Tuning NO coverage promotes ampere-level electrosynthesis of a nylon-6 precursor

Tuning NO coverage promotes ampere-level electrosynthesis of a nylon-6 precursor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Tuning NO coverage promotes ampere-level electrosynthesis of a nylon-6 precursor Bin Zhang, Yongmeng Wu, Xinyu Liu, Rong Yang, Chuanqi Cheng, Ziyang Song This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4791713/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Aug, 2025 Read the published version in Nature Synthesis → Version 1 posted You are reading this latest preprint version Abstract The electrocatalytic synthesis of cyclohexanone oxime from NO and cyclohexanone with high Faradaic efficiency at ampere-level current density is highly desirable but highly challenging. Here, theoretical calculations reveal that NO coverage on the Ag catalyst plays a critical role in cyclohexanone oxime electrosynthesis. We then adjust the local NO concentration experimentally by tuning the NO concentration and reaction rate. We find that low NO coverage benefits NH 3 formation, whereas high coverage delivers cyclohexanone oxime and N-2 (N 2 O and N 2 ) products. A mechanistic study indicates that with increasing NO coverage, the active sites transfer from bridge step sites to hollow terrace sites, which results in weaker adsorption of O* species, leading to the stable existence of the NH 2 OH* intermediate rather than decomposing to form NH₃. However, N‒N coupling also easily occurs at high NO coverage. This mechanistic understanding further inspires us to develop a doping strategy to break the equivalent catalyst surface sites, which can inhibit NO–NO coupling at high NO coverage and thus realize high cyclohexanone oxime Faradaic efficiency at high current density. A Ru-doped Ag catalyst is thus developed, realizing 86% cyclohexanone oxime Faradaic efficiency at a current density of 1.0 A cm − 2 , far exceeding the reported performance. Physical sciences/Chemistry/Green chemistry/Sustainability Physical sciences/Chemistry/Catalysis/Electrocatalysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Cyclohexanone oxime (CYC) is an important precursor for the production of nylon-6, with an annual global demand of approximately 10 million tons and a global market size of approximately $ 25 billion 1 – 4 . The industrial production of CYC generally involves a two-step and complex process in which NH 2 OH is first produced via the Raschig method, after which NH 2 OH reacts with cyclohexanone to form CYC 5 – 8 . This two-step method requires explosive H 2 , strongly acidic conditions and precious metal catalysts, causing concerns about safety, cost, and sustainability. Moreover, the transportation and storage of concentrated NH 2 OH are at risk of explosion. The electrocatalytic construction of C‒N bonds from nitric oxide (NO x ) and carbonaceous sources has emerged as a sustainable strategy for synthesizing organic nitrogenous compounds from inorganic nitrogen sources 9 – 16 . Specifically, CYC aqueous electrosynthesis has been realized by using nitric oxide (NO, NO 2 − ) and cyclohexanone as the N and C sources, respectively 17 , 18 . A mechanistic study revealed that the spontaneous condensation of cyclohexanone with NH 2 OH intermediates produced by NO x electroreduction is the key step in the formation of CYC. However, NO x reduction is a multi-electron process involving a variety of nitrogen-containing intermediates 19 – 21 , resulting in multiple byproducts and an undesirable low CYC Faradaic efficiency (FE). Moreover, the partial current density of the CYC is still tens of milliamps (mA), which is far from suitable for industrial application at large current densities of ≥ 200 mA cm − 2 . Recent advances in improving the CYC electrosynthesis FE and current density have focused on screening electrode materials, mostly through trial-and-error modes 22 – 26 . Therefore, understanding the origin of the activity and selectivity of CYC and developing an effective regulation strategy to synthesize CYC with high FE at large current densities are highly desirable but remain unexplored. In this article, using density functional theory (DFT) calculations, we first assess the influence of NO coverage on the key elementary steps that branch NH 2 OH versus NH 3 . We find that improving NO coverage benefits the NH 2 OH pathway. However, excessive NO coverage also decreases the NO−NO coupling energy barrier to form N-2 (N 2 O and N 2 ) byproducts. In subsequent experiments, we adjust the local NO concentration at the catalyst–electrolyte interface by tuning the combination of the NO supply concentration and reaction rate. We achieve an 89% CYC FE and a 206 mA cm − 2 current density under 50% NO at − 3.0 V over a Ag catalyst. A mechanistic study reveals that at low coverage, NO occupies the Ag step site with strong bridge adsorption, which is preferable for NH 3 production. At high NO coverage, the active sites transfer from bridge step sites to hollow terrace sites, accompanied by a downshift in the d -band center, leading to weak adsorption of O* species; thus, the NH 2 OH* intermediate is stable rather than decomposing to form NH₃, and the NH₂OH pathway accordingly becomes dominant. Moreover, N‒N coupling easily occurs at high NO coverage. This mechanistic understanding inspired us to speculate that a doping strategy to break the equivalent catalyst surface sites can inhibit NO–NO coupling at high NO coverage and thus realize a high CYC FE at high current density. Accordingly, a Ru-doped Ag (AgRu) catalyst is developed, and an 86% CYC FE was achieved at a current density of 1.0 A cm − 2 . Results Reaction process analysis During the process of CYC electrosynthesis from NO and cyclohexanone, possible competitive reactions include the hydrogen evolution reaction (HER, I), the over hydrogenation of NH 2 OH to NH 3 (II) and the N‒N coupling products of N 2 O and N 2 (III) (Fig. 1 a). An inherently selective catalyst should possess a large Δ G HER and weak NH 2 OH adsorption energy to avoid the competitive reactions of (I) and (II). Accordingly, we calculated the NH 2 OH desorption energy of several metals that are commonly used in NO x reduction and found that Ag had the lowest NH 2 OH desorption energy ( G des , Fig. 1 b). The experimental results show that Ag foil exhibits the optimum CYC FE among these metal foils (Fig. 1 c and Supplementary Fig. 1). To increase the active area, Ag 2 O-derived Ag nanoparticles were used as catalysts (Supplementary Figs. 2‒6 and Supplementary Notes 1‒3). To achieve high-current-density CYC electrosynthesis, a high local concentration of NO is desirable to overcome the mass transfer limitations. However, high NO coverage may cause easier coupling of NO 27 , thus leading to side reactions (III). In this regard, we speculate that NO coverage on the catalyst surface may play a vital role in CYC electrosynthesis. Low NO coverage may benefit NH 3 and H 2 formation because of excess H* but insufficient NO, high NO coverage leads to the NO‒NO coupling reaction to produce N 2 O and N 2 (N-2) byproducts, and appropriate NO coverage is required to form NH 2 OH to condense with cyclohexanone to form CYC (Fig. 1 d). These considerations encouraged us to study the effect of NO coverage on the CYC product. Prediction of the effect of NO coverage on the performance of cyclohexanone oxime We attempted to understand the connection between NO coverage and CYC production with the aid of DFT calculations by modelling low-coordination Ag to represent Ag 2 O-derived Ag nanoparticles (Supplementary Tables 1‒6 and Supplementary Note 4). The possible reaction pathways are shown in Supplementary Fig. 7. To identify coverage-dependent reaction pathways, various reaction sites were considered (Supplementary Fig. 8 and Supplementary Note 5). Then, three NO coverages of 1/4, 1/2 and 3/4 monolayers (ML) were analysed in detail. We first compare the adsorption free energies ( G ad ) of NOH* and NHO*, the O- and N-terminal hydrogenation intermediates of NO, under different NO coverages and find that NHO* is more stable than NOH* at different NO coverages; thus, NO* prefers hydrogenation via the N atom to generate NHO* rather than NOH* (Supplementary Fig. 9). This result also indicates that the NHO* pathway to NH 4 + is inhibited in our system 28 , 29 . Similarly, by comparing the adsorption free energies of NHOH* and NH 2 O*, the NHOH pathway was excluded (Supplementary Fig. 10). Thus, the probable pathways to NH 2 OH and NH 3 are NO*→NHO*→NH 2 O*→NH 2 OH*→NH 2 OH or NO*→NHO*→NH 2 O*→O* + NH 3 →OH* + NH 3 →H 2 O + NH 3 . We compared the reaction free energies of the two pathways at NO coverages of 1/4, 1/2 and 3/4 ML (Fig. 2 a, Supplementary Figs. 11 and 12 and Supplementary Table 7). We focus on the key elementary steps that branch NH 2 OH versus NH 3 , that is, the O-terminal hydrogenation of NH 2 O* to NH 2 OH* and then to NH 3 * (NH 2 O*→NH 2 OH*→NH 2 OH) or the N-terminal hydrogenation to NH 3 (NH 2 O*→O* + NH 3 (2)). At 1/4 ML, path (2) is more thermodynamically favourable than path (1); thus, NH 3 formation is undoubtedly the dominant product. However, when the NO coverage increases to 1/2 and 3/4 the ML, path (1) becomes more favourable than path (2); thus, the NH₂OH pathway is dominant. We further evaluated the effect of NO coverage on the HER. As shown in Fig. 2 b and Supplementary Fig. 13. The water dissociation energy barriers at 0, 1/4, 1/2, and 3/4 ML NO coverages on the Ag sites are 1.15, 1.33, 1.36 and 1.40 eV, respectively. Thus, high NO coverage can restrain the HER. Furthermore, the influence of NO coverage on N-2 product formation was studied. By calculating the reaction free energies of a series of possible N‒N coupling pathways, the most likely N‒N coupling pathway is determined to be NO*+NO*→N 2 O 2 *→NO-NOH*→N 2 O* (Supplementary Figs. 14‒17 and Supplementary Notes. 7 and 8). The activation energy of NO*+NO*→N 2 O 2 * decreases as the NO coverage increases (Fig. 2 c). This finding indicates that NO−NO coupling easily occurs at high NO concentrations. These calculation results show that the Ag catalyst easily produces NH 3 under low NO coverage but produces NH 2 OH and N-2 products under high NO coverage. Experimental proof of the effect of NO coverage on cyclohexanone oxime performance The above results inspired us to experimentally study the influence of surface coverage of NO on CYC production. According to Henry’s law (Eq. ( 1 )) 30 , 31 , the local NO concentration is correlated with p NO ; thus, NO coverage regulation can be realized by controlling the local NO concentration or NO partial pressure ( p NO ). $$\:\:{\theta\:}_{\text{N}\text{O}}={\theta\:}_{*}{p}_{\text{N}\text{O}}{\text{e}}^{-\frac{{E}_{\text{a}\text{d}\left(\text{N}\text{O}\text{*}\right)}}{RT}}$$ 1 where θ * is the coverage of free surface sites, E ad (NO*) is the NO adsorption energy on the surface, R is the ideal gas constant and T is the temperature. We experimentally verified the Ag surface NO coverage variation under different NO concentrations via in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR−SEIRAS). We used the ratio of the peak area of NO to that of D 2 O ( S NO* / S D2O* ) obtained at a potential of − 0.8 V (a potential where NO is adsorbed but not reduced) to reflect the surface NO coverage. As the supplied NO concentration increases from 10–70%, the value of S NO* / S D2O* increases from 1.33 to 6.44 (Fig. 3 a and Supplementary Fig. 18). A further increase in the NO concentration cannot increase the NO coverage, indicating that the surface NO coverage reaches its maximum at a 70% NO concentration. These results demonstrate that the Ag surface NO coverage can be adjusted by altering the NO input concentration. We thus tested the CYC electrosynthesis performance at input NO gas concentrations ranging from 10 to 100% across a range of applied potentials. A gas diffusion electrode (GDE) was used to enhance mass transfer (Supplementary