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. 2025 Aug 7;147(36):32809–32817. doi: 10.1021/jacs.5c08836

Interlayer Expansion Enables Electrochemical Domino C–N Coupling for Formaldoxime Formation in Aqueous Media

Ruijie Yi †, Xiaoyong Mo †, Hei Tung Yau †, Tao Zhou †, Zhengxiao Guo †, Shu-Chih Haw ‡, Edmund C M Tse †,*
PMCID: PMC12435446  PMID: 40775610

Abstract

Upcycling C- and N-containing pollutants into value-added resources is key to achieving a sustainable society in the near future. In recent years, coelectrolysis powered by renewable energy sources to generate structurally complicated and functionally diverse C–N bonds is highly desirable yet more challenging compared with C-only or N-only reduction reactions. Oximes, which contain C=N bonds, are important precursors in medicine and the fine chemical industry. Previous attempts to coreduce carbon dioxide and nitrate or nitrite yielded formaldoxime (H2C=NOH) as a byproduct with low selectivity. Herein, we demonstrate a new tandem electrocatalytic pathway to produce H2C=NOH as the target product using NiFe layered double hydroxides (LDHs) as efficient catalysts. Upon expanding the interlayer spacing of NiFe LDH using dodecyl-sulfonate as an intercalating anion, this catalyst displays a record-high Faradaic efficiency for H2C=NOH of 31% in aqueous solution at −1.9 V vs reversible hydrogen electrode. Our findings also show that the lengths of alkyl chains can tune the immediate microenvironment surrounding the dual Ni–Fe active sites, thus boosting the C–N coupling yield rate. Kinetic isotopic effect studies and control experiments under H2 are further carried out to interrogate the electrocatalytic mechanism of this tandem C–N bond formation process. Overall, this study offers a compelling approach to form a C–N bond via a green electrosynthesis scheme in an aqueous medium. Furthermore, this study underscores the importance of precisely regulating the electrochemical microenvironment for enhancing the synergy between dual-metal active sites for efficient domino electrosynthesis.

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Introduction

Transforming C- and N-containing wastes and pollutants into valuable resources is essential for achieving carbon neutrality and establishing a circular nitrogen economy. − To realize the sustainable development goals (SDGs) highlighted by the United Nations, conventional strategies at high temperatures and elevated pressures have been exploited to synthesize earth-abundant feedstocks from carbonaceous wastes (C-wastes) as well as remove nitrogenous toxins (N-toxins) from soil and groundwater. − However, these individual strategies involving organic solvents tend to treat C-wastes and N-toxins separately, thus limiting the cost effectiveness and resource efficiency of these trash-to-treasure conversion processes. , Instead of forming low-value C- and N-products independently, this upcycling process can become more desirable by producing structurally complicated and functionally diverse organonitrogen compounds that are widely present in the pharmaceutical and fine chemical industries. − Hence, there is an urgent need to develop new methodologies that can utilize C-wastes and N-toxins as resources and simultaneously convert them into valuable products featuring C–N bonds under ambient conditions in an environmentally friendly and highly efficient manner. −

Electrochemical coreduction at room temperature and ambient pressure in aqueous solvent powered by renewable energy can serve as a practical alternative for coupcycling to achieve C,N products exclusively with high C-/N-atom efficiencies. Specifically, urea synthesis is a prime example for electrocatalytic C–N bond formation from C- and N-sources. − Using a PdCu alloy supported on TiO2 as an electrocatalyst, Wang et al. reported a direct reaction pathway between nitrogen (N2) and carbon dioxide (CO2) to form urea with a Faradaic efficiency (FE) of 9%. The activity was limited by the solubility and activity of these two gaseous reactants. Subsequently, Zhang et al. reported an alternative strategy to synthesize urea from nitrite (NO2 –) and CO2 with an FE of 23% for urea using oxygen-vacancy-rich ZnO porous nanosheets as catalysts. While urea is a useful commodity, other C–N products beyond urea are actively being pursued and can potentially be achieved by exploiting green electrocatalytic coreduction.

Oximes, which feature C=N bonds, are important reactants in organic synthesis as key intermediates to generate aldehydes for use in pharmaceutical and fine chemical industries. , To synthesize formaldoxime (H2C=NOH), the C-source, the N-source, and the catalysts need to be chosen carefully. Zou et al. showed that a metal Fe catalyst can achieve an FE for benzaldoxime of 12% after 12 h of C–N coupling between aldehydes and NO x . Recently, Wang et al. reported the coreduction of CO2 and nitrate (NO3 –) to yield methylamine (CH3NH2) with 13% FE and H2C=NOH with 6% FE using cobalt β-tetraaminophthalocyanine/carbon nanotube (CoPc-NH2/CNT) hybrid material as the catalyst. Previous work also demonstrated that the use of NO2 – instead of NO3 – as the N-source improves C–N coupling efficiency because the sluggish reduction from NO3 – to NO2 – is bypassed. − Although direct C–N bond formation to generate methylamine and H2C=NOH is promising, the efficiency of this C–N coupling reaction still has substantial room for improvement.

Herein, we report an electrochemical domino process to convert NO2 – and formaldehyde (H2CO) into H2C=NOH with alkyl-chain-intercalated NiFe layered double hydroxides (LDHs) as catalysts (Figure ). NiFe LDHs are selected because they (i) exhibit a lamellar structure with high surface area for efficient reactant replenishment and product removal, , (ii) contain bimetallic sites that facilitate synergistic interactions with substrates and key intermediates, , (iii) display high electrocatalytic activity toward NO3 –/NO2 – reduction reactions (NO3RR/NO2RR), − and (iv) feature robust morphology with enhanced stability during operation. Interlayer expanding agents with designated alkyl chain lengths and head groups are incorporated to tune the nanosheet spacing and hydrophobicity as a strategy to promote C–N formation.

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Schematic diagrams of H2C=NOH electrosynthesis using an interlayer-expanded LDH catalyst.

