Enhancing local K⁺ adsorption by high-density cube corners for efficient electroreduction of CO₂ to C₂₊ products

Abstract

Reducing carbon dioxide (CO₂) to high value-added chemicals using renewable electricity is a promising approach to reducing CO₂ levels in the air and mitigating the greenhouse effect, which depends on high-efficiency electrocatalysts. Copper-based catalysts can be used for electroreduction of CO₂ to produce C₂₊ products with high added value, but suffer from poor stability and low selectivity. Herein, we propose a strategy to enhance the field effect by varying the cubic corner density on the surface of Cu₂O microspheres for improving the electrocatalytic performance of CO₂ reduction to C₂₊ products. Finite element method (FEM) simulation results show that the high density of cubic corners helps to enhance the local electric field, which increases the K⁺ concentration on the catalyst surface. The results of CO₂ electroreduction tests show that the FE_C2+ of the Cu₂O catalyst with high-density cubic corners is 71% at a partial current density of 497 mA cm⁻². Density functional theory (DFT) calculations reveal that Cu₂O (111) and Cu₂O (110) can effectively reduce the energy barrier of C–C coupling and improve the FE_C2+ at high K⁺ concentrations relative to Cu₂O (100). This study provides a new perspective for the design and development of efficient CO₂RR catalysts.

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Introduction

The massive extraction and utilization of fossil fuels has brought about a dramatic increase in the amount of CO₂ in the atmosphere, leading to global warming and climate change, which poses serious environmental problems.¹ The efficient capture and recycling of CO₂ is widely recognized as the key to mitigating environmental problems related to the greenhouse effect and sea level rise, and promoting sustainable development.^2–4 In recent years, it has been found that the electrochemical conversion of CO₂ into C₂₊ products with high application value, using renewable electricity, is one of the most promising technologies for realizing the carbon cycle.^5–12 Currently, Cu-based catalysts are attracting attention as the only catalysts that can realize C–C coupling and electroreduction of CO₂ to C₂₊ products.^13–21

Nevertheless, the thermodynamics and kinetics of C–C coupling are relatively slow in the CO₂RR.^8,22–26 Therefore, modification of Cu-based catalysts, such as crystal surface modulation,^27–29 surface restructuring,^30–33 and oxidation state optimization,^16,34–36 to improve the efficiency of C₂₊ products remains a hot topic and challenge. The adjustment of the crystal surface or surface structure has a significant effect on improving the performance of Cu-based catalysts.³⁷ On the one hand, the exposed faces of Cu-based catalysts have a great influence on the catalytic activity and selectivity in the CO₂RR process.^38,39 On the other hand, the field effect induced by the tip structure of Cu-based catalysts plays an important role in the CO₂RR process.^40–42 Numerous studies have found that the active sites of the CO₂RR are usually located on the top corners and ridges of the catalysts.^43–45 Previous reports have focused on the effects of vertex curvature or array orientation on the field effect; however, the vertices and ridges on the exposed surface are particularly critical to catalytic activity and selectivity, while the effects of vertex density or tip-exposed crystal faces on the catalyst surface for the catalytic performance have been rarely reported, and also their effects on the CO₂RR are unknown.

Herein, we investigated the effect of the density of cubic corners on the field effect with FEM simulations, and the effect of the vertices and ridges on the cubic corners on the catalytic performance was studied by DFT calculations. The FEM simulation results found that the higher density of the cube corners had a stronger influence on the field effect, which is favorable for the aggregation and adsorption of K⁺. In the experiment, we prepare a Cu₂O microsphere with cubic corners on the surface,⁴⁶ which is the same as the results of FEM simulation. DFT calculations demonstrate that, at stronger electric fields and higher K⁺ concentrations, the Cu₂O (111) and (110) faces on the cube corner contribute to the adsorption and C–C coupling of *CO intermediates, as well as to the desorption of C₂₊ products. This work fills the gap in the application of the localized electric field induced by different density nano-arrays in CO₂ electroreduction, and also illustrates the roles of vertices and ridges on the exposed crystal in CO₂ electroreduction, which provides new perspectives for the design of efficient CO₂RR catalysts and contributes to the mitigation of environmental problems caused by greenhouse gases.