Fig. 19). When the NO concentration increases from 10 to 100%, an overall increase in both the total current density (Supplementary Figs. 20 and 21) and the NO reduction partial current density (Fig. 3 b) is observed. The increase in the NO reduction current density follows a linear increase in the potential window of − 1.35 to − 3.6 V at NO concentrations of 10%, 20% and 50%. At a more negative potential, the tendency of the current density to increase slows due to NO mass transport limitations, with a characteristic increase in hydrogen production (Supplementary Fig. 22). Further increasing the NO concentration to 70% and 100% results in the current density growth limitation shifting to a more negative potential of − 6.6 V (Supplementary Fig. 23). The tendency of the CYC partial current density first increases and then decreases as the applied potential decreases, and the inflection point of the potential negatively shifts as the NO concentration increases from 10 to 100% (Fig. 3 c). A similar situation is observed for the N-2 product partial current density, while the NH 4 + partial current density is negatively correlated with NO coverage (Supplementary Figs. 24 and 25). CYC, NH 4 + , H 2 and N-2 products all present NO concentration-related FEs (Figs. 3 d − f and Supplementary Fig. 26). Generally, a moderate NO concentration (50%) is conducive to the production of CYC, a low NO concentration (10 and 20%) is beneficial for NH 4 + formation, and a high NO concentration favours N 2 O and N 2 products (70 and 100%). The potential-dependent FEs of products present different tendencies under different NO concentrations. Specifically, the CYC FE is potentially highly dependent on NO concentrations of 10, 20 and 50%, and it decreases sharply at potentials less than − 3.0 V (Fig. 3 d). This is probably due to the insufficient NO supply caused by rapid NO consumption at negative potentials under low NO concentrations. However, the CYC FE depends less on the potential when the NO concentration increases to 70 and 100%. This is because under high NO concentrations, NO is in excess, so the consumption of NO at large potentials can hardly affect the local concentration of NO within the potential range of − 1.35 to − 4.3 V. A further decrease in the potential leads to a decrease in the CYC FE because the HER occurs (Supplementary Fig. 27). NH 4 + FE is negatively correlated with the NO concentration (Fig. 3 e). At 10, 20 and 50% NO concentrations, the NH 4 + FE increases as the applied potential decreases until NO mass transfer limitations appear, which is indicated by the observation of H 2 . At 70% and 100% NO, hardly any NH 4 + is produced, and the amount of N-2 products increases. The variation tendency of the N-2 products is opposite to that of NH 4 + , in which the FE increases with increasing NO concentration and remains constant within the potential range of − 1.35 to − 4.3 V under pure NO conditions (Fig. 3 f). The product distributions at various NO concentrations and potentials were analysed (Supplementary Figs. 28–32 and Supplementary Notes 9 and 10). At low NO concentrations (10 and 20%), NH 4 + is the primary byproduct, and the NH 4 + FE increases as the potential decreases until H 2 is present. With increasing NO concentration, the NH 4 + FE gradually decreases, while the N-2 products emerge as the main byproducts. Under pure NO conditions, N-2 products are the only byproducts, and ~ 50% of the FEs are maintained from − 1.35 to − 6.6 V. The key to CYC production is thus to constrain operating conditions such that NO availability is neither too high (promoting N 2 O and N 2 ) nor too low (promoting NH 3 and H 2 ), which is in agreement with the calculation results. Mechanistic studies To gain insight into the nature of the difference in product distribution under low and high NO concentrations, DFT calculations combined with in situ ATR−SEIRAS experiments were conducted. We simulate NO adsorption at low and high coverages and find that adsorbate reorganization occurs as the coverage increases (Supplementary Fig. 33 and Supplementary Note 11). At low coverage, NO reasonably occupies the bridge step site (B1) with strong bridge adsorption. At high coverage, the dense NO at the step site is squeezed and migrates to the terrace hollow site near the step site (H2) with weak hollow adsorption. Next, we investigated the reasons for the order of site preference and the extent of adsorbate reorganization during adsorption. We calculated the NO adsorption energy and effective d -band center at the B1 and H2 sites from low to high coverage (Figs. 4 a, Supplementary Fig. 34 and Supplementary Note 12). We find that there is an excellent correlation between the adsorption energy and the d -band center—the lower the d -band center is, the weaker the adsorption ability. We thus believe that the essential reason for the product distribution variance is the change in the center of the catalyst d -band at different NO coverages 32 . Under low coverage, the B1 site possesses stronger NO adsorption ability and a higher d -band center than the H2 site. Thus, NO tends to adsorb strongly on the B1 site at low coverage and hydrogenates to NH₃O*, which decomposes to NH₃ and O* immediately. This is why NH 3 is produced under low NO coverage. Under high coverage, the B1 sites that preadsorb NO have difficulty adsorbing more NO due to the steric effect; thus, NO tends to adsorb at H2 sites, making the B1 and H2 sites both active sites. The effective d -band centers of the B1 and H2 sites of Ag strongly correlate with the site changes. Accordingly, the differences in selectivity with coverage can be correlated with changes in active sites. Specifically, the H2 sites exhibit weaker adsorption of O species, leading to the stable existence of the NH 2 OH* intermediate, rather than decomposing to form NH₃ and *O species. Thus, the NH 2 OH pathway becomes dominant. The above results are further verified experimentally. Potential-dependent electrochemical in situ ATR−SEIRAS was conducted at NO concentrations of 10, 20, 50, 70 and 100% (Figs. 4 b − c and Supplementary Figs. 35 and 36). Because the wide H 2 O peak at approximately 1600 cm − 1 overlaps with the peaks of NO, we conducted the test in D 2 O. At low NO concentrations of 10 and 20%, only one peak at approximately 1555 cm – 1 is observed, which is ascribed to bridge adsorption at the step site (B1) of NO* (Fig. 4 b and Supplementary Fig. 36a) 33 , 34 . When the NO concentration increases above 50%, the peak at 1555 cm – 1 first appears, and then another peak at approximately 1630 cm – 1 (hollow adsorption at the terrace site of NO*, H2) appears, indicating the migration of NO from the step site to the terrace site when NO adsorption at the step site is saturated at high NO concentrations (Supplementary Figs. 36b,c) 32 . At the 100% NO concentration, the peak at 1555 cm – 1 shifts to a higher wavenumber as the potential negatively shifts (Fig. 4 c), possibly because of the effects of the adjacent NO* at the H2 site, known as “adsorbate − adsorbate interactions”, which are usually observed at very high adsorbate coverage 35 . These results further demonstrate that coverage induces a change in the site preference of preadsorbed NO; that is, NO prefers to adsorb on bridge sites at low coverage but on hollow sites at high coverage, which is in accordance with the calculation results. In addition to NO, the production of NH 2 OH under low and high NO coverage was identified by the ATR−SEIRAS and control experiments. Under 20% NO, NH 2 OH is detected at 2904 cm –125 in the tested potential range of − 0.8 to − 2.1 V (Fig. 4 d). In comparison, the NH 2 OH* peak at 100% NO appears at − 0.9 V but disappears at potentials more negative than − 1.2 V (Fig. 4 e) because under high NO concentrations, NO is rapidly adsorbed on the catalyst surface with increasing applied potential, resulting in high surface NO coverage at step sites. High NO coverage results in NH 2 OH being squeezed and migrating to the terrace hollow site or desorbed to the solution to condense with cyclohexanone. Thus, no NH 2 OH signal can be detected on the Ag surface as the applied potential decreases. Additionally, an N 2 O signal is observed for 100% NO but is absent for 20% NO according to infrared spectroscopy, in accordance with the calculation and performance test results. On the basis of the above analysis, reaction pathways under low and high NO coverages are proposed (Fig. 4 f). Under low NO coverage, NO adsorbs strongly at the step position and then is hydrogenated in the pathway of NO*→NHO*→NH 2 O*→NH 3 . Under high NO coverage, the NO preadsorbs at the step site experiences an adsorbate reorganization and finally adsorbs at the step and terrace sites uniformly with a weaker bond energy. Then, it is hydrogenated via the following pathway: NO*→ NHO*→ NH 2 O*→NH 2 OH. NH 2 OH migrates to the terrace hollow site or desorbs to the electrolyte and condenses with cyclohexanone to yield CYC. Moreover, NO−NO coupling products of N 2 O and N 2 inevitably formed. Inspired by the above mechanistic study, we can improve the CYC FE in two ways. One is modulating the NO coverage on the catalyst surface by controlling the NO concentration and applying potential accurately to balance the NO supply and consumption. Here, we achieve an 89.2% CYC FE under a 50% NO concentration at − 3.0 V at a current density of 206 mA cm – 2 . However, this regulation strategy has difficulty achieving a high current density because the tightly controlled NO concentration establishes a mass transfer constraint. Thus, another strategy involving breaking the equivalent catalyst surface sites to restrict the NO−NO coupling reaction under high NO concentrations is preferable for achieving high-current-density CYC electrosynthesis. Doping suppresses N−N coupling at high NO coverage for ampere-level electrosynthesis of cyclohexanone oxime Doping heterogeneous atoms is an effective strategy for breaking equivalent Ag sites 36 , 37 . Moreover, the electronic structure change caused by doping needs to be considered because it is correlated with the adsorption ability. The electron redistribution caused by doping may result in electron-rich states and electron-deficient states at the interface 38 . According to the above results, weak adsorption at the Ag step site is required to avoid NH 3 byproducts, and electron deficiency states at the step position are thus desired. We thus attempted to introduce a series of metal atoms with different electronegativities into Ag catalysts and found that Ru is a good dopant (Supplementary Fig. 37). Specifically, AgRu has asymmetrical charge sites, and some electron-deficient Ag sites are exposed at the step sites, which is favourable for NH 2 OH formation but not for NO − NO coupling (Fig. 5 a). As a result, AgRu has the largest NO − NO coupling barrier, which is expected to inhibit the NO − NO coupling reaction (Fig. 5 b and Supplementary Fig. 38). Therefore, Ru-doped Ag catalysts with different Ru contents (denoted as AgRu-x, where x represents the atomic percentage of Ru) were designed and synthesized (Supplementary Note 13). SEM, TEM, mapping, and XRD and XPS results verify the successful synthesis of the AgRu catalysts (Fig. 5 c, Supplementary Figs. 39 and 40 and Supplementary Notes 14 and 15). Potential-dependent electrochemical in situ IR spectra under 100% NO over AgRu-1.3 was conducted (Supplementary Fig. 41). Unlike that of the Ag catalyst, only one peak at approximately 1650 cm – 1 is observed, which is attributed to the hollow adsorption at the terrace site (H2) of NO*. The bridge adsorption at the step site (B1) of NO*, at which N‒N coupling tends to occur, is absent. This phenomenon accords with the theoretical prediction and experimental results: Ru doping causes electron-deficient Ag sites at the step sites, weakens NO adsorption and inhibits NO − NO coupling. Thus, NO prefers to occupy H2 sites and yields NH 2 OH. The LSV