Salt-Free Glycine Electrosynthesis via C−N Coupling Boosted by the Lattice Strain in Atomically Thin p-Block Bismuthene

Salt-Free Glycine Electrosynthesis via C−N Coupling Boosted by the Lattice Strain in Atomically Thin p-Block Bismuthene | 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 Salt-Free Glycine Electrosynthesis via C−N Coupling Boosted by the Lattice Strain in Atomically Thin p-Block Bismuthene Zhenguo Huang, Minghong Huang, Sheng-Hua Zhou, Lei Jiao, Qi-Long Zhu, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7471908/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Electrochemical C − N coupling using simple inorganic feedstocks offers a sustainable route to valuable organonitrogen compounds such as amino acids. Herein, we present an atomically-thin and acid-resistant p -block bismuthene (Bi-ene) derived via the reconstruction of a Bi-based metal − organic framework, where the enriched atomic misarrangement induces significant lattice strain that modulates the local electronic structure of the resultant Bi-ene, significantly boosting its electrocatalytic activity. Such defective Bi-ene exhibits an exceptional electrocatalytic performance for reductive C − N coupling in a salt-free acidic system, achieving a remarkable Faradaic efficiency (FE) of 95.7% and an ultrahigh yield rate of 1161 µmol cm − 2 h − 1 for NH 2 OH generation via the nitrate reduction reaction (NtrRR). Further, the efficient co-reduction of HNO 3 and oxalic acid (OA) over Bi-ene simultaneously generates NH 2 OH and glyoxylic acid (GX) respectively, which undergo effective C − N coupling to produce glycine with a high yield of 455.4 µmol cm⁻ 2 h⁻ 1 . Moreover, the Bi-ene demonstrates stable performance for over 120 hours at an industrial-relevant current density of 200 mA cm − 2 . Operando spectroscopy and calculations reveal that the strain in lattice-distorted Bi-ene optimizes the intermediate adsorption through modulating local electronic structure and thus enhances the efficacy for glycine electrosynthesis. Physical sciences/Chemistry/Electrochemistry/Electrocatalysis Physical sciences/Energy science and technology Electrocatalytic C-N coupling Amino acids Lattice strain Bismuthene Nitrate reduction reaction Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Glycine, the simplest amino acid, plays a pivotal role in numerous metabolic pathways and holds significant value in various industrial applications, such as a key precursor in pharmaceutical manufacturing, chemical synthesis, and biochemical formulations. 1 However, traditional methods of glycine synthesis, such as the Strecker synthesis or enzymatic pathways, often involve toxic reagents or limited efficiency, thereby restricting their sustainability and scalability. 2 , 3 , 4 Recently, renewables-powered electrochemical strategies have emerged as a promising green route for amino acid synthesis. 5 Specifically, the electrocatalytic reforming of abundant inorganic nitrogen sources and carbon-based feedstocks into C − N coupled products offers a sustainable and scalable pathway. 6 , 7 This approach enables direct C − N bond formation under mild conditions, thereby not only reducing energy input and chemical waste but also contributing to the remediation of excess carbon and nitrogen in the environment. 8 , 9 , 10 Electrosynthesis of amino acid commonly involves a nucleophilic substitution reaction, wherein NH 2 OH condenses with an electrophilic carbon center to generate a key oxime intermediate that serves as a precursor to C − N bond formation. 11 , 12 , 13 Although nitrate salts are commonly used to provide nitrogen, the presence of alkali metal cations (e.g., Na⁺, K⁺) can interfere with the local electric field and compete for active sites on the catalyst surface, affecting the selectivity for key intermediates such as NH 2 OH. 14 , 15 In contrast, HNO 3 offers a salt-free alternative that simplifies the electrolyte composition and enhances NH 2 OH production. The inherently acidic environment of HNO 3 eliminates the need for external proton sources, thereby facilitating proton-coupled electron transfer steps that are essential for the selective reduction of NO 3 − to NH 2 OH. 16 , 17 Additionally, the high solubility and ionic conductivity of HNO 3 enhance mass transport and charge transfer kinetics during electrolysis, contributing to the overall system efficiency. Importantly, HNO 3 can be sustainably synthesized from abundant atmospheric nitrogen and water via a hybrid plasma–electrolysis process. 18 On the carbon side, aldehydes and ketones such as pyruvic acid and glyoxylic acid (GX) are often used as carbonyl sources in amino acid synthesis. 19 , 20 , 21 , 22 However, these feedstocks necessitate energy intensive separation-purification processes. In contrast, utilizing upstream carbon-based molecules as direct reactants could provide a more cost-effective pathway for amino acid production by simplifying the chemical processes involved. Oxalic acid (OA), a C 2 product derived from CO 2 electroreduction, 23 , 24 , 25 is regarded a viable and cost-effective platform molecule that can be selectively reduced into electrophilic GX, 26 , 27 which could react with NH 2 OH to form a crucial oxime intermediate. 28 , 29 , 30 Hence, the electrochemical co-reduction of OA and HNO 3 holds great promise for the sustainable and integrated synthesis of glycine. However, this pathway, to the best of our knowledge, has not been reported, and its realization remains challenging due to the complexity and competition among multiple reactions. Specifically, the OA reduction reaction (OARR) is a two-electron process, while NtrRR requires a six-electron reduction to form NH 2 OH. Achieving the simultaneous and selective activation of both pathways on a single catalyst is inherently difficult, owing to their distinct kinetic barriers and thermodynamic demands. Therefore, recent catalysts typically suffer from either low FE and inadequate current density, leading to a low yield rate of glycine. 30 , 31 To address this, a bifunctional catalyst that enables NtrRR and OARR to simultaneously form NH 2 OH and GX, respectively, is highly desired. This dual catalytic functionality is crucial for promoting in situ C − N coupling between NH 2 OH and GX intermediates, thus enabling efficient glycine production within the cathodic compartment. Among various catalytic materials, p -block metals have shown significant potential for electrocatalytic organosynthesis due to their low cost, high stability, and minimal hydrogen evolution reaction (HER) activity. 32 , 33 As a representative p -block metal, bismuth offers a low overpotential for NtrRR and can stabilize key intermediates in both nitrogen and carbon reduction pathways, making it a promising candidate for catalytic C − N bond formation. 18 , 34 Despite their potential, Bi-based catalysts have been rarely explored for selective amino acid electrosynthesis, primarily due to their limited intrinsic activity and site accessibility, which significantly constrain their electrocatalytic performance. Structural engineering has been widely used to tune the properties of Bi electrocatalysts and improve their activity and selectivity. Previous studies have demonstrated that ultrathin Bi nanostructures enable high electrocatalytic efficiency due to enhanced active site exposure. 32 , 35 Furthermore, introducing lattice defects into Bi nanolayers would further improve the intrinsic activity, as these defects modulate the electronic structures, optimize adsorption energies of key intermediates, and create additional active sites for catalytic reactions. However, the generation of abundant lattice defects within the Bi nanolayers remains challenging because of its intrinsic crystallographic stability. Compared to conventional inorganic precursors, Bi-based metal − organic frameworks (MOFs) offer highly tunable chemical environments and facile structural reconstruction owing to the weak coordination between Bi centers and organic linkers. The electro-reductive reconstruction of a Bi-based MOF precursor can induce substantial atomic rearrangement via dynamic removal of the organic linkers to yield ultrathin metallic Bi layers enriched with structural defects. Herein, we report a highly efficient electrochemical C − N coupling approach for salt-free glycine synthesis through the co-reduction of OA and HNO 3 , which is catalyzed by atomically thin bismuthene (Bi-ene) with abundant lattice distortion, reconstructed from a Bi-based MOF (Scheme 1 ). Specifically, the defective Bi-ene nanosheets (NSs) exhibit exceptional performance for the electrosynthesis of NH 2 OH via NtrRR, delivering a high yield rate of 1161 µmol cm − 2 h − 1 at − 1.1 V vs. Ag/AgCl, as well as excellent FE NH2OH exceeding 90% with high selectivity (> 95%) over a broad potential range. Further, in the co-reduction of HNO 3 and OA, Bi-ene effectively balances the different electron requirements (6 vs. 2 e⁻) by the two reduction reactions, enabling the efficient coupling of in situ generated NH 2 OH and GX for glycine production under acidic conditions, with a remarkable FE and yield rate of 68.2% and 455 µmol cm⁻ 2 h⁻ 1 , respectively. Operando characterizations combined with DFT calculations reveal that the atomic misarrangement-induced lattice strain in Bi-ene modulates the local electronic structure, creating abundant and highly active sites and a favorable adsorption environment that synergistically promote NH 2 OH formation and consequent glycine synthesis. Moreover, Bi-ene exhibits excellent substrate versatility, accommodating a wide range of α-keto acid skeletons for the electrosynthesis of C − N bond-containing compounds. This work highlights the significant potential of electrosynthesis that is salt-free, sustainable and cost-effective. Results and Discussion Characterizations The Bi-ene electrocatalyst was obtained via a two-step process (Fig. 1 a). First, the rod-shaped Bi-MOF, the pre-catalyst with high surface area, was prepared using a solvothermal method (Supplementary Figs. S1-3). 36 , 37 The X-ray diffraction (XRD) analysis confirms that the as-synthesized MOF adopts CAU-17 structure (Supplementary Fig. S1 ). Subsequently, an electroreduction treatment was performed on Bi-CAU-17 to in situ generate Bi-ene nanosheets (NSs). 32 The XRD patterns confirm the complete transformation from Bi-CAU-17 to metallic Bi-ene, where the diffraction peaks associated with Bi-CAU-17 disappeared with the appearance of new peaks at 27.2°, 37.9°, and 39.6° corresponding to the (012), (104), and (110) planes of metallic bismuth (Supplementary Fig. S4). Scanning electron microscope (SEM) images show that the electrochemically generated Bi-ene NSs exhibit a graphene-like ultrathin morphology without significant aggregation (Fig. 1 b and Supplementary Fig. S5). Atomic force microscopy (AFM) measurements show that the thickness of the Bi-ene NSs ranges from 1.43 to 1.54 nm (Fig. 1 c), corresponding to approximately 4 atomic layers. Meanwhile, X-ray photoelectron spectroscopy (XPS) spectra clearly reveal the emergence of a new pair of Bi 0 signals following the electrochemical reconstruction (Fig. 1 d), providing further evidence for the transformation of Bi-CAU-17 to Bi-ene, which is in agreement with the XRD results. Further structural insight was gained from TEM analysis, which confirms the two-dimensional (2D) nature of the Bi-ene NSs (Fig. 1 e). As shown in Fig. 1 f, the high-resolution TEM (HR-TEM) images of the representative Bi-ene NSs reveal pronounced atomic misarrangements that lead to high-density lattice distortions and local strain. In addition, the lattice distortion can be easily observed in a single Bi-ene NS (Supplementary Fig. S6), demonstrating that the electrochemical reconstruction of the Bi-CAU-17 precursor effectively generates substantial atomic structural defects. The inverse fast Fourier transform (FFT) image uncovers the lattice distortion, as marked with “T” symbols in Figs. 1 g and 1 h, which arises from facet mismatch. Additionally, the FFT pattern in Fig. 1 i displays chain-like diffraction features, further confirming the presence of planar defects. 