Economically viable electrocatalytic ethylene production with high yield and selectivity

Electrocatalytic semihydrogenation of acetylene provides a clean pathway to the production of ethylene (C2H4), one of the most widely used petrochemical feedstocks. However, its performance is still well below that of the thermocatalytic route, leaving the practical feasibility of this electrochemical process questionable. Here our techno-economic analysis shows that this process becomes profitable if the Faraday efficiency exceeds 85% at a current density of 0.2 A cm−2. As a result, we design a Cu nanoparticle catalyst with coordinatively unsaturated sites to steer the reaction towards these targets. Our electrocatalyst synthesized on gas diffusion layer coated carbon paper enables a high C2H4 yield rate of 70.15 mmol mg−1 h−1 and a Faraday efficiency of 97.7% at an industrially relevant current density of 0.5 A cm−2. Combined characterizations and calculations reveal that this performance can be attributed to the favourable combination of a higher energy barrier for the coupling of active hydrogen atoms (H*) and weak absorption of *C2H4. The former suppresses the competitive hydrogen evolution reaction, whereas the latter avoids overhydrogenation and C–C coupling. Further life cycle assessment evidences the economic feasibility and sustainability of the process. Our work suggests a way towards rational design and manipulation of nanocatalysts that could find wider and greener catalytic applications. Ethylene is a widely used petrochemical feedstock for the manufacture of various critical chemicals. Here the authors show a rationally designed Cu catalyst that enables electrocatalytic production with high performance and economic feasibility as well as sustainability.

Article https://doi.org/10.1038/s41893-023-01084-x of US$0.03 per kWh ( Fig. 1a and Supplementary Fig. 3). In addition, the costs of C 2 H 4 production through the proposed ESAE process decrease rapidly along with increases in the current density and FE of C 2 H 4 (Supplementary Fig. 4 and Supplementary Note 2). As a result, a ≥85% FE of C 2 H 4 under industrially relevant current densities (≥0.2 A cm −2 ) was determined as a basic target for ESAE.
To design a suitable electrode with relatively high ethylene FE and yield, three factors should be considered: (1) low activation energy for water dissociation and small Gibbs free energy (ΔG H* ) for H* formation 33,34 , (2) high energy barriers for H* coupling to suppress competitive HER, and (3) easy desorption of ethylene to avoid overhydrogenation and C-C coupling 35,36 . We first conducted DFT calculations to evaluate Cu materials. Periodic Cu slabs were used as the model of bulk Cu, and Cu clusters were used for nanosized Cu with rich unsaturated sites for comparison because the size could alter the hydrogen-involved behaviour of Cu catalysts in the thermocatalytic process (Supplementary Note 3 and Supplementary Table 2). The energy barrier for H 2 O activation and cleavage over nanosized Cu is lower than that of bulk Cu (1.39 versus 1.67 eV) (Fig. 1b, Supplementary Figs. 5 and 6, and Supplementary Notes 4 and 5), demonstrating the better H 2 O dissociation ability over nanosized Cu. In addition, the formation of H* over nanosized Cu is exothermic, while it is endothermic over bulk Cu, suggesting the more favourable formation of H* over nanosized Cu. The H* coupling barrier over nanosized Cu is larger than over the corresponding bulk Cu under different coverage of H* (Supplementary Fig. 7 and Supplementary Note 6), indicating that nanosized Cu can hinder the competitive HER. Moreover, a lower energy is required for the desorption of the adsorbed ethylene over nanosized Cu (Supplementary Fig. 8 and Supplementary Note 7), thus preventing the overhydrogenation of C 2 H 4 to C 2 H 6 . Furthermore, the energy change profiles of transition states (TSs) during the coupling process show that both the relaxation steps and the coupling barrier of nanosized Cu are higher than those of the bulk Cu counterpart, indicating that C-C coupling for C 4+ production can be effectively avoided over nanosized Cu (Supplementary Fig. 9 and Supplementary Note 8). These calculated results reveal that nanosized Cu with rich unsaturated sites can not only promote H* formation but also suppress competitive HER and acetylene overhydrogenation, thus accelerating ethylene production.

