A cyanide-free route towards the electrosynthesis of nitriles

Domain: biology
Published: 2026-03-17
Editorial outcome: major_revision

Abstract
The manufacture of nitriles is critical to various industrial applications, but poor selectivity results in the significant release of pollutive byproducts such as CO , NO and toxic cyanide. Here, we report the electrochemical conversion of benzaldehyde to benzonitrile at near-unity selectivity, during which Co O clusters-decorated Cu O electrocatalyst activates the C−N bond of an unstable intermediate species. Operando spectroelectrochemical studies and theoretical calculations reveal that benzaldehyde couples with NH to form the phenylmethanimine intermediate bound atop Cu2+ active sites, which facilitates hydrogen transfer from the imine group to nearby surface oxygen. Our electrochemical system can convert aromatic and aliphatic aldehydes to the corresponding nitriles at Faradaic efficiencies of 78-97%. This can be paired with cathodic NO reduction, which produces a commensurable amount of NH to that consumed even at a current density of 200 mA cm-2. Our work offers a clean synthetic route to otherwise-pollutive chemicals, and also expands the repertoire of organonitrogen compounds that can be accessed by electrocatalysis.

Introduction
Nitriles have far-ranging applications in pharmaceuticals, agrochemicals, dyes and polymers1. For example, benzonitrile is manufactured at 10 million kg per year due to its importance as a building block in pharmaceuticals and melamine resins2. Currently, nitriles are manufactured through the ammoxidation of alkanes3,4, alcohols or aldehydes5 with ammonia and oxygen at high temperatures (Fig. 1a). These conditions require heavy energy consumption and result in low selectivity, leading to the release of CO , NO and over-oxidation products6. Other synthesis methods, such as the Sandmeyer reaction and Rosenmund-von Braun reaction, require stoichiometric amounts of toxic cyanide reagents7,8 (Fig. 1b); more than one million tons of cyanide are consumed per year by the chemicals industry9, which generate hazardous wastes due to incomplete cyanide consumption or production of cyanide derivatives10. Thus, it is important to develop cleaner methods of nitriles synthesis that can utilize renewable energy and benign conditions, while avoiding cyanide reagents.

Recently, there has been great interest in electrochemical C−N coupling reactions, as they offer a sustainable route for producing valuable organonitrogen compounds such as urea, amides, amines, oximes and amino acids11-25. Comparatively, nitriles have a higher degree of unsaturation; a different electrochemical route must be designed to access this type of C≡N bond. Previously, it has been reported that copper salt can catalyze the thermal ammoxidation of aldehydes to nitriles; Cu2+ binds to the aldimine intermediate to form an iminylcuprate complex, which then dissociates to Cu+ and the nitrile product26. This led us to consider the possibility of enabling ‘electrochemical ammoxidation’ by building Cuδ+ into our electrocatalyst. We also note that the oxidative nature of the reaction means that it can be coupled to the cathodic nitrogen oxides reduction reaction (NO RR) to NH , which suggests that waste NO in industrial exhaust can be utilized as a N-source to enhance the sustainability of the reaction (Fig. 1c).

In this work, we demonstrate the electrocatalytic conversion of benzaldehyde to benzonitrile using NH as a benign nitrogen source under ambient conditions. This is achieved with an electrocatalyst comprising Co O clusters-decorated Cu O nanorod array (Co OS/Cu O), which enabled Faradaic efficiency of 98.7(±1.1)% and near-unity selectivity under an applied potential of 1.35 V vs. RHE. The electrocatalyst remains stable with Faradaic efficiency averaging 95.4(±2.5)% over 100 hours. Operando spectroelectrochemical and density function theory (DFT) studies show that benzaldehyde couples with NH to form an unstable phenylmethanimine intermediate, which subsequently undergoes Cuδ+-mediated electrochemical dehydrogenation to benzonitrile. The electrochemical benzaldehyde-to-benzonitrile conversion can be integrated into reaction pathways that enable the nitrilation of more challenging alcohol and alkyl groups. Our electrochemical system can also convert other aromatic and aliphatic aldehydes, including those derived from CO , to the corresponding nitriles with Faradaic efficiencies of 78-97%. Finally, we demonstrated tandem benzonitrile electrosynthesis and NO RR at current densities up to 200 mA cm-2.

Results
Electrocatalyst design and characterization
We prepared the Co O /Cu O electrocatalyst by chemical oxidation of copper foam in an aqueous NaOH and (NH ) S O solution, which embellished the surface with Cu(OH) nanorods, followed by immersion in a solution containing ZIF-67 metal-organic framework and annealing in air at 350°C (see characterization of the Cu(OH) and ZIF-67/Cu(OH) nanorod arrays in Supplementary Figs. 1-2). Co K-edge X-ray absorption near-edge structure (XANES) spectroscopy indicated that the ZIF-67 was successfully converted to Co O , as the absorption edge of Co O /Cu O displayed identical features to that of the Co O standard (Supplementary Fig. 3). The Fourier-transformed extended X-ray absorption fine structure (EXAFS) spectra revealed oscillations corresponding to Co−O, the Co−Co bond with octahedral centers, and the Co−Co bond with octahedral and tetrahedral centers, which further confirms the formation of Co O cluster27. High-angle annular dark-field scanning TEM (HAADF-STEM) with corresponding EDX mapping showed that the Co O cluster took the form of a slightly concave octahedron attached to the tip of the Cu O nanorod (Fig. 2a and Supplementary Fig. 4). Scanning electron microscopy (SEM) revealed an array of cluster-on-nanorod morphology on the copper foam surface (Fig. 2b). The X-ray diffraction (XRD) pattern showed peaks at 35.5°, 38.7°, 61.5° corresponding to (11-1), (111) and (11-3) lattice planes of CuO, as well as 36.5° and 61.5° corresponding to (111) and (220) lattice planes of Cu O (Supplementary Fig. 5)28. This is corroborated by high-resolution transmission electron microscopy (HRTEM), which revealed crystalline phases with lattice spacings of 0.242 and 0.234 nm corresponding to Cu O(111) and CuO(111), respectively. It should be noted that both Cu O(110) and Cu O(111) facets were observed (Supplementary Fig. 6), with the dominant one being the (111) surface. The Co O cluster also appeared to be highly crystalline, with lattice spacings of 0.246 and 0.287 nm corresponding to (311) and (220) planes (Fig. 2c).

Electrochemical conversion of benzaldehyde to benzonitrile
The electrochemical C−N coupling of benzaldehyde and ammonia to benzonitrile was conducted in a three-electrode H-type cell, with a working electrode comprising Co O /Cu O on copper foam, an Ag/AgCl reference electrode and a platinum plate counter electrode (Supplementary Fig. 7). The optimal anolyte concentration comprised 0.04 M benzaldehyde, 2.0 M NH and 0.1 M NaOH in a 41:9 water:acetonitrile mixture (Supplementary Fig. 8-9). The catholyte is an aqueous 0.1 M NaOH solution, and is separated from the anolyte by Nafion® 117 membrane. The Faradaic efficiencies towards benzonitrile showed a volcano-type tendency in the potential range of 1.15-1.65 V vs. RHE, with the optimal Faradaic efficiency at 98.7(±1.1)% at 1.35 V vs. RHE (Fig. 2d). Beyond 1.55 V vs. RHE, the Faradaic efficiency decreases significantly due to competing NH oxidation reaction. This is corroborated by the linear sweep voltammetry (LSV) curve, which revealed the NH oxidation peak to be about 1.5 V vs. RHE under reaction conditions (Supplementary Fig. 10). The yield of benzonitrile reached 48.6(±6.7)% after 1 hour of reaction at 1.55 V vs. RHE, and further increased to 75.0(±1.5)% after 3 hours (Supplementary Fig. 11). The selectivity towards benzonitrile was ~100% with no obvious byproducts detected (Fig. 2d and Supplementary Figs. 12-13). No benzonitrile was detected at open-circuit voltage (OCV), without applied potential or in the absence of NH , which confirms the electrochemical nature of the reaction and the important role of NH as the nitrogen source (Supplementary Fig. 14).

We investigated the robustness of the Co O /Cu O electrocatalyst by subjecting it to a constant potential of 1.35 V vs. RHE for 100 hours, during which portions of the electrolyte were periodically removed for analysis and replaced with fresh electrolyte. Under these conditions, the electrocatalyst achieved a stable current density of ~10 mA cm-2, with an average Faradaic efficiency of 95.4(±2.5)% (Fig. 2e). Post-reaction characterizations of the electrocatalyst (i.e., SEM, EDX, XANES, EXAFS and X-ray photoelectron spectroscopy (XPS), see Supplementary Figs. 15-18) showed no obvious change in the structure or composition, which suggests its compatibility for long-term operation.