38 , 39 The measured interplanar spacing of 0.33 nm corresponds to the (012) plane of rhombohedral Bi, indicating that the Bi-ene NSs retain the main crystallinity (Fig. 1 j). These results provide strong evidence that the electrochemical reconstruction of Bi-CAU-17 not only produces 2D metallic Bi with atomically thin nanosheet structure but also induces extensive lattice strain associated with structural defects. Compared to the well-ordered lattice, such strained structural disorder is expected to modulate the electronic properties and enhances the catalytic performance of the resultant Bi-ene NSs. 40 , 41 , 42 The energy dispersive X-ray spectrometry (EDX) images confirm the homogeneous distribution of Bi and O elements throughout the nanosheet architecture (Fig. 1 k). Individual NtrRR and OARR performance evaluation Given the critical role of NH 2 OH generated from NtrRR in facilitating C − N coupling for amino acid synthesis, the electrocatalytic NtrRR performance of Bi-ene electrodes was first evaluated in an H-cell under Ar atmosphere, using 0.5 M HCl and 0.5 M HNO 3 as the catholyte (Fig. 2 a). As shown by the linear sweep voltammetry (LSV) curves, the current density in the HNO 3 -containing electrolyte is significantly higher compared to that in pure HCl electrolyte, indicating the effective electroreduction of HNO 3 on the Bi-ene catalyst (Supplementary Fig. S7). Moreover, compared to NaNO 3 , the use of HNO 3 led to a substantially higher cathodic current density, suggesting the important role of the rich protons in NtrRR (Supplementary Fig. S8a). This is further supported by the lower Tafel slope in HNO 3 (216.9 vs. 241.7 mV dec − 1 , Supplementary Fig. S8b), indicating the faster reaction kinetics. Additionally, electrochemical impedance spectroscopy (EIS) data (Supplementary Fig. S8c) show a notably smaller semicircle in HNO 3 , reflecting reduced charge transfer resistance and improved interfacial electron transport. These results collectively highlight the fast kinetic and mass transport afforded by the acidic HNO 3 environment. 43 To further probe the electrocatalytic behavior, chronoamperometry electrolysis (CPE) was conducted, during which gaseous products carried by the Ar flow were continuously analyzed using online gas chromatography (GC), while the liquid-phase products were collected and qualitatively identified via proton nuclear magnetic resonance ( 1 H NMR) spectroscopy and UV − Vis spectrophotometry. As illustrated in Fig. 2 b and Supplementary Figs. S9-10, the Bi-ene catalyst demonstrated exceptional electrocatalytic performance for HNO 3 reduction, with NH 2 OH being the predominant product across the entire potential range. Specifically, FE NH2OH reached 95.7% at − 0.95 V and remained above 90% in a broad potential window (− 0.7 to − 1.1 V) with minimal gas production (FE gas <5%), indicating that the competitive HER is effectively suppressed, even in the strongly acidic conditions. Additionally, the selectivity for NH 2 OH maintained consistently above 95% at all applied potentials, with the highest selectivity of 98.7% achieved at − 0.95 V (Fig. 2 c). Furthermore, the NH 2 OH yield rate reached an impressive 1161 µmol cm − 2 h − 1 at − 1.1 V, marking the highest yield rate for NH 2 OH reported in recent studies (Fig. 2 d, Supplementary Table S1 ). Control experiment confirms that Bi-ene served as the active species for NO 3 − electroreduction into NH 2 OH (Supplementary Fig. S11). To assess the catalytic stability of Bi-ene, cyclic stability tests were conducted for nitrate electroreduction, and each cycle involved continuous electrolysis at − 100 mA cm − 2 for 4 hours. Over the course of 10 cycles, the average FE for NH 2 OH consistently exceeded 90.0%, while the cumulative NH 2 OH yield showed a linear increase to a final value of 22 mmol (Fig. 2 e). Additionally, Bi-ene demonstrated excellent long-term stability at − 100 mA cm − 2 for 60 h (Fig. 2 f). Next, the OARR performance of Bi-ene was also evaluated in a 0.5 M HCl solution containing 0.5 M OA, where GX and glycolic acid (GC) were identified as the exclusive organic products by 1 H NMR spectroscopy. As depicted in Fig. 2 g and Supplementary Figs. S12-13, Bi-ene shows an excellent catalytic performance toward 2e − OARR for desired GX production with a high FE up to 71.7%, demonstrating its high OA-to-GX selectivity (Supplementary Fig. S14). These results prove that the Bi-ene catalyst is able to serve as a bifunctional catalyst, exhibiting high electrocatalytic activity and selectivity for both the NtrRR to NH 2 OH and OARR to GX at low overpotentials. Electrochemical C − N Coupling using OA and HNO feedstocks Motivated by the outstanding activity of the Bi-ene catalyst in both NtrRR and OARR, we further explored its capability for the selective electrosynthesis of glycine via the co-reduction of OA and HNO 3 feedstocks (Fig. 3 a). Electrocatalytic glycine synthesis was conducted in a solution with 0.5 M HCl + 0.5 M HNO 3 + 0.5 M OA. As illustrated in Fig. 3 b, the co-electrolysis of OA and HNO 3 exhibited an increase in current density and a more favorable onset potential compared to individual NtrRR and OARR. The mutual promotion between NtrRR and OARR should originate from these two electroreductions and the subsequent condensation of their respective intermediates, i.e., NH 2 OH and GX to glyoxylic acid oxime (GAO), which facilitate their rapid consumption. The successful formation of the C − N bond was unequivocally confirmed by 1 H NMR spectroscopy, which displayed distinct signals attributed to GAO and glycine in the reaction mixtures (Fig. 3 c). Impressively, Bi-ene achieved FEs exceeding 50% for glycine formation, displaying a dependence on the applied potential over the range of − 0.7 to − 1.1 V (Fig. 3 d and Supplementary Fig. S15). A maximum FE for glycine of 68.2% was obtained at − 0.95 V. Additionally, the partial current density for glycine ( j glycine ) on Bi-ene showed a sustained increase as the potential increased, reaching a maximum value of 168.0 mA cm − 2 and a corresponding glycine yield rate of 455.4 µmol cm − 2 h − 1 at − 1.1 V (Fig. 3 e). Comparatively, the commercial Bi catalyst (bulk-Bi with microparticle morphology) showed poor performance, with glycine FE and j glycine being 37.1% and 12.2 mA cm − 2 at − 0.95 V, far smaller than those of Bi-ene (Fig. 3 f and Supplementary Figs. S16-18). Moreover, the bulk-Bi required more negative potentials, suggesting a much weaker C − N formation capability than the MOF-derived Bi-ene (Supplementary Figs. S19-20). The double-layer capacitance (C dl ), derived from cyclic voltammetry (CV) at varying scan rates (Supplementary Fig. S21) was employed to estimate the electrochemical surface areas (ECSA) of the catalysts. Bi-ene displayed a notably larger ECSA as compared to bulk-Bi, suggesting a greater abundance of electrochemically accessible active sites for glycine synthesis. After normalizing j glycine by ECSA, Bi-ene delivered a value that is 8.5 times higher than bulk-Bi at − 1.1 V, demonstrating that the lattice-distorted Bi-ene is more active for glycine production. EIS revealed the reduced interfacial resistance on Bi-ene, as evidenced by a smaller Nyquist semicircle diameter (Supplementary Fig. S21d), suggesting the enhanced charge-transfer kinetics. Overall, these comparative results demonstrate that the in situ generated ultrathin Bi-ene with unique atomic misarrangement facilitates the simultaneous reduction of OA and NO 3 − , thereby improving glycine synthesis efficiency. To elucidate the C − N coupling mechanism occurring on the Bi-ene catalyst during the co-electroreduction of OA and HNO 3 , a time-resolved control experiment was conducted to monitor the evolution of key intermediates and products (Supplementary Fig. S22). Within the first hour of electrolysis, GAO accumulated rapidly and exhibited a higher concentration than glycine, indicating that GAO is formed as an early intermediate. As the reaction progressed, the GAO concentration stabilized and then gradually declined, while glycine continued to accumulate, reaching 160 mM after 4 hours. This temporal relationship suggests that GAO condensed from the NH 2 OH and GX serves as the key intermediate and undergoes progressive conversion into glycine during electrolysis. Interestingly, GX remained at consistently low concentrations throughout the process, implying that once formed via the OARR, GX is rapidly consumed through condensation with NH 2 OH produced from the NtrRR to form GAO. This observation is consistent with the electrophilic character of GX and the nucleophilic nature of NH 2 OH, facilitating their spontaneous coupling (Supplementary Fig. S23). The swift turnover of GX contributes to the high overall efficiency of the stepwise glycine synthesis. As a proof, the electrocatalytic co-reduction of GX and NH 2 OH on the Bi-ene electrode resulted in the rapid formation of both GAO and glycine at a remarkably low onset potential, indicating a kinetically favorable process (Supplementary Fig. S24). Furthermore, control experiments, where OA or HNO 3 was replaced with GX or NH 2 OH, respectively, demonstrated that both GX/HNO 3 and OA/NH 2 OH co-reduction systems effectively yielded glycine (Supplementary Figs. S25-26). Notably, the OA/NH 2 OH system achieved the highest FE of 81.2% at − 0.8 V (Supplementary Fig. S27). These results indicate that GX and NH 2 OH act as essential intermediates in the overall reaction pathway. Their efficient coupling constitutes the key C − N bond-forming step in glycine electrosynthesis, highlighting the mechanistic significance of oxime intermediate formation and subsequent reductive amination. Besides, the isotopic-labelling experiments using 15 NO 3 − as the nitrogen source confirmed that the generated NH 2 OH originates from 15 NO 3 − , 18 rather than from any extraneous nitrogen-containing impurities (Fig. 3 g and Supplementary Figs. S28-30). In addition to catalytic activity and selectivity, long-term stability was also evaluated by conducting tests at − 0.95 V. The glycine yield accumulated continuously to 16.5 mmol over 12 consecutive cycles without noticeable decline in production performance (Fig. 3 h), demonstrating excellent electrochemical stability. Furthermore, in the prolonged electrolysis in a flow cell, Bi-ene maintained a consistent FE glycine of ~ 60% over 120 hours at an industrially relevant current density of − 200 mA cm − 2 (Fig. 3 i and Supplementary Fig. S31). The post-reaction characterizations revealed that the morphology, elemental composition, and crystal structure of Bi-ene remained largely unchanged, confirming its structural robustness under the long-term operating conditions (Supplementary Fig. S32-34). To the best of our knowledge, the as-prepared Bi-ene represents the first catalyst enabling salt-free glycine electrosynthesis through electrochemical C − N coupling, demonstrating exceptional efficiency among the reported metal-based systems (Fig. 3 j, Supplementary Table S2). Reaction mechanism studies by operando spectroscopies and DFT calculations To gain deeper insight into the C − N coupling mechanism on the Bi-ene surface, we conducted the operando Fourier-transform infrared (FTIR) spectroscopy analysis (Fig. 4 a) to track the evolution of key intermediates during the co-electrolysis of OA and HNO 3 . Compared with NtrRR, more vibrational features were observed, indicative of chemical interactions between nitrogen- and carbon-based intermediates during the co-reduction of OA and HNO 3 (Fig. 4 a). Specifically, the decreased intensity of the peak at 1720 cm − 1 (C = O of OA) and the enhanced signal at 1242 cm − 1 indicate the progressive consumption of OA and the formation of *NH 2 OH, respectively. 29 , 44 The early appearance of the *NH 2 OH signal at a relatively lower potential (− 0.6 V) highlights the favorable kinetics of NtrRR. As the potential becomes more negative, the emergence of peaks at 1643 cm − 1 (C = N), 1593 cm − 1 (C − N−H), and 1380 cm − 1 (CH 2 ) suggests the reaction of GX with *NH 2 OH forming the oxime group (C = N − OH) of GAO intermediates, which is subsequently converted into glycine. 45 , 46 , 47 The temporal correlation between the depletion of OA signals, the accumulation of NH 2 OH, and the appearance of glycine-associated vibrational modes highlights stepwise reactions involving the formation and coupling of two reactive intermediates of NH 2 OH and GX. These spectral features collectively support that the Bi-ene catalyst promotes the selective electrosynthesis of glycine via the co-reduction of OA and HNO 3 . To further validate this mechanism and gain insights into the structural evolution and active sites of Bi-ene during the co-electroreduction of OA and HNO 3 , operando synchrotron-based X-ray absorption spectroscopy (XAS) was performed. Operando XANES and EXAFS analyses revealed a cathodic shift in the Bi L 3 -edge toward the energy position of metallic Bi, indicating the reduction of Bi 3+ species to Bi 0 (Fig. 4 b), 48 which is catalytically responsible for driving the selective transformation of OA and HNO 3 to glycine. Additionally, a poisoning experiment was performed in the electrolyte containing potassium thiocyanate (KSCN), a known metal site inhibitor. 