Fluorine-induced d-band center shift of the Nb site boosts anodic formamide electrosynthesis

Fluorine-induced d-band center shift of the Nb site boosts anodic formamide electrosynthesis | 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 Fluorine-induced d-band center shift of the Nb site boosts anodic formamide electrosynthesis Fan Dong, Shiyong Mou, Siyuan Liu, Weidong Dai, Yanjuan Sun This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4079378/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Anodic oxidative amidation (EOA) strategies offer a sustainable and potentially promising route for amide synthesis. However, the efficiency and activity of catalysts under oxidative conditions are highly dependent on noble metals. Herein, we present our experimental findings and fundamental understanding that fluorine-doped Nb 2 O 5 nanosheet arrays on carbon fiber (F-Nb 2 O 5 /CP) serve as an efficient and robust non-noble catalyst for the electrochemical synthesis of formamide from ammonia and methanol under ambient conditions. In 0.5 M KHCO 3 solution, this catalyst achieved a high Faradaic efficiency of 52.0%, with an N selectivity of 79.1% at 1.5 V versus Hg/HgO electrode. The catalyst exhibited remarkable stability, maintaining its performance over 120 h. By integrating in-situ spectroscopy studies with density functional theory calculations, we revealed that fluorine doping induces a shift in the d-band center of the Nb site. This shift alters the adsorption behavior of OH - and * NH 2 intermediate on the F-Nb 2 O 5 (100) surface, thereby effectively lowering the C-N coupling energy barrier, and boosting the production of formamide. Physical sciences/Chemistry/Electrochemistry/Electrocatalysis Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials Physical sciences/Chemistry/Green chemistry/Sustainability Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Amide synthesis is crucial due to its extensive applications in biological systems, chemical feedstock, and the pharmaceutical industry. 1 , 2 , 3 , 4 Formamide, the simplest amide, serves as a versatile solvent and building block in chemical synthesis and industrial processes, garnering recent research interest. 4 , 5 The traditional reaction for Formamide synthesis often involves fossil-fuel-derived CO, formic acid, and NH 3 under harsh conditions. These synthesis processes require high temperatures and high pressures, resulting in huge energy consumption and CO 2 emissions, leading to environmental concerns. 6 , 7 Consequently, there is a pressing need for the development of sustainable and efficient methodologies for the synthesis of amide under milder conditions. In response to this, researchers investigated innovative electro-synthetic techniques capable of selectively producing amide products with high energy efficiency, leveraging abundant and renewable feedstocks. 8 , 9 , 10 , 11 , 12 The electrochemical synthesis of amide products can be approached in two ways. On one hand, it can be achieved through the cathodic reduction amination route. 8 , 9 , 10 On the other hand, anodic oxidative amidation (EOA) strategies present a potentially promising amide synthesis route. 13 , 14 , 15 , 16 , 17 These strategies offer an alternative to the slow kinetics of the anodic oxygen evolution reaction, a persistent challenge in the field. The exploration and optimization of EOA could pave the way for more efficient and sustainable amide synthesis processes from cost-effective and renewable carbon/nitrogen feedstocks, specifically, methanol and NH 3 . 14 , 16 , 17 , 18 , 19 However, EOA strategies face hurdles, including the durability and activity of catalysts under harsh oxidative conditions, and the dependence on noble metals hinders their practical application. Furthermore, in-situ electrochemical infrared and Raman spectroscopy often rely on noble metal catalysts for surface enhancement, potentially leading to discrepancies in catalyst performance evaluation. 20 , 21 As such, there is an urgent need to develop non-noble transition metal catalysts with enhanced activity and stability for EOA strategies, and the ability to enhance in-situ electrochemical spectroscopic signals for capturing key intermediates in mechanistic studies. Niobium pentoxide (Nb 2 O 5 ), a nontoxic and noteworthy transition metal oxide, is renowned for its unique Lewis and Brønsted acid sites, potent redox ability, and abundant adsorption sites. Its potential applications extend to gas sensors, catalysts, electrochemistry, lithium batteries, and photoelectrodes, which have garnered significant attention in the scientific community. 22 , 23 , 24 Furthermore, Nb 2 O 5 has shown promise as a non-noble material capable of achieving high sensitivity in surface-enhanced Raman scattering detection applications. 25 Importantly, doping of halide to adjust the electronic configuration has emerged as an effective method to enhance the efficiency and stability of electrocatalysts. Particularly, fluorine doping can effectively alter the electronic structure of active sites, thereby enhancing the durability of electro-oxidation. This stems from fluoride’s high electronegativity and low reactivity, which prevent it from easily dissociating from the catalyst surface, thus reducing the loss of active sites. 23 , 26 , 27 Recent studies have reported that halide salts can electrochemically increase the active sites of transition metal-based catalysts under alkaline conditions, they have also been identified as effective redox catalysts via paired electrolysis for C-N bond coupling reactions. 28 , 29 , 30 , 31 Consequently, fluorine-doped Nb 2 O 5 is expected to serve as an efficient and stable catalyst for the EOA process. Moreover, it shows promise as a substrate for in-situ electrochemical spectroscopy studies. In this work, we report our experimental and fundamental understanding that fluorine-doped orthorhombic Nb 2 O 5 nanosheet arrays on carbon fiber (F-Nb 2 O 5 /CP) act as an efficient electrocatalyst for the electrochemical formamide synthesis from ammonia and methanol. In 0.5 M KHCO 3 solution, this catalyst demonstrated a high Faradaic efficiency of 52.0%, with an N selectivity of 79.1% at 1.50 V versus a Hg/HgO electrode. This performance favorably aligns with the behaviors of most anodic amide electrocatalysts previously reported (Table S1 ). Key intermediates and products in the reaction process were accurately captured using a series of in-situ and ex-situ detection techniques. Density functional theory calculations reveal that fluorine doping shifts the d-band center of the Nb site, which consequently affects the adsorption behavior of OH − and * NH 2 intermediate on the F-Nb 2 O 5 (100) surface. As a result, it effectively reduces the C-N coupling energy barrier and boosts the production rate of formamide. Our study provides new perspectives into fluorine dopants’ role in boosting the activity and stability of Nb 2 O 5 and broadens its use as a non-noble semiconductor substrate for surface-enhanced Raman spectroscopy. Results and discussion Two forms of orthorhombic Nb 2 O 5 (T-Nb 2 O 5 ) were synthesized utilizing the previously reported method. 22 , 32 As shown in Fig. 1a, F-Nb 2 O 5 /CP was derived from the calcination of orthorhombic Nb 3 O 7 F precursor on carbon fiber under argon conditions. T-Nb 2 O 5 nanoparticles on carbon fiber (Nb 2 O 5 /CP) were synthesized using the same method without HF for comparison. X-ray diffraction spectroscopy (XRD) results (Fig. 1b) show that the diffraction peaks of F-Nb 2 O 5 can be indexed to the orthorhombic Nb 2 O 5 phase (PDF 00-030-0873). In comparison, the diffraction peaks of Nb 2 O 5 (Supplementary Fig. 1a) were indexed to the orthorhombic Nb 2 O 5 phase (PDF 00-027-1003). F-doping slightly shifted the diffraction peaks to lower angles, resulting in the expansion of the crystal lattice. The scanning electron microscopy (SEM) images indicate the well-maintained nanosheet morphologies of F-Nb 2 O 5 /CP (Fig. 1c, d) after heat treatment of the Nb 3 O 7 F/CP precursor (Supplementary Fig. 1e, f), with the length of rectangular sheets ranging from 400 to 900 nm and a thickness of around 50 nm. The rectangular sheet structure (Fig. 1e) was further confirmed by transmission electron microscopy (TEM). The high-resolution TEM image (Fig. 1f) shows two groups of lattice fringes with spacings of 0.395 nm and 0.365 nm, in good agreement with the spacings of the (001) and (080) planes of Nb 2 O 5 , respectively, indicating that these nanoflakes are mostly exposed with the (100) facet. 22 The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and Energy dispersive spectroscopy (EDS) elemental mapping results shown in Fig. 1g demonstrate the uniform distribution of Nb, O, and F elements. The orthorhombic phase and the doped F element of Nb 2 O 5 were further confirmed by Raman and X-ray photoelectron spectroscopy (XPS) analysis. Figure 2a depicts the Raman spectrum of F-Nb 2 O 5 with the typical Nb–F vibrational band at 132 cm − 1 . The bands at 230 cm − 1 , 304 cm − 1 , and 690 cm − 1 are attributed to the Nb − O bond stretching vibration, confirming the orthorhombic phase of Nb 2 O 5 with F doping. 22 , 23 , 33 The band at 994 cm − 1 was attributed to the peak of the short Nb-O bond, which could enhance the performance of methanol oxidation. 34 In contrast, Fig. 2b exhibits a relatively weak vibrational band at 126 cm − 1 , indicating the absence of F doping. The bands at 228 cm − 1 , 309 cm − 1 , and 689 cm − 1 also confirm the orthorhombic phase of Nb 2 O 5 . 35 , 36 , 37 The survey XPS spectrum for F-Nb 2 O 5 demonstrates that it is composed of F 1s, O 1s, Nb 3p, Nb 3d, and Nb 4p peaks, confirming the doping of the F element (Fig. 2c). The distinct F 1s peak shown in the high-resolution F 1s XPS spectrum (Fig. 2d) at a binding energy of 685.2 eV suggests that the F ion was substituted into the lattice of F-Nb 2 O 5 . The high-resolution XPS spectrum for O 1s, shown in Fig. 2e, can be fitted into characteristic peaks with binding energies at 530.0 and 532.4 eV. The peak at 530.0 eV is attributed to the Nb − O bond, while the 532.4 eV peak arises due to the existence of loosely bonded oxygen on the surface of Nb 2 O 5 . 