Investigation of reaction mechanism
Having established the efficacy of Co O /Cu O towards benzonitrile production, we studied the role of different components in the electrocatalyst. The Cu O electrocatalyst without Co O clusters was also prepared (see characterization in Supplementary Figs. 19-20) and yielded a Faradaic efficiency of 71.8(±3.1)% at 1.35 V vs. RHE, which suggests that Cu O functions as the main catalytic component driving the benzaldehyde-to-benzonitrile conversion (Supplementary Fig. 21). Only trace benzonitrile product was detected when pristine copper foam (CF) was used as the working electrode (Supplementary Fig. 22), which suggests that either Cu2+ or Cu+ should function as the electrocatalytic active site in Cu O. We performed operando electrochemical impedance spectroscopy (EIS) to study the electrode/electrolyte interface during reaction (Fig. 3a)29. At potentials between 0.5-1.0 V vs. RHE, we observed a signal in the middle-frequency region (100-102 Hz) that corresponds to the electrooxidation of the Cu O catalyst (i.e., Cu0Cu+Cu2+). This is consistent with the cyclic voltammetry (CV) curve, which showed two distinct oxidation peaks at 0.60 and 0.85 V vs. RHE corresponding to Cu0Cu+ and Cu0/Cu+Cu2+, respectively28 (Supplementary Fig. 23). At potentials >1.05 V vs. RHE, the signal is observed in the low-frequency region (10-1-100 Hz), which is related to the appearance of oxidation species on the surface of the electrode. This signifies that the structural evolution of Cuδ+ is complete and the benzaldehyde electrosynthesis occurs. In situ Raman spectroscopy showed distinctive peaks at 218 and 294 cm−1 at OCV, which can be attributed to Cu O and CuO, respectively (Fig. 3b and Supplementary Figs. 24-25). In the absence of benzaldehyde and NH , the Cu O peak disappeared at 1.35 V vs. RHE, indicating the oxidation of Cu+ to Cu2+. With benzaldehyde and NH , the Cu O peak can still be observed at 1.35 V vs. RHE, while the CuO peak showed reduced intensity compared to that at OCV, which suggests that Cu2+ catalyzed the benzaldehyde-to-benzonitrile conversion and was reverted to Cu+ in the process.

The reaction mechanism was further probed using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), by tracking the adsorbed intermediates and products on Cu O/CF at potentials from OCV to 1.65 V vs. RHE (Fig. 3c and Supplementary Fig. 26). Under OCV, peaks were observed at 1700, 1371, 1233 and 1138 cm-1, which could be assigned to the C=O stretching vibration of benzaldehyde, alcoholic O−H group, the N−H twisting vibration of CH −NH structure and the NH stretching vibration of CH −NH structure, respectively23,30. This implies that NH , which has a relatively strong nucleophilicity, can spontaneously attack benzaldehyde to form amino(phenyl)methanol, which undergoes dehydration to generate the unstable *benzyl-azane intermediate. As the potential increased to 1.15 V vs. RHE, the NH peak at 1138 cm-1 is diminished while the N−H peak at 1233 cm-1 is slightly enhanced. We observed the emergence of peaks corresponding to the N−H stretching vibration of CH=NH structure at 1296 cm-1, C=N stretching vibration at 1624 cm-1 and C≡N stretching vibration at 2259 cm-1, which indicates the formation of phenylmethanimine intermediate and benzonitrile product23,30. As the potential increases up to 1.65 V vs. RHE, the NH and N−H absorption peaks of unstable amino(phenyl)methanol and *benzyl-azane intermediates are weakened, whereas the C=N bond and C≡N peaks of phenylmethanimine and benzonitrile are generally strengthened. This signified that amino(phenyl)methanol and *benzyl-azane intermediates rapidly converted to the critical phenylmethanimine intermediate, which subsequently could be dehydrogenated to generate the benzonitrile. Liquid chromatography-quadrupole time of flight mass spectrometry (LC-QTOF) also ascertained the presence of phenylmethanimine intermediate and benzonitrile product in the post-reaction anolyte (Fig. 3d). The use of 15N-labelled NH yielded 15N-labelled phenylmethanimine and benzonitrile, which reinforced the important role of NH as a nitrogen source in benzonitrile electrosynthesis (Supplementary Fig. 27). Taken together, we postulate that NH readily undergoes C−N coupling with the carbonyl group of benzaldehyde to form an unstable phenylmethanimine intermediate, which subsequently undergoes Cuδ+-mediated electrochemical dehydrogenation to yield the benzonitrile product (Fig. 3e).

We further investigated the Cuδ+-mediated dehydrogenation step through density functional theory (DFT) calculations. A CuO(111) slab model with four atomic layers was constructed, upon which several initial adsorption geometries were examined. The most stable configuration features the imine nitrogen of phenylmethanimine (Ph−CH=NH) binding to a single two-coordinate Cu atom (Configuration 1 in Supplementary Fig. 28). This geometry suggests a possible adsorption mode in which the =NH moiety is in proximity with the surface, potentially enabling the abstraction of the N-bound hydrogen. Within the computational hydrogen electrode (CHE) framework, this hydrogen is removed as a coupled proton–electron pair rather than transferred to or stabilized on any surface atoms31. The resultant molecule adopts an sp3-like configuration and relocates to a bridge site coordinated by two Cu atoms (Supplementary Figs. 29c,d). The hydrogen atom from the CH= moiety is then abstracted by the surface to form the nitrile product (C≡N), culminating in the final state where the nitrogen atom bind s atop a single Cu atom (Supplementary Figs. 29e,f). This second hydrogen transfer is calculated to be thermodynamically more favorable than the first, as reflected by the downhill reaction energy (G). Overall, the G of phenylmethanimine dehydrogenation on CuO(111) is 0.70 eV (Fig. 3f and Supplementary Table 2). In contrast, phenylmethanimine dehydrogenation on Cu O(110) has a higher G of 1.16 eV (Fig. 3f and Supplementary Figs. 30-31), suggesting that Cu2+ species may be more effective for phenylmethanimine dehydrogenation than Cu+ species under the modeled conditions. This is substantiated by Bader charge analysis of the adsorbed phenylmethanimine on CuO(111). As reaction progresses, the phenylmethanimine molecular fragment exhibits an increasingly positive charge; from +0.16 in the initial adsorbed state to +0.85 in the first dehydrogenated intermediate and +2.10 in the final nitrile product (Supplementary Table 3). Correspondingly, CuO(111) exhibits increasingly negative charge (−0.16 → −0.85 → −2.10), which is indicative that the surface Cu2⁺ accepts electrons from phenylmethanimine and is reduced to Cu⁺.

To elucidate the influence of the Co O cluster, we similarly examined the phenylmethanimine dehydrogenation step on the Co O (311) surface (Fig. 3f and Supplementary Figs. 32-33). The calculated G of 0.96 eV lies between those of CuO(111) and Cu O(111), indicating an intermediate oxidizing strength within this computational model. It should be noted that these DFT results are based on idealized static slab models and mainly provide qualitative trends under real catalytic conditions. Experimentally, the Faradaic efficiency of benzaldehyde-to-benzonitrile conversion using Co O clusters supported on carbon paper is 32.6(±3.8)% (Supplementary Fig. 34), which suggests that the Co O clusters provide additional active sites that contribute to the enhanced Faradaic efficiency of Co O /Cu O. This is corroborated by the increased double-layer capacitance (C ) of Co O /Cu O compared to Cu O (2.06 versus 1.70 mF cm−2, see Fig. 4a and Supplementary Fig. 35). We also investigated the electronic structure of Co O /Cu O through XPS analysis (Fig. 4b-4c and Supplementary Figs. 36-37). High-resolution Co 2p XPS spectrum showed a negative shift compared to that of pure Co O powder, signifying a lower average Co oxidation state. Cu 2p XPS spectrum of Co O /Cu O showed a higher energy shift compared to that of Cu O, which indicates a higher average Cu oxidation state and suggests electron transfer from Cu to Co within the Co O /Cu O material. The higher average Cu oxidation state promotes the Cuδ+-mediated dehydrogenation step, thereby enabling higher Faradaic efficiencies for electrochemical benzaldehyde-to-benzonitrile conversion (Supplementary Fig. 34). Therefore, the decoration of Co O clusters on Cu O electrocatalyst not only increases the active sites, but can potentially modulate the electronic structure of the electrocatalyst, resulting in a higher average Cu oxidation state promoting the Cuδ+-mediated dehydrogenation step.