20 , 49 Upon KSCN addition, both the FE and j for glycine formation declined markedly relative to the unpoisoned system (Fig. S35), strongly implicating the metallic Bi centers as the primary active sites responsible for C − N bond formation. To gain mechanistic insight into the experimental observations, DFT calculations were performed to elucidate the effect of lattice strain on facilitating NtrRR and enhancing glycine formation. Based on HRTEM analysis, three representative models were constructed, including the pristine Bi (012) facet, Bi (012) edge, and defective Bi (012) plane with planar distortions (Fig. S36). The adsorption configurations and activation barriers of HNO 3 on the above catalytic sites were first evaluated, revealing favorable adsorption with moderate binding energies, thereby facilitating surface activation. As shown in Fig. 4 c, the formation of NH 2 OH proceeds via the protonation of adsorbed *NO to form the *NHO intermediate, followed by the desorption of *NH 2 OH to release NH 2 OH. Notably, the endothermic protonation of *NO 2 to *NO 2 H, identified as the rate-determining step in NtrRR, show a high Gibbs free energy change (ΔG = 0.305 eV) on intact Bi (012) plane. In contrast, the defective Bi-ene substantially lowers this energy barrier to 0.062 eV, demonstrating enhanced catalytic activity and a strong preference for NH 2 OH formation at lattice defect sites. Furthermore, compared to the relatively low free energy barrier of 0.062 eV for the protonation of *NO 2 , the energy required for direct proton activation reaches 1.25 eV, indicating significantly hindered hydrogen evolution on the Bi-ene catalyst (Fig. 4 d). This is consistent with the observed low FEs for HER on Bi-ene. Importantly, the electro-reductive hydrogenation of GAO to glycine was demonstrated to be both kinetically accessible and thermodynamically favorable, as evidenced by the exergonic nature of the overall process (Fig. 4 e). The Gibbs free energy profiles on different Bi surfaces exhibit similar trends along the reaction pathway. However, a notable difference emerges in the final desorption step of *HOOCCH 2 NH 2 , where the ΔG on defective Bi (012) is only 0.058 eV, significantly lower than that (0.319 eV) of intact Bi (012). This thermodynamic advantage suggests that the release of glycine is more favorable on the Bi-ene defective sites, contributing to its enhanced catalytic performance. These theoretical insights underscore the superior catalytic performance of lattice-distorted Bi-ene compared to the counterparts, in promoting key reaction steps such as NH 2 OH formation and GAO reduction and facilitating the desorption of the final product, consistent with experimental results. To further evaluate catalyst effectiveness, various metal foils (Cu, Ti, Ag, Pt) were tested as the cathodic catalysts for glycine electrosynthesis (Fig. 4 f). While Cu and Ag favored NH 3 formation, and Pt and Ti primarily promoted H 2 evolution, Bi-ene stood out by delivering the highest glycine selectivity and yield among all metals examined. Substrate expansion Encouraged by this catalytic efficacy, we expanded the application of Bi-ene in the electrocatalytic C − N coupling. A series of structurally diverse α-keto acids were subjected to co-electrolysis with HNO 3 using Bi-ene as the catalyst. Remarkably, each substrate was efficiently converted into the corresponding α-amino acid with high FEs, as confirmed by 1 H NMR spectroscopy (Scheme 2 , Supplementary Figs. S37-42), for example, achieving a FE of 48.8% for alanine and 40.2% for aspartic acid. These results demonstrate that Bi-ene is capable of accommodating a wide range of α-keto acid skeletons, including both linear and branched chains with increasing molecular complexity. Besides, the catalytic system is also applicable to alternative nitrogen sources, as evidenced by the efficient electrochemical synthesis of sarcosine (FE = 64.3%) and N-ethylglycine (FE = 53%) when replacing NH 2 OH with N-methylhydroxylamine and N-ethylhydroxylamine, respectively. These findings highlight the potential of MOF-derived Bi-ene in efficient electrosynthesis of α-amino acids with variable carbon skeletons (C 2 − C 5 ) and nitrogen functionalities under mild electrochemical conditions. Conclusion In summary, this study highlights a salt-free electrosynthesis of glycine via the simultaneous electrochemical reduction of OA and HNO 3 , enabled by an atomically thin lattice-distorted Bi-ene catalyst. The Bi-ene catalyst exhibits unique bifunctional properties that promote efficient C − N coupling of NH 2 OH and GX in situ -generated from the co-electrolysis of HNO 3 and OA, achieving remarkable glycine production with a high yield rate of 455.4 µmol cm − 2 h − 1 and a FE of 68.2%. Spectroscopic characterizations combined with DFT calculations reveal that the in situ electrochemical reconstruction of Bi-MOF to Bi-ene under reductive conditions induces substantial lattice strain that modulates the local electronic environment, which stabilizes key reaction intermediates and lowering the energy barriers. This work deepens the understanding of electrocatalytic C − N coupling pathways and demonstrates the efficacy of lattice defects in tailoring the electronic structures and reactivity of metal catalysts. Methods Synthesis of Bi-CAU-17 Bi-CAU-17 was synthesized based on reported procedures with slight modifications. Specifically, 375 mg of 1,3,5-benzenetricarboxylic acid (H 3 BTC) and 750 mg of bismuth nitrate pentahydrate [Bi(NO 3 ) 3 ·5H 2 O] were dispersed in 30 mL of methanol under continuous stirring at room temperature for 30 minutes. The homogeneous mixture was then transferred into a 50 mL Teflon-lined stainless-steel autoclave and subjected to solvothermal treatment at 120°C for 24 hours. After cooling to room temperature, the resulting precipitates were collected via centrifugation, washed multiple times with methanol to remove unreacted species, and subsequently dried at 60°C. Synthesis of Bi-ene electrode Bi-ene was synthesized via an electrochemical reconstruction of Bi-CAU-17 in a standard three-electrode electrochemical setup. To prepare the catalyst ink, 10.0 mg of Bi-CAU-17 was ultrasonically dispersed for 1 hour in a solvent mixture comprising 700 µL of ethanol, 200 µL of H 2 O, 50 µL of DMF and 50 µL of 5 wt% Nafion solution. Subsequently, 200 µL of the resulting suspension was drop-cast onto both sides of a 1.0 × 1.0 cm 2 carbon paper (CP) electrode, yielding a total Bi-CAU-17 loading of 2.0 mg cm⁻ 2 . The Bi-CAU-17 electrodes were subjected to consecutive cyclic voltammetry (CV) scans for 100 cycles at a rate of 100 mV s⁻¹ within the potential window of − 0.2 to − 1 V vs. Ag/AgCl in an Ar-saturated electrolyte. 2. Characterizations X-ray diffraction (XRD) patterns of the synthesized materials and electrode samples were collected using a Rigaku MiniFlex 600 benchtop diffractometer equipped with Cu K α radiation. Surface morphology and microstructural features were examined via scanning electron microscopy (SEM, JEOL JSM-7800F), while detailed structural information at the nanoscale was obtained through transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) using an FEI Tecnai G2 F30 microscope. X-ray photoelectron spectroscopy (XPS) measurements were conducted on a Thermo Fisher ESCALAB 250Xi spectrometer employing monochromatic Al K α radiation (E = 1486.2 eV). The C 1s peak at 284.8 eV was used as the reference for binding energy calibration. Atomic force microscopy (AFM) images were captured using a Bruker Dimension ICON system. In situ attenuated total reflectance infrared (ATR-IR) spectra were acquired on a NICOLET 6700 spectrometer to monitor dynamic surface species during electrochemical processes. 3. Electrochemical measurements Electrochemical experiments, including linear sweep voltammetry (LSV) and controlled potential electrolysis (CPE), were performed using a two-compartment H-type cell connected to a CHI 660E electrochemical workstation. The cathodic and anodic chambers were separated by a Nafion N-117 proton exchange membrane. A platinum mesh served as the counter electrode, while a saturated Ag/AgCl electrode was used as the reference. CPEs including OARR, NtrRR, co-reduction of OA and HNO 3 , co-reduction of OA and NH 2 OH, co-reduction of GX and HNO 3 , co-reduction of GX and NH 2 OH, were carried out in 0.5 M HCl + 0.5 M OA, 0.5 M HCl + 0.5 M HNO 3 , 0.5 M HCl + 0.5 M OA + 0.5 M HNO 3 , 0.5 M OA + 0.5 M NH 2 OH·HCl, 0.5 M HCl + 0.5 M GX + 0.5 M HNO 3 and 0.5 M GX + 0.5 M NH 2 OH·HCl, respectively. Prior to electrolysis, Ar gas was purged through the catholyte for 30 minutes to remove dissolved oxygen. All electrolysis was carried out at predetermined potentials under ambient temperature. 4. Identification and quantification of products Following electrolysis, gaseous products were analyzed using an Agilent 7890B gas chromatograph. Liquid-phase products, including glycine, glyoxylic acid (GX), glycolic acid (GC), hydroxylamine (NH 2 OH), and glyoxylic acid oxime (GAO), were quantified via proton nuclear magnetic resonance ( 1 H NMR) spectroscopy with water suppression using a Bruker AVANCE 600 MHz instrument. For a typical analysis, 0.5 mL of the electrolyte was mixed with 0.1 mL of a 10 mM DMSO/D 2 O solution which was used as the internal standard. For NH 2 OH detection, 1 mL of the electrolyte was first mixed with 15 µL of 50 wt% GX solution. After oximation, 0.5 mL of the solution was mixed with 0.1 mL of a 10 mM DMSO/D 2 O solution and then used as the rest sample. Additional species such as nitrite (NO 2 ⁻) and ammonium (NH 4 ⁺) were also determined by UV–Vis spectroscopy. Detailed protocols for UV–Vis quantification of nitrogen-containing species are provided below. Detection of NO 2 ⁻ To prepare the colorimetric reagent, 0.4 g of 3-aminobenzenesulfonamide, 0.02 g of N-(1-naphthyl) ethylenediamine dihydrochloride, and 1 mL of concentrated phosphoric acid were dissolved in 5 mL of deionized water. After the electrochemical reaction was completed, 400 µL of the electrolyte was mixed with 100 µL of the prepared color reagent and 3.5 mL of deionized water. The resulting mixture was allowed to stand at room temperature for 20 minutes before being analyzed using UV − Vis spectroscopy. The calibration curve of NO 2 ⁻ is shown in Supplementary Fig. S44. NH 3 Detection Ammonia concentration was determined using the indophenol blue colorimetric method. Three separate reagents were prepared for color development: Reagent A was obtained by dissolving 10 g NaOH, 12.5 g salicylic acid, and 12.5 g sodium citrate in 250 mL of deionized water; Reagent B consisted of 7.1 mL of NaClO solution (≥ 5% active chlorine content) diluted to 100 mL with water; and Reagent C was prepared by dissolving 1 g sodium nitroferricyanide in 100 mL of water. For the assay, 1 mL of the diluted electrolyte was successively combined with 1 mL of Reagent A, 0.5 mL of Reagent B, and 0.1 mL of Reagent C. The mixture was allowed to react under ambient conditions, and the absorbance was recorded at 654 nm using a UV–Vis spectrophotometer. The calibration curve of NH 3 is shown in Supplementary Fig. S45. Faradaic efficiency (FE) calculation The Faradaic efficiency (FE) of ammonia was calculated based on the quantified NH 3 concentration. The FE for each liquid product could be calculated as follows: where n x is the total mole of the liquid product x after electrochemical reaction, N is the total number of electrons required to generate the product, F is the Faraday constant (96485 C mol − 1 ), Q is the total charge during the electrocatalytic process. The yield rate was calculated on the basis of the following equation: Yield rate (n x ) = n x /A/t where n x is the total mole of the liquid product x after electrochemical reaction, A is the geometric area (cm − 2 ); t is the reaction time (h). Declarations Supporting Information The detailed information for the experimental section and additional characterization are provided in the Supporting Information. Acknowledgements Q.-L.Z. is grateful for the financial support of the National Key Research and Development Program of China (2021YFA1500402), the National Natural Science Foundation of China (NSFC) (22175174 and 52332007), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB1170000), and the Natural Science Foundation of Fujian Province (2021J06033). Z.H. acknowledges support under the Australian Research Council’s Discovery Projects funding scheme (DP250102613 and DP250103803). References Xue Y-P, Cao C-H, Zheng Y-G. Enzymatic asymmetric synthesis of chiral amino acids. Chem.Soc.Rev. 47 , 1516-1561 (2018). Gröger H. Catalytic Enantioselective Strecker Reactions and Analogous Syntheses. Chem. Rev. 103 , 2795-2828 (2003). Pulletikurti S, Yadav M, Springsteen G, Krishnamurthy R. Prebiotic synthesis of α-amino acids and orotate from α-ketoacids potentiates transition to extant metabolic pathways. Nat. Chem. 14 , 1142-1150 (2022). Wu R , et al. 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Electrocatalytic N–C–N coupling over a hierarchically ordered open single-atom superstructure toward organonitrogen synthesis. Nat. Commun. 16 , 3564 (2025). Li M , et al. Electrosynthesis of amino acids from NO and α-keto acids using two decoupled flow reactors. Nat. Catal. 6 , 906-915 (2023). Xu M-Y , et al. Electrosynthesis of Organonitrogen Compounds via Hydroxylamine-Mediated Cascade Reactions. Angew. Chem. Int. Ed. 64 , e202422637 (2025). Li L , et al. Computational Insights for Electrocatalytic Synthesis of Glycine. ACS Catal. 