Results and discussion

FEM simulation

We used COMSOL Multiphysics field simulations to investigate the effect of the density of cubic corners on the local electric field and K⁺ concentration. Five models with different cube corner densities (Fig. S1†) were developed using FEM, and the localized electric field and K⁺ concentration on their cube corners were also investigated.

As shown in Fig. 1a–c and S2–S4,† significant local electric field aggregation effects can be observed for a single cube corner. According to the principle of electric field superposition, as the number of cube corners increases, the electric field strength of the cube angle shows an increasing trend. M3 is a microsphere composed of cubic inflections (Fig. 1c), which has the highest density of cubic corners and the maximum localized electric field strength of 565 V m⁻¹. We simulated the K⁺ concentration on the cubic corner surface using the transport of diluted species (tds) physics modules in COMSOL Multiphysics. From Fig. 1a and b and S5–S7,† it is found that the distribution of K⁺ concentration is positively correlated with the distribution of local electric field strength. As the local electric field intensity increases, the K⁺ concentration on the cube corner surface gradually increases, with M3 having the maximum K⁺ concentration of 3.39 M. The localized electric field facilitates the adsorption and aggregation of K⁺, which is mainly caused by the field effect induced reagent concentration, because positively charged K⁺ will be aggregated on the corner surfaces of the cube possessing a strong negative electric field under electrostatic action. The high concentrations of K⁺ facilitate the adsorption of CO₂ and the generation of C₂₊ products (Fig. 1d).

Fig. 1 (a) The electric field (upper half) and K⁺ concentration (lower half) distribution on M-4 and M-5 through COMSOL Multiphysics simulations. (b) The electric field and K⁺ concentration at the tips of M-4 and M-5. (c) The electric field distribution on M-3. (d) A schematic illustration of the local electric field and K⁺ ions on the Cu₂O cube corner for promoting C₂ formation.

Catalyst synthesis and characterization

Cu₂O-X microspheres with cube corners were synthesized using a solvothermal method (X is the volume of water used, which is 0, 0.5, 1, 2, 4, and 10 mL respectively, and the corresponding samples are named Cu₂O-0, Cu₂O-0.5, Cu₂O-1, Cu₂O-2, Cu₂O-4, and Cu₂O-10, respectively). The synthesis mechanism and synthesis process of Cu₂O-0 are shown in Fig. 2a and S8.† In order to better observe the growth mechanism of the Cu₂O-0 catalyst, its liquid color and product morphology were investigated over time during the synthesis process (Fig. S9†). The scanning electron microscopy (SEM) images of Cu₂O-0 are shown in Fig. 2b and c, and it can be seen that the surface of Cu₂O-0 microspheres has a large number of cube corners. The transmission electron microscopy (TEM) image (Fig. 2d) shows more visually that Cu₂O-0 consists of microspheres with numerous vertices and ridges on the surface. The angles of the vertices are mostly 90°, which better indicates that the tips of the surface on the Cu₂O-0 microspheres are cubic inflection corners. From the inset in Fig. 2b, the air/water contact angle of Cu₂O-0 is 141°, which indicates that it has good hydrophobicity. Fig. S10† shows the air/water contact angle of Cu₂O-X. Fig. 2e–g show the high-resolution TEM (HRTEM) images of Cu₂O-0. Fig. 2e shows the Cu₂O crystal planes at the corners of different cubes (as shown in the inset). HRTEM images (Fig. 2f and g) and FFT patterns (inset) show that the lattice spaces are 0.301, 0.246 and 0.213 nm respectively, which can be well matched with the (110), (111) and (200) crystal planes of cubic Cu₂O. The SEM and HRTEM analyses showed that the morphology of Cu₂O-X did not change significantly with increasing water content (Fig. S11†). The peaks located at 29.6°, 36.4°, and 42.3° correspond to the (110), (111), and (200) crystal planes of Cu₂O (JCPDS: PDF#99-0041), respectively, which indicates that the synthesized material is predominantly Cu₂O and has a good crystallinity (Fig. 2h). Fig. S12† shows that the Cu₂O-X catalysts with different water contents have the same Cu₂O phase. Fig. 2i shows that Cu is predominantly +1-valent, some of which is +2-valent; the Cu²⁺ in the XPS is most likely caused by the oxidation of the Cu₂O when it is exposed in the air. In summary, the synthesized catalysts are consistent with the FEM model.