Electrosynthesis of various nitriles and utilization of NO
The broad applicability of Co O /Cu O electrocatalyst was demonstrated through the electrochemical conversion of various aldehydes to the corresponding nitriles at near-unity selectivities (Supplementary Fig. 38). An application scenario is the electrosynthesis of 2,6-dichlorobenzonitrile, an important herbicide with a market size of $23 million per year32,33; we achieved Faradaic efficiency of 81.2(±1.7)% at 1.35 V vs. RHE. The presence of electron-withdrawing groups such as −Cl, −Br and −CN generally led to higher Faradaic efficiencies of 93-97%, as the enhanced electrophilicity of these benzaldehydes promotes C−N coupling with nucleophilic NH . For electron-donating −CH and −OCH groups, Faradaic efficiencies were lower at 84.2(±6.1) and 77.8(±2.5)%. The Co O /Cu O electrocatalyst can be extended to the electrosynthesis of aliphatic nitriles, such as acetonitrile with a Faradaic efficiency of 86.2(±4.7)%. It should be noted that the acetaldehyde precursor can be obtained from electrochemical CO reduction reaction, thereby enabling the electrosynthesis of nitriles from renewable sources34. We also demonstrated that nitrile electrosynthesis can be integrated into reaction pathways starting from precursors with alcohol and even alkyl groups (Fig. 4d). For example, the electrochemical benzyl alcohol-to-benzonitrile conversion can be achieved Faradaic efficiency at 43.1(±2.0)% (Supplementary Fig. 39). The electrochemical toluene-to-benzonitrile conversion was conducted in two stages; toluene was first oxidized at 100 mA cm-2 for 2 h using a CoO /IrO on Ti mesh electrode to activate the C(sp3)−H bond and achieve sufficient benzaldehyde intermediate, after which NH was added and the reaction continued at 25 mA cm-2 to enable benzonitrile using the Co O /Cu O electrocatalyst (Supplementary Fig. 40).

Finally, we considered that the electrochemical valorization of waste NO to nitrogenous chemicals can mitigate pollution and reduce dependence on valuable NH as a nitrogen source. We therefore coupled cathodic NO RR with anodic benzonitrile electrosynthesis in a single electrochemical cell, with the former acting as a NH supply for the latter. The cathode was oxide-derived Cu (OD-Cu) synthesized by electrochemically reducing Cu O (Supplementary Fig. 41), and the catholyte comprised 0.1 M KNO in 1 M NaOH. As NH in the anolyte can crossover the Nafion membrane and lead to a higher-than-actual NO RR Faradaic efficiency, we employed a decoupled electrolyzer connected by O /H O redox couple, which can better separate the catholyte and anolyte in order to accurately quantify the amount of NH produced at the cathode (Supplementary Fig. 42). Notably, the NH consumption at anode was comparable to NH production at cathode even at current densities up to 200 mA cm-2, which signifies that waste NO can be viably incorporated into valuable nitriles (Figure 4e, Faradaic efficiencies can be found in Supplementary Fig. 43). This also means that the achieved partial current densities and production rates are competitive with other reported nitrile electrosynthesis, while maintaining near-unity selectivity (Supplementary Table 4).

Methods
Materials
All the chemicals and solvent were commercially available and directly used without further purification. Cu foam (Cu>99%, thickness 0.5 mm, 100 PPI) was purchased from Latech Scientific Supply Pte. Ltd. Hydrochloric Acid (37%, HCl), Sodium hydroxide (≥98%, NaOH), Ammonium persulphate (≥98%, (NH ) S O ), Cobalt(II) nitrate (≥98%, Co(NO ) ·6H O), Potassium nitrite (≥96%, KNO ), Benzaldehyde (purified by redistillation, ≥99.5%), Ammonium hydroxide solution (puriss., 30-33% NH in H O), Ammonium-15N hydroxide solution (3 N in H O, 98 atom% 15N), Benzonitrile (≥98%) were purchased from Sigma-Aldrich. 2-methylimidazole (>98%) was purchased from TCI. Acetonitrile (HPLC grade, ≥99.9%, MeCN) was purchased from Fisher Scientific Korea Ltd. Deuterium oxide (D, 99.9%, D O) and Dimethyl sulfoxide-D6 (D, 99.9%, DMSO-d6) were purchased from Cambridge Isotope Laboratories, Inc. 4-Chlorobenzaldehyde (>99%), 4-Chlorobenzonitrile (>97%), 4-Bromobenzaldehyde (>99%), 4-Bromobenzonitrile (>98%), 4-Cyanobenzaldehyde (>98%), 1,4-Dicyanobenzene (>98%), 2,6-Dichlorobenzaldehyde (>99%), 2,6-Dichlorobenzonitrile (>97%), 4-Methylbenzaldehyde (>99%), p-Tolunitrile (>98%), 4-Methoxybenzaldehyde (>99%), 4-Methoxybenzonitrile (>99%), Acetaldehyde (puriss, p.a., anhydrous, ≥99.5%) were purchased from Sigma-Aldrich.

Synthesis and characterization of the Co O /Cu O nanorod array electrocatalyst
The Co O /Cu O electrocatalyst was synthesized by the modified chemical oxidation followed by annealing procedure. Cu foam was ultrasonically cleaned in 3 M HCl solution for 10 min, then in a mixture of acetone and deionized water for another 10 min. The pretreated Cu foam was soaked into a 40 mL aqueous solution containing 4 g NaOH and 1.5 g (NH ) S O for 1 h, then washed with deionized water and ethanol. The resultant Cu(OH) nanorod array was prepared after drying at 60°C. Cu(OH) was immersed into 2 mmol cobaltous nitrate hexahydrate in methanol solution for 10 min, after which 8 mmol 2-methylimidazole in methanol solution was added under stirring and allowed to stand for 6 h. The resultant ZIF-67/Cu(OH) was taken out, washed with deionized water and methanol, dried at 60°C, then annealed at 350°C for 3 h, 2°C min-1 to form the Co O /Cu O electrocatalyst.

Electrocatalyst characterization
To characterize the Co O /Cu O electrocatalyst, X-ray diffraction (XRD) was detected on Bruker® D8 ADVANCE with Cu Kα source. Scanning electron microscopy (SEM) images were obtained on a Hitachi SU8220 FESEM at an accelerating voltage of 5 kV. Energy-dispersive X-ray (EDX) spectroscopy was collected with an on-board AMTEK® Octane Elite EDS System, with an accelerating voltage of 20 kV. Transmission electron microscopy (TEM) images were obtained on TEM JEOL 2100F. X-ray photoelectron spectroscopy (XPS) was measured on a PHI Quantum 2000 XPS system. X-Ray absorption spectroscopy (XAS) was conducted on XAFCA beamline at the Singapore Synchrotron Light Source (SSLS).

Evaluation of electrochemical performance
The electrochemical benzaldehyde-to-benzonitrile conversions were conducted in H-type electrolytic cell (purchased from Tianjin Aida). The electrolyte was prepared individually before each experimental run. The anolyte comprised 0.04 M benzaldehyde, 2.0 M NH and 0.1 M NaOH in 41:9 water:acetonitrile mixture (pH=13.16(±0.07)). The catholyte was 0.1 M aqueous NaOH catholyte. The overall reactor configuration comprised 15 mL of anolyte and 15 mL of catholyte, separated by Nafion® 117 membrane (size 2.5 cm by 2.5 cm, thickness 0.18mm). The Nafion® 117 membrane was activated in 0.5 M H SO solution at 80°C for 2 hours and stored in MilliQ water (18.2 MΩ). The working electrode was Co O /Cu O electrocatalyst on copper foam (1×1 cm2), the counter electrode was a platinum plate, and the reference was an Ag/AgCl (saturated KCl) electrode. Unless otherwise stated, the duration of the electrochemical reaction is 1 hour. All electrochemical measurements were performed using the Metrohm Autolab potentiostat PGSTAT204 without iR correction. All the potentials were provided without iR corrected and converted to reversible hydrogen electrode (RHE) with the following equation:
E = E + 0.0591 × pH + 0.197 (1)
RHE Ag/AgCl

The cyclic voltammetry (CV) and linear sweep voltammetry (LSV) curves were measured at a scan rate of 5 mV s-1. In situ electrochemical impedance spectroscopy (EIS) tests were tested at the potentials of 0.45 to 1.65 V vs. RHE with a frequency range from 10−1 to 105 Hz with an alternating-current amplitude of 10 mV. Electrochemical double-layer capacitance (C ) measurement was carried out by CV method with different scan rates in the non-Faradaic region. The C value was obtained from the slopes of the current density–scan rate plots. The 100-hour stability test was conducted at 1.35 V vs. RHE, during which portions of the electrolyte were periodically removed for analysis and replaced with fresh electrolyte. In universality tests and the integrated electrosynthesis system starting from other precursors, different precursors were added to the anolyte using a similar electrolysis procedure.

The qualitative and quantitative analysis of the products produced in anolyte was determined using high-performance liquid chromatography (HPLC, Agilent 1260) equipped with a DAD detector and an Eclipse Plus C18 column (4.6×150 mm). The mobile phase is ultrapure water/acetonitrile (v/v = 70% : 30%) with a flow rate of 1.0 ml min-1 and column temperature of 25°C. The formation of products in anolyte was further ensured by 1H nuclear magnetic resonance (NMR, Bruker AV400SB) with water suppression and liquid chromatography-quadrupole time of flight mass spectrometry (LC-QTOF, Agilent 6545) with 90% ultrapure water and 10% acetonitrile as flowing eluent.