14 , 13381-13389 (2024). Guo M, Zhang Y, Guo C, Yu Y. Electrochemical Synthesis of Hydroxylamine. Angew. Chem. Int. Ed. 64 , e202509053 (2025). Zhang J , et al. Evidence for Distinct Active Sites on Oxide-Derived Cu for Electrochemical Nitrate Reduction. J. Am. Chem. Soc. 146 , 30708-30714 (2024). Zhang R , et al. Electrochemical nitrate reduction in acid enables high-efficiency ammonia synthesis and high-voltage pollutes-based fuel cells. Nat. 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Mater. 37 , 2409864 (2024). Angamuthu R, Byers P, Lutz M, Spek AL, Bouwman E. Electrocatalytic CO 2 Conversion to Oxalate by a Copper Complex. Science 327 , 313-315 (2010). Paris AR, Bocarsly AB. High-Efficiency Conversion of CO 2 to Oxalate in Water Is Possible Using a Cr-Ga Oxide Electrocatalyst. ACS Catal. 9 , 2324-2333 (2019). Cheng Y, Hou P, Pan H, Shi H, Kang P. Selective electrocatalytic reduction of carbon dioxide to oxalate by lead tin oxides with low overpotential. Appl. Catal B-Environ. 272 , 118954 (2020). Cheng Y, Xu W, Hou J, Kang P. Temperature-Dependent Electrosynthesis of C 2 Oxygenates from Oxalic Acid Using Gallium Tin Oxides. ACS Catal. 13 , 3676-3683 (2023). Watanabe R, Yamauchi M, Sadakiyo M, Abe R, Takeguchi T. CO 2 -free electric power circulation via direct charge and discharge using the glycolic acid/oxalic acid redox couple. Energy Environ. Sci. 8 , 1456-1462 (2015). Rapson HDC, Bird AE. The electrochemical preparation of glycine. J. Appl. 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A 12 , 20638-20654 (2024). Wang Y , et al. BiPO 4 -Derived 2D Nanosheets for Efficient Electrocatalytic Reduction of CO 2 to Liquid Fuel. Angew. Chem. Int. Ed. 60 , 7681-7685 (2021). Zhang E , et al. Bismuth Single Atoms Resulting from Transformation of Metal–Organic Frameworks and Their Use as Electrocatalysts for CO 2 Reduction. J. Am. Chem. Soc. 141 , 16569-16573 (2019). Ouyang H , et al. Selective Capture of Toxic Selenite Anions by Bismuth-based Metal–Organic Frameworks. Angew. Chem. Int. Ed. 57 , 13197-13201 (2018). Wu Z-Z , et al. Gerhardtite as a Precursor to an Efficient CO-to-Acetate Electroreduction Catalyst. J. Am. Chem. Soc. 145 , 24338-24348 (2023). Yin P-F , et al. Preparation of Amorphous SnO 2 -Encapsulated Multiphased Crystalline Cu Heterostructures for Highly Efficient CO 2 Reduction. Adv. Mater. 34 , 2201114 (2022). Huang H , et al. Understanding of Strain Effects in the Electrochemical Reduction of CO 2 : Using Pd Nanostructures as an Ideal Platform. Angew. Chem. Int. Ed. 56 , 3594-3598 (2017). Zhang M , et al. Engineering a conductive network of atomically thin bismuthene with rich defects enables CO 2 reduction to formate with industry-compatible current densities and stability. Energy Environ. Sci. 14 , 4998-5008 (2021). Zhang Y, Liu H, Zhao S, Xie C, Huang Z, Wang S. Insights into the Dynamic Evolution of Defects in Electrocatalysts. Adv. Mater. 35 , 2209680 (2023). Lv Y , et al. Highly Efficient Electrochemical Nitrate Reduction to Ammonia in Strong Acid Conditions with Fe 2 M-Trinuclear-Cluster Metal–Organic Frameworks. Angew. Chem. Int. Ed. 62 , e202305246 (2023). Fang J-Y , et al. Ampere-level current density ammonia electrochemical synthesis using CuCo nanosheets simulating nitrite reductase bifunctional nature. Nat. Commun. 13 , 7899 (2022). Zhao R , et al. Achieving over 90% Faradaic Efficiency in Cyclohexanone Oxime Electrosynthesis Using the Cu–Mo Dual-Site Catalyst. J. Am. Chem. Soc. 146 , 27956-27963 (2024). Yuan Y , et al. Electrocatalytic ORR–coupled ammoximation for efficient oxime synthesis. Sci. Adv. 10 , eado1755. Thiam MM, Ebrahimi M. The Adsorption of Neutral Glycine Molecules on Ice Nanolayers. e-J. Surf. Sci. Nanotechnol. 7 , 693-698 (2009). Chen Z , et al. Monitoring chalcogenide ions–guided in situ transform active sites of tailored bismuth electrocatalysts for CO 2 reduction to formate. Proc. Natl. Acad. Sci. 122 , e2420922122 (2025). Ni W , et al. Electroreduction of Carbon Dioxide Driven by the Intrinsic Defects in the Carbon Plane of a Single Fe–N 4 Site. Adv. Mater. 33 , 2003238 (2021). Schemes Schemes are available in the Supplementary Files section. Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.docx Scheme1.png Scheme 1. Schematic illustration of the electrochemical route for glycine production via coupled reduction of OA and HNO 3 . Scheme2.png Scheme 2. Examples of the substrate expansion for amino acid electrosynthesis. Molecular structures of the target amino acid products, along with their corresponding FEs, obtained via the electrolysis of (a) HNO 3 with various α-keto acids and (b) OA with different hydroxylamine derivatives. Cite Share Download PDF Status: Posted 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-7471908","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":513181210,"identity":"92af1fa3-0469-4849-94d3-63f26eb2d8b9","order_by":0,"name":"Zhenguo Huang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAUlEQVRIiWNgGAWjYDACCShtACYrUAWJ0XIGwidBC2MbEVrkZzcfe/i1zYbBXCL52cOv8w7XyTcwH7zNw2CX2IBDC+OcY+nGsm1pDJYz0syNZbcdljA4wJZszcOQjFMLs0SOmbRk22EGgxsJQAZICwOPmTQPAzNOLWwS+d+gWtKBjDmHJeQb+L8BtdTj1MIjkcMm+RGsJcdM8mPDYQmGAzxsQC2HcWqRkEgzk2Y4l8ZjcOZNmTTDsXTJDYfZjC3nGBw3xqVFfkbyM8kfZTZyBsfTt0n+qLHml29vfnjjTUW1LC4t4CDgAToQxgCSIMIAj3ogYPyBzhgFo2AUjIJRgAwA39tOGmNiPk0AAAAASUVORK5CYII=","orcid":"","institution":"[email protected]","correspondingAuthor":true,"prefix":"","firstName":"Zhenguo","middleName":"","lastName":"Huang","suffix":""},{"id":513181211,"identity":"0022ac73-4604-44eb-9f5a-b23dcf7dd79c","order_by":1,"name":"Minghong Huang","email":"","orcid":"https://orcid.org/0009-0007-1278-9773","institution":"University of Technology Sydney","correspondingAuthor":false,"prefix":"","firstName":"Minghong","middleName":"","lastName":"Huang","suffix":""},{"id":513181212,"identity":"150418a8-9204-4db5-b378-b138eeed8399","order_by":2,"name":"Sheng-Hua Zhou","email":"","orcid":"","institution":"Jiangsu University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Sheng-Hua","middleName":"","lastName":"Zhou","suffix":""},{"id":513181213,"identity":"ef3ffbfb-2a32-41c8-84ed-57ada6342dce","order_by":3,"name":"Lei Jiao","email":"","orcid":"","institution":"Xiamen University","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Jiao","suffix":""},{"id":513181214,"identity":"05a87e4d-7de4-4c06-8dfa-139f52be572b","order_by":4,"name":"Qi-Long Zhu","email":"","orcid":"https://orcid.org/0000-0001-9956-8517","institution":"Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Qi-Long","middleName":"","lastName":"Zhu","suffix":""},{"id":513181215,"identity":"09909b66-7365-481f-8168-35d9e18ac7d4","order_by":5,"name":"Cheng-Jie Yang","email":"","orcid":"","institution":"Tamkang University","correspondingAuthor":false,"prefix":"","firstName":"Cheng-Jie","middleName":"","lastName":"Yang","suffix":""},{"id":513181216,"identity":"ba801589-d72b-479b-8fae-1efc238e9637","order_by":6,"name":"Chung-Li Dong","email":"","orcid":"https://orcid.org/0000-0002-4289-4677","institution":"Tamkang University","correspondingAuthor":false,"prefix":"","firstName":"Chung-Li","middleName":"","lastName":"Dong","suffix":""},{"id":513181217,"identity":"b555f7ca-c154-4d8a-b762-a011cb391ffa","order_by":7,"name":"Dong-Dong Ma","email":"","orcid":"","institution":"Fujian Institute of Research on the Structure of Matter","correspondingAuthor":false,"prefix":"","firstName":"Dong-Dong","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2025-08-27 13:05:36","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7471908/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7471908/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91122568,"identity":"f9a5fe22-3df4-416d-98e5-c7b7b47f9998","added_by":"auto","created_at":"2025-09-11 19:21:44","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1434745,"visible":true,"origin":"","legend":"\u003cp\u003eSynthesis and characterizations of the Bi-ene NSs. (a) Illustration of the preparation. (b-d) SEM, AFM and XPS analyses. (e) TEM and (f) HR-TEM images. (g, h) Inverse FFT patterns taken from the yellow and orange dashed square in (f). (i) FFT image taken from the orange dashed square in (f). (j) Inverse FFT pattern taken from the green dashed square in (f). (k) EDX elemental mapping images.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/b12c1e607d684a08cf7fe443.png"},{"id":91122567,"identity":"891c0426-4ee1-4d3a-90dd-29a7597faf4c","added_by":"auto","created_at":"2025-09-11 19:21:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":593777,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of NH\u003csub\u003e2\u003c/sub\u003eOH production via the electrocatalytic reduction of HNO\u003csub\u003e3\u003c/sub\u003e. (b) FE and (c) selectivity and yield rates of NH\u003csub\u003e2\u003c/sub\u003eOH in 0.5 M HCl+ 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e over Bi-ene at different potentials. (d) Comparison on FE and yield rates of NH\u003csub\u003e2\u003c/sub\u003eOH with reported electrocatalysts. (e) FE and accumulated NH\u003csub\u003e2\u003c/sub\u003eOH yield in 0.5 M HCl+ 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e for 10 cycles at −100 mA cm\u003csup\u003e−2\u003c/sup\u003e. (f) Durability test at −100 mA cm\u003csup\u003e−2\u003c/sup\u003e for 60 h. (g) FE of H\u003csub\u003e2\u003c/sub\u003e, GX and GC for OARR in 0.5 M HCl+ 0.5 M OA.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/d36d6d5564731c6d1c9c3b15.png"},{"id":91122575,"identity":"f149ae45-2101-4c54-8cb0-cf33c2da4b37","added_by":"auto","created_at":"2025-09-11 19:21:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1782816,"visible":true,"origin":"","legend":"\u003cp\u003eGlycine production via electrocatalytic co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e. (a) Schematic illustration of the reaction pathway involving NtrRR and OARR, (b) LSV curves, (c) \u003csup\u003e1\u003c/sup\u003eH NMR spectra of the products, (d) FEs of different products and (e) partial current density and yield rates of glycine over Bi-ene at different potentials in 0.5 M HCl+ 0.5 M OA + 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e. (f) Comparison of FE and \u003cem\u003ej \u003c/em\u003eof glycine\u003cem\u003e \u003c/em\u003ebetween Bi-ene and bulk-Bi at −0.95 V. (g) \u003csup\u003e1\u003c/sup\u003eH NMR spectra of the electrolytes after electrolysis using NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e and \u003csup\u003e15\u003c/sup\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e as the reagents. (h) FE and accumulated yield of glycine in the 12-cycle tests at −0.95 V. (i) Durability test of Bi-ene in a flow cell at −200 mA cm\u003csup\u003e−2 \u003c/sup\u003efor 120 h. (j) Performance comparison of Bi-ene with reported electrocatalysts.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/7f031dd21ea989f800dbaefe.png"},{"id":91122570,"identity":"6320b448-402d-4e91-9c98-f2c3623d6bbb","added_by":"auto","created_at":"2025-09-11 19:21:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2055163,"visible":true,"origin":"","legend":"\u003cp\u003eReaction mechanism studies. (a) \u003cem\u003eOperando\u003c/em\u003e FTIR spectra for the co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e over Bi-ene, as well as standalone NtrRR. (b) \u003cem\u003eOperando\u003c/em\u003e XAFS profiles of Bi-ene recorded under different applied potentials. Gibbs free energy diagrams for the formation of (c) NH\u003csub\u003e2\u003c/sub\u003eOH, (d) H\u003csub\u003e2\u003c/sub\u003e, and (e) glycine on different Bi (012) sites. (f) Comparison of glycine FE and yield rates at −0.95 V over various metal-based catalysts.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/db69d3cd3e061ace94dec4d5.png"},{"id":92091117,"identity":"785efc7d-9328-4ba4-a546-ff6c2782b5fc","added_by":"auto","created_at":"2025-09-24 13:39:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7161586,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/396b7d05-3c6b-4c3a-9e73-c1dc5077b41d.pdf"},{"id":91122577,"identity":"d705b80e-a38a-4967-b03d-6990ecaa292d","added_by":"auto","created_at":"2025-09-11 19:21:44","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16474501,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/31afb07ff228165b7b942817.docx"},{"id":91122572,"identity":"1f243676-d364-4367-8a19-bab1eaecaba5","added_by":"auto","created_at":"2025-09-11 19:21:44","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":335783,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1.\u003c/strong\u003e Schematic illustration of the electrochemical route for glycine production via coupled reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/f22040e61f203af0835a6d0b.png"},{"id":91123101,"identity":"064217e5-1192-437f-aa74-1ab95e30f3d0","added_by":"auto","created_at":"2025-09-11 19:29:44","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":237209,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 2. \u003c/strong\u003eExamples of the substrate expansion for amino acid electrosynthesis. Molecular structures of the target amino acid products, along with their corresponding FEs, obtained via the electrolysis of (a) HNO\u003csub\u003e3\u003c/sub\u003e with various α-keto acids and (b) OA with different hydroxylamine derivatives.