Electrocatalyst synthesis and characterizations
The abovementioned nanosized Cu with rich unsaturated sites was designedly synthesized on GDL-CP through a facile electrodeposition strategy (Fig. 2a). To avoid the formation of large Cu particles in typical electrodeposition (Supplementary Fig. 10 and Supplementary Note 9), the slow dissolution of copper nitrate on the hydrophobic surface of GDL-CP causes the gradual release of Cu cations to form Cu(OH) 2 , which acts as the in situ Cu source for electrodeposition preparation of low-coordination Cu nanoparticles (ED-Cu NPs). The formation process of ED-Cu NPs was monitored by in situ potential-dependent X-ray diffraction (XRD) (Fig. 2b). The peak at 54.5° is one of the characteristic peaks of CP ( JCPDS No.   33,37 . The XRD peaks that appeared in the initial sample immersed in aqueous KOH without electricity are ascribed to Cu(OH) 2 , which is consistent with the results of the Raman spectra discussed later, affirming the existence of Cu(OH) 2 intermediates (Supplementary Fig. 11 and Supplementary Note 10) 38 . Two characteristic peaks at 43.3° and 50.6° corresponding to the (111) and (200) crystal facets of cubic Cu (ref. 39 ) appeared at approximately −0.4 V versus reverse hydrogen electrode (RHE), in line with the reduction peak of copper nitrate in the linear sweep voltammetry (LSV) curves and the Pourbaix diagram of the Cu-O system (Supplementary Fig. 12 and Supplementary Note 11) 40 . The two peaks became stronger with a potential negative shift. The results of in situ potential-dependent XRD patterns thus suggest that copper nitrate can completely transform into metallic Cu during the electrodeposition process. The electrodeposition However, its advance is still hindered by the severe hydrogen evolution reaction (HER), resulting in a relatively low ethylene yield and Faraday efficiency (FE) 17 . At present, the deficiency of techno-economic analysis (TEA) makes the target of the ESAE process unclear. Performing TEA of the as-proposed technique and developing efficient catalytic materials to suppress the competitive HER and produce ethylene with high efficiency at industrially relevant current densities is thus urgently needed.
Copper (Cu)-based materials have been proven to be excellent catalyst candidates for the SAE process to remove C 2 H 2 impurities from C 2 H 4 -rich gas streams and for selective semihydrogenation of alkynes 18,19 . Very recently, Wang et al. reported the possibility of C 2 H 4 production over Cu macroparticles with a size of 1-2 μm through the ESAE process 17 . However, the FE of C 2 H 4 is highly dependent on the precise control of the current density. The FE of C 2 H 4 above 60 mA cm −2 is lower than 50%, which is unfavourable for the large-scale production of C 2 H 4 . It is thus highly significant to design an efficient catalyst for C 2 H 4 production with high FE at industrially relevant current densities (≥0.1 A cm −2 ). In comparison with bulk and macrosized Cu, Cu nanostructures with a diameter of approximately 5 nm are both experimentally 20,21 and theoretically 22 proven to be more favourable in H 2 dissociation in thermocatalytic hydrogenation reactions due to unsaturated coordination 23,24 . Conversely, unsaturated Cu nanoparticles are supposed to impede the coupling of active hydrogen atoms (H*) to release H 2 in the ESAE process, lowering the selectivity and FE of undesirable H 2 . In this regard, low-coordination Cu nanostructures are promising electrocatalysts for C 2 H 4 production through the ESAE process at an industrially relevant current density. In addition, a gas diffusion electrode is necessary for continuous synthesis [25][26][27] . Furthermore, direct growth of nanosized catalysts on gas diffusion electrodes can not only avoid the use of any polymer binders 28 or difficult-to-remove surfactants 29 (which may block the gas diffusion channels) but also enhance the bonding strength between the catalysts and gas diffusion electrodes, leading to improved mass transfer and electrode durability 30 . However, the direct synthesis and use of low-coordination Cu nanoparticles on a gas diffusion layer coated carbon paper (GDL-CP) electrode for industrialization-oriented ethylene production is still a highly challenging task.
Here we performed a preliminary TEA of this ESAE process, showing a profitable target of a ≥85% C 2 H 4 FE at a current density of ≥0.2 A cm −2 . We designed GDL-CP-supported Cu nanoparticles with rich unsaturated sites (denoted as ED-Cu NPs), and these turned to be an outstanding electrocatalyst for the ESAE process. ED-Cu NPs deliver a C 2 H 4 FE of 97.7% at a current density of 0.5 A cm −2 with a single-pass C 2 H 2 conversion rate of 12.4% and a C 2 H 4 production rate of 70.15 mmol mg −1 h −1 , substantially outperforming the commercial Cu counterpart and the electrodeposited Cu macrosized particles. Cu nanoparticles with rich unsaturated sites were revealed to promote H* formation and suppress competitive HER and acetylene overhydrogenation, thus accelerating ethylene production. Moreover, the in situ spectroscopic characterization revealed that the ESAE process follows the H* addition mechanism. Subsequently, the kinetic isotope effect (KIE) measurement and density functional theory (DFT) calculations suggest that sufficient H* on ED-Cu NPs enables high ethylene FE in a wide window of current densities. Furthermore, a cradle-to-gate life cycle assessment confirms the sustainability of the ESAE strategy.