The Faradaic efficiency, reaction rate, selectivity, conversion and yield for liquid product are calculated using the following equations:
Faradaic efficiency (%) = (N × F × C × V) / Q × 100% (2)
Reaction rate (μmol cm-1 h-1) = (C × V) / (S × t) (3)
Selectivity (%) = (C × V) / n × 100% (4)
Conversion (%) = n / n × 100% (5)
Yield (%) = Conversion × Selectivity (6)
where N is the number of electron transfer to generated product, F is the Faraday constant (96485 C mol−1), C is the concentration of liquid products after the electrosynthesis reaction, V is the volume of the electrolyte, Q is the total charge during the electrosynthesis process, S is the electrode area, t is the electrolysis time, n is the mole amount of consumed feedstock, n is the mole amount of initial feedstock.

Operando spectroelectrochemical studies
In situ ATR-SEIRAS was conducted using PerkinElmer Frontier FT-IR spectrometer equipped with a mercury cadmium telluride (MCT) detector. The measurements were carried out in a commercial electrochemical cell containing benzaldehyde and NH in 0.1 M aqueous NaOH electrolyte. The electrode was Cu O electrocatalyst on an Au film chemically deposited on the reflecting plane of the ATR Si prism. The background spectrum without applied potential was acquired at electrolyte condition before each systemic measurement. In situ spectra were collected under potentials of OCV and 1.15-1.65 V vs. RHE, by averaging 50 scans with a resolution of 4 cm-1 and subtracting the infrared background.

In situ Raman spectra were recorded using a Horiba LabRam Odyssey Nano Raman Spectrometer system with 633 nm laser. The Raman cell was equipped with a working electrode comprising Cu O deposited on carbon paper, an Ag/AgCl reference electrode and a Pt wire counter electrode. The cell was filled with benzaldehyde and NH in 0.1 M NaOH electrolyte. An Olympus N2667700 water immersion objective was submerged in the electrolyte to collect in situ Raman spectra under different electrochemical conditions.

Density functional theory (DFT) calculations
All periodic slab calculations were carried out using density functional theory (DFT) as implemented in the Vienna Ab initio Simulation Package (VASP)35. The Perdew–Burke–Ernzerhof (PBE)36 exchange-correlation functional within the generalized gradient approximation (GGA) was employed, along with projector-augmented wave (PAW)37 potentials and a plane-wave energy cutoff of 500 eV. Dispersion interactions were accounted for using the DFT-D3 method38.

Slab models of CuO(111) and Cu O(111) and Co O (311) surfaces were constructed with four atomic layers, where the bottom three layers were fixed during structural optimizations. The CuO(111) slab has lattice parameters a = 17.30 Å, b = 18.95 Å, and c = 28.26 Å, with interaxial angles α = β = 90° and γ = 107.76°. The Cu O(111) surface adopts a = 18.12 Å, b = 18.12 Å, and c = 31.10 Å, with α = β = 90° and γ = 120.00°. The Co O (311) slab exhibits a = 19.85 Å, b = 22.93 Å, and c = 26.31 Å, with α = β = 90° and γ = 106.78°. In all models, the c-axis is oriented normal to the surface plane, and a vacuum region of approximately 20 Å was added along this direction to prevent spurious interactions between periodic images. Brillouin zone sampling was performed using a Γ-centered 1 × 1 × 1 k-point mesh for all adsorption geometry optimizations39. Structural relaxations were conducted until the forces on each atom were below 0.02 eV/Å and the total energy change between successive steps was less than 10-5 eV. To account for the on-site Coulomb interactions in the localized 3d orbitals, the DFT+U method40 was applied with U = 7.0 eV for Cu in CuO41 and U = 4.0 eV for Co in Co O 42.

To rigorously assess the influence of k-point sampling for slabs of this size, we performed a convergence test on the Cu O model (Supplementary Table 1). Increasing the k-point mesh from 1×1×1 to 2×2×1 resulted in only marginal variations (≤0.01 eV) in the computed energy profiles, thereby confirming that Γ-point sampling is sufficient for this lateral cell dimension. On this basis, and given the nearly identical cell sizes across all three systems, the Γ-point (1×1×1) mesh validated for Cu O was consistently used for the CuO and Co O slabs in all subsequent calculations.

For all surfaces, only coordinatively unsaturated (CUS) metal sites were considered as potential adsorption sites. Guided by the surface symmetry and the locations of coordinatively unsaturated sites, we evaluated three, two, and three distinct adsorption geometries on the CuO(111), Cu O(111) and Co O (311) surfaces, respectively.