\u003c/p\u003e","description":"","filename":"Scheme2.png","url":"https://assets-eu.researchsquare.com/files/rs-7471908/v1/bd3f081b2b22eb73792409e9.png"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Salt-Free Glycine Electrosynthesis via C−N Coupling Boosted by the Lattice Strain in Atomically Thin p-Block Bismuthene","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlycine, the simplest amino acid, plays a pivotal role in numerous metabolic pathways and holds significant value in various industrial applications, such as a key precursor in pharmaceutical manufacturing, chemical synthesis, and biochemical formulations.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e However, traditional methods of glycine synthesis, such as the Strecker synthesis or enzymatic pathways, often involve toxic reagents or limited efficiency, thereby restricting their sustainability and scalability.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Recently, renewables-powered electrochemical strategies have emerged as a promising green route for amino acid synthesis.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e Specifically, the electrocatalytic reforming of abundant inorganic nitrogen sources and carbon-based feedstocks into C\u0026thinsp;\u0026minus;\u0026thinsp;N coupled products offers a sustainable and scalable pathway.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e This approach enables direct C\u0026thinsp;\u0026minus;\u0026thinsp;N bond formation under mild conditions, thereby not only reducing energy input and chemical waste but also contributing to the remediation of excess carbon and nitrogen in the environment.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eElectrosynthesis of amino acid commonly involves a nucleophilic substitution reaction, wherein NH\u003csub\u003e2\u003c/sub\u003eOH condenses with an electrophilic carbon center to generate a key oxime intermediate that serves as a precursor to C\u0026thinsp;\u0026minus;\u0026thinsp;N bond formation.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e Although nitrate salts are commonly used to provide nitrogen, the presence of alkali metal cations (e.g., Na⁺, K⁺) can interfere with the local electric field and compete for active sites on the catalyst surface, affecting the selectivity for key intermediates such as NH\u003csub\u003e2\u003c/sub\u003eOH.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e In contrast, HNO\u003csub\u003e3\u003c/sub\u003e offers a salt-free alternative that simplifies the electrolyte composition and enhances NH\u003csub\u003e2\u003c/sub\u003eOH production. The inherently acidic environment of HNO\u003csub\u003e3\u003c/sub\u003e eliminates the need for external proton sources, thereby facilitating proton-coupled electron transfer steps that are essential for the selective reduction of NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e to NH\u003csub\u003e2\u003c/sub\u003eOH.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Additionally, the high solubility and ionic conductivity of HNO\u003csub\u003e3\u003c/sub\u003e enhance mass transport and charge transfer kinetics during electrolysis, contributing to the overall system efficiency. Importantly, HNO\u003csub\u003e3\u003c/sub\u003e can be sustainably synthesized from abundant atmospheric nitrogen and water via a hybrid plasma\u0026ndash;electrolysis process.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e On the carbon side, aldehydes and ketones such as pyruvic acid and glyoxylic acid (GX) are often used as carbonyl sources in amino acid synthesis.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e However, these feedstocks necessitate energy intensive separation-purification processes. In contrast, utilizing upstream carbon-based molecules as direct reactants could provide a more cost-effective pathway for amino acid production by simplifying the chemical processes involved. Oxalic acid (OA), a C\u003csub\u003e2\u003c/sub\u003e product derived from CO\u003csub\u003e2\u003c/sub\u003e electroreduction,\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e is regarded a viable and cost-effective platform molecule that can be selectively reduced into electrophilic GX,\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e which could react with NH\u003csub\u003e2\u003c/sub\u003eOH to form a crucial oxime intermediate.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e Hence, the electrochemical co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e holds great promise for the sustainable and integrated synthesis of glycine. However, this pathway, to the best of our knowledge, has not been reported, and its realization remains challenging due to the complexity and competition among multiple reactions. Specifically, the OA reduction reaction (OARR) is a two-electron process, while NtrRR requires a six-electron reduction to form NH\u003csub\u003e2\u003c/sub\u003eOH. Achieving the simultaneous and selective activation of both pathways on a single catalyst is inherently difficult, owing to their distinct kinetic barriers and thermodynamic demands. Therefore, recent catalysts typically suffer from either low FE and inadequate current density, leading to a low yield rate of glycine.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e To address this, a bifunctional catalyst that enables NtrRR and OARR to simultaneously form NH\u003csub\u003e2\u003c/sub\u003eOH and GX, respectively, is highly desired. This dual catalytic functionality is crucial for promoting \u003cem\u003ein situ\u003c/em\u003e C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling between NH\u003csub\u003e2\u003c/sub\u003eOH and GX intermediates, thus enabling efficient glycine production within the cathodic compartment.\u003c/p\u003e\u003cp\u003eAmong various catalytic materials, \u003cem\u003ep\u003c/em\u003e-block metals have shown significant potential for electrocatalytic organosynthesis due to their low cost, high stability, and minimal hydrogen evolution reaction (HER) activity.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e As a representative \u003cem\u003ep\u003c/em\u003e-block metal, bismuth offers a low overpotential for NtrRR and can stabilize key intermediates in both nitrogen and carbon reduction pathways, making it a promising candidate for catalytic C\u0026thinsp;\u0026minus;\u0026thinsp;N bond formation.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e Despite their potential, Bi-based catalysts have been rarely explored for selective amino acid electrosynthesis, primarily due to their limited intrinsic activity and site accessibility, which significantly constrain their electrocatalytic performance. Structural engineering has been widely used to tune the properties of Bi electrocatalysts and improve their activity and selectivity. Previous studies have demonstrated that ultrathin Bi nanostructures enable high electrocatalytic efficiency due to enhanced active site exposure.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e Furthermore, introducing lattice defects into Bi nanolayers would further improve the intrinsic activity, as these defects modulate the electronic structures, optimize adsorption energies of key intermediates, and create additional active sites for catalytic reactions. However, the generation of abundant lattice defects within the Bi nanolayers remains challenging because of its intrinsic crystallographic stability. Compared to conventional inorganic precursors, Bi-based metal\u0026thinsp;\u0026minus;\u0026thinsp;organic frameworks (MOFs) offer highly tunable chemical environments and facile structural reconstruction owing to the weak coordination between Bi centers and organic linkers. The electro-reductive reconstruction of a Bi-based MOF precursor can induce substantial atomic rearrangement via dynamic removal of the organic linkers to yield ultrathin metallic Bi layers enriched with structural defects.\u003c/p\u003e\u003cp\u003eHerein, we report a highly efficient electrochemical C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling approach for salt-free glycine synthesis through the co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e, which is catalyzed by atomically thin bismuthene (Bi-ene) with abundant lattice distortion, reconstructed from a Bi-based MOF (Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Specifically, the defective Bi-ene nanosheets (NSs) exhibit exceptional performance for the electrosynthesis of NH\u003csub\u003e2\u003c/sub\u003eOH via NtrRR, delivering a high yield rate of 1161 \u0026micro;mol cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at \u0026minus;\u0026thinsp;1.1 V vs. Ag/AgCl, as well as excellent FE\u003csub\u003eNH2OH\u003c/sub\u003e exceeding 90% with high selectivity (\u0026gt;\u0026thinsp;95%) over a broad potential range. Further, in the co-reduction of HNO\u003csub\u003e3\u003c/sub\u003e and OA, Bi-ene effectively balances the different electron requirements (6 vs. 2 e⁻) by the two reduction reactions, enabling the efficient coupling of \u003cem\u003ein situ\u003c/em\u003e generated NH\u003csub\u003e2\u003c/sub\u003eOH and GX for glycine production under acidic conditions, with a remarkable FE and yield rate of 68.2% and 455 \u0026micro;mol cm⁻\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e h⁻\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, respectively. Operando characterizations combined with DFT calculations reveal that the atomic misarrangement-induced lattice strain in Bi-ene modulates the local electronic structure, creating abundant and highly active sites and a favorable adsorption environment that synergistically promote NH\u003csub\u003e2\u003c/sub\u003eOH formation and consequent glycine synthesis. Moreover, Bi-ene exhibits excellent substrate versatility, accommodating a wide range of α-keto acid skeletons for the electrosynthesis of C\u0026thinsp;\u0026minus;\u0026thinsp;N bond-containing compounds. This work highlights the significant potential of electrosynthesis that is salt-free, sustainable and cost-effective.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eCharacterizations\u003c/h2\u003e\u003cp\u003eThe Bi-ene electrocatalyst was obtained via a two-step process (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). First, the rod-shaped Bi-MOF, the pre-catalyst with high surface area, was prepared using a solvothermal method (Supplementary Figs. S1-3).\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e The X-ray diffraction (XRD) analysis confirms that the as-synthesized MOF adopts CAU-17 structure (Supplementary Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Subsequently, an electroreduction treatment was performed on Bi-CAU-17 to \u003cem\u003ein situ\u003c/em\u003e generate Bi-ene nanosheets (NSs).\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e The XRD patterns confirm the complete transformation from Bi-CAU-17 to metallic Bi-ene, where the diffraction peaks associated with Bi-CAU-17 disappeared with the appearance of new peaks at 27.2\u0026deg;, 37.9\u0026deg;, and 39.6\u0026deg; corresponding to the (012), (104), and (110) planes of metallic bismuth (Supplementary Fig. S4). Scanning electron microscope (SEM) images show that the electrochemically generated Bi-ene NSs exhibit a graphene-like ultrathin morphology without significant aggregation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and Supplementary Fig. S5). Atomic force microscopy (AFM) measurements show that the thickness of the Bi-ene NSs ranges from 1.43 to 1.54 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), corresponding to approximately 4 atomic layers. Meanwhile, X-ray photoelectron spectroscopy (XPS) spectra clearly reveal the emergence of a new pair of Bi\u003csup\u003e0\u003c/sup\u003e signals following the electrochemical reconstruction (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed), providing further evidence for the transformation of Bi-CAU-17 to Bi-ene, which is in agreement with the XRD results.\u003c/p\u003e\u003cp\u003eFurther structural insight was gained from TEM analysis, which confirms the two-dimensional (2D) nature of the Bi-ene NSs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef, the high-resolution TEM (HR-TEM) images of the representative Bi-ene NSs reveal pronounced atomic misarrangements that lead to high-density lattice distortions and local strain. In addition, the lattice distortion can be easily observed in a single Bi-ene NS (Supplementary Fig. S6), demonstrating that the electrochemical reconstruction of the Bi-CAU-17 precursor effectively generates substantial atomic structural defects. The inverse fast Fourier transform (FFT) image uncovers the lattice distortion, as marked with \u0026ldquo;T\u0026rdquo; symbols in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh, which arises from facet mismatch. Additionally, the FFT pattern in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei displays chain-like diffraction features, further confirming the presence of planar defects.