Calculation-assisted electrocatalyst designs
We first simulated a TEA of the proposed ESAE process for C 2 H 4 production at the industrial manufacturing level on the basis of a recently reported model (Supplementary Note 1) 31,32 . The parameters used in the TEA follow what is reported in the literature 11 Fig. 13 and Supplementary Note 12), suggesting the complete conversion of the copper precursor and the formation of ED-Cu NPs because of the absence of characteristic peaks of metallic Cu(0) species 39,41 . Moreover, X-ray absorption spectroscopy (XAS) was used to further validate the electronic configuration and local coordination environment of the ED-Cu NPs. The Cu K-edge X-ray absorption near-edge structure spectra of ED-Cu NPs exhibit similar features to those of Cu foil (Fig. 2c), agreeing with the in situ XRD results. In addition, the continuous Cauchy wavelet transform was applied to the extended X-ray absorption fine structure (EXAFS) spectra (Fig. 2d). The similar spectra of ED-Cu NPs and Cu foil further indicate that the parent copper nitrate is completely converted into metallic Cu. The local coordination environment of the as-obtained ED-Cu NPs was analysed by the corresponding k 3 -weighted Fourier-transformed EXAFS curves (Fig. 2e). The Cu-Cu bonds with a bond length of 2.3 Å and Cu-O bonds with a bond length of 1.5 Å of the ED-Cu NPs are consistent with Cu foil 39,42 . However, in comparison with Cu foil, the increased coordination number of the Cu-O bonds and the reduced coordination number of the Cu-Cu bonds of ED-Cu NPs further illustrate that the ED-Cu NPs are more sensitive to oxygen in air than the bulk Cu, ascribed to the unsaturated site in the low-coordination Cu. The high-resolution transmission electron microscopy images (Fig. 2f) show that the fringe spacing of 0.208 nm matches well with the (111) lattice plane of Cu, confirming the metallic nature of the ED-Cu NPs. The high-angle annular dark-field image, the associated scanning transmission electron microscope energy-dispersive X-ray spectroscopy (EDS) element mapping images (Fig. 2g,h) and the corresponding size distribution (Supplementary Fig. 14 and Supplementary Note 13) suggest that the ED-Cu NPs with an average diameter of approximately 3-5 nm are highly dispersed on GDL-CP. All these results demonstrate the successful preparation of ED-Cu NPs with unsaturated Cu sites.

ESAE
The performance of electrocatalytic acetylene semihydrogenation over ED-Cu NPs and over commercial Cu was evaluated in a three-electrode flow cell with a gas diffusion layer under galvanostatic conditions (Fig. 3a). The performance evaluations in acidic, neutral and basic electrolytes suggest that the alkaline solution is preferable (Supplementary Fig. 15 and Supplementary Note 14). We thus chose a 1.0 M KOH aqueous solution and pure C 2 H 2 as the electrolyte and reaction gas, respectively (Supplementary Fig. 16). Interestingly, the LSV curves show that there is a much lower onset potential and slightly higher current densities in the potential range from 0 V to −1.0 V versus RHE over ED-Cu NPs than those of commercial Cu under an Ar atmosphere ( Supplementary  Fig. 17). The as-observed results suggest that H 2 O activation proceeds more easily on nanosized Cu, agreeing with the prediction from the DFT calculation. Moreover, ED-Cu NPs exhibit smaller current densities at potentials more negative than −1.0 V versus RHE than commercial Cu (Supplementary Fig. 17 and Supplementary Note 15) because of their higher energy barriers in H* self-coupling to form H 2 gas. In addition, a noticeable increase in current density can be observed when Ar is switched to C 2 H 2 from the LSV curves (Supplementary Fig. 18 and Supplementary Note 16), suggesting that C 2 H 2 can be activated over metallic Cu. The ESAE process was analysed in the current density range from 0.1 to 1.0 A cm −2 (Fig. 3b,c). The FE of C 2 H 4 reaches above ~90%, and the H 2 byproduct is almost undetectable in a wide range of current densities from 0.1 to 0.5 A cm −2 on ED-Cu NPs ( Supplementary Fig. 19a Tables  3 and 4). However, the FE of C 2 H 4 decreases rapidly with more H 2 , and a small amount of overhydrogenated ethane (C 2 H 6 ) is produced at current densities higher than 0.2 A cm −2 over commercial Cu (Supplementary Fig. 19b). In addition, the obtained C 2 H 4 production rate of ED-Cu NPs at a current density of 0.5 A cm −2 is 70. 15 Fig. 26 and Supplementary Note 20) shows that ED-Cu NPs exhibit higher normalized partial current densities and larger turnover frequency values of C 2 H 4 than their commercial counterpart, highlighting the high intrinsic activity of ED-Cu NPs. Furthermore, the performance and size distribution comparison of ED-Cu NPs with different loadings of Cu precursor suggests that the      , indicating that the proposed catalysts exhibited potential-and current-density-independent ESAE activity. Our low-cost catalyst can thus operate under fluctuant renewable energy sources, which is highly challenging for other catalysts.
The additional experiment shows that the as-proposed ESAE process can also be driven by the electricity generated from renewable solar energy (Supplementary Video 1), further highlighting the potential of our strategy as a sustainable alternative or complementary method to the traditional petroleum route for C 2 H 4 production.