The dehydrogenation step was modeled using the computational hydrogen electrode (CHE) approach, where the chemical potential of H+ + e- is referenced to 0.5H 43. This method avoids explicitly modeling H adsorption sites. The Gibbs free energy was corrected by including zero-point energy and entropy contributions obtained from vibrational frequency calculations.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Xian et al. report the electrochemical conversion of benzaldehyde to benzonitrile on Co3O4/CuxO (Co3O4 clusters-decorated CuxO). Operando spectroelectrochemical studies and DFT calculations are performed to study the mechanism. It can be paired with cathodic NOx reduction, which produces a commensurate amount of NH3 that is consumed.\n1. As the target products are nitriles, will acetonitrile in the solvent affect the experimental results? Can the addition of acetonitrile to the solvent be avoided?\n2. In the DFT calculations, only the dehydrogenation of phenylmethanimine (Ph−CH=NH) is studied. How about the reactions from benzaldehyde to phenylmethanimine? Especially the C-N coupling, which is important for this work and should be studied.\n3. The CuO(111) and Cu2O(110) surfaces are chosen for DFT calculations. Why these two surfaces?\n4. Only one k-point is used in the DFT calculations. What are the sizes of the models? Maybe more k-points are needed.\n5. The Hubbard U value is set as 7 eV for CuO. How about Cu2O?\n6. How is the free energy data in Figure 3f calculated? Did they use the computational hydrogen electrode model?", "reviewer_2": "In this manuscript, the author has reported the electrochemical synthesis of nitrile from aldehyde without toxic cyanide. By using Co3O4/CuxO electrocatalyst, the Faradaic efficiency and selectivity achieved both over 90 %. Moreover, the experimental and theoretical analysis revealed that CuxO activated the electrochemical oxidation of the CN double bond to the CN triple bond. Based on the results, the author proposed that the nitrile production from waste NOx can be achieved by using the NOxRR reaction.\nThe data interpretation and conclusion of this manuscript are well-established. But the author should clarify the novelty, difference, and advantage of this reaction, compared with the other cyanation reactions without cyanide. For instance, similar works about the electrochemical synthesis of nitrile from aldehyde by using ammonia or NOxRR have already been reported as follows. (Y. Xiao et al., Green Chem., 27, 5715, 2025, Y. Maeda et al., RSC Adv., 15, 17562, 2025, C. Xue et al, JACS, 147, 32896, 2025 etc). After careful reading of the whole manuscript, the proposed reaction is interesting, but this work is not suitable for publication in Nat. Commun. since the novelty of this work does not meet the standard for Nat. Commun. Moreover, some concerns shown below should be adequately addressed.\n1. The article title seems to be exaggerated. This work mainly shows that Co2O3/CuxO electrocatalyst promotes the electrochemical conversion from aldehyde to nitrile. The generality of the reaction was not proved in this manuscript. The author should modify the title.\n2. The author used CuxO nanorod for the catalyst. Why did the author use the nanorod? Are there any morphological effects? The author should clarify whether the nanorods have a significant effect on the electrochemical reaction other than the increment of the surface area compared with the CuxO plate anode.\n3. The experimental details of the electrolysis were not described. The concentration of benzaldehyde was 40 mM. What is the volume of the electrolyte? What is the duration of the electrolysis? In addition, what is the yield of benzonitrile?\n4. The manuscript indicated that toluene was also converted to benzonitrile in two-stage electrolysis. But the electrode in the oxidation of toluene to benzaldehyde was not Co2O3/CuxO, but CoOx/IrO2, which is not described in the manuscript, only shown in the caption of the supplementally Figure. This is the misleading. The fact that the other electrocatalyst is necessary for the conversion from toluene to benzonitrile should be mentioned in the manuscript.\n5. The tandem benzonitrile synthesis and NOxRR electrolyser is an interesting result. The amount of the produced ammonia is much lower than the initial amount of ammonia in the anolyte. Toward the practical application of the tandem electrolysis, since the amount of the produced ammonia is too small compared with the concentration of ammonia in the initial electrolyte, it seems that the ammonia production by NOxRR has little effect on the concentration of ammonia. In addition, one benzonitrile stoichiometrically reacts with one ammonia in the overall reaction. But the concentration of ammonia is much higher than that of benzaldehyde. Is there a positive or negative effect on the nitrile synthesis when the concentration of ammonia is varied?", "reviewer_3": "The manuscript “A cyanide-free route towards the electrosynthesis of nitriles” reports an electrochemical strategy to convert aldehydes to nitriles with high selectivity using CuxO/Co3O4 electrocatalysts. The work is well presented, and the results are impressive. The authors demonstrate near-unity selectivity for benzaldehyde-to-benzonitrile conversion, supported by extensive characterization and operando studies. The figures are of high quality, particularly the TEM and elemental mapping, which convincingly illustrate the catalyst architecture. Overall, this is a valuable contribution to the field of sustainable electrocatalysis.\nHowever, I do notice there are gaps for improvement, especially the computational component:\n1. The computation of free energy considers only limited configurations. For a system of this size, the adsorption location and molecular orientation can significantly influence the calculated energetics. A more systematic search for adsorption geometries (including different binding sites and angular orientations) should be performed, or at least discussed.\n2. In Figure 3, the authors claim that Cu remains in an oxidized state during operation. A Bader charge analysis or similar method should be performed to clarify the degree of oxidation under reaction conditions.\n3. The manuscript lacks key information about the computational setup. Details such as the model construction and the lattice constant are missing. This information is critical for reproducibility and for evaluating the reliability of the theoretical conclusions.\n4. The authors should discuss the potential consequences of not including Co3O4 explicitly in the computational model.", "reviewer_4": "This manuscript reports a cyanide-free catalytic system for the synthesis of nitriles via electrocoupling of benzaldehyde and ammonia in an aqueous solution with the Co3O4 clusters-decorated CuxO electrocatalyst. Aromatic and aliphatic aldehydes electrochemically convert to the corresponding nitriles at Faradaic efficiencies of 78-97%. Besides the interesting results, the authors need to clarify some important issues. I recommend a major revision before reconsideration.\n1. The as-prepared Co3O4/CuxO electrocatalyst shows a heterogeneous structure. Co3O4 particles are modified on the top of the CuOx Nano wires; the contact edge of Co3O4/CuxO is very small compared with Co3O4 or CuxO. Co3O4, CuxO, and/or the contact edge may work as the active sites. The authors need to provide more experimental results to clarify this issue.\n2. Line 106, when discussing selectivity, you need to provide the conversion rate at the same time.\n3. Line 113, in an electrolysis period, the catalytic current should decrease with the increase of the conversion. Here, 10 mA cm-2 should belong to the background current, or NH3 oxidation reaction, not the electrochemical C−N coupling reaction.\n4. Line 124, when copper foam was used as the working electrode, the surface Cu0 should be oxidized to CuxO under applied conditions; hence, the conclusion that ‘Cu0 has little activity towards benzonitrile formation’ is unreasonable.\n5. The property of Co3O4 for the electrochemical C−N coupling reaction should be investigated, respectively, for further comparison."}, "author_response": "A point-by-point response to reviewers’ comments\nWe sincerely thank the editor for handling our manuscript and the reviewers for their careful\nassessment and valuable comments, which have helped improve the quality of our work.\nAddressing all points raised, we have revised the manuscript through careful consideration,\nconducted additional experiments, and consulted relevant literature. To facilitate review, all\nchanges in the manuscript and Supplementary Information are highlighted in yellow. We detail\nour point-by-point responses to the reviewers’ comments and corresponding revisions below.\nReviewer #1 (Remarks to the Author):\nXian et al. report the electrochemical conversion of benzaldehyde to benzonitrile on\nCo O /Cu O (Co O clusters-decorated Cu O). Operando spectroelectrochemical studies and\n3 4 x 3 4 x\nDFT calculations are performed to study the mechanism. It can be paired with cathodic NO\nx\nreduction, which produces a commensurate amount of NH that is consumed.\n3\n1. As the target products are nitriles, will acetonitrile in the solvent affect the experimental\nresults? Can the addition of acetonitrile to the solvent be avoided?\nResponse: Thank you very much for your question. In the case where benzaldehyde and other\nsubstituted aromatic aldehydes were used as reactants, the addition of acetonitrile was\nnecessary as these are only slightly soluble in water. Supplementary Fig. 7 shows that the\nFaradaic efficiency towards benzonitrile was lower at 45.1(±3.8)% in a fully aqueous\nelectrolyte, in comparison to the 71.8(±3.1)% achieved with a 41:9 water: acetonitrile ratio.\nTo eliminate the possibility that the C≡N group comes from acetonitrile, we performed the\nelectrochemical conversion of benzaldehyde to benzonitrile using 15N-labelled NH .\nobserved the generation of 15N-labelled phenylmethanimine intermediate and 15N-labelled\nbenzonitrile product, which is strongly indicative that the C≡N group was formed by the\ncoupling of aldehyde and NH , followed by the electro-oxidative dehydrogenation of CH=NH\n3\ngroup (Supplementary Fig. 26).\nFor the electrochemical conversion of acetaldehyde to acetonitrile, a fully aqueous electrolyte\nwas used. This is because acetaldehyde is highly soluble in water and we did not want to cause\nconfusion between acetonitrile solvent and acetonitrile product. Using the Co O /Cu O\n3 4 x\nelectrocatalyst and under an applied potential of 1.35 V vs. RHE, the Faradaic efficiency and\nselectivity towards acetonitrile were 86.2(±4.7)% and 93.6(±6.4)%, respectively.