Electrosynthesis of NH3 from low-concentration NO on cascade dual-site catalysts in neutral media

Electrosynthesis of NH3 from low-concentration NO on cascade dual-site catalysts in neutral media | 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 Electrosynthesis of NH 3 from low-concentration NO on cascade dual-site catalysts in neutral media Min Liu, Xiaoxi Guo, Tongwei Wu, Hengfeng Li, Yanning Zhang, Chao Ma, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6497629/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Sep, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Electrosynthesis of NH 3 from low-concentration NO (NORR) in neutral media offers a sustainable nitrogen fixation strategy but is hindered by weak NO adsorption, slow water dissociation, and sluggish hydrogenation kinetics. Herein, we propose a new strategy that successfully overcomes these limitations through using an electron-donating motif to modulate NO-affinitive catalysts, thereby creating dual active site with synergistic functionality. Specifically, we integrate electron-donating nanoparticles into a Fe single-atom catalyst (Fe SAC ), where Fe sites ensure strong NO adsorption, while electron-donating motifs promote water dissociation and NO hydrogenation. In situ X-ray absorption spectroscopy (XAS), in situ attenuated total reflection-infrared spectroscopy (ATR-IR), and theoretical calculations reveal that electron-donating motifs increase Fe site electron density, strengthening NO adsorption. Additionally, these motifs also promote water dissociation, supplying protons to lower the NO hydrogenation barrier. This synergistic interplay enables a cascade reaction mechanism, delivering a remarkable Faradaic efficiency (FE) of 90.3% and a NH 3 yield rate of 709.7 µg h − 1 mg cat . −1 under 1.0 vol% NO in neutral media, outperforming pure Fe SAC (NH 3 yield rate: 444.2 µg h − 1 mg cat . −1 , FE: 56.6%) and prior high-NO-concentration systems. Notably, a record NH 3 yield of 3123.8 µg h − 1 mg cat . −1 was achieved in a membrane electrode assembly (MEA) electrolyzer under a 1.0 vol% NO. This work establishes a new paradigm in NORR by simultaneously enhancing NO adsorption, water dissociation, and hydrogenation kinetics, providing a scalable route for efficient NH 3 electrosynthesis from dilute NO sources. Physical sciences/Chemistry/Electrochemistry/Electrocatalysis Physical sciences/Materials science/Nanoscale materials/Electronic properties and materials Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Nitric oxide (NO) is a harmful atmospheric pollutant primarily emitted from industrial processes and vehicle exhaust, posing severe environmental and health risks. 1 – 6 Selective catalytic reduction (SCR) is the predominant method for mitigating NO emissions. 6 – 10 Nevertheless, it requires temperatures of 300–400°C and uses ammonia as a reducing agent, thus restricting its efficiency under near-ambient conditions and failing to generate any value-added products. Electrochemical NO reduction (NORR) under mild conditions, utilizing renewable electricity and water, offers a sustainable route to both NO removal and ammonia (NH 3 ) production—an essential fertilizer and potential hydrogen carrier—via a carbon-free process. 11 – 13 Large-scale NORR requires neutral water conditions to enable earth-abundant transition metal catalysts, which are unstable in acidic media, and to facilitate direct seawater use without desalination. 14 , 15 However, its efficiency in neutral media is severely restricted by low NO solubility, sluggish water dissociation, and slow NO hydrogenation kinetics. Most current research focuses on engineering electron-deficient sites to strengthen NO adsorption for NORR under neutral media, even at low NO concentrations. 16 – 23 Among these catalysts, Fe-based catalysts exhibit remarkable efficiency in enhancing the performance of low-concentration NORR. 19 , 22 , 23 This becomes particularly effective when Fe sites are in a low oxidation state with sharp d-state defect features, enabling energy-aligned orbital configurations that facilitate the adsorption and activation of NO molecules. 19 Moreover, as one of the most cost-effective and abundant elements in the earth, 24 Fe also plays a pivotal role in biological nitrogenases, enabling efficient natural nitrogen fixation. 25 However, the current approach of enhancing NO affinity on catalysts overlooks the critical challenge of inherently slow water dissociation and NO hydrogenation kinetics in neutral media. Electron-donating materials have demonstrated significant catalytic efficiency in water dissociation reactions, 26 which are essential for supplying protons to promote NO hydrogenation. 18 – 21 Inspired by aforementioned guidance, we propose a novel and universal strategy to improve neutral NORR performance by integrating electron-donating motifs into NO-affinitive catalysts, forming a dual-active-site architecture with synergistic functionality. To demonstrate this strategy and its underlying mechanism, we selected Pt nanoparticles (Pt NPs ) as the electron donor, incorporated into an Fe single-atom catalyst (Fe SAC ) with NO-affinitive ability, as a representative case for detailed analysis. In situ X-ray absorption spectroscopy (XAS), attenuated total reflection-infrared spectroscopy (ATR-IR), and density functional theory (DFT) calculations confirmed that Pt NPs serve as electron donors, increasing the electron density at the Fe sites for stronger NO adsorption, while also facilitating water dissociation to supply protons and significantly promoting the subsequent hydrogenation of NO intermediate. The synergistic interplay between these dual sites enables a cascade reaction mechanism. As a result, the Pt NPs /Fe SAC catalyst achieved a NH 3 yield rate of 709.7 µg h − 1 mg cat . −1 and a Faraday efficiency (FE) of 90.3% at -0.6 V under 1.0 vol% NO/Ar in neutral media, outperforming Fe SAC alone (NH 3 yield rate: 444.2 µg h − 1 mg cat . −1 , FE: 56.6%) and surpassing previously reported NORR systems under high NO concentrations (above 10%) in various medias. Notably, in a membrane electrode assembly (MEA) electrolyzer, the system achieved a record-breaking NH 3 yield of 3123.8 µg h − 1 mg cat . −1 . This approach was successfully extended to other electron-donating nanoparticles, such as Au, highlighting its broad applicability for efficient NORR in neutral media. Results Computational predictions DFT calculations were performed to understand the mechanism underlying the enhanced NORR activity. Fe single atoms coordinated with pyridine-4N in graphene (FeN 4 ) were chosen as the catalyst model due to their high stability (Fig. 1a). 27 To simulate the nanoparticle environment, nine Pt atoms were introduced into the FeN 4 structure (FeN 4 -Pt, Fig. 1b). Before Pt loading, Fe single atom in FeN 4 exhibited partially unoccupied orbitals above the Fermi level (Fig. 1c). After Pt loading, these unoccupied orbitals shifted towards the Fermi level, indicating electron injection into Fe (Fig. 1d). Bader charge analysis confirmed that Fe received ~0.12e - (Fig. 1e), increasing its electron density and reactivity. 28 Therefore, the incorporation of Pt nanoparticle into FeN 4 creates a dual active site, see Fig.1f. We firstly investigated water dissociation on both FeN 4 and FeN 4 -Pt sites (Fig. 2a and 2b). On FeN 4 site, the dissociation of H 2 O into *H and *OH required a free energy of 1.45 eV. However, in FeN 4 -Pt, H 2 O adsorbed at Pt sites, reducing the dissociation energy to 0.99 eV, demonstrating the role of Pt in facilitating proton supply for NORR. Next, the free energy pathway for NO to NH 3 conversion was calculated and a significant enhancement in the NO adsorption capability on FeN 4 -Pt (-1.36 eV) compared to FeN 4 (0.05 eV) was revealed (Fig. 2c). The first proton step (*NO → *HNO) was energetically favorable on both catalysts, but the activation barrier was reduced from 1.50 eV (FeN 4 ) to 0.54 eV (FeN 4 -Pt). The second protonation led to the formation of *NH 2 O (FeN 4 -Pt, ΔG = 0.55 eV) instead of *HNOH (FeN 4 , ΔG = 0.40 eV), thus shifting the reaction pathway. The third protonation on FeN 4 -Pt led to *NH 2 OH formation, but its high desorption energy (3.18 eV) made *NH 2 OH an unlikely byproduct. Instead, *NH 2 OH underwent hydrogenation to *NH 2 + H 2 O, followed by an exothermic step to NH 3 (ΔG = 0.23 eV). Overall, Pt NPs enhance NORR by donating electrons to Fe, strengthening NO adsorption, and accelerating water dissociation to supply protons for NO hydrogenation. This synergistic cascade mechanism significantly boosts NH 3 synthesis efficiency in neutral low-concentration NO conditions (Fig. 2d). Catalyst characterization The Fe SAC and Pt NPs /Fe SAC catalysts were synthesized based on computational guidance. Fe SAC was synthesized through pyrolysis followed by acid etching, while Pt NPs were subsequently loaded onto Fe SAC by a thermal reduction method. High-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Fe SAC (Fig. 3a) revealed that isolated atomic sites are randomly dispersed on nitrogen doped carbon (NC) without observable metal clusters or particles, consistent with the X-ray diffraction (XRD, Supplementary Fig.1) result. Inductively coupled plasma optical emission spectrometer (ICP-OES) confirmed a Fe content of 0.66 wt% in Fe SAC (Table S1). In contrast, HAADF-STEM images of Pt NPs /Fe SAC showed Pt NPs with a size of ~3 nm and a lattice distance of 0.214 nm, corresponding to the (111) crystal plane (Fig. 3b). XRD pattern further confirmed the presence of Pt NPs (Supplementary Fig.1). As illustrated in Fig. 3c, Fe SAC are densely distributed around Pt nanoparticles, and energy dispersion X-ray spectroscopy (EDX, Fig. 3d) mapping confirmed the uniform dispersion of Fe, C, and N elements, with Pt as the primary nanoparticle component. ICP-OES results showed Fe and Pt contents of 0.62 wt% and 0.84 wt%, respectively (Table S1). To investigate the chemical state and atomic structure, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were employed. The Fe K-edge X-ray absorption near-edge structure (XANES) spectra revealed that Fe in Fe SAC lies between +2 and +3 oxidation states (Fig. 3e). Notably, Pt incorporation induces a negative shift in the Fe K-edge, indicating a reduced Fe oxidation state, consistent with the theoretical predictions shown in Fig. 1. Fourier transformed (FT) k 2 -weighted extended X-ray absorption fine structure (EXAFS) analysis (Fig. 3f) confirmed the absence of Fe clusters, as FePc, Fe SAC and Pt NPs /Fe SAC exhibited a prominent Fe-N scattering peak at 1.51 Å. 29,30 EXAFS fitting curves revealed that the average coordination numbers of Fe SAC and Pt NPs /Fe SAC are 4.4 and 4.2, respectively, indicating that Fe is coordinated with four nitrogen atoms (Fe-N 4 ) in both systems. The bond lengths for Fe-N are 1.96 and 1.97 Å, respectively (Supplementary Fig.2 and Table S2). Additionally, wavelet transform (WT) analysis of Fe K-edge EXAFS oscillations (Supplementary Fig.3) displays a strong signal with a maximum intensity at 3.8 Å -1 for Pt NPs /Fe SAC , corresponding to the Fe-N first coordination shell, which is similar to Fe SAC . 