Electrosynthesis of 1,3-butadiene from dilute acetylene over coordination-modulated dicopper molecular catalysts

Abstract

Electrosynthesis of 1,3-butadiene from acetylene offers a promising alternative to energy-intensive industrial processes. Nonetheless, achieving selective hydrodimerization of acetylene remains challenging due to competing side reactions, particularly for dilute coal-derived acetylene. Herein, we synthesize a series of dicopper paddlewheel Cu₂(LCOO)₄ (L = tert-butyl, isopropyl, ethyl, and methyl), featuring bidentate bridging carboxylate ligands with specific Cu···Cu distances for electrocatalytic hydrodimerization of acetylene to 1,3-butadiene. Through catalyst benchmarking, in situ spectroscopy and computational analysis, we reveal that sequential modulation of carboxylate ligands (methyl → ethyl → isopropyl → tert-butyl) progressively enriches electron density at dicopper sites while strengthening structural robustness across the Cu₂(LCOO)₄ series. The optimized Cu₂(tert-butylCOO)₄ exhibits favorable reaction energetics for acetylene dimerization and subsequent hydrogenation, achieving 91% Faradaic efficiency with a 1,3-butadiene formation rate of 0.93 mmol h⁻¹ cm⁻² in a flow cell. For simulated production of 1,3-butadiene from coal-derived acetylene (15%) in a membrane electrode assembly system, this catalyst demonstrates 83% Faradaic efficiency at −300 mA. This work highlights an effective coordination modulation strategy for producing 1,3-butadiene via dicopper molecular catalysts.

Electrosynthesis of 1,3-butadiene from dilute coal-derived acetylene is promising yet remains challenging due to competing side reactions. Here, the authors develop coordination-modulated dicopper molecular catalysts to steer the electrocatalytic dilute acetylene toward 1,3-butadiene.

Introduction

1,3-butadiene represents a pivotal feedstock in industrial chemistry, particularly for manufacturing rubber and plastic materials¹. Current production of 1,3-butadiene predominantly employs extractive distillation of C4 streams from naphtha cracking^2,3, a methodology that hinges on energy-intensive processes and finite petroleum reserves. In light of growing sustainability concerns, developing alternative production pathways has become a critical research priority. A promising approach involves the electrocatalytic hydrodimerization of coal-derived acetylene^4,5, providing a petroleum-independent route for producing 1,3-butadiene under ambient conditions with water as the hydrogen source^6–10.

Electrocatalytic hydrodimerization of acetylene to 1,3-butadiene typically occurs as a side reaction during the semihydrogenation of acetylene to ethylene, primarily due to the significantly lower Faradaic efficiency and minimal partial current density of 1,3-butadiene compared to ethylene^11–17. Recently, by using a potassium iodide catholyte, Cu₂O nanocube-derived catalysts selectively coupled acetylene to yield 1,3-butadiene¹⁸. Despite advancements, selective electrosynthesis of 1,3-butadiene is hindered by competitive side reactions, especially when processing dilute coal-derived acetylene. This challenge stems from the complexity of hydrodimerization process, including acetylene adsorption, activation, and complex multipoint relay carbon-carbon hydrodimerization, all of which necessitate a precise spatial arrangement of catalytic sites. Continuous catalytic sites benefit the oligomerization of acetylene/intermediates, generating oligomers such as polyacetylene that potentially poison the catalyst^19–21. This contrasts sharply with the isolated single site, which predominantly favours unilateral reactions (Supplementary Fig. 1)^22,23. Therefore, catalytic sites with specific distances are essential for acetylene hydrodimerization to 1,3-butadiene; however, implementing such precision in inorganic materials presents significant obstacles. Given this, the strategic integration of dimetal sites into the well-defined molecular skeleton holds significant promise for advancing the production of 1,3-butadiene^24–27. Meanwhile, the molecular skeleton offers flexible coordinating ligands that can effectively fulfill the requirements for multi-step acetylene hydrodimerization through coordination modulation^28–30.

In this work, a series of dicopper paddlewheel Cu₂(LCOO)₄ (L = tert-butyl (^tBu), isopropyl (ⁱPr), ethyl (Et), and methyl (Me)), bridged by bidentate carboxylate ligands with specific Cu···Cu distances, are developed for electrosynthesis of 1,3-butadiene. Through sequential modulation of the carboxylate ligands (Me → Et → ⁱPr → ^tBu), we demonstrate progressive enhancement of electron density at dicopper sites and structural stability within the Cu₂(LCOO)₄ series. Among them, Cu₂(^tBuCOO)₄ delivers optimal performance, attributed to its most electron-rich Cu sites that thermodynamically favor acetylene dimerization and subsequent hydrogenation steps. As a result, Cu₂(^tBuCOO)₄ achieves a 1,3-butadiene Faradaic efficiency (FEC₄H₆) of 91% at −0.55 V vs. the reversible hydrogen electrode (vs. RHE), with a partial current density (JC₄H₆) of −50 mA cm⁻² and a formation rate (FRC₄H₆) of 0.93 mmol h⁻¹ cm⁻² in 0.5 M K₂SO₄ catholyte using a flow cell. Particularly simulating the production of 1,3-butadiene from coal-derived acetylene (15%) in a membrane electrode assembly (MEA) system, Cu₂(^tBuCOO)₄ exhibits FEC₄H₆ exceeding 82% at currents of ≤ −300 mA, and remains above 60% at −600 mA with a full-cell voltage (E_cell) of 1.94 V, while demonstrating 30-h stability at −300 mA.

Results and discussion

Synthesis and structural characterization of Cu₂(^tBuCOO)₄

Figure 1a illustrates the synthesis of the dicopper paddlewheel Cu₂(^tBuCOO)₄, featuring bidentate bridging tert-butylcarboxylate ligands. This Cu₂(^tBuCOO)₄ was synthesized by reacting Cu(NO₃)₂·3H₂O with potassium pivalate (^tBuCOOK), and its crystallographic structure was subsequently determined through single-crystal X-ray diffraction (SCXRD) analysis. As revealed by the crystallographic structure in Fig. 1a and Supplementary Table 1, Cu₂(^tBuCOO)₄ exhibited a distinctive paddlewheel configuration with dicopper sites (intramolecular Cu···Cu distance: 2.57 Å). In this structure, four tert-butylcarboxylate ligands (^tBuCOO) occupied the equatorial positions, functioning as bidentate bridges to coordinate two axially distributed Cu atoms through Cu-O bonds (Supplementary Fig. 2). Besides, two solvent molecules (H₂O) coordinated weakly to the dicopper sites along the axial outward direction, architecting a distorted square-pyramidal geometry around each Cu site (Supplementary Fig. 3 and Supplementary Table 2). Furthermore, optical microscopy (Fig. 1a), scanning electron microscopy (SEM, Supplementary Fig. 4), and energy dispersive spectroscopy (EDS, Supplementary Fig. 5) visualized that Cu₂(^tBuCOO)₄ crystallized as micron-sized plates (5 ~ 10 μm) with the uniformly distributed elements of Cu, C, and O. The high phase purity and crystallinity of Cu₂(^tBuCOO)₄ were unequivocally confirmed by comparing the powder X-ray diffraction (PXRD) pattern with simulated diffraction result derived from single crystal structural data (Fig. 1b).