\n(Supplementary Fig. 37).\n2. In the DFT calculations, only the dehydrogenation of phenylmethanimine (Ph−CH=NH) is\nstudied. How about the reactions from benzaldehyde to phenylmethanimine? Especially the C-\nN\ncoupling, which is important for this work and should be studied.\nResponse: Thank you very much for this valuable suggestion. In our mechanism, the\nconversion of benzaldehyde to the phenylmethanimine intermediate proceeds via a\nhomogeneous nucleophilic addition–condensation sequence in solution: NH , a relatively\n3\nstrong nucleophile, readily attacks the carbonyl carbon of benzaldehyde to form a hemiaminal\nintermediate, which then dehydrates to yield phenylmethanimine (Angew. Chem. Int. Ed. 2023,\n62, e202313313). This transformation is known to be fast and thermodynamically favorable\nunder our reaction conditions and does not constitute the rate-limiting step.\nBy contrast, the subsequent dehydrogenation of phenylmethanimine to benzonitrile occurs on\nthe catalyst surface and represents the electrochemical, rate-determining step of the overall\nprocess. For this reason, our DFT calculations were focused on the surface-mediated\ndehydrogenation of phenylmethanimine to benzonitrile, which directly governs the observed\ncatalytic activity and selectivity. We have clarified this mechanistic rationale and the role of\nthe C−N coupling step in the revised manuscript (Fig. 3e and Supplementary Fig. 25).\n3. The CuO(111) and Cu O(110) surfaces are chosen for DFT calculations. Why these two\n2\nsurfaces?\nResponse: We chose these surfaces to match the experimentally observed dominant facets and\nto ensure that the DFT models represent the catalytically relevant terminations. Specifically,\nCuO(111) was selected because HRTEM and XRD indicate it is the predominant exposed facet\nin our samples (Fig. 2c and Supplementary Fig. 5), consistent with it being a low‐energy, stable\nsurface. For Cu O, our earlier calculations used the (110) surface; however, new HRTEM\n2\ncharacterization shows that the Cu O domains are primarily bounded by the (111) facet (Fig.\n2\n2c and Supplementary Fig. 6). We have therefore updated the DFT calculations to Cu O(111)\n2\nso that both oxide models directly reflect the actual surface structures present under our\nexperimental conditions.\n4. Only one k-point is used in the DFT calculations. What are the sizes of the models? Maybe\nmore k-points are needed.\nResponse: As detailed in the Methods section, the slab models constructed for CuO(111),\nCu O(111), and Co O (311) all exhibit an approximately rhombic in-plane geometry, with\n2 3 4\nlateral dimensions consistently on the order of ~20 Å × 20 Å. Given their close similarity in\nreal-space cell dimensions, these systems are expected to require comparable sampling\ndensities in reciprocal space.\nTo rigorously assess the influence of k-point sampling for slabs of this size, we performed a\nconvergence test on the Cu O model (Supplementary Table 1). Increasing the k-point mesh\n2\nfrom 1×1×1 to 2×2×1 resulted in only marginal variations (≤0.01 eV) in the computed energy\nprofiles, thereby confirming that Γ-point sampling is sufficient for this lateral cell dimension.\nOn this basis, and given the nearly identical cell sizes across all three systems, the Γ-point\n(1×1×1) mesh validated for Cu O was consistently used for the CuO and Co O slabs in all\n2 3 4\nsubsequent calculations. The two adsorption configurations compared in Supplementary Table\n1 (Configuration 1 and Configuration 2) are illustrated in Supplementary Fig. 29. For the\ncalculations including on-site Coulomb interactions, a DFT+U correction of U = 5 eV was\napplied to the Cu 3d orbitals (J. Chem. Phys. 2009, 131, 124703). These details, along with the\ndata for the convergence test, have now been updated in the revised manuscript (Supplementary\nFig. 29 and Supplementary Table 1).\n5. The Hubbard U value is set as 7 eV for CuO. How about Cu O?\ncorrelated Cu2+ (3d9) states and the associated magnetic moments. In contrast, Cu O contains\n2\nclosed-shell Cu+ (3d10), and its valence electronic structure is already well described at the\ngeneralized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE)\nfunctional level. As a result, the application of a U correction has only a marginal effect on its\nstructural and energetic properties.\nTo quantitatively assess this, we performed a k-point and U-dependence convergence test for\nthe Cu O(111) slab (Supplementary Table 1). Introducing U (5 eV) on Cu d-states leads to only\n2\nnegligible variations in the relative adsorption free energies (≤0.01 eV), confirming that the\nenergy profile trends are insensitive to the inclusion of U. This is consistent with previous\nliterature reports showing that GGA and GGA+U yield nearly identical energies for Cu O due\n2\nto its fully occupied 3d shell and the absence of magnetic moments in Cu+ (J. Chem. Phys.\n2009, 131, 124703). Therefore, we did not apply the U correction to Cu O in our calculations.\n2\n6. How is the free energy data in Figure 3f calculated? Did they use the computational hydrogen\nelectrode model?\nResponse: In our initial analysis, we estimated protonation energetics by explicitly adsorbing\nH atoms on the surface. However, we found that the relative energetics can be sensitive to the\nspecific H adsorption site, which complicates a direct comparison among different materials.\nWe agree with the reviewer that the CHE model circumvents this issue by referencing the\nproton–electron pair to 0.5H , thereby providing a uniform thermodynamic baseline. Per the\n2\nreviewer’s request, we have recalculated all free energy profiles in Fig. 3f to ensure consistency\nand comparability across the different systems, and added a description of the CHE model in\nthe Methods section of the Supplementary Information.\nReviewer #2 (Remarks to the Author):\nIn this manuscript, the author has reported the electrochemical synthesis of nitrile from\naldehyde without toxic cyanide. By using Co O /Cu O electrocatalyst, the Faradaic efficiency\n3 4 x\nand selectivity achieved both over 90 %. Moreover, the experimental and theoretical analysis\nrevealed that Cu O activated the electrochemical oxidation of the CN double bond to the CN\nx\ntriple bond. Based on the results, the author proposed that the nitrile production from waste\nNO can be achieved by using the NO RR reaction.\nx x\nThe data interpretation and conclusion of this manuscript are well-established. But the author\nshould clarify the novelty, difference, and advantage of this reaction, compared with the other\ncyanation reactions without cyanide. For instance, similar works about the electrochemical\nsynthesis of nitrile from aldehyde by using ammonia or NO RR have already been reported as\nx\nfollows. (Y. Xiao et al., Green Chem., 27, 5715, 2025, Y. Maeda et al., RSC Adv., 15, 17562,\n2025, C. Xue et al, JACS, 147, 32896, 2025 etc). After careful reading of the whole manuscript,\nthe proposed reaction is interesting, but this work is not suitable for publication in Nat.\nCommun. since the novelty of this work does not meet the standard for Nat. Commun.\nMoreover, some concerns shown below should be adequately addressed.\nResponse: Thank you very much for your comments. The previous works employed a different\nmethod for nitrile electrosynthesis (J. Am. Chem. Soc. 2025, 147, 32896), or focused on\ndemonstrating the aldehyde to nitrile conversion on commercial electrodes, such as Ni foam,\nPt or Pb foils (Green Chem. 2025, 27, 5715; RSC Adv. 2025, 15, 17562). Here, our innovation\ncomes from the development of a Co O clusters-decorated Cu O electrocatalyst that can\n3 4 x\nactivate the C−N bond of an unstable intermediate species, thereby converting aromatic and\naliphatic aldehydes to the corresponding nitriles at Faradaic efficiencies of 78-97%. We also\nperformed operando spectroelectrochemical studies and theoretical calculations to reveal that\nbenzaldehyde couples with NH to form the phenylmethanimine intermediate bound atop Cu2+\n3\nactive sites, which facilitates hydrogen transfer from the imine group to nearby surface oxygen.\nThis advancement in catalyst and mechanistic understanding allows us to achieve partial\ncurrent density and production rate that are 10x and 20x of the highest reported (Supplementary\nFig. 43). The catalyst also enabled near-unity selectivity towards the nitrile product, thereby\navoiding the undesired byproducts in previously-reported systems.\nFurthermore, we demonstrate how our strategy can be integrated into reaction pathways to\nenable the nitrilation of more challenging alcohol and alkyl groups. We also coupled cathodic\nNO RR with anodic benzonitrile electrosynthesis in a single electrochemical cell, with the\nx\nformer acting as a NH supply for the latter. The NH consumption at anode was comparable\n3 3\nto NH production at cathode even at current densities up to 200 mA cm-2, which signifies that\n3\nwaste NO can be viably incorporated into valuable nitriles.\nx\n1. The article title seems to be exaggerated. This work mainly shows that Co O /Cu O\n2 3 x\nelectrocatalyst promotes the electrochemical conversion from aldehyde to nitrile. The\ngenerality of the reaction was not proved in this manuscript. The author should modify the title.\nResponse: Thank you very much for your comment. The generality of the reaction had been\nproven through the electro-conversion of aromatic and aliphatic aldehydes to valuable nitriles\nusing a Co O clusters-decorated Cu O electrocatalyst, which achieved high Faradaic\n3 4 x\nefficiencies of 78-97% and near-unity selectivities (Supplementary Fig. 37). We also\ndemonstrated that nitrile electrosynthesis can be integrated into reaction pathways starting from\nprecursors with alcohol and even alkyl groups, thereby enabling some generality with starting\nreactants of different functional groups (Fig. 4d).\n2. The author used Cu O nanorod for the catalyst. Why did the author use the nanorod? Are\nx\nthere any morphological effects? The author should clarify whether the nanorods have a\nsignificant effect on the electrochemical reaction other than the increment of the surface area\ncompared with the Cu O plate anode.\nx\nResponse: Thank you very much for your suggestion. We designed the three-dimensional Cu O\nx\nnanorod to increase the contact and reactive area between reactants and catalysts and enhance\nthe exposure of active sites, which is critical for steering selectivity towards the target reaction\n(Chem. Rev. 2025, 125, 1332−1419; ACS Catal. 