29 Impressively, no Fe-Fe signal was detected in WT contour plots for either Fe SAC or Pt NPs /Fe SAC , further confirming the atomically dispersed Fe in both catalysts. XPS analysis of the Pt 4f region (Fig. 3g) showed two Pt 0 peaks at 71.8 (4f 7/2 ) and 75.1 eV (4f 5/2 ) along with two Pt 2+ peaks at 72.7 (4f 7/2 ) and 76.0 eV (4f 5/2 ) in Pt NPs /Fe SAC (Fig. 2g), likely due to partial surface oxidation or electron donation from adjacent Fe atoms. 31,32 The successful synthesis and characterization of Pt NPs /Fe SAC confirmed its distinct structural features, including reduced Fe oxidation states upon Pt incorporation and stable Fe-N 4 coordination. Effect of Pt NPs /Fe SAC in low concentration NORR To demonstrate the cascade reaction mechanism during the dynamic catalytic process of NORR in the Pt NPs /Fe SAC dual-site catalyst, in situ electrochemical XAS and attenuated total reflection-infrared (ATR-IR) spectroscopies were conducted. As shown in Fe K-edge XANES spectra of Pt NPs /Fe SAC (Fig. 4a), the white-line peak intensity increased as the applied potential decreases from open circuit potential (OCP) to -0.3 V, indicating that NO adsorption on Fe sites leads to an increase in coordination number. A shift of the adsorption edge to higher energy suggested an increased oxidation state of Fe. As the potential further decreased to -0.6 V, the white-line peak intensity diminished, implying NO consumption and reduction of Fe valence state, confirming Fe SAC as the real active sites. The EXAFS spectra (Fig. 4b) further revealed the dynamic evolution of Fe’s local coordination. The Fe-N peak was enhanced with decreasing the applied potentials, suggesting that the intermediates adsorb on Fe sites. A notable negative shift from OCP to -0.3 V, suggested the formation of a shorter Fe-N bond due to NO adsorption. When the potential was further reduced to -0.6 V, the peak moved from 1.53 to 1.58 Å, signaling the occurrence of NORR and aligning well with the XANES results. Next, in situ ATR-IR spectroscopy was employed to identify the adsorbed intermediates. As shown in Fig. 4c and 4e, both Fe SAC and Pt NPs /Fe SAC displayed peaks corresponding to NO adsorption, including vertical mode (1774 cm -1 , NO v ) and bent mode (1695 cm -1 , NO b ). 19,33 The higher intensity of these peaks in Pt NPs /Fe SAC indicated stronger NO adsorption. With the potentials shifted from OCP to -1.0 V, the intensity of NO b peak increased, suggesting effective NO activation at Fe sites. As illustrated in Fig. 4d and 4f, the NO b peak intensity in Pt NPs /Fe SAC spectra is much stronger than that of Fe SAC , implying that the lower valence state of Fe site induced by introduction of Pt nanoparticles is more conducive to activate NO, in agreement with the DFT results shown in Fig. 1 and 2. Compared to Fe SAC , the peak of -OH bending vibration at 1648 cm -1 was strengthened in Pt NPs /Fe SAC spectra, indicating that the Pt nanoparticles facilitate H 2 O electrolysis to produce *H, which is beneficial for subsequent NO hydrogenation (Fig. 4d and 4f). 34,35 This was further verified by the electron paramagnetic resonance (EPR) technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a hydrogen radical (·H) trapping reagent. 36,37 As shown in Supplementary Fig.5, distinct ·H signals were detected for Pt NPs /Fe SAC but absent in Fe SAC , confirming enhanced hydrogen generation. Hydrogenated intermediates NH x (1412 and 1530 cm -1 ) were progressively formed at lower potentials, ultimately converting to NH 4 + (1465 cm -1 ). 38-40 Overall, these results clearly demonstrated Pt NPs served as electron donors, increasing Fe site electron density to enhance NO adsorption while simultaneously promoting water dissociation to supply protons for efficient NORR. These results clearly demonstrated that a cascade reaction mechanism occurs on the dual-site catalyst, Pt NPs /Fe SAC , thereby promoting NORR, see Fig. 4g. NORR performance evaluation The NORR performance was evaluated in 0.5 M K 2 SO 4 electrolyte, using an air-tight H cell. Prior to electrolysis, high-purity Ar was purged into the electrolyte to remove residual oxygen. As shown in Fig. 5a, the linear sweep voltammetry (LSV) curves revealed a significant increase in current density for Pt NPs /Fe SAC in 1 vol% NO atmosphere compared to Ar-saturated conditions, confirming effective NO reduction on the catalyst surface. Compare to Fe SAC, Pt NPs /NC and NC, the Pt NPs /Fe SAC showed the largest current density gap, indicating superior NORR activity (Supplementary Fig.6). As depicted in Fig. 5b, the NH 3 yield rate and FE of Pt NPs /Fe SAC increase steadily with applied potentials from -0.4 to -0.6 V, reaching the maximum values of 709.7 μg h -1 mg cat. -1 and 90.3% at -0.6 V, outperforming previously reported NORR catalysts (Table S4). NH 3 quantification via colorimetric method (Supplementary Fig.7) and nuclear magnetic resonance (NMR) spectroscopy (Supplementary Fig.8) yielded consistent results, ensuring measurement accuracy (Supplementary Fig.14). However, at the applied potentials beyond -0.6 V, NORR performance of Pt NPs /Fe SAC declined due to the competing HER. In comparison, Fe SAC obtained its highest NORR performance at -0.7 V with a NH 3 yield of 444.2 μg h -1 mg cat. -1 and FE of 56.6% (Fig. 5c and S9), while Pt NPs /NC and bare NC exhibited negligible NORR activity (Fig. 5c). DFT and in-situ electrochemical experiments clearly verified that Pt NPs served as electron donors, increasing the electron density at the Fe single-atom site to promote NO adsorption, while facilitating water dissociation for proton supply and promoting NO hydrogenation. This dual role enabled efficient NO-to-NH 3 conversion with high activity and selectivity by activating the cascade reaction mechanism. To validate that NH 3 originated from NO reduction, control experiments were conducted under three conditions: (1) electrolysis at -0.6 V in Ar-saturated electrolyte, (2) testing at OCP in NO-saturated electrolyte, and (3) testing in NO-saturated electrolyte with bare carbon paper (CP) as work electrode (Fig. 5d). Only negligible NH 3 was detected in these cases, confirming that NH 3 formation on Pt NPs /Fe SAC exclusively results from NO reduction. Additionally, an isotope labeling experiment was performed to exclude the possibility of nitrogen contamination. The laboratory-produced 15 NO was used as the feeding gas for NORR at -0.6 V for 1 h. As shown in Fig. 5e, the NMR analysis conclusively verified that the generated NH 3 is originated from NO. Electrocatalyst stability is crucial for long-term energy conversion and storage. Pt NPs /Fe SAC demonstrated excellent durability, maintaining stable NH 3 yield and FE over ten consecutive cycles (Fig. 5f). A long-term stability test (>70 h, Supplementary Fig.15) showed no significant decline in current density, further confirming its robust electrochemical stability. Post-reaction characterization revealed minor catalyst changes: XRD pattern showed weakened Pt diffraction peaks, suggesting partial Pt dissolution (Supplementary Fig.16). ICP analysis detected trace amounts of Pt in the electrolyte post-NORR (Table S3). XANES analysis exhibited a slight increase in Fe valence state after NORR test (Supplementary Fig.17a). EXAFS spectra revealed no Fe-Fe bond formation, confirming Fe remains atomically dispersed (Supplementary Fig.17b). To mitigate NO mass transport limitations due to its low solubility (~1.92 mmol L -1 atm -1 in water at 25 °C), NORR was conducted in a membrane electrode assembly (MEA) electrolyzer . 41,42 Compared to H-cell, the MEA significantly enhanced current density, suggesting improved NO utilization (Fig. 5g). As shown in Fig. 5h, increasing the applied cell voltage from 1.2 to 1.6 V leads to higher NH 3 yield and FE. Notably, Pt NPs /Fe SAC achieved a record-breaking NH 3 yield of 3123.8 μg h -1 mg cat. -1 and FE of 94.5% at 1.6 V (Fig. 5h), surpassing all previously reported NORR catalyst even tests under high NO concentration (Fig. 5i). To explore alternative metal nanoparticles, Au NPs /Fe SAC was synthesized for NO-to-NH 3 conversion. TEM images (Supplementary Fig.18) and XRD patterns (Supplementary Fig.19) clearly verified that successful Au nanoparticle deposition. The obtained Au NPs /Fe SAC achieved optimal NH 3 yield of 595.4 μg h -1 mg cat. -1 and FE of 78.9% at -0.5 V, further demonstrating the versatility of metal-modified Fe SAC systems. Conclusions In summary, we present an electron-donating particle-mediated strategy that integrates Pt NPs as the electron donor into the Fe SAC electrocatalyst to construct dual-active-site architectures, thereby enhancing NO adsorption while promoting water dissociation and NO hydrogenation for significantly improving neutral NORR at low NO concentration (1 vol%). In situ spectro-electrochemical experiments, coupled with theoretical calculations, confirmed that the Pt nanoparticles serve as electron donors, increasing the electron density at the Fe single-atom site to promote NO adsorption, while facilitating water dissociation to provide protons and thus reducing the activation energy of NO hydrogenation. The synergistic interplay between these dual sites enables a cascade reaction mechanism achieving a superior NORR performance with a NH 3 FE up to 90.3% and a high NH 3 yield rate of 709.7 µg cm − 2 h − 1 under 1 vol% NO concentration at -0.6 V, outperforming Fe SAC (NH 3 yield rate: 444.2 µg h − 1 mg cat . −1 , FE: 56.6%) and prior high-NO-concentration systems. Notably, in a MEA electrolyzer, the system achieved a record-breaking NH 3 yield of 3123.8 µg h − 1 mg cat . −1 . This work not only offers an attractive earth-abundant nanocatalyst for NH 3 electrosynthesis at low NO concentrations, but also provides a novel methodology for designing superior electrocatalytic NORR systems through a dual-active-site strategy, paving the way for large scale NH 3 electrosynthesis. Methods Chemicals Ketjen black ecp600JD (KJ), Nafion and carbon paper (CP) were purchased from Suzhou Sinero Thechology Co., Ltd (Suzhou, China). Sodium hydroxide (NaOH), sodium nitrite (NaNO 2 ), p-aminobenzenesulfonic acid (pAA, C 6 H 7 NO 3 S) m-phenylenediamine (mPDA, C 6 H 8 N 2 ) ammonium persulfate ((NH 4 ) 2 S 2 O 8 ), iron chloride hexahydrate (FeCl 3 ·6H 2 O), polyvinylpyrrolidone (PVP), sodium hypochlorite (NaClO) and ethylene glycol (EG) were obtained from Aldrich Chemical Reagent Co., Ltd. (Shanghai, China). Chloroplatinic acid hexahydrate (H 2 PtCl 6 ·6H 2 O), gold chloride trihydrate (HAuCl 4 ·3H 2 O), salicylic acid (C 7 H 6 O 3 ), trisodium citrate dihydrate (Na 3 C 6 H 5 O 7 ·2H 2 O), sodium nitroferricyanide (III) dihydrate (Na 2 Fe(CN) 5 NO·2H 2 O), dimethyl sulfoxide (DMSO- d 6), ammonium chloride ( 14 NH 4 Cl, 15 NH 4 Cl), sodium borohydride (NaNH 4 ), sodium nitrite (Na 15 NO 2 ) were bought from Macklin Chemical Reagent Co., Ltd. (Shanghai, China). Fe powder, potassium thiocyanate (KSCN) and hydrochloric acid (HCl) were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the reagents were used as received. The water used throughout all experiments was purchased from Wahaha Group