Mechanism of the high selectivity for ethylene
To elucidate the reaction pathway of the ESAE process, we performed a series of in situ and ex situ characterizations. First, in situ Raman spectra were carried out to investigate the reaction intermediates during the ESAE process in the potential range of −0.6 to −1.2 V versus RHE, within the corresponding potential range in the performance evaluation under galvanostatic conditions (Supplementary Fig. 31). The peaks located at 1,700 cm −1 and 1,560 cm −1 in Fig. 4a are assigned to the *C≡C bond of C 2 H 2 and the generated *C=C bond 14,17,18 adsorbed on ED-Cu NPs in C 2 H 2 -saturated solution, respectively. The intensity of *C 2 H 2 decreases while the intensity of *C=C increases rapidly as the electrode potential becomes more negative, suggesting that the original C 2 H 2 is hydrogenated to *C 2 H 4 . Moreover, in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, which is highly sensitive to intermediates, was conducted to probe the mechanism of the ESAE process. As shown in Fig. 4b, the *C 2 H 2 adsorbed species can also be detected at 1,641 cm −1 over ED-Cu NPs. a c b d Fig. 4 | The hydrogenation pathway and mechanism of C 2 H 4 production. a, In situ Raman spectra of ED-Cu NPs using C 2 H 2 as the feeding gas. b, In situ ATR-FTIR spectra over ED-Cu NPs in the C 2 H 2 -saturated electrolyte. c, The quasiin-situ electron paramagnetic resonance trapping for hydrogen and carbon radicals over ED-Cu NPs. DMPO, 5,5-dimethyl-1-pyrroline-N-oxide. d, Free-energy diagram for acetylene semihydrogenation reactions over nanosized Cu. e, Schematic illustration of the mechanism of enhanced C 2 H 4 production over ED-Cu NPs.
Article https://doi.org/10.1038/s41893-023-01084-x commercial Cu (Fig. 4c, Supplementary Fig. 33 and Supplementary Notes 25 and 26) 33 . The extremely low concentration of protons in our alkaline electrolytes does not favour the proton-coupled electron transfer process. An H* addition transfer hydrogenation pathway is thus rationally proposed in the ESAE process. Namely, H* formed by H 2 O dissociation is first transferred to *C 2 H 2 , which is activated and adsorbed on the surface of the ED-Cu electrode to generate *C 2 H 3 . Another H* is then coupled with *C 2 H 3 to produce the target C 2 H 4 . Generally, H 2 O dissociation and C 2 H 2 hydrogenation are involved during the ESAE process. To further understand the enhanced production of C 2 H 4 over ED-Cu NPs, we explored the reaction mechanism using DFT calculations, the KIE and controlled experiments. The DFT calculation results show that ED-Cu NPs exhibit a higher energy barrier for H* self-coupling than that for the *C 2 H 2 hydrogenation process compared with commercial Cu (Fig. 4d, Supplementary Figs. 34-37 and Supplementary Note 27). These DFT comparison results indicate that sufficient hydrogen radicals adsorbed on electrodes are more likely to participate in the *C 2 H 2 hydrogenation process rather than self-coupling to generate H 2 over ED-Cu NPs. The KIE experiment was carried out between the same potential range with performance evaluation and in situ characterization. As shown in Supplementary Fig. 38, the k H /k D values among the four selected potentials are all larger than 2, indicating that the O-H cleavage of the H 2 O dissociation part is the rate-determining step of the whole ESAE process 33,39 . This rate-determining step is also supported by the difference in the energy barriers of the H 2 O dissociation and C 2 H 2 hydrogenation processes (Figs. 1b and 4d), indicating the importance of H* formation and reserves in the ESAE process. Consequently, the cyclic voltammogram curve in 1.0 M KOH solution was conducted to confirm the behaviour of H*. The distinctly larger peak of H* suggests the existence of abundant H* and the relatively stronger H* adsorption ability of ED-Cu NPs 35,46 (Supplementary Fig. 39 and Supplementary Note 28), further affirming the DFT calculation results of H 2 O activation (Fig. 1b). Accordingly, a schematic illustration of the whole reaction route is given in Supplementary Fig. 40, and the in-depth origins for the enhanced C 2 H 4 selectivity at industrially relevant current densities are summarized in Fig. 4e. On the one hand, the increased H 2 O activation and dissociation ability enable enough H* to participate in the subsequent H* addition transfer hydrogenation process. On the other hand, the higher energy barrier of H* coupling and the easier desorption of C 2 H 4 hinders the competitive HER and undesired overhydrogenation and further guarantees the progress of the transfer hydrogenation process to efficiently produce C 2 H 4 .