22 , 32 , 32 , 38 In the high-resolution Nb 3d XPS spectrum (Fig. 2f), Nb atoms in Nb 3d 5/2 and Nb 3d 3/2 electronic configurations can be observed at 207.8 and 210.6 eV. Moreover, the two small binding energy peaks appearing around 206.5 and 209.2 eV are ascribed to the Nb–F bond. 22 , 33 XPS analysis of Nb 2 O 5 /CP were detailed in Supplementary Fig. 2, which notably demonstrates the absence of the fluorine element. The aforementioned results substantiate the successful fabrication of F-Nb 2 O 5 /CP, with the (100) facet exposed. We evaluated the electrocatalytic synthesis of formamide from the co-oxidation of methanol and NH 3 using a two-compartment cell separated by a Nafion117 membrane. The three-electrode system was composed of F-Nb 2 O 5 /CP or Nb 2 O 5 /CP as the working electrode, Hg/HgO as the reference electrode, and a Pt plate as the counter electrode. All potentials are reported versus the Hg/HgO scale unless otherwise noted. All subsequent tests were based on the optimized methanol-to-ammonia ratio, which is a molar ratio of 8:1 (Supplementary Fig. 3). The activity of electrocatalytic formamide synthesis was evaluated by linear sweep voltammetry (LSV) in 0.5 M KHCO 3 . As shown in Fig. 3a, the current density slightly increased in the presence of 20 mM methanol from the onset potential of 1.2 V, then decreased compared to the LSV curve of 0.5 M KHCO 3 . This suggests that electrochemical methanol oxidation and water oxidation are competitive reactions on the surface of F-Nb 2 O 5 /CP. Interestingly, the LSV curve exhibits a sharply increased current density and a low onset potential with the presence of 2.5 mM NH 3 and methanol in the electrolyte, indicating the co-oxidation behavior of methanol and NH 3 . Similar trends of competitive reactions, onset potential, and oxidation current density were observed with the Nb 2 O 5 /CP catalyst, as shown in Supplementary Fig. 4a. Based on the results above, a potential window ranging from 1.2 to 1.9 V was selected for the study of electrocatalytic formamide synthesis. The steady current densities observed in the chronoamperometry curves at different applied potentials (Supplementary Fig. 5) indicate the robust electrochemical oxidation stability of F-Nb 2 O 5 /CP during the electrocatalytic synthesis tests of formamide. High-performance liquid chromatography (HPLC) was used for qualitative and quantitative analysis of the electrochemically produced formamide (Supplementary Fig. 6a, b), which was further cross-verified by gas chromatography − mass spectrometry (GC − MS) and 1H-nuclear magnetic resonance ( 1 H NMR, Supplementary Fig. 7). UV − Vis and Ion Chromatography (IC) were employed for the detection of byproducts such as H 2 O 2 (Supplementary Fig. 6c, d), HCOO − , NO 2 − , and NO 3 − . The Faradaic efficiency, product distribution, and yield of formamide show a volcano-like trend (Fig. 3b) as the applied potential increases from 1.2 to 1.9 V. The FEformamide on F-Nb 2 O 5 /CP achieves 52.0%, with a yield of 252 µmol cm − 2 h − 1 at − 1.5 V. Meanwhile, the selectivity of N and C, calculated from the consumption of NH 3 and methanol (Supplementary Fig. 8), are 79.1% and 20.5% respectively. The FEformamide and yield on Nb 2 O 5 /CP achieve 25.6%, with a yield of 96 µmol cm − 2 h − 1 at − 1.6 V (Supplementary Fig. 4b). An isotope-labeled experiment was performed to validate the origin of the formamide products. Figure 4c displays the total ion chromatography (TIC) of formamide and 15 N-labeled formamide, where the N source was NH 3 and 15 NH 3 . Correspondingly, the mass spectra of 15 N-labeled formamide (m/z = 46) rise more sharply than that of the formamide, as depicted in Fig. 3d, thereby proving the N source of formamide. Moreover, no TIC signals from other organic compounds were observed, indicating that the product of the C–N coupling reaction is formamide on F-Nb 2 O 5 /CP. Control experiments were conducted to validate the reaction pathway. Initially, a significant increase in both the yield and Faraday efficiency (94%) of formamide was observed when formaldehyde was used as a substitute for the carbon source (Fig. 3e). This finding suggests that the aldehyde intermediate, derived from methanol, plays a pivotal role in the C-N coupling process. However, when NH 2 OH was substituted for the NH 3 feedstock, there was a marked reduction in both the yield and Faraday efficiency of formamide. This indicates that NH 2 OH may not act as a key intermediate in the reaction. Furthermore, in a 0.5 M NaOH solution, there is a noticeable decrease in both the Faraday efficiency and yield of formamide. This can be ascribed to the competitive reaction that involves nucleophilic reagents, namely, OH − and NH 3 derivatives, indicating that C-N coupling may proceed through a nucleophilic attack process. 13 The results of the long-term stability test are shown in Fig. 4f, where both the current density and FEformamide remain steady over 120 hours. The long-term stability of the F-Nb 2 O 5 /CP catalysts after the test, as confirmed by XPS (Supplementary Fig. 9), XRD, and SEM analyses (Supplementary Fig. 10), indicating the robust electrochemical oxidation stability for the anodic formamide synthesis. Studies have indicated that the adsorption of halogen ions is potential dependence, where reactions between these ions and adsorbed species produce oxidation-resistant compounds, even at high anodic potentials. 39 , 40 Fig. 3g displays that the FEformamide on Nb 2 O 5 /CP was effectively increasing when 10 mM of fluoride or chloride ions were added to the solution. Conversely, after the addition of 10 mM bromide or iodide ions to the solution, the FE formamide sharply decreases. Thus, it can be concluded that fluoride and chloride ions appear to facilitate the anodic amide synthesis process. To evaluate whether the performance of catalysis is influenced by the electrochemically active surface area (ECSA) of F-Nb 2 O 5 /CP and Nb 2 O 5 /CP, we conducted measurements of the double-layer capacitance (Cdl). Supplementary Fig. 11a and 11b display the cyclic voltammograms (CVs) of F-Nb 2 O 5 /CP and Nb 2 O 5 /CP at various scan rates (10–100 mV s – 1 ), respectively. As shown in Fig. 3h, the Cdl of F-Nb 2 O 5 /CP (3.9 mF cm – 2 ) is nearly equivalent to but marginally lower than that of Nb 2 O 5 /CP (4.3 mF cm – 2 ). This suggests that F-Nb 2 O 5 /CP possesses a slightly smaller ECSA. Furthermore, Nb 2 O 5 /CP exhibits lower charge transfer resistance in the Nyquist plots (Fig. 3i). Hence, it can be inferred that the contribution to the C-N bond formation activity is not derived from the ECSA or the catalyst's impedance. Instead, it primarily stems from the doping of fluorine. Given the fact that Nb 2 O 5 nanoparticles have been identified as a promising non-noble semiconductor for surface-enhanced Raman substrates, capturing the reaction intermediates using in-situ Raman spectroscopy on F-Nb 2 O 5 /CP is of interest. As displayed in Fig. 4a, the in-situ Raman spectra of F-Nb 2 O 5 /CP were captured under operando conditions at various operating potentials. As the applied potential escalated from the open circuit potential (OCP) to 1.9 V, significant peaks centered at 1336 cm − 1 and 1580 cm − 1 emerged on F-Nb 2 O 5 /CP. These peaks correspond to the stretching vibrations of the C–N and NH 2 , thereby affirming the presence of the * NH 2 intermediate and the formation of the C–N bond. 20 , 41 To further reveal the changes in reaction intermediates, we performed in-situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The in-situ IR spectra signals of F-Nb 2 O 5 /CP ranged from OCP to 1.9 V (Fig. 4b). The characteristic IR peaks of the amide were successfully traced as the potential changed. The spectral features in the wavenumber region of 2900–3400 cm − 1 are identified as ν(NH 2 ), corresponding to the amide A bands (typically found within the 3300–3500 cm − 1 range). Notably, the emergence of new bands at 1631, 1498, and 1238 cm − 1 can be observed. These bands can be respectively classified as the amide I band (generally within the 1600–1800 cm − 1 range), the amide II band (typically within the 1470–1570 cm − 1 range), and the amide III bands (usually found within 1250 to 1350 cm − 1 range)., which can be assigned to δ(NH 2 ), ν(C = O), and ν(C − N) of adsorbed formamide. 42 The key intermediate species of * CHO and * CH 2 O were successfully detected at 1366 and 1418 cm − 1 , respectively. This observation aligns with the electrocatalytic C–N bond coupling processes that lead to the production of formamide, achieved through the coupling of * CH 2 O/ * CHO with * NH 2 intermediates. To gain further insights into the electrocatalytic C–N bond coupling process, online differential electrochemical mass spectrometry (DEMS) was employed. Importantly, an experiment utilizing 15 N-labeled NH 3 was conducted to differentiate between the anodic formation of N 2 and CO during the reaction, given their identical mass-charge ratio of 28. As shown in Fig. 4c, the potential-dependent mass signals of m/z = 44, assigned to CO 2 , and m/z = 28, assigned to CO, were observed during the LSV scan. Interestingly, the intensities of the m/z = 29, m/z = 30, assigned to 15 N 2 , and m/z = 31 peaks are negligible in our test (Fig. 4d). This deviates from the DEMS test results reported in previous literature on formamide electrochemical synthesis, suggesting that our reaction may involve distinct reaction intermediates and pathways. The intensity of the m/z = 32 peak can be ascribed to the competitive oxygen evolution reaction. It is also noteworthy that the intensity of mass signals of m/z = 33 and m/z = 34, attributed to 15 NH 2 OH, is quite faint, implying that it may not be a key intermediate. The potential-dependent mass signals of m/z = 45 and m/z = 46 can be respectively attributed to the formation of formamide and 15 N-labeled formamide. From the results, we can deduce the following. Firstly, ammonia does not readily oxidize to nitrogen, nitrite, and nitrate on the surface of F-Nb 2 O 5 , indicating that * NH 2 , derived from the dehydrogenation of NH 3 , serves as the key intermediate. Secondly, the oxidation products of methanol primarily comprise CO and CO 2, with trace amounts of formic acid, suggesting the existence of an aldehyde intermediate. It can be postulated that the yield of in-situ aldehyde intermediates may be a limiting factor in the production rate of formamide. To extract a further level of insights into the formamide electro-synthetic pathways, DFT calculations, and AIMD calculations were implemented on F-Nb 2 O 5 (100) and Nb 2 O 5 (100) surfaces toward electro-formamide synthesis. The Gibbs free energy change during the C-N coupling reaction was meticulously analyzed. Figure 5a and 5b illustrate the first pathway for the electro-synthesis of formamide on F-Nb 2 O 5 (100) and Nb 2 O 5 (100), respectively. The corresponding atomic configurations are depicted in the Supplementary Figs. 13 and 14. A thermodynamically viable path was identified for the production of an aldehyde intermediate, following the sequence CH 3 OH * → CH 3 O * → CH 2 O * . The formation of CH 3 O * is an uphill process on both catalysts, but it is more favorable on F-Nb 2 O 5 (100) with an energy barrier of 0.12 eV. It is noteworthy that the formation of * NH 2 on F-Nb 2 O 5 (100) is a downhill process with an energy barrier of 0.12 eV. This is in stark contrast to the process on Nb 2 O 5 (100), which is an uphill process and has a significantly higher energy barrier of 1.01 eV. Initially, the C-N bond is formed via the nucleophilic attack of the * NH 2 intermediate on the * CH 2 O intermediate. Subsequently, the resulting * NH 2 CH 2 O intermediate undergoes a dehydrogenation step to produce formamide. A transition state search was conducted to further investigate the differences in electrocatalytic performance. The findings reveal that F-Nb 2 O 5 presents a lower kinetic barrier, with an energy of 0.29 eV. The formation of the C-N bond process and free energy change have been corroborated by the results of the restrictive molecular dynamics slow growth simulation (Supplementary Fig. 15a, b). In contrast, the C-N coupling barrier for Nb 2 O 5 is considerably high at 0.97 eV. The intermediate is more predisposed to dehydrogenate to * CHO, as opposed to C-N coupling. The * NH 2 tends to extract H from * CH 2 O, forming adsorbed * NH 3 , which exhibits a catalyst-like behavior. This could serve as one explanation for the high nitrogen selectivity and low carbon selectivity observed on the Nb 2 O 5 catalyst. Ultimately, the desorption barrier of formamide from the surface of the F-Nb 2 O 5 catalyst is 0.02 eV lower than that of the Nb 2 O 5 surface. Supplementary Fig. 12 a and b illustrate the second pathway, which involves the formation of a C-N bond via a nucleophilic attack between the * NH 2 and * CHO intermediates on F-Nb 2 O 5 (100) and Nb 2 O 5 (100). The corresponding atomic configurations are depicted in the Supplementary Figs. 16 and 17. F-Nb 2 O 5 (100) presents a lower barrier of 0.24 eV compared to the first pathway. However, * CHO tends to be preferentially oxidized to CO products, as identified by the slow growth simulation (refer to Supplementary Fig. 14c, and 14d), and the production of CO was confirmed by the DEMS results. In contrast, the barrier for * CHO