Co., Ltd. (Hangzhou, China). Preparation of NC 1.0 g of KJ was dispersed in 30 mL H 2 O and sonicated in an ice bath for 2 h to labeled A1. Separately, 0.74 g pAA was dissolved in 30 mL H 2 O. To this solution, 9 mL of 1 M NaOH, 4 mL of 1 M NaNO 2 and 21 mL of 1 M HCl were added to prepare the diazo salt (labeled A2), maintain the reaction at 0°C. Subsequently, the A2 was mixed with A1. To initiate surface grafting of the diazonium salt, 0.7 g of reduced Fe powder was introduced. Afterward, 25 mL concentrated HCl, 7.6 g of mPDA, 23 mL of 1 M FeCl 3 and 70 mL of 2 M (NH 4 ) 2 S 2 O 8 solution were added, and the reaction was allowed to react overnight. After filtration, the product was washed with water for 3 times and vacuum drying overnight to yield the NC precursor. Preparation of Fe SAC 0.6 g of the NC precursor was ultrasonically dispersed in 30 mL H 2 O, followed by the addition of 1.8 mL of 1 M FeCl 3 and 6 mL of 1 M KSCN. The solvent was removed by rotary evaporation, and the residue was heated to 950°C for 1 h under an Ar atmosphere. The obtained black powder was dispersed in 50 mL of 1 M HCl solution overnight at 80°C. Then, the powder was washed with water 3 times, and drying overnight. Finally, the dried powder was heated at 950°C for 3 h in an Ar atmosphere to yield Fe SAC . Preparation of Pt NPs /Fe SAC 100 mg Fe SAC was dispersed in 20 mL of EG. Next, 5 mg H 2 PtCl 6 ·6H 2 O was dispersed in 20 mL of EG and then dripped into Fe SAC . The obtained suspension was stirred for 2 h at room temperature and then treated at 160°C for 90 min. Afterward, the final product was washed 3 times and dried overnight. The Pt NPs was synthesized by replacing the Fe SAC to NC. Preparation of Au NPs /Fe SAC 100 mg of Fe SAC and 10 mg of PVP were dispersed in 30 mL H 2 O. Then, 400 µL of a 10 mg/mL HAuCl 4 solution was added dropwise, followed by 100 mg of NaNH 4 dissolved in 20 mL H 2 O to reduce HAuCl 4 . The mixture was stirred for 10 min at room temperature. Electrochemical measurements Electrochemical measurements were performed with a CHI660E electrochemical station (CH Instruments, Inc., Shanghai) in a H-cell under ambient condition, which was separated by Nafion 211 membrane. The Pt NPs /Fe SAC , Ag/AgCl and graphite rod acted as the working electrode, reference electrode and counter electrode, respectively. The reference electrode was calibrated to the reversible hydrogen electrode (RHE) scale in all measurements using the following equation: E (RHE) = E (Ag/AgCl) + (0.059 pH + 0.197) V. High purity Ar gas (99.999%) was bubbled into cathode chamber with the flow rate of 30 sccm for 30 min to removal oxygen before NORR. Then, the low-concentration NO (1% v/v) was firstly washed by 4 M KOH and then fed at 30 sccm for 30 min to saturate the electrolyte, maintain a constant flow during the electrochemical tests. For NORR tested in MEA, the RuO 2 supported on nickel foam (RuO 2 /NF) as anode tested in 1 M KOH, while Pt NPs /Fe SAC was used as the cathode for NORR and the tail gas was absorbed by 1 M HCl. Determination of NH 3 The produced NH 3 was quantified by the indophenol blue method 43 and NMR. For indophenol blue method, standard NH 3 solution with a series of concentrations were used to calibrated the concentration-absorbance curves. The fitting curve (y = 0.3435x + 0.05843, R 2 = 0.9999) showed good linear relation of absorbance value with NH 3 concentration. All electrolytes were diluted 10 times before testing unless otherwise specified. For 1 H NMR measurements, the electrolyte after electrolysis was diluted 2 times with 1 M HCl to adjust the pH to acidic. Then, 100 mL DMSO-d6 was added in 500 µL acidified electrolyte. Determination of FE and NH 3 Yield The FE for NH 3 synthesis was calculated as the amount of electric charge used for NH 3 production divided by the total charge passed through the electrodes during electrolysis. The total amount of NH 3 produced was measured using colorimetric methods. The FE could be calculated as follows: FE = 3 × F × [NH 3 ] × V / (17 × Q) ×100% (1) NH 3 yield was calculated using the following equation: NH 3 yield = [NH 3 ] × V / (m cat . × t) (2) where F is the Faraday constant, [NH 3 ] is the measured NH 3 concentration, V is the volume of the electrolyte in the cathodic chamber, Q is the total quantity of applied electricity; t is the reduction time; m cat . is the loaded mass of catalyst on carbon paper. Electrochemical in situ ATR-IR measurements The in situ electrochemical ATR-IR measurements were conducted on a Nicolet iS50 FT-IR spectrometer with a liquid nitrogen-cooled MCT-A detector. The Si prism loaded with catalyst, Pt plate and Ag/AgCl were used as the working electrode, counter electrode and reference electrode, respectively, with 0.5 M K 2 SO 4 as electrolyte. During the process of tests, 1% NO was bubbled into the electrolyte with the flow rate of 10 sccm. Prior to testing, the Si prism was coated with Au film. The Si prism was first polished by 100 nm Al 2 O 3 . Next, the Si prism was soaked in a piranha solution for 30 min to removal organic contaminants. Then, the reflecting surface was immersed in a mixture of the Au plating solution (5.75 mM NaAuCl 4 ·2H 2 O + 0.025 M NH 4 Cl + 0.075 M Na 2 SO 3 + 0.025 M Na 2 S 2 O 3 + 0.026 M NaOH) and a 2 wt % HF solution at 60°C for 5 min. Afterward, the Au film was rinsed with deionized water and dried with N 2 . In situ ATR-IR spectra were collected at OCP and different applied potentials. Electrochemical in situ XAFS measurements The in situ XAFS measurements were conducted in the fluorescence mode using a home-made electrochemical cell. The Pt NPs /Fe SAC , Ag/AgCl and graphite rod were used as working electrode, reference electrode and counter electrode, respectively. Relevant measurements were conducted in NO-saturated 0.5 M K 2 SO 4 electrolyte. The XAS spectra were recorded at OCP and different applied potentials. Computation and model details All simulations were carried out using density functional theory as implemented in the GPAW software 44 , 45 version 19.8.1. The exchange-correlation effects were accounted for using the BEEF-vdW-functional, which combines the generalized gradient approximation with the Langreth-Lundqvist van der Waals-functional to achieve accurate adsorption energies. A 2×2×1 k-point mesh was used and all the calculations were spin-polarized. To model the solvent at the electrochemical interface, a hybrid implicit/explicit approach was employed, where 40 explicit water molecules surrounded the electrode surface, and the remaining water was modeled using the SCMVD 46 dielectric continuum model. The positions and orientations of the explicit water molecules were optimized using the minima hopping global optimization method 47 as implemented in ASE. 48 The free energies of the reaction intermediates were defined as by Δ G = Δ E + Δ ZPE – TΔ S , where Δ E , Δ ZPE , T , and Δ S represent the reaction energy, zero-point energy, temperature (298.15 K), and the entropy, respectively. Enhanced Sampling The slow growth sampling approach 49 , 50 in the constrained molecular dynamics simulation method can be used to describe the kinetic energy barrier in the reaction process by setting a suitable collective variable (CV, ξ ), which changes from state 1 to state 2 at a certain transformation rate \(\mathop \xi \limits^{ \cdot }\) . The work performed throughout the entire process from state 1 to state 2 can be calculated using the following formula: \(w_{{state1 \to state2}}^{{}}=\int_{{\xi (state1)}}^{{\xi (state2)}} {\left( {\frac{{\partial V(q)}}{{\partial \xi }}} \right)} \cdot \mathop \xi \limits^{ \cdot } dt\) Where V(q) represents the free energy, and \(\frac{{\partial V(q)}}{{\partial \xi }}\) is calculated using the SHAKE algorithm. When approaching the infinitesimal limit \(\mathop \xi \limits^{ \cdot }\) , the work \(w_{{state1 \to state2}}^{{}}\) required from state 1 to state 2 corresponds to the difference in free energy. In the SG sampling method, \(\partial \xi\) is selected to 0.0005Å, and the final reaction's free energy barrier can be obtained by aggregating the free energy distribution diagram. Declarations Acknowledgements This work was supported by National Natural Science Foundation of China (Nos. 22072015, 21927811, and 52202214), Natural Science Foundation of Sichuan Province (No. 2023NSFSC0954), China National Postdoctoral Program for Innovative Talents (No. BX2021053), and China Postdoctoral Science Foundation (No. 2021M700680). The authors thank BL11B beamline of the Shanghai Synchrotron Radiation Facility (SSRF) for providing the XAFS beamtime. The numerical calculations in this paper have been done on Computing Center in Xi'an. Contributions T.W. and X.G. conceived the idea, wrote the original draft, and collected and analyzed the data. X.G. and T.W. performed the DFT calculations and experiments. C.M. provided the HAADF-STEM characterization. M.L. supervised this project. All authors contributed and reviewed the manuscript. Competing interests The authors declare no competing financial interests. 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J Am Chem Soc 142:7036–7046 Wang Y et al (2024) Phase-regulated active hydrogen behavior on molybdenum disulfide for electrochemical nitrate-to-ammonia conversion. Angew Chem Int Ed 63:e202315109 Zhou J et al (2023) Linear adsorption enables NO selective electroreduction to hydroxylamine on single Co sites. Angew Chem Int Ed 62:e202305184 Han S et al (2023) Ultralow overpotential nitrate reduction to ammonia via a three-step relay mechanism. Nat Catal 6:402–414 Chen K et al (2023) Self-tandem electrocatalytic NO reduction to NH 3 on a W single-atom catalyst. Nano Lett 23:1735–1742 Cheon S et al (2022) Electro-synthesis of ammonia from dilute nitric oxide on a gas diffusion electrode. ACS Energy Lett 7:958–965 Li M et al (2022) A pair–electrosynthesis for formate at ultra–low voltage via coupling of CO 2 reduction and formaldehyde oxidation. Nano-Micro Lett 14:211 Zhu D et al (2013) Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction. Nat Mater 12:836–841 Mortensen JJ et al (2005) Real-space grid implementation of the projector augmented wave method. Phys Rev B 71:035109 Enkovaara J et al (2010) Electronic structure calculations with GPAW: a real-space implementation of the projector augmented-wave method. J Phys Condens Matter 22:253202 Held A et al (2014) Simplified continuum solvent model with a smooth cavity based on volumetric Data. J Chem Phys 141:174108 Peterson AA (2014) Global optimization of adsorbate-surface structures while preserving molecular identity. Top Catal 57:40–53 Larsen AH et al (2017) The atomic simulation environment—a Python library for working with atoms. J Phys Condens Matter 29:273002 Woo TK et al (1997) A combined car – Parrinello QM/MM implementation for Ab initio molecular dynamics simulations of extended systems: application to transition metal catalysis. J Phys Chem B 101:7877–7880 Jarzynski C (1997) Nonequilibrium equality for free energy differences. Phys. Rev. Lett. 78, 2690 – 2693 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.docx Supplementary Information Cite Share Download PDF Status: Published