Fig. 2 (a) Schematic formation mechanism of the Cu₂O-0 catalyst. (b and c) SEM images of the Cu₂O-0 catalyst. (d) TEM image of the Cu₂O-0 catalyst. (e–g) HRTEM images of the Cu₂O-0 catalyst. (h) The XRD pattern of the Cu₂O-0 catalyst. (i) The XPS spectrum of the Cu₂O-0 catalyst.

Electrochemical CO₂RR performance evaluation

Tests of the CO₂ electroreduction properties of the catalysts were performed in a flow cell (Fig. S13†). The linear sweep voltammetry (LSV) test results (Fig. 3a and S14†) show that Cu₂O-0 has greater positive onset potential and greater negative current density, indicating that Cu₂O-0 has higher CO₂RR activity. The liquid and gas products were examined by ¹H NMR spectroscopy (Fig. S15†) and gas chromatography (GC) (Fig. S16 and S17†), respectively. In terms of product distribution, the reduction products of all Cu₂O-X catalysts had the same trend with increasing applied current, with the faradaic efficiency (FE) of C₂₊ increasing and then decreasing, and the FE of H₂ decreasing and then increasing (Fig. 3b and S18†). From Fig. 3c and d, it was found that the Cu₂O-0 catalyst possessed the largest FE_C2+ and the smallest FE_H2. The FE_C2+ and FE_H2 of the Cu₂O-0 catalyst were 71% and 12% at a partial current density of 497 mA cm⁻², respectively. Moreover, the FE_C2+ of the Cu₂O-0 catalyst was 1.8 times higher than the FE_C2+ of the Cu₂O-10 catalyst.

Fig. 3 (a) The LSV curves of the Cu₂O-0 catalyst under an N₂ atmosphere and CO₂ atmosphere. (b) FEs of various products on the Cu₂O-0 catalyst during the CO₂RR at different current densities. (c) C₂₊ and H₂ FEs and current densities vs. applied potential of the Cu₂O-0 catalyst. (d) C₂₊ FEs of Cu₂O-X catalysts. (e) Comparison of the adsorbed-K⁺ concentration on Cu₂O-X catalysts. (f) Results of CO adsorption responses on Cu₂O-X catalysts under different applied voltages. (g) Deconvoluted Cu Auger LMM spectra of the Cu₂O-0 catalyst before and after the CO₂RR. (h) CO₂RR stability on the Cu₂O-0 catalyst at 700 mA cm⁻².

We have conducted multiple studies to better understand the differences in catalytic performance of different Cu₂O-X catalysts. By recording the cyclic voltammetry curves (Fig. S19†) of Cu₂O-X catalysts at different scan rates in the non-Faraday zone, their double-layer capacitance (C_dl) (Fig. S20†) was calculated, which was used to estimate their surface roughness coefficient (R_f) and electrochemically active surface area (ECSA) (Fig. S21 and Table S1†). The results showed that the Cu₂O-0 catalyst had the largest C_dl (42.8 mF cm⁻²), R_f (713.3), and ECSA (713.3 cm²), thus indicating that the Cu₂O-0 catalyst can produce more active sites than other Cu₂O-X catalysts, which is more favorable for the CO₂RR. Meanwhile, Fig. S22† shows that the Cu₂O-0 catalyst has the smallest Tafel slope, which also indicates that the Cu₂O-0 catalyst has the best CO₂RR performance.