Fig. 1. Synthesis illustration and structural characterization of the dicopper paddlewheel Cu₂(^tBuCOO)₄.

a Schematic representation for the synthesis of Cu₂(^tBuCOO)₄, including its single crystal structure and corresponding optical microscopy photograph. b Experimental and simulated PXRD patterns of Cu₂(^tBuCOO)₄ crystal. Inset: molecular structure of Cu₂(^tBuCOO)₄ with solvent molecules (H₂O) omitted for clarity. c UV-Vis absorption spectrum of Cu₂(^tBuCOO)₄. d Raman and e FT-IR spectra of Cu₂(^tBuCOO)₄ and ^tBuCOOK precursor. f Normalized Cu K-edge XANES and g FT-EXAFS spectra in R-space of Cu₂(^tBuCOO)₄ using Cu foil, Cu₂O, and CuO as references.

Additionally, the molecular structure of Cu₂(^tBuCOO)₄ was validated by various spectroscopic techniques. The ultraviolet-visible (UV-Vis) absorption spectrum of Cu₂(^tBuCOO)₄ displayed two peaks at 313 nm and 352 nm, assigned to the charge transfer between ligand and metal (Fig. 1c), alongside the intra-ligand charge transition (250 nm) and Cu d-d charge transition (676 nm), manifesting the formation of the Cu-ligand complex³¹. Compared to the ^tBuCOOK precursor, Raman signals associated with the deformation vibrations of Cu-Cu-O and O-Cu-O bonds were observed at 163 cm⁻¹, 185 cm⁻¹, and 207 cm⁻¹ for Cu₂(^tBuCOO)₄ (Fig. 1d)^32,33. Similarly, Fourier transform infrared (FT-IR) spectrum of Cu₂(^tBuCOO)₄ displayed a characteristic Cu-O stretching vibration at 620 cm⁻¹ (Fig. 1e)^34,35. Meanwhile, the Δν (COO⁻) value (160 cm⁻¹), representing the difference between antisymmetric (1573 cm⁻¹) and symmetric (1413 cm⁻¹) carboxylate stretching modes, provided spectroscopic evidence for the bidentate bridging coordination of Cu-O bonds^36,37. X-ray absorption spectroscopy (XAS) was employed to further investigate the electronic structure and local coordination environment of Cu sites in Cu₂(^tBuCOO)₄. The Cu K-edge X-ray absorption near edge structure (XANES) spectrum of Cu₂(^tBuCOO)₄ closely resembled that of standard CuO, indicating a Cu²⁺oxidation state (Fig. 1f). This result corresponds to its Cu 2p (Cu 2p_3/2, 935.1 eV) and Cu LMM Auger (571.3 eV) X-ray photoelectron spectroscopy (XPS) spectra (Supplementary Fig. 6)^38,39. Moreover, a small pre-edge peak observed at 8978 eV, assigned to the 1 s → 3 d transition for the Cu²⁺ d⁹ configuration, also confirmed the presence of Cu^2+40–42. Fourier-transformed k³-weighted extended X-ray absorption fine structure (FT-EXAFS) spectrum of Cu₂(^tBuCOO)₄ revealed a distinct peak associated with the Cu-O scattering path at 1.53 Å in the first shell (Fig. 1g), consistent with the deconvoluted Cu-O peak at 530.2 eV in the high-resolution O 1 s spectrum (Supplementary Fig. 6). Unlike Cu foil, no prominent Cu-Cu peak was detected at 2.24 Å in Cu₂(^tBuCOO)₄, excluding the formation of Cu clusters. These spectroscopic findings corroborate the crystallographically determined paddlewheel configuration of Cu₂(^tBuCOO)₄ with dicopper sites, wherein each axial Cu atom establishes bidentate bridges with four O atoms from distinct equatorial tert-butylcarboxylate ligands.

Electrocatalytic performance of Cu₂(^tBuCOO)₄ in 1,3-butadiene electrosynthesis

The electrosynthesis of 1,3-butadiene for Cu₂(^tBuCOO)₄ was first investigated in a three-electrode flow cell, with 0.5 M K₂SO₄ as catholyte and pure acetylene as feed gas (Supplementary Fig. 7). As illustrated by the polarization curve (Supplementary Fig. 8), Cu₂(^tBuCOO)₄ delivered a current density of −164 mA cm⁻² at −1.0 V vs. RHE under pure acetylene feed. Replacing acetylene with argon led to a substantial decrease in current density, indicating enhanced electrocatalytic activity of Cu₂(^tBuCOO)₄ towards acetylene. The output stream from potentiostatic electrolysis (−0.65 V vs. RHE) using acetylene or argon feed was analysed by gas chromatography (GC). The formation of 1,3-butadiene (C₄H₆) was observed exclusively with acetylene feed, whereas no corresponding signal was detected under argon (Fig. 2a). The identity of C₄H₆ product was further verified by mass spectrometry (MS), which showed fragmentation patterns identical to those of 1,3-butadiene reference (Fig. 2b), demonstrating its formation through electrocatalytic acetylene hydrodimerization of Cu₂(^tBuCOO)₄.

Fig. 2. Electrocatalytic performance of Cu₂(^tBuCOO)₄ for 1,3-butadiene electrosynthesis benchmarked against commercial Cu-based electrocatalysts in a three-electrode flow cell.

a GC profiles of gaseous products from Cu₂(^tBuCOO)₄-catalyzed potentiostatic electrocatalysis (−0.65 V vs. RHE) under acetylene or argon feed. b MS analysis of C₄H₆ product from Cu₂(^tBuCOO)₄, referenced to 1,3-butadiene standard. c Product FE distributions and JC₄H₆ as a function of applied potentials (E) for Cu₂(^tBuCOO)₄ under pure acetylene without iR compensation. Comparison of d FEC₄H₆ and e JC₄H₆ between Cu₂(^tBuCOO)₄ and commercial Cu-based catalysts at an equivalent Cu loading. The error bars of FEC₄H₆ and error bands of JC₄H₆ in c-e represent the standard deviation from three independent experiments. f FEC₄H₆ (top) and JC₄H₆ (bottom) of Cu₂(^tBuCOO)₄ for acetylene hydrodimerization with 15%, 50% and 100% acetylene concentrations.