curves show that the introduction of Ru enhances both the HER and NO reduction activities (Supplementary Fig. 42). Then, constant-current electrolysis experiments at current densities of 0.1, 0.2, 0.3, 0.4, 0.5 and 1.0 A cm − 2 were conducted under a pure NO atmosphere. The AgRu catalysts exhibit a higher CYC FE and lower N-2 product FE than Ag at every tested current density, in which AgRu-1.3 shows the best performance (Supplementary Figs. 43 and 44). Impressively, an 86% CYC FE and a 10.7 mmol h – 1 cm – 2 yield rate are achieved at a current density of 1.0 A cm − 2 over AgRu-1.3 (Fig. 5 d‒f) 17 , 18 , 22 – 26 , 39 , 40 , exceeding the reported performance (Fig. 5 f and Supplementary Table 8). The increase in the Faraday efficiency (FE) with increasing current density at a 100% NO concentration occurs because the high reaction rate at a relatively high current density drove the quick consumption of local NO, which lowers NO coverage and thus restrain N‒N coupling, thus improving the cyclohexanone oxime FE. Additionally, the CYC electrosynthesis performance and catalyst composition can be maintained for 35 h at 0.1 A cm − 2 under pure NO, verifying the good durability of the catalyst (Fig. 5 g). Moreover, our strategy can be used to synthesize 15 N-pyridine oximes using 15 NO as the nitrogen source. An important labelled compound of 15 N-pralidoxime, the active ingredient in medications such as Atnaa, Duodote (with atropine), pralidoxime chloride and protopam chloride, was synthesized using the as-prepared 15 N-pyridine oximes as building blocks (Supplementary Fig. 45 and Supplementary Note 15). Discussion In summary, we experimentally and theoretically discover that the performance of cyclohexanone for the electrosynthesis of NO and cyclohexanone is closely related to NO coverage on the low-coordination Ag catalyst surface. With increasing local NO concentration, the dominant electrosynthesis products undergo the transformation of NH 3 to cyclohexanone oxime and N-2 (N 2 O and N 2 ) products. On the basis of spectral characterization and density functional theory (DFT) calculations, we can assign the origin of the selectivity difference to the transformation of active sites from step sites to terrace sites under high coverage. Specifically, at low coverage, NO occupies the Ag step site with strong bridge adsorption, which is preferable for NH 3 production. At high NO coverage, the transfer of active sites from bridge step sites to hollow terrace sites results in weak adsorption of O* species; thus, the NH 2 OH* intermediate is stable rather than decomposing to form NH₃, and the NH₂OH pathway accordingly becomes dominant.. Moreover, N‒N coupling easily occurs at high NO coverage. These results inspire the introduction of Ru to break equivalent catalyst surface sites, thus inhibiting NO−NO coupling at high NO coverage. Accordingly, cyclohexanone oxime with an 86% Faradaic efficiency at a current density of 1.0 A cm − 2 was achieved. This work not only paves the way for the industrial mass production of cyclohexanone oxime via electrosynthesis but also reveals the effect of NO coverage on cyclohexanone oxime electrosynthesis. Our work will inspire the efficient electrosynthesis of other nitrogenous compounds via C‒N bond construction. Methods Materials preparation The Ag 2 O nanoparticles were synthesized via a precipitation reaction. First, 10 mmol of AgNO 3 was dissolved in 100 ml of deionized water. Then, 50 ml of NaOH (0.2 M) was added to the AgNO 3 solution while stirring. The Ag 2 O sediment was separated by centrifugation, washed with deionized water and ethanol several times and then dried at 60°C overnight. Characterization The morphology of the catalysts was observed via field emission scanning electron microscopy (FEI Apreo S LoVac) and transmission electron microscopy (FEI Tecnai G2 F20). X − ray photoelectron spectroscopy measurements were performed on a Thermo Fisher Scientific K-Alpha spectrometer. All the peaks were calibrated by the binding energy of 284.8 eV of the C 1 s spectrum. X − ray diffraction tests were performed on a Rigaku SmartLab 9 kW diffraction system. In situ ATR-FTIR was performed on a Nicolet 6700 FTIR spectrometer with silicon as the prismatic window. 1 H NMR data were recorded on a Bruker AVANCE III 400 MHz NMR instrument. Electrode fabrication Two milligrams of Ag 2 O powder was suspended in a mixture containing 10 µl of Nafion solution (5 wt%) and 1 ml of ethanol via ultrasonication. The above homogeneous ink was subsequently dropped onto carbon paper (Toray, 2 cm × 1 cm) with a Ag 2 O loading of 2.0 mg cm − 2 . The Ag electrode was formed in situ by pretreating the Ag 2 O electrode at a constant potential of − 1.8 V versus Ag/AgCl for 10 min before the electrochemical tests. The NiFe 2 O 4 anode was prepared by following a previously reported procedure. Briefly, 0.4362 g of Ni(NO 3 ) 2 ·6H 2 O, 0.202 g of Fe(NO 3 ) 3 ·9H 2 O, 0.6 g of urea and 0.148 g of NH 4 F were dissolved in 40 ml of deionized water. A piece of freshly treated Ni foam (2 cm × 2 cm, 99.99%, 1.5 mm thick; Kunshan) was immersed in the solution and transferred to a Teflon-lined stainless steel autoclave, and hydrothermal treatment was carried out at 120°C for 6 h in an oven. NiFe 2 O 4 /Ni-foam was obtained by calcining the as-prepared precursor in air at 650°C. Electrochemical measurements Electrochemical tests were carried out using a CS350MA (CorrTest) electrochemical workstation. The H-type cell was equipped with a three-electrode system, which is depicted in Supplementary Fig. 1. The geometric area of the working electrode was 1 × 1 cm 2 , and the metal foil catalysts were treated with 0.5 M H 2 SO 4 and acetone before use. The reference electrode was an Ag/AgCl electrode containing a saturated KCl solution, and a graphite rod served as the counter electrode. The two chambers were separated by a pretreated Nafion 117 (Fuel Cell Store) membrane. The cathode and anode electrolytes were both 25 ml 0.9 M NaClO 4 + 0.1 M NaOH (pH 12.5), and the cathode electrolyte contained 4 mmol cyclohexanone. The cathodic electrolyte was first purged with Ar gas for 30 min and then purged with pure NO gas for presaturation. After that, the inlet and outlet valves were switched off to form a closed gas circuit, and the internal recycling flow rate was maintained at 10 ml min − 1 during the catalytic process. There was a gas storage tank with a capacity of 98.0 ml in the gas pipeline, and a peristaltic pump was applied to implement circulation of the gas feed. When the reaction was complete, Ar gas was again used to exhaust the gas from the device. The applied potentials were referenced to the Ag/AgCl reference electrode (saturated KCl solution). Flow cell electrochemical tests were carried out in a gas-fed three-compartment flow electrolyser and a two-compartment flow electrolyser with an electrode area of 1.0 cm 2 . The flow cell configurations are depicted in Supplementary Fig. 19, which consists of a working electrode, an anion exchange membrane or cation exchange membrane and a NiFe 2 O 4 /Ni-foam anode. Foams were compressed before use. Fumasep FAA-3-50 (Fumatech) and Nafion 117 (Fuel Cell Store) were used as separators for alkaline and acidic electrolytes, respectively. Sodium hydroxide (NaOH; Aladdin) and sodium perchlorate (NaClO 4 ; Aladdin) were used to prepare the electrolyte. The catholyte (0.1 M NaOH + 0.9 M NaClO 4 ) was prepared by mixing 1.0 M NaOH and 1.0 M NaClO 4 solutions. NaOH (1 M) was employed as the anolyte. The catholyte and anolyte were allowed to flow at 30 ml min − 1 by using peristaltic pumps (Baoding Lead Fluid Technology). The NO flow rate at different concentrations was 40 sccm, which was controlled by an electronic flow meter. Electrochemical in situ ATR−SEIRAS spectra measurements In situ attenuated total reflection Fourier transform infrared spectroscopy (ATR−SEIRAS) was performed on a Nicolet 6700 FTIR spectrometer equipped with mercury–cadmium–telluride (MCT). A detector with silicon as the prismatic window. First, Ag 2 O ink (pure ethanol as the dispersant) was carefully dropped on the surface of the gold film, which was chemically deposited on the surface of the silicon prismatic before each experiment. Then, the deposited silicon prismatic served as the working electrode. Pt foil and Ag/AgCl electrodes containing saturated KCl solution were used as the counter and reference electrodes, respectively. A 0.1 M NaOH + 0.9 M NaClO 4 (D 2 O or H 2 O was used as the solvent) solution was used as the electrolyte. Before spectral acquisition, the working electrode was pretreated at a potential of − 1.8 V versus Ag/AgCl for 10 min for the in situ formation of Ag. For NO electroreduction, the electrolyte was aerated with different concentrations of NO gas via peristaltic pumps. The spectra were recorded at intervals of 0.1 V with a continuous change in the applied potential from − 0.7 to − 2.1 V Ag/AgCl. The background spectrum of the catalyst electrode was acquired at an open-circuit voltage before each systemic measurement. Declarations Competitive interests The authors declare no competitive interests. Author Contributions B.Z. conceived the idea and directed the project. Y.W. and B.Z. designed the experiments. X.L. and Y.W. carried out the experiments. R.Y. and C.C. performed the DFT calculations. Z.S. assisted with some experiments. X.L., Y.W. and B.Z. analysed the data. Y.W. wrote the paper. B.Z. revised the paper. All the authors discussed the results and commented on the paper. Acknowledgements We acknowledge the National Natural Science Foundation of China (22271213 to B.Z. and 22401212 to Y.W.). Availability of data and materials All the data needed to evaluate the conclusions in the paper are presented in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors. References HDIN Research. Global nylon 6 production capacity to reach 8.86 million tons in 2024. www.hdinresearch.com/news/56 (2019). Thomas, J. M. & Raja, R. Design of a “green” one-step catalytic production of ε-caprolactam (precursor of nylon-6). Proc. Natl. Acad. Sci. U.S.A. 102 , 13732−13736 (2005). Yuan, Y. et al . Electrocatalytic ORR–coupled ammoximation for efficient oxime synthesis. Sci. Adv. 10 , eado1755 (2024). Lewis, R. J. et al. Highly efficient catalytic production of oximes from ketones using in situ–generated H 2 O 2. Science 376 , 615−620 (2022). Benson, R. E., Cairns, T. L. & Whitman, G. M. Synthesis of hydroxylamine. J. Am. Chem. Soc. 78 , 4202−4205 (1956). Mokaya, R. & Poliakoff, M. A cleaner way to nylon? Nature 437 , 1243−1244 (2005). Kong, X. et al. Synthesis of hydroxylamine from air and water via a plasma-electrochemical cascade pathway. Nat Sustain 7 , 652–660 (2024). Jia, S. et al. Synthesis of hydroxylamine via ketone-mediated nitrate electroreduction. J. Am. Chem. Soc. 146 , 10934–10942 (2024). Li, J., Zhang, Y., Kuruvinashetti, K. & Kornienko, N. Construction of C–N bonds from small-molecule precursors through heterogeneous electrocatalysis. Nat. Rev. Chem. 6 , 303−319 (2022). Li, J. et al . Heterogeneous electrosynthesis of C–N, C–S and C–P products using CO 2 as a building block. Nat. Synth . 3 , 809–824 (2024). Liu, C., Gao, Y. & Zhang, B. Organonitrogen electrosynthesis from CO 2 and nitrogenous sources in water. Nat. Synth. 3 , 794–796 (2024). Jouny, M. et al. Formation of carbon–nitrogen bonds in carbon monoxide electrolysis. Nat. Chem. 11 , 846−851 (2019). Tao, Z., Rooney, C. L., Liang, Y. & Wang, H. Accessing organonitrogen compounds via C–N coupling in electrocatalytic CO 2 reduction. J. Am. Chem. Soc. 143 , 19630−19642 (2021). Jiao, Y., Li, H., Jiao, Y. & Qiao, S.-Z. Activity and selectivity roadmap for C–N electro-coupling on mxenes. J. Am. Chem. Soc. 145 , 15572−15580 (2023). Wu, Y., Jiang, Z., Lin, Z., Liang, Y. & Wang, H. Direct electrosynthesis of methylamine from carbon dioxide and nitrate. Nat. Sustain. 4 , 725−730 (2021). Liu, X., Jiao, Y., Zheng, Y., Jaroniec, M. & Qiao, S.