According to the FEM simulation results, it is illustrated that the high density of cubic corners contributes to the adsorption of K⁺ and CO. To validate the FEM simulation results and to demonstrate the advantages of high-density cubic corners, we performed K⁺ and CO adsorption experiments (schematic shown in Fig. S23 and S24†). Fig. 3e and f and Table S2† show that the adsorption capacity of K⁺ and CO on the Cu₂O-X catalysts increases gradually with the increase of the cube corner density, and the Cu₂O-0 catalyst has the largest cube corner density and the strongest K⁺ and CO adsorption capacity.

As shown in Fig. 3h, the Cu₂O-0 catalyst also exhibited excellent long-term stability, operating at a constant current density of 700 mA cm⁻² for 24 h without a significant change in the applied voltage or FE_C2+, with the FE_C2+ remaining around 70%. In order to better understand the long-term stability and selectivity of the Cu₂O-0 catalyst, SEM, XRD, and XPS were used to characterize the Cu₂O-X catalyst before and after the CO₂RR. From Fig. S25,† the morphology of the Cu₂O-0 catalyst was almost unchanged before and after the CO₂RR. XRD (Fig. S26 and S27†) patterns showed that the physical phase of the Cu₂O-0 catalyst was maintained before and after the reaction. The Cu Auger LMM spectra (Fig. 3g and S28†) were recorded and deconvoluted to distinguish Cu⁺ and Cu⁰ before and after the CO₂RR.⁴⁷ The ratio of the Cu⁰ fraction increased from 17.14% to 20.23%, and the ratio of the Cu⁺ fraction decreased from 68.72% to 65.34% in the Cu₂O-0 catalyst. The Cu Auger LMM spectra illustrated that Cu⁺ in the Cu₂O-0 catalyst was well maintained during the CO₂RR process. The reason for Cu⁺ being maintained in the Cu₂O-0 catalyst may be due to the high density of cubic corners on the Cu₂O-0 catalyst microspheres, which gives the surface a strong localized electric field and high K⁺ concentration, leading to accelerated electron transport on the cubic corner surface and the inhibition of the redox reaction of Cu⁺/Cu⁰.⁴⁷ These lead to the excellent selectivity and long-term stability of the Cu₂O-0 catalyst.

In situ Raman and in situ FT-IR measurements

To further understand the reaction mechanism of the CO₂RR, we performed in situ Raman and in situ FT-IR tests on the Cu₂O-0 and Cu₂O-4 during the CO₂RR. The in situ Raman testing equipment is shown in Fig. S29.† As shown in Fig. 4a and S30a,† Cu₂O-0 and Cu₂O-4 show two peaks around ∼280 and ∼365 cm⁻¹, which are caused by the rotational and stretching vibrations of *CO on the Cu active site after applying the voltage.^48–50 In addition, the Cu₂O-0 and Cu₂O-4 catalysts have three peaks associated with Cu^δ+ near ∼415, ∼520, and ∼620 cm⁻¹ in the low-energy region (Fig. 4b and S30b†), corresponding to the modes resulting from a multi-phonon process – the T_2g vibrational mode and the T_1u mode of Cu₂O.^{47,49,51–55} With the increase of applied potential, the Cu⁺ characteristic peaks (∼520 cm⁻¹) of Cu₂O-0 catalysts are well preserved, and this is consistent with the XRD (Fig. S26†) and XPS (Fig. 3g) results measured before and after the CO₂RR, fully indicating that the Cu valence state in the Cu₂O-0 catalyst is stable during the CO₂RR process. In the high-energy region, the signals near ∼1015 and ∼1066 cm⁻¹ are attributed to the adsorption of HCO₃⁻ and CO₃²⁻ (Fig. 4c and S30c†),^50,56 respectively, which are formed on the surface of the catalyst after CO₂ is dissolved in the electrolyte. The local hydrogen proton concentration and local microenvironment around the catalysts during the CO₂RR were evaluated by monitoring the ratio of HCO₃⁻ and CO₃²⁻ adsorbed on the catalyst surface (Fig. S31†).^56,57 The results show that the local hydrogen proton depletion on the surface of the Cu₂O-0 catalyst is more stable than that of the Cu₂O-4 catalyst, thus maintaining the stability of the local microenvironment and the durability of the C₂₊ products on the catalyst.⁵⁰ In addition, the signals generated in the regions around ∼1840 cm⁻¹ and ∼2060 cm⁻¹ belong to the bridge-boundary *CO (*CO_bridge) and top-boundary *CO (*CO_atop) conformations,^48,58 respectively. As the cathode applied voltage became more negative, the *CO_bridge signal on the Cu₂O-0 catalyst changed weakly (Fig. 4d), and the *CO_bridge signal on the Cu₂O-4 catalyst basically disappeared (Fig. S30d†), suggesting that most of the *CO intermediates were bound at the top and a small portion of them were bound at the bridge sites in the Cu₂O-0 catalyst, whereas the *CO intermediates were mainly from the top of the Cu₂O-4 catalyst. The mixing of *CO_bridge and *CO_atop is more favorable for the C–C coupling.^59,60 Therefore, the *CO intermediates on the Cu₂O-0 catalyst are more favorable for C–C coupling and the production of C₂₊ products.