and * NH 2 coupling on the Nb 2 O 5 surface is only 0.12 eV. This process, however, is hindered by the dehydrogenation step of * NH 3 , which has a significantly higher barrier of 1.01 eV. To ascertain whether the C-N coupling process pathway involves a nucleophilic attack, we performed an electrostatic potential (ESP) analysis of the * NH 2 + * CH 2 O process (Fig. 5c). The analysis revealed that * CH 2 O possesses an electrophilic carbon center, which subsequently undergoes a nucleophilic attack by the adjacent * NH 2 . Ultimately, the thermodynamically favorable reaction pathway on F-Nb 2 O 5 (100) was unveiled, as depicted in Scheme 1. This pathway involves the nucleophilic attack of the ammonia-derived * NH 2 on the methanol-derived * CH 2 O, followed by a dehydrogenation process to form formamide. To further investigate the contribution of F-doping to the C-N coupling process, we performed a computational analysis of the electronic structural properties at the Nb sites. Figure 5d displays the projected density of states (PDOS) of the d orbitals of the Nb sites, confirming a significant downshift in the band center of the F-doped Nb site, from 0.507 eV to -1.659 eV, which could significantly impact the electrochemical reaction performance. Given the significance of OH − adsorption under alkaline conditions, Fig. 5e presents the Crystal Orbital Hamilton Population (COHP) analysis results of the adsorbed OH − intermediate on the surfaces of F-Nb 2 O 5 (100) and Nb 2 O 5 (100). The findings suggest that OH − adsorption is more thermodynamically favorable on F-Nb 2 O 5 (100), primarily due to the contribution of single-electron adsorption. This is confirmed by differential charge density results (Supplementary Fig. 18), which show that the Nb site adjacent to the F element, exhibiting an electron-deficient state, is a significant contributor. As illustrated in Fig. 5f, the COHP results of the adsorbed * NH 2 intermediate suggest that the * NH 2 intermediate exhibits greater stability on the F-Nb 2 O 5 (100) surface, which is evidenced by the relationship between the adsorption energy and ICOHP data. The interaction between the pz orbital of the adsorbed * OH and * NH 2 intermediate, and the dz2 orbital of Nb, plays a significant role in the formation of the Nb-O and Nb-N bonds, respectively. This could be a crucial factor in understanding the adsorption strength on metal surfaces, particularly in the context of back-donation interactions. Interestingly, the COHP results of the adsorbed * CH 2 O (Supplementary Fig. 19) show that the Nb-O bond originates from the contribution of O 2p and Nb 5s. On the F-Nb 2 O 5 (100) surface, * CH 2 O shows stable and moderate adsorption energy, not affected by the downshift of the d-band center. These results are in accordance with the Sabatier principle, which states that an effective catalyst should demonstrate a moderate binding strength with the reactants. 43 , 44 Therefore, by elucidating the mechanism of fluorine doping in boosting C-N coupling, we can conclude that F-Nb 2 O 5 (100) is more favorable for the electrochemical anodic formamide synthesis. Conclusion In conclusion, our study demonstrates that F-doped orthorhombic Nb 2 O 5 nanosheet arrays on carbon fiber paper (F-Nb 2 O 5 /CP) serve as an effective and robust electrocatalyst for the electrochemical synthesis of formamide from ammonia and methanol. Achieving a high Faradaic efficiency of 52.0% and an N selectivity of 79.1% at 1.50 V vs. Hg/HgO electrode in a 0.5 M KHCO 3 solution. Our in-situ and ex-situ detection methodologies have effectively pinpointed key intermediates and products within the reaction process, thereby contributing to a fundamental comprehension of the reaction pathway. Fluorine doping not only enhances the electrochemical oxidation stability and activity for anodic formamide synthesis but also, as revealed by density functional theory calculations, induces a downshift in the d-band center of the Nb site, which consequently affects the adsorption behavior of OH − and * NH 2 intermediates on the F-Nb 2 O 5 (100) surface. As a result, it effectively reduces the C-N coupling energy barrier and boosts the production rate of formamide. Our work provides new perspectives on the role of fluorine dopants in enhancing the activity and stability of Nb 2 O 5 , and expanding its application scope when utilized as a non-noble semiconductor substrate for surface-enhanced Raman spectroscopy. Methods Materials Synthesis Synthesis of F-Nb 2 O 5 nanosheets on carbon nanofiber paper (F-Nb 2 O 5 /CP). In a typical synthesis, 0.15 g Nb powder, and 0.3 mL HF was added into 30 mL distilled water, and the mixture solution was transferred into a 50 mL Teflon-lined autoclave containing a 2×3 cm carbon nanofiber paper and kept in an oven at 180 ºC for 12 h. The obtained Nb 3 O 7 F nanosheets on carbon fiber paper (Nb 3 O 7 F/CP) precursor solid was washed thoroughly with deionized water and dried at 80 ºC overnight. The as-prepared Nb 3 O 7 F/CP precursor was annealed at 600 ºC for 1 h in air to obtain F-Nb 2 O 5 /CP. Synthesis of Nb 2 O 5 nanoparticles on carbon nanofiber paper (Nb 2 O 5 /CP) was synthesized by a hydrothermal method from niobium oxalate. In a typical synthesis, 0.8 g niobium oxalate was added into 30 mL distilled water, the mixture solution was transferred into a 50 mL Teflon-lined autoclave containing a 2×3 cm carbon fiber paper and kept in oven at 180 ºC for 12 h. Then precursor was annealed at 600 ºC for 1 h in air to obtain Nb 2 O 5 /CP. Materials Characterization XRD patterns were obtained from a Shimazu XRD-6100 diffractometer with Cu Kα radiation (40 kV, 30 mA) of wavelength 0.154 nm (Japan). Scanning electron microscopy (SEM, Gemini SEM 30), high-resolution transmission electron microscopy (HRTEM, Tecnai F30), X-ray photoelectron spectroscopy (XPS, ESCALAB250Xi), and Horiba XploRA PLUS Raman spectrometer were used to characterize the structure and composition of the catalysts. Electrochemical measurements Before tests, the Nafion proton exchange membrane was pretreated by heating in 3% H 2 O 2 solution, 0.5 M H 2 SO 4 and ultrapure water at 80°C for 1 h, respectively. Electrochemical measurements were performed on a CHI 760D electrochemical analyzer (CHI Instruments, Inc., Shanghai) in a standard three-electrode system using F-Nb 2 O 5 /CP or Nb 2 O 5 /CP as working electrode, Hg/HgO as reference electrode, and Pt foil as counter electrode. Polarization curves were obtained using LSV with a scan rate of 5 mV s – 1 . The long-term durability test was performed using chronopotentiometric measurements. Detection and quantification of possible products Detection and quantification of formamide were performed on Shimadzu HPLC with SPD-M40 photodiode array detector using 4.6 × 250 mm C18 Superb 5um column, 90:10 water-acetonitrile solution was used as the mobile phase. Further cross-verified of formamide was performed on an Agilent 7890 gas chromatograph system equipped with mass detectors, and a headspace autosampler (ColinTech), the separation was achieved using a DB-624 column (100% polyethylene glycol, 60 m long with a 0.25 mm i.d. and 1.0 µm film thickness), 1 H nuclear magnetic resonance (NMR) spectra were collected on a superconducting-magnet NMR spectrometer (BRUKER AscendTM 600 MHz) and dimethyl sulphoxide was used as an internal to calibrate the chemical shifts in the spectra. Detection and quantification of HCOO − , NO 2 − , and NO 3 − were performed on the Shimadzu ion chromatograph system with a CDD-10A VP conductivity detector. The H 2 O 2 concentration in the electrolyte was determined using a Shimadzu UV-2600 UV spectrophotometer by potassium titanium oxalate method with a maximum response at 400 nm. FE was determined using the following equation: FE = Amount of electrons required to form the products/Total amount of electrons supplied to the system×100% In-situ Raman tests For in-situ Raman experiments, in situ, Raman spectroscopy was conducted on a Horiba XploRA PLUS Raman spectrometer. The in-situ experiments were conducted with a custom-made electrochemical cell with Pt foil as the counter electrode and Hg/HgO as reference electrode. The excitation wavelength was 638 nm and a 50 × microscope objective with a numerical aperture of 0.55 was used. The spectra of the preconditioned electrode at each applied potential were collected for 60 seconds. In situ ATR SEIRAS A typical reactor of ATR-SEIRAS consists of two chambers with three electrodes. For the working electrode, 20 uL catalyst ink (5 mg mL − 1 ) was dropped onto the Si crystal, and dried in air before a test. Platinum sheet and Hg/HgO electrode were used as the counter and reference electrodes, respectively. 0.5 M KHCO 3 electrolyte were injected into anode and cathode chamber, respectively. An INVENIO R FT-IR (Bruker) spectrometer equipped with a liquid nitrogen cooled mercury cadmium telluride detector was used for the in-situ ATR-SEIRAS test and all spectra were given by the absorbance (-log(R⁄R 0 )). The spectral resolution was 4 cm − 1 and the scanning time was 0.5 min for each curve. The potential-dependent ATR-SEIRAS was carried out with the chronoamperometry test from 1.2 V to 1.9 V (vs.Hg/HgO). Online differential electrochemical mass spectrometry (DEMS) measurement Online DEMS was carried out to detect the volatile matters during the real-time electrolysis process (Shanghai Linglu Instrument & Equipment Co). The signal was collected through a hydrophobic polytetrafluoroethylene (PTFE) membrane. The electrolysis reaction occurred on one side of the PTFE membrane and the produced volatile matter was brought to the other side through a pump. The potential-dependent Online DEMS was carried out with the LSV test from 1.0 V to 1.9 V (vs.Hg/HgO) with a scan rate of 10 mV s − 1 .Sequentially, those matters were detected by mass spectrometry. Computational details The spin-polarized first-principles calculations based on the Density Functional Theory (DFT) were performed using the Vienna Ab initio Simulation Package (VASP). 45 , 46 , 47 The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional within the generalized gradient approximation (GGA) was employed to describe the exchange-correlation energy. 48 The projector-augmented-wave (PAW) method was adopted for the pseudopotentials. 49 The energy cutoff for the plane wave basis expansion was set to 500 eV. The force on each atom was set as 0.02 eV Å – 1 for the convergence criterion. The (100) surface of Nb 2 O 5 was used to investigate the anodic formamide electro-synthesis performance. The slab model was constructed in a four-layer 2×3 (100) surface, with a vacuum layer of 15 Å in the z direction to avoid the interaction between layers. The sampling in the Brillouin zone was set with 3×3×1 by the Monk Horst-Pack method. 50 The van der Waals interaction was considered by using the DFT-D3 method. The free energies of the anodic formamide electro-synthesis steps were calculated using the equation: △G=△E DFT +△E ZPE -T ΔS , where △E DFT is the DFT energy difference, the △E ZPE , and T ΔS are obtained by the zero-point energy correction and analysis of the variation of entropy, respectively. We conducted an ab initio molecular dynamics (AIMD) simulation at 300 K and constructed the corresponding free energy profiles. The simulation utilized a time step of 0.5 fs, with the convergence criteria for each electronic step set to 1×10 − 6 eV, using the gamma point of the Brillouin zone using a Nose-Hoover thermostat. The free energy profile for this reaction was obtained using the slow-growth method, employing a step size of 0.0005 Å. Crystal Orbital Hamilton Population (COHP) analysis was performed with the LOBSTER code. 51 Declarations Data availability The data that support the findings of this study are available within the article and its Supplementary Information files or from the corresponding author upon reasonable request. AUTHOR INFORMATION * Corresponding Author [email protected] , [email protected] (Fan Dong). Conflict of interest The authors declare that they have no conflict of interest. Acknowledgments This work was supported by the National Key R&D Project of China (Grant No. 2020YFA0710000), National Natural Science Foundation of China (Grant Nos. 22225606, 22276029). 