-Z. Mechanism of C–N bonds formation in electrocatalytic urea production revealed by ab initio molecular dynamics simulation. Nat. Commun. 13 , 5471 (2022). Zhang, X. et al. Direct electro-synthesis of valuable C=N compound from NO. Chem. Catal. 2 , 1807−1818 (2022). Wu, Y. et al. Electrosynthesis of a nylon-6 precursor from cyclohexanone and nitrite under ambient conditions. Nat. Commun. 14 , 3057 (2023). Chen, F.-Y. et al. Efficient conversion of low-concentration nitrate sources into ammonia on a Ru-dispersed Cu nanowire electrocatalyst. Nat. Nanotechnol. 17 , 759−767 (2022). Han, S. et al. Ultralow overpotential nitrate reduction to ammonia via a three-step relay mechanism. Nat. Catal. 6 , 402−414 (2023). Shao, J. et al . Electrochemical synthesis of ammonia from nitric oxide using a copper–tin alloy catalyst. Nat Energy 8 , 1273–1283 (2023). Jia, S. et al. Integration of plasma and electrocatalysis to synthesize cyclohexanone oxime under ambient conditions using air as a nitrogen source. Chem. Sci. 14 , 13198−13204 (2023). Liao, P., Kang, J., Xiang, R., Wang, S. & Li, G. Electrocatalytic systems for NO x valorization in organonitrogen synthesis. Angew. Chem. Int. Ed. 63 , e202311752 (2024). Wu, Y. et al. Electrocatalytic synthesis of nylon-6 precursor at almost 100 % yield. Angew. Chem. Int. Ed. 62 , e202305491 (2023). Sharp, J. et al. Sustainable electrosynthesis of cyclohexanone oxime through nitrate reduction on a Zn–Cu alloy catalyst. ACS Catal. 14 , 3287−3297 (2024). Luo, L. et al. Electrosynthesis of the nylon-6 precursor from nitrate and cyclohexanone over a rutile TiO 2 catalyst. CCS Chem. https://doi.org/10.31635/ccschem.024.202403988 (2024). Ko, B. H., Hasa, B., Shin, H., Zhao, Y. & Jiao, F. Electrochemical reduction of gaseous nitrogen oxides on transition metals at ambient conditions. J. Am. Chem. Soc. 144 , 1258−1266 (2022). Yang, R. et al . Descriptor-based volcano relations predict single atoms for hydroxylamine electrosynthesis. Angew. Chem. Int. Ed. 63 , e202317167 (2024). Guo, P. et al . Computational insights on structural sensitivity of cobalt in NO electroreduction to ammonia and hydroxylamine. J. Am. Chem. Soc. 146 , 13974–13982 (2024). Wang, Z., Cao, X. M., Zhu, J. & Hu, P. Activity and coke formation of nickel and nickel carbide in dry reforming: A deactivation scheme from density functional theory. J. Catal. 311 , 469−480 (2014). Li, J. et al. Constraining CO coverage on copper promotes high-efficiency ethylene electroproduction. Nat. Catal. 2 , 1124−1131 (2019). Hammer, B. & Nørskov, J. K. Adsorbate reorganization at steps: NO on Pd(211). Phys. Rev. Lett. 79 , 4441−4444 (1997). Beltramo, G. L. & Koper, M. T. M. Nitric oxide reduction and oxidation on stepped Pt[n(111)×(111)] electrodes. Langmuir 19 , 8907−8915 (2003). Li, T. et al. A spectroscopic study on nitrogen electrooxidation to nitrate. Angew. Chem. Int. Ed. 62 , e202217411 (2023). Guo, C. et al. Computational design of spinel oxides through coverage-dependent screening on the reaction phase diagram. ACS Catal. 12, 6781−6793 (2022). Li, J. et al. Cascade dual sites modulate local CO coverage and hydrogen-binding strength to boost CO 2 electroreduction to ethylene. J. Am. Chem. Soc. 146 , 5693−5701 (2024). Gao, D., Arán-Ais, R.M., Jeon, H.S., Cuenya, B. R. Rational catalyst and electrolyte design for CO 2 electroreduction towards multicarbon products. Nat. Catal. 2 , 198–210 (2019). Karatok M. et al . Achieving ultra-high selectivity to hydrogen production from formic acid on Pd–Ag alloys. J. Am. Chem. Soc. 145, 9, 5114–5124 (2023). Zhao, R. et al. Achieving over 90% faradaic efficiency in cyclohexanone oxime electrosynthesis using the Cu−Mo dual-site catalyst. J. Am. Chem. Soc. 146 , 27956−27963 (2024). Zhang, F. et al. A Pickering-emulsion-droplet-integrated electrode for the continuous-flow electrosynthesis of oximes. Nat. Synth (2025). https://doi.org/10.1038/s44160-024-00713-3. Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.docx Supplementary Information Cite Share Download PDF Status: Published Journal Publication published 07 Aug, 2025 Read the published version in Nature Synthesis → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4791713","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":415366938,"identity":"f072814d-9cc8-4679-96ad-85a31fe1644d","order_by":0,"name":"Bin Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYBACAwYeEGXDwNgApHhI0JImQbKWwxJgHlFazPnPHvxc8Ot8HfOMBMYHb9sY5M0JabFsOJcsPbPvtgTjjARmw7ltDIY7Gwg57GCPgTRvD1gLmzRvG0OCwQFCWg7zGP/m7TkH0sL+mzgtx3jMpHl+HADbwkyUFsseHjNr3oZkycaeh82Sc85JGG4gpMWc/4zxbZ4/dvyG7ckHP7wps5EnaAsYMLYxMBg2gCNTghj1IPCHgUGeWLWjYBSMglEw8gAADxE8LaFiNyQAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-0542-1819","institution":"Tianjin University","correspondingAuthor":true,"prefix":"","firstName":"Bin","middleName":"","lastName":"Zhang","suffix":""},{"id":415366939,"identity":"d540e519-284f-4d1a-81b4-3e63a80cd643","order_by":1,"name":"Yongmeng Wu","email":"","orcid":"https://orcid.org/0000-0003-2778-6018","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Yongmeng","middleName":"","lastName":"Wu","suffix":""},{"id":415366940,"identity":"20aeb149-2d69-46aa-9b38-b5104d88d806","order_by":2,"name":"Xinyu Liu","email":"","orcid":"https://orcid.org/0009-0002-0867-4096","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Xinyu","middleName":"","lastName":"Liu","suffix":""},{"id":415366941,"identity":"9e24b09d-4374-4678-98d3-e34339bc31a0","order_by":3,"name":"Rong Yang","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Rong","middleName":"","lastName":"Yang","suffix":""},{"id":415366942,"identity":"e7d0ee4f-c992-4ba0-a58a-d082dcae78a3","order_by":4,"name":"Chuanqi Cheng","email":"","orcid":"https://orcid.org/0000-0002-3366-8395","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Chuanqi","middleName":"","lastName":"Cheng","suffix":""},{"id":415366943,"identity":"c8135fca-8df9-43df-be12-f190d3d7c3d8","order_by":5,"name":"Ziyang Song","email":"","orcid":"https://orcid.org/0000-0001-8569-9284","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Ziyang","middleName":"","lastName":"Song","suffix":""}],"badges":[],"createdAt":"2024-07-24 02:05:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4791713/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4791713/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s44160-025-00851-2","type":"published","date":"2025-08-07T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":77233010,"identity":"a5ca0d29-ba7a-4897-9860-50368191d87b","added_by":"auto","created_at":"2025-02-26 12:40:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1630669,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eReaction process diagram and catalyst screening. a, \u003c/strong\u003ePossible reactions during the CYC electrosynthesis process. \u003cstrong\u003eb, \u003c/strong\u003eCalculated\u003cstrong\u003e \u003c/strong\u003eNH\u003csub\u003e2\u003c/sub\u003eOH* desorption energy (\u003cem\u003eG\u003c/em\u003e\u003csub\u003edes\u003c/sub\u003e) for different metals. \u003cstrong\u003ec, \u003c/strong\u003eCYC electrosynthesis performance over different metals. The reactions were carried out at 10 mA cm\u003csup\u003e‒2\u003c/sup\u003e for 2 h using 20 mL of electrolyte (0.9 M NaClO\u003csub\u003e4 \u003c/sub\u003e+ 0.1 M NaOH) containing 4 mmol of cyclohexanone.\u003cstrong\u003e d, \u003c/strong\u003eSpeculated\u003cstrong\u003e \u003c/strong\u003ediagram of the effect of NO coverage on different products.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/2c3f90ac47e1071c58e4ed3c.png"},{"id":77231283,"identity":"7f5e148a-2343-4fe3-a9ff-67e7148ff194","added_by":"auto","created_at":"2025-02-26 12:24:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1766351,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDFT calculation results for the effects of NO coverage. a, \u003c/strong\u003eThe calculated free energy diagrams for NO reduction at NO coverages of 1/4 and 3/4 ML over low-coordination Ag. \u003cstrong\u003eb, \u003c/strong\u003eWater dissociation energy barriers at 1/4 and 3/4 ML NO coverages over low-coordination Ag.\u003cstrong\u003e c,\u003c/strong\u003e NO‒NO coupling free energy at NO coverages of 1/4 and 1/2 ML over low-coordination Ag.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/54803423609263772691d007.png"},{"id":77231285,"identity":"672d0c33-ca0b-46d3-9332-250204adc8e1","added_by":"auto","created_at":"2025-02-26 12:24:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2565180,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCYC electrosynthesis performance as a function of NO coverage. \u003c/strong\u003e(\u003cstrong\u003ea\u003c/strong\u003e) The ratio of the peak area of NO* to D\u003csub\u003e2\u003c/sub\u003eO* (\u003cem\u003eS\u003c/em\u003e\u003csub\u003eNO*\u003c/sub\u003e/\u003cem\u003eS\u003c/em\u003e\u003csub\u003eD2O*\u003c/sub\u003e) obtained at a potential of –0.8 V. \u003cstrong\u003eb‒c, \u003c/strong\u003eNO reduction current density (\u003cstrong\u003eb\u003c/strong\u003e) and CYC partial current density (\u003cstrong\u003ec\u003c/strong\u003e) of CYC electrosynthesis at different NO concentrations. \u003cstrong\u003ed‒f, \u003c/strong\u003eThe Faradic efficiency of CYC (\u003cstrong\u003ed\u003c/strong\u003e), NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e (\u003cstrong\u003ee\u003c/strong\u003e) and N-2 products (\u003cstrong\u003ef\u003c/strong\u003e) at different NO concentrations. The error bars correspond to the standard deviation of at least two independent measurements.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/48114875c678e24f6dc300d1.png"},{"id":77231726,"identity":"adf6ad0a-730e-4da5-9333-4b6043ea88f9","added_by":"auto","created_at":"2025-02-26 12:32:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":3008849,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanistic study. a, \u003c/strong\u003eThe function of the NO adsorption energy and effective \u003cem\u003ed\u003c/em\u003e-band center under different coverages. All the adsorption energies are calculated with reference to gas-phase NO, H\u003csub\u003e2\u003c/sub\u003e, and H\u003csub\u003e2\u003c/sub\u003eO (l)\u003csub\u003e.\u003c/sub\u003e B1: bridge step site; H2: hollow site. The blue and red dots represent the last adsorbed NO at the H (blue) or B (red) site, respectively. B1-B1 represent the first and second NO molecules sequentially adsorbed at the B1 site; B1-B1-H2 represents the first and second NO molecules sequentially adsorbed at the B1 site; and the third NO molecule adsorbed at the H2 site. B1-B1-H2-B1 and B1-B1-H2-B1-H2 represent the different adsorbed sites that are similar to the description of B1-B1-H2. \u003cstrong\u003eb‒e,\u003c/strong\u003e Potential-dependent electrochemical in situ IR spectra under 100% (blue) and 20% (red) NO. \u003cstrong\u003ef, \u003c/strong\u003eThe proposed reaction pathway for CYC electrosynthesis under low (left) and high NO coverage (right).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/2418933810e6306f24d82a60.png"},{"id":77231290,"identity":"efe75129-ed1c-4f6d-a8d3-a52b51f21541","added_by":"auto","created_at":"2025-02-26 12:24:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3407855,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCalculational and experimental results of Ru-Ag for CYC electrosynthesis. a, \u003c/strong\u003eBader charge distributions for low-coordination Ag (left) and low-coordination AgRu (right) surfaces.\u003cstrong\u003e b, \u003c/strong\u003eNO‒NO coupling free energy at NO coverages of 1/2 ML over low-coordination Ag and low-coordination AgRu. \u003cstrong\u003ec, \u003c/strong\u003eSEM, TEM and corresponding EDS mapping images of AgRu-1.3.\u003cstrong\u003e d‒e, \u003c/strong\u003eCYC electrosynthesis performance at constant current densities of 0.1 to 1.0 A cm\u003csup\u003e‒2\u003c/sup\u003e. \u003cstrong\u003ef, \u003c/strong\u003eComparison of the CYC FE and CYC partial current densities of this work and previously reported systems. \u003cstrong\u003eg,\u003c/strong\u003e Durability test of AgRu-1.3. The error bars correspond to the standard deviation of at least two independent measurements, and the center value for the error bars is the average of the three independent measurements.