The potential-dependent product FE distributions for acetylene hydrodimerization over Cu₂(^tBuCOO)₄ were then investigated (Fig. 2c). Remarkably, Cu₂(^tBuCOO)₄ exhibited an optimal FEC₄H₆ of 91% at −0.55 V, while maintaining its values above 61% throughout the potential range from −0.55 V to −0.85 V. At −0.85 V, Cu₂(^tBuCOO)₄ achieved a JC₄H₆ of −50 mA cm⁻² and a FRC₄H₆ of 0.93 mmol h⁻¹ cm⁻². To benchmark these results, comparative studies were conducted using commercial Cu-based catalysts (Cu, CuO, and Cu₂O catalysts characterized in Supplementary Fig. 9) with an equivalent Cu loading of 0.48 mg cm⁻², determined from the optimized loading of Cu₂(^tBuCOO)₄ (details in Supplementary Figs. 10–11). As shown by the comparison in Fig. 2d, e and Supplementary Fig. 12, Cu₂(^tBuCOO)₄ demonstrated improved FEC₄H₆ and JC₄H₆ relative to commercial Cu-based catalysts within the potential window of −0.55 V to −0.85 V. Specifically, the FEC₄H₆ of Cu₂(^tBuCOO)₄ reached 91% at −0.55 V, substantially surpassing commercial CuO (80%), Cu₂O (77%), and Cu (67%) catalysts (Fig. 2d). At −0.85 V, Cu₂(^tBuCOO)₄ exhibited a significantly higher JC₄H₆ of −50 mA cm⁻² compared to commercial CuO (−13 mA cm⁻²), Cu₂O (−5 mA cm⁻²), and Cu (−8 mA cm⁻²) catalysts (Fig. 2e). Considering the dilution of coal-derived acetylene, we next investigated the hydrodimerization performance of Cu₂(^tBuCOO)₄ at lower acetylene concentrations of 15% and 50% (Fig. 2f and Supplementary Fig. 13). Although JC₄H₆ at −0.85 V decreased from −50 mA cm⁻² (pure acetylene) to −30 mA cm⁻² (15% acetylene), FEC₄H₆ at −0.55 V was maintained at 84% (15% acetylene) relative to the 91% obtained for pure acetylene. Notably, Cu₂(^tBuCOO)₄ exhibited competitive performance relative to previously reported Cu-based electrocatalysts, particularly regarding its FEC₄H₆ and JC₄H₆ at low C₂H₂ concentrations (Supplementary Fig. 14 and Supplementary Table 3)^18,43,44. To establish the necessity of dicopper within the paddlewheel structure, a comparative study was conducted utilizing dicopper (named Cu₂) and monocopper (named Cu₁) molecular catalysts (Supplementary Fig. 15 and Supplementary Note 1). Cu₂ displayed markedly improved performance relative to Cu₁, with 23% enhanced FEC₄H₆ and 5-fold higher JC₄H₆ at −0.8 V (Supplementary Fig. 16). These results clearly demonstrate that dicopper paddlewheel complex preferentially electrocatalyzes acetylene hydrodimerization to 1,3-butadiene over the competing acetylene semihydrogenation to ethylene.

Coordination modulation of Cu₂(LCOO)₄ for improved 1,3-butadiene electrosynthesis

A series of dicopper paddlewheel Cu₂(LCOO)₄, bearing three distinct carboxylate ligands (L = ⁱPr, Et, and Me), were synthesized as controls (Fig. 3a) for investigating the mechanism of acetylene hydrodimerization over Cu₂(^tBuCOO)₄. The dicopper paddlewheel configuration with bidentate bridging carboxylates was confirmed for all Cu₂(LCOO)₄ (L = ⁱPr, Et, and Me) through comprehensive characterization (SCXRD, PXRD, optical microscopy, UV-Vis, Raman, FT-IR, XPS, SEM, and EDS analyses in Supplementary Figs. 17–31 and Supplementary Note 2). Additionally, FT-EXAFS and Cu K-edge XANES spectra demonstrated that all Cu₂(LCOO)₄ featured Cu-O coordination and Cu²⁺ sites (Fig. 3b, c), substantiating their structural homology with Cu₂(^tBuCOO)₄ despite different carboxylate ligands. It is noteworthy that carboxylate ligands greatly affect the electronic structure of Cu sites, as evidenced by the negative energy shift of the absorption edge from Cu₂(MeCOO)₄ to Cu₂(^tBuCOO)₄ in the Cu K-edge XANES (Fig. 3c). This observation was further reinforced by Cu L-edge spectra (Supplementary Fig. 32), where characteristic L₃ (931.2 eV) and L₂ (951.2 eV) transitions progressively decreased in peak intensity in the order Me > Et > ⁱPr > ^tBu, signifying an increased Cu electron density across the Cu₂(LCOO)₄ series^45,46. UV-Vis absorption wavelength also underwent a red shift as the carboxylate functional groups varied from Me to ^tBu, which reflects enhanced carboxylate ligand-to-Cu charge transfer (Fig. 3d)³⁰. Correspondingly, the negative shift in Cu²⁺ binding energy from Cu₂(MeCOO)₄ to Cu₂(^tBuCOO)₄ implied progressively stronger electron-donating capacity of carboxylate ligands to the Cu sites (Fig. 3e)^47,48. Regardless of the ligand effect, four Cu₂(LCOO)₄ complexes exhibited comparable intramolecular and intermolecular Cu···Cu distances (Supplementary Fig. 33 and Supplementary Table 4).

Fig. 3. Coordination modulation of dicopper molecular catalysts for 1,3-butadiene electrosynthesis in a three-electrode flow cell.

a Molecular structures of dicopper paddlewheel Cu₂(LCOO)₄ with four distinct carboxylate ligands (L = ^tBu, ⁱPr, Et, and Me). For clarity of visualization, solvent molecules have been omitted. b FT-EXAFS in R-space and c normalized Cu K-edge XANES spectra for Cu₂(LCOO)₄ and the references. d UV-Vis absorption spectra showing carboxylate ligand-to-metal charge transfer in Cu₂(LCOO)₄. e Cu LMM Auger spectra of Cu₂(LCOO)₄. f FEC₄H₆ and g JC₄H₆ at various potentials (E) of Cu₂(LCOO)₄ catalysts in 0.5 M K₂SO₄ catholyte under pure acetylene feed without iR compensation. The error bars of FEC₄H₆ and error bands of JC₄H₆ in f, g represent the standard deviation from three independent experiments.

Subsequently, four Cu₂(LCOO)₄ complexes (L = ^tBu, ⁱPr, Et, and Me) were systematically evaluated for electrocatalytic acetylene hydrodimerization. In a three-electrode flow cell (0.5 M K₂SO₄ catholyte, pure acetylene feed), Cu₂(^tBuCOO)₄ delivered the highest current density of −164 mA cm⁻² at −1.0 V vs. RHE (Supplementary Fig. 34), substantially surpassing Cu₂(ⁱPrCOO)₄ (−118 mA cm⁻²), Cu₂(EtCOO)₄ (−93 mA cm⁻²), and Cu₂(MeCOO)₄ (–78 mA cm⁻²). Across the potential range of −0.55 V to −0.85 V, Cu₂(^tBuCOO)₄ achieved the maximum FEC₄H₆ compared to other Cu₂(LCOO)₄ (L = ⁱPr, Et, and Me), while consistently keeping FEC₄H₆ values above 61% throughout this range (Fig. 3f and Supplementary Fig. 34). As depicted in Fig. 3g and Supplementary Fig. 35, a positive correlation was observed between JC₄H₆ and the series of carboxylate ligands (Me → Et → ⁱPr → ^tBu), with Cu₂(^tBuCOO)₄ emerging as the optimal catalyst for acetylene hydrodimerization, presumably owing to its strongly electron-donating ^tBuCOO ligand.

Electrocatalytic acetylene hydrodimerization by Cu₂(LCOO)₄ in MEA systems

The viability of Cu₂(LCOO)₄ molecular catalysts for practical implementation is fundamentally determined by their 1,3-butadiene electrosynthesis performance within MEA systems^49,50. Accordingly, we investigated electrocatalytic acetylene hydrodimerization using Cu₂(LCOO)₄ as the cathode in a catholyte-free MEA system with humidified acetylene feed (Fig. 4a and Supplementary Fig. 36). Here, iridium oxide supported on titanium felt (IrO₂/Ti felt) served as the anode for the oxygen evolution reaction in 1 M KOH anolyte. Under humidified pure acetylene feed in a MEA system (cathodic area: 1 × 1 cm²), Cu₂(^tBuCOO)₄ produced current densities ranging from −20 mA cm⁻² to −70 mA cm⁻² within the E_cell window of 1.75 V to 2.03 V. Concomitantly, Cu₂(^tBuCOO)₄ maintained FEC₄H₆ values above 51% over this voltage window, culminating in a maximal FEC₄H₆ of 85% at an E_cell of 1.75 V (Fig. 4b). By contrast, other Cu₂(LCOO)₄ complexes (L = ⁱPr, Et, and Me) exhibited lower FEC₄H₆ and less favorable E_cell under identical conditions (Fig. 4c and Supplementary Figs. 37–38). The FEC₄H₆ of Cu₂(LCOO)₄ at −60 mA cm⁻² exhibited a stepwise increase across the carboxylate ligand series (Me → Et → ⁱPr → ^tBu), reaching values of 32%, 45%, 54%, and 62%, respectively. This positive correlation between FEC₄H₆ and carboxylate ligands aligned with observations from flow cell experiments.