\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e The measured interplanar spacing of 0.33 nm corresponds to the (012) plane of rhombohedral Bi, indicating that the Bi-ene NSs retain the main crystallinity (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ej). These results provide strong evidence that the electrochemical reconstruction of Bi-CAU-17 not only produces 2D metallic Bi with atomically thin nanosheet structure but also induces extensive lattice strain associated with structural defects. Compared to the well-ordered lattice, such strained structural disorder is expected to modulate the electronic properties and enhances the catalytic performance of the resultant Bi-ene NSs.\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e The energy dispersive X-ray spectrometry (EDX) images confirm the homogeneous distribution of Bi and O elements throughout the nanosheet architecture (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ek).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eIndividual NtrRR and OARR performance evaluation\u003c/h3\u003e\n\u003cp\u003eGiven the critical role of NH\u003csub\u003e2\u003c/sub\u003eOH generated from NtrRR in facilitating C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling for amino acid synthesis, the electrocatalytic NtrRR performance of Bi-ene electrodes was first evaluated in an H-cell under Ar atmosphere, using 0.5 M HCl and 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e as the catholyte (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). As shown by the linear sweep voltammetry (LSV) curves, the current density in the HNO\u003csub\u003e3\u003c/sub\u003e-containing electrolyte is significantly higher compared to that in pure HCl electrolyte, indicating the effective electroreduction of HNO\u003csub\u003e3\u003c/sub\u003e on the Bi-ene catalyst (Supplementary Fig. S7). Moreover, compared to NaNO\u003csub\u003e3\u003c/sub\u003e, the use of HNO\u003csub\u003e3\u003c/sub\u003e led to a substantially higher cathodic current density, suggesting the important role of the rich protons in NtrRR (Supplementary Fig. S8a). This is further supported by the lower Tafel slope in HNO\u003csub\u003e3\u003c/sub\u003e (216.9 vs. 241.7 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, Supplementary Fig. S8b), indicating the faster reaction kinetics. Additionally, electrochemical impedance spectroscopy (EIS) data (Supplementary Fig. S8c) show a notably smaller semicircle in HNO\u003csub\u003e3\u003c/sub\u003e, reflecting reduced charge transfer resistance and improved interfacial electron transport. These results collectively highlight the fast kinetic and mass transport afforded by the acidic HNO\u003csub\u003e3\u003c/sub\u003e environment.\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e To further probe the electrocatalytic behavior, chronoamperometry electrolysis (CPE) was conducted, during which gaseous products carried by the Ar flow were continuously analyzed using online gas chromatography (GC), while the liquid-phase products were collected and qualitatively identified via proton nuclear magnetic resonance (\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR) spectroscopy and UV\u0026thinsp;\u0026minus;\u0026thinsp;Vis spectrophotometry. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Supplementary Figs. S9-10, the Bi-ene catalyst demonstrated exceptional electrocatalytic performance for HNO\u003csub\u003e3\u003c/sub\u003e reduction, with NH\u003csub\u003e2\u003c/sub\u003eOH being the predominant product across the entire potential range. Specifically, FE\u003csub\u003eNH2OH\u003c/sub\u003e reached 95.7% at \u0026minus;\u0026thinsp;0.95 V and remained above 90% in a broad potential window (\u0026minus;\u0026thinsp;0.7 to \u0026minus;\u0026thinsp;1.1 V) with minimal gas production (FE\u003csub\u003egas\u003c/sub\u003e\u0026lt;5%), indicating that the competitive HER is effectively suppressed, even in the strongly acidic conditions. Additionally, the selectivity for NH\u003csub\u003e2\u003c/sub\u003eOH maintained consistently above 95% at all applied potentials, with the highest selectivity of 98.7% achieved at \u0026minus;\u0026thinsp;0.95 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Furthermore, the NH\u003csub\u003e2\u003c/sub\u003eOH yield rate reached an impressive 1161 \u0026micro;mol cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at \u0026minus;\u0026thinsp;1.1 V, marking the highest yield rate for NH\u003csub\u003e2\u003c/sub\u003eOH reported in recent studies (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Control experiment confirms that Bi-ene served as the active species for NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e electroreduction into NH\u003csub\u003e2\u003c/sub\u003eOH (Supplementary Fig. S11). To assess the catalytic stability of Bi-ene, cyclic stability tests were conducted for nitrate electroreduction, and each cycle involved continuous electrolysis at \u0026minus;\u0026thinsp;100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for 4 hours. Over the course of 10 cycles, the average FE for NH\u003csub\u003e2\u003c/sub\u003eOH consistently exceeded 90.0%, while the cumulative NH\u003csub\u003e2\u003c/sub\u003eOH yield showed a linear increase to a final value of 22 mmol (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). Additionally, Bi-ene demonstrated excellent long-term stability at \u0026minus;\u0026thinsp;100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for 60 h (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef).\u003c/p\u003e\u003cp\u003eNext, the OARR performance of Bi-ene was also evaluated in a 0.5 M HCl solution containing 0.5 M OA, where GX and glycolic acid (GC) were identified as the exclusive organic products by \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR spectroscopy. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg and Supplementary Figs. S12-13, Bi-ene shows an excellent catalytic performance toward 2e\u003csup\u003e\u0026minus;\u003c/sup\u003e OARR for desired GX production with a high FE up to 71.7%, demonstrating its high OA-to-GX selectivity (Supplementary Fig. S14). These results prove that the Bi-ene catalyst is able to serve as a bifunctional catalyst, exhibiting high electrocatalytic activity and selectivity for both the NtrRR to NH\u003csub\u003e2\u003c/sub\u003eOH and OARR to GX at low overpotentials.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eElectrochemical C − N Coupling using OA and HNO feedstocks\u003c/h3\u003e\n\u003cp\u003eMotivated by the outstanding activity of the Bi-ene catalyst in both NtrRR and OARR, we further explored its capability for the selective electrosynthesis of glycine via the co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e feedstocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Electrocatalytic glycine synthesis was conducted in a solution with 0.5 M HCl\u0026thinsp;+\u0026thinsp;0.5 M HNO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;0.5 M OA. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, the co-electrolysis of OA and HNO\u003csub\u003e3\u003c/sub\u003e exhibited an increase in current density and a more favorable onset potential compared to individual NtrRR and OARR. The mutual promotion between NtrRR and OARR should originate from these two electroreductions and the subsequent condensation of their respective intermediates, i.e., NH\u003csub\u003e2\u003c/sub\u003eOH and GX to glyoxylic acid oxime (GAO), which facilitate their rapid consumption. The successful formation of the C\u0026thinsp;\u0026minus;\u0026thinsp;N bond was unequivocally confirmed by \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR spectroscopy, which displayed distinct signals attributed to GAO and glycine in the reaction mixtures (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Impressively, Bi-ene achieved FEs exceeding 50% for glycine formation, displaying a dependence on the applied potential over the range of \u0026minus;\u0026thinsp;0.7 to \u0026minus;\u0026thinsp;1.1 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and Supplementary Fig. S15). A maximum FE for glycine of 68.2% was obtained at \u0026minus;\u0026thinsp;0.95 V. Additionally, the partial current density for glycine (\u003cem\u003ej\u003c/em\u003e\u003csub\u003eglycine\u003c/sub\u003e) on Bi-ene showed a sustained increase as the potential increased, reaching a maximum value of 168.0 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a corresponding glycine yield rate of 455.4 \u0026micro;mol cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at \u0026minus;\u0026thinsp;1.1 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Comparatively, the commercial Bi catalyst (bulk-Bi with microparticle morphology) showed poor performance, with glycine FE and \u003cem\u003ej\u003c/em\u003e\u003csub\u003eglycine\u003c/sub\u003e being 37.1% and 12.2 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at \u0026minus;\u0026thinsp;0.95 V, far smaller than those of Bi-ene (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef and Supplementary Figs. S16-18). Moreover, the bulk-Bi required more negative potentials, suggesting a much weaker C\u0026thinsp;\u0026minus;\u0026thinsp;N formation capability than the MOF-derived Bi-ene (Supplementary Figs. S19-20). The double-layer capacitance (C\u003csub\u003edl\u003c/sub\u003e), derived from cyclic voltammetry (CV) at varying scan rates (Supplementary Fig. S21) was employed to estimate the electrochemical surface areas (ECSA) of the catalysts. Bi-ene displayed a notably larger ECSA as compared to bulk-Bi, suggesting a greater abundance of electrochemically accessible active sites for glycine synthesis. After normalizing \u003cem\u003ej\u003c/em\u003e\u003csub\u003eglycine\u003c/sub\u003e by ECSA, Bi-ene delivered a value that is 8.5 times higher than bulk-Bi at \u0026minus;\u0026thinsp;1.1 V, demonstrating that the lattice-distorted Bi-ene is more active for glycine production. EIS revealed the reduced interfacial resistance on Bi-ene, as evidenced by a smaller Nyquist semicircle diameter (Supplementary Fig. S21d), suggesting the enhanced charge-transfer kinetics. Overall, these comparative results demonstrate that the \u003cem\u003ein situ\u003c/em\u003e generated ultrathin Bi-ene with unique atomic misarrangement facilitates the simultaneous reduction of OA and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, thereby improving glycine synthesis efficiency.\u003c/p\u003e\u003cp\u003eTo elucidate the C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling mechanism occurring on the Bi-ene catalyst during the co-electroreduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e, a time-resolved control experiment was conducted to monitor the evolution of key intermediates and products (Supplementary Fig. S22). Within the first hour of electrolysis, GAO accumulated rapidly and exhibited a higher concentration than glycine, indicating that GAO is formed as an early intermediate. As the reaction progressed, the GAO concentration stabilized and then gradually declined, while glycine continued to accumulate, reaching 160 mM after 4 hours. This temporal relationship suggests that GAO condensed from the NH\u003csub\u003e2\u003c/sub\u003eOH and GX serves as the key intermediate and undergoes progressive conversion into glycine during electrolysis. Interestingly, GX remained at consistently low concentrations throughout the process, implying that once formed via the OARR, GX is rapidly consumed through condensation with NH\u003csub\u003e2\u003c/sub\u003eOH produced from the NtrRR to form GAO. This observation is consistent with the electrophilic character of GX and the nucleophilic nature of NH\u003csub\u003e2\u003c/sub\u003eOH, facilitating their spontaneous coupling (Supplementary Fig. S23). The swift turnover of GX contributes to the high overall efficiency of the stepwise glycine synthesis. As a proof, the electrocatalytic co-reduction of GX and NH\u003csub\u003e2\u003c/sub\u003eOH on the Bi-ene electrode resulted in the rapid formation of both GAO and glycine at a remarkably low onset potential, indicating a kinetically favorable process (Supplementary Fig. S24). Furthermore, control experiments, where OA or HNO\u003csub\u003e3\u003c/sub\u003e was replaced with GX or NH\u003csub\u003e2\u003c/sub\u003eOH, respectively, demonstrated that both GX/HNO\u003csub\u003e3\u003c/sub\u003e and OA/NH\u003csub\u003e2\u003c/sub\u003eOH co-reduction systems effectively yielded glycine (Supplementary Figs. S25-26). Notably, the OA/NH\u003csub\u003e2\u003c/sub\u003eOH system achieved the highest FE of 81.2% at \u0026minus;\u0026thinsp;0.8 V (Supplementary Fig. S27). These results indicate that GX and NH\u003csub\u003e2\u003c/sub\u003eOH act as essential intermediates in the overall reaction pathway. Their efficient coupling constitutes the key C\u0026thinsp;\u0026minus;\u0026thinsp;N bond-forming step in glycine electrosynthesis, highlighting the mechanistic significance of oxime intermediate formation and subsequent reductive amination. Besides, the isotopic-labelling experiments using \u003csup\u003e15\u003c/sup\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e as the nitrogen source confirmed that the generated NH\u003csub\u003e2\u003c/sub\u003eOH originates from \u003csup\u003e15\u003c/sup\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e,\u003csup\u003e18\u003c/sup\u003e rather than from any extraneous nitrogen-containing impurities (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg and Supplementary Figs. S28-30).