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/b188017fd4b69921f4d14428.png"},{"id":88596693,"identity":"e74a9358-1e70-4847-be71-bf574d54e29f","added_by":"auto","created_at":"2025-08-08 07:07:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":13401399,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/5c5db972-dc47-4c1a-abd5-c3d9f3413a98.pdf"},{"id":77231296,"identity":"79afa08f-6f60-4bed-8615-98930bff8e8c","added_by":"auto","created_at":"2025-02-26 12:24:08","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":23938983,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4791713/v1/009c7266729b6b6b72de5934.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Tuning NO coverage promotes ampere-level electrosynthesis of a nylon-6 precursor","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCyclohexanone oxime (CYC) is an important precursor for the production of nylon-6, with an annual global demand of approximately 10\u0026nbsp;million tons and a global market size of approximately \u003cspan\u003e$\u003c/span\u003e25 billion\u003csup\u003e \u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e \u003c/sup\u003e. The industrial production of CYC generally involves a two-step and complex process in which NH\u003csub\u003e2\u003c/sub\u003eOH is first produced via the Raschig method, after which NH\u003csub\u003e2\u003c/sub\u003eOH reacts with cyclohexanone to form CYC\u003csup\u003e \u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e \u003c/sup\u003e. This two-step method requires explosive H\u003csub\u003e2\u003c/sub\u003e, strongly acidic conditions and precious metal catalysts, causing concerns about safety, cost, and sustainability. Moreover, the transportation and storage of concentrated NH\u003csub\u003e2\u003c/sub\u003eOH are at risk of explosion.\u003c/p\u003e \u003cp\u003eThe electrocatalytic construction of C‒N bonds from nitric oxide (NO\u003csub\u003ex\u003c/sub\u003e) and carbonaceous sources has emerged as a sustainable strategy for synthesizing organic nitrogenous compounds from inorganic nitrogen sources\u003csup\u003e\u003cspan additionalcitationids=\"CR10 CR11 CR12 CR13 CR14 CR15\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Specifically, CYC aqueous electrosynthesis has been realized by using nitric oxide (NO, NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) and cyclohexanone as the N and C sources, respectively\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. A mechanistic study revealed that the spontaneous condensation of cyclohexanone with NH\u003csub\u003e2\u003c/sub\u003eOH intermediates produced by NO\u003csub\u003ex\u003c/sub\u003e electroreduction is the key step in the formation of CYC. However, NO\u003csub\u003ex\u003c/sub\u003e reduction is a multi-electron process involving a variety of nitrogen-containing intermediates\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, resulting in multiple byproducts and an undesirable low CYC Faradaic efficiency (FE). Moreover, the partial current density of the CYC is still tens of milliamps (mA), which is far from suitable for industrial application at large current densities of \u0026ge;\u0026thinsp;200 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Recent advances in improving the CYC electrosynthesis FE and current density have focused on screening electrode materials, mostly through trial-and-error modes\u003csup\u003e\u003cspan additionalcitationids=\"CR23 CR24 CR25\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Therefore, understanding the origin of the activity and selectivity of CYC and developing an effective regulation strategy to synthesize CYC with high FE at large current densities are highly desirable but remain unexplored.\u003c/p\u003e \u003cp\u003eIn this article, using density functional theory (DFT) calculations, we first assess the influence of NO coverage on the key elementary steps that branch NH\u003csub\u003e2\u003c/sub\u003eOH versus NH\u003csub\u003e3\u003c/sub\u003e. We find that improving NO coverage benefits the NH\u003csub\u003e2\u003c/sub\u003eOH pathway. However, excessive NO coverage also decreases the NO\u0026minus;NO coupling energy barrier to form N-2 (N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e) byproducts. In subsequent experiments, we adjust the local NO concentration at the catalyst\u0026ndash;electrolyte interface by tuning the combination of the NO supply concentration and reaction rate. We achieve an 89% CYC FE and a 206 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e current density under 50% NO at \u0026minus;\u0026thinsp;3.0 V over a Ag catalyst. A mechanistic study reveals that at low coverage, NO occupies the Ag step site with strong bridge adsorption, which is preferable for NH\u003csub\u003e3\u003c/sub\u003e production. At high NO coverage, the active sites transfer from bridge step sites to hollow terrace sites, accompanied by a downshift in the \u003cem\u003ed\u003c/em\u003e-band center, leading to weak adsorption of O* species; thus, the NH\u003csub\u003e2\u003c/sub\u003eOH* intermediate is stable rather than decomposing to form NH₃, and the NH₂OH pathway accordingly becomes dominant. Moreover, N‒N coupling easily occurs at high NO coverage. This mechanistic understanding inspired us to speculate that a doping strategy to break the equivalent catalyst surface sites can inhibit NO\u0026ndash;NO coupling at high NO coverage and thus realize a high CYC FE at high current density. Accordingly, a Ru-doped Ag (AgRu) catalyst is developed, and an 86% CYC FE was achieved at a current density of 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eReaction process analysis\u003c/h2\u003e \u003cp\u003eDuring the process of CYC electrosynthesis from NO and cyclohexanone, possible competitive reactions include the hydrogen evolution reaction (HER, I), the over hydrogenation of NH\u003csub\u003e2\u003c/sub\u003eOH to NH\u003csub\u003e3\u003c/sub\u003e (II) and the N‒N coupling products of N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e(III) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). An inherently selective catalyst should possess a large Δ\u003cem\u003eG\u003c/em\u003e\u003csub\u003eHER\u003c/sub\u003e and weak NH\u003csub\u003e2\u003c/sub\u003eOH adsorption energy to avoid the competitive reactions of (I) and (II). Accordingly, we calculated the NH\u003csub\u003e2\u003c/sub\u003eOH desorption energy of several metals that are commonly used in NO\u003csub\u003ex\u003c/sub\u003e reduction and found that Ag had the lowest NH\u003csub\u003e2\u003c/sub\u003eOH desorption energy (\u003cem\u003eG\u003c/em\u003e\u003csub\u003edes\u003c/sub\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The experimental results show that Ag foil exhibits the optimum CYC FE among these metal foils (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;1). To increase the active area, Ag\u003csub\u003e2\u003c/sub\u003eO-derived Ag nanoparticles were used as catalysts (Supplementary Figs.\u0026nbsp;2‒6 and Supplementary Notes 1‒3). To achieve high-current-density CYC electrosynthesis, a high local concentration of NO is desirable to overcome the mass transfer limitations. However, high NO coverage may cause easier coupling of NO\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e, thus leading to side reactions (III). In this regard, we speculate that NO coverage on the catalyst surface may play a vital role in CYC electrosynthesis. Low NO coverage may benefit NH\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003e formation because of excess H* but insufficient NO, high NO coverage leads to the NO‒NO coupling reaction to produce N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e (N-2) byproducts, and appropriate NO coverage is required to form NH\u003csub\u003e2\u003c/sub\u003eOH to condense with cyclohexanone to form CYC (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). These considerations encouraged us to study the effect of NO coverage on the CYC product.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePrediction of the effect of NO coverage on the performance of cyclohexanone oxime\u003c/h3\u003e\n\u003cp\u003eWe attempted to understand the connection between NO coverage and CYC production with the aid of DFT calculations by modelling low-coordination Ag to represent Ag\u003csub\u003e2\u003c/sub\u003eO-derived Ag nanoparticles (Supplementary Tables\u0026nbsp;1‒6 and Supplementary Note 4). The possible reaction pathways are shown in Supplementary Fig.\u0026nbsp;7. To identify coverage-dependent reaction pathways, various reaction sites were considered (Supplementary Fig.\u0026nbsp;8 and Supplementary Note 5). Then, three NO coverages of 1/4, 1/2 and 3/4 monolayers (ML) were analysed in detail. We first compare the adsorption free energies (\u003cem\u003eG\u003c/em\u003e\u003csub\u003ead\u003c/sub\u003e) of NOH* and NHO*, the O- and N-terminal hydrogenation intermediates of NO, under different NO coverages and find that NHO* is more stable than NOH* at different NO coverages; thus, NO* prefers hydrogenation via the N atom to generate NHO* rather than NOH* (Supplementary Fig.\u0026nbsp;9). This result also indicates that the NHO* pathway to NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is inhibited in our system\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Similarly, by comparing the adsorption free energies of NHOH* and NH\u003csub\u003e2\u003c/sub\u003eO*, the NHOH pathway was excluded (Supplementary Fig.\u0026nbsp;10). Thus, the probable pathways to NH\u003csub\u003e2\u003c/sub\u003eOH and NH\u003csub\u003e3\u003c/sub\u003e are NO*\u0026rarr;NHO*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eO*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eOH*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eOH or NO*\u0026rarr;NHO*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eO*\u0026rarr;O* + NH\u003csub\u003e3\u003c/sub\u003e\u0026rarr;OH* + NH\u003csub\u003e3\u003c/sub\u003e\u0026rarr;H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;NH\u003csub\u003e3\u003c/sub\u003e. We compared the reaction free energies of the two pathways at NO coverages of 1/4, 1/2 and 3/4 ML (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, Supplementary Figs.\u0026nbsp;11 and 12 and Supplementary Table\u0026nbsp;7). We focus on the key elementary steps that branch NH\u003csub\u003e2\u003c/sub\u003eOH versus NH\u003csub\u003e3\u003c/sub\u003e, that is, the O-terminal hydrogenation of NH\u003csub\u003e2\u003c/sub\u003eO* to NH\u003csub\u003e2\u003c/sub\u003eOH* and then to NH\u003csub\u003e3\u003c/sub\u003e* (NH\u003csub\u003e2\u003c/sub\u003eO*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eOH*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eOH) or the N-terminal hydrogenation to NH\u003csub\u003e3\u003c/sub\u003e (NH\u003csub\u003e2\u003c/sub\u003eO*\u0026rarr;O* + NH\u003csub\u003e3\u003c/sub\u003e (2)). At 1/4 ML, path (2) is more thermodynamically favourable than path (1); thus, NH\u003csub\u003e3\u003c/sub\u003e formation is undoubtedly the dominant product. However, when the NO coverage increases to 1/2 and 3/4 the ML, path (1) becomes more favourable than path (2); thus, the NH₂OH pathway is dominant.\u003c/p\u003e \u003cp\u003eWe further evaluated the effect of NO coverage on the HER. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;13. The water dissociation energy barriers at 0, 1/4, 1/2, and 3/4 ML NO coverages on the Ag sites are 1.15, 1.33, 1.36 and 1.40 eV, respectively. Thus, high NO coverage can restrain the HER.\u003c/p\u003e \u003cp\u003eFurthermore, the influence of NO coverage on N-2 product formation was studied. By calculating the reaction free energies of a series of possible N‒N coupling pathways, the most likely N‒N coupling pathway is determined to be NO*+NO*\u0026rarr;N\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e*\u0026rarr;NO-NOH*\u0026rarr;N\u003csub\u003e2\u003c/sub\u003eO* (Supplementary Figs.