Fig. 4 In situ Raman spectra of the Cu₂O-0 catalyst in the range 200–450 cm⁻¹ (a), 400–750 cm⁻¹ (b), 900–1150 cm⁻¹ (c) and 1800–2200 cm⁻¹ (d) at various applied potentials (vs. RHE). (e) Ratio of the low-frequency and high-frequency bands in the range 2000–2200 cm⁻¹ of Cu₂O-0 and Cu₂O-4 catalysts at various applied potentials. (f and g) In situ FT-IR spectra of the Cu₂O-0 catalyst at various applied potentials (vs. RHE).

The *CO_atop intermediates on the catalyst can be divided into low and high frequency bands (LFB and HFB). According to previous studies, the signal in the LFB belongs to a dynamic *CO intermediate, which contributes to subsequent C–C coupling. The HFB stretching band is attributed to the separated static *CO intermediate, which makes it difficult to perform C–C coupling.^48,60 As seen in Fig. 4e, we compared the LFB and HFB band intensities. The low/high value of the Cu₂O-0 catalyst is larger than that of the Cu₂O-4 catalyst, indicating that the Cu₂O-0 catalyst is more favorable for C–C coupling and C₂₊ product generation.⁵⁰ Through observing the changes in the intensity of the *CO_atop peaks, it is found that as the external applied voltage becomes more negative, the *CO intermediates first accumulate, then C–C coupling generates C₂₊ products on the Cu₂O-0 catalyst. Due to the involvement of more *CO intermediates in C–C coupling, the *CO peak intensity shows a decreasing trend on the Cu₂O-0 catalyst (Fig. 4d),⁶¹ while the relative intensity of the HFB (Fig. S30d†) tends to increase at higher potentials on the Cu₂O-4 catalyst, indicating an increase in static *CO intermediates and a decrease in C–C coupling ability on the Cu₂O-4 catalyst.⁴⁸ This is consistent with the electrochemical CO₂RR results.