Fig. 4. Electrocatalytic acetylene hydrodimerization over dicopper molecular catalysts in the MEA system.

a Exploded view of the MEA configuration. Experiments were conducted with cathodic areas of b–d 1 × 1 cm² and e, f 5 × 5 cm². Two types of acetylene feeds were assessed: humidified pure acetylene (100%, b, c) and simulated coal-derived acetylene (15%, d–f). b Product FE distributions and corresponding E_cell versus current densities (J) for Cu₂(^tBuCOO)₄ without iR compensation. c Comparison of FEC₄H₆ among different Cu₂(LCOO)₄ molecular catalysts (L = ^tBu, ⁱPr, Et, and Me) under identical MEA conditions. d FEC₄H₆ as a function of current densities for Cu₂(^tBuCOO)₄ at different gas flow rates. The error bands and error bars in (b–d) represent the standard deviation from three independent experiments. e FEC₄H₆ and E_cell versus applied currents, as well as (f) long-term operational stability at −300 mA for Cu₂(^tBuCOO)₄ in an enlarged MEA electrolyzer (gas flow rate: 60 sccm).

For emulating the industrial 1,3-butadiene production from coal-derived acetylene, we performed the electrocatalytic hydrodimerization of acetylene over Cu₂(^tBuCOO)₄ in a MEA electrolyzer with humidified 15% acetylene (Ar balance)^4,5. Given that the gas flow rate directly impacts acetylene diffusion and mass transport, particularly with dilute acetylene feed, we initially studied the acetylene hydrodimerization of Cu₂(^tBuCOO)₄ using 15% acetylene at different flow rates (Fig. 4d and Supplementary Figs. 39–40). Cu₂(^tBuCOO)₄ exhibited optimal performance at a flow rate of 60 standard cubic centimetres per minute (sccm), reaching a FEC₄H₆ of 78% at −20 mA cm⁻² (E_cell = 1.72 V) and maintaining FEC₄H₆ values above 46% at −70 mA cm⁻² (E_cell = 1.97 V). However, at −70 mA cm⁻², the FEC₄H₆ dropped to 28% at 30 sccm and 26% at 100 sccm, attributed to enhanced side reactions resulting from insufficient mass transport at low flow rates and limited reactant-catalyst residence time at high flow rates⁸. Remarkably, the MEA performance of Cu₂(^tBuCOO)₄ was competitive with that of previously reported Cu-based catalysts for the electrosynthesis of 1,3-butadiene in a two-electrode configuration (Supplementary Table 5). Furthermore, Cu₂(^tBuCOO)₄ enabled efficient 1,3-butadiene electrosynthesis in an enlarged MEA electrolyzer (5 × 5 cm²) with 15% acetylene feed at 60 sccm (Supplementary Fig. 41). As shown in Fig. 4e and Supplementary Fig. 42, the FEC₄H₆ exceeded 82% at currents of ≤ −300 mA and remained above 60% at -600 mA (E_cell = 1.94 V). Additionally, Cu₂(^tBuCOO)₄ demonstrated 30 h stability at −300 mA, sustaining FEC₄H₆ between 87% and 69% with a stable E_cell ranging from 1.73 V to 1.88 V (Fig. 4f). Moreover, the preliminary techno-economic analysis (TEA) established the economic viability of C₄H₆ electrosynthesis pathway from 15% coal-derived acetylene, utilizing the specific parameters applied in a 25 cm² MEA electrolyzer (Supplementary Note 3 and Supplementary Fig. 43).

Mechanistic insights into 1,3-butadiene electrosynthesis over Cu₂(LCOO)₄

In order to elucidate the mechanism of acetylene hydrodimerization over Cu₂(LCOO)₄, operando XAS experiments were first performed on the Cu₂(LCOO)₄ electrodes to identify their true active sites under working conditions (Supplementary Fig. 44). For the Cu₂(^tBuCOO)₄, no apparent changes in the Cu K-edge were observed from the XANES and corresponding first-order derivative spectra throughout the electrocatalytic process, suggesting its Cu sites stabilized at the +2 state (Fig. 5a and Supplementary Fig. 45). Quasi-in situ XPS spectra of Cu₂(^tBuCOO)₄ further indicated the stabilization of Cu²⁺ sites during acetylene hydrodimerization (Supplementary Fig. 46). When the applied potential varied from open circuit potential (OCP) to −0.85 V vs. RHE, Cu₂(^tBuCOO)₄ retained identical Cu-O coordination without any additional Cu-Cu scattering path, as verified by FT-EXAFS and wavelet-transformed EXAFS (WT-EXAFS) (Fig. 5b, c). Meanwhile, the coordination numbers of the Cu-O and Cu-Cu paths held steady at ~ 4 and ~ 1 according to quantitative EXAFS fitting analysis (Supplementary Fig. 47 and Supplementary Table 6). Furthermore, quasi-in situ XRD patterns and FT-IR spectra of Cu₂(^tBuCOO)₄ electrode after acetylene hydrodimerization exhibited characteristic crystalline peaks and distinct spectral features related to Cu-O stretching and carboxylate stretching vibrations, in agreement with the pristine Cu₂(^tBuCOO)₄ electrode (Supplementary Fig. 48). The proton nuclear magnetic resonance (¹H NMR) spectrum of the catholyte collected after the reaction revealed no ligands associated with Cu₂(^tBuCOO)₄, suggesting no substantial leaching or breakdown (Supplementary Fig. 49). These results, together with ex-situ HAADF-STEM and elemental mapping images (Supplementary Fig. 50), confirm that Cu₂(^tBuCOO)₄ preserved its structural integrity during electrocatalysis, consistent with the observations reported for Cu molecular catalysts⁵¹. Similarly, the XAS results for Cu₂(ⁱPrCOO)₄ and Cu₂(EtCOO)₄ demonstrated their Cu²⁺ sites and Cu-O coordination persisted throughout the acetylene hydrodimerization (Fig. 5d, e, Supplementary Figs. 51–56 and Supplementary Tables 7–8). These findings were further substantiated by analyses of quasi-in situ XPS spectra, XRD patterns and FT-IR spectra, as well as ex-situ ¹H NMR, HAADF-STEM and elemental mapping images (Supplementary Figs. 57–64).

Fig. 5. Mechanistic investigation of 1,3-butadiene electrosynthesis over dicopper molecular catalysts.