\u0026nbsp;14‒17 and Supplementary Notes. 7 and 8). The activation energy of NO*+NO*\u0026rarr;N\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e* decreases as the NO coverage increases (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). This finding indicates that NO\u0026minus;NO coupling easily occurs at high NO concentrations. These calculation results show that the Ag catalyst easily produces NH\u003csub\u003e3\u003c/sub\u003e under low NO coverage but produces NH\u003csub\u003e2\u003c/sub\u003eOH and N-2 products under high NO coverage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eExperimental proof of the effect of NO coverage on cyclohexanone oxime performance\u003c/h3\u003e\n\u003cp\u003eThe above results inspired us to experimentally study the influence of surface coverage of NO on CYC production. According to Henry\u0026rsquo;s law (Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e))\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e, the local NO concentration is correlated with \u003cem\u003ep\u003c/em\u003e\u003csub\u003eNO\u003c/sub\u003e; thus, NO coverage regulation can be realized by controlling the local NO concentration or NO partial pressure (\u003cem\u003ep\u003c/em\u003e\u003csub\u003eNO\u003c/sub\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\:{\\theta\\:}_{\\text{N}\\text{O}}={\\theta\\:}_{*}{p}_{\\text{N}\\text{O}}{\\text{e}}^{-\\frac{{E}_{\\text{a}\\text{d}\\left(\\text{N}\\text{O}\\text{*}\\right)}}{RT}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e*\u003c/sub\u003e is the coverage of free surface sites, \u003cem\u003eE\u003c/em\u003e\u003csub\u003ead\u003c/sub\u003e (NO*) is the NO adsorption energy on the surface, \u003cem\u003eR\u003c/em\u003e is the ideal gas constant and \u003cem\u003eT\u003c/em\u003e is the temperature.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe experimentally verified the Ag surface NO coverage variation under different NO concentrations via in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR\u0026minus;SEIRAS). We used the ratio of the peak area of NO to that of D\u003csub\u003e2\u003c/sub\u003eO (\u003cem\u003eS\u003c/em\u003e\u003csub\u003eNO*\u003c/sub\u003e/\u003cem\u003eS\u003c/em\u003e\u003csub\u003eD2O*\u003c/sub\u003e) obtained at a potential of \u0026minus;\u0026thinsp;0.8 V (a potential where NO is adsorbed but not reduced) to reflect the surface NO coverage. As the supplied NO concentration increases from 10\u0026ndash;70%, the value of \u003cem\u003eS\u003c/em\u003e\u003csub\u003eNO*\u003c/sub\u003e/\u003cem\u003eS\u003c/em\u003e\u003csub\u003eD2O*\u003c/sub\u003e increases from 1.33 to 6.44 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;18). A further increase in the NO concentration cannot increase the NO coverage, indicating that the surface NO coverage reaches its maximum at a 70% NO concentration. These results demonstrate that the Ag surface NO coverage can be adjusted by altering the NO input concentration.\u003c/p\u003e \u003cp\u003eWe thus tested the CYC electrosynthesis performance at input NO gas concentrations ranging from 10 to 100% across a range of applied potentials. A gas diffusion electrode (GDE) was used to enhance mass transfer (Supplementary Fig.\u0026nbsp;19). When the NO concentration increases from 10 to 100%, an overall increase in both the total current density (Supplementary Figs.\u0026nbsp;20 and 21) and the NO reduction partial current density (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) is observed. The increase in the NO reduction current density follows a linear increase in the potential window of \u0026minus;\u0026thinsp;1.35 to \u0026minus;\u0026thinsp;3.6 V at NO concentrations of 10%, 20% and 50%. At a more negative potential, the tendency of the current density to increase slows due to NO mass transport limitations, with a characteristic increase in hydrogen production (Supplementary Fig.\u0026nbsp;22). Further increasing the NO concentration to 70% and 100% results in the current density growth limitation shifting to a more negative potential of \u0026minus;\u0026thinsp;6.6 V (Supplementary Fig.\u0026nbsp;23). The tendency of the CYC partial current density first increases and then decreases as the applied potential decreases, and the inflection point of the potential negatively shifts as the NO concentration increases from 10 to 100% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). A similar situation is observed for the N-2 product partial current density, while the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e partial current density is negatively correlated with NO coverage (Supplementary Figs.\u0026nbsp;24 and 25).\u003c/p\u003e \u003cp\u003eCYC, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003e and N-2 products all present NO concentration-related FEs (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed\u0026thinsp;\u0026minus;\u0026thinsp;f and Supplementary Fig.\u0026nbsp;26). Generally, a moderate NO concentration (50%) is conducive to the production of CYC, a low NO concentration (10 and 20%) is beneficial for NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e formation, and a high NO concentration favours N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e products (70 and 100%). The potential-dependent FEs of products present different tendencies under different NO concentrations. Specifically, the CYC FE is potentially highly dependent on NO concentrations of 10, 20 and 50%, and it decreases sharply at potentials less than \u0026minus;\u0026thinsp;3.0 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). This is probably due to the insufficient NO supply caused by rapid NO consumption at negative potentials under low NO concentrations. However, the CYC FE depends less on the potential when the NO concentration increases to 70 and 100%. This is because under high NO concentrations, NO is in excess, so the consumption of NO at large potentials can hardly affect the local concentration of NO within the potential range of \u0026minus;\u0026thinsp;1.35 to \u0026minus;\u0026thinsp;4.3 V. A further decrease in the potential leads to a decrease in the CYC FE because the HER occurs (Supplementary Fig.\u0026nbsp;27). NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e FE is negatively correlated with the NO concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). At 10, 20 and 50% NO concentrations, the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e FE increases as the applied potential decreases until NO mass transfer limitations appear, which is indicated by the observation of H\u003csub\u003e2\u003c/sub\u003e. At 70% and 100% NO, hardly any NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is produced, and the amount of N-2 products increases. The variation tendency of the N-2 products is opposite to that of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, in which the FE increases with increasing NO concentration and remains constant within the potential range of \u0026minus;\u0026thinsp;1.35 to \u0026minus;\u0026thinsp;4.3 V under pure NO conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003eThe product distributions at various NO concentrations and potentials were analysed (Supplementary Figs.\u0026nbsp;28\u0026ndash;32 and Supplementary Notes 9 and 10). At low NO concentrations (10 and 20%), NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is the primary byproduct, and the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e FE increases as the potential decreases until H\u003csub\u003e2\u003c/sub\u003e is present. With increasing NO concentration, the NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e FE gradually decreases, while the N-2 products emerge as the main byproducts. Under pure NO conditions, N-2 products are the only byproducts, and ~\u0026thinsp;50% of the FEs are maintained from \u0026minus;\u0026thinsp;1.35 to \u0026minus;\u0026thinsp;6.6 V. The key to CYC production is thus to constrain operating conditions such that NO availability is neither too high (promoting N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e) nor too low (promoting NH\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003e), which is in agreement with the calculation results.\u003c/p\u003e\n\u003ch3\u003eMechanistic studies\u003c/h3\u003e\n\u003cp\u003eTo gain insight into the nature of the difference in product distribution under low and high NO concentrations, DFT calculations combined with in situ ATR\u0026minus;SEIRAS experiments were conducted. We simulate NO adsorption at low and high coverages and find that adsorbate reorganization occurs as the coverage increases (Supplementary Fig.\u0026nbsp;33 and Supplementary Note 11). At low coverage, NO reasonably occupies the bridge step site (B1) with strong bridge adsorption. At high coverage, the dense NO at the step site is squeezed and migrates to the terrace hollow site near the step site (H2) with weak hollow adsorption. Next, we investigated the reasons for the order of site preference and the extent of adsorbate reorganization during adsorption. We calculated the NO adsorption energy and effective \u003cem\u003ed\u003c/em\u003e-band center at the B1 and H2 sites from low to high coverage (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, Supplementary Fig.\u0026nbsp;34 and Supplementary Note 12). We find that there is an excellent correlation between the adsorption energy and the \u003cem\u003ed\u003c/em\u003e-band center\u0026mdash;the lower the \u003cem\u003ed\u003c/em\u003e-band center is, the weaker the adsorption ability. We thus believe that the essential reason for the product distribution variance is the change in the center of the catalyst \u003cem\u003ed\u003c/em\u003e-band at different NO coverages\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. Under low coverage, the B1 site possesses stronger NO adsorption ability and a higher \u003cem\u003ed\u003c/em\u003e-band center than the H2 site. Thus, NO tends to adsorb strongly on the B1 site at low coverage and hydrogenates to NH₃O*, which decomposes to NH₃ and O* immediately. This is why NH\u003csub\u003e3\u003c/sub\u003e is produced under low NO coverage. Under high coverage, the B1 sites that preadsorb NO have difficulty adsorbing more NO due to the steric effect; thus, NO tends to adsorb at H2 sites, making the B1 and H2 sites both active sites. The effective \u003cem\u003ed\u003c/em\u003e-band centers of the B1 and H2 sites of Ag strongly correlate with the site changes. Accordingly, the differences in selectivity with coverage can be correlated with changes in active sites. Specifically, the H2 sites exhibit weaker adsorption of O species, leading to the stable existence of the NH\u003csub\u003e2\u003c/sub\u003eOH* intermediate, rather than decomposing to form NH₃ and *O species. Thus, the NH\u003csub\u003e2\u003c/sub\u003eOH pathway becomes dominant.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe above results are further verified experimentally. Potential-dependent electrochemical in situ ATR\u0026minus;SEIRAS was conducted at NO concentrations of 10, 20, 50, 70 and 100% (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb\u0026thinsp;\u0026minus;\u0026thinsp;c and Supplementary Figs.\u0026nbsp;35 and 36). Because the wide H\u003csub\u003e2\u003c/sub\u003eO peak at approximately 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e overlaps with the peaks of NO, we conducted the test in D\u003csub\u003e2\u003c/sub\u003eO. At low NO concentrations of 10 and 20%, only one peak at approximately 1555 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is observed, which is ascribed to bridge adsorption at the step site (B1) of NO* (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;36a)\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. When the NO concentration increases above 50%, the peak at 1555 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e first appears, and then another peak at approximately 1630 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (hollow adsorption at the terrace site of NO*, H2) appears, indicating the migration of NO from the step site to the terrace site when NO adsorption at the step site is saturated at high NO concentrations (Supplementary Figs.