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DFT-Calculated IR Spectrum Amide I, II, and III Band Contributions of N-Methylacetamide Fine Components. ACS Omega 5 , 8572-8578 (2020). Medford AJ, et al. From the Sabatier principle to a predictive theory of transition-metal heterogeneous catalysis. J. Catal. 328 , 36-42 (2015). Zhu X, Li Y. Insights into the Structure-Sensitive Catalytic Performance of Palladium–Copper Alloys in Electrochemical Urea Synthesis. ACS . Catal . 13 , 15322-15330 (2023). Kresse, Georg, and Jürgen Furthmüller. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6 ,15-50 (1996). Kozlov, Almudena Notario-Estévez Sergey M., Francesc Viñes, and Francesc Illas. Electronic-structure-based chemical descriptors:(in) dependence on self-interaction and Hartree-Fock exchange. Phy. Rev. B 54 .11169-11186 (1996). Kresse, Georg, and Jürgen Hafner. Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium. Phys. Rev. B 49 , 14251–14269 (1994). Perdew, John P., et al. Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B 46 , 6671–6687, (1992). Blöchl, Peter E. "Projector augmented-wave method. Phys. Rev. B 50 .17953–17979 (1994). Monkhorst, Hendrik J., and James D. Pack. Special points for Brillouin-zone integrations. Phys. Rev. B 13 . 5188–5192 (1976). Maintz, Stefan, et al. LOBSTER: A tool to extract chemical bonding from plane‐wave based DFT. J. Comput. Chem. 37 1030–1035 (2016). Schemes Scheme 1 is available in the Supplementary Files section Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.docx TableofContentsEntry.doc Scheme1.png Scheme 1 │ a Reaction pathway of formamide synthesis on F-Nb 2 O 5 catalysts. 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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-4079378","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":279569006,"identity":"e45aa26c-527d-4f3d-a612-0a05783618e7","order_by":0,"name":"Fan Dong","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAqklEQVRIiWNgGAWjYDCCwwcYmBkYbHj42RuI1XIsgbGZgSFNRrLnAGlaDtsY3HAgUgffMebnjwvbzvMw3GBg/PAxhwgtksfYDJtntt3mYZzdwCw5cxsRWgzu9zA28wK1MMscYGPmJUrLMR6QlnM8bBIJpGk5wMNDtBaQX2bPOJfMI8FzsJk4vwBD7MHngjI7e/vjzQc/fCRGCxJgbCBN/SgYBaNgFIwC3AAAwXg1IT3qq+YAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-2890-9964","institution":"University of Electronic Science and Technology of China","correspondingAuthor":true,"prefix":"","firstName":"Fan","middleName":"","lastName":"Dong","suffix":""},{"id":279569007,"identity":"b8b4a374-a5df-4027-a31f-70121db5411c","order_by":1,"name":"Shiyong Mou","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Shiyong","middleName":"","lastName":"Mou","suffix":""},{"id":279569008,"identity":"b355fcd6-e45b-4b95-b6e0-645547e1e4c6","order_by":2,"name":"Siyuan Liu","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Siyuan","middleName":"","lastName":"Liu","suffix":""},{"id":279569010,"identity":"b3ddab03-209d-4c26-bd20-be0a920944a7","order_by":3,"name":"Weidong Dai","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Weidong","middleName":"","lastName":"Dai","suffix":""},{"id":279569011,"identity":"4c576643-f70c-483d-8666-ddbfbb770fcd","order_by":4,"name":"Yanjuan Sun","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Yanjuan","middleName":"","lastName":"Sun","suffix":""}],"badges":[],"createdAt":"2024-03-12 02:40:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4079378/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4079378/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52882304,"identity":"64e4cabe-2a41-4a8e-a6fd-7e6f3e107964","added_by":"auto","created_at":"2024-03-18 09:39:43","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":539204,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Schematic illustration of the synthesis of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalysts. \u003cstrong\u003eb\u003c/strong\u003e XRD patterns of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. \u003cstrong\u003ec\u003c/strong\u003e and \u003cstrong\u003ed\u003c/strong\u003e SEM image of the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP. \u003cstrong\u003ee\u003c/strong\u003e TEM image, \u003cstrong\u003ef\u003c/strong\u003e HRTEM image, and \u003cstrong\u003eg\u003c/strong\u003e HAADF-STEM image and corresponding EDS elemental mapping of the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanosheets.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/f3fbf5586ee31794b177eac3.png"},{"id":52882291,"identity":"bdb2baaa-ce4a-4598-8818-1c46eace865d","added_by":"auto","created_at":"2024-03-18 09:39:39","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":239967,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Raman spectra of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalyst. \u003cstrong\u003eb\u003c/strong\u003e Raman spectra of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. \u003cstrong\u003ec\u003c/strong\u003e XPS Survey spectrum of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalysts. High-resolution XPS spectra of \u003cstrong\u003ed\u003c/strong\u003e F 1s and \u003cstrong\u003ee\u003c/strong\u003e O 1s and \u003cstrong\u003ef\u003c/strong\u003e Nb 3d of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalysts.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/1b6f5e3d3f3cb2375ea9abf9.png"},{"id":52882322,"identity":"5da58fe5-5f13-44cf-8130-94ddbe36b2a6","added_by":"auto","created_at":"2024-03-18 09:39:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":654958,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e LSV curves of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP in 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e solution, with methanol and NH\u003csub\u003e3\u003c/sub\u003e. \u003cstrong\u003eb\u003c/strong\u003e FEs of oxidation products on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP at different potentials. \u003cstrong\u003ec\u003c/strong\u003e The total ion chromatography (TIC) of \u003csup\u003e14\u003c/sup\u003eN formamide and \u003csup\u003e15\u003c/sup\u003eN labeled formamide. \u003cstrong\u003ed\u003c/strong\u003e Corresponding mass spectra of \u003csup\u003e14\u003c/sup\u003eN formamide and \u003csup\u003e15\u003c/sup\u003eN labeled formamide. \u003cstrong\u003ee\u003c/strong\u003e C, N source and electrolyte changed for formamide synthesis. \u003cstrong\u003ef\u003c/strong\u003e long-term electrolysis test on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP. \u003cstrong\u003eg\u003c/strong\u003e Halide effect on Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP for formamide synthesis. \u003cstrong\u003eh\u003c/strong\u003e The capacitive current densities as a function of scan rates for F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP. \u003cstrong\u003ei\u003c/strong\u003e Nyquist plots of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/f6bce5dc21370fe0571b25c8.png"},{"id":52882318,"identity":"d67725cc-e9b9-4a11-a058-ca75254dd248","added_by":"auto","created_at":"2024-03-18 09:39:45","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":452199,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Potential-dependent in-situ Raman spectra of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalyst for formamide synthesis. \u003cstrong\u003eb\u003c/strong\u003e Potential-dependent in situ FTIR-ATR spectra of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalyst for formamide synthesis. Real-time online DEMS for \u003cstrong\u003ec\u003c/strong\u003e CO\u003csub\u003e2\u003c/sub\u003e, CO products, and \u003cstrong\u003ed\u003c/strong\u003e for other intermediate.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/90aed7aa0a1b87ad2f289bfe.png"},{"id":52882306,"identity":"6e87b5fb-3d9a-4e00-b0e0-ba25edaa6ee8","added_by":"auto","created_at":"2024-03-18 09:39:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":622397,"visible":true,"origin":"","legend":"\u003cp\u003eGibbs free energy diagram of formamide synthesis path 1 on \u003cstrong\u003ea\u003c/strong\u003e F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface and \u003cstrong\u003eb\u003c/strong\u003e Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface. Gibbs free energy diagram of formamide synthesis path 2 on \u003cstrong\u003ec\u003c/strong\u003e The electrostatic potential (ESP) of \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e + \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO. \u003cstrong\u003ed\u003c/strong\u003e Analysis of projected density of states (pDOS) of Nb-d and corresponding d-band center for F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. \u003cstrong\u003ee\u003c/strong\u003e COHP analysis of \u003csup\u003e*\u003c/sup\u003eOH\u003csup\u003e-\u003c/sup\u003e on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface. \u003cstrong\u003ef\u003c/strong\u003e COHP analysis of \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/8db9b888566fb584333f1b21.png"},{"id":56573889,"identity":"84fa80f8-29cf-40c2-a36a-71bb638db6e2","added_by":"auto","created_at":"2024-05-16 03:53:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3282012,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/10bcd395-3adc-40d4-ad63-1f9be397cd7f.pdf"},{"id":52882305,"identity":"84a6a4f6-dec0-45d0-8008-1c68f20b93f3","added_by":"auto","created_at":"2024-03-18 09:39:43","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5657931,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/e9e8b065aea148d8fccbff65.docx"},{"id":52882310,"identity":"b6f309e5-2436-4503-94c3-9ad3bb72457d","added_by":"auto","created_at":"2024-03-18 09:39:45","extension":"doc","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":291840,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"TableofContentsEntry.doc","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/8b6fae7dd8cf3a2db5c6e1ae.doc"},{"id":52882303,"identity":"4c356cf9-9e6b-48fe-9d2a-5c7b28a90f46","added_by":"auto","created_at":"2024-03-18 09:39:43","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":163610,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e │ \u003cstrong\u003ea\u003c/strong\u003e Reaction pathway of formamide synthesis on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e catalysts.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-4079378/v1/93393cad5a6300f1f21457cf.png"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Fluorine-induced d-band center shift of the Nb site boosts anodic formamide electrosynthesis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAmide synthesis is crucial due to its extensive applications in biological systems, chemical feedstock, and the pharmaceutical industry.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Formamide, the simplest amide, serves as a versatile solvent and building block in chemical synthesis and industrial processes, garnering recent research interest.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e The traditional reaction for Formamide synthesis often involves fossil-fuel-derived CO, formic acid, and NH\u003csub\u003e3\u003c/sub\u003e under harsh conditions. These synthesis processes require high temperatures and high pressures, resulting in huge energy consumption and CO\u003csub\u003e2\u003c/sub\u003e emissions, leading to environmental concerns.