Operando a Cu K-edge XANES, b FT-EXAFS spectra in R-space, and c WT-EXAFS contour plots for Cu₂(^tBuCOO)₄ electrode during acetylene hydrodimerization. Cu foil, Cu₂O, and CuO are included as references in (a–c). Operando d Cu K-edge XANES and e FT-EXAFS spectra in R-space of four Cu₂(LCOO)₄ electrodes at OCP and −0.85 V vs. RHE. f Charge density difference for adsorbed C₂H₂ on the Cu₂(LCOO)₄ (L = ^tBu, ⁱPr, and Et). Blue, red, brown, and white spheres represent Cu, O, C, and H atoms, respectively. Cyan and yellow indicate charge depletion and accumulation, respectively. g Free energy diagrams for electrocatalytic acetylene hydrodimerization on various Cu₂(LCOO)₄ at 0 V vs. SHE. Inset: detailed configuration of reaction intermediates on Cu₂(^tBuCOO)₄, represented by blue, red, brown, and white spheres for Cu, O, C, and H atoms, respectively. h Potential-dependent in situ ATR-SEIRAS spectra of Cu₂(^tBuCOO)₄ electrode during electrocatalytic acetylene hydrodimerization. i In situ Raman spectra of electrocatalytic acetylene hydrodimerization process for Cu₂(^tBuCOO)₄ electrode, recorded from OCP to −0.6 V vs. RHE.

Conversely, a Cu⁰ peak at ~ 8981 eV appeared in the Cu K-edge XANES spectra of Cu₂(MeCOO)₄ once the applied potential deviated from OCP (Fig. 5d). This peak was clearly discernible in the first-order derivative XANES spectra (Supplementary Fig. 65) and matched the Cu⁰ peak identified from quasi-in situ XPS results (Supplementary Fig. 66). Moreover, FT-EXAFS and WT-EXAFS spectra of Cu₂(MeCOO)₄ at −0.85 V vs. RHE closely resembled those of the Cu foil standard (Fig. 5e and Supplementary Fig. 67), with the Cu-Cu coordination number approaching ~ 5 (Supplementary Fig. 68 and Supplementary Table 9). Besides, no characteristic crystalline and vibrational peaks were detected in the quasi-in situ XRD and FT-IR results for Cu₂(MeCOO)₄ electrode after the reaction (Supplementary Fig. 69). Concurrently, ¹H NMR spectrum of the catholyte obtained post-reaction displayed methyl protons referencing to pure acetic acid (Supplementary Fig. 70). These results suggested structural reconstruction of Cu₂(MeCOO)₄, which was also observed via ex-situ HAADF-STEM and HR-TEM (Supplementary Figs. 71–72). This dynamic reconstruction of Cu₂(MeCOO)₄ probably arises from its lower binding energy between Cu and ligands relative to other Cu₂(LCOO)₄ catalysts (Supplementary Fig. 73). Additionally, the role of Cu sites within these intact complexes (Cu₂(LCOO)₄, L = ^tBu, ⁱPr, and Et) was further elucidated by comparing their electrocatalytic performance with that of corresponding pristine carboxylic acid ligands (LCOOH, L = ^tBu, ⁱPr, and Et). The pristine ligands showed minimal catalytic activity relative to the complexes (Supplementary Fig. 74), confirming that the Cu active sites in these complexes primarily drive the 1,3-butadiene electrosynthesis.

Second, molecular dynamics (MD) simulations were performed at 298.15 K to examine the steric hindrance of alkyl substituents (^tBu, ⁱPr, and Et) within Cu₂(LCOO)₄ on acetylene adsorption and diffusion. Initial analyses, including molecular density and mean square displacement (MSD), suggested that steric hindrance had a negligible impact on the overall acetylene adsorption capacity and its transport to the catalyst surface (Supplementary Figs. 75–77 and Supplementary Note 4). We then computed the radial distribution function (RDF) to assess the local accessibility of acetylene around the Cu sites. Cu₂(EtCOO)₄ exhibited a significantly higher g value at its secondary peak (5.5 Å, g ≈ 3.1) compared to Cu₂(ⁱPrCOO)₄ (5.7 Å, g ≈ 2.3) and Cu₂(^tBuCOO)₄ (6.0 Å, g ≈ 1.6) (Supplementary Fig. 78 and Supplementary Note 4). This indicates that acetylene accessibility to the Cu sites increases in the order of ^tBu < ⁱPr < Et, attributable to decreasing steric hindrance^52,53. Despite this observed difference in local steric hindrance, Cu₂(^tBuCOO)₄ consistently achieved optimal performance. To elucidate the electronic contribution distinct from steric effects, charge density difference and Bader charge analyses were conducted. The carboxylate ligands enriched the electron density at Cu sites in the order of Et < ⁱPr < ^tBu, which correlated positively with their FEC₄H₆ at −60 mA cm⁻² in the MEA system (Supplementary Fig. 79). Moreover, the charge density difference revealed that Cu₂(^tBuCOO)₄, with more electron-rich Cu sites, exhibited greater electron donation to adsorbed acetylene (0.145 e⁻) than Cu₂(ⁱPrCOO)₄ (0.141 e⁻) and Cu₂(EtCOO)₄ (0.131 e⁻), implying a stronger acetylene activation capability (Fig. 5f). Consequently, the enhanced electron density of Cu active sites is the primary factor contributing to its competitive catalytic performance, offsetting the unfavorable effects of local steric hindrance. Mechanistically, this enriched electron density enhances back-donation into the antibonding π* orbital of *C₂H₂^9,54, weakening the C≡C triple bond and intrinsically boosting the reactivity of acetylenic carbons toward C-C coupling. Simultaneously, the dicopper paddlewheel configuration spatially co-activates two *C₂H₂ intermediates in close proximity, and this synergy between electronic activation and geometric pre-organization collectively benefits the C-C coupling energetics. Furthermore, we investigated free energy diagrams of Cu₂(^tBuCOO)₄ along the precoupling and prehydrogenation pathways (Supplementary Fig. 80). Among these pathways, the most energetically favorable route involves the intermolecular dicopper-mediated precoupling of *C₂H₂ to *C₄H₄ (∆G values = −1.87 eV), followed by hydrogenation to *C₄H₅ (∆G = −0.06 eV) (Supplementary Fig. 81). Accordingly, free energy diagrams of other Cu₂(LCOO)₄ catalysts were also performed via the precoupling pathway (Fig. 5g). All Cu₂(LCOO)₄ energetically favored the precoupling of *C₂H₂ into *C₄H₄. Notably, the subsequent hydrogenation of *C₄H₄ to *C₄H₅ was exothermic for Cu₂(^tBuCOO)₄, but endothermic for other Cu₂(LCOO)₄ catalysts, thus defining this step as the rate-determining step (RDS). The corresponding ∆G_RDS declined in the sequence of Et (0.29 eV) → ⁱPr (0.27 eV) → ^tBu (−0.06 eV), in line with progressive enhancement in hydrodimerization performance from Et to ^tBu.