2025, 15, 5706–5717). As suggested, we\nfurther clarified the effect of the nanorod morphology by comparing its electrochemical\nperformance with that of Cu O plate anodes.\nWe first prepared Cu O plate anodes by the electrooxidation deposition method (defined as\nx\nplate-1) and the chemical oxidation method using H O (defined as plate-2) (J. Nanomater.\n2 2\n2023, 8987633, 19; ACS Appl. Mater. Interfaces 2022, 14, 34761–34769). XRD patterns\nconfirmed that the Cu O plate anodes comprise both Cu O and CuO, and SEM images showed\nx 2\nthe irregular particulate structures of Cu O on Cu foam (Fig. R1). As seen on in Fig. R2, the\nx\nFaradaic efficiency achieved with the Cu O nanorod anode is much higher than that with the\nx\nCu O plate anodes. This is indicative that the three-dimensional nanorod morphology does\nx\ncontribute to the superior electrochemical performance of our Cu O electrocatalyst. This can\nx\nbe attributed to increased surface area, as the double layer capacitance (C ) of the Cu O\ndl x\nnanorod anode is much higher than that of the Cu O plate anodes (1.70 versus 0.88 and 0.65\nx\nmF cm-2, Fig. R3).\n3. The experimental details of the electrolysis were not described. The concentration of\nbenzaldehyde was 40 mM. What is the volume of the electrolyte? What is the duration of the\nelectrolysis? In addition, what is the yield of benzonitrile?\nResponse: Thank you very much for your questions. The electrolyte volume is 15 mL of\nanolyte and 15 mL of catholyte, and the duration of the electrochemical reaction is 1 hour\nunless otherwise stated. These experimental details are now included in “Evaluation of\nelectrochemical performance” under the Methods section.\nWe now include the benzonitrile yields achieved at potentials 1.15-1.65 V vs RHE\n(Supplementary Fig. 10a) The yield of benzonitrile reached 48.6(±6.7)% after 1 hour of\nreaction at 1.55 V vs. RHE, and further increased to 75.0(±1.5)% after 3 hours (Supplementary\nFig. 10b).\n4. The manuscript indicated that toluene was also converted to benzonitrile in two-stage\nelectrolysis. But the electrode in the oxidation of toluene to benzaldehyde was not Co O /Cu O,\n2 3 x\nbut CoO /IrO , which is not described in the manuscript, only shown in the caption of the\nx 2\nsupplementally Figure. This is the misleading. The fact that the other electrocatalyst is\nnecessary for the conversion from toluene to benzonitrile should be mentioned in the\nmanuscript.\nResponse: Thank you very much for the suggestion. To improve the clarity, we have now\nincluded the catalyst description for the electrochemical toluene oxidation component in the\nrevised manuscript (Page 12, line 234-236).\n5. The tandem benzonitrile synthesis and NO RR electrolyser is an interesting result. The\nx\namount of the produced ammonia is much lower than the initial amount of ammonia in the\nanolyte. Toward the practical application of the tandem electrolysis, since the amount of the\nproduced ammonia is too small compared with the concentration of ammonia in the initial\nelectrolyte, it seems that the ammonia production by NO RR has little effect on the\nx\nconcentration of ammonia. In addition, one benzonitrile stoichiometrically reacts with one\nammonia in the overall reaction. But the concentration of ammonia is much higher than that of\nbenzaldehyde. Is there a positive or negative effect on the nitrile synthesis when the\nconcentration of ammonia is varied?\nResponse: Thank you very much for the comment. In a continuous process, the amount of\nproduced ammonia should be roughly equivalent to the amount consumed in the benzaldehyde-\nto-benzonitrile conversion. The concentration of ammonia in the electrolyte does not affect this\nmass balance; in a typical chemical engineering process, separation and combination units will\nbe integrated with the system to recycle the ammonia from the anolyte and recombine it with\nammonia from the catholyte. Thus, the amount of ammonia in the system should not fluctuate\nsubstantially as long as the amount of ammonia produced matches the amount of ammonia\nconsumed.\nSince the concentration of ammonia in the electrolyte does not affect the mass balance, we\nwould want to use the concentration that can yield the best Faradaic efficiency for nitrile\nsynthesis. We performed the electrochemical benzaldehyde-to-benzonitrile reaction under\ndifferent NH concentrations. It can be seen that the Faradaic efficiency generally increases\n3\nwith NH concentration, and the optimal concentration is 2 M (Supplementary Fig. 8). This is\n3\nbecause high NH concentrations can lead to higher availability and stability of the\n3\nphenylmethanimine intermediate for the subsequent electrochemical dehydrogenation.\nReviewer #3 (Remarks to the Author):\nThe manuscript “A cyanide-free route towards the electrosynthesis of nitriles” reports an\nelectrochemical strategy to convert aldehydes to nitriles with high selectivity using\nCu O/Co O electrocatalysts. The work is well presented, and the results are impressive. The\nx 3 4\nauthors demonstrate near-unity selectivity for benzaldehyde-to-benzonitrile conversion,\nsupported by extensive characterization and operando studies. The figures are of high quality,\nparticularly the TEM and elemental mapping, which convincingly illustrate the catalyst\narchitecture. Overall, this is a valuable contribution to the field of sustainable electrocatalysis.\nHowever, I do notice there are gaps for improvement, especially the computational component:\n1. The computation of free energy considers only limited configurations. For a system of this\nsize, the adsorption location and molecular orientation can significantly influence the\ncalculated energetics. A more systematic search for adsorption geometries (including different\nbinding sites and angular orientations) should be performed, or at least discussed.\nResponse: Thank you very much for your suggestion. In response, we have explored multiple\npossible adsorption configurations for the CuO, Cu O, and Co O systems. Guided by surface\n2 3 4\nsymmetry and the locations of coordinatively unsaturated (CUS) sites, we evaluated three, two,\nand three distinct initial geometries on the CuO(111), Cu O(111), and Co O (311) surfaces,\n2 3 4\nrespectively. The optimized geometries and their relative energies are now presented in\nSupplementary Figs. 27, 29, and 31. All subsequent reaction steps and free energy analyses\nreported in the main text were performed using this most stable adsorption geometry, shown in\nSupplementary Figs. 28, 30, and 32. These data and the corresponding discussion have now\nbeen updated in the revised manuscript (Supplementary Figs. 27-32 and Pages 9-10, lines 175-\n180 and 188-190).\n2. In Figure 3, the authors claim that Cu remains in an oxidized state during operation. A Bader\ncharge analysis or similar method should be performed to clarify the degree of oxidation under\nreaction conditions.\nResponse: Thank you very much for the suggestion. To clarify the evolution of Cu oxidation\nstate during the reaction, we performed a Bader charge analysis for all intermediates on the\nCuO(111) surface (Supplementary Table 3). The results show that the molecular fragment\nbecomes progressively more positively charged along the reaction sequence (charges from\n+0.16 to +0.85 to +2.10), while the CuO surface becomes correspondingly reduced (charges\nfrom −0.16 to −0.85 to −2.10). This reciprocal charge redistribution is fully consistent with the\noxidation pathway of the organic fragment:\n*Ph−CH=NH → *Ph−CH=N → *Ph−C≡N\nwhich involves a net two-electron transfer. These findings confirm that the oxidized Cu2⁺\ncenters act as electron acceptors, driving the oxidative transformation of the adsorbed species\nrather than being fully reduced to metallic Cu during turnover. These data and the\ncorresponding discussion are now updated in the revised manuscript (Supplementary Table 3\nand Page 10, lines 190-196).\n3. The manuscript lacks key information about the computational setup. Details such as the\nmodel construction and the lattice constant are missing. This information is critical for\nreproducibility and for evaluating the reliability of the theoretical conclusions.\nResponse: Thank you very much for the comment. In the revised manuscript and\nSupplementary information, we have added detailed information on the slab construction for\nall three systems in the Methods section, including the lattice parameters, slab thickness, and\nvacuum spacing. We have also included the k-point convergence test for the Cu O(111) surface\n2\nin Supplementary Table 1 and Supplementary Fig. 29, which justifies the use of the Γ-centered\n1×1×1 k-point mesh for all three surfaces of comparable lateral dimensions. These additions\nensure the reproducibility of our calculations and support the reliability of the theoretical\nconclusions.\n4. The authors should discuss the potential consequences of not including Co O explicitly in\n3 4\nthe computational model.\nResponse: Thank you very much for this helpful comment. To address this point, we explicitly\ncalculated the reaction pathway on the Co O (311) surface. Co O contains both Co3⁺ and Co2⁺\n3 4 3 4\ncenters, forming a mixed-valence Co3⁺/Co2⁺ redox couple with higher intrinsic oxidizing\ncapability than Cu O. The surface Co3⁺ sites readily accept electrons and reduce to Co2⁺, which\n2\nthermodynamically enables Co O to oxidize Cu⁺ in Cu O to Cu2⁺, thereby promoting the\n3 4 2\nconversion of Cu O into CuO under reaction conditions. Our calculated free-energy profile on\n3 4 2\n3f), reflecting its intermediate oxidizing strength. This trend supports the mechanistic\ninterpretation that Co O facilitates the oxidation of Cu O to CuO and increases the effective\n3 4 2\noxidation state of Cu during the reaction. A key reason why CuO exhibits even stronger\noxidizing capability than Co O is the electronic structure of the Cu2⁺ centers. CuO contains\n3 4\nCu2⁺ (3d9), which has a strong thermodynamic driving force to accept an electron and form the\nfully filled Cu⁺ (3d10) configuration. This Cu2⁺ → Cu⁺ reduction is energetically more favorable\nthan the Co3⁺ (low-spin d6) → Co2⁺(d7) reduction in Co O . Although Co3⁺ can also accept\n3 4\nelectrons, its driving force is weaker because the d6 → d7 transition does not yield a closed-\nshell configuration. As a result, CuO is more “electron-hungry” and acts as a stronger oxidant,\nwhich is fully consistent with our calculated free-energy profiles and the observed catalytic\ntrend (CuO > Co O > Cu O). The data and corresponding discussion are now updated in the\n3 4 2\nrevised manuscript (Supplementary Table 2, Fig. 3f, and Page 10, lines 197-200).