Discussion
To confirm the economic potential of the proposed ESAE process in C 2 H 4 production as an alternative or complementary method to the petroleum or shale gas route, we propose the subdivided costs of the entire technological process consisting of the arc pyrolysis process of coal and electrocatalytic C 2 H 2 semihydrogenation in Fig. 5a and Supplementary Table 5. The electricity cost accounts for the highest proportion, which can be conquered soon with the development of renewable electricity generation technology. In addition, the total costs of separation equipment and operation are as high as 17.6%, the second largest cost. In this regard, developing an efficient catalyst to suppress undesired H 2 at high current densities to lower the separation cost is of great significance. The electrosynthesis of C 2 H 4 through electrochemical semihydrogenation of coal-derived C 2 H 2 with high selectivity and FE therefore possesses huge economic potential. Moreover, a life cycle assessment of CO 2 emissions from cradle to gate was conducted to prove the environmentally friendly potential of the proposed ESAE strategy (Supplementary Note 29) 47 . The amount of CO 2 emissions per kilogram of C 2 H 4 as a function of electricity carbon intensity is shown in Fig. 5b. The CO 2 emission amount of the coal-derived strategy is much higher than that of the petroleum route (3.2 kg CO 2 per kg C 2 H 4 ) using electricity from a traditional thermal power plant (Supplementary Tables 6 and 7). However, a break-even point appears when the carbon intensity of the electricity is lower than 73 g of CO 2 equivalent per kWh. Fortunately, the carbon intensity of renewable electricity such as solar and wind power generation could meet the standard 48 . In addition, the CO 2 emission of our proposed ESAE process is expected to be further reduced by increasing the energy efficiency by lowering the cell voltage ( Supplementary Fig. 41   The abovementioned results indicate that the proposed ESAE process for coal-derived acetylene deserves to be developed from the aspects of both the economy and the environment. In summary, the results of the TEA demonstrate that the ESAE process is an efficient alternative or complementary method to produce C 2 H 4 at an industrially relevant current density (≥0.2 A cm −2 ) with tremendous economic potential. The DFT calculations show that low-coordination nanosized Cu is a promising candidate for inhibiting the competing HER due to the high energy barrier for H* coupling to release H 2 , leading to higher C 2 H 4 production. Low-coordination ED-Cu NPs with a size of 3-5 nm are thus designedly synthesized and proven to be an efficient cathode for C 2 H 4 production at 0.5 A cm −2 with a 97.7% FE and a production rate of 70.15 mmol mg −1 h −1 through the ESAE process, greatly outperforming the commercial Cu counterpart (13.44 mmol mg −1 h −1 ) and electrodeposited Cu macrosized particles (12.37 mmol mg −1 h −1 ). Moreover, an H* addition mechanism is proposed for C 2 H 4 formation by a series of in situ spectroscopic characterizations. The KIE and DFT results also suggest that sufficient H* on ED-Cu enables a high C 2 H 4 FE in a wide current density window. Furthermore, our strategy is a potential alternative or complementary method to the petroleum route, as shown by cradle-to-gate life cycle assessment. The FE of C 2 H 4 and the conversion of C 2 H 2 over ED-Cu NPs can remain unchanged over a wide range of potentials or current densities. The process can thus operate under fluctuant renewable energy sources, which is highly challenging for other catalysts, further highlighting the potential of our strategy. Our work may not only establish a green and sustainable electrocatalytic complementary strategy for continuous C 2 H 4 production with high yield and selectivity but also offer a paradigm for designing nanocatalysts to inhibit the competitive HER during electrocatalytic transfer hydrogenation using water as the hydrogen source.

Chemicals
Copper nitrides (Cu(NO 3 ) 2 ), potassium hydroxide (KOH) and 5,5-dimethyl-1-pyrroline-N-oxide were purchased from Aladdin. Ar and pure C 2 H 2 gas were purchased from Taiya. GDL-CP was purchased from Gaossunion. Deionized water was used in all the experimental processes. All chemicals were of analytical grade and used without further purification.

Fabrication of GDL-CP-supported copper nitrate (GDL-CP Cu(NO 3 ) 2 ) electrodes
GDL-CP Cu(NO 3 ) 2 electrodes were fabricated by the traditional spin-casting method. The commercial GDL-CP was cut into a rectangular shape with a size of 1.2 × 3.3 cm 2 as the electrode substrate. Specifically, Cu(NO 3 ) 2 was dissolved in a mixed solvent of water and ethanol with a volume ratio of 1/2 to form a solution at a concentration of 2 mg ml −1 . The as-prepared solution was then spin-coated on the GDL-CP substrates with 1 ml on each substrate under a constant spin speed of 500 rpm.

