using the following formula: C_dl = I_c/ᴠ, where I_c represents the working electrode current at a certain potential, and ᴠ denotes the scan rate.

Gaseous products such as C₂H₄, CO, and H₂ were analyzed using a gas chromatograph (Agilent Technologies 7890A, Santa Clara, CA, USA) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). C₂H₄ was detected via FID (Figure S9), while H₂ and CO were detected via TCD (Figures S10 and S11). Liquid products were collected and analyzed using a GC2014 gas chromatograph and ¹H NMR technique, where the GC2014 gas chromatograph with HS-9A headspace injection was used to detect CH₃OH and C₂H₅OH (Figure S12), and the ¹H NMR technique was used to detect HCOOH (Figure S13).

The Faradaic efficiency for specific products was calculated using the following formula: FE = Z × n × F/Q, where n represents the amount of substance, Z represents the number of electrons transferred for product formation, F is the Faraday constant (96,485 C/mol), and Q represents the total charge passed during electrolysis. The partial current density for a specific product is equal to the total current density multiplied by the Faradaic efficiency of that product.

4. Conclusions

In summary, we propose a derivative strategy for Cu-MOF-74 and successfully synthesized a CuO-400 electrocatalyst by controlling the calcination temperature and time. This catalyst can be converted into CuO, while maintaining the rod-like porous structure of Cu-MOF-74 during calcination; the optimal calcination conditions are 400 °C for 1 h. When applied to CO₂ electrochemical reduction reactions, CuO-400 exhibited a high electrocatalytic performance, with C2 as the main product and a maximum Faradaic efficiency for C2 of 51.7%. Compared to the uncalcined Cu-MOF-74, CuO-400 showed reduced hydrogen evolution ability, and its catalytic performance towards CO₂RR surpassed those of CuO-n and CuO-c catalysts. Additionally, CuO-400 exhibited a higher stability compared to CuO-n and CuO-c, without significant collapse before and after electrolysis. This work presents a simple strategy to utilize morphology effects for improving the selectivity of copper-based catalysts in converting CO₂ into C2 products, which can be widely applied to prepare other Cu-MOF-derived catalysts for highly selective CO₂ reduction.