Selective electroreduction of CO₂ into CO over Ag and Cu decorated carbon nanoflakes

Abstract

The electrocatalytic CO₂ reduction reaction (eCO₂RR) has the potential to effectively cut carbon emission. However, the activity and selectivity of eCO₂RR catalysts are topical due to the intricacy of the reaction components and mechanism. Herein, we have decorated silver and copper nanoparticles over carbon nanoflakes to achieve an Ag–Cu NPs/C system that enables selective reduction of CO₂ into CO. The catalyst is prepared by incorporating Ag nanoparticles into a Cu-BTC MOF (HKUST-1) and subsequent carbonization that alters the surface composition, with improved activity and faradaic efficiency (FE) towards selective CO₂ reduction. The evaluation of electrocatalytic performance reveals that the synthesized catalyst exhibits enhanced electrocatalytic activity and selectivity with a FE_CO of ∼ 90% at −0.79 V_RHE and a current density (j) of 44.15 mA cm⁻² compared to Ag-NPs and Cu/C. The durability test over 40 h confirms the outstanding stability of Ag–Cu NPs/C. The lower Tafel slope value of only 75 mV dec⁻¹ corresponds to the fast reaction kinetics on the surface of Ag–Cu NPs/C. The synthetic protocol in this work offers an easy approach to the betterment of a cost-effective electrocatalyst with improved FE.

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Introduction

Using carbon dioxide (CO₂) as an alternative source of fuel is one approach to reduce CO₂ emission and to provide a green source of energy.^1–4 The electrochemical CO₂ reduction reaction (eCO₂RR) is considered the most efficient technique⁵ for the sustainable conversion of carbon dioxide into various valuable compounds^6,7 such as acids,⁸ carbon monoxide (CO),⁹ alcohols,¹⁰ and hydrocarbons.^11,12 Carbon monoxide could be used as a starting material for the production of various useful chemicals.¹³

The eCO₂RR faces a few challenges including thermodynamic stability and kinetically inert nature of CO₂.^14–16 The conversion of CO₂ into CO also competes with the hydrogen evolution reaction (HER).¹⁷ Therefore, development of highly selective and efficient eCO₂RR catalysts is a major challenge.^18,19 Many electrocatalysts, such as single-atom catalysts, metallic nanoparticles, metal organic frameworks (MOFs), covalent organic frameworks (COFs), and metal-free carbon based catalysts, have been utilized for the eCO₂RR to CO.^20–22 MOF derived carbon serves as an ideal support²³ due to its high surface area, porosity, thermal stability, and chemical stability.^24–26 In MOF derived nanomaterials, the inbuilt synergism between metallic nanoparticles dispersed over the carbon matrix results in improved catalytic performance.^27–29

Recently, catalysts based on transition metals have been explored as CO₂ reduction catalysts.^30,31 Precious metals such as Au, Ag, and Pd are highly active in the eCO₂RR to CO but their high cost hinders the commercialization.^32–35 Thus, non-noble metal based catalysts are the topic of interest nowadays. The incorporation of non-noble metals into precious metal based catalysts reduces the cost and has the ability to enhance activity towards CO₂ reduction.^36,37 The intermediate (*COOH) binding strength during the conversion of CO₂ determines the effectiveness of the catalyst.³⁸ The catalyst with optimum binding strength can efficiently catalyze the cathodic CO₂ reduction.³⁹ According to the famous volcano plot, silver and copper possess weaker and stronger binding energies for *COOH, respectively.^40,41 The combination of copper and silver to obtain cost effective and efficient electrocatalysts with optimum binding strength can be a good choice.⁴²

For example, Francesco et al. found that silver nanowires show a FE of 80% for CO at −1.4 V_RHE.⁴³ Mani et al. employed a molecular silver complex immobilized on graphitized mesoporous carbon for the eCO₂RR to CO and achieved a FE of 90% at −1.05 V_RHE.⁴⁴ Similarly, Yang et al. reported using oxide derived nanoporous silver for the conversion of CO₂ to CO and observed a faradaic efficiency of 87% at −0.8 V_RHE.⁴⁵ According to Zhipeng et al., the formation of CO by using Cu/Ag(S) can achieve a FE of 90% and 2.9 mA cm⁻² at −1.0 V_RHE.⁴⁶ Similarly Zekun et al. investigated the Cu_0.3Zn_9.7 electrocatalyst and revealed a FE of up to 90.69% for CO at −1.2 V_RHE.⁴⁷ Similarly, Cheng et al. proposed that the electrochemical reduction of CO₂ on the AgCu alloy facilitates C–C coupling kinetics, which retains a faradaic efficiency of 94 ± 4% towards multi-carbon products.⁴⁸ A. Harsh et al. found that the Ag₅₀Cu₅₀/p-Si catalyst converts CO₂ to CO and CH₄ with optimal faradaic efficiencies of 26% for CO and 18.2% at −0.72 V_RHE for CH₄.⁴⁹ Tao et al. reported that the Cu–Ag biphasic catalyst achieved a high FE_CO of 80.25% with a partial CO current density (j_CO) of −4.88 mA cm⁻² at −0.9 V_RHE.⁵⁰ These reports further reveal that catalytic performance and properties can be tuned via alteration of surface components.⁵¹