Synthesis of GDL-CP-supported Cu nanoparticles
The electrodeposition of GDL-CP Cu(NO 3 ) 2 was performed in the flow cell reactor using an electrochemical workstation (CS150H, CorrTest). The electrolyte was 1.0 M KOH, and the reference electrode was a Hg/ HgO electrode with 1.0 M KOH as the inner reference electrolyte. A platinum (Pt) foil was used as the counter electrode. Note that the apparatus conditions were all the same as those for the performance evaluation, except the atmosphere was Ar rather than C 2 H 2 . The as-prepared GDL-CP Cu(NO 3 ) 2 electrode was fixed with conductive copper tape and used as the working electrode. The continuous LSV measurement was conducted in the voltage range of 0 to −1.5 V versus RHE at a scan rate of 5 mV s −1 until the reductive peak disappeared.

Synthesis of GDL-CP-supported Cu microparticles
The electrodeposition method was carried out in a typical H-cell electrolytic tank according to the previous literature 49 . First, the deposition solution consisted of 0.4 M Cu(NO 3 ) 2 and 3 M lactic acid, and the pH value was adjusted to 11.5 using NaOH powder. A Ag/AgCl electrode with saturated KCl as the inner reference electrolyte and a Pt foil were used as the reference and counter electrodes. Then, the as-prepared solution was preheated in a 60 °C water bath, and electrodeposition was performed under −0.4 V versus RHE; the deposition amount was controlled by adjusting the Coulombs passed through the electrodeposition process.

Characterizations
Ex situ and in situ XRD was performed on a Bruker D8 Focus Diffraction System using a Cu Kα source (λ = 0.154178 nm) and a Rigaku Smart-lab9KW Diffraction System using a Cu Kα source (λ = 0.15406 nm), respectively. Transmission electron microscopy images were obtained with a JEOL-2100F system equipped with EDAX Genesis XM2. The operando online SFC-DEMS analysis was conducted by QAS 100 provided by Linglu Instruments. The in situ ATR-FTIR was performed on a Nicolet 6700 FTIR spectrometer with silicon as the prismatic window. The in situ Raman spectroscopy was acquired on a Renishaw inVia reflex Raman microscope under the excitation of a 532 nm laser. The XAS measurements were undertaken at the 1W1B beamline of the Beijing Synchrotron Radiation Facility. The XAS spectra were analysed with the ATHENA software package (Athena 0.9.26) (ref. 50 ). The gas chromatograph was measured on a Shimadzu GC-2010 Plus with a ShinCarbon ST100/120 column and barrier discharge ionization detector. Helium was used as the carrier gas. The injection temperature was set at 240 °C.

Electrochemical measurements in the flow cell
Electrochemical measurements were carried out in a typical flow cell consisting of a GDL as the working electrode, a Pt foil as the counter electrode and Hg/HgO as the reference electrode using a CS150H electrochemical workstation. The cathode cell and anode cell were separated by a Nafion 117 proton exchange membrane. The cathode and anode electrolytes were both 1.0 M KOH solution, and a peristaltic pump was applied to implement the circulation of the liquid phase. The gas flow rate was controlled by the mass flowmeter. A schematic illustration of the flow cell is shown in Fig. 3a. Before the performance tests, the working electrode was fixed at the interface between the gas flow block and the cathodic electrolyte block by conductive copper tape. First, the in situ electrodeposition of GDL-CP Cu(NO 3 ) 2 through a series of negative-direction LSV processes was carried out under an Ar atmosphere at a flow rate of 30 ml min −1 . Then, after the ED-Cu NPs were formed in situ, the Ar gas was switched to pure C 2 H 2 gas with the flow rate maintained at 30 ml min −1 . The electrochemical semihydrogenation of acetylene was conducted at different current densities for 10-20 min to achieve relatively stable and reliable performance parameters before the quantitative analysis. The gas at the flow cell outlet was directly introduced into the gas chromatograph for the analysis of the products. The procedure and reaction setup of electrochemical semihydrogenation of acetylene over commercial Cu was similar to that for ED-Cu NPs except that the in situ electrodeposition process for the working electrode was excluded. All LSV curves were iR compensated with a compensation level of 80%. For Tafel slopes, the LSV curves were replotted by using the logarithms of current density as the x axis and potential as the y axis. The obtained slopes of the linear part of the replotted figure were then Tafel slopes.

The quantitative analysis of the C 2 H 2 conversion
The products were subjected to the GC-2010 gas chromatograph equipped with an activated carbon packed column (with He as the carrier gas) and barrier discharge ionization detector. All experiments were repeated three times. The calculation of the C 2 H 2 conversion and Article https://doi.org/10.1038/s41893-023-01084-x the evolution rate of different products was performed using equations (1) and (2), and the FEs of different products were calculated using equation (3). Turnover frequency (TOF) for C 2 H 4 was calculated using equation (4): TOF (min −1 ) = amount of C 2 H 4 molecules produced per min amount of Cu sites (4) where X represents the different products, including H 2 , C 2 H 4 and C 2 H 6 ; C is the concentration of X in standard gas; m is the mass of metallic Cu over the electrode; n is the moles of different products, including H 2 , C 2 H 4 and C 2 H 6 ; A is the area of the C 2 H 2 outlet; B is the area of the C 2 H 2 inlet; S is the gas flow rate; a is the electron transfer number; F is the Faraday constant; and Q is the total Coulomb number of the ESAE process.