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e Consequently, there is a pressing need for the development of sustainable and efficient methodologies for the synthesis of amide under milder conditions. In response to this, researchers investigated innovative electro-synthetic techniques capable of selectively producing amide products with high energy efficiency, leveraging abundant and renewable feedstocks.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eThe electrochemical synthesis of amide products can be approached in two ways. On one hand, it can be achieved through the cathodic reduction amination route.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e On the other hand, anodic oxidative amidation (EOA) strategies present a potentially promising amide synthesis route.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e These strategies offer an alternative to the slow kinetics of the anodic oxygen evolution reaction, a persistent challenge in the field. The exploration and optimization of EOA could pave the way for more efficient and sustainable amide synthesis processes from cost-effective and renewable carbon/nitrogen feedstocks, specifically, methanol and NH\u003csub\u003e3\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e However, EOA strategies face hurdles, including the durability and activity of catalysts under harsh oxidative conditions, and the dependence on noble metals hinders their practical application. Furthermore, in-situ electrochemical infrared and Raman spectroscopy often rely on noble metal catalysts for surface enhancement, potentially leading to discrepancies in catalyst performance evaluation.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e As such, there is an urgent need to develop non-noble transition metal catalysts with enhanced activity and stability for EOA strategies, and the ability to enhance in-situ electrochemical spectroscopic signals for capturing key intermediates in mechanistic studies.\u003c/p\u003e\u003cp\u003eNiobium pentoxide (Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e), a nontoxic and noteworthy transition metal oxide, is renowned for its unique Lewis and Brønsted acid sites, potent redox ability, and abundant adsorption sites. Its potential applications extend to gas sensors, catalysts, electrochemistry, lithium batteries, and photoelectrodes, which have garnered significant attention in the scientific community.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e Furthermore, Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e has shown promise as a non-noble material capable of achieving high sensitivity in surface-enhanced Raman scattering detection applications.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e Importantly, doping of halide to adjust the electronic configuration has emerged as an effective method to enhance the efficiency and stability of electrocatalysts. Particularly, fluorine doping can effectively alter the electronic structure of active sites, thereby enhancing the durability of electro-oxidation. This stems from fluoride’s high electronegativity and low reactivity, which prevent it from easily dissociating from the catalyst surface, thus reducing the loss of active sites.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e Recent studies have reported that halide salts can electrochemically increase the active sites of transition metal-based catalysts under alkaline conditions, they have also been identified as effective redox catalysts via paired electrolysis for C-N bond coupling reactions.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e Consequently, fluorine-doped Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e is expected to serve as an efficient and stable catalyst for the EOA process. Moreover, it shows promise as a substrate for in-situ electrochemical spectroscopy studies.\u003c/p\u003e\u003cp\u003eIn this work, we report our experimental and fundamental understanding that fluorine-doped orthorhombic Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanosheet arrays on carbon fiber (F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP) act as an efficient electrocatalyst for the electrochemical formamide synthesis from ammonia and methanol. In 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e solution, this catalyst demonstrated a high Faradaic efficiency of 52.0%, with an N selectivity of 79.1% at 1.50 V versus a Hg/HgO electrode. This performance favorably aligns with the behaviors of most anodic amide electrocatalysts previously reported (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Key intermediates and products in the reaction process were accurately captured using a series of in-situ and ex-situ detection techniques. Density functional theory calculations reveal that fluorine doping shifts the d-band center of the Nb site, which consequently affects the adsorption behavior of OH\u003csup\u003e−\u003c/sup\u003e and \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate on the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface. As a result, it effectively reduces the C-N coupling energy barrier and boosts the production rate of formamide. Our study provides new perspectives into fluorine dopants’ role in boosting the activity and stability of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and broadens its use as a non-noble semiconductor substrate for surface-enhanced Raman spectroscopy.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eTwo forms of orthorhombic Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (T-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e) were synthesized utilizing the previously reported method.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e As shown in Fig.\u0026nbsp;1a, F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP was derived from the calcination of orthorhombic Nb\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003eF precursor on carbon fiber under argon conditions. T-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanoparticles on carbon fiber (Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP) were synthesized using the same method without HF for comparison. X-ray diffraction spectroscopy (XRD) results (Fig.\u0026nbsp;1b) show that the diffraction peaks of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e can be indexed to the orthorhombic Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e phase (PDF 00-030-0873). In comparison, the diffraction peaks of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;1a) were indexed to the orthorhombic Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e phase (PDF 00-027-1003). F-doping slightly shifted the diffraction peaks to lower angles, resulting in the expansion of the crystal lattice. The scanning electron microscopy (SEM) images indicate the well-maintained nanosheet morphologies of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP (Fig.\u0026nbsp;1c, d) after heat treatment of the Nb\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003eF/CP precursor (Supplementary Fig.\u0026nbsp;1e, f), with the length of rectangular sheets ranging from 400 to 900 nm and a thickness of around 50 nm. The rectangular sheet structure (Fig.\u0026nbsp;1e) was further confirmed by transmission electron microscopy (TEM). The high-resolution TEM image (Fig.\u0026nbsp;1f) shows two groups of lattice fringes with spacings of 0.395 nm and 0.365 nm, in good agreement with the spacings of the (001) and (080) planes of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, respectively, indicating that these nanoflakes are mostly exposed with the (100) facet.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and Energy dispersive spectroscopy (EDS) elemental mapping results shown in Fig.\u0026nbsp;1g demonstrate the uniform distribution of Nb, O, and F elements.\u003c/p\u003e\u003cp\u003eThe orthorhombic phase and the doped F element of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e were further confirmed by Raman and X-ray photoelectron spectroscopy (XPS) analysis. Figure\u0026nbsp;2a depicts the Raman spectrum of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e with the typical Nb–F vibrational band at 132 cm\u003csup\u003e− 1\u003c/sup\u003e. The bands at 230 cm\u003csup\u003e− 1\u003c/sup\u003e, 304 cm\u003csup\u003e− 1\u003c/sup\u003e, and 690 cm\u003csup\u003e− 1\u003c/sup\u003e are attributed to the Nb − O bond stretching vibration, confirming the orthorhombic phase of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e with F doping.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e The band at 994 cm\u003csup\u003e− 1\u003c/sup\u003e was attributed to the peak of the short Nb-O bond, which could enhance the performance of methanol oxidation.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e In contrast, Fig.\u0026nbsp;2b exhibits a relatively weak vibrational band at 126 cm\u003csup\u003e− 1\u003c/sup\u003e, indicating the absence of F doping. The bands at 228 cm\u003csup\u003e− 1\u003c/sup\u003e, 309 cm\u003csup\u003e− 1\u003c/sup\u003e, and 689 cm\u003csup\u003e− 1\u003c/sup\u003e also confirm the orthorhombic phase of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e The survey XPS spectrum for F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e demonstrates that it is composed of F 1s, O 1s, Nb 3p, Nb 3d, and Nb 4p peaks, confirming the doping of the F element (Fig.\u0026nbsp;2c). The distinct F 1s peak shown in the high-resolution F 1s XPS spectrum (Fig.\u0026nbsp;2d) at a binding energy of 685.2 eV suggests that the F ion was substituted into the lattice of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. The high-resolution XPS spectrum for O 1s, shown in Fig.\u0026nbsp;2e, can be fitted into characteristic peaks with binding energies at 530.0 and 532.4 eV. The peak at 530.0 eV is attributed to the Nb − O bond, while the 532.4 eV peak arises due to the existence of loosely bonded oxygen on the surface of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e In the high-resolution Nb 3d XPS spectrum (Fig.\u0026nbsp;2f), Nb atoms in Nb 3d\u003csub\u003e5/2\u003c/sub\u003e and Nb 3d\u003csub\u003e3/2\u003c/sub\u003e electronic configurations can be observed at 207.8 and 210.6 eV. Moreover, the two small binding energy peaks appearing around 206.5 and 209.2 eV are ascribed to the Nb–F bond.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e XPS analysis of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP were detailed in Supplementary Fig.\u0026nbsp;2, which notably demonstrates the absence of the fluorine element. The aforementioned results substantiate the successful fabrication of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP, with the (100) facet exposed.\u003c/p\u003e\u003cp\u003eWe evaluated the electrocatalytic synthesis of formamide from the co-oxidation of methanol and NH\u003csub\u003e3\u003c/sub\u003e using a two-compartment cell separated by a Nafion117 membrane. The three-electrode system was composed of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP or Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP as the working electrode, Hg/HgO as the reference electrode, and a Pt plate as the counter electrode. All potentials are reported versus the Hg/HgO scale unless otherwise noted. All subsequent tests were based on the optimized methanol-to-ammonia ratio, which is a molar ratio of 8:1 (Supplementary Fig.\u0026nbsp;3). The activity of electrocatalytic formamide synthesis was evaluated by linear sweep voltammetry (LSV) in 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e. As shown in Fig.