In this work, we report an efficient eCO₂RR system using bimetallic silver and copper nanoparticles supported over carbon nanoflakes (Ag–Cu NPs/C), which was synthesized through pyrolysis of a composite, i.e. silver incorporated in a Cu-BTC MOF (HKUST-1), under reducing environment (H₂) in the high temperature range. HKUST-1 exhibits high stability, large pore size, high surface area, tunable structure, and cost effectiveness which make it a feasible choice to be used as a precursor for the synthesis of nanomaterials. The as-prepared catalyst performs better than conventional Ag or Cu based catalysts. Dispersion of silver and copper nanoparticles over carbon nanoflakes (Ag–Cu NPs/C) facilitates selective and active catalytic conversion of CO₂ to CO.

Experimental

Synthesis of the Cu-BTC MOF (HKUST-1)

A solvothermal approach, based on the existing procedure,⁵² was used with minor modifications to synthesize the Cu-BTC MOF (HKUST-1). For this purpose, 400 mg of copper nitrate trihydrate was dissolved in 12 mL of a water:ethanol mixture followed by the addition of 246 mg of benzene-1,3,5-tricarboxylic acid. The above mixture was placed in a Teflon lined autoclave, which was placed in an oven at 120 °C for 12 h. The reaction mixture was allowed to cool to room temperature. The bluish green product was filtered, washed with water and ethanol, and dried in a vacuum oven for further use. The XRD pattern of HKUST-1 and the simulated pattern are shown in Fig. S1 (ESI†) which shows the successful synthesis of pure HKUST-1.

Synthesis of Ag@CuBTC

The synthesized Cu-BTC MOF was used to synthesize Ag@Cu-BTC. For this purpose, 600 mg of the thermally evacuated HKUST-1 MOF was dispersed in ethylene glycol and sonicated for an hour. 250 mg of polyvinylpyrrolidone (PVP) and 400 mg of AgNO₃ were then added to this suspension and subsequently refluxed for 2 h at 160 °C. After cooling, the product was filtered, washed with ethanol and water mixture, and dried in a vacuum oven.

Synthesis of Ag–Cu NPs/C

The weighed amount of Ag@CuBTC was placed in a tube furnace which was heated at various set temperatures under a hydrogen atmosphere. Ag–Cu NPs/C was formed during the carbonization of the composite, which was done for six hours in a reducing environment (H₂) at various temperatures, including 550 °C, 600 °C, 700 °C, and 850 °C, with a ramping rate of 10 °C min⁻¹ (Scheme 1). For comparison, Ag-NPs and Cu/C were also synthesized by following this method.

Scheme 1 Graphical illustration of the synthesis of Ag–Cu NPs/C.

Electrochemical measurements

Electrochemical measurements were used to estimate the prepared material's capacity to reduce CO₂. Using a GAMRY E-5000, all electrochemical investigations were carried out at ambient temperature. The eCO₂RR was evaluated in a gas tight H-type cell configured with a three-electrode system. This system featured anodic and cathodic compartments partitioned by a proton exchange membrane (PEM; Nafion 117). The drop-casting method was used to prepare working electrodes. For uniform mixing, a solution of 5 mg synthesized catalyst, 1 mL ethanol, and 20 μL of Nafion solution was sonicated for 3 h in a water bath. This homogenized slurry was applied uniformly onto a 1 cm² fluorine doped tin oxide (FTO) electrode. The coated electrodes were given their appropriate names after being dried for the whole night at 70 °C in an oven. The prepared catalyst on FTO acted as a working electrode where the CO₂ reduction occurs. The counter electrode used in this experiment was a graphite rod; the reference electrode was Ag/AgCl; and the electrolyte was 0.1 M KHCO₃. Before performing each electrochemical experiment, the electrolyte was degassed by purging high-purity argon for at least 30 min and then saturated with carbon dioxide. The Nernst equation used for converting potential values from Ag/AgCl to a standard RHE is as follows:

E_RHE = E_Ag/AgCl + 0.0592(pH) + 0.1976

where 0.0592 is equivalent to a factor ; 0.1976 = E° (standard electrode potential of Ag/AgCl).