\nReviewer #4 (Remarks to the Author):\nThis manuscript reports a cyanide-free catalytic system for the synthesis of nitriles via\nelectrocoupling of benzaldehyde and ammonia in an aqueous solution with the Co O clusters-\n3 4\ndecorated Cu O electrocatalyst. Aromatic and aliphatic aldehydes electrochemically convert to\nx\nthe corresponding nitriles at Faradaic efficiencies of 78-97%. Besides the interesting results,\nthe authors need to clarify some important issues. I recommend a major revision before\nreconsideration.\n1. The as-prepared Co O /Cu O electrocatalyst shows a heterogeneous structure. Co O\n3 4 x 3 4\nparticles are modified on the top of the CuO Nano wires; the contact edge of Co O /Cu O is\nx 3 4 x\nvery small compared with Co O or Cu O. Co O , Cu O, and/or the contact edge may work as\n3 4 x 3 4 x\nthe active sites. The authors need to provide more experimental results to clarify this issue.\nResponse: Thank you very much for the suggestion. We agree that intuitively, the contact edge\nof Co O /Cu O should be small as Co O particles are modified on the top of the CuO\n3 4 x 3 4 x\nnanowires. Hence, we believe that the enhanced Faradaic efficiency of Co O /Cu O could\n3 4 x\nmainly be due to an increase in active sites, and we now acknowledge as such in the revised\nmanuscript. This is corroborated by the increased double layer capacitance (C ) of Co O /Cu O\ndl 3 4 x\ncompared to that of Cu O (2.06 versus 1.70 mF cm-2) (Fig. 4a and Supplementary Fig. 34).\nx\nHowever, we have also observed that the Co O clusters can modulate the electronic structure\n3 4\nof Cu O electrocatalyst. High-resolution Co 2p XPS spectrum showed a negative shift\nx\ncompared to that of pure Co O powder, signifying lower average Co oxidation state. Cu 2p\n3 4\nXPS spectrum of Co O /Cu O showed a higher energy shift compared to that of Cu O, which\n3 4 x x\nindicates higher average Cu oxidation state and suggests electron transfer from Cu to Co within\nthe Co O /Cu O material (Fig. 4b-4c). Thus, we cannot disregard the possibility that this higher\n3 4 x\naverage Cu oxidation state can promote the Cuδ+-mediated dehydrogenation step and enable\nincreased Faradaic efficiency.\n2. Line 106, when discussing selectivity, you need to provide the conversion rate at the same\ntime.\nResponse: Thank you very much for the suggestion. We now provide the corresponding\nbenzaldehyde conversion rates at different applied potentials in Supplementary Fig. 12.\n3. Line 113, in an electrolysis period, the catalytic current should decrease with the increase of\nthe conversion. Here, 10 mA cm-2 should belong to the background current, or NH oxidation\n3\nreaction, not the electrochemical C−N coupling reaction.\nResponse: Thank you very much for the comment. To elucidate the origin of the 10 mA cm-2\ncurrent, we tracked the reactants and products over a time period of 60 min. Fig. R4 show that\nbenzaldehyde was increasingly consumed, while the yield of benzonitrile increased almost\nlinearly with time. The Faradaic efficiencies of benzaldehyde-to-benzonitrile are about 92.9-\n97.6%, which indicates that most of the current is funneled towards the production of\nbenzonitrile. Linear sweep voltammetry also revealed the NH oxidation peak to be about 1.5\nbe due to NH oxidation reaction, as the 100 hour electrochemical reaction was performed at\n3\n1.35 V vs. RHE.\n4. Line 124, when copper foam was used as the working electrode, the surface Cu0 should be\noxidized to Cu O under applied conditions; hence, the conclusion that ‘Cu0 has little activity\nx\ntowards benzonitrile formation’ is unreasonable.\nResponse: Thank you very much for the comment. For better clarity, we have now removed\nthe conclusion that ‘Cu0 has little activity towards benzonitrile formation’.\n5. The property of Co O for the electrochemical C−N coupling reaction should be investigated,\n3 4\nrespectively, for further comparison.\nResponse: Thank you very much for the suggestion. To elucidate the influence of the Co O\n3 4\ncluster, we performed electrochemical benzaldehyde-to-benzonitrile conversion using Co O\n3 4\nclusters-on-carbon paper. The resultant Faradaic efficiency is 32.6(±3.8)%, which suggests that\nthe Co O clusters do contribute active sites that can lead to the enhanced Faradaic efficiency\n3 4\nof Co O /Cu O (Supplementary Fig. 33). This is corroborated by the increased double layer\n3 4 x\ncapacitance (C ) of Co O /Cu O compared to Cu O (2.06 versus 1.70 mF cm-2, see Fig. 4a and\ndl 3 4 x x\nSupplementary Fig. 34). DFT calculations show that the phenylmethanimine dehydrogenation\nstep on the Co O (311) surface has an intermediate energy barrier of 0.96 eV, which suggests\n3 4\nthat the oxidizing strength Co O (311) is between that of CuO (111) and Cu O (111) (Fig. 3f,\n3 4 2\nSupplementary Fig. 32).\nWe also do not rule out the possibility that the Co O clusters can modulate the electronic\n3 4\nstructure of Cu O electrocatalyst, leading to higher average Cu oxidation state that can promote\nx\nthe Cuδ+-mediated dehydrogenation step and enable increased Faradaic efficiency. This is\ncorroborated by high-resolution Co 2p XPS spectrum, which showed a negative shift compared\nto that of pure Co O powder, signifying lower average Co oxidation state. Cu 2p XPS spectrum\n3 4\nof Co O /Cu O showed a higher energy shift compared to that of Cu O, which indicates higher\n3 4 x x\naverage Cu oxidation state and suggests electron transfer from Cu to Co within the Co O /Cu O\n3 4 x\nmaterial (Fig. 4b-4c)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I have no more comments regarding the theoretical calculations.", "reviewer_2": "The author proposed the correct responses to my questions and comments. The manuscript was well-modified and includes the significant results and insights on the electrocatalysts for the nitrile synthesis. I would recommend the publication in Nat. Commun. after responding to the following minor comments.\nIn Fig.4(d), the Faradaic efficiency from benzaldehyde to benzonitrile after the electrochemical conversion from toluene to benzaldehyde, shown as the blue bar in Fig4d, is quite lower than that of the direct conversion from benzaldehyde to benzonitrile. The reason should be explained.", "reviewer_3": "The authors have performed additional computations, and the conclusion is more solid. I would recommend acceptance.", "reviewer_4": "The authors addressed most of the issues raised in the first round. I recommend its publication after minor revisions.\nIn order to clarify the importance of the contact edge of Co O /Cu O, the authors need to make a further investigation with the Co O /Cu O hybrid catalyst."}, "author_response": "A point-by-point response to reviewers’ comments\nWe sincerely thank the editor for handling our manuscript and the reviewers for their\nfurther comments, which have helped improve the quality of our work. The point-by-\npoint response to the reviewers’ comments are specified and discussed as shown below:\nReviewer #1 (Remarks to the Author):\nI have no more comments regarding the theoretical calculations.\nResponse: Thank you very much for your kind review of our revised manuscript.\nReviewer #2 (Remarks to the Author):\nThe author proposed the correct responses to my questions and comments. The\nmanuscript was well-modified and includes the significant results and insights on the\nelectrocatalysts for the nitrile synthesis. I would recommend the publication in Nat.\nCommun. after responding to the following minor comments.\nIn Fig.4(d), the Faradaic efficiency from benzaldehyde to benzonitrile after the\nelectrochemical conversion from toluene to benzaldehyde, shown as the blue bar in\nFig4d, is quite lower than that of the direct conversion from benzaldehyde to\nbenzonitrile. The reason should be explained.\nResponse: Thank you very much for your question. For the direct electrooxidation of\nbenzaldehyde to benzonitrile, the benzaldehyde concentration is 40 mM. For the\nproduction of benzonitrile starting from toluene, the concentration of benzaldehyde\nobtained from the electrochemical conversion of toluene was 29.1(±2.4) mM, and the\nresidual toluene concentration is 124.3(±3.2) mM. This suggests reduced mass transport\nof benzaldehyde to the catalyst surface, as well as competition from toluene for\nadsorption sites. The toluene molecules could partially occupy the active sites or hinder\nthe optimal binding configuration required for the selective oxidation of benzaldehyde\nto benzonitrile, thereby suppressing its Faradaic efficiency. To improve clarity, we have\nnow added this information and explanation to the revised Supplementary Information\n(Supplementary Fig. 39).\nReviewer #3 (Remarks to the Author):\nThe authors have performed additional computations, and the conclusion is more solid.\nI would recommend acceptance.\nResponse: Thank you very much for your kind review of our revised manuscript.\nReviewer #4 (Remarks to the Author):\nThe authors addressed most of the issues raised in the first round. I recommend its\npublication after minor revisions.\nIn order to clarify the importance of the contact edge of Co O /Cu O, the authors need\n3 4 x\nto make a further investigation with the Co O /Cu O hybrid catalyst.\n3 4 x\nResponse: Thank you very much for your question. We further clarified the significance\nof the contact edge between Co O and Cu O by comparing the electrochemical\n3 4 x\nperformance of the Co O /Cu O hybrid catalyst against that of a physically mixed\n3 4 x\nCo O +Cu O catalyst. The latter was prepared by drop-casting the Co O ink onto the\n3 4 x 3 4\nCu O electrode. The Faradaic efficiency of Co O +Cu O is inferior to that of the\nx 3 4 x\nCo O /Cu O electrocatalyst, and comparable to that of Cu O electrocatalyst\n3 4 x x\n(Supplementary Fig. 33). This indicates that the interfacial interaction is critical, and is\nconsistent with our observation that the Co O /Cu O contact edge results in a higher\n3 4 x\naverage Cu oxidation state, which promotes the Cuδ+-mediated dehydrogenation step\nand enables increased Faradaic efficiency. The data and explanation are now updated\nin the revised Supplementary Information (Supplementary Fig. 33)."}]

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