Results and Discussion

Cl– NiFe LDH and interlayer-expanded NiFe LDH are explored as catalysts for electrochemical C–N bond formation using H2CO and NO2 – as the C- and N-sources. First, Cl– NiFe LDH without CO3 2– intercalation is prepared via a hydrothermal synthesis process following a published protocol (Figure S1a). Next, interlayer-expanded NiFe LDH is prepared by replacing the Cl– in NiFe LDH with alkyl sulfonates via direct anion exchange and intercalation (see the Methods section for detailed procedure). To investigate the effect of LDH interlayer expansion on the electrocatalytic C–N bond formation process, the carbon chain length of the alkyl sulfonates is altered from C6 to C14. Our experiments show that acidic conditions of pH 2.5 are crucial for the anion exchange process by suppressing the dissolved CO2 (aq) and carbonate concentrations in water. Aqueous medium is further found to be essential for introducing interlayer expanding agents into Cl– NiFe LDH by promoting chloride dissolution from the LDH interlayers.

The overall structure and morphology of as-prepared LDH samples are characterized using X-ray and electron microscopic techniques. The powder X-ray diffraction (PXRD) patterns show that the (003) peak shifts to a lower angle as the carbon chain length increases from C6 to C14, indicating that the interlayer spacing expands from 1.71 to 2.70 nm according to Bragg’s law (Figure a and Table S1). Scanning transmission electron microscopy (STEM) is used to further provide direct evidence that the interlayer distance of LDH has increased. Cl– NiFe LDH and interlayer-expanded NiFe LDHs (i.e., C10–SO3 – NiFe LDH, C12–SO3 – NiFe LDH, and C14–SO3 – NiFe LDH) show obvious differences in lattice fringes with interlayer spacings of 0.83, 2.06, 2.41, and 2.73 nm respectively (Figures b, c, and S2), which are consistent with the PXRD results. Scanning electron microscopy (SEM) images show the layered structure of C12–SO3 – NiFe LDH, and energy dispersive spectroscopy (EDS) elemental mapping shows that Ni and Fe are uniformly distributed across the LDH nanosheets (Figures d, S3, and S4). Inductively coupled plasma mass spectrometry (ICP-MS) and EDS are also used to obtain the Ni:Fe ratio, which is found to be 3:1 (Table S2). The PXRD, STEM, SEM, and EDS results corroborate that after the overnight anion exchange process chloride is replaced by sulfonate-based interlayer expanding agents with alkyl chain lengths varying from C6 to C14, respectively. The ratios of intercalated anions versus metal cations before and after intercalation are investigated using X-ray photoelectron spectroscopy (XPS) and EDS (Figure S5, Table S3, and Table S4). Figure S5 illustrates that the major peaks of Cl– NiFe LDH correspond to Ni 2p, Fe 2p, C 1s, O 1s, and Cl 2p, whereas the major peaks of C12–SO3 – NiFe LDH are assigned to Ni 2p, Fe 2p, C 1s, O 1s, and S 2p. Both in Cl– NiFe LDH and C12–SO3 – NiFe LDH, the ratio of Ni:Fe is almost 3:1, which is consistent with the results of EDS and ICP-MS. Cl– NiFe LDH displays a nearly 1:1 ratio of Cl:Fe. Conversely, in C12–SO3 – NiFe LDH, the ratio of Cl:Fe decreases drastically to 0.093:1 while the ratio of S:Fe approaches 1:1. EDS results also show similar Cl:Fe and S:Fe ratios in Cl– NiFe LDH and C12–SO3 – NiFe LDH, which verify the successful replacement of Cl– by C12–SO3 – after overnight intercalation.

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(a) PXRD patterns of NiFe LDH intercalated with alkyl sulfonates (lengths of alkyl chains range from C6 to C14). STEM images of NiFe LDHs with (b) Cl– and (c) C12–SO3 – as the intercalating anions. (d) SEM images of the C12–SO3 – NiFe LDH. (e) High-resolution Ni 2p XPS spectrum of the C12–SO3 – NiFe LDH. (f) High-resolution Fe 2p XPS spectrum of C12–SO3 – NiFe LDH. (g) Ni L-edge XANES spectra of Ni powder (black), Ni­(OH)2 (blue), and C12–SO3 – NiFe LDH (green). (h) Fe L-edge XANES spectra of FeCl2 (blue), Fe2O3 (navy), and C12–SO3 – NiFe LDH (green). (i) FTIR spectra of C12–SO3 – NiFe LDH (green), C12–SO3Na (purple), and Cl– NiFe LDH (red).

To further verify the oxidation state of the metals in the nanosheets of C12–SO3 – NiFe LDH, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) are performed. The high-resolution Ni 2p spectrum shows two main Ni 2p peaks, Ni 2p3/2 (873.8 eV) and Ni 2p1/2 (856.1 eV) with two satellite peaks, indicative of the presence of Ni2+ (Figure e). The high-resolution Fe 2p spectrum shows two peaks (712.7 and 725.4 eV), indicating the presence of Fe3+ (Figure f). XAS is performed to verify the oxidation states of Ni and Fe (Figures g and h) (see SI Note 1 for preparation details). Both the Ni and Fe L-edge X-ray absorption near-edge structure (XANES) spectra display two well-separated peaks, which are assigned to Ni2+ and Fe3+ with the use of Ni, Ni­(OH)2, FeCl2, and Fe2O3 standards. , Taken together, these results show that the oxidation states of Ni and Fe in C12–SO3 – NiFe LDH remain the same as that of Cl– NiFe LDH after the anion exchange process (Figure S6).

Fourier-transform infrared spectroscopy (FTIR) is performed to verify the presence of alkyl sulfonate in interlayer-expanded LDH (Figure i). In the FTIR spectra of Cl– NiFe LDH and C12–SO3 – NiFe LDH, a wide band at 3418 cm–1 is observed in both cases and is thus attributed to ν­(H2O). Using C12–SO3Na as a reference, two bands at 2923 and 2854 cm–1 in the FTIR spectrum of C12–SO3 – NiFe LDH are assigned as CH2 asymmetrical and symmetrical stretches, respectively. Next, two subtle doublets near 1469 cm–1 are attributed to the CH2 scissoring vibration. Lastly, the broad band at 1160 cm–1 and the sharp band at 1042 cm–1 are assigned as the asymmetric and symmetric stretching modes of S–O in both C12–SO3Na and C12–SO3 – NiFe LDH. These FTIR results demonstrate that C12–SO3 – is intercalated into the NiFe LDH nanosheets with the integrity of its headgroup and carbon chain unperturbed.