\u0026nbsp;36b,c)\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. At the 100% NO concentration, the peak at 1555 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e shifts to a higher wavenumber as the potential negatively shifts (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), possibly because of the effects of the adjacent NO* at the H2 site, known as \u0026ldquo;adsorbate\u0026thinsp;\u0026minus;\u0026thinsp;adsorbate interactions\u0026rdquo;, which are usually observed at very high adsorbate coverage\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. These results further demonstrate that coverage induces a change in the site preference of preadsorbed NO; that is, NO prefers to adsorb on bridge sites at low coverage but on hollow sites at high coverage, which is in accordance with the calculation results.\u003c/p\u003e \u003cp\u003eIn addition to NO, the production of NH\u003csub\u003e2\u003c/sub\u003eOH under low and high NO coverage was identified by the ATR\u0026minus;SEIRAS and control experiments. Under 20% NO, NH\u003csub\u003e2\u003c/sub\u003eOH is detected at 2904 cm\u003csup\u003e\u0026ndash;125\u003c/sup\u003e in the tested potential range of \u0026minus;\u0026thinsp;0.8 to \u0026minus;\u0026thinsp;2.1 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). In comparison, the NH\u003csub\u003e2\u003c/sub\u003eOH* peak at 100% NO appears at \u0026minus;\u0026thinsp;0.9 V but disappears at potentials more negative than \u0026minus;\u0026thinsp;1.2 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) because under high NO concentrations, NO is rapidly adsorbed on the catalyst surface with increasing applied potential, resulting in high surface NO coverage at step sites. High NO coverage results in NH\u003csub\u003e2\u003c/sub\u003eOH being squeezed and migrating to the terrace hollow site or desorbed to the solution to condense with cyclohexanone. Thus, no NH\u003csub\u003e2\u003c/sub\u003eOH signal can be detected on the Ag surface as the applied potential decreases. Additionally, an N\u003csub\u003e2\u003c/sub\u003eO signal is observed for 100% NO but is absent for 20% NO according to infrared spectroscopy, in accordance with the calculation and performance test results.\u003c/p\u003e \u003cp\u003eOn the basis of the above analysis, reaction pathways under low and high NO coverages are proposed (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). Under low NO coverage, NO adsorbs strongly at the step position and then is hydrogenated in the pathway of NO*\u0026rarr;NHO*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eO*\u0026rarr;NH\u003csub\u003e3\u003c/sub\u003e. Under high NO coverage, the NO preadsorbs at the step site experiences an adsorbate reorganization and finally adsorbs at the step and terrace sites uniformly with a weaker bond energy. Then, it is hydrogenated via the following pathway: NO*\u0026rarr; NHO*\u0026rarr; NH\u003csub\u003e2\u003c/sub\u003eO*\u0026rarr;NH\u003csub\u003e2\u003c/sub\u003eOH. NH\u003csub\u003e2\u003c/sub\u003eOH migrates to the terrace hollow site or desorbs to the electrolyte and condenses with cyclohexanone to yield CYC. Moreover, NO\u0026minus;NO coupling products of N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e inevitably formed.\u003c/p\u003e \u003cp\u003eInspired by the above mechanistic study, we can improve the CYC FE in two ways. One is modulating the NO coverage on the catalyst surface by controlling the NO concentration and applying potential accurately to balance the NO supply and consumption. Here, we achieve an 89.2% CYC FE under a 50% NO concentration at \u0026minus;\u0026thinsp;3.0 V at a current density of 206 mA cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. However, this regulation strategy has difficulty achieving a high current density because the tightly controlled NO concentration establishes a mass transfer constraint. Thus, another strategy involving breaking the equivalent catalyst surface sites to restrict the NO\u0026minus;NO coupling reaction under high NO concentrations is preferable for achieving high-current-density CYC electrosynthesis.\u003c/p\u003e\n\u003ch3\u003eDoping suppresses N−N coupling at high NO coverage for ampere-level electrosynthesis of cyclohexanone oxime\u003c/h3\u003e\n\u003cp\u003eDoping heterogeneous atoms is an effective strategy for breaking equivalent Ag sites\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Moreover, the electronic structure change caused by doping needs to be considered because it is correlated with the adsorption ability. The electron redistribution caused by doping may result in electron-rich states and electron-deficient states at the interface\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. According to the above results, weak adsorption at the Ag step site is required to avoid NH\u003csub\u003e3\u003c/sub\u003e byproducts, and electron deficiency states at the step position are thus desired. We thus attempted to introduce a series of metal atoms with different electronegativities into Ag catalysts and found that Ru is a good dopant (Supplementary Fig.\u0026nbsp;37). Specifically, AgRu has asymmetrical charge sites, and some electron-deficient Ag sites are exposed at the step sites, which is favourable for NH\u003csub\u003e2\u003c/sub\u003eOH formation but not for NO\u0026thinsp;\u0026minus;\u0026thinsp;NO coupling (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). As a result, AgRu has the largest NO\u0026thinsp;\u0026minus;\u0026thinsp;NO coupling barrier, which is expected to inhibit the NO\u0026thinsp;\u0026minus;\u0026thinsp;NO coupling reaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;38). Therefore, Ru-doped Ag catalysts with different Ru contents (denoted as AgRu-x, where x represents the atomic percentage of Ru) were designed and synthesized (Supplementary Note 13). SEM, TEM, mapping, and XRD and XPS results verify the successful synthesis of the AgRu catalysts (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, Supplementary Figs.\u0026nbsp;39 and 40 and\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSupplementary Notes 14 and 15). Potential-dependent electrochemical in situ IR spectra under 100% NO over AgRu-1.3 was conducted (Supplementary Fig.\u0026nbsp;41). Unlike that of the Ag catalyst, only one peak at approximately 1650 cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e is observed, which is attributed to the hollow adsorption at the terrace site (H2) of NO*. The bridge adsorption at the step site (B1) of NO*, at which N‒N coupling tends to occur, is absent. This phenomenon accords with the theoretical prediction and experimental results: Ru doping causes electron-deficient Ag sites at the step sites, weakens NO adsorption and inhibits NO\u0026thinsp;\u0026minus;\u0026thinsp;NO coupling. Thus, NO prefers to occupy H2 sites and yields NH\u003csub\u003e2\u003c/sub\u003eOH. The LSV curves show that the introduction of Ru enhances both the HER and NO reduction activities (Supplementary Fig.\u0026nbsp;42). Then, constant-current electrolysis experiments at current densities of 0.1, 0.2, 0.3, 0.4, 0.5 and 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e were conducted under a pure NO atmosphere. The AgRu catalysts exhibit a higher CYC FE and lower N-2 product FE than Ag at every tested current density, in which AgRu-1.3 shows the best performance (Supplementary Figs.\u0026nbsp;43 and 44). Impressively, an 86% CYC FE and a 10.7 mmol h\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e yield rate are achieved at a current density of 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e over AgRu-1.3 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed‒f)\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan additionalcitationids=\"CR23 CR24 CR25\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e, exceeding the reported performance (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef and Supplementary Table\u0026nbsp;8). The increase in the Faraday efficiency (FE) with increasing current density at a 100% NO concentration occurs because the high reaction rate at a relatively high current density drove the quick consumption of local NO, which lowers NO coverage and thus restrain N‒N coupling, thus improving the cyclohexanone oxime FE. Additionally, the CYC electrosynthesis performance and catalyst composition can be maintained for 35 h at 0.1 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e under pure NO, verifying the good durability of the catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg). Moreover, our strategy can be used to synthesize \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-pyridine oximes using \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eNO as the nitrogen source. An important labelled compound of \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-pralidoxime, the active ingredient in medications such as Atnaa, Duodote (with atropine), pralidoxime chloride and protopam chloride, was synthesized using the as-prepared \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-pyridine oximes as building blocks (Supplementary Fig.\u0026nbsp;45 and Supplementary Note 15).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, we experimentally and theoretically discover that the performance of cyclohexanone for the electrosynthesis of NO and cyclohexanone is closely related to NO coverage on the low-coordination Ag catalyst surface. With increasing local NO concentration, the dominant electrosynthesis products undergo the transformation of NH\u003csub\u003e3\u003c/sub\u003e to cyclohexanone oxime and N-2 (N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e) products. On the basis of spectral characterization and density functional theory (DFT) calculations, we can assign the origin of the selectivity difference to the transformation of active sites from step sites to terrace sites under high coverage. Specifically, at low coverage, NO occupies the Ag step site with strong bridge adsorption, which is preferable for NH\u003csub\u003e3\u003c/sub\u003e production. At high NO coverage, the transfer of active sites from bridge step sites to hollow terrace sites results in weak adsorption of O* species; thus, the NH\u003csub\u003e2\u003c/sub\u003eOH* intermediate is stable rather than decomposing to form NH₃, and the NH₂OH pathway accordingly becomes dominant.. Moreover, N‒N coupling easily occurs at high NO coverage. These results inspire the introduction of Ru to break equivalent catalyst surface sites, thus inhibiting NO\u0026minus;NO coupling at high NO coverage. Accordingly, cyclohexanone oxime with an 86% Faradaic efficiency at a current density of 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was achieved. This work not only paves the way for the industrial mass production of cyclohexanone oxime via electrosynthesis but also reveals the effect of NO coverage on cyclohexanone oxime electrosynthesis. Our work will inspire the efficient electrosynthesis of other nitrogenous compounds via C‒N bond construction.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eMaterials preparation\u003c/h2\u003e \u003cp\u003eThe Ag\u003csub\u003e2\u003c/sub\u003eO nanoparticles were synthesized via a precipitation reaction. First, 10 mmol of AgNO\u003csub\u003e3\u003c/sub\u003e was dissolved in 100 ml of deionized water. Then, 50 ml of NaOH (0.2 M) was added to the AgNO\u003csub\u003e3\u003c/sub\u003e solution while stirring. The Ag\u003csub\u003e2\u003c/sub\u003eO sediment was separated by centrifugation, washed with deionized water and ethanol several times and then dried at 60\u0026deg;C overnight.