Third, operando electrochemical impedance spectroscopy (EIS) was carried out on Cu₂(LCOO)₄ to probe interfacial behavior and reaction kinetics during acetylene hydrodimerization⁵⁵. The frequency and phase angle intensity in the Bode plots derived from the EIS spectra reflected the charge transfer associated with reduction processes at the catalyst/electrolyte interface^56,57. For Cu₂(^tBuCOO)₄, changing the feed gas from argon to acetylene resulted in phase angle peaks shifting to higher frequencies along with decreased intensities, signifying a faster charge transfer process (Supplementary Fig. 82)^57,58. Clearly, acetylene electroreduction kinetics were accelerated from Cu₂(EtCOO)₄ to Cu₂(^tBuCOO)₄, as demonstrated by their reduced peak intensity and high-frequency shift of the phase angle peak at −0.5 V (Supplementary Fig. 83a). Meanwhile, Cu₂(^tBuCOO)₄ exhibited a lower charge transfer resistance ( ~ 42 Ω) than Cu₂(ⁱPrCOO)₄ ( ~ 92 Ω) and Cu₂(EtCOO)₄ ( ~ 126 Ω) (Supplementary Fig. 83b), further suggesting its rapid kinetics of acetylene hydrodimerization⁵⁸. Afterwards, in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) was employed to monitor the electrocatalytic acetylene hydrodimerization on Cu₂(LCOO)₄ (L = ^tBu, ⁱPr, and Et) electrodes (Supplementary Fig. 84). Upon switching the potential from OCP to −0.5 V, Cu₂(^tBuCOO)₄ displayed characteristic bands at 1106 and 1500 cm⁻¹ assigned to the dimerization intermediate *C₄H₄ (Fig. 5h)^44,59. Meanwhile, bands corresponding to hydrogenated *C₄H₆ species appeared at 1261 cm⁻¹ (C−H bending), 1331 cm⁻¹ (=CH₂ bending), 1384 and 1451 cm⁻¹ (=CH₂ scissoring), and 1569 cm⁻¹ (C=C stretching), matching the spectral features of adsorbed 1,3-butadiene^60–62. These features intensified at more negative potentials, reflecting the efficient accumulation of intermediates conducive to 1,3-butadiene production. By contrast, Cu₂(ⁱPrCOO)₄ exhibited comparable *C₄H₄ intensity but considerably weaker *C₄H₆ signals (Supplementary Fig. 85a), whereas Cu₂(EtCOO)₄ showed minimal *C₄H₆ variation alongside a new band at 1179 cm⁻¹ assignable to *C₂H₄ (Supplementary Fig. 85b)⁶³, suggesting competing acetylene semihydrogenation to ethylene. To further corroborate the ATR‑SEIRAS results, in situ electrochemical Raman spectra were recorded at various potentials for Cu₂(^tBuCOO)₄ (Supplementary Fig. 86). Upon applying negative potentials (Fig. 5i), the C≡C stretching vibration appeared at 1964 cm⁻¹, showing a redshift relative to gas‑phase acetylene (1974 cm⁻¹), indicative of π-adsorbed acetylene (*C₂H₂)^64,65. Concurrently, the C≡C and C=C stretching vibrations were detected at 2106 and 1541 cm⁻¹, attributable to vinyl acetylene (*C₄H₄) existing as an isomer of CH=CH−CH=CH intermediate^44,59, in good agreement with the *C₄H₄ configuration predicted by the free energy diagram of Cu₂(^tBuCOO)₄. As the potential increased from 0 V to −0.6 V, a characteristic peak at 1685 cm⁻¹ was significantly intensified, attributed to the C=C symmetric stretching vibration of 1,3-butadiene (*C₄H₆)^66–68. During the aforementioned in situ Raman processes, Cu₂(^tBuCOO)₄ electrode retained its integrity, as evidenced by unchanged characteristic peaks for O-Cu-O bending, COO rocking, and C-C stretching (Supplementary Fig. 87)^33,69. Importantly, no polyacetylene signals were observed for Cu₂(^tBuCOO)₄, whereas distinct polyacetylene peaks appeared for commercial Cu catalysts (Supplementary Fig. 88). This contrast underscores the superiority of dicopper sites over continuous Cu surfaces in suppressing polyacetylene formation. Beyond these surface-sensitive spectroscopic probes, online differential electrochemical mass spectrometry (DEMS) was employed to monitor volatile intermediates and gaseous products (Supplementary Figs. 89–90). Signals for the C₄H₄ intermediate (m/z = 52) and the C₄H₆ product (m/z = 54) were detected concurrently. Substituting D₂O for H₂O in the 0.5 M K₂SO₄ electrolyte yielded an m/z = 56 signal (C₄H₄D₂) alongside the C₄H₄ signal, directly proving that H₂O serves as the hydrogen source for the hydrogenation of C₄H₄ into C₄H₆. Combined with in situ ATR-SEIRAS and Raman observations described above, these converging results from three independent techniques confirm the stepwise reaction pathway: C-C coupling of C₂H₂ to form the C₄H₄ intermediate, followed by its hydrogenation to generate C₄H₆.

In summary, we designed a series of dicopper molecular catalysts with bidentate bridging carboxylate ligands, developing a coordination modulation strategy that effectively orients the electrocatalytic acetylene hydrodimerization towards 1,3-butadiene production. Remarkably, Cu₂(^tBuCOO)₄ with tert-butylcarboxylate ligands demonstrated competitive performance for 1,3-butadiene electrosynthesis compared to previously reported Cu-based catalysts under both pure acetylene and simulated coal-derived acetylene feeds. Mechanistic studies unveiled that this improved hydrodimerization performance originates from the optimized electron-donating character of tert-butylcarboxylate ligands, which preserves Cu site integrity while facilitating acetylene dimerization and subsequent hydrogenation. This work underscores the significance of strategic coordination modulation in molecular dicopper sites for advanced 1,3-butadiene electrosynthesis.

Mothods

Chemicals and materials

All chemical reagents were commercially available and were employed without any treatment. Potassium pivalate (^tBuCOOK, 98%), pivalic acid (^tBuCOOH, 99%), isobutyric acid (ⁱPrCOOH, 99%), propionic acid (EtCOOH, 99%), acetic acid (MeCOOH, 99%), copper (II) oxide (CuO, 99.5%), deuterated water (D₂O, 99.8%), and 5 wt% Nafion solution were obtained from Adamas. Copper (II) hydroxide (Cu(OH)₂, 94%), cuprous (I) oxide (Cu₂O, 99.5%), and copper (Cu, 99.9%) catalysts were purchased from Shanghai Macklin Biochemical Co., Ltd. Copper (II) nitrate trihydrate (Cu(NO₃)₂·3H₂O, 99%), acetone (CH₃COCH₃, 99.5%), and hydrochloric acid (HCl, CP, 36 ~ 38%) were acquired from Sinopharm Chemical Reagent Co., Ltd. Methanol (CH₃OH, 99.9%), ethanol (CH₃CH₂OH, 99.9%), ethyl acetate (C₄H₈O₂, 99.5%), cyclohexane (C₆H₁₂, 99.9%), n-hexane (C₆H₁₄, 99%), 1,4-dioxane (C₄H₈O₂, 99.5%), and isopropanol ((CH₃)₂CHOH, 99.7%) were supplied by Guangdong Guanghua Sci-Tech Co., Ltd. Iridium chloride hydrate (IrCl₃·3H₂O, 99.9%) was purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd. Potassium sulphate (K₂SO₄, 99%) was achieved from Shanghai Titan Scientific Co., Ltd. Titanium felt was purchased from KunShan Kuangxun Ltd. (China). The carbon paper with a gas diffusion layer (Sigracet 29 BC) and anion exchange membrane (AEM) was offered by the Fuel Cell Store. All electrolytes were prepared fresh as needed using ultra-pure water produced by a high-Q distillation system ( > 18.25 MΩ) and were stored at room temperature (25 °C).