Electrochemical in situ XRD measurements. The in situ electrochemical XRD patterns were measured with a Rigaku Smartlab9KW
Diffraction System using a Cu Kα source (λ = 0.15406 nm). The electrolytic cell used in the in situ XRD measurement was homemade by Teflon. The Pt wire and Hg/HgO electrode were used as the counter and reference electrodes, respectively. Diffraction patterns were recorded within a 2θ range of 30-80° under the applied potential from OCP to −0.7 V versus RHE. The scanning rate was 10° min −1 .
Electrochemical in situ Raman spectra measurements. The in situ electrochemical Raman spectroscopy was recorded on a Renishaw inVia reflex Raman microscope under the excitation of a 532 nm laser under controlled potentials by an electrochemical workstation. We used a homemade Teflon electrolytic cell equipped with a piece of round quartz glass for the incident laser and the protection of the tested samples. Before the experiments, the electrolyte was pretreated with pure C 2 H 2 gas to obtain C 2 H 2 -saturated KOH. The working electrode was parallel to the quartz glass to keep the plane of the sample perpendicular to the incident laser. Pt wire was rolled in a circle around the working electrode to serve as the counter electrode. The reference electrode was Hg/HgO with an internal reference electrolyte of 1.0 M KOH. The spectrum was recorded under an applied potential of −0.35 V versus RHE and every 30 s under the applied potential from OCP to −1.2 V versus RHE.
Electrochemical in situ ATR-FTIR spectra measurements. The in situ ATR-FTIR was performed on a Nicolet 6700 FTIR spectrometer equipped with an MCTA detector with silicon as the prismatic window and an ECIR-II cell by Linglu Instruments. First, Cu(NO 3 ) 2 ink was carefully dropped on the surface of the gold film, which was chemically deposited on the surface of the silicon prismatic before each experiment. The deposited silicon prismatic then served as the working electrode. The Pt foil and Hg/HgO with an internal reference electrolyte of 1.0 M KOH were used as the counter and reference electrodes, respectively. A 1.0 M KOH solution was employed as the electrolyte.
The electrolyte was presaturated with pure C 2 H 2 gas, and the gas was continuously bubbled during the whole measurement. Before spectral acquisition, the working electrode was pretreated through a series of continuous LSV measurements in the voltage range of 0 to −1.5 V versus RHE for the in situ formation of ED-Cu NPs. The spectrum was recorded every 30 s under the applied potential from OCP to −1.2 V versus RHE.

Electrochemical operando online SFC-DEMS analysis.
The operando online SFC-DEMS analysis was conducted by QAS 100 provided by Linglu Instruments. Because the products in the proposed ESAE process are all in the gas phase, operando experiments were conducted to monitor the distribution of the products during the reaction on-stream, clarifying the selectivity issues more directly and clearly. The flow cell used in the performance evaluation and the DEMS were coupled to ensure that the gas at the flow cell outlet was directly injected into the negatively pressured gas circuit system of the DEMS through a quartz capillary that was inserted into the outlet of the flow cell. The rectangular wave current density was applied from 0.1 to 0.5 A cm −2 with a constant interval of 400 s by the CS150H electrochemical workstation. During the experiment, the flow rate of C 2 H 2 gas and electrolyte was set the same as in the performance evaluation.

Computational details
In this work, all DFT calculations were performed using the Vienna Ab initio Simulation Package 51 . The projector augmented wave pseudopotential 52 with the PBE generalized gradient approximation exchange correlation function 53 was utilized in the computations. The cut-off energy of the plane wave basis set was 500 eV, and a Monkhorst-Pack mesh of 3 × 3 × 1 was used in K-sampling in the adsorption energy calculation. The long-range dispersion interaction was described by the DFT-D3 method. The electrolyte was incorporated implicitly with the Poisson-Boltzmann model implemented in VASPsol 54 . The relative permittivity of the media was chosen as ϵ r = 78.4, corresponding to that of water. The Debye length for the electrolyte was set to 3.0 Å, which corresponds to an electrolyte concentration of 1.0 M. All atoms were fully relaxed with an energy convergence tolerance of 10 −5 eV per atom, and the final force on each atom was <0.01 eV Å −1 . The TS searches were performed using the Dimer method in the VTST package 195 (ref. 55 ). The final force on each atom was <0.05 eV Å −1 . The TS search was conducted by using the climbing-image nudged elastic band method to generate initial guess geometries, followed by the dimer method to converge to the saddle points. In this work, face-centred cubic phase copper (Cu) was used (a = b = c = 3.621 Å, α = β = γ = 90.0°, Fm3 m). The bulk model of the sample was built by the 3 × 3 supercell of Cu (111) with four layers of Cu. All periodic slabs had a vacuum layer of at least 15 Å. The bottom layer of atoms was fixed at their optimized bulk-truncated positions during geometry optimization, and the rest of the atoms could relax. The model of the nanosized sample was built by a cluster of 38 Cu atoms in a 20 Å × 20 Å × 25 Å unit cell, and all the atoms could relax.