\u0026nbsp;3a, the current density slightly increased in the presence of 20 mM methanol from the onset potential of 1.2 V, then decreased compared to the LSV curve of 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e. This suggests that electrochemical methanol oxidation and water oxidation are competitive reactions on the surface of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP. Interestingly, the LSV curve exhibits a sharply increased current density and a low onset potential with the presence of 2.5 mM NH\u003csub\u003e3\u003c/sub\u003e and methanol in the electrolyte, indicating the co-oxidation behavior of methanol and NH\u003csub\u003e3\u003c/sub\u003e. Similar trends of competitive reactions, onset potential, and oxidation current density were observed with the Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalyst, as shown in Supplementary Fig.\u0026nbsp;4a. Based on the results above, a potential window ranging from 1.2 to 1.9 V was selected for the study of electrocatalytic formamide synthesis. The steady current densities observed in the chronoamperometry curves at different applied potentials (Supplementary Fig.\u0026nbsp;5) indicate the robust electrochemical oxidation stability of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP during the electrocatalytic synthesis tests of formamide.\u003c/p\u003e\u003cp\u003eHigh-performance liquid chromatography (HPLC) was used for qualitative and quantitative analysis of the electrochemically produced formamide (Supplementary Fig.\u0026nbsp;6a, b), which was further cross-verified by gas chromatography − mass spectrometry (GC − MS) and 1H-nuclear magnetic resonance (\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR, Supplementary Fig.\u0026nbsp;7). UV − Vis and Ion Chromatography (IC) were employed for the detection of byproducts such as H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;6c, d), HCOO\u003csup\u003e−\u003c/sup\u003e, NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e, and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e. The Faradaic efficiency, product distribution, and yield of formamide show a volcano-like trend (Fig.\u0026nbsp;3b) as the applied potential increases from 1.2 to 1.9 V. The FEformamide on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP achieves 52.0%, with a yield of 252 µmol cm\u003csup\u003e− 2\u003c/sup\u003e h\u003csup\u003e− 1\u003c/sup\u003e at − 1.5 V. Meanwhile, the selectivity of N and C, calculated from the consumption of NH\u003csub\u003e3\u003c/sub\u003e and methanol (Supplementary Fig.\u0026nbsp;8), are 79.1% and 20.5% respectively. The FEformamide and yield on Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP achieve 25.6%, with a yield of 96 µmol cm\u003csup\u003e− 2\u003c/sup\u003e h\u003csup\u003e− 1\u003c/sup\u003e at − 1.6 V (Supplementary Fig.\u0026nbsp;4b). An isotope-labeled experiment was performed to validate the origin of the formamide products. Figure\u0026nbsp;4c displays the total ion chromatography (TIC) of formamide and \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-labeled formamide, where the N source was NH\u003csub\u003e3\u003c/sub\u003e and \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eNH\u003csub\u003e3\u003c/sub\u003e. Correspondingly, the mass spectra of \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-labeled formamide (m/z = 46) rise more sharply than that of the formamide, as depicted in Fig.\u0026nbsp;3d, thereby proving the N source of formamide. Moreover, no TIC signals from other organic compounds were observed, indicating that the product of the C–N coupling reaction is formamide on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP. Control experiments were conducted to validate the reaction pathway. Initially, a significant increase in both the yield and Faraday efficiency (94%) of formamide was observed when formaldehyde was used as a substitute for the carbon source (Fig.\u0026nbsp;3e). This finding suggests that the aldehyde intermediate, derived from methanol, plays a pivotal role in the C-N coupling process. However, when NH\u003csub\u003e2\u003c/sub\u003eOH was substituted for the NH\u003csub\u003e3\u003c/sub\u003e feedstock, there was a marked reduction in both the yield and Faraday efficiency of formamide. This indicates that NH\u003csub\u003e2\u003c/sub\u003eOH may not act as a key intermediate in the reaction. Furthermore, in a 0.5 M NaOH solution, there is a noticeable decrease in both the Faraday efficiency and yield of formamide. This can be ascribed to the competitive reaction that involves nucleophilic reagents, namely, OH\u003csup\u003e−\u003c/sup\u003e and NH\u003csub\u003e3\u003c/sub\u003e derivatives, indicating that C-N coupling may proceed through a nucleophilic attack process. \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e The results of the long-term stability test are shown in Fig.\u0026nbsp;4f, where both the current density and FEformamide remain steady over 120 hours. The long-term stability of the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP catalysts after the test, as confirmed by XPS (Supplementary Fig.\u0026nbsp;9), XRD, and SEM analyses (Supplementary Fig.\u0026nbsp;10), indicating the robust electrochemical oxidation stability for the anodic formamide synthesis.\u003c/p\u003e\u003cp\u003eStudies have indicated that the adsorption of halogen ions is potential dependence, where reactions between these ions and adsorbed species produce oxidation-resistant compounds, even at high anodic potentials.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e Fig.\u0026nbsp;3g displays that the FEformamide on Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP was effectively increasing when 10 mM of fluoride or chloride ions were added to the solution. Conversely, after the addition of 10 mM bromide or iodide ions to the solution, the FE\u003csub\u003eformamide\u003c/sub\u003e sharply decreases. Thus, it can be concluded that fluoride and chloride ions appear to facilitate the anodic amide synthesis process. To evaluate whether the performance of catalysis is influenced by the electrochemically active surface area (ECSA) of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP, we conducted measurements of the double-layer capacitance (Cdl). Supplementary Fig.\u0026nbsp;11a and 11b display the cyclic voltammograms (CVs) of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP at various scan rates (10–100 mV s\u003csup\u003e–\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e), respectively. As shown in Fig.\u0026nbsp;3h, the Cdl of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP (3.9 mF cm\u003csup\u003e–\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) is nearly equivalent to but marginally lower than that of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP (4.3 mF cm\u003csup\u003e–\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e). This suggests that F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP possesses a slightly smaller ECSA. Furthermore, Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP exhibits lower charge transfer resistance in the Nyquist plots (Fig.\u0026nbsp;3i). Hence, it can be inferred that the contribution to the C-N bond formation activity is not derived from the ECSA or the catalyst's impedance. Instead, it primarily stems from the doping of fluorine.\u003c/p\u003e\u003cp\u003eGiven the fact that Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanoparticles have been identified as a promising non-noble semiconductor for surface-enhanced Raman substrates, capturing the reaction intermediates using in-situ Raman spectroscopy on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP is of interest. As displayed in Fig.\u0026nbsp;4a, the in-situ Raman spectra of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP were captured under operando conditions at various operating potentials. As the applied potential escalated from the open circuit potential (OCP) to 1.9 V, significant peaks centered at 1336 cm\u003csup\u003e− 1\u003c/sup\u003e and 1580 cm\u003csup\u003e− 1\u003c/sup\u003e emerged on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP. These peaks correspond to the stretching vibrations of the C–N and NH\u003csub\u003e2\u003c/sub\u003e, thereby affirming the presence of the \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate and the formation of the C–N bond.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e To further reveal the changes in reaction intermediates, we performed in-situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The in-situ IR spectra signals of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP ranged from OCP to 1.9 V (Fig.\u0026nbsp;4b). The characteristic IR peaks of the amide were successfully traced as the potential changed. The spectral features in the wavenumber region of 2900–3400 cm\u003csup\u003e− 1\u003c/sup\u003e are identified as ν(NH\u003csub\u003e2\u003c/sub\u003e), corresponding to the amide A bands (typically found within the 3300–3500 cm\u003csup\u003e− 1\u003c/sup\u003e range). Notably, the emergence of new bands at 1631, 1498, and 1238 cm\u003csup\u003e− 1\u003c/sup\u003e can be observed. These bands can be respectively classified as the amide I band (generally within the 1600–1800 cm\u003csup\u003e− 1\u003c/sup\u003e range), the amide II band (typically within the 1470–1570 cm\u003csup\u003e− 1\u003c/sup\u003e range), and the amide III bands (usually found within 1250 to 1350 cm\u003csup\u003e− 1\u003c/sup\u003e range)., which can be assigned to δ(NH\u003csub\u003e2\u003c/sub\u003e), ν(C = O), and ν(C − N) of adsorbed formamide.\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e The key intermediate species of \u003csup\u003e*\u003c/sup\u003eCHO and \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO were successfully detected at 1366 and 1418 cm\u003csup\u003e− 1\u003c/sup\u003e, respectively. This observation aligns with the electrocatalytic C–N bond coupling processes that lead to the production of formamide, achieved through the coupling of \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO/\u003csup\u003e*\u003c/sup\u003eCHO with \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediates.\u003c/p\u003e\u003cp\u003eTo gain further insights into the electrocatalytic C–N bond coupling process, online differential electrochemical mass spectrometry (DEMS) was employed. Importantly, an experiment utilizing \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-labeled NH\u003csub\u003e3\u003c/sub\u003e was conducted to differentiate between the anodic formation of N\u003csub\u003e2\u003c/sub\u003e and CO during the reaction, given their identical mass-charge ratio of 28. As shown in Fig.\u0026nbsp;4c, the potential-dependent mass signals of m/z = 44, assigned to CO\u003csub\u003e2\u003c/sub\u003e, and m/z = 28, assigned to CO, were observed during the LSV scan. Interestingly, the intensities of the m/z = 29, m/z = 30, assigned to \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN\u003csub\u003e2\u003c/sub\u003e, and m/z = 31 peaks are negligible in our test (Fig.\u0026nbsp;4d). This deviates from the DEMS test results reported in previous literature on formamide electrochemical synthesis, suggesting that our reaction may involve distinct reaction intermediates and pathways. The intensity of the m/z = 32 peak can be ascribed to the competitive oxygen evolution reaction. It is also noteworthy that the intensity of mass signals of m/z = 33 and m/z = 34, attributed to \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003eOH, is quite faint, implying that it may not be a key intermediate. The potential-dependent mass signals of m/z = 45 and m/z = 46 can be respectively attributed to the formation of formamide and \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eN-labeled formamide. From the results, we can deduce the following. Firstly, ammonia does not readily oxidize to nitrogen, nitrite, and nitrate on the surface of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, indicating that \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e, derived from the dehydrogenation of NH\u003csub\u003e3\u003c/sub\u003e, serves as the key intermediate. Secondly, the oxidation products of methanol primarily comprise CO and CO\u003csub\u003e2,\u003c/sub\u003e with trace amounts of formic acid, suggesting the existence of an aldehyde intermediate. It can be postulated that the yield of in-situ aldehyde intermediates may be a limiting factor in the production rate of formamide.