Electrolysis is conducted to convert NO2 – and H2CO into H2C=NOH using carbon cloths coated with Cl– NiFe LDH and interlayer-expanded NiFe LDHs as working electrodes and 0.1 M PBS (pH 6.8) sparged with Ar containing 0.5 M NaNO2 and 0.5 M H2CO as the electrolyte solution (Figure a). After conducting electrolysis for 1 h, the solution is analyzed using nuclear magnetic resonance (NMR) to quantify the soluble products. Resonances at 7.10 ppm are consistent with H2C=NOH standard, indicating that the desired product with a newly formed C–N bond is generated (Figure S7). By adjusting the ratio of Ni:Fe of Cl– NiFe LDH, it is found that, when the Ni:Fe ratio is 3:1, the maximum Faradaic efficiency (FE) and yield rate (YR) for H2C=NOH are 12% and 8 mmol·gcat –1·h–1 at −1.9 V vs RHE, respectively (Figures b and S11). Of note, the 12% FE for H2C=NOH obtained by our Cl– NiFe LDH is twice the published selectivity record (6%). Therefore, the Ni:Fe ratio of 3:1 is used in subsequent studies for the coelectrolysis of NO2 – and H2CO to generate H2C=NOH.

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(a) Comparison of C–N coupling reaction catalyzed by Cl– NiFe LDH and C12–SO3 – NiFe LDH upon changing catalyst interface and microenvironment. (b) FE of Cl– NiFe LDH with the Ni:Fe ratio ranging from 4:1 to 1:1. (c) LSV curves of C12–SO3 – NiFe LDH in different electrolytes. (d) FE for H2C=NOH using Cl– NiFe LDH and interlayer-expanded NiFe LDH with alkyl chain lengths increasing from C6–C14.

Interlayer-expanded NiFe LDHs are next explored as electrocatalysts to improve the selectivity and yield rate of H2C=NOH electrosynthesis, because an enlarged lattice spacing induced by molecular interlayer expansion agents is hypothesized to promote the on-surface C–N coupling step. Linear sweep voltammetry (LSV) is used to probe the catalytic performance of interlayer-expanded NiFe LDH for electrochemical C–N bond formation (Figure S8). Compared with Cl– NiFe LDH, C12–SO3 – NiFe LDH shows a similar LSV profile. To further gain insight into the catalytic activity of C12–SO3 – NiFe LDH for the conversion of NO2 – and H2CO into H2C=NOH, LSV curves are recorded in four 0.1 M PBS solutions (gray) containing NO2 – and H2CO (red), NO2 – only (green), and H2CO only (orange). As shown in Figure c, in the absence of H2CO, a more positive onset potential and a higher current density are observed, indicating that the NO2 – reduction reaction (NO2RR) is energetically more favorable. In the absence of NaNO2, the current density is significantly decreased relative to the case with both NO2 – and H2CO present. We next perform open-circuit potential (OCP) measurements to probe the binding behavior of absorbates in the inner Helmholtz layer. As shown in Figure S9, the introduction of H2CO induces a slight change in the OCP (Δ = 0.0002 V), while the addition of NO2 – results in a substantial change in the OCP in the absence and presence of H2CO (Δ = 0.0078 V and Δ = 0.0061 V). These results indicate a favorable adsorption of NO2 – on C12–SO3 – NiFe LDH, which aligns with the observation from LSV that the onset potential becomes more positive upon the introduction of NO2 – introduction. Next, to elucidate the changes in current density from LSV, we quantify the product distribution in 0.1 M PBS solutions without and with NO2 – and/or H2CO (Figure S10). The results show that the presence of H2CO partially suppresses the HER, leading to the decrease in the overall current density observed. On the other hand, NO2RR promotes the generation of N-containing species regardless of the presence of H2CO. These results indicate that favorable NO2RR on C12–SO3 – NiFe LDH leads to the buildup of NH2OH at the interface that could be exploited for C–N coupling by trapping the N-intermediates with H2CO.

Due to the promising performance of interlayer-expanded NiFe LDH in producing H2C=NOH, the reaction conditions are thoroughly optimized by tuning intercalating alkyl chains, applied potentials, and substrate concentration. The headgroup is hypothesized to modulate surface binding affinity between interlayer expanding agents and NiFe LDH nanosheets. We therefore prepared interlayer-expanded NiFe LDH using alkyl chains carrying different headgroups (see SI Note 1 for characterization data of NiFe LDHs with their interlayers expanded by C12–SO4 – and C12–HPO4 –) (Figures S1b, S12, and S13). Using C12–SO3 –, C12–HPO4 –, and C12–SO4 – as intercalated alkyl chains, C12–SO3 – NiFe LDH is optimal to generate H2C=NOH with a 31% FE. Notably, the 31% FE for H2C=NOH achieved by our C12–SO3 – NiFe LDH is ∼4 times higher than the FE record in literature (6%).

We next explored the effect of alkyl chain length of the interlayer expanding agent on the C–N bond coupling efficiency. Longer length might result in enlarged interlayer spacing to increase the probability of N-intermediates and H2CO to encounter each other. NiFe LDH intercalated with alkyl chain–SO3 – of lengths ranging from C6 to C14 are utilized and analyzed for electrosynthesis of H2C=NOH. As shown in Figures d and S14, upon increasing the alkyl chain length from C6 to C12, both the FE and yield rate increase. Upon further increasing the alkyl chain length from C12 to C14, both the FE and yield rate do not improve further. We next explored the applied potential and reactant concentration to facilitate C–N bond coupling (Figures S15, S16, S17, S18, S19, and S20). The YR of NO2RR decreases at potentials more positive than −1.9 V, while H2CO is being reduced to MeOH at potentials more negative than −1.9 V. Therefore, these combined effects lower the collision frequency between intermediates, thus suppressing electrocatalytic C–N coupling efficiency. Taken together, the optimization results demonstrate that C12–SO3 – NiFe LDH exhibits the highest FE of 31% and the highest YR of 16 mmol·gcat –1·h–1 at–1.9 V vs RHE in 0.1 M PBS with 0.5 M NaNO2 and 0.5 M HCHO, which is ∼2.6 times higher than that of Cl– NiFe LDH. These results highlight that by tuning the anions connected to metal sites or the distance between interlayers, the tandem C–N coupling performance of NiFe LDH can be optimized through modifying the concentration of key intermediates in the microenvironment surrounding the nanosheets.