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization\u003c/h2\u003e \u003cp\u003eThe morphology of the catalysts was observed via field emission scanning electron microscopy (FEI Apreo S LoVac) and transmission electron microscopy (FEI Tecnai G2 F20). X\u0026thinsp;\u0026minus;\u0026thinsp;ray photoelectron spectroscopy measurements were performed on a Thermo Fisher Scientific K-Alpha spectrometer. All the peaks were calibrated by the binding energy of 284.8 eV of the C 1\u003cem\u003es\u003c/em\u003e spectrum. X\u0026thinsp;\u0026minus;\u0026thinsp;ray diffraction tests were performed on a Rigaku SmartLab 9 kW diffraction system. In situ ATR-FTIR was performed on a Nicolet 6700 FTIR spectrometer with silicon as the prismatic window. \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR data were recorded on a Bruker AVANCE III 400 MHz NMR instrument.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eElectrode fabrication\u003c/h2\u003e \u003cp\u003eTwo milligrams of Ag\u003csub\u003e2\u003c/sub\u003eO powder was suspended in a mixture containing 10 \u0026micro;l of Nafion solution (5 wt%) and 1 ml of ethanol via ultrasonication. The above homogeneous ink was subsequently dropped onto carbon paper (Toray, 2 cm \u0026times; 1 cm) with a Ag\u003csub\u003e2\u003c/sub\u003eO loading of 2.0 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The Ag electrode was formed in situ by pretreating the Ag\u003csub\u003e2\u003c/sub\u003eO electrode at a constant potential of \u0026minus;\u0026thinsp;1.8 V versus Ag/AgCl for 10 min before the electrochemical tests. The NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e anode was prepared by following a previously reported procedure. Briefly, 0.4362 g of Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, 0.202 g of Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO, 0.6 g of urea and 0.148 g of NH\u003csub\u003e4\u003c/sub\u003eF were dissolved in 40 ml of deionized water. A piece of freshly treated Ni foam (2 cm \u0026times; 2 cm, 99.99%, 1.5 mm thick; Kunshan) was immersed in the solution and transferred to a Teflon-lined stainless steel autoclave, and hydrothermal treatment was carried out at 120\u0026deg;C for 6 h in an oven. NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/Ni-foam was obtained by calcining the as-prepared precursor in air at 650\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical measurements\u003c/h2\u003e \u003cp\u003eElectrochemical tests were carried out using a CS350MA (CorrTest) electrochemical workstation. The H-type cell was equipped with a three-electrode system, which is depicted in Supplementary Fig.\u0026nbsp;1. The geometric area of the working electrode was 1 \u0026times; 1 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, and the metal foil catalysts were treated with 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and acetone before use. The reference electrode was an Ag/AgCl electrode containing a saturated KCl solution, and a graphite rod served as the counter electrode. The two chambers were separated by a pretreated Nafion 117 (Fuel Cell Store) membrane. The cathode and anode electrolytes were both 25 ml 0.9 M NaClO\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;0.1 M NaOH (pH 12.5), and the cathode electrolyte contained 4 mmol cyclohexanone. The cathodic electrolyte was first purged with Ar gas for 30 min and then purged with pure NO gas for presaturation. After that, the inlet and outlet valves were switched off to form a closed gas circuit, and the internal recycling flow rate was maintained at 10 ml min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e during the catalytic process. There was a gas storage tank with a capacity of 98.0 ml in the gas pipeline, and a peristaltic pump was applied to implement circulation of the gas feed. When the reaction was complete, Ar gas was again used to exhaust the gas from the device. The applied potentials were referenced to the Ag/AgCl reference electrode (saturated KCl solution).\u003c/p\u003e \u003cp\u003eFlow cell electrochemical tests were carried out in a gas-fed three-compartment flow electrolyser and a two-compartment flow electrolyser with an electrode area of 1.0 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The flow cell configurations are depicted in Supplementary Fig.\u0026nbsp;19, which consists of a working electrode, an anion exchange membrane or cation exchange membrane and a NiFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/Ni-foam anode. Foams were compressed before use. Fumasep FAA-3-50 (Fumatech) and Nafion 117 (Fuel Cell Store) were used as separators for alkaline and acidic electrolytes, respectively. Sodium hydroxide (NaOH; Aladdin) and sodium perchlorate (NaClO\u003csub\u003e4\u003c/sub\u003e; Aladdin) were used to prepare the electrolyte. The catholyte (0.1 M NaOH\u0026thinsp;+\u0026thinsp;0.9 M NaClO\u003csub\u003e4\u003c/sub\u003e) was prepared by mixing 1.0 M NaOH and 1.0 M NaClO\u003csub\u003e4\u003c/sub\u003e solutions. NaOH (1 M) was employed as the anolyte. The catholyte and anolyte were allowed to flow at 30 ml min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e by using peristaltic pumps (Baoding Lead Fluid Technology). The NO flow rate at different concentrations was 40 sccm, which was controlled by an electronic flow meter.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical in situ ATR\u0026minus;SEIRAS spectra measurements\u003c/h2\u003e \u003cp\u003eIn situ attenuated total reflection Fourier transform infrared spectroscopy (ATR\u0026minus;SEIRAS) was performed on a Nicolet 6700 FTIR spectrometer equipped with mercury\u0026ndash;cadmium\u0026ndash;telluride (MCT). A detector with silicon as the prismatic window. First, Ag\u003csub\u003e2\u003c/sub\u003eO ink (pure ethanol as the dispersant) was carefully dropped on the surface of the gold film, which was chemically deposited on the surface of the silicon prismatic before each experiment. Then, the deposited silicon prismatic served as the working electrode. Pt foil and Ag/AgCl electrodes containing saturated KCl solution were used as the counter and reference electrodes, respectively. A 0.1 M NaOH\u0026thinsp;+\u0026thinsp;0.9 M NaClO\u003csub\u003e4\u003c/sub\u003e (D\u003csub\u003e2\u003c/sub\u003eO or H\u003csub\u003e2\u003c/sub\u003eO was used as the solvent) solution was used as the electrolyte. Before spectral acquisition, the working electrode was pretreated at a potential of \u0026minus;\u0026thinsp;1.8 V versus Ag/AgCl for 10 min for the in situ formation of Ag. For NO electroreduction, the electrolyte was aerated with different concentrations of NO gas via peristaltic pumps. The spectra were recorded at intervals of 0.1 V with a continuous change in the applied potential from \u0026minus;\u0026thinsp;0.7 to \u0026minus;\u0026thinsp;2.1 V Ag/AgCl. The background spectrum of the catalyst electrode was acquired at an open-circuit voltage before each systemic measurement.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompetitive interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competitive interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e \u003cp\u003eB.Z. conceived the idea and directed the project. Y.W. and B.Z. designed the experiments. X.L. and Y.W. carried out the experiments. R.Y. and C.C. performed the DFT calculations. Z.S. assisted with some experiments. X.L., Y.W. and B.Z. analysed the data. Y.W. wrote the paper. B.Z. revised the paper. All the authors discussed the results and commented on the paper.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe acknowledge the National Natural Science Foundation of China (22271213 to B.Z. and 22401212 to Y.W.).\u003c/p\u003e\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e \u003cp\u003eAll the data needed to evaluate the conclusions in the paper are presented in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eHDIN Research. Global nylon 6 production capacity to reach 8.86 million tons in 2024.\u0026nbsp;www.hdinresearch.com/news/56 (2019).\u003c/li\u003e\n \u003cli\u003eThomas, J. M. \u0026amp; Raja, R. Design of a \u0026ldquo;green\u0026rdquo; one-step catalytic production of \u0026epsilon;-caprolactam (precursor of nylon-6). \u003cem\u003eProc. Natl. Acad. Sci. 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Soc.\u003c/em\u003e \u003cstrong\u003e146\u003c/strong\u003e, 27956\u0026minus;27963 (2024).\u003c/li\u003e\n \u003cli\u003eZhang, F. \u003cem\u003eet al.\u003c/em\u003e A Pickering-emulsion-droplet-integrated electrode for the continuous-flow electrosynthesis of oximes. \u003cem\u003eNat. Synth\u003c/em\u003e (2025). https://doi.org/10.1038/s44160-024-00713-3.\u003cstrong\u003e\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4791713/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4791713/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe electrocatalytic synthesis of cyclohexanone oxime from NO and cyclohexanone with high Faradaic efficiency at ampere-level current density is highly desirable but highly challenging. Here, theoretical calculations reveal that NO coverage on the Ag catalyst plays a critical role in cyclohexanone oxime electrosynthesis. We then adjust the local NO concentration experimentally by tuning the NO concentration and reaction rate. We find that low NO coverage benefits NH\u003csub\u003e3\u003c/sub\u003e formation, whereas high coverage delivers cyclohexanone oxime and N-2 (N\u003csub\u003e2\u003c/sub\u003eO and N\u003csub\u003e2\u003c/sub\u003e) products. A mechanistic study indicates that with increasing NO coverage, the active sites transfer from bridge step sites to hollow terrace sites, which results in weaker adsorption of O* species, leading to the stable existence of the NH\u003csub\u003e2\u003c/sub\u003eOH* intermediate rather than decomposing to form NH₃. However, N‒N coupling also easily occurs at high NO coverage. This mechanistic understanding further inspires us to develop a doping strategy to break the equivalent catalyst surface sites, which can inhibit NO\u0026ndash;NO coupling at high NO coverage and thus realize high cyclohexanone oxime Faradaic efficiency at high current density. A Ru-doped Ag catalyst is thus developed, realizing 86% cyclohexanone oxime Faradaic efficiency at a current density of 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, far exceeding the reported performance.\u003c/p\u003e","manuscriptTitle":"Tuning NO coverage promotes ampere-level electrosynthesis of a nylon-6 precursor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-26 12:24:03","doi":"10.21203/rs.3.rs-4791713/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-synthesis","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"natsynth","sideBox":"Learn more about [Nature Synthesis](https://www.nature.com/natsynth/)","snPcode":"","submissionUrl":"https://mts-natsynth.nature.com/cgi-bin/main.plex","title":"Nature Synthesis","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"61108e61-e4a0-4b43-b680-e662781e90ff","owner":[],"postedDate":"February 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":44292677,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"},{"id":44292678,"name":"Physical sciences/Chemistry/Catalysis/Electrocatalysis"}],"tags":[],"updatedAt":"2025-08-08T07:06:57+00:00","versionOfRecord":{"articleIdentity":"rs-4791713","link":"https://doi.org/10.1038/s44160-025-00851-2","journal":{"identity":"nature-synthesis","isVorOnly":false,"title":"Nature Synthesis"},"publishedOn":"2025-08-07 04:00:00","publishedOnDateReadable":"August 7th, 2025"},"versionCreatedAt":"2025-02-26 12:24:03","video":"","vorDoi":"10.1038/s44160-025-00851-2","vorDoiUrl":"https://doi.org/10.1038/s44160-025-00851-2","workflowStages":[]},"version":"v1","identity":"rs-4791713","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4791713","identity":"rs-4791713","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}