In situ FT-IR tests was performed to investigate the reaction pathways of the C₂₊ products (Fig. S32†). In Fig. 4f and g and S33,† the peaks at ∼1720 and ∼2050 cm⁻¹ are the characteristic peaks of *CO_bridge and *CO_atop,^62,63 respectively. This is the same species of *CO intermediates observed in in situ Raman spectra. The characteristic peaks at ∼1330 and ∼1440 cm⁻¹ belong to the C–OH and C–O stretching modes of *COOH intermediates, respectively, which help to generate *CO intermediates on the catalysts.^64,65 Compared with Cu₂O-4, the *COOH peak intensity on Cu₂O-0 is significantly stronger, but its *CO_atop peak intensity is weak, indicating that the *CO intermediates produced by *COOH on Cu₂O-0 are more involved in C–C coupling and C₂₊ products.⁶⁶ The absorption peaks near ∼1090, ∼1180 and ∼1590 cm⁻¹ are attributed to *OC₂H₅ and *OCCOH intermediates, respectively, which are key intermediates of C₂₊ products.^56,63,67 The *OCCO intermediates appear at ∼1530 cm⁻¹, indicating that the C–C coupling mode on the catalyst is likely due to dimerization of the *CO intermediate, leading to further hydrogenation into *OCCOH.^68–70 As the applied voltage becomes more negative, the accumulation of *CHO (∼1041 and ∼1480 cm⁻¹) and the weakening of *OCCHO (∼1290 cm⁻¹) peak intensity on the Cu₂O-0 catalyst indicate that it is difficult to achieve C–C coupling of *CO + *CHO, which also indirectly confirms that the C–C coupling mode is *CO + *CO.^62,71

The performance differences between Cu₂0-0 and Cu₂0-4 were understood by in-depth analysis of *CO intermediates. Research findings suggest that the intermixing of *CO_bridge and *CO_atop was more favorable for the production of the C₂₊ products, which may be due to the ease of *CO_bridge in promoting *CO dimerization.⁷² With the increase of negative voltage, the intensity of *CO_bridge on Cu₂O-0 does not change obviously, but the intensity of the *CO_atop first enhances and then decreases, indicating that *CO intermediates accumulate first, and then more *CO intermediates participate in the C–C coupling process on Cu₂O-0.⁶³ The change trend of *CO_atop on the Cu₂O-0 catalyst in the in situ FT-IR spectrum is consistent with its in situ Raman spectrum (Fig. 4d). However, as the applied voltage increases, the *CO_bridge peak (∼1720 cm⁻¹) of the Cu₂O-4 catalyst decreases and almost disappears. At the same time, the intensity of the *CO_atop peak (∼2050 cm⁻¹) gradually increases (Fig. S33†), indicating that C–C coupling occurs with difficulty on the Cu₂O-4 catalyst.⁶³ The results of in situ FT-IR are consistent with those of in situ Raman and electrochemical CO₂RR.

DFT theoretical calculations

DFT theoretical calculations were used to gain a deeper understanding of the mechanism of Cu₂O-X catalysts promoting the electro-reduction of CO₂ to C₂₊ products. We performed DFT calculations to investigate the adsorption capacity of the reaction intermediate *CO and the product C₂H₄ at the Cu₂O (100), (111) and (110) interface at different K⁺ concentrations as well as the Gibbs free energy of the C–C coupling. We developed a DFT model of the same Cu₂O crystal surface as the catalyst under study (Fig. S34†). As shown in Fig. 5a and b and S35–S40, and Tables S3 and S4,† *CO and *C₂H₄ adsorption on the Cu₂O (100) crystallite were stronger than that on Cu₂O (111) and (110) crystallites. It was very difficult for C₂H₄ to overflow from the Cu₂O (100) crystal surface, so the amount of C₂₊ product produced by the Cu₂O (100) crystal surface was low. Unlike the Cu₂O (100) crystal faces, the adsorption of *CO was weaker on the Cu₂O (111) and (110) crystal faces, but the introduction of K⁺ led to the enhancement of *CO adsorption; at the same time, the adsorption of *C₂H₄ on the Cu₂O (111) and (110) crystal faces was weaker, and the C₂H₄ produced was readily desorbed out from the Cu₂O (111) and (110) crystal faces, so the amount of C₂₊ product produced by the Cu₂O (111) and (110) crystal faces was higher.

Fig. 5 Adsorption energies of (a) CO and (b) C₂H₄ on three crystalline surfaces of Cu₂O (100), (111) and (110) at three K⁺ concentrations of 0 K⁺, 1 K⁺ and 2 K⁺, respectively. (c) Adsorption configurations of reaction intermediates on the Cu₂O (110) structure at the K⁺ concentrations of 2 K⁺. Gibbs free energy pathways for C–C coupling on three crystalline surfaces of Cu₂O (100), (111) and (110) at three K⁺ concentrations of 0 K⁺ (d), 1 K⁺ (e) and 2 K⁺ (f), respectively.