Quantification of the products

The gaseous products of the eCO₂RR including CO and H₂ were identified by using gas chromatography equipped with a capillary column of Stabil wax (30 m × 0.32 mm I.D.), a 5 μm thick film, and a TCD detector. The Faraday efficiency for CO is calculated by using the following formula, given below.
where FE_CO indicates the Faraday efficiency of CO, n denotes the number of electrons transferred i.e., for CO, n is equal to 2, n_CO(g) is the quantity of CO in the headspace, and n_{CO(dissloved)} is the quantity of CO dissolved in the electrolyte; it has a value of 1.774 × 10⁻⁵ and is calculated based on Henry's law; F represents the faradaic constant whose value is 96 485 C mol⁻¹, I is the total current in amperes (A), and t is the reaction time in seconds (s).

Results and discussion

Powder X-ray diffraction (PXRD) patterns of all the as-prepared materials are presented in Fig. 1(a) and it can be observed from the graph that the XRD spectra of Ag–Cu NPs/C reflect the characteristic peaks of Ag, at 2θ of (38.2°, 44.5°, 64.7°, and 77.7°) and Cu at 2θ of (43.39°, 50.49°, and 74.13°) corresponding to the crystalline planes of Ag (111) (200) (220) (311) and Cu (111) (200) (220), respectively. The diffraction peak at ca. 25° represents the crystal face of porous carbon, as depicted in Fig. S2(a) and (b) (ESI†). The distinct peaks of Ag and Cu match with the standard Ag card (JCPDS no. 03-065-2871) and Cu (JCPDS no. 00-003-1005). All the diffraction peaks correspond to metallic silver, copper, and carbon, and no other impurities can be detected.

Fig. 1 Comparative PXRD patterns of Ag-NPs (red), Cu/C (blue), and Ag–Cu NPs/C (black) along with their JCPDS. XPS data of Ag–Cu NPs/C (b), Ag 3d (c) and Cu 2p (d) C1s. (e)–(g) TEM images of Ag–Cu NPs/C at different resolutions (100 nm, 50 nm, and 10 nm).

X-ray photoelectron spectroscopy (XPS) was utilized to examine the electronic properties and the elemental composition of the surface of the Ag–Cu NPs/C catalyst. The XPS spectra obtained for Ag–Cu NPs/C are illustrated in Fig. 1(b)–(d). After careful analysis of the spectra, peaks associated with the elements Ag, Cu, and C were recognized. The Ag 3d and Cu 2p high-resolution scans from Ag–Cu NPs/C are shown in Fig. 1(b) and (c), respectively. The two prominent peaks of Ag 3d noticed at 368.2 eV and 374.2 eV are due to Ag 3d_5/2 and Ag 3d_3/2 of the Ag⁰, respectively (Fig. 1(b)). The high-resolution profile of Cu 2p reveals the presence of two characteristic peaks at 932.8 eV and 953.0 eV attributed to Cu 2p_3/2 and Cu 2p_1/2, respectively (Fig. 1(c)). These peaks represent the formation of copper nanoparticles. The C 1s XPS spectra of Ag–Cu NPs/C are displayed in Fig. 1(d), with the peaks at binding energies of 284.8 eV and 284.5 given to the C–C bond and C=C, respectively. The presence of silver and copper peaks implies the successful incorporation of bimetallic nanoparticles into carbon nanoflakes.