Journal Publication published 26 Sep, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6497629","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":446724986,"identity":"556c9961-ffe1-4bd8-992a-2b5cc2d245f5","order_by":0,"name":"Min Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAs0lEQVRIiWNgGAWjYDACZgbGAwkMNhAOD5FaGIBa0kjRAgQHGBgOk6BFt533wIGHbefl5WckMD5428Ygb05Ii9lhvoQDiW23DTfcSGA2nNvGYLizgaAWHgOQlgQDiQQ2ad42hgSDA8RpOZcAdBj7b1K0AAPtRgIbM/FaEs4lG24487BZcs45CcMNBLWcP2P48EeZnbx8e/LBD2/KbOQJ2oIEGBuAhATx6kfBKBgFo2AU4AYAowVAFfo0KHsAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-9007-4817","institution":"Central South University","correspondingAuthor":true,"prefix":"","firstName":"Min","middleName":"","lastName":"Liu","suffix":""},{"id":446724987,"identity":"26c8ceb1-e98b-425e-923d-7e8b6a9578b5","order_by":1,"name":"Xiaoxi Guo","email":"","orcid":"","institution":"Central South University","correspondingAuthor":false,"prefix":"","firstName":"Xiaoxi","middleName":"","lastName":"Guo","suffix":""},{"id":446724988,"identity":"674a7f05-65b2-409c-a63f-8770643dcfc0","order_by":2,"name":"Tongwei Wu","email":"","orcid":"https://orcid.org/0000-0003-1922-9545","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Tongwei","middleName":"","lastName":"Wu","suffix":""},{"id":446724989,"identity":"871f3d2c-d511-4fb1-ab45-132aaf5955d2","order_by":3,"name":"Hengfeng Li","email":"","orcid":"","institution":"School of Materials Science and Engineering, Central South University","correspondingAuthor":false,"prefix":"","firstName":"Hengfeng","middleName":"","lastName":"Li","suffix":""},{"id":446724990,"identity":"546561c6-d576-4ab7-9a22-e7b464609bc8","order_by":4,"name":"Yanning Zhang","email":"","orcid":"https://orcid.org/0000-0002-3839-2965","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Yanning","middleName":"","lastName":"Zhang","suffix":""},{"id":446724991,"identity":"778ef432-b75d-44ca-a1e6-fecc75a01a00","order_by":5,"name":"Chao Ma","email":"","orcid":"https://orcid.org/0000-0001-8599-9340","institution":"Hunan University","correspondingAuthor":false,"prefix":"","firstName":"Chao","middleName":"","lastName":"Ma","suffix":""},{"id":446724992,"identity":"6d3db4e0-a2f7-4c01-a06f-b107b272d081","order_by":6,"name":"Hongmei Li","email":"","orcid":"","institution":"Central South University","correspondingAuthor":false,"prefix":"","firstName":"Hongmei","middleName":"","lastName":"Li","suffix":""},{"id":446724993,"identity":"355be9c5-bda5-4783-af85-06f43ed6a858","order_by":7,"name":"Liyuan Chai","email":"","orcid":"","institution":"Central South University","correspondingAuthor":false,"prefix":"","firstName":"Liyuan","middleName":"","lastName":"Chai","suffix":""},{"id":446724994,"identity":"2ad3945f-bb77-4218-9e64-492f992d9cc5","order_by":8,"name":"Haitao Zhao","email":"","orcid":"","institution":"The Hong Kong Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Haitao","middleName":"","lastName":"Zhao","suffix":""}],"badges":[],"createdAt":"2025-04-21 16:20:30","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6497629/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6497629/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-63365-7","type":"published","date":"2025-09-26T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81256373,"identity":"7e0c12fa-6788-437d-9cc1-118ea5e570ac","added_by":"auto","created_at":"2025-04-24 04:52:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":160172,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTheoretical calculations.\u003c/strong\u003e Atom configurations of (\u003cstrong\u003ea\u003c/strong\u003e) FeN\u003csub\u003e4\u003c/sub\u003e and (\u003cstrong\u003eb\u003c/strong\u003e) FeN\u003csub\u003e4\u003c/sub\u003e-Pt. Corresponding DOS plots of Fe atom in (\u003cstrong\u003ec\u003c/strong\u003e) FeN\u003csub\u003e4\u003c/sub\u003e and (\u003cstrong\u003ed\u003c/strong\u003e) FeN\u003csub\u003e4\u003c/sub\u003e-Pt. (\u003cstrong\u003ee\u003c/strong\u003e) Bader charge analysis of Fe atom in FeN\u003csub\u003e4\u003c/sub\u003e and FeN\u003csub\u003e4\u003c/sub\u003e-Pt, respectively. (\u003cstrong\u003ef\u003c/strong\u003e) Schematic diagram of dual site catalyst.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/e172def9f70ce5618ed728ca.png"},{"id":81256374,"identity":"12605a0a-d7f9-4c52-8bcc-8a2dc8abe257","added_by":"auto","created_at":"2025-04-24 04:52:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":150056,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eReaction mechanism.\u003c/strong\u003e The free energy of water dissociation on (\u003cstrong\u003ea\u003c/strong\u003e) FeN\u003csub\u003e4\u003c/sub\u003e and (\u003cstrong\u003eb\u003c/strong\u003e) FeN\u003csub\u003e4\u003c/sub\u003e-Pt. (\u003cstrong\u003ec\u003c/strong\u003e) The reaction free energies of NORR pathways on FeN\u003csub\u003e4\u003c/sub\u003e and FeN\u003csub\u003e4\u003c/sub\u003e-Pt. \u003cstrong\u003e(d)\u003c/strong\u003e Comparation between traditional and cascade mechanisms.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/89b9206f0d1311a87742ca1d.png"},{"id":81257243,"identity":"b65691b3-ccaf-47fd-857d-ffc3a08db208","added_by":"auto","created_at":"2025-04-24 05:08:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":405506,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural characterizations of catalysts.\u003c/strong\u003e HAADF-STEM images of (\u003cstrong\u003ea\u003c/strong\u003e) Fe\u003csub\u003eSAC\u003c/sub\u003e and (\u003cstrong\u003eb, c\u003c/strong\u003e) Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. (\u003cstrong\u003ed\u003c/strong\u003e) EDX mapping images of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. (\u003cstrong\u003ee\u003c/strong\u003e) Fe K-edge XANES spectra of Fe foil, FePc, Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. (\u003cstrong\u003ef\u003c/strong\u003e) FT-EXAFS spectra at Fe K-edge. (\u003cstrong\u003eg\u003c/strong\u003e) XPS spectrum of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e in Pt 4f region.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/6f999f8e93f81307172aeaae.png"},{"id":81256377,"identity":"93a53797-55c3-47bc-bd07-1dea0e700be6","added_by":"auto","created_at":"2025-04-24 04:52:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":276193,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eIn situ\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e XAS and ATR-IR spectra of NORR.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) \u003cem\u003eIn situ\u003c/em\u003e Fe K-edge XANES spectra of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e at different potentials. (Inset) Magnified white-line peak and pre-edge XANES region. (\u003cstrong\u003eb\u003c/strong\u003e) Corresponding FT-EXAFS spectra at Fe K-edge. Potential-dependent \u003cem\u003ein situ\u003c/em\u003e ATR-IR spectra of (\u003cstrong\u003ec\u003c/strong\u003e) Fe\u003csub\u003eSAC\u003c/sub\u003e and (\u003cstrong\u003ee\u003c/strong\u003e) Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. Corresponding 2D ATR-IR contour map of (\u003cstrong\u003ed\u003c/strong\u003e) Fe\u003csub\u003eSAC\u003c/sub\u003e and (\u003cstrong\u003ef\u003c/strong\u003e) Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. (\u003cstrong\u003eg\u003c/strong\u003e) Reaction mechanisms.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/3cc2b6024f67739d446db014.png"},{"id":81256751,"identity":"48490778-4e8d-4381-a4a3-7efa236435bf","added_by":"auto","created_at":"2025-04-24 05:00:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":221724,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical NORR performance.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) LSV curves of Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e in Ar- and 1 vol% NO-saturated 0.5 M K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. (\u003cstrong\u003eb\u003c/strong\u003e) NH\u003csub\u003e3\u003c/sub\u003e yield and FE with 1 vol% NO over Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e at each given potential. (\u003cstrong\u003ec\u003c/strong\u003e) The NH\u003csub\u003e3\u003c/sub\u003e yield of Pt\u003csub\u003eNPs\u003c/sub\u003e, NC, Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. (\u003cstrong\u003ed\u003c/strong\u003e) NH\u003csub\u003e3\u003c/sub\u003e yield of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e under different conditions. (\u003cstrong\u003ee\u003c/strong\u003e) \u003csup\u003e1\u003c/sup\u003eH NMR spectra of the electrolyte fed by \u003csup\u003e15\u003c/sup\u003eNO and \u003csup\u003e14\u003c/sup\u003eNO for NORR over the Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e at -0.6 V. (\u003cstrong\u003ef\u003c/strong\u003e) NORR cycling stability test over the Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e at -0.6 V. (\u003cstrong\u003eg\u003c/strong\u003e) LSV curves of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e test in MEA electrolyzer and H cell. (\u003cstrong\u003eh\u003c/strong\u003e) Corresponding NH\u003csub\u003e3\u003c/sub\u003e yield and FE of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e. (\u003cstrong\u003ei\u003c/strong\u003e) Comparison of NORR performance with other electrocatalysts.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/fe6b4e6e221b6e7163ccee9f.png"},{"id":92305111,"identity":"80ae92e9-af33-44fb-8725-9f5e595f867f","added_by":"auto","created_at":"2025-09-27 07:10:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2168736,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/6b16ae97-1a2b-4415-b830-c806022e7db0.pdf"},{"id":81256749,"identity":"09198af0-1d3a-4dfa-a876-212309e5503d","added_by":"auto","created_at":"2025-04-24 05:00:55","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1966864,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6497629/v1/7959c7e168711f08a5b55661.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eElectrosynthesis of NH\u003csub\u003e3\u003c/sub\u003e from low-concentration NO on cascade dual-site catalysts in neutral media\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNitric oxide (NO) is a harmful atmospheric pollutant primarily emitted from industrial processes and vehicle exhaust, posing severe environmental and health risks.\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e Selective catalytic reduction (SCR) is the predominant method for mitigating NO emissions.\u003csup\u003e\u003cspan additionalcitationids=\"CR7 CR8 CR9\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e Nevertheless, it requires temperatures of 300\u0026ndash;400\u0026deg;C and uses ammonia as a reducing agent, thus restricting its efficiency under near-ambient conditions and failing to generate any value-added products. Electrochemical NO reduction (NORR) under mild conditions, utilizing renewable electricity and water, offers a sustainable route to both NO removal and ammonia (NH\u003csub\u003e3\u003c/sub\u003e) production\u0026mdash;an essential fertilizer and potential hydrogen carrier\u0026mdash;via a carbon-free process.\u003csup\u003e\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e Large-scale NORR requires neutral water conditions to enable earth-abundant transition metal catalysts, which are unstable in acidic media, and to facilitate direct seawater use without desalination.