To verify that Nafion does not replace the alkyl chains, we employ PXRD to analyze the structure and interlayer spacings of Cl– after overnight treatment with Nafion solution (see SI Note 13 for experimental details). As shown in Figure S21, the (003) peak of Cl– NiFe LDH remains unchanged following exposure to Nafion solution, maintaining a peak position identical to that of the pristine material. This observation indicates that Nafion cannot substitute the intercalated sulfonate anions within the LDH sheets. To assess the influence of Nafion on electrocatalytic performance, we prepare a Nafion-free catalyst ink and evaluate its activity for C–N electrocatalytic formation. In Figure S22, the FE for H2C=NOH is 31% with or without Nafion as a binder in the catalyst ink. Collectively, our findings demonstrate that Nafion neither displaces the intercalated alkyl chains nor significantly impacts the electrocatalytic C–N coupling selectivity when used as a binder, while Nafion serves primarily as a binder to improve the robustness of the catalyst-electrode interface.

A recyclability test is next conducted to validate the practical applicability of our catalyst. This stability test entails five continuous cycles of H2C=NOH electrosynthesis with each cycle lasting 1 h. The results of the continuous 5-cycle test for H2C=NOH electrosynthesis show that the catalyst maintains its FE and YR over a total operation time of 5 h (Figure S23), corroborating its high durability under operating conditions. Postmortem SEM, PXRD, and FTIR results demonstrate that after 5 cycles, the catalyst retains the morphology and structure of the catalyst in its freshly prepared state (Figures S24, S25, and S26). Postmortem XAS is conducted to further show that there are no significant changes in the oxidation states of Ni and Fe after the coelectrolysis process with H2CO and NO2 – (Figure S27).

To gain deeper insights into the oxidation state and structural stability of C12–SO3 – NiFe LDH, K-edge XANES and the corresponding Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) spectroscopy are next conducted (Figure S28). The Ni K-edge and Fe K-edge XANES spectra after electrolysis reveal that the pre-edge feature and position are nearly identical with their corresponding spectra before electrolysis, indicating that the valence of Ni and Fe in C12–SO3 – NiFe LDH before and after the electrocatalytic C–N coupling reaction remains the same. In addition, FT-EXAFS analysis provides further evidence for structural stability. In Figure S28b, the characteristic coordination environment of the C12–SO3 – NiFe LDH remains essentially unchanged after electrolysis. These peaks are also consistent with the reference Ni­(OH)2 spectrum, which are attributed to Ni–OH. In Figure S28d, the main peaks in the Fe K-edge FT-EXAFS remain unchanged after H2C=NOH electrosynthesis. These XAS results indicate that both the valence of Ni and Fe and the structure of C12–SO3 – NiFe LDH remain stable during long-term electrocatalytic C–N formation.

To further understand the origin of protons on the carbon of H2C=NOH, D2O and D2CO are used instead of H2O and H2CO during the electrocatalytic process (Entries 1, 2, 3, and 4 in Table S5). 1H and 2D NMR spectra are used to detect the presence of H2C=NOH and D2C=NOH. 1H NMR results demonstrate that the resonances of CH2NOH can be detected only when the substrate is H2CO (Figure S29). When H2CO is replaced by D2CO, D2C=NOH can be detected only by 2D NMR rather than 1H NMR (Figure S30). These results corroborate that the protons on the carbon of H2C=NOH originate from the H2CO reactant.

Because hydroxylamine (NH2OH) and ammonia (NH3) are observed as products in NO2RR catalyzed by NiFe LDH (Figure S31 and Table S6), , experiments are conducted using NH2OH and NH3 to investigate which of these N-species is responsible for tandem C–N coupling (Entries 5, 6, and 7 in Table S5). H2C=NOH is detected only when the reaction involves NH2OH, hence indicating that NH2OH is a key N-intermediate in the electrocatalytic H2C=NOH synthesis process. To elucidate the reaction mechanism of H2C=NOH electrosynthesis, electrochemical in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is employed to identify key intermediates. The in situ IR measurement of C12–SO3 – NiFe LDH is conducted from −1.0 V to −2.4 V vs Ag/AgCl (Figures a and b). Two new absorption bands at 2852 and 2912 cm–1 are assigned to the N–H stretches in *NH2OH. This key observation is also supported by the bands at 1120 cm–1, corresponding to the N–O stretch of adsorbed *NH2OH intermediates. Our observation suggests the formation of NH2OH during the electrocatalytic C–N coupling from NO2RR, which is also consistent with our control experiments.

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ATR-FTIR spectra for the electrocatalytic C–N coupling from H2CO and NO2 – over the C12–SO3 – NiFe LDH (a) from 2700 to 3100 cm–1 and (b) from 900 to 1300 cm–1. (c) Schematic illustration of the H2C=NOH generation pathway.

Notably, after the reaction system is saturated with H2 in the absence of applied potential or current, no H2C=NOH can be detected (Entry 8 in Table S5 and Figure S32). Hence, the reduction of the NO2 – is attributed to the applied potential and current rather than H2 produced by HER, highlighting the major role of the applied potential and current for facilitating NO2RR during H2C=NOH electrosynthesis in the presence of H2CO and NO2 – (Figure c).

To assess the role of intercalated alkyl chains in the electrocatalytic C–N coupling process, we employed a partition method to evaluate the solubility difference of key C,N-species in an alkyl environment. In this partition experiment, aqueous solutions of three critical C,N-species, NaNO2, NH2OH, and H2CO, are separately mixed with equal volumes of hexane, dodecane, and hexadecane, respectively. After extraction, the residual concentrations of NaNO2, NH2OH, and H2CO in the aqueous phase are quantified using UV–vis and NMR (Table S7 and Figure S33). Our analytical results reveal that NH2OH and H2CO show similar partition behaviors in these three alkane solvents, indicating minimal solubility dependence on alkyl chain length. However, NaNO2 exhibits an observable chain-length-dependent solubility with optimal partition in dodecane.