\u003c/p\u003e\u003cp\u003eTo extract a further level of insights into the formamide electro-synthetic pathways, DFT calculations, and AIMD calculations were implemented on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surfaces toward electro-formamide synthesis. The Gibbs free energy change during the C-N coupling reaction was meticulously analyzed. Figure\u0026nbsp;5a and 5b illustrate the first pathway for the electro-synthesis of formamide on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100), respectively. The corresponding atomic configurations are depicted in the Supplementary Figs.\u0026nbsp;13 and 14. A thermodynamically viable path was identified for the production of an aldehyde intermediate, following the sequence CH\u003csub\u003e3\u003c/sub\u003eOH\u003csup\u003e*\u003c/sup\u003e → CH\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e*\u003c/sup\u003e → CH\u003csub\u003e2\u003c/sub\u003eO\u003csup\u003e*\u003c/sup\u003e. The formation of CH\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e*\u003c/sup\u003e is an uphill process on both catalysts, but it is more favorable on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) with an energy barrier of 0.12 eV. It is noteworthy that the formation of \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) is a downhill process with an energy barrier of 0.12 eV. This is in stark contrast to the process on Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100), which is an uphill process and has a significantly higher energy barrier of 1.01 eV. Initially, the C-N bond is formed via the nucleophilic attack of the \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate on the \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO intermediate. Subsequently, the resulting \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003eCH\u003csub\u003e2\u003c/sub\u003eO intermediate undergoes a dehydrogenation step to produce formamide. A transition state search was conducted to further investigate the differences in electrocatalytic performance. The findings reveal that F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e presents a lower kinetic barrier, with an energy of 0.29 eV. The formation of the C-N bond process and free energy change have been corroborated by the results of the restrictive molecular dynamics slow growth simulation (Supplementary Fig.\u0026nbsp;15a, b). In contrast, the C-N coupling barrier for Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e is considerably high at 0.97 eV. The intermediate is more predisposed to dehydrogenate to \u003csup\u003e*\u003c/sup\u003eCHO, as opposed to C-N coupling. The \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e tends to extract H from \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO, forming adsorbed \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e3\u003c/sub\u003e, which exhibits a catalyst-like behavior. This could serve as one explanation for the high nitrogen selectivity and low carbon selectivity observed on the Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e catalyst. Ultimately, the desorption barrier of formamide from the surface of the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e catalyst is 0.02 eV lower than that of the Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e surface.\u003c/p\u003e\u003cp\u003eSupplementary Fig.\u0026nbsp;12 a and b illustrate the second pathway, which involves the formation of a C-N bond via a nucleophilic attack between the \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e and \u003csup\u003e*\u003c/sup\u003eCHO intermediates on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100). The corresponding atomic configurations are depicted in the Supplementary Figs.\u0026nbsp;16 and 17. F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) presents a lower barrier of 0.24 eV compared to the first pathway. However, \u003csup\u003e*\u003c/sup\u003eCHO tends to be preferentially oxidized to CO products, as identified by the slow growth simulation (refer to Supplementary Fig.\u0026nbsp;14c, and 14d), and the production of CO was confirmed by the DEMS results. In contrast, the barrier for \u003csup\u003e*\u003c/sup\u003eCHO and \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e coupling on the Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e surface is only 0.12 eV. This process, however, is hindered by the dehydrogenation step of \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e3\u003c/sub\u003e, which has a significantly higher barrier of 1.01 eV. To ascertain whether the C-N coupling process pathway involves a nucleophilic attack, we performed an electrostatic potential (ESP) analysis of the \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e + \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO process (Fig.\u0026nbsp;5c). The analysis revealed that \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO possesses an electrophilic carbon center, which subsequently undergoes a nucleophilic attack by the adjacent \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e. Ultimately, the thermodynamically favorable reaction pathway on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) was unveiled, as depicted in Scheme 1. This pathway involves the nucleophilic attack of the ammonia-derived \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e on the methanol-derived \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO, followed by a dehydrogenation process to form formamide.\u003c/p\u003e\u003cp\u003eTo further investigate the contribution of F-doping to the C-N coupling process, we performed a computational analysis of the electronic structural properties at the Nb sites. Figure\u0026nbsp;5d displays the projected density of states (PDOS) of the d orbitals of the Nb sites, confirming a significant downshift in the band center of the F-doped Nb site, from 0.507 eV to -1.659 eV, which could significantly impact the electrochemical reaction performance. Given the significance of OH\u003csup\u003e−\u003c/sup\u003e adsorption under alkaline conditions, Fig.\u0026nbsp;5e presents the Crystal Orbital Hamilton Population (COHP) analysis results of the adsorbed OH\u003csup\u003e−\u003c/sup\u003e intermediate on the surfaces of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) and Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100). The findings suggest that OH\u003csup\u003e−\u003c/sup\u003e adsorption is more thermodynamically favorable on F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100), primarily due to the contribution of single-electron adsorption. This is confirmed by differential charge density results (Supplementary Fig.\u0026nbsp;18), which show that the Nb site adjacent to the F element, exhibiting an electron-deficient state, is a significant contributor. As illustrated in Fig.\u0026nbsp;5f, the COHP results of the adsorbed \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate suggest that the \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate exhibits greater stability on the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface, which is evidenced by the relationship between the adsorption energy and ICOHP data. The interaction between the pz orbital of the adsorbed \u003csup\u003e*\u003c/sup\u003eOH and \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate, and the dz2 orbital of Nb, plays a significant role in the formation of the Nb-O and Nb-N bonds, respectively. This could be a crucial factor in understanding the adsorption strength on metal surfaces, particularly in the context of back-donation interactions. Interestingly, the COHP results of the adsorbed \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO (Supplementary Fig.\u0026nbsp;19) show that the Nb-O bond originates from the contribution of O 2p and Nb 5s. On the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface, \u003csup\u003e*\u003c/sup\u003eCH\u003csub\u003e2\u003c/sub\u003eO shows stable and moderate adsorption energy, not affected by the downshift of the d-band center. These results are in accordance with the Sabatier principle, which states that an effective catalyst should demonstrate a moderate binding strength with the reactants.\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e Therefore, by elucidating the mechanism of fluorine doping in boosting C-N coupling, we can conclude that F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) is more favorable for the electrochemical anodic formamide synthesis.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, our study demonstrates that F-doped orthorhombic Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanosheet arrays on carbon fiber paper (F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP) serve as an effective and robust electrocatalyst for the electrochemical synthesis of formamide from ammonia and methanol. Achieving a high Faradaic efficiency of 52.0% and an N selectivity of 79.1% at 1.50 V vs. Hg/HgO electrode in a 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e solution. Our in-situ and ex-situ detection methodologies have effectively pinpointed key intermediates and products within the reaction process, thereby contributing to a fundamental comprehension of the reaction pathway. Fluorine doping not only enhances the electrochemical oxidation stability and activity for anodic formamide synthesis but also, as revealed by density functional theory calculations, induces a downshift in the d-band center of the Nb site, which consequently affects the adsorption behavior of OH\u003csup\u003e−\u003c/sup\u003e and \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediates on the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface. As a result, it effectively reduces the C-N coupling energy barrier and boosts the production rate of formamide. Our work provides new perspectives on the role of fluorine dopants in enhancing the activity and stability of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, and expanding its application scope when utilized as a non-noble semiconductor substrate for surface-enhanced Raman spectroscopy.\u003c/p\u003e"},{"header":"Methods","content":"\n\u003ch3\u003eMaterials Synthesis\u003c/h3\u003e\n\u003cp\u003eSynthesis of F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanosheets on carbon nanofiber paper (F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP). In a typical synthesis, 0.15 g Nb powder, and 0.3 mL HF was added into 30 mL distilled water, and the mixture solution was transferred into a 50 mL Teflon-lined autoclave containing a 2\u0026times;3 cm carbon nanofiber paper and kept in an oven at 180 \u0026ordm;C for 12 h. The obtained Nb\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003eF nanosheets on carbon fiber paper (Nb\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003eF/CP) precursor solid was washed thoroughly with deionized water and dried at 80 \u0026ordm;C overnight. The as-prepared Nb\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003eF/CP precursor was annealed at 600 \u0026ordm;C for 1 h in air to obtain F-Nb\u003csub\u003e2\u003c/sub\u003e O \u003csub\u003e5\u003c/sub\u003e/CP.