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e However, its efficiency in neutral media is severely restricted by low NO solubility, sluggish water dissociation, and slow NO hydrogenation kinetics.\u003c/p\u003e \u003cp\u003eMost current research focuses on engineering electron-deficient sites to strengthen NO adsorption for NORR under neutral media, even at low NO concentrations.\u003csup\u003e\u003cspan additionalcitationids=\"CR17 CR18 CR19 CR20 CR21 CR22\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e Among these catalysts, Fe-based catalysts exhibit remarkable efficiency in enhancing the performance of low-concentration NORR.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e This becomes particularly effective when Fe sites are in a low oxidation state with sharp d-state defect features, enabling energy-aligned orbital configurations that facilitate the adsorption and activation of NO molecules.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e Moreover, as one of the most cost-effective and abundant elements in the earth,\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e Fe also plays a pivotal role in biological nitrogenases, enabling efficient natural nitrogen fixation.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e However, the current approach of enhancing NO affinity on catalysts overlooks the critical challenge of inherently slow water dissociation and NO hydrogenation kinetics in neutral media.\u003c/p\u003e \u003cp\u003eElectron-donating materials have demonstrated significant catalytic efficiency in water dissociation reactions,\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e which are essential for supplying protons to promote NO hydrogenation.\u003csup\u003e\u003cspan additionalcitationids=\"CR19 CR20\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e Inspired by aforementioned guidance, we propose a novel and universal strategy to improve neutral NORR performance by integrating electron-donating motifs into NO-affinitive catalysts, forming a dual-active-site architecture with synergistic functionality. To demonstrate this strategy and its underlying mechanism, we selected Pt nanoparticles (Pt\u003csub\u003eNPs\u003c/sub\u003e) as the electron donor, incorporated into an Fe single-atom catalyst (Fe\u003csub\u003eSAC\u003c/sub\u003e) with NO-affinitive ability, as a representative case for detailed analysis. \u003cem\u003eIn situ\u003c/em\u003e X-ray absorption spectroscopy (XAS), attenuated total reflection-infrared spectroscopy (ATR-IR), and density functional theory (DFT) calculations confirmed that Pt\u003csub\u003eNPs\u003c/sub\u003e serve as electron donors, increasing the electron density at the Fe sites for stronger NO adsorption, while also facilitating water dissociation to supply protons and significantly promoting the subsequent hydrogenation of NO intermediate. The synergistic interplay between these dual sites enables a cascade reaction mechanism. As a result, the Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e catalyst achieved a NH\u003csub\u003e3\u003c/sub\u003e yield rate of 709.7 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e and a Faraday efficiency (FE) of 90.3% at -0.6 V under 1.0 vol% NO/Ar in neutral media, outperforming Fe\u003csub\u003eSAC\u003c/sub\u003e alone (NH\u003csub\u003e3\u003c/sub\u003e yield rate: 444.2 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e, FE: 56.6%) and surpassing previously reported NORR systems under high NO concentrations (above 10%) in various medias. Notably, in a membrane electrode assembly (MEA) electrolyzer, the system achieved a record-breaking NH\u003csub\u003e3\u003c/sub\u003e yield of 3123.8 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e. This approach was successfully extended to other electron-donating nanoparticles, such as Au, highlighting its broad applicability for efficient NORR in neutral media.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eComputational predictions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDFT calculations were performed to understand the mechanism underlying the enhanced NORR activity. Fe single atoms coordinated with pyridine-4N in graphene (FeN\u003csub\u003e4\u003c/sub\u003e) were chosen as the catalyst model due to their high stability (Fig. 1a).\u003csup\u003e27\u003c/sup\u003e To simulate the nanoparticle environment, nine Pt atoms were introduced into the FeN\u003csub\u003e4\u003c/sub\u003e structure (FeN\u003csub\u003e4\u003c/sub\u003e-Pt, Fig. 1b). Before Pt loading, Fe single atom in FeN\u003csub\u003e4\u003c/sub\u003e exhibited partially unoccupied orbitals above the Fermi level (Fig. 1c). After Pt loading, these unoccupied orbitals shifted towards the Fermi level, indicating electron injection into Fe (Fig. 1d). Bader charge analysis confirmed that Fe received ~0.12e\u003csup\u003e-\u003c/sup\u003e (Fig. 1e), increasing its electron density and reactivity.\u003csup\u003e28\u0026nbsp;\u003c/sup\u003eTherefore, the incorporation of Pt nanoparticle into FeN\u003csub\u003e4\u003c/sub\u003e creates a dual active site, see Fig.1f.\u003c/p\u003e\n\u003cp\u003eWe firstly investigated water dissociation on both FeN\u003csub\u003e4\u003c/sub\u003e and FeN\u003csub\u003e4\u003c/sub\u003e-Pt sites (Fig. 2a and 2b). On FeN\u003csub\u003e4\u003c/sub\u003e site, the dissociation of H\u003csub\u003e2\u003c/sub\u003eO into *H and *OH required a free energy of 1.45 eV. However, in FeN\u003csub\u003e4\u003c/sub\u003e-Pt, H\u003csub\u003e2\u003c/sub\u003eO adsorbed at Pt sites, reducing the dissociation energy to 0.99 eV, demonstrating the role of Pt in facilitating proton supply for NORR.\u003c/p\u003e\n\u003cp\u003eNext, the free energy pathway for NO to NH\u003csub\u003e3\u003c/sub\u003e conversion was calculated and a significant enhancement in the NO adsorption capability on FeN\u003csub\u003e4\u003c/sub\u003e-Pt (-1.36 eV)\u0026nbsp;compared to FeN\u003csub\u003e4\u0026nbsp;\u003c/sub\u003e(0.05 eV) was\u0026nbsp;revealed\u0026nbsp;(Fig. 2c).\u0026nbsp;The first proton step (*NO \u0026rarr; *HNO) was energetically favorable on both catalysts, but the activation barrier was reduced from 1.50 eV (FeN\u003csub\u003e4\u003c/sub\u003e) to 0.54 eV (FeN\u003csub\u003e4\u003c/sub\u003e-Pt). The second protonation led to the formation of *NH\u003csub\u003e2\u003c/sub\u003eO (FeN\u003csub\u003e4\u003c/sub\u003e-Pt, \u0026Delta;G = 0.55 eV) instead of *HNOH (FeN\u003csub\u003e4\u003c/sub\u003e, \u0026Delta;G = 0.40 eV), thus shifting the reaction pathway. The third protonation on FeN\u003csub\u003e4\u003c/sub\u003e-Pt led to *NH\u003csub\u003e2\u003c/sub\u003eOH formation, but its high desorption energy (3.18 eV) made *NH\u003csub\u003e2\u003c/sub\u003eOH an unlikely byproduct. Instead, *NH\u003csub\u003e2\u003c/sub\u003eOH underwent hydrogenation to *NH\u003csub\u003e2\u003c/sub\u003e + H\u003csub\u003e2\u003c/sub\u003eO, followed by an exothermic step to NH\u003csub\u003e3\u003c/sub\u003e (\u0026Delta;G = 0.23 eV).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOverall, Pt\u003csub\u003eNPs\u003c/sub\u003e enhance NORR by donating electrons to Fe, strengthening NO adsorption, and accelerating water dissociation to supply protons for NO hydrogenation. This synergistic cascade mechanism significantly boosts NH\u003csub\u003e3\u003c/sub\u003e synthesis efficiency in neutral low-concentration NO conditions (Fig. 2d).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCatalyst characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e catalysts were synthesized based on computational guidance. Fe\u003csub\u003eSAC\u003c/sub\u003e was synthesized through pyrolysis followed by acid etching, while Pt\u003csub\u003eNPs\u003c/sub\u003e were subsequently loaded onto Fe\u003csub\u003eSAC\u003c/sub\u003e by a thermal reduction method. High-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Fe\u003csub\u003eSAC\u003c/sub\u003e (Fig. 3a) revealed that isolated atomic sites are randomly dispersed on nitrogen doped carbon (NC) without observable metal clusters or particles, consistent with the X-ray diffraction (XRD, Supplementary Fig.1) result. Inductively coupled plasma optical emission spectrometer (ICP-OES) confirmed a Fe content of 0.66 wt% in Fe\u003csub\u003eSAC\u003c/sub\u003e (Table S1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn contrast, HAADF-STEM images of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e showed Pt\u003csub\u003eNPs\u003c/sub\u003e with a size of ~3 nm and a lattice distance of 0.214 nm, corresponding to the (111) crystal plane (Fig. 3b). XRD pattern further confirmed the presence of Pt\u003csub\u003eNPs\u003c/sub\u003e (Supplementary Fig.1). As illustrated in Fig. 3c, Fe\u003csub\u003eSAC\u003c/sub\u003e are densely distributed around Pt nanoparticles, and energy dispersion X-ray spectroscopy (EDX, Fig. 3d) mapping confirmed the uniform dispersion of Fe, C, and N elements, with Pt as the primary nanoparticle component. ICP-OES results showed Fe and Pt contents of 0.62 wt% and 0.84 wt%, respectively (Table S1).\u003c/p\u003e\n\u003cp\u003eTo investigate the chemical state and atomic structure, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were employed. The Fe K-edge X-ray absorption near-edge structure (XANES) spectra revealed that Fe in Fe\u003csub\u003eSAC\u003c/sub\u003e lies between +2 and +3 oxidation states (Fig. 3e). Notably, Pt incorporation induces a negative shift in the Fe K-edge, indicating a reduced Fe oxidation state, consistent with the theoretical predictions shown in Fig. 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFourier transformed (FT) \u003cem\u003ek\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e-weighted extended X-ray absorption fine structure (EXAFS) analysis (Fig. 3f) confirmed the absence of Fe clusters, as FePc, Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e exhibited a prominent Fe-N scattering peak at 1.51 \u0026Aring;.\u003csup\u003e29,30\u003c/sup\u003e EXAFS fitting curves revealed that the average coordination numbers of Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e are 4.4 and 4.2, respectively, indicating that Fe is coordinated with four nitrogen atoms (Fe-N\u003csub\u003e4\u003c/sub\u003e) in both systems. The bond lengths for Fe-N are 1.96 and 1.97 \u0026Aring;, respectively (Supplementary Fig.2 and Table S2). Additionally, wavelet transform (WT) analysis of Fe K-edge EXAFS oscillations (Supplementary Fig.3) displays a strong signal with a maximum intensity at 3.8 \u0026Aring;\u003csup\u003e-1\u003c/sup\u003e for Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e, corresponding to the Fe-N first coordination shell, which is similar to Fe\u003csub\u003eSAC\u003c/sub\u003e.\u003csup\u003e29\u003c/sup\u003e Impressively, no Fe-Fe signal was detected in WT contour plots for either Fe\u003csub\u003eSAC\u003c/sub\u003e or Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e, further confirming the atomically dispersed Fe in both catalysts.