To further elucidate the importance of NO2 – adsorption and reduction in the electrocatalytic H2C=NOH process, N-only reduction reactions are conducted in 0.1 M PBS with 0.5 M NaNO2 at −1.9 V vs RHE using C6-SO3 –, C12–SO3 –, and C16–SO3 – NiFe LDH as electrocatalysts. Figure S34 shows that C12–SO3 – NiFe LDH exhibits optimal FE and YR for NH2OH, consistent with the trend observed in the electrocatalytic C–N coupling process. These findings suggest that the alkyl-chain-length-dependent solubility of NaNO2 impacts its local concentration at the surface active sites, regulating the subsequent NO2 – reduction reaction efficiency and electrocatalytic C–N coupling activity and selectivity. This finding provides a molecular-level explanation for the superior electrocatalytic performance of C12–SO3 – NiFe LDH as well as the importance of adsorption of NO2 – to active sites in NiFe LDHs during H2C=NOH electrosynthesis.

Now that we have achieved the optimal electrocatalytic C–N coupling using C12–SO3 – NiFe LDH as the electrocatalyst, with the highest FE of 31% and the highest YR of 16 mmol·g·cat–1·h–1 at −1.9 V vs RHE, we further explore the industrial applicability of H2C=NOH electrosynthesis by conducting scaled-up electrolysis in 0.1 M PBS with 0.5 M NaNO2 and 0.5 M H2CO using a 50 mL flow-cell prototype. After 1 h electrolysis, the yield rate for H2C=NOH is enhanced significantly from 16 mmol·g·cat–1·h–1 to 280 mmol·g·cat–1·h–1, representing a 17.5-fold enhancement. To demonstrate the broad applicability of our tandem electrocatalytic strategy, we extended the substrate scope to include acetaldehyde, acetone, and cyclohexanone as alternative carbon sources and optimize the applied potentials. Table shows the performance of scale-up electrocatalytic C–N coupling using a flow electrolyzer. As summarized in Table , the optimal yield rates of C=N–OH containing products, including acetaldoxime, acetoxime, and cyclohexanone oxime, are 265, 128, and 214 mmol·g·cat–1·h–1 respectively, which highlights the industrial prospect of our strategy to drastically improve the yield rate for oxime products.

1. YR for Formaldoxime, Acetaldoxime, Acetoxime, and Cyclohexanone Oxime.

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Conclusions

Dual upgrading of C-wastes and N-toxins into versatile organonitrogens enables the simultaneous removal of pollutants and generation of value-added feedstocks via electrocatalysis powered by green energy sources. Here, we report a domino electrochemical strategy to conduct C–N bond formation and drive the electrosynthesis of formaldoxime (H2C=NOH) in aqueous solution with high activity and selectivity. In this work, a series of nonprecious-metal-layered double hydroxides (LDHs) featuring Ni and Fe surface sites are designed and prepared as electrocatalysts for tandem reduction and C–N coupling between nitrite and formaldehyde. Cl– NiFe LDH generates H2C=NOH with a Faradaic efficiency (FE) of 12%, which doubles the FE (6%) displayed by the best catalyst reported in a previous work. The interlayer spacings of LDHs are further enlarged by using interlayer expansion agents to promote the C–N bond formation efficiency. Intriguingly, interlayer-expanded C12–SO3 – NiFe LDH exhibits a record-high FE of 31% for H2C=NOH. Experiments using interlayer expansion agents with varying tail lengths further demonstrate that the FE and yield rate (YR) for H2C=NOH exhibit a positive correlation with interlayer spacing. These results show that H2C=NOH electrosynthesis can be efficiently achieved using interlayer-expanded NiFe LDH without a noble catalyst, high temperature, or elevated pressure. Mechanistic studies involving isotopic labeling, deuterated solvent, alternative N-sources, and H2 gas as reducing equivalents identify that (i) H2CO is the source of the protons on the carbon of H2C=NOH, (ii) the partial reduction of NO2 – generates NH2OH as a key intermediate for H2C=NOH formation, and (iii) interfacial electrocatalysis serves a critical role in driving C–N coupling at room temperature and ambient pressure. Taken together, this sequential electrochemical strategy not only boosts the catalytic performance of NiFe LDH toward H2C=NOH electrosynthesis via tailoring the microenvironment of the dual active sites featuring earth-abundant metals but also offers a sustainable route for the simultaneous resourcification of C- and N-pollutants that contribute toward establishing a circular carbon and nitrogen economy.

Supplementary Material

ja5c08836_si_001.pdf (1.8MB, pdf)

Acknowledgments

E.C.M.T. would like to express gratitude to the Innovation and Technology Commission for an ITSP Seed Project (ITF: ITS/271/22) on an interfacial electrocatalysis project and a TSSSU Scheme (ITC: TSSSU/HKU/23/05/2) on a waste-to-resource upcycling initiative. R.Y. was partially supported by the Shenzhen Science and Technology Innovation Commission Basic Science General Program (SZSTI: JCYJ20210324122011031). The authors also thank the Research Grants Council in Hong Kong for a Theme-based Research Scheme (TRS: T23-713/22-R), an Early Career Scheme (ECS: 27301120), and General Research Funds (GRF: 17308323, 17308724) for upgrading the materials characterization infrastructure at the HKU-CAS Joint Laboratory on New Materials and supporting research activities on green electrocatalysis and clean production. The work described in this paper was partially supported by a grant from the Co-funding Mechanism on Joint Laboratories with the Chinese Academy of Sciences (CAS) sponsored by the Research Grants Council of the Hong Kong Special Administrative Region, China and the CAS (Project No. JLFS/P-701/24). We thank Wanying Wang and Pamela A. Lie for their help with initial studies. We also thank the support from Frankie Y.F. Chan at the HKU Electron Microscope Unit (EMU) and staff members at the National Synchrotron Radiation Research Centre (NSRRC) for help with nanomaterials characterization.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.5c08836.

  • Supplemental experimental details, catalyst characterizations, NMR spectra, and additional electrochemical data (PDF)

The authors declare no competing financial interest.