\u003c/p\u003e\u003cp\u003eIn addition to catalytic activity and selectivity, long-term stability was also evaluated by conducting tests at \u0026minus;\u0026thinsp;0.95 V. The glycine yield accumulated continuously to 16.5 mmol over 12 consecutive cycles without noticeable decline in production performance (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh), demonstrating excellent electrochemical stability. Furthermore, in the prolonged electrolysis in a flow cell, Bi-ene maintained a consistent FE\u003csub\u003eglycine\u003c/sub\u003e of ~\u0026thinsp;60% over 120 hours at an industrially relevant current density of \u0026minus;\u0026thinsp;200 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei and Supplementary Fig. S31). The post-reaction characterizations revealed that the morphology, elemental composition, and crystal structure of Bi-ene remained largely unchanged, confirming its structural robustness under the long-term operating conditions (Supplementary Fig. S32-34). To the best of our knowledge, the as-prepared Bi-ene represents the first catalyst enabling salt-free glycine electrosynthesis through electrochemical C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling, demonstrating exceptional efficiency among the reported metal-based systems (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej, Supplementary Table S2).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction mechanism studies by\u003c/b\u003e \u003cb\u003eoperando\u003c/b\u003e \u003cb\u003espectroscopies and DFT calculations\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo gain deeper insight into the C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling mechanism on the Bi-ene surface, we conducted the \u003cem\u003eoperando\u003c/em\u003e Fourier-transform infrared (FTIR) spectroscopy analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea) to track the evolution of key intermediates during the co-electrolysis of OA and HNO\u003csub\u003e3\u003c/sub\u003e. Compared with NtrRR, more vibrational features were observed, indicative of chemical interactions between nitrogen- and carbon-based intermediates during the co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Specifically, the decreased intensity of the peak at 1720 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O of OA) and the enhanced signal at 1242 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicate the progressive consumption of OA and the formation of *NH\u003csub\u003e2\u003c/sub\u003eOH, respectively.\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e The early appearance of the *NH\u003csub\u003e2\u003c/sub\u003eOH signal at a relatively lower potential (\u0026minus;\u0026thinsp;0.6 V) highlights the favorable kinetics of NtrRR. As the potential becomes more negative, the emergence of peaks at 1643 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;N), 1593 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;\u0026minus;\u0026thinsp;N\u0026minus;H), and 1380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (CH\u003csub\u003e2\u003c/sub\u003e) suggests the reaction of GX with *NH\u003csub\u003e2\u003c/sub\u003eOH forming the oxime group (C\u0026thinsp;=\u0026thinsp;N\u0026thinsp;\u0026minus;\u0026thinsp;OH) of GAO intermediates, which is subsequently converted into glycine.\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e The temporal correlation between the depletion of OA signals, the accumulation of NH\u003csub\u003e2\u003c/sub\u003eOH, and the appearance of glycine-associated vibrational modes highlights stepwise reactions involving the formation and coupling of two reactive intermediates of NH\u003csub\u003e2\u003c/sub\u003eOH and GX. These spectral features collectively support that the Bi-ene catalyst promotes the selective electrosynthesis of glycine via the co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eTo further validate this mechanism and gain insights into the structural evolution and active sites of Bi-ene during the co-electroreduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e, \u003cem\u003eoperando\u003c/em\u003e synchrotron-based X-ray absorption spectroscopy (XAS) was performed. \u003cem\u003eOperando\u003c/em\u003e XANES and EXAFS analyses revealed a cathodic shift in the Bi L\u003csub\u003e3\u003c/sub\u003e-edge toward the energy position of metallic Bi, indicating the reduction of Bi\u003csup\u003e3+\u003c/sup\u003e species to Bi\u003csup\u003e0\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), \u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e which is catalytically responsible for driving the selective transformation of OA and HNO\u003csub\u003e3\u003c/sub\u003e to glycine. Additionally, a poisoning experiment was performed in the electrolyte containing potassium thiocyanate (KSCN), a known metal site inhibitor.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e Upon KSCN addition, both the FE and \u003cem\u003ej\u003c/em\u003e for glycine formation declined markedly relative to the unpoisoned system (Fig. S35), strongly implicating the metallic Bi centers as the primary active sites responsible for C\u0026thinsp;\u0026minus;\u0026thinsp;N bond formation.\u003c/p\u003e\u003cp\u003eTo gain mechanistic insight into the experimental observations, DFT calculations were performed to elucidate the effect of lattice strain on facilitating NtrRR and enhancing glycine formation. Based on HRTEM analysis, three representative models were constructed, including the pristine Bi (012) facet, Bi (012) edge, and defective Bi (012) plane with planar distortions (Fig. S36). The adsorption configurations and activation barriers of HNO\u003csub\u003e3\u003c/sub\u003e on the above catalytic sites were first evaluated, revealing favorable adsorption with moderate binding energies, thereby facilitating surface activation. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, the formation of NH\u003csub\u003e2\u003c/sub\u003eOH proceeds via the protonation of adsorbed *NO to form the *NHO intermediate, followed by the desorption of *NH\u003csub\u003e2\u003c/sub\u003eOH to release NH\u003csub\u003e2\u003c/sub\u003eOH. Notably, the endothermic protonation of *NO\u003csub\u003e2\u003c/sub\u003e to *NO\u003csub\u003e2\u003c/sub\u003eH, identified as the rate-determining step in NtrRR, show a high Gibbs free energy change (ΔG\u0026thinsp;=\u0026thinsp;0.305 eV) on intact Bi (012) plane. In contrast, the defective Bi-ene substantially lowers this energy barrier to 0.062 eV, demonstrating enhanced catalytic activity and a strong preference for NH\u003csub\u003e2\u003c/sub\u003eOH formation at lattice defect sites. Furthermore, compared to the relatively low free energy barrier of 0.062 eV for the protonation of *NO\u003csub\u003e2\u003c/sub\u003e, the energy required for direct proton activation reaches 1.25 eV, indicating significantly hindered hydrogen evolution on the Bi-ene catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). This is consistent with the observed low FEs for HER on Bi-ene. Importantly, the electro-reductive hydrogenation of GAO to glycine was demonstrated to be both kinetically accessible and thermodynamically favorable, as evidenced by the exergonic nature of the overall process (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). The Gibbs free energy profiles on different Bi surfaces exhibit similar trends along the reaction pathway. However, a notable difference emerges in the final desorption step of *HOOCCH\u003csub\u003e2\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e, where the ΔG on defective Bi (012) is only 0.058 eV, significantly lower than that (0.319 eV) of intact Bi (012). This thermodynamic advantage suggests that the release of glycine is more favorable on the Bi-ene defective sites, contributing to its enhanced catalytic performance. These theoretical insights underscore the superior catalytic performance of lattice-distorted Bi-ene compared to the counterparts, in promoting key reaction steps such as NH\u003csub\u003e2\u003c/sub\u003eOH formation and GAO reduction and facilitating the desorption of the final product, consistent with experimental results. To further evaluate catalyst effectiveness, various metal foils (Cu, Ti, Ag, Pt) were tested as the cathodic catalysts for glycine electrosynthesis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). While Cu and Ag favored NH\u003csub\u003e3\u003c/sub\u003e formation, and Pt and Ti primarily promoted H\u003csub\u003e2\u003c/sub\u003e evolution, Bi-ene stood out by delivering the highest glycine selectivity and yield among all metals examined.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eSubstrate expansion\u003c/h3\u003e\n\u003cp\u003eEncouraged by this catalytic efficacy, we expanded the application of Bi-ene in the electrocatalytic C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling. A series of structurally diverse α-keto acids were subjected to co-electrolysis with HNO\u003csub\u003e3\u003c/sub\u003e using Bi-ene as the catalyst. Remarkably, each substrate was efficiently converted into the corresponding α-amino acid with high FEs, as confirmed by \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR spectroscopy (Scheme \u003cspan refid=\"Sch2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Supplementary Figs. S37-42), for example, achieving a FE of 48.8% for alanine and 40.2% for aspartic acid. These results demonstrate that Bi-ene is capable of accommodating a wide range of α-keto acid skeletons, including both linear and branched chains with increasing molecular complexity. Besides, the catalytic system is also applicable to alternative nitrogen sources, as evidenced by the efficient electrochemical synthesis of sarcosine (FE\u0026thinsp;=\u0026thinsp;64.3%) and N-ethylglycine (FE\u0026thinsp;=\u0026thinsp;53%) when replacing NH\u003csub\u003e2\u003c/sub\u003eOH with N-methylhydroxylamine and N-ethylhydroxylamine, respectively. These findings highlight the potential of MOF-derived Bi-ene in efficient electrosynthesis of α-amino acids with variable carbon skeletons (C\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026minus;\u0026thinsp;C\u003csub\u003e5\u003c/sub\u003e) and nitrogen functionalities under mild electrochemical conditions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, this study highlights a salt-free electrosynthesis of glycine via the simultaneous electrochemical reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e, enabled by an atomically thin lattice-distorted Bi-ene catalyst. The Bi-ene catalyst exhibits unique bifunctional properties that promote efficient C − N coupling of NH\u003csub\u003e2\u003c/sub\u003eOH and GX \u003cem\u003ein situ\u003c/em\u003e-generated from the co-electrolysis of HNO\u003csub\u003e3\u003c/sub\u003e and OA, achieving remarkable glycine production with a high yield rate of 455.4 µmol cm\u003csup\u003e− 2\u003c/sup\u003e h\u003csup\u003e− 1\u003c/sup\u003e and a FE of 68.2%. Spectroscopic characterizations combined with DFT calculations reveal that the \u003cem\u003ein situ\u003c/em\u003e electrochemical reconstruction of Bi-MOF to Bi-ene under reductive conditions induces substantial lattice strain that modulates the local electronic environment, which stabilizes key reaction intermediates and lowering the energy barriers. This work deepens the understanding of electrocatalytic C − N coupling pathways and demonstrates the efficacy of lattice defects in tailoring the electronic structures and reactivity of metal catalysts.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch2\u003eSynthesis of Bi-CAU-17\u003c/h2\u003e\u003cp\u003eBi-CAU-17 was synthesized based on reported procedures with slight modifications. Specifically, 375 mg of 1,3,5-benzenetricarboxylic acid (H\u003csub\u003e3\u003c/sub\u003eBTC) and 750 mg of bismuth nitrate pentahydrate [Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e·5H\u003csub\u003e2\u003c/sub\u003eO] were dispersed in 30 mL of methanol under continuous stirring at room temperature for 30 minutes. The homogeneous mixture was then transferred into a 50 mL Teflon-lined stainless-steel autoclave and subjected to solvothermal treatment at 120°C for 24 hours. After cooling to room temperature, the resulting precipitates were collected via centrifugation, washed multiple times with methanol to remove unreacted species, and subsequently dried at 60°C.