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eXPS analysis of the Pt 4f region (Fig. 3g) showed two Pt\u003csup\u003e0\u0026nbsp;\u003c/sup\u003epeaks at 71.8 (4f\u003csub\u003e7/2\u003c/sub\u003e) and 75.1 eV (4f\u003csub\u003e5/2\u003c/sub\u003e) along with two Pt\u003csup\u003e2+\u003c/sup\u003e peaks at 72.7 (4f\u003csub\u003e7/2\u003c/sub\u003e) and 76.0 eV (4f\u003csub\u003e5/2\u003c/sub\u003e) in Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e (Fig. 2g), likely due to partial surface oxidation or electron donation from adjacent Fe atoms.\u003csup\u003e31,32\u003c/sup\u003e The successful synthesis and characterization of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e confirmed its distinct structural features, including reduced Fe oxidation states upon Pt incorporation and stable Fe-N\u003csub\u003e4\u003c/sub\u003e coordination.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e in low concentration NORR\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo demonstrate the cascade reaction mechanism during the dynamic catalytic process of NORR in the Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e dual-site catalyst, \u003cem\u003ein situ\u003c/em\u003e electrochemical XAS and attenuated total reflection-infrared (ATR-IR) spectroscopies were conducted. As shown in Fe K-edge XANES spectra of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e (Fig. 4a), the white-line peak intensity increased as the applied potential decreases from open circuit potential (OCP) to -0.3 V, indicating that NO adsorption on Fe sites leads to an increase in coordination number. A shift of the adsorption edge to higher energy suggested an increased oxidation state of Fe. As the potential further decreased to -0.6 V, the white-line peak intensity diminished, implying NO consumption and reduction of Fe valence state, confirming Fe\u003csub\u003eSAC\u003c/sub\u003e as the real active sites.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe EXAFS spectra (Fig. 4b) further revealed the dynamic evolution of Fe\u0026rsquo;s local coordination. The Fe-N peak was enhanced with decreasing the applied potentials, suggesting that the intermediates adsorb on Fe sites. A notable negative shift from OCP to -0.3 V, suggested the formation of a shorter Fe-N bond due to NO adsorption. When the potential was further reduced to -0.6 V, the peak moved from 1.53 to 1.58 \u0026Aring;, signaling the occurrence of NORR and aligning well with the XANES results.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNext, \u003cem\u003ein situ\u003c/em\u003e ATR-IR spectroscopy was employed to identify the adsorbed intermediates. As shown in Fig. 4c and 4e, both Fe\u003csub\u003eSAC\u003c/sub\u003e and Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e displayed peaks corresponding to NO adsorption, including vertical mode (1774 cm\u003csup\u003e-1\u003c/sup\u003e, NO\u003csub\u003ev\u003c/sub\u003e) and bent mode (1695 cm\u003csup\u003e-1\u003c/sup\u003e, NO\u003csub\u003eb\u003c/sub\u003e).\u003csup\u003e19,33\u003c/sup\u003e The higher intensity of these peaks in Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e indicated stronger NO adsorption. With the potentials shifted from OCP to -1.0 V, the intensity of NO\u003csub\u003eb\u003c/sub\u003e peak increased, suggesting effective NO activation at Fe sites. As illustrated in Fig. 4d and 4f, the NO\u003csub\u003eb\u003c/sub\u003e peak intensity in Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e spectra is much stronger than that of Fe\u003csub\u003eSAC\u003c/sub\u003e, implying that the lower valence state of Fe site induced by introduction of Pt nanoparticles is more conducive to activate NO, in agreement with the DFT results shown in Fig. 1 and 2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompared to Fe\u003csub\u003eSAC\u003c/sub\u003e, the peak of -OH bending vibration at 1648 cm\u003csup\u003e-1\u003c/sup\u003e was strengthened in Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e spectra, indicating that the Pt nanoparticles facilitate H\u003csub\u003e2\u003c/sub\u003eO electrolysis to produce *H, which is beneficial for subsequent NO hydrogenation (Fig. 4d and 4f).\u003csup\u003e34,35\u003c/sup\u003e This was further verified by the electron paramagnetic resonance (EPR) technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a hydrogen radical (\u0026middot;H) trapping reagent.\u003csup\u003e36,37\u003c/sup\u003e As shown in Supplementary Fig.5, distinct \u0026middot;H signals were detected for Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e but absent in Fe\u003csub\u003eSAC\u003c/sub\u003e, confirming enhanced hydrogen generation. Hydrogenated intermediates NH\u003csub\u003ex\u003c/sub\u003e (1412 and 1530 cm\u003csup\u003e-1\u003c/sup\u003e) were progressively formed at lower potentials, ultimately converting to NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e (1465 cm\u003csup\u003e-1\u003c/sup\u003e).\u003csup\u003e38-40\u003c/sup\u003e Overall, these results clearly demonstrated Pt\u003csub\u003eNPs\u003c/sub\u003e served as electron donors, increasing Fe site electron density to enhance NO adsorption while simultaneously promoting water dissociation to supply protons for efficient NORR. These results clearly demonstrated that a cascade reaction mechanism occurs on the dual-site catalyst, Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e, thereby promoting NORR, see Fig. 4g.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNORR performance evaluation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe NORR performance was evaluated in 0.5 M K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte, using an air-tight H cell. Prior to electrolysis, high-purity Ar was purged into the electrolyte to remove residual oxygen. As shown in Fig. 5a, the linear sweep voltammetry (LSV) curves revealed a significant increase in current density for Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e in 1 vol% NO atmosphere compared to Ar-saturated conditions, confirming effective NO reduction on the catalyst surface. Compare to Fe\u003csub\u003eSAC,\u003c/sub\u003e Pt\u003csub\u003eNPs\u003c/sub\u003e/NC and NC, the Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e showed the largest current density gap, indicating superior NORR activity (Supplementary Fig.6).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAs depicted in Fig. 5b, the NH\u003csub\u003e3\u003c/sub\u003e yield rate and FE of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e increase steadily with applied potentials from -0.4 to -0.6 V, reaching the maximum values of 709.7 \u0026mu;g h\u003csup\u003e-1\u003c/sup\u003e mg\u003csub\u003ecat.\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e and 90.3% at -0.6 V, outperforming previously reported NORR catalysts (Table S4). NH\u003csub\u003e3\u003c/sub\u003e quantification via colorimetric method (Supplementary Fig.7) and nuclear magnetic resonance (NMR) spectroscopy (Supplementary Fig.8) yielded consistent results, ensuring measurement accuracy (Supplementary Fig.14). However, at the applied potentials beyond -0.6 V, NORR performance of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e declined due to the competing HER. In comparison, Fe\u003csub\u003eSAC\u003c/sub\u003e obtained its highest NORR performance at -0.7 V with a NH\u003csub\u003e3\u003c/sub\u003e yield of 444.2 \u0026mu;g h\u003csup\u003e-1\u003c/sup\u003e mg\u003csub\u003ecat.\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e and FE of 56.6% (Fig. 5c and S9), while Pt\u003csub\u003eNPs\u003c/sub\u003e/NC and bare NC exhibited negligible NORR activity (Fig. 5c).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDFT and \u003cem\u003ein-situ\u003c/em\u003e electrochemical experiments clearly verified that Pt\u003csub\u003eNPs\u003c/sub\u003e served as electron donors, increasing the electron density at the Fe single-atom site to promote NO adsorption, while facilitating water dissociation for proton supply and promoting NO hydrogenation. This dual role enabled efficient NO-to-NH\u003csub\u003e3\u003c/sub\u003e conversion with high activity and selectivity by activating the cascade reaction mechanism.\u003c/p\u003e\n\u003cp\u003eTo validate that NH\u003csub\u003e3\u003c/sub\u003e originated from NO reduction, control experiments were conducted under three conditions: (1) electrolysis at -0.6 V in Ar-saturated electrolyte, (2) testing at OCP in NO-saturated electrolyte, and (3) testing in NO-saturated electrolyte with bare carbon paper (CP) as work electrode (Fig. 5d). Only negligible NH\u003csub\u003e3\u003c/sub\u003e was detected in these cases, confirming that NH\u003csub\u003e3\u003c/sub\u003e formation on Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e exclusively results from NO reduction. \u003cstrong\u003eAdditionally, an isotope labeling experiment was performed to exclude the possibility of nitrogen contamination. The laboratory-produced \u003csup\u003e15\u003c/sup\u003eNO was used as the feeding gas for NORR at -0.6 V for 1 h. As shown in Fig. 5e, the NMR analysis conclusively verified that the generated NH\u003csub\u003e3\u003c/sub\u003e is originated from NO.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eElectrocatalyst stability is crucial for long-term energy conversion and storage. Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e demonstrated excellent durability, maintaining stable NH\u003csub\u003e3\u003c/sub\u003e yield and FE over ten consecutive cycles (Fig. 5f). A long-term stability test (\u0026gt;70 h, Supplementary Fig.15) showed no significant decline in current density, further confirming its robust electrochemical stability. Post-reaction characterization revealed minor catalyst changes: XRD pattern showed weakened Pt diffraction peaks, suggesting partial Pt dissolution (Supplementary Fig.16). ICP analysis detected trace amounts of Pt in the electrolyte post-NORR (Table S3). XANES analysis exhibited a slight increase in Fe valence state after NORR test (Supplementary Fig.17a). EXAFS spectra revealed no Fe-Fe bond formation, confirming Fe remains atomically dispersed (Supplementary Fig.17b).\u003c/p\u003e\n\u003cp\u003eTo mitigate NO mass transport limitations due to its low solubility (~1.92 mmol L\u003csup\u003e-1\u003c/sup\u003e atm\u003csup\u003e-1\u003c/sup\u003e in water at 25 \u0026deg;C), NORR was conducted in a membrane electrode assembly (MEA) electrolyzer .\u003csup\u003e41,42\u003c/sup\u003e Compared to H-cell, the MEA significantly enhanced current density, suggesting improved NO utilization (Fig. 5g). As shown in Fig. 5h, increasing the applied cell voltage from 1.2 to 1.6 V leads to higher NH\u003csub\u003e3\u003c/sub\u003e yield and FE. Notably, Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e achieved a record-breaking NH\u003csub\u003e3\u003c/sub\u003e yield of 3123.8\u0026nbsp;\u0026mu;g h\u003csup\u003e-1\u003c/sup\u003e mg\u003csub\u003ecat.\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e and FE of 94.5% at 1.6 V (Fig. 5h), surpassing all previously reported NORR catalyst even tests under high NO concentration (Fig. 5i).