\u003c/p\u003e \u003cp\u003eSynthesis of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanoparticles on carbon nanofiber paper (Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP) was synthesized by a hydrothermal method from niobium oxalate. In a typical synthesis, 0.8 g niobium oxalate was added into 30 mL distilled water, the mixture solution was transferred into a 50 mL Teflon-lined autoclave containing a 2\u0026times;3 cm carbon fiber paper and kept in oven at 180 \u0026ordm;C for 12 h. Then precursor was annealed at 600 \u0026ordm;C for 1 h in air to obtain Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP.\u003c/p\u003e\n\u003ch3\u003eMaterials Characterization\u003c/h3\u003e\n\u003cp\u003eXRD patterns were obtained from a Shimazu XRD-6100 diffractometer with Cu Kα radiation (40 kV, 30 mA) of wavelength 0.154 nm (Japan). Scanning electron microscopy (SEM, Gemini SEM 30), high-resolution transmission electron microscopy (HRTEM, Tecnai F30), X-ray photoelectron spectroscopy (XPS, ESCALAB250Xi), and Horiba XploRA PLUS Raman spectrometer were used to characterize the structure and composition of the catalysts.\u003c/p\u003e\n\u003ch3\u003eElectrochemical measurements\u003c/h3\u003e\n\u003cp\u003eBefore tests, the Nafion proton exchange membrane was pretreated by heating in 3% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e solution, 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and ultrapure water at 80\u0026deg;C for 1 h, respectively. Electrochemical measurements were performed on a CHI 760D electrochemical analyzer (CHI Instruments, Inc., Shanghai) in a standard three-electrode system using F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP or Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP as working electrode, Hg/HgO as reference electrode, and Pt foil as counter electrode. Polarization curves were obtained using LSV with a scan rate of 5 mV s\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The long-term durability test was performed using chronopotentiometric measurements.\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eDetection and quantification of possible products\u003c/h2\u003e \u003cp\u003eDetection and quantification of formamide were performed on Shimadzu HPLC with SPD-M40 photodiode array detector using 4.6 \u0026times; 250 mm C18 Superb 5um column, 90:10 water-acetonitrile solution was used as the mobile phase. Further cross-verified of formamide was performed on an Agilent 7890 gas chromatograph system equipped with mass detectors, and a headspace autosampler (ColinTech), the separation was achieved using a DB-624 column (100% polyethylene glycol, 60 m long with a 0.25 mm i.d. and 1.0 \u0026micro;m film thickness),\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH nuclear magnetic resonance (NMR) spectra were collected on a superconducting-magnet NMR spectrometer (BRUKER AscendTM 600 MHz) and dimethyl sulphoxide was used as an internal to calibrate the chemical shifts in the spectra. Detection and quantification of HCOO\u003csup\u003e\u0026minus;\u003c/sup\u003e, NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e were performed on the Shimadzu ion chromatograph system with a CDD-10A VP conductivity detector. The H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration in the electrolyte was determined using a Shimadzu UV-2600 UV spectrophotometer by potassium titanium oxalate method with a maximum response at 400 nm.\u003c/p\u003e \u003cp\u003eFE was determined using the following equation:\u003c/p\u003e \u003cp\u003eFE\u0026thinsp;=\u0026thinsp;Amount of electrons required to form the products/Total amount of electrons supplied to the system\u0026times;100%\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eIn-situ Raman tests\u003c/h2\u003e \u003cp\u003eFor in-situ Raman experiments, in situ, Raman spectroscopy was conducted on a Horiba XploRA PLUS Raman spectrometer. The in-situ experiments were conducted with a custom-made electrochemical cell with Pt foil as the counter electrode and Hg/HgO as reference electrode. The excitation wavelength was 638 nm and a 50 \u0026times; microscope objective with a numerical aperture of 0.55 was used. The spectra of the preconditioned electrode at each applied potential were collected for 60 seconds.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eIn situ ATR SEIRAS\u003c/h3\u003e\n\u003cp\u003eA typical reactor of ATR-SEIRAS consists of two chambers with three electrodes. For the working electrode, 20 uL catalyst ink (5 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was dropped onto the Si crystal, and dried in air before a test. Platinum sheet and Hg/HgO electrode were used as the counter and reference electrodes, respectively. 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e electrolyte were injected into anode and cathode chamber, respectively. An INVENIO R FT-IR (Bruker) spectrometer equipped with a liquid nitrogen cooled mercury cadmium telluride detector was used for the in-situ ATR-SEIRAS test and all spectra were given by the absorbance (-log(R\u0026frasl;R\u003csub\u003e0\u003c/sub\u003e)). The spectral resolution was 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the scanning time was 0.5 min for each curve. The potential-dependent ATR-SEIRAS was carried out with the chronoamperometry test from 1.2 V to 1.9 V (vs.Hg/HgO).\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eOnline differential electrochemical mass spectrometry (DEMS) measurement\u003c/h2\u003e \u003cp\u003eOnline DEMS was carried out to detect the volatile matters during the real-time electrolysis process (Shanghai Linglu Instrument \u0026amp; Equipment Co). The signal was collected through a hydrophobic polytetrafluoroethylene (PTFE) membrane. The electrolysis reaction occurred on one side of the PTFE membrane and the produced volatile matter was brought to the other side through a pump. The potential-dependent Online DEMS was carried out with the LSV test from 1.0 V to 1.9 V (vs.Hg/HgO) with a scan rate of 10 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.Sequentially, those matters were detected by mass spectrometry.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eComputational details\u003c/h2\u003e \u003cp\u003eThe spin-polarized first-principles calculations based on the Density Functional Theory (DFT) were performed using the Vienna Ab initio Simulation Package (VASP).\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional within the generalized gradient approximation (GGA) was employed to describe the exchange-correlation energy.\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e The projector-augmented-wave (PAW) method was adopted for the pseudopotentials.\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e The energy cutoff for the plane wave basis expansion was set to 500 eV. The force on each atom was set as 0.02 eV \u0026Aring;\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e for the convergence criterion. The (100) surface of Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e was used to investigate the anodic formamide electro-synthesis performance. The slab model was constructed in a four-layer 2\u0026times;3 (100) surface, with a vacuum layer of 15 \u0026Aring; in the z direction to avoid the interaction between layers. The sampling in the Brillouin zone was set with 3\u0026times;3\u0026times;1 by the Monk Horst-Pack method.\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e The van der Waals interaction was considered by using the DFT-D3 method. The free energies of the anodic formamide electro-synthesis steps were calculated using the equation: △G=△E\u003csub\u003eDFT\u003c/sub\u003e+△E\u003csub\u003eZPE\u003c/sub\u003e-T\u003csub\u003eΔS\u003c/sub\u003e, where △E\u003csub\u003eDFT\u003c/sub\u003e is the DFT energy difference, the △E\u003csub\u003eZPE\u003c/sub\u003e, and T\u003csub\u003eΔS\u003c/sub\u003e are obtained by the zero-point energy correction and analysis of the variation of entropy, respectively. We conducted an ab initio molecular dynamics (AIMD) simulation at 300 K and constructed the corresponding free energy profiles. The simulation utilized a time step of 0.5 fs, with the convergence criteria for each electronic step set to 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e eV, using the gamma point of the Brillouin zone using a Nose-Hoover thermostat. The free energy profile for this reaction was obtained using the slow-growth method, employing a step size of 0.0005 \u0026Aring;. Crystal Orbital Hamilton Population (COHP) analysis was performed with the LOBSTER code.\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available within the article and its Supplementary Information files or from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAUTHOR INFORMATION\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003csup\u003e*\u003c/sup\u003e\u003c/strong\u003e\u003cstrong\u003eCorresponding Author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\[email protected], [email protected] (Fan Dong).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Key R\u0026amp;D Project of China (Grant No. 2020YFA0710000), National Natural Science Foundation of China (Grant Nos. 22225606, 22276029).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003ePattabiraman VR, Bode JW. 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Chem.\u003c/em\u003e \u003cstrong\u003e37\u003c/strong\u003e 1030\u0026ndash;1035 (2016).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4079378/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4079378/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAnodic oxidative amidation (EOA) strategies offer a sustainable and potentially promising route for amide synthesis. However, the efficiency and activity of catalysts under oxidative conditions are highly dependent on noble metals. Herein, we present our experimental findings and fundamental understanding that fluorine-doped Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e nanosheet arrays on carbon fiber (F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e/CP) serve as an efficient and robust non-noble catalyst for the electrochemical synthesis of formamide from ammonia and methanol under ambient conditions. In 0.5 M KHCO\u003csub\u003e3\u003c/sub\u003e solution, this catalyst achieved a high Faradaic efficiency of 52.0%, with an N selectivity of 79.1% at 1.5 V versus Hg/HgO electrode. The catalyst exhibited remarkable stability, maintaining its performance over 120 h. By integrating in-situ spectroscopy studies with density functional theory calculations, we revealed that fluorine doping induces a shift in the d-band center of the Nb site. This shift alters the adsorption behavior of OH\u003csup\u003e-\u003c/sup\u003e and \u003csup\u003e*\u003c/sup\u003eNH\u003csub\u003e2\u003c/sub\u003e intermediate on the F-Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (100) surface, thereby effectively lowering the C-N coupling energy barrier, and boosting the production of formamide.\u003c/p\u003e","manuscriptTitle":"Fluorine-induced d-band center shift of the Nb site boosts anodic formamide electrosynthesis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-18 09:38:17","doi":"10.21203/rs.3.rs-4079378/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d597fd34-60a3-409d-a3a0-73b430a68b08","owner":[],"postedDate":"March 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":29442540,"name":"Physical sciences/Chemistry/Electrochemistry/Electrocatalysis"},{"id":29442541,"name":"Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials"},{"id":29442542,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"}],"tags":[],"updatedAt":"2024-05-16T03:45:12+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-18 09:38:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4079378","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4079378","identity":"rs-4079378","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}