\u003c/p\u003e\u003ch3\u003eSynthesis of Bi-ene electrode\u003c/h3\u003e\u003cp\u003eBi-ene was synthesized via an electrochemical reconstruction of Bi-CAU-17 in a standard three-electrode electrochemical setup. To prepare the catalyst ink, 10.0 mg of Bi-CAU-17 was ultrasonically dispersed for 1 hour in a solvent mixture comprising 700 µL of ethanol, 200 µL of H\u003csub\u003e2\u003c/sub\u003eO, 50 µL of DMF and 50 µL of 5 wt% Nafion solution. Subsequently, 200 µL of the resulting suspension was drop-cast onto both sides of a 1.0 × 1.0 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e carbon paper (CP) electrode, yielding a total Bi-CAU-17 loading of 2.0 mg cm⁻\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The Bi-CAU-17 electrodes were subjected to consecutive cyclic voltammetry (CV) scans for 100 cycles at a rate of 100 mV s⁻¹ within the potential window of − 0.2 to − 1 V vs. Ag/AgCl in an Ar-saturated electrolyte.\u003c/p\u003e\u003cp\u003e\u003cb\u003e2. Characterizations\u003c/b\u003e\u003c/p\u003e\u003cp\u003eX-ray diffraction (XRD) patterns of the synthesized materials and electrode samples were collected using a Rigaku MiniFlex 600 benchtop diffractometer equipped with Cu K\u003csub\u003eα\u003c/sub\u003e radiation. Surface morphology and microstructural features were examined via scanning electron microscopy (SEM, JEOL JSM-7800F), while detailed structural information at the nanoscale was obtained through transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) using an FEI Tecnai G2 F30 microscope. X-ray photoelectron spectroscopy (XPS) measurements were conducted on a Thermo Fisher ESCALAB 250Xi spectrometer employing monochromatic Al K\u003csub\u003eα\u003c/sub\u003e radiation (E = 1486.2 eV). The C 1s peak at 284.8 eV was used as the reference for binding energy calibration. Atomic force microscopy (AFM) images were captured using a Bruker Dimension ICON system. \u003cem\u003eIn situ\u003c/em\u003e attenuated total reflectance infrared (ATR-IR) spectra were acquired on a NICOLET 6700 spectrometer to monitor dynamic surface species during electrochemical processes.\u003c/p\u003e\u003cp\u003e\u003cb\u003e3. Electrochemical measurements\u003c/b\u003e\u003c/p\u003e\u003cp\u003eElectrochemical experiments, including linear sweep voltammetry (LSV) and controlled potential electrolysis (CPE), were performed using a two-compartment H-type cell connected to a CHI 660E electrochemical workstation. The cathodic and anodic chambers were separated by a Nafion N-117 proton exchange membrane. A platinum mesh served as the counter electrode, while a saturated Ag/AgCl electrode was used as the reference. CPEs including OARR, NtrRR, co-reduction of OA and HNO\u003csub\u003e3\u003c/sub\u003e, co-reduction of OA and NH\u003csub\u003e2\u003c/sub\u003eOH, co-reduction of GX and HNO\u003csub\u003e3\u003c/sub\u003e, co-reduction of GX and NH\u003csub\u003e2\u003c/sub\u003eOH, were carried out in 0.5 M HCl + 0.5 M OA, 0.5 M HCl + 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e, 0.5 M HCl + 0.5 M OA + 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e, 0.5 M OA + 0.5 M NH\u003csub\u003e2\u003c/sub\u003eOH·HCl, 0.5 M HCl + 0.5 M GX + 0.5 M HNO\u003csub\u003e3\u003c/sub\u003e and 0.5 M GX + 0.5 M NH\u003csub\u003e2\u003c/sub\u003eOH·HCl, respectively. Prior to electrolysis, Ar gas was purged through the catholyte for 30 minutes to remove dissolved oxygen. All electrolysis was carried out at predetermined potentials under ambient temperature.\u003c/p\u003e\u003cp\u003e\u003cb\u003e4. Identification and quantification of products\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFollowing electrolysis, gaseous products were analyzed using an Agilent 7890B gas chromatograph. Liquid-phase products, including glycine, glyoxylic acid (GX), glycolic acid (GC), hydroxylamine (NH\u003csub\u003e2\u003c/sub\u003eOH), and glyoxylic acid oxime (GAO), were quantified via proton nuclear magnetic resonance (\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR) spectroscopy with water suppression using a Bruker AVANCE 600 MHz instrument. For a typical analysis, 0.5 mL of the electrolyte was mixed with 0.1 mL of a 10 mM DMSO/D\u003csub\u003e2\u003c/sub\u003eO solution which was used as the internal standard. For NH\u003csub\u003e2\u003c/sub\u003eOH detection, 1 mL of the electrolyte was first mixed with 15 µL of 50 wt% GX solution. After oximation, 0.5 mL of the solution was mixed with 0.1 mL of a 10 mM DMSO/D\u003csub\u003e2\u003c/sub\u003eO solution and then used as the rest sample. Additional species such as nitrite (NO\u003csub\u003e2\u003c/sub\u003e⁻) and ammonium (NH\u003csub\u003e4\u003c/sub\u003e⁺) were also determined by UV–Vis spectroscopy. Detailed protocols for UV–Vis quantification of nitrogen-containing species are provided below.\u003c/p\u003e\u003ch2\u003eDetection of NO\u003csub\u003e2\u003c/sub\u003e⁻\u003c/h2\u003e\u003cp\u003eTo prepare the colorimetric reagent, 0.4 g of 3-aminobenzenesulfonamide, 0.02 g of N-(1-naphthyl) ethylenediamine dihydrochloride, and 1 mL of concentrated phosphoric acid were dissolved in 5 mL of deionized water. After the electrochemical reaction was completed, 400 µL of the electrolyte was mixed with 100 µL of the prepared color reagent and 3.5 mL of deionized water. The resulting mixture was allowed to stand at room temperature for 20 minutes before being analyzed using UV − Vis spectroscopy. The calibration curve of NO\u003csub\u003e2\u003c/sub\u003e⁻ is shown in Supplementary Fig. S44.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eNH\u003csub\u003e3\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003eDetection\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAmmonia concentration was determined using the indophenol blue colorimetric method. Three separate reagents were prepared for color development: Reagent A was obtained by dissolving 10 g NaOH, 12.5 g salicylic acid, and 12.5 g sodium citrate in 250 mL of deionized water; Reagent B consisted of 7.1 mL of NaClO solution (\u0026ge;\u0026thinsp;5% active chlorine content) diluted to 100 mL with water; and Reagent C was prepared by dissolving 1 g sodium nitroferricyanide in 100 mL of water. For the assay, 1 mL of the diluted electrolyte was successively combined with 1 mL of Reagent A, 0.5 mL of Reagent B, and 0.1 mL of Reagent C. The mixture was allowed to react under ambient conditions, and the absorbance was recorded at 654 nm using a UV\u0026ndash;Vis spectrophotometer. The calibration curve of NH\u003csub\u003e3\u003c/sub\u003e is shown in Supplementary Fig. S45.\u003c/p\u003e\n\u003ch2\u003eFaradaic efficiency (FE) calculation\u003c/h2\u003e\n\u003cp\u003eThe Faradaic efficiency (FE) of ammonia was calculated based on the quantified NH\u003csub\u003e3\u003c/sub\u003e concentration.\u003c/p\u003e\n\u003cp\u003eThe FE for each liquid product could be calculated as follows:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere n\u003csub\u003ex\u003c/sub\u003e is the total mole of the liquid product x after electrochemical reaction, N is the total number of electrons required to generate the product, F is the Faraday constant (96485 C mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), Q is the total charge during the electrocatalytic process.\u003c/p\u003e\n\u003cp\u003eThe yield rate was calculated on the basis of the following equation:\u003c/p\u003e\n\u003cp\u003eYield rate (n\u003csub\u003ex\u003c/sub\u003e)\u0026thinsp;=\u0026thinsp;n\u003csub\u003ex\u003c/sub\u003e/A/t\u003c/p\u003e\n\u003cp\u003ewhere n\u003csub\u003ex\u003c/sub\u003e is the total mole of the liquid product x after electrochemical reaction, A is the geometric area (cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e); t is the reaction time (h).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupporting Information\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe detailed information for the experimental section and additional characterization are provided in the Supporting Information.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQ.-L.Z. is grateful for the financial support of the National Key Research and Development Program of China (2021YFA1500402), the National Natural Science Foundation of China (NSFC) (22175174 and 52332007), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB1170000), and the Natural Science Foundation of Fujian Province (2021J06033). Z.H. acknowledges support under the Australian Research Council\u0026rsquo;s Discovery Projects funding scheme (DP250102613 and DP250103803).\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eXue Y-P, Cao C-H, Zheng Y-G. Enzymatic asymmetric synthesis of chiral amino acids. \u003cem\u003eChem.Soc.Rev.\u003c/em\u003e \u003cstrong\u003e47\u003c/strong\u003e, 1516-1561 (2018).\u003c/li\u003e\n\u003cli\u003eGr\u0026ouml;ger H. Catalytic Enantioselective Strecker Reactions and Analogous Syntheses. \u003cem\u003eChem. Rev.\u003c/em\u003e \u003cstrong\u003e103\u003c/strong\u003e, 2795-2828 (2003).\u003c/li\u003e\n\u003cli\u003ePulletikurti S, Yadav M, Springsteen G, Krishnamurthy R. Prebiotic synthesis of \u0026alpha;-amino acids and orotate from \u0026alpha;-ketoacids potentiates transition to extant metabolic pathways. \u003cem\u003eNat. 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Mater.\u003c/em\u003e \u003cstrong\u003e33\u003c/strong\u003e, 2003238 (2021).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eSchemes are available in the Supplementary Files section.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Electrocatalytic C-N coupling, Amino acids, Lattice strain, Bismuthene, Nitrate reduction reaction","lastPublishedDoi":"10.21203/rs.3.rs-7471908/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7471908/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrochemical C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling using simple inorganic feedstocks offers a sustainable route to valuable organonitrogen compounds such as amino acids. Herein, we present an atomically-thin and acid-resistant \u003cem\u003ep\u003c/em\u003e-block bismuthene (Bi-ene) derived via the reconstruction of a Bi-based metal\u0026thinsp;\u0026minus;\u0026thinsp;organic framework, where the enriched atomic misarrangement induces significant lattice strain that modulates the local electronic structure of the resultant Bi-ene, significantly boosting its electrocatalytic activity. Such defective Bi-ene exhibits an exceptional electrocatalytic performance for reductive C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling in a salt-free acidic system, achieving a remarkable Faradaic efficiency (FE) of 95.7% and an ultrahigh yield rate of 1161 \u0026micro;mol cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for NH\u003csub\u003e2\u003c/sub\u003eOH generation via the nitrate reduction reaction (NtrRR). Further, the efficient co-reduction of HNO\u003csub\u003e3\u003c/sub\u003e and oxalic acid (OA) over Bi-ene simultaneously generates NH\u003csub\u003e2\u003c/sub\u003eOH and glyoxylic acid (GX) respectively, which undergo effective C\u0026thinsp;\u0026minus;\u0026thinsp;N coupling to produce glycine with a high yield of 455.4 \u0026micro;mol cm⁻\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e h⁻\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Moreover, the Bi-ene demonstrates stable performance for over 120 hours at an industrial-relevant current density of 200 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. \u003cem\u003eOperando\u003c/em\u003e spectroscopy and calculations reveal that the strain in lattice-distorted Bi-ene optimizes the intermediate adsorption through modulating local electronic structure and thus enhances the efficacy for glycine electrosynthesis.\u003c/p\u003e","manuscriptTitle":"Salt-Free Glycine Electrosynthesis via C−N Coupling Boosted by the Lattice Strain in Atomically Thin p-Block Bismuthene","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-11 19:21:39","doi":"10.21203/rs.3.rs-7471908/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bc4e334c-eb31-4d60-93c1-6926fbd2c275","owner":[],"postedDate":"September 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":54518208,"name":"Physical sciences/Chemistry/Electrochemistry/Electrocatalysis"},{"id":54518209,"name":"Physical sciences/Energy science and technology"}],"tags":[],"updatedAt":"2025-09-24T13:30:54+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-11 19:21:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7471908","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7471908","identity":"rs-7471908","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}