\u003c/p\u003e\n\u003cp\u003eTo explore alternative metal nanoparticles, Au\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e was synthesized for NO-to-NH\u003csub\u003e3\u003c/sub\u003e conversion. TEM images (Supplementary Fig.18) and XRD patterns (Supplementary Fig.19) clearly verified that successful Au nanoparticle deposition. The obtained Au\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e achieved optimal NH\u003csub\u003e3\u003c/sub\u003e yield of 595.4 \u0026mu;g h\u003csup\u003e-1\u003c/sup\u003e mg\u003csub\u003ecat.\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e and FE of 78.9% at -0.5 V, further demonstrating the versatility of metal-modified Fe\u003csub\u003eSAC\u003c/sub\u003e systems.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, we present an electron-donating particle-mediated strategy that integrates Pt\u003csub\u003eNPs\u003c/sub\u003e as the electron donor into the Fe\u003csub\u003eSAC\u003c/sub\u003e electrocatalyst to construct dual-active-site architectures, thereby enhancing NO adsorption while promoting water dissociation and NO hydrogenation for significantly improving neutral NORR at low NO concentration (1 vol%). \u003cem\u003eIn situ\u003c/em\u003e spectro-electrochemical experiments, coupled with theoretical calculations, confirmed that the Pt nanoparticles serve as electron donors, increasing the electron density at the Fe single-atom site to promote NO adsorption, while facilitating water dissociation to provide protons and thus reducing the activation energy of NO hydrogenation. The synergistic interplay between these dual sites enables a cascade reaction mechanism achieving a superior NORR performance with a NH\u003csub\u003e3\u003c/sub\u003e FE up to 90.3% and a high NH\u003csub\u003e3\u003c/sub\u003e yield rate of 709.7 \u0026micro;g cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under 1 vol% NO concentration at -0.6 V, outperforming Fe\u003csub\u003eSAC\u003c/sub\u003e (NH\u003csub\u003e3\u003c/sub\u003e yield rate: 444.2 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e, FE: 56.6%) and prior high-NO-concentration systems. Notably, in a MEA electrolyzer, the system achieved a record-breaking NH\u003csub\u003e3\u003c/sub\u003e yield of 3123.8 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e. This work not only offers an attractive earth-abundant nanocatalyst for NH\u003csub\u003e3\u003c/sub\u003e electrosynthesis at low NO concentrations, but also provides a novel methodology for designing superior electrocatalytic NORR systems through a dual-active-site strategy, paving the way for large scale NH\u003csub\u003e3\u003c/sub\u003e electrosynthesis.\u003c/p\u003e \u003c/div\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eChemicals\u003c/h2\u003e \u003cp\u003eKetjen black ecp600JD (KJ), Nafion and carbon paper (CP) were purchased from Suzhou Sinero Thechology Co., Ltd (Suzhou, China). Sodium hydroxide (NaOH), sodium nitrite (NaNO\u003csub\u003e2\u003c/sub\u003e), p-aminobenzenesulfonic acid (pAA, C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eNO\u003csub\u003e3\u003c/sub\u003eS) m-phenylenediamine (mPDA, C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003e) ammonium persulfate ((NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e), iron chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), polyvinylpyrrolidone (PVP), sodium hypochlorite (NaClO) and ethylene glycol (EG) were obtained from Aldrich Chemical Reagent Co., Ltd. (Shanghai, China). Chloroplatinic acid hexahydrate (H\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), gold chloride trihydrate (HAuCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO), salicylic acid (C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), trisodium citrate dihydrate (Na\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO), sodium nitroferricyanide (III) dihydrate (Na\u003csub\u003e2\u003c/sub\u003eFe(CN)\u003csub\u003e5\u003c/sub\u003eNO\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO), dimethyl sulfoxide (DMSO-\u003cem\u003ed\u003c/em\u003e6), ammonium chloride (\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eNH\u003csub\u003e4\u003c/sub\u003eCl, \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eNH\u003csub\u003e4\u003c/sub\u003eCl), sodium borohydride (NaNH\u003csub\u003e4\u003c/sub\u003e), sodium nitrite (Na\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003eNO\u003csub\u003e2\u003c/sub\u003e) were bought from Macklin Chemical Reagent Co., Ltd. (Shanghai, China). Fe powder, potassium thiocyanate (KSCN) and hydrochloric acid (HCl) were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the reagents were used as received. The water used throughout all experiments was purchased from Wahaha Group Co., Ltd. (Hangzhou, China).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePreparation of NC\u003c/h3\u003e\n\u003cp\u003e1.0 g of KJ was dispersed in 30 mL H\u003csub\u003e2\u003c/sub\u003eO and sonicated in an ice bath for 2 h to labeled A1. Separately, 0.74 g pAA was dissolved in 30 mL H\u003csub\u003e2\u003c/sub\u003eO. To this solution, 9 mL of 1 M NaOH, 4 mL of 1 M NaNO\u003csub\u003e2\u003c/sub\u003e and 21 mL of 1 M HCl were added to prepare the diazo salt (labeled A2), maintain the reaction at 0\u0026deg;C. Subsequently, the A2 was mixed with A1. To initiate surface grafting of the diazonium salt, 0.7 g of reduced Fe powder was introduced. Afterward, 25 mL concentrated HCl, 7.6 g of mPDA, 23 mL of 1 M FeCl\u003csub\u003e3\u003c/sub\u003e and 70 mL of 2 M (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e solution were added, and the reaction was allowed to react overnight. After filtration, the product was washed with water for 3 times and vacuum drying overnight to yield the NC precursor.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Fe\u003csub\u003eSAC\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003e0.6 g of the NC precursor was ultrasonically dispersed in 30 mL H\u003csub\u003e2\u003c/sub\u003eO, followed by the addition of 1.8 mL of 1 M FeCl\u003csub\u003e3\u003c/sub\u003e and 6 mL of 1 M KSCN. The solvent was removed by rotary evaporation, and the residue was heated to 950\u0026deg;C for 1 h under an Ar atmosphere. The obtained black powder was dispersed in 50 mL of 1 M HCl solution overnight at 80\u0026deg;C. Then, the powder was washed with water 3 times, and drying overnight. Finally, the dried powder was heated at 950\u0026deg;C for 3 h in an Ar atmosphere to yield Fe\u003csub\u003eSAC\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003e100 mg Fe\u003csub\u003eSAC\u003c/sub\u003e was dispersed in 20 mL of EG. Next, 5 mg H\u003csub\u003e2\u003c/sub\u003ePtCl\u003csub\u003e6\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO was dispersed in 20 mL of EG and then dripped into Fe\u003csub\u003eSAC\u003c/sub\u003e. The obtained suspension was stirred for 2 h at room temperature and then treated at 160\u0026deg;C for 90 min. Afterward, the final product was washed 3 times and dried overnight. The Pt\u003csub\u003eNPs\u003c/sub\u003e was synthesized by replacing the Fe\u003csub\u003eSAC\u003c/sub\u003e to NC.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Au\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003e100 mg of Fe\u003csub\u003eSAC\u003c/sub\u003e and 10 mg of PVP were dispersed in 30 mL H\u003csub\u003e2\u003c/sub\u003eO. Then, 400 \u0026micro;L of a 10 mg/mL HAuCl\u003csub\u003e4\u003c/sub\u003e solution was added dropwise, followed by 100 mg of NaNH\u003csub\u003e4\u003c/sub\u003e dissolved in 20 mL H\u003csub\u003e2\u003c/sub\u003eO to reduce HAuCl\u003csub\u003e4\u003c/sub\u003e. The mixture was stirred for 10 min at room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical measurements\u003c/h2\u003e \u003cp\u003eElectrochemical measurements were performed with a CHI660E electrochemical station (CH Instruments, Inc., Shanghai) in a H-cell under ambient condition, which was separated by Nafion 211 membrane. The Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e, Ag/AgCl and graphite rod acted as the working electrode, reference electrode and counter electrode, respectively. The reference electrode was calibrated to the reversible hydrogen electrode (RHE) scale in all measurements using the following equation: E (RHE)\u0026thinsp;=\u0026thinsp;E (Ag/AgCl) + (0.059 pH\u0026thinsp;+\u0026thinsp;0.197) V. High purity Ar gas (99.999%) was bubbled into cathode chamber with the flow rate of 30 sccm for 30 min to removal oxygen before NORR. Then, the low-concentration NO (1% v/v) was firstly washed by 4 M KOH and then fed at 30 sccm for 30 min to saturate the electrolyte, maintain a constant flow during the electrochemical tests. For NORR tested in MEA, the RuO\u003csub\u003e2\u003c/sub\u003e supported on nickel foam (RuO\u003csub\u003e2\u003c/sub\u003e/NF) as anode tested in 1 M KOH, while Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e was used as the cathode for NORR and the tail gas was absorbed by 1 M HCl.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of NH\u003csub\u003e3\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eThe produced NH\u003csub\u003e3\u003c/sub\u003e was quantified by the indophenol blue method\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e and NMR. For indophenol blue method, standard NH\u003csub\u003e3\u003c/sub\u003e solution with a series of concentrations were used to calibrated the concentration-absorbance curves. The fitting curve (y\u0026thinsp;=\u0026thinsp;0.3435x\u0026thinsp;+\u0026thinsp;0.05843, R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9999) showed good linear relation of absorbance value with NH\u003csub\u003e3\u003c/sub\u003e concentration. All electrolytes were diluted 10 times before testing unless otherwise specified. For \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR measurements, the electrolyte after electrolysis was diluted 2 times with 1 M HCl to adjust the pH to acidic. Then, 100 mL DMSO-d6 was added in 500 \u0026micro;L acidified electrolyte.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of FE and NH\u003csub\u003e3\u003c/sub\u003e Yield\u003c/h2\u003e \u003cp\u003eThe FE for NH\u003csub\u003e3\u003c/sub\u003e synthesis was calculated as the amount of electric charge used for NH\u003csub\u003e3\u003c/sub\u003e production divided by the total charge passed through the electrodes during electrolysis. The total amount of NH\u003csub\u003e3\u003c/sub\u003e produced was measured using colorimetric methods. The FE could be calculated as follows:\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eFE\u0026thinsp;=\u0026thinsp;3 \u0026times; F \u0026times; [NH\u003csub\u003e3\u003c/sub\u003e] \u0026times; V / (17 \u0026times; Q) \u0026times;100% (1)\u003c/h2\u003e \u003cp\u003eNH\u003csub\u003e3\u003c/sub\u003e yield was calculated using the following equation:\u003c/p\u003e \u003cp\u003eNH\u003csub\u003e3\u003c/sub\u003e yield = [NH\u003csub\u003e3\u003c/sub\u003e] \u0026times; V / (m\u003csub\u003ecat\u003c/sub\u003e. \u0026times; t) (2)\u003c/p\u003e \u003cp\u003ewhere F is the Faraday constant, [NH\u003csub\u003e3\u003c/sub\u003e] is the measured NH\u003csub\u003e3\u003c/sub\u003e concentration, V is the volume of the electrolyte in the cathodic chamber, Q is the total quantity of applied electricity; t is the reduction time; m\u003csub\u003ecat\u003c/sub\u003e. is the loaded mass of catalyst on carbon paper.