Synthesis of dicopper paddlewheel Cu₂(^tBuCOO)₄

Cu₂(^tBuCOO)₄ was synthesized by reacting Cu(NO₃)₂·3H₂O with ^tBuCOOK in aqueous solution. Typically, 1 mmol of Cu(NO₃)₂·3H₂O was dissolved in 15 mL ultra-pure water. An aqueous solution of ^tBuCOOK (2 mmol in 15 mL ultra-pure water) was then added slowly to the above solution, resulting in the precipitation of blue crystals. Finally, the blue product was collected by vacuum filtration and washed thoroughly with ultra-pure water (3 × 50 mL). Product yield: 49%. Elemental analysis calculated (%) for C₂₀H₄₀Cu₂O₁₀: C 42.32, H 7.12, O 28.19; found (%): C 42.38, H 7.09, O 28.09.

Synthesis of dicopper paddlewheel Cu₂(LCOO)₄ (L = ⁱPr, Et, and Me)

A series of dicopper paddlewheel Cu₂(LCOO)₄ was synthesized using corresponding carboxylic acids and copper (II) precursors. Specifically, Cu₂(ⁱPrCOO)₄ was synthesized from ⁱPrCOOH and CuO; Cu₂(EtCOO)₄ from EtCOOH and Cu(OH)₂; and Cu₂(MeCOO)₄ from MeCOOH and CuO. Generally, carboxylic acid (2 equiv.) was dissolved in ethanol (100 mL), except for Cu₂(ⁱPrCOO)₄ where ultra-pure water was used as solvent. Then the copper precursor (1.05 equiv.) was added under continuous stirring. The mixture was refluxed at 100 °C for 12 h, yielding a blue solution. After filtration to remove excess copper precursor, the filtrate was refined by rotary evaporation and dried under vacuum. The crude products were recrystallized from different solvent systems: methanol/ethyl, acetate/H₂O for Cu₂(EtCOO)₄ and Cu₂(MeCOO)₄, and 1,4-dioxane/n-hexane for Cu₂(ⁱPrCOO)₄, affording blue-green crystals. For Cu₂(ⁱPrCOO)₄, yield: 36%; elemental analysis calculated (%) for C₂₀H₃₆Cu₂O₁₀: C 42.62, H 6.45, O 28.39; found (%): C 42.59, H 6.27, O 28.28. For Cu₂(EtCOO)₄, yield: 40%; elemental analysis calculated (%) for C₁₂H₂₄Cu₂O₁₀: C 31.65, H 5.32, O 35.13; found (%): C 31.57, H 5.14, O 34.95. For Cu₂(MeCOO)₄, yield: 39%; elemental analysis calculated (%) for C₈H₁₆Cu₂O₁₀: C 24.06, H 4.05, O 40.07; found (%): C 24.09, H 3.99, O 40.32.

Single-crystal X-ray crystallography

SCXRD data were collected on a Bruker D8 VENTURE diffractometer using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) for the structural determination of Cu₂(LCOO)₄. Detailed crystallographic data and structure refinement parameters are summarized in Supplementary Table 1. The crystal structures were solved using the SHELXT program and refined by full-matrix least-squares methods on F² values using SHELXL-2014, as implemented in the Olex2 software package. All non-hydrogen atoms were refined with anisotropic parameters, and hydrogen atoms were integrated into the calculated positions and refined with a fixed geometry based on their carrier atoms. Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre (CCDC 2444725 ~ 2444728). Additional crystallographic details are provided in Supplementary Table 2 and Supplementary Table 4.

Preparation of the cathode

10 mg of catalyst and 10 µL of Nafion solution (5 wt%) were ultrasonically dispersed in acetone to prepare the catalyst ink (10 mg mL⁻¹). This ink was air-sprayed onto gas diffusion electrodes (GDEs) with cathodic areas of 2 × 0.5 cm² (flow cell), 1 × 1 cm² (MEA), followed by infrared drying for 10 min to achieve a Cu loading of 0.48 mg cm⁻². For the scalability test (cathodic area: 5 × 5 cm²), the Cu loading was maintained at this level by proportionally scaling up the ink volume.

Synthesis of IrO₂/Ti felt anode

IrO₂-supported Ti felt (IrO₂/Ti felt) as an anode was fabricated on a Ti felt substrate via a dip-coating method followed by the thermal decomposition process⁷⁰. The Ti felt was first cleaned with an acetone/water mixture and then etched in 6 M HCl for 30 min. Later, the etched Ti felt was immersed in an isopropanol/HCl (6 M) solution (9:1 v/v) containing IrCl₃·3H₂O (30 mg). Afterwards, the Ti felt was calcined at 500 °C for 10 min. These procedures were repeated until achieving an IrO₂ loading of 2 mg cm⁻².

Electrochemical measurements

All electrochemical measurements were conducted under ambient conditions (25 °C) using a CHI 1140D electrochemical workstation. For 1,3-butadiene electrosynthesis in a three-electrode flow cell (cathodic area: 2 × 0.5 cm²), the catalyst-sprayed GDE, Hg/HgO, and IrO₂/Ti felt were employed as the working, reference, and counter electrodes, respectively. The cathode and anode compartments were separated by an anion exchange membrane (Fumasep FAB-PK-130). Both catholyte (0.5 M K₂SO₄, pH = 6.7 ± 0.2) and anolyte (1 M KOH, pH = 13.6 ± 0.1) were circulated at a steady rate of 10 mL min⁻¹. Pure acetylene feed was continuously supplied to the gaseous chamber at 30 sccm. Polarization curves were recorded at a scan rate of 20 mV s⁻¹ without iR compensation. All applied potentials were converted to the RHE scale according to the following equation: E (vs. RHE) = E (vs. Hg/HgO) + 0.099 V + 0.059 V × pH⁷¹. For the quantification of gaseous products, chronoamperometric measurements were conducted for 15 min at each applied potential to ensure steady-state conditions. To assess the structural stability of the catalyst, continuous electrolysis was performed at representative potentials for 60 min prior to post-reaction characterizations. Operando electrochemical impedance spectroscopy of catalysts was performed in 0.5 M K₂SO₄ catholyte at different potentials under acetylene and argon feed with the frequency ranging from 0.1 Hz to 10,000 Hz.

Electrocatalytic acetylene hydrodimerization was performed in two types of MEA electrolyzers with cathodic areas of 1 × 1 cm² and 5 × 5 cm². Both electrolyzers were identical in design and assembly, differing only in their electrode dimensions. The catalyst-sprayed GDE and IrO₂/Ti felt served as the cathode and anode, respectively. The cathode and anode chambers were separated by an anion exchange membrane (SciMater AEM2093), with the anodic channel circulating 1 M KOH at a rate of 10 mL min⁻¹ and the cathodic channel feeding humidified acetylene (100% or 15% balanced with Ar). The gas flow rate was maintained at 60 sccm using mass flow controllers unless otherwise specified. Chronopotentiometric measurements were carried out at various currents to assess the gaseous products and stability of catalysts. The potentials presented herein were E_cell. For the long-term stability test, the anolyte was periodically replaced to maintain constant ionic concentration and conductivity.