Transmission electron microscopy (TEM) analysis is a promising technique for characterizing the morphology and structure of materials at the nanoscale. The TEM images of bimetallic silver nanoparticles incorporated into carbon in the form of nanoflakes (C) depict the unique morphology of the catalyst material and the distribution of silver and copper NPs throughout the carbon nanoflake support. In contrast, the catalyst material was synthesized through the pyrolysis of the Ag@Cu-BTC MOF, which gives it distinct morphological features with fully exposed nanoflakes like structures illustrated in Fig. 1(e)–(g). It represents metallic particles with an almost spherical shape, and the calculated lattice fringes d-spacing is 0.344 nm. The sizes of the metallic particles are determined by HRTEM and fall within the range of 10 nm to 40 nm. The high efficiency and selectivity of synthesized electrocatalysts may be attributed to the specific porous, nanoflakes of carbon and the synergistic effect of smaller sized Ag–Cu nanoparticles. The individual spherical nanoparticles can be seen for Ag–Cu NPs/C, which confirms the successful formation of both silver and copper nanoparticles that are dispersed over carbon nanoflakes. As shown in Fig. 1(e)–(g), various structures of NPs have been produced; however, the two discrete spherical dark and black contrasting TEM images made it challenging to distinguish between Ag and Cu nanocomponents. The confirmation of elements and surface quantification was also confirmed by EDX analyses (Fig. S6, ESI†). The actual ratio of Ag and Cu in the optimized catalyst is 1 : 0.75 as confirmed by edx and ICP techniques.

Electrochemical studies of Ag–Cu NPs/C

Linear sweep voltammetry (LSV) was used to examine the material's ability to function as an electrode for the reduction of CO₂. In 0.1 M KHCO₃ solution saturated with Ar and CO₂, Ag–Cu NPs/C (850 °C) was analyzed at a rate of 10 mV s⁻¹ within a potential window of 0 to (−1.5 V) vs. Ag/AgCl. In CO₂ saturated solution, the LSV results of Ag–Cu NPs/C show better current density (j) and lower overpotential (η) than those of the Ar saturated medium (Fig. 2(a)). To gain a better understanding, an investigation of the eCO₂RR was carried out for Ag-NPs, Cu/C, and Ag–Cu NPs/C (Fig. 2(b)). The LSV results of Ag–Cu NPs/C exhibit low η and significantly improved j response for CO₂ reduction than those of Ag-NPs and Cu/C, confirming the higher activity of Ag–Cu NPs/C. A comparative LSV profile of Ag–Cu NPs/C, which was synthesized by calcination under a reducing environment at different temperatures of 550 °C, 600 °C, 700 °C and 850 °C, reveals the catalytic activity in a CO₂-saturated medium. The recorded j for the electrocatalysts follows in this order: Ag–Cu NPs/C 550 °C (17.22 mA cm⁻²) < Ag–Cu NPs/C 600 °C (20.1 mA cm⁻²) < Ag–Cu NPs/C 700 °C (25.02 mA cm⁻²) < Ag–Cu NPs/C 850 °C (44.14 mA cm⁻²) (as illustrated in Fig. 2(c)). It appears that catalytic activity is found to enhance with an increase in carbonization temperature. The maximum catalytic activity is achieved for Ag–Cu NPs/C (850 °C), with a low onset potential of 0.430 V_RHE and a maximum j of 44.14 mA cm⁻². This indicates that with the increase in temperature, the particle size decreases and per unit active surface area increases. This in turn enhances CO₂ adsorption and the kinetics of the eCO₂RR. Fig. 2(d) demonstrates the partial CO current density (j_CO) for all synthesized electrocatalysts, notably Ag–Cu NPs/C 850 °C exhibits superior activity in the eCO₂RR over all the remaining synthesized electrocatalysts.

Fig. 2 Cathodic LSV results of (a) Ag–Cu NPs/C in Ar and CO₂ saturated solutions, (b) Ag-NPs, Cu/C and Ag–Cu NPs/C and (c) Ag–Cu NPs/C synthesized at different temperatures. (d) Partial CO (j_CO) of all the synthesized electrocatalysts. (e) EIS (Nyquist plot) of Ag–C at different temperatures. (f) Tafel plot of Ag–Cu NPs/C at different temperatures.

The electrochemical impedance spectroscopy (EIS) experiment depicted in Fig. 2(e) was conducted within the frequency limits of 0.01 Hz to 10³ kHz to investigate the overall charge transfer resistance in the circuit. The spectra obtained by plotting Z_realvs. Z_imag components of the circuit are called the Nyquist plot. The Rpo value determined by fitting is 93.3 ohm for Ag–Cu NPs/C which is small and confirms the faster electron transfer at the interface, resulting in enhanced reduction performance of the eCO₂RR, with a smaller charge transfer resistance (R_ct). Comparing the impedance results of all the synthesized catalysts indicates that our optimum electrocatalyst, Ag–Cu NPs/C (850°), has the smallest resistance to charge transfer having a smaller semicircular diameter, which is attributed to the synergistic interaction of copper and silver (as illustrated in Fig. 2(e)).