\u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrochemical\u003c/b\u003e \u003cb\u003ein situ\u003c/b\u003e \u003cb\u003eATR-IR measurements\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe \u003cem\u003ein situ\u003c/em\u003e electrochemical ATR-IR measurements were conducted on a Nicolet iS50 FT-IR spectrometer with a liquid nitrogen-cooled MCT-A detector. The Si prism loaded with catalyst, Pt plate and Ag/AgCl were used as the working electrode, counter electrode and reference electrode, respectively, with 0.5 M K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e as electrolyte. During the process of tests, 1% NO was bubbled into the electrolyte with the flow rate of 10 sccm. Prior to testing, the Si prism was coated with Au film. The Si prism was first polished by 100 nm Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. Next, the Si prism was soaked in a piranha solution for 30 min to removal organic contaminants. Then, the reflecting surface was immersed in a mixture of the Au plating solution (5.75 mM NaAuCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;0.025 M NH\u003csub\u003e4\u003c/sub\u003eCl\u0026thinsp;+\u0026thinsp;0.075 M Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;0.025 M Na\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;0.026 M NaOH) and a 2 wt % HF solution at 60\u0026deg;C for 5 min. Afterward, the Au film was rinsed with deionized water and dried with N\u003csub\u003e2\u003c/sub\u003e. \u003cem\u003eIn situ\u003c/em\u003e ATR-IR spectra were collected at OCP and different applied potentials.\u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrochemical\u003c/b\u003e \u003cb\u003ein situ\u003c/b\u003e \u003cb\u003eXAFS measurements\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe \u003cem\u003ein situ\u003c/em\u003e XAFS measurements were conducted in the fluorescence mode using a home-made electrochemical cell. The Pt\u003csub\u003eNPs\u003c/sub\u003e/Fe\u003csub\u003eSAC\u003c/sub\u003e, Ag/AgCl and graphite rod were used as working electrode, reference electrode and counter electrode, respectively. Relevant measurements were conducted in NO-saturated 0.5 M K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte. The XAS spectra were recorded at OCP and different applied potentials.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eComputation and model details\u003c/h2\u003e \u003cp\u003eAll simulations were carried out using density functional theory as implemented in the GPAW software\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e,\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e version 19.8.1. The exchange-correlation effects were accounted for using the BEEF-vdW-functional, which combines the generalized gradient approximation with the Langreth-Lundqvist van der Waals-functional to achieve accurate adsorption energies. A 2\u0026times;2\u0026times;1 k-point mesh was used and all the calculations were spin-polarized. To model the solvent at the electrochemical interface, a hybrid implicit/explicit approach was employed, where 40 explicit water molecules surrounded the electrode surface, and the remaining water was modeled using the SCMVD\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e dielectric continuum model. The positions and orientations of the explicit water molecules were optimized using the minima hopping global optimization method\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e as implemented in ASE.\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe free energies of the reaction intermediates were defined as by Δ\u003cem\u003eG\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Δ\u003cem\u003eE\u003c/em\u003e\u0026thinsp;+\u0026thinsp;Δ\u003cem\u003eZPE\u003c/em\u003e \u0026ndash; TΔ\u003cem\u003eS\u003c/em\u003e, where Δ\u003cem\u003eE\u003c/em\u003e, Δ\u003cem\u003eZPE\u003c/em\u003e, \u003cem\u003eT\u003c/em\u003e, and Δ\u003cem\u003eS\u003c/em\u003e represent the reaction energy, zero-point energy, temperature (298.15 K), and the entropy, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eEnhanced Sampling\u003c/h2\u003e \u003cp\u003eThe slow growth sampling approach\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e,\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e in the constrained molecular dynamics simulation method can be used to describe the kinetic energy barrier in the reaction process by setting a suitable collective variable (CV, ξ ), which changes from state 1 to state 2 at a certain transformation rate\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mathop \\xi \\limits^{ \\cdot }\\)\u003c/span\u003e\u003c/span\u003e. The work performed throughout the entire process from state 1 to state 2 can be calculated using the following formula:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(w_{{state1 \\to state2}}^{{}}=\\int_{{\\xi (state1)}}^{{\\xi (state2)}} {\\left( {\\frac{{\\partial V(q)}}{{\\partial \\xi }}} \\right)} \\cdot \\mathop \\xi \\limits^{ \\cdot } dt\\)\u003c/span\u003e \u003c/span\u003e \u003c/p\u003e \u003cp\u003eWhere V(q) represents the free energy, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{{\\partial V(q)}}{{\\partial \\xi }}\\)\u003c/span\u003e\u003c/span\u003e is calculated using the SHAKE algorithm. When approaching the infinitesimal limit\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mathop \\xi \\limits^{ \\cdot }\\)\u003c/span\u003e\u003c/span\u003e, the work \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(w_{{state1 \\to state2}}^{{}}\\)\u003c/span\u003e\u003c/span\u003e required from state 1 to state 2 corresponds to the difference in free energy. In the SG sampling method, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\partial \\xi\\)\u003c/span\u003e\u003c/span\u003e is selected to 0.0005\u0026Aring;, and the final reaction's free energy barrier can be obtained by aggregating the free energy distribution diagram.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by National Natural Science Foundation of China (Nos. 22072015, 21927811, and 52202214), Natural Science Foundation of Sichuan Province (No. 2023NSFSC0954), China National Postdoctoral Program for Innovative Talents (No. BX2021053), and China Postdoctoral Science Foundation (No. 2021M700680). The authors thank BL11B beamline of the Shanghai Synchrotron Radiation Facility (SSRF) for providing the XAFS beamtime. The numerical calculations in this paper have been done on Computing Center in Xi\u0026apos;an.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eT.W. and X.G. conceived the idea, wrote the original draft, and collected and analyzed the data. X.G. and T.W. performed the DFT calculations and experiments. C.M. provided the HAADF-STEM characterization. M.L. supervised this project. All authors contributed and reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence and requests for materials should be addressed to M.L.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eButtignol F et al (2024) Iron-catalysed cooperative redox mechanism for the simultaneous conversion of nitrous oxide and nitric oxide. Nat Catal 7:1305\u0026ndash;1315\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhosh P et al (2024) Get to Know NO. Nat Chem 16:1382\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHwang J et al (2021) Regulating oxygen activity of perovskites to promote NO\u003csub\u003ex\u003c/sub\u003e oxidation and reduction kinetics. 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Lett.\u003c/em\u003e 78, 2690\u0026thinsp;\u0026ndash;\u0026thinsp;2693\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6497629/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6497629/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrosynthesis of NH\u003csub\u003e3\u003c/sub\u003e from low-concentration NO (NORR) in neutral media offers a sustainable nitrogen fixation strategy but is hindered by weak NO adsorption, slow water dissociation, and sluggish hydrogenation kinetics. Herein, we propose a new strategy that successfully overcomes these limitations through using an electron-donating motif to modulate NO-affinitive catalysts, thereby creating dual active site with synergistic functionality. Specifically, we integrate electron-donating nanoparticles into a Fe single-atom catalyst (Fe\u003csub\u003eSAC\u003c/sub\u003e), where Fe sites ensure strong NO adsorption, while electron-donating motifs promote water dissociation and NO hydrogenation. \u003cem\u003eIn situ\u003c/em\u003e X-ray absorption spectroscopy (XAS), \u003cem\u003ein situ\u003c/em\u003e attenuated total reflection-infrared spectroscopy (ATR-IR), and theoretical calculations reveal that electron-donating motifs increase Fe site electron density, strengthening NO adsorption. Additionally, these motifs also promote water dissociation, supplying protons to lower the NO hydrogenation barrier. This synergistic interplay enables a cascade reaction mechanism, delivering a remarkable Faradaic efficiency (FE) of 90.3% and a NH\u003csub\u003e3\u003c/sub\u003e yield rate of 709.7 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e under 1.0 vol% NO in neutral media, outperforming pure Fe\u003csub\u003eSAC\u003c/sub\u003e (NH\u003csub\u003e3\u003c/sub\u003e yield rate: 444.2 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e, FE: 56.6%) and prior high-NO-concentration systems. Notably, a record NH\u003csub\u003e3\u003c/sub\u003e yield of 3123.8 \u0026micro;g h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e mg\u003csub\u003ecat\u003c/sub\u003e.\u003csup\u003e\u0026minus;1\u003c/sup\u003e was achieved in a membrane electrode assembly (MEA) electrolyzer under a 1.0 vol% NO. This work establishes a new paradigm in NORR by simultaneously enhancing NO adsorption, water dissociation, and hydrogenation kinetics, providing a scalable route for efficient NH\u003csub\u003e3\u003c/sub\u003e electrosynthesis from dilute NO sources.\u003c/p\u003e","manuscriptTitle":"Electrosynthesis of NH3 from low-concentration NO on cascade dual-site catalysts in neutral media","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-24 04:52:51","doi":"10.21203/rs.3.rs-6497629/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7fc0abed-64a2-44f1-9204-0dab144aa878","owner":[],"postedDate":"April 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":47601849,"name":"Physical sciences/Chemistry/Electrochemistry/Electrocatalysis"},{"id":47601850,"name":"Physical sciences/Materials science/Nanoscale materials/Electronic properties and materials"}],"tags":[],"updatedAt":"2025-09-27T07:10:13+00:00","versionOfRecord":{"articleIdentity":"rs-6497629","link":"https://doi.org/10.1038/s41467-025-63365-7","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-09-26 04:00:00","publishedOnDateReadable":"September 26th, 2025"},"versionCreatedAt":"2025-04-24 04:52:51","video":"","vorDoi":"10.1038/s41467-025-63365-7","vorDoiUrl":"https://doi.org/10.1038/s41467-025-63365-7","workflowStages":[]},"version":"v1","identity":"rs-6497629","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6497629","identity":"rs-6497629","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}