Products analysis

The quantitative analysis of gaseous products was carried out using an online gas chromatography (GC-9790plus, Fuli) equipped with flame ionization (FID) and thermal conductivity (TCD) detectors. For both the three-electrode (−0.55 to −0.85 V vs. RHE) and MEA (−20 to −600 mA) measurements, the FE of gaseous products was calculated according to the following equation:

$$\text{FE }\left(\%\right)=\frac{{c_i\times z}_{\text{i}}\times \nu \times \text{F}}{i_{total}\times {\text{V}}_m}\times 100$$

where c_i and z_i represent the concentration (ppm) and the number of electrons transferred for the i-th product (i = C₄H₆, C₂H₄, and H₂), respectively, ν denotes the gas flow rate (mL min⁻¹), F is the Faradaic constant (96485 C mol⁻¹), i_total is the total current of the electrocatalytic reaction (A), and V_m is the gas molar volume.

The formation rate of C₄H₆ (FRC₄H₆) was calculated based on the following equation¹²:

$${\text{FR}}_{{\text{C}}_4{\text{H}}_6}\left({\text{mmol}}^{-1}{\text{h}}^{-1}{\text{cm}}^{-2}\right)=\frac{Q\times {\text{FE}}_{{\text{C}}_4{\text{H}}_6}}{z\times \text{F}\times t\times A}$$

where Q and FEC₄H₆ represent the total charge passed during electrolysis and the Faradaic efficiency of C₄H₆, respectively, z denotes the number of electrons transferred for C₄H₆ formation, F is the Faradaic constant (96485 C mol⁻¹), t represents the electrolysis duration (h), and A is the geometric area of the cathode (cm²).

Theoretical calculation

Density functional theory (DFT) calculations were implemented using the Vienna ab initio simulation package (VASP) according to the projector augmented wave (PAW) methods⁷². The wave function of valence electrons was expanded based on the plane-wave basis set with a kinetic-energy cutoff of 400 eV. Exchange-correlation interactions were treated using the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA)^73–75. Grimme’s zero damping D³ method was employed to account for the van der Waals interactions⁷⁶. Hellmann-Feynman forces were computed within the total energy of 10⁻⁴eV and the force convergence criterion of 0.05 eV Å⁻¹ to conduct structural relaxations. Herein, computational models of Cu₂(LCOO)₄ complexes were built to represent the catalysts (Supplementary Data 1), while preserving the relative orientation and spatial arrangement found in the corresponding crystal structures. A 20 Å vacuum layer was established along three orthogonal directions, and Brillouin-zone sampling was performed with single gamma point. The computational hydrogen electrode model proposed by Nørskov et al. was adopted for the Gibbs free energy change (ΔG) calculation of each elementary step during the acetylene hydrodimerization process⁷⁷. The ΔG value was computed using the equation of ΔG = ΔE + ΔZPE − TΔS + eU, where ΔE is the DFT-computed reaction energy of adsorbed reactant and product species on the catalyst; ΔZPE and ΔS refer to the variations in the zero-point energy and entropy between the adsorbed species and the gas-phase molecules at 298.15 K, calculated from vibrational frequencies; e is the electron transfer number and U denotes the applied potential, which was set to 0 for simplicity. To elucidate the influence of diverse substituents within Cu₂(LCOO)₄ on acetylene adsorption and mass transfer, molecular dynamics (MD) simulations were executed employing GROMACS v2022.05⁷⁸. The computational cell, with dimensions of 6 × 6 × 8 nm³, was populated by 1000 acetylene molecules in conjunction with the Cu₂(LCOO)₄ models (Supplementary Data 1) via the PACKMOL program⁷⁹. Canonical ensemble (NVT) simulations were carried out at 298.15 K using a V-rescale thermostat.

Characterizations

SEM and elemental mapping images were characterized by a field-emission FEI-Verios G4 microscope integrated with an EDS spectrometer at 10 kV. MS analysis was performed using a Thermo Fisher Scientific Trace 1300-ISQ 7000 system coupled with a TG-5SILMS capillary column. FT-IR spectra were acquired utilizing the ATR mode of a Bruker Tensor II spectrometer. UV-Vis spectroscopy was performed using a Unico UV-4802 spectrophotometer. The PXRD patterns were recorded on a Bruker D8 Advance X-ray diffractometer equipped with Cu-Kα source (λ = 1.5405 Å) at an operating current and voltage of 40 mA and 40 kV. XPS data were obtained using a Kratos AXIS Ultra DLD apparatus with Al Kα X-ray source. Quasi-in situ XPS spectra were obtained using a custom-made inert atmosphere transfer vessel to transfer electrodes into the XPS system without air exposure. All spectra were referenced to the adventitious carbon C 1 s peak at 284.8 eV for binding energy calibration. Elemental analysis was conducted using an EMA 502 Elemental Micro Analyzer (VELP Scientifica). ¹H NMR spectra of catholyte collected after electrocatalytic acetylene hydrodimerization were performed on a Bruker Avance NEO 500 MHz spectrometer. Cu L-edge XAS measurements were carried out at the XMCD beamline of the National Synchrotron Radiation Laboratory in Hefei.

Operando Cu K-edge XAS spectra were recorded in transmission mode at the Shanghai Light Source utilizing a custom-built electrochemical cell. The cell comprised a catalyst-sprayed GDE, graphite rod, and Ag/AgCl as working, counter, and reference electrodes, operating with 0.5 M K₂SO₄ electrolyte under continuous acetylene purging. All XAS data were processed through normalization and energy calibration against Cu foil at 8979 eV using the Athena program. The k³-weighted χ(k) data in k-space were Fourier transformed to R-space without phase correction and fitted within the k = 2 ~ 11 Å⁻¹ and R = 1 ~ 3 Å ranges using crystal structures of the catalysts in Artemis software.

In situ Raman spectroscopy was conducted on a LabRAM HR800 confocal Raman spectrophotometer (532 nm excitation) using a flow cell setup with the quartz optical window. The cathodic and anodic chambers were supplied with 0.5 M K₂SO₄ and 1 M KOH solutions, respectively, both maintained at a flow rate of 10 mL min⁻¹ by peristaltic pumps. The acetylene gas flow was regulated at 30 sccm using a mass flow controller.

In situ ATR-SEIRAS was performed using a Bruker INVENIO R Fourier transform infrared spectrometer equipped with a three-electrode cell. A platinum wire served as the counter electrode, while a saturated Ag/AgCl electrode was employed as the reference electrode. The working electrode was fabricated by air-spraying a catalyst ink onto the GDE. A saturated solution of acetylene in 0.5 M K₂SO₄ was used as the electrolyte.

Online DEMS (Pfeiffer PrismaPro) was employed to monitor volatile intermediates and products in real time during electrocatalytic acetylene hydrodimerization, using a three-electrode cell comprising the catalyst-sprayed GDE (working electrode), a platinum wire (counter electrode), and an Ag/AgCl electrode (reference electrode). During the measurements, 0.5 M K₂SO₄ electrolyte was bubbled with acetylene, and the gaseous products diffused through the hydrophobic polytetrafluoroethylene (PTFE) membrane (pore diameter ≤ 20 nm, Linglu) into the vacuum chamber for analysis.

Author contributions

W.Z.X. and P.F.G. contributed equally to this work. W.Z.X. carried out the experiments and wrote the manuscript. P.F.G. conducted computational simulations. J.F.W., R.D., M.T.L., and L.F.T. assisted with material characterization and analyzed the experimental results. M.R.L. and N.F. assisted with the theoretical calculations. L.Z. and B.L.Z. conceived the project and revised the manuscript. Z.J.L. contributed to in situ electrochemical measurements. All authors reviewed and commented on this article.

Peer review

Peer review information

Nature Communications thanks Antonio Leyva-Perez and the other anonymous reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper and its supplementary information files. Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-026-72739-4.