Reporting summary
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Data availability
The spreadsheets used for the cost analyses and CO 2 emissions and for Supplementary Tables 1-7 are available in Supplementary Data 1 and 2. Source data are provided with this paper.

March 2021
Corresponding author(s): Bin Zhang Last updated by author(s): Feb 5, 2023 Reporting Summary Nature Portfolio wishes to improve the reproducibility of the work that we publish. This form provides structure for consistency and transparency in reporting. For further information on Nature Portfolio policies, see our Editorial Policies and the Editorial Policy Checklist.

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The exact sample size (n) for each experimental group/condition, given as a discrete number and unit of measurement A statement on whether measurements were taken from distinct samples or whether the same sample was measured repeatedly The statistical test(s) used AND whether they are one-or two-sided Only common tests should be described solely by name; describe more complex techniques in the Methods section.
A description of all covariates tested A description of any assumptions or corrections, such as tests of normality and adjustment for multiple comparisons A full description of the statistical parameters including central tendency (e.g. means) or other basic estimates (e.g. regression coefficient) AND variation (e.g. standard deviation) or associated estimates of uncertainty (e.g. confidence intervals) For null hypothesis testing, the test statistic (e.g. F, t, r) with confidence intervals, effect sizes, degrees of freedom and P value noted

Data analysis
OriginPro 2023 (Education version) was used to conduct the data analysis and data fitting.
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Data
Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A description of any restrictions on data availability -For clinical datasets or third party data, please ensure that the statement adheres to our policy All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials.

Human research participants
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Ethics oversight
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Field-specific reporting
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Blinding
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Behavioural & social sciences study design
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Authentication
Describe the authentication procedures for each cell line used OR declare that none of the cell lines used were authenticated.

Mycoplasma contamination
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Commonly misidentified lines (See ICLAC register)
Name any commonly misidentified cell lines used in the study and provide a rationale for their use.

Specimen provenance
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Specimen deposition
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Dating methods
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Ethics oversight
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Animals and other research organisms
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Laboratory animals
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Wild animals
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Ethics oversight
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Clinical data Policy information about clinical studies
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Study protocol
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Data collection
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Outcomes
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Dual use research of concern
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Hazards
Could the accidental, deliberate or reckless misuse of agents or technologies generated in the work, or the application of information presented in the manuscript, pose a threat to:

Experiments of concern
Does the work involve any of these experiments of concern: No Yes Confirm that both raw and final processed data have been deposited in a public database such as GEO.
Confirm that you have deposited or provided access to graph files (e.g. BED files) for the called peaks.

Data access links
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Files in database submission
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March 2021
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Methodology Replicates
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Sequencing depth
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Antibodies
Describe the antibodies used for the ChIP-seq experiments; as applicable, provide supplier name, catalog number, clone name, and lot number.
Peak calling parameters Specify the command line program and parameters used for read mapping and peak calling, including the ChIP, control and index files used.

Data quality
Describe the methods used to ensure data quality in full detail, including how many peaks are at FDR 5% and above 5-fold enrichment.

Software
Describe the software used to collect and analyze the ChIP-seq data. For custom code that has been deposited into a community repository, provide accession details.

Flow Cytometry
Plots Confirm that: The axis labels state the marker and fluorochrome used (e.g. CD4-FITC).
The axis scales are clearly visible. Include numbers along axes only for bottom left plot of group (a 'group' is an analysis of identical markers).
All plots are contour plots with outliers or pseudocolor plots.
A numerical value for number of cells or percentage (with statistics) is provided.

Methodology Sample preparation
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Instrument
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Software
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Cell population abundance
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Gating strategy
Describe the gating strategy used for all relevant experiments, specifying the preliminary FSC/SSC gates of the starting cell population, indicating where boundaries between "positive" and "negative" staining cell populations are defined.
Tick this box to confirm that a figure exemplifying the gating strategy is provided in the Supplementary Information. Behavioral performance measures State number and/or type of variables recorded (e.g. correct button press, response time) and what statistics were used to establish that the subjects were performing the task as expected (e.g. mean, range, and/or standard deviation across subjects).