References

  1. El Sawy E. N., Birss V. I.. Nanoengineered Ircore@Ptshell Nanoparticles with Controlled Pt Shell Coverages for Direct Methanol Electro-Oxidation. ACS Appl. Mater. Interfaces. 2018;10:3459–3469. doi: 10.1021/acsami.7b13080. [DOI] [PubMed] [Google Scholar]
  2. Ren W., Xu A., Chan K., Hu X.. A Cation Concentration Gradient Approach to Tune the Selectivity and Activity of CO2 Electroreduction. Angew. Chem., Int. Ed. 2022;61:e202214173. doi: 10.1002/anie.202214173. [DOI] [PubMed] [Google Scholar]
  3. Stroka J. R., Kandemir B., Matson E. M., Bren K. L.. Electrocatalytic Multielectron Nitrite Reduction in Water by an Iron Complex. ACS Catal. 2020;10:13968–13972. doi: 10.1021/acscatal.0c03600. [DOI] [Google Scholar]
  4. Artz J., Müller T. E., Thenert K., Kleinekorte J., Meys R., Sternberg A., Bardow A., Leitner W.. Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle Assessment. Chem. Rev. 2018;118:434–504. doi: 10.1021/acs.chemrev.7b00435. [DOI] [PubMed] [Google Scholar]
  5. Azeem B., KuShaari K., Man Z. B., Basit A., Thanh T. H.. Review on Materials & Methods to Produce Controlled Release Coated Urea Fertilizer. J. Controlled Release. 2014;181:11–21. doi: 10.1016/j.jconrel.2014.02.020. [DOI] [PubMed] [Google Scholar]
  6. Liu Z., Wang K., Chen Y., Tan T., Nielsen J.. Third-generation Biorefineries as the Means to Produce Fuels and Chemicals from CO2 . Nat. Catal. 2020;3:274–288. doi: 10.1038/s41929-019-0421-5. [DOI] [Google Scholar]
  7. Akter T., Pan H., Barile C. J.. Tandem Electrocatalytic CO2 Reduction inside a Membrane with Enhanced Selectivity for Ethylene. J. Phys. Chem. C. 2022;126:10045–10052. doi: 10.1021/acs.jpcc.2c01663. [DOI] [Google Scholar]
  8. Xu D., Li Y., Yin L., Ji Y., Niu J., Yu Y.. Electrochemical Removal of Nitrate in Industrial Wastewater. Front. Env. Sci. Eng. 2018;12:9. doi: 10.1007/s11783-018-1033-z. [DOI] [Google Scholar]
  9. Pan H., Barile C. J.. Bifunctional Nickel and Copper Electrocatalysts for CO2 Reduction and the Oxygen Evolution Reaction. J. Mater. Chem. A. 2020;8:1741–1748. doi: 10.1039/C9TA12055F. [DOI] [Google Scholar]
  10. Kim H. E., Wi D. H., Lee J. S., Choi K.-S.. Photoelectrochemical Nitrate and Nitrite Reduction Using Cu2O Photocathodes. ACS Energy Lett. 2024;9:1993–1995. doi: 10.1021/acsenergylett.4c00256. [DOI] [Google Scholar]
  11. Rennert K., Errickson F., Prest B. C., Rennels L., Newell R. G., Pizer W., Kingdon C., Wingenroth J., Cooke R., Parthum B., Smith D., Cromar K., Diaz D., Moore F. C., Müller U. K., Plevin R. J., Raftery A. E., Ševčíková H., Sheets H., Stock J. H., Tan T., Watson M., Wong T. E., Anthoff D.. Comprehensive Evidence Implies a Higher Social Cost of CO2 . Nature. 2022;610:687–692. doi: 10.1038/s41586-022-05224-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Xiang X., Guo L., Wu X., Ma X., Xia Y.. Reduction of Carbon Dioxide into Tetraiodomethane at 1 atm. Environ. Chem. Lett. 2012;10:413–418. doi: 10.1007/s10311-012-0379-x. [DOI] [Google Scholar]
  13. Wang W., Gan L., Lemmon J. P., Chen F., Irvine J. T. S., Xie K.. Enhanced Carbon Dioxide Electrolysis at Redox Manipulated Interfaces. Nat. Commun. 2019;10:1550. doi: 10.1038/s41467-019-09568-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Abeyweera S. C., Simukaitis M., Wei Q., Sun Y.. Interfaced Ag/Cu Nanostructures Derived from Metal Thiolate Nanoplates: A Highly Selective Catalyst for Electrochemical Reduction of CO2 to Ethanol. SmartMat. 2022;3:173–182. doi: 10.1002/smm2.1096. [DOI] [Google Scholar]
  15. Zhang W., Jia B., Liu X., Ma T.. Surface and Interface Chemistry in Metal-Free Electrocatalysts for Electrochemical CO2 Reduction. SmartMat. 2022;3:5–34. doi: 10.1002/smm2.1090. [DOI] [Google Scholar]
  16. Li J., Zhang Y., Kuruvinashetti K., Kornienko N.. Construction of C–N Bonds from Small-Molecule Precursors through Heterogeneous Electrocatalysis. Nat. Rev. Chem. 2022;6:303–319. doi: 10.1038/s41570-022-00379-5. [DOI] [PubMed] [Google Scholar]
  17. Liu S., Tao H., Liu Q., Xu Z., Liu Q., Luo J.-L.. Rational Design of Silver Sulfide Nanowires for Efficient CO2 Electroreduction in Ionic Liquid. ACS Catal. 2018;8:1469–1475. doi: 10.1021/acscatal.7b03619. [DOI] [Google Scholar]
  18. Chen X., Chen J., Alghoraibi N. M., Henckel D. A., Zhang R., Nwabara U. O., Madsen K. E., Kenis P. J. A., Zimmerman S. C., Gewirth A. A.. Electrochemical CO2-to-Ethylene Conversion on Polyamine-Incorporated Cu Electrodes. Nat. Catal. 2021;4:20–27. doi: 10.1038/s41929-020-00547-0. [DOI] [Google Scholar]
  19. Vitaku E., Smith D. T., Njardarson J. T.. Analysis of the Structural Diversity, Substitution Patterns, and Frequency of Nitrogen Heterocycles among U.S. FDA Approved Pharmaceuticals. J. Med. Chem. 2014;57:10257–10274. doi: 10.1021/jm501100b. [DOI] [PubMed] [Google Scholar]
  20. Luo Y., Xie K., Ou P., Lavallais C., Peng T., Chen Z., Zhang Z., Wang N., Li X.-Y., Grigioni I., Liu B., Sinton D., Dunn J. B., Sargent E. H.. Selective Electrochemical Synthesis of Urea from Nitrate and CO2 via Relay Catalysis on Hybrid Catalysts. Nat. Catal. 2023;6:939–948. doi: 10.1038/s41929-023-01020-4. [DOI] [Google Scholar]
  21. Chen K., Ma D., Zhang Y., Wang F., Yang X., Wang X., Zhang H., Liu X., Bao R., Chu K.. Urea Electrosynthesis from Nitrate and CO2 on Diatomic Alloys. Adv. Mater. 2024;36:2402160. doi: 10.1002/adma.202402160. [DOI] [PubMed] [Google Scholar]
  22. Fang Q., Ning C., Ju M.-G.. Bimetallic Catalysts for Urea Electrosynthesis. Chem. Catal. 2023;3:100668. doi: 10.1016/j.checat.2023.100668. [DOI] [Google Scholar]
  23. Tao Z., Rooney C. L., Liang Y., Wang H.. Accessing Organonitrogen Compounds via C–N Coupling in Electrocatalytic CO2 Reduction. J. Am. Chem. Soc. 2021;143:19630–19642. doi: 10.1021/jacs.1c10714. [DOI] [PubMed] [Google Scholar]
  24. Gao Y., Wang J., Sun M., Jing Y., Chen L., Liang Z., Yang Y., Zhang C., Yao J., Wang X.. Tandem Catalysts Enabling Efficient C–N Coupling toward the Electrosynthesis of Urea. Angew. Chem., Int. Ed. 2024;63:e202402215. doi: 10.1002/anie.202402215. [DOI] [PubMed] [Google Scholar]
  25. Liu J., Guo X., Frauenheim T., Gu Y., Kou L.. Urea Electrosynthesis Accelerated by Theoretical Simulations. Adv. Funct. Mater. 2024;34:2313420. doi: 10.1002/adfm.202313420. [DOI] [Google Scholar]
  26. Zhong Y., Xiong H., Low J., Long R., Xiong Y.. Recent Progress in Electrochemical C–N Coupling Reactions. eScience. 2023;3:100086. doi: 10.1016/j.esci.2022.11.002. [DOI] [Google Scholar]
  27. Chen C., Zhu X., Wen X., Zhou Y., Zhou L., Li H., Tao L., Li Q., Du S., Liu T., Yan D., Xie C., Zou Y., Wang Y., Chen R., Huo J., Li Y., Cheng J., Su H., Zhao X., Cheng W., Liu Q., Lin H., Luo J., Chen J., Dong M., Cheng K., Li C., Wang S.. Coupling N2 and CO2 in H2O to Synthesize Urea under Ambient Conditions. Nat. Chem. 2020;12:717–724. doi: 10.1038/s41557-020-0481-9. [DOI] [PubMed] [Google Scholar]
  28. Meng N., Huang Y., Liu Y., Yu Y., Zhang B.. Electrosynthesis of Urea from Nitrite and CO2 over Oxygen Vacancy-Rich ZnO Porous Nanosheets. Cell Rep. Phys. Sci. 2021;2:100378. doi: 10.1016/j.xcrp.2021.100378. [DOI] [Google Scholar]
  29. Rykaczewski K. A., Wearing E. R., Blackmun D. E., Schindler C. S.. Reactivity of Oximes for Diverse Methodologies and Synthetic Applications. Nat. Synth. 2022;1:24–36. doi: 10.1038/s44160-021-00007-y. [DOI] [Google Scholar]
  30. Bolotin D. S., Bokach N. A., Demakova M. Y., Kukushkin V. Y.. Metal-Involving Synthesis and Reactions of Oximes. Chem. Rev. 2017;117:13039–13122. doi: 10.1021/acs.chemrev.7b00264. [DOI] [PubMed] [Google Scholar]
  31. Chen W., Wu Y., Jiang Y., Yang G., Li Y., Xu L., Yang M., Wu B., Pan Y., Xu Y., Liu Q., Chen C., Peng F., Wang S., Zou Y.. Catalyst Selection over an Electrochemical Reductive Coupling Reaction toward Direct Electrosynthesis of Oxime from NOx and Aldehyde. J. Am. Chem. Soc. 2024;146:6294–6306. doi: 10.1021/jacs.3c14687. [DOI] [PubMed] [Google Scholar]
  32. Wu Y., Jiang Z., Lin Z., Liang Y., Wang H.. Direct Electrosynthesis of Methylamine from Carbon Dioxide and Nitrate. Nat. Sustain. 2021;4:725–730. doi: 10.1038/s41893-021-00705-7. [DOI] [Google Scholar]
  33. Zeng Y., Priest C., Wang G., Wu G.. Restoring the Nitrogen Cycle by Electrochemical Reduction of Nitrate: Progress and Prospects. Small Methods. 2020;4:2000672. doi: 10.1002/smtd.202000672. [DOI] [Google Scholar]
  34. Guo S., Heck K., Kasiraju S., Qian H., Zhao Z., Grabow L. C., Miller J. T., Wong M. S.. Insights into Nitrate Reduction over Indium-Decorated Palladium Nanoparticle Catalysts. ACS Catal. 2018;8:503–515. doi: 10.1021/acscatal.7b01371. [DOI] [Google Scholar]
  35. Shibata M., Yoshida K., Furuya N.. Electrochemical Synthesis of Urea on Reduction of Carbon Dioxide with Nitrate and Nitrite Ions using Cu-Loaded Gas-Diffusion Electrode. J. Electroanal. Chem. 1995;387:143–145. doi: 10.1016/0022-0728(95)03992-P. [DOI] [Google Scholar]
  36. Li P., Li R., Liu Y., Xie M., Jin Z., Yu G.. Pulsed Nitrate-to-Ammonia Electroreduction Facilitated by Tandem Catalysis of Nitrite Intermediates. J. Am. Chem. Soc. 2023;145:6471–6479. doi: 10.1021/jacs.3c00334. [DOI] [PubMed] [Google Scholar]
  37. Wang Z., Richards D., Singh N.. Recent Discoveries in the Reaction Mechanism of Heterogeneous Electrocatalytic Nitrate Reduction. Catal. Sci. Technol. 2021;11:705–725. doi: 10.1039/D0CY02025G. [DOI] [Google Scholar]
  38. Johnsen R. E., Krumeich F., Norby P.. Structural and Microstructural Changes during Anion Exchange of CoAl Layered Double Hydroxides: a In Situ X-ray Powder Diffraction Study. J. Appl. Crystallogr. 2010;43:434–447. doi: 10.1107/S0021889810011805. [DOI] [Google Scholar]
  39. Mathiesen J. K., Johnsen R. E., Blennow A. S., Norby P.. Understanding the Structural Changes in Lithiated Graphite through High-Resolution Operando Powder X-ray Diffraction. Carbon. 2019;153:347–354. doi: 10.1016/j.carbon.2019.06.103. [DOI] [Google Scholar]
  40. Murphy E., Liu Y., Matanovic I., Rüscher M., Huang Y., Ly A., Guo S., Zang W., Yan X., Martini A., Timoshenko J., Cuenya B. R., Zenyuk I. V., Pan X., Spoerke E. D., Atanassov P.. Elucidating Electrochemical Nitrate and Nitrite Reduction over Atomically-Dispersed Transition Metal Sites. Nat. Commun. 2023;14:4554. doi: 10.1038/s41467-023-40174-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Gao Q., Pillai H. S., Huang Y., Liu S., Mu Q., Han X., Yan Z., Zhou H., He Q., Xin H., Zhu H.. Breaking Adsorption-Energy Scaling Limitations of Electrocatalytic Nitrate Reduction on Intermetallic CuPd Nanocubes by Machine-Learned Insights. Nat. Commun. 2022;13:2338. doi: 10.1038/s41467-022-29926-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Trotochaud L., Young S. L., Ranney J. K., Boettcher S. W.. Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation. J. Am. Chem. Soc. 2014;136:6744–6753. doi: 10.1021/ja502379c. [DOI] [PubMed] [Google Scholar]
  43. Burke M. S., Zou S., Enman L. J., Kellon J. E., Gabor C. A., Pledger E., Boettcher S. W.. Revised Oxygen Evolution Reaction Activity Trends for First-Row Transition-Metal (Oxy)­hydroxides in Alkaline Media. J. Phys. Chem. Lett. 2015;6:3737–3742. doi: 10.1021/acs.jpclett.5b01650. [DOI] [PubMed] [Google Scholar]
  44. Du F., Li J., Wang C., Yao J., Tan Z., Yao Z., Li C., Guo C.. Active Sites-Rich Layered Double Hydroxide for Nitrate-to-Ammonia Production with High Selectivity and Stability. Chem. Eng. J. 2022;434:134641. doi: 10.1016/j.cej.2022.134641. [DOI] [Google Scholar]
  45. Dang L., Liang H., Zhuo J., Lamb B. K., Sheng H., Yang Y., Jin S.. Direct Synthesis and Anion Exchange of Noncarbonate-Intercalated NiFe-Layered Double Hydroxides and the Influence on Electrocatalysis. Chem. Mater. 2018;30:4321–4330. doi: 10.1021/acs.chemmater.8b01334. [DOI] [Google Scholar]
  46. Qiao R., Wray L. A., Kim J.-H., Pieczonka N. P. W., Harris S. J., Yang W.. Direct Experimental Probe of the Ni­(II)/Ni­(III)/Ni­(IV) Redox Evolution in LiNi0.5Mn1.5O4 Electrodes. J. Phys. Chem. C. 2015;119:27228–27233. doi: 10.1021/acs.jpcc.5b07479. [DOI] [Google Scholar]
  47. Xian J., Li S., Su H., Liao P., Wang S., Zhang Y., Yang W., Yang J., Sun Y., Jia Y., Liu Q., Liu Q., Li G.. Electrocatalytic Synthesis of Essential Amino Acids from Nitric Oxide Using Atomically Dispersed Fe on N-Doped Carbon. Angew. Chem., Int. Ed. Engl. 2023;62:e202304007. doi: 10.1002/anie.202304007. [DOI] [PubMed] [Google Scholar]
  48. Lee T., Yeh K. L., You J. X., Fan Y. C., Cheng Y. S., Pratama D. E.. Reproducible Crystallization of Sodium Dodecyl Sulfate.1/8 Hydrate by Evaporation, Antisolvent Addition, and Cooling. ACS. Omega. 2020;5:1068–1079. doi: 10.1021/acsomega.9b03067. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Zhou P., Lv X., Tao S., Wu J., Wang H., Wei X., Wang T., Zhou B., Lu Y., Frauenheim T., Fu X., Wang S., Zou Y.. Heterogeneous-Interface-Enhanced Adsorption of Organic and Hydroxyl for Biomass Electrooxidation. Adv. Mater. 2022;34:2204089. doi: 10.1002/adma.202204089. [DOI] [PubMed] [Google Scholar]
  50. Arikawa Y., Otsubo Y., Fujino H., Horiuchi S., Sakuda E., Umakoshi K.. Nitrite Reduction Cycle on a Dinuclear Ruthenium Complex Producing Ammonia. J. Am. Chem. Soc. 2018;140:842–847. doi: 10.1021/jacs.7b12020. [DOI] [PubMed] [Google Scholar]
  51. Mondol P., Thind J. K., Barile C. J.. Selective Electrocatalytic Nitrate Reduction to Ammonia Using Nafion-Covered Cu Electrodeposits. J. Phys. Chem. C. 2023;127:8054–8061. doi: 10.1021/acs.jpcc.3c01242. [DOI] [Google Scholar]
  52. Chen W., Wu Y., Jiang Y., Yang G., Li Y., Xu L., Yang M., Wu B., Pan Y., Xu Y., Liu Q., Chen C., Peng F., Wang S., Zou Y.. Catalyst Selection over an Electrochemical Reductive Coupling Reaction toward Direct Electrosynthesis of Oxime from NOx and Aldehyde. J. Am. Chem. Soc. 2024;146:6294–6306. doi: 10.1021/jacs.3c14687. [DOI] [PubMed] [Google Scholar]
  53. Li M., Wu Y., Zhao B.-H., Cheng C., Zhao J., Liu C., Zhang B.. Electrosynthesis of Amino Acids from NO and α-Keto Acids using Two Decoupled Flow Reactors. Nat. Catal. 2023;6:906–915. doi: 10.1038/s41929-023-01012-4. [DOI] [Google Scholar]

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