From the in situ characterization and DFT calculations (Fig. S41†), the pathway diagram of the Cu₂O-X catalyst to generate C₂₊ products was constructed and is shown in Fig. S42.†⁶¹ The critical step to generate C₂₊ products is the coupling of two *CO intermediates into *OCCO intermediates. Fig. 5c shows the schematic diagram of the CO₂RR on the Cu₂O (110) crystal surface under 2 K⁺ concentration. Fig. S43–S45† are schematic diagrams of the modeling of C–C coupling as well as hydrogenation. From Fig. 5d–f and S46–S49, and Table S5,† it is found that the Gibbs free energies of C–C coupling on all three crystalline surfaces of Cu₂O (100), (111) and (110) are decreasing with the increase of K⁺ concentration. The Gibbs free energy of C–C coupling on the Cu₂O (110) (0.31 eV) and (111) (0.45 eV) crystal surfaces is smaller than that on the Cu₂O (100) (0.46 eV) crystal surface at 2 K⁺ concentration, which suggests that the Cu₂O (110) and (111) crystal surfaces are more favorable for C–C coupling at high K⁺ concentration. At the same time, experimental support was provided for the DFT calculation results (Fig. S50†). In the experiment, Cu₂O catalysts with different crystal planes were synthesized and the electrocatalytic CO₂ reduction performance was studied. It was found that the experimental results were consistent with the DFT calculation results.

Conclusions

In summary, we propose a strategy to enhance the field effect and thus improve the catalyst's performance for the electroreduction of CO₂ by changing the density of cubic corner arrays on the catalyst surface. CO₂RR experimental results indicated that the FE_C2+ of the Cu₂O catalyst with high-density cubic corners was 71% at a partial current density of 497 mA cm⁻², and the FE_C2+ of this Cu₂O-0 catalyst was 1.8 times higher than the FE_C2+ of the microcubic Cu₂O catalyst. Moreover, the cubic corner arrays on the surface of Cu₂O microspheres help to improve the hydrophobicity of the catalyst and reduce the occurrence of its competing HER. FEM simulations and DFT calculations demonstrated that the high density of cubic corners contributed to the enhancement of the local electric field, which increased the K⁺ concentration in the local microenvironment and enhanced the adsorption of *CO intermediates on the catalyst surface. The increase in the density of cubic corners leads to a higher number of vertices (Cu₂O (111)) and ridges (Cu₂O (110)). Relative to Cu₂O (100), Cu₂O (111) and Cu₂O (110) can effectively reduce the energy barrier of C–C coupling and improve the Faraday efficiency of C₂₊ products at high K⁺ concentrations. This strategy can not only effectively improve the CO₂RR performance of the catalysts, but also indicates that the surface structure of the catalysts plays an important role in their CO₂RR performance, which provides a new idea for the design of efficient CO₂RR catalysts.

Data availability

Data supporting the findings of this study are available within the article ESI.†

Author contributions

Hu Zang: conceptualization, data curation, formal analysis, investigation, methodology, software, writing – original draft, and writing – review & editing; Changjiang Liu, Qinyuan Ji, Jiahao Wang, and Haiyan Lu: data curation, formal analysis, investigation, and software; Nan Yu: investigation, methodology, software and validation; Baoyou Geng: conceptualization, formal analysis, investigation, methodology, resources, funding acquisition, supervision, project administration, and writing – review & editing.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

We thank the National Natural Science Foundation of China (22171005), the Anhui Province Outstanding Research and Innovation Team Project for Universities (2023AH010030), and the University Synergy Innovation Program of Anhui Province (GXXT-2020-005, GXXT-2021-012, GXXT-2021-013, and GXXT-2022-007) for supporting this work.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4sc02170c

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