Tafel slope analysis was carried out to obtain a mechanistic understanding of the eCO₂RR and to evaluate the charge transfer kinetics on the catalyst's surface. The Tafel slope (η vs. log j) is shown in Fig. 2(f). The catalyst material (Ag–Cu NPs/C 850 °C) shows a lower Tafel value of only 75 mV dec⁻¹. The comparatively low Tafel slope obtained for Ag–Cu NPs/C (850 °C) compared to all the synthesized electrocatalysts is attributed to the synergistic effect of Ag and Cu. The presence of copper modifies the d-band of silver and enhances the CO₂ reduction reaction's selectivity and activity.

Chronoamperometry (CA) is the continuous measurement of current over time at a fixed potential and is an essential component of electroanalytical techniques. To evaluate the stability of the catalyst material, long term controlled potential electrolysis (CPE) of the CO₂ reduction reaction was performed through CA at different potentials from −0.4 V_RHE to −0.8 V_RHE. In CPE studies, the working electrode is held at a constant potential (V), and the current vs. time response is recorded. The result of the durability test over 10 h for all potentials is shown in Fig. 3(a), which indicates no remarkable change in j, confirming that the optimum electrocatalyst Ag–Cu NPs/C 850 °C is stable enough, making it suitable for long time use in the reduction of CO₂. Moreover, the long term stability test of the optimum ratio at −0.79 V_RHE for 40 h showing only a 2% loss in activity is illustrated in Fig. S7 (ESI†). During the stability test, various parameters, such as catalytic activity, selectivity, and structural integrity, were monitored to ascertain any potential degradation or deactivation of the catalyst. The results indicated a consistent performance with a minimal loss in catalytic efficiency, thereby underscoring the robustness and reliability of the catalyst under continuous operational conditions.

Fig. 3 (a) CA of Ag–Cu NPs/C 850 °C at different potentials over 10 h. (b) Gas chromatogram of Ag–Cu NPs/C 850 °C at −0.79 V_RHE. (c) FE_CO% at various applied potentials from −0.4 V_RHE to −0.9 V_RHE. (d) Linear Cdl plot of Ag–Cu NPs/C at different temperatures. (e) Comparative FE_CO% of Cu NPs/C, Ag NPs and Ag–Cu NPs/C. (f) TOF of Ag–Cu NPs/C at different temperatures.

Product analysis shows that carbon monoxide (CO) is the main gaseous product formed in the eCO₂RR. Gas chromatography (GC) was performed using helium as a carrier gas and the gas quantification was achieved by generating calibration curves from the standard of CO. The chromatogram shows peaks for CO₂ and CO, which were detected at distinct time intervals. The retention time (R_t) for CO₂ in the column was 5.3 min, while the R_t for CO was 7.4 min. After 1 h, a short peak of CO was observed; the intensity of the CO peak was increased after 2–10 h, while the intensity of the CO₂ peak decreased which confirms that some of the CO₂ actively participated in the reaction and converted to CO as illustrated in Fig. 3(b). The change in FE_CO% by using all the synthesized Ag–Cu NPs/C electrocatalysts at various potentials (from −0.4 V_RHE to −0.9 V_RHE) shows that the maximum FE_CO% is obtained at a potential of −0.79 V_RHE, which indicates that the selectivity of CO depends on the applied potential and is summarized in Fig. 3(c).

The change in FE_CO% of the optimum ratio of the synthesized electrocatalyst (Ag–Cu NPs/C 850 °C) was analyzed by performing the eCO₂RR at a fixed potential of −0.79 V_RHE with the continued bubbling of CO₂ for 10 h as shown in Fig. S3 (ESI†). As illustrated in Fig. 3(e), the electrocatalytic performance of Cu/C, Ag-NPs, and Ag–Cu NPs/C, the comparative FE_CO% graph shows that Ag–Cu NPs/C exhibits superior faradaic efficiency with a value of 90% than those of pure silver (75%) and copper (20%) metal. This indicates that the selectivity of the eCO₂RR to CO has been improved by combining Ag with MOF-derived Cu/C and can be controlled by adjusting the applied potential.

The electrochemically active surface area (ECSA) of the electrodes was measured using an electrical double-layer capacitance (C_dl) as an indicator to further explore how the electrode material influences electrocatalytic performance. Cyclic voltammetry (CV) was carried out in the non-faradaic region at various scan rates ranging from 5 to 50 mV s⁻¹ as presented in Fig. S4(a)–(d) (ESI†). The straight line is obtained by plotting scanning rates against the corresponding current and the slope of the straight-line yields the C_dl value. The calculated C_dl values of 5.075 mF cm⁻², 5.945 mF cm⁻², 6.48 mF cm⁻², and 8.497 mF cm⁻² for Ag–Cu NPs/C 550 °C, Ag–Cu NPs/C 600 °C, Ag–Cu NPs/C 700 °C, and Ag–Cu NPs/C 850 °C, respectively, are demonstrated in Fig. 3(d). By using the formula the ECSA was calculated, where C_s is the specific capacitance, and its value is 0.029 mF cm⁻². The maximum ECSA value obtained for Ag–Cu NPs/C 850 °C was 293 cm² as illustrated in Fig. S5 (ESI†). A catalyst with a larger value of the ESCA will possess more active sites thereby improving its performance for the eCO₂RR (high j and low η).

The turnover frequency (TOF) for CO₂ reduction was evaluated at various potentials between −0.4 V and −0.8 V (vs. RHE) in a CO₂-saturated medium to estimate the intrinsic performance of Ag and Cu active sites. The optimum electrocatalyst Ag–Cu NPs/C 850 °C gives a high TOF value of ∼19 × 10³ h⁻¹ at −0.8 V_RHE, much higher (14.6 times) than that of Ag–Cu NPs/C 550 °C (∼1.30 × 10³ h⁻¹ at −0.8 V_RHE). The higher TOF value of Ag–Cu NPs/C 850 °C indicates a faster rate of the eCO₂RR to CO (as illustrated in Fig. 3(f)). Table 1 presents the comparative analysis of Ag–Cu based electrocatalysts with the recent literature.

Table 1 Comparison of previously reported Ag–Cu bimetallic catalysts with our work for the eCO₂RR

Catalyst	Electrolyte (KHCO3) M	Electrolytic cell setup	Applied potential (V vs. RHE)	FECO%	Ref.
Ag–Cu NPs/C	0.1	H-Cell	−0.79	90	This work
Ag83Cu17	0.5	H-Cell	−1.10	74	53
Ag dendrites on Cu foam	0.5	Flow cell	−0.80	95.7	54
Ag1.01%/CuO	0.1	H-Cell	−0.70	91.2	55
Ag@Cu-7	0.1	H-Cell	−1.06	82	56
Cu/Ag layered	0.1	H-Cell	−0.80	89.1	57
Ag96Cu4	0.1	Flow cell	−1.0	98.7	58
Ag84Cu16 dendrite	0.5	H-Cell	−0.645	43.9	59
AgCu-50	0.1	H-Cell	−0.60	58.4	60
Ag/Cu NWs	0.5	H-Cell	−0.82	39.6	61
Spongeous Ag91Cu9	0.1	H-Cell	−0.70	80.6	62
Ag88Cu12 aerogel	0.1 M NaHCO3	H-Cell	−0.89	89.40	63

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Conclusions

In summary, we presented an Ag–Cu based bimetallic nanomaterial, Ag–Cu NPs/C, and evaluated its performance in the eCO₂RR to CO. Ag–Cu NPs/C was synthesized by the incorporation of silver nanoparticles into Cu-BTC metal organic frameworks and subsequent carbonization at higher temperature under a hydrogen environment. The as-prepared catalyst has shown high performance for the eCO₂RR, with a FE_CO value of ∼ 90% at −0.79 V_RHE and a j-value of 44.15 mA cm⁻² at a low onset potential of 0.430 V_RHE. The stability test over 10 h also confirms the excellent performance of Ag–Cu NPs/C. The nanostructure, dispersion, and synergistic combination of silver and copper nanoparticles are responsible for accelerating the activity and selectivity for the conversion of CO₂ to CO. The results demonstrate the potential of this material for the development of sustainable CO₂ reduction technologies.

Data availability statement

The data underlying this study will be available upon request.

Conflicts of interest

There are no conflicts to declare.

Note added after first publication

This article replaces the version published on 6th August 2024, which contained errors in Scheme 1.

Acknowledgements

This work is supported by the Chinese Academy of Sciences (CAS) (2024PVA0016). MAN acknowledges the CAS for